Settlements induced by tunneling in Soft Ground

ITA/AITES Report 2006on

Settlements induced by tunneling in Soft Ground

Presented by the WG ‘‘Research’’

Eric Leca,Animateur Barry New,General Reporter Available online 1February 2007

Abstract

This document is primarily designed to inform participants directly involved in construction (owners,engineers,design o?ces,contractors,etc.).It is also to inform private and public decision makers,or even local residents,and to clarify the current mis-conceptions on the so-called ‘‘zero settlement promise’’by giving a well-documented presentation on the admissible settlement concept.This document serves as a ?rst stage.It shall be revised in due course to provide methods for estimating settlement and provide damage criteria derived from experience.We may assume that with the support of owners,who are directly concerned with the consequences of their works,there will be considerable feedback from the many work sites under way at the time of writing these recommendations.

Introduction by Yann Leblais,Animateur ITA Working Group (Research)

For a period of several years The International Tun-neling Association Working Group (Research)has con-sidered the impact of tunneling beneath urban areas and wide-ranging discussions on the subject have taken place during the meetings.Whilst a general consensus view on the main issues and principles has been achieved,it is natural that there remains a variety of emphasis in the approaches and techniques adopted by Member Nations.Further,because of recent progress in the ability of tunneling machines to cope with di?cult ground condi-tions,the ground movements produced have been greatly reduced.Whilst the largely empirical predictive methods remain much the same,their application is constantly evolving as recent case history data becomes available.The Working Group is therefore considering the creation of a case history database of ground movements caused by tunneling from projects throughout the world.This may greatly assist contractors,designers and owners because the reduced impacts of tunneling will be quanti?ed and projects considered more favorably due to the reduced impacts particularly when tunneling beneath cities.It is felt that a robust database demonstrating the improved ability of the tunneling industry to control ground movements would give owners added con?dence in proceeding with the exploitation of underground space beneath our cities.

A Working Group of the French Tunneling Association (Leblais et al.,1996)has published a substantial and authoritative review paper ‘Settlements Induced by Tun-neling’.This paper forms the basis for this report together with some additions and revisions to re?ect,as far as is possible,the comments received from representatives of the ITA Member Nations and discussions within the Re-search Working Group.

Acknowledgements

The general reporters are grateful for the assistance of the Research Working Group Animateur,Yann Leblais,Vice-Animateur,Yoshihiro Takano and all Working Group colleagues from Member Nations,as well others from many nations who have contributed to this report.The data from the Channel Tunnel Rail Link are pre-sented by kind permission of Union Railways (North)Ltd.

1.Purpose of the recommendation

Density of land usage is an important element of the construction of new public or private infrastructure.Similar attention must be paid in this respect to increasing demand from the communities for more areas free of road tra?c.Both aspects contribute to more underground

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projects being undertaken,as well as an increased use of underground space.The construction of new underground facilities however will inevitably interfere with existing surface buildings and underground structures,given that no blueprint exists for actual underground land usage.

It is trivial to state that underground infrastructure must be constructed within the subsoil,and that the main uncertainties designers and contractors have to face in undertaking such projects relate to the ground conditions that will eventually be encountered during construction.

Local residents and businesses may be a?ected by such works,be it during construction or in the longer term.

The response of existing structures to tunneling induced ground movements depends on their geometry,construc-tion type and overall structural condition.This emphasizes one major unknown in evaluating the actual impact of underground works on existing overlying buildings,as there is usually little knowledge among property owners of the history of deformations experienced by the structure previously,and even less when it comes to building foundations.

The purpose of this document is to provide some clar-i?cation on the soil/structure interactions phenomena in-volved in the construction of underground structures (other than open cuts),as well as a review of the ap-proaches developed to evaluate,measure,prevent and treat such e?ects,with due account of associated con-tractual issues.

The document is meant to provide recommendations on the way to approach settlements induced by tunneling in soft grounds.

On the other hand,it is not intended to be used as a tool for obtaining calculation recipes on foreseeable settle-ments.There are two main reasons for this:

–Evaluating settlements is principally based on engineer-ing judgment and experience and remains an input from specialists.

–Research is still underway in this area within the inter-national scienti?c community.

It should also be reminded that every project should be assessed on a case-by-case basis,using expert opinion,as well as available literature.

2.Tunnelling-induced ground movements

The relationship between surface settlements and tunnel depth is neither simple nor linear.In reality, ground movements depend on a number of factors including(1)geological,hydro-geological and geotech-nical conditions,(2)tunnel geometry and depth,(3) excavation methods and(4)the quality of workmanship and management.It is however clear that a shallow tunnel will tend to have a greater e?ect on surface structures than a deep one.

The construction of a tunnel inevitably a?ects existing ground stresses and hydro-geological conditions.This modi?cation of the natural stress conditions is typically accompanied by a rapid inward displacement of the face and convergence of the tunnel walls(Fig.1).In soft cohesive soils,additional long term deformations may be observed as a result of pore pressure changes induced by the tunneling works.

The magnitude,orientation and the location of ground movements around the opening depends on the geotech-nical conditions encountered,existing geostatic stresses and surface loads,hydro-geological conditions,as well as the techniques used for tunnel excavation and ground support.Where the strength of the ground mass is ex-ceeded,signi?cant displacements can be generated,both in terms of magnitude and acceleration.This may lead to the formation of shear planes within the ground mass,with detrimental e?ects in terms of required tunnel support (gravity loads)as well as limitation of ground movements.

Typically,the construction of an unsupported tunnel opening in soft ground would generate large ground dis-placements which,in turn could lead to the formation of a failure zone behind the face(Fig.2a).In weaker grounds, the failure zone may propagate towards the ground ahead of the tunnel face(Fig.2b).

A good appreciation of the risk for failure to occur at the tunnel face is essential,both from the standpoint of providing a safe working environment and evaluating the probability for large settlements to occur,given that ground movement at the face accounts to one major source of tunneling induced surface settlements.

2.1.Face stability

Analyzing tunnel face stability provides an indication of the most probable failure mechanisms,as well as

of Fig.1.Displacements of the excavation pro?les:basic

cross-sections.

Fig.2.(a)Yielded zone rear of the face.(b)Yielded zone ahead of the face.

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parameters to be taken into consideration in the evalua-tion of ground movements induced by tunneling.Based on the nature of the grounds encountered,two types of failure mechanisms may be observed.

In the case of cohesive soils(Fig.3)face failure involves a large volume of ground ahead of the working front.This mechanism leads to the formation of a sinkhole at the ground surface with a width larger than one tunnel diameter.

In the case of cohesionless soils,failure tends to prop-agate along a chimney like mechanism above the tunnel face(Fig.4).

Both mechanisms have been evidenced in centrifuge tests carried out in clays(Fig.3)and dry sand(Fig.4).

Such conclusions are consistent with the results pro-vided by theoretical studies(Chambon and Corte′,1989, 1990;Dormieux and Leca,1993;Leca and Dormieux, 1990,1992;Leca and Panet,l988)as well as?eld obser-vations(Clough and Leca,1993).They are however based on the consideration of idealized conditions and should,of course,be adjusted to account for the actual conditions found on each individual worksite:non-homogeneous grounds and water in?ows.In particular,in water-bearing sands,ground stability will be considerably in?uenced by hydraulic gradients induced by seepage towards the face.

It is also worth mentioning that the mechanisms shown in Figs.3and4refer to failure conditions and re?ect the general trend for ground deformations at the face rather than the actual pattern of tunneling induced displace-ments.

2.2.Propagation of movements towards the surface

Ground movements initiated at the tunnel opening will tend to propagate towards the ground surface.The extent and time scale of this phenomenon will typically be dependent upon the geotechnical and geometrical condi-tions,as well as construction methods used on the site.

Two propagation modes have been identi?ed,based on the conclusions of in situ measurements and observations. These modes can be used to evaluate,in a transverse plane,the degree of propagation of displacements initiated at the opening.They will be referred to,in the following, as primary mode and secondary mode(Pantet,1991).

The primary mode(Fig.5)occurs as ground stresses are released at the face.It is characterized by the formation of a zone of loosened ground above the excavation.The height of this zone is typically1–1.5times the tunnel diameter and about one diameter wide.Two compression zones develop laterally along the vertical direction.For deeper tunnels(C/D>2.5),the observed tunneling impact at the ground surface is generally limited(Cording and Hansmire,l975;Leblais and Bochon,1991;Pantet,1991).

The secondary mode(Fig.6)may occur subsequently, when the tunnel is located close to the surface(C/D<2.5) and insu?cient con?ning support exists.These conditions result in the formation of a‘rigid’ground block,bounded by two single or multiple shear planes extending from the tunnel to the surface.Displacements at the ground surface above the opening are of the same order of magnitude as those generated at the opening.

These ground response mechanisms typically lead to vertical and horizontal displacements that tend to

develop Fig.3.Face collapse:basic diagram in cohesive ground

soils. Fig.4.Face collapse:basic diagram in dry granular

soils.

Fig.5.Primary mode:basic transverse

cross-section. Fig.6Secondary mode:basic transverse cross-section.

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at the ground surface as excavation proceeds;this results in what is referred to as the settlement trough (Fig.7).For practical purposes,the observed three-dimensional trough is conventionally characterized by means of a transverse trough and a longitudinal trough along the tunnel center-plane.

2.3.Main parameters involved in the stability of the opening during construction

Regardless of the nature of the ground,the magnitude and distribution of tunneling induced surface settlements depend on the ground layering (e.g.alternated heteroge-neous layers),deformability (in the short and long terms),induced (K 0…1)and structural anisotropy (strength and deformability).Of course,the ground response to tun-neling will also be in?uenced by existing hydro-geological conditions on the site.For example,stability time will be dependent upon the ground permeability.

It is clear that a good understanding of the site’s geo-technical conditions is essential for assessing these funda-mental parameters.This emphasizes the absolute need for a high quality ground investigation to be completed [refer on these aspects to the AFTES recommendation ‘‘The selection of parameters and tests for the design and con-struction of underground structures’’(AFTES,1994)].Theoretical and experimental works on tunnel face stability have allowed the identi?cation of a limited number of key parameters that (together with seepage conditions)can be used to characterize the stability of the opening.These parameters are described in Fig.8.2.3.1.Purely cohesive soil (clay)

For tunnels in clayey grounds,the overload factor N ,de?ned (Broms and Bennemark,1967)as:

N ?c H

S u

where H is the depth to tunnel axis,c is the soil unit weight,and s u is the undrained shear strength of the ground prior to excavation has been identi?ed as the fundamental ratio for characterizing the instability of the face.

Another two parameters also need to be considered:C

D

and c D

S u ,where C is the depth of cover and D is the tunnel diameter.

The ?rst ratio controls the e?ect of depth on the sta-bility condition,while the second accounts for the possi-bility of localized failures to occur at the face.

In the more general case,where a surcharge is applied at the ground surface and a support pressure is used at the face,the overload factor,N ,can be expressed as follows:N ?c H tr S àr T

S

u

r s :surcharge acting on the ground surface

r T :support pressure applied at the face

Field observations (Peck,1969)show that N values ranging from 5to 7typically result in tunneling di?culties and may cause tunnel face instability.Subject to more re?ned considerations,as indicated by experimental (cen-trifuge testing)and theoretical ?ndings,it can typically be established that:

–when N 63

the overall stability of the tunnel face is usually ensured;–when 3

special consideration must be taken of the evaluation of the settlement risk,with large amounts of ground losses being expected to occur at the face when N P 5;–when 6

on average,the face is unstable.As for the other two parameters,the following general criteria can be considered with care:

C D

<2

a detailed analysis of the face stability is required

4

S u

localized failure can occur at the face.

Moreover,special care must be exercised if the tunnel support is installed at some distance P behind the face,with face stability being dependent on the magnitude of the P/D ratio (Scho?eld,1980).

The above parameters,which control the stability of the ground mass at the working face,may

in?uence

Fig.7.Three-dimensional settlement

trough.

Fig.8.Stability parameters.

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surface settlements when the ground is subjected to stresses close to its shear strength.Some correlations have been established between the overload factor N and the magnitude of surface settlements (Clough and Schmidt,1981).

2.3.2.Cohesionless soils (sand)

The face of a tunnel in cohesionless ground cannot in theory be stable.However,these ground conditions usu-ally exhibit a slight cohesion that will in?uence the sta-bility conditions,at least temporarily (e.g.capillary tension).

The factors of instability in such grounds are also more di?cult to assess given that works on these structures are more recent.It must also be kept in mind that the propagation of ground motion towards the surface is in?uenced by other parameters such as the ground deformability and anisotropy (Lee and Rowe,1989).

Theoretical and experimental studies relating to dry sands indicate that the tunnel depth (C/D ratio)is of lesser in?uence than in cohesive ground,whereas the tunnel diameter has a determining e?ect,with stability conditions

being primarily controlled by the ratio,c D

r T and the soil’s friction angle,u 0.

2.3.3.Cohesive frictional grounds

A more comprehensive analysis of tunnel face stability in a frictional,cohesive ground mass (i.e.with a strength characterized by a cohesion c 0and a friction angle,u 0)leads to four controlling parameters:

c H c

;

c D c ;r T c

and u 0

where r c ?2c 0

cos u

1àsin u 0

2.3.4.Rock

For shallow tunnels in rock,the ground strength is rarely reached as a result of stress changes induced by excavation.The present recommendation does not spe-ci?cally cover the speci?c case of hard rock tunneling for which stability is primarily controlled by structural

parameters (strati?cation,joint orientation and continu-ity,etc).

2.4.Convergence of the excavation

In addition to face stability,ground movement is also in?uenced by the convergence of the tunnel lining.

It should be kept in mind that one essential factor in reducing wall convergence is the early installation of a sti?support system behind the tunnel face,or even ahead of the face.This is clearly illustrated on a convergence-con?nement diagram (Fig.9),where it can be shown that a sti?er support system (K 1>K 2)installed closer to the face (Ur 1

3.Causes for construction induced settlements

Before discussing the di?erent approaches for estimat-ing ground movements induced by underground excava-tion,it is desirable to review on the basis of the current state-of-the-art,the di?erent causes of tunneling induced settlements.Prevention and remedial techniques will be addressed later in the document (Section 6).

Generally speaking,movements along the tunnel cen-ter-line are initiated at some distance ahead of the face and keep increasing until a complete support system is in place.Therefore one must di?erentiate between the settlements associated with the methods of excavation used at the face,and the settlements that occur behind the face.

Given the fundamental progress brought in this respect by the shield technology and associated developments,one must di?erentiate between continuous shield-driven con-struction and sequential tunneling techniques.The term ‘‘sequential’’in the latter is preferred to ‘‘conventional’’which is often associated to methods poorly suited to the control of settlements (ribs and wood)and do not re?ect the richness of recent technical advances.

Settlements associated with groundwater and worksite conditions will be generally dealt with at the end of the chapter.It must also be mentioned that the following sections relate to the generic case of an isolated tunnel structure.For the purpose of simplicity,it has been con-sidered preferable to focus on the basic principles,rather than addressing such speci?c conditions as that of side-by-side tunnel excavation (simultaneous or staged),so that no additional factor would in?uence an already complex sit-uation.It must however be recognized that the latter may result in aggravated conditions as regards the impact of tunneling induced settlements.3.1.Case of the sequential method

For works of this type,four major settlement sources can be

identi?ed:

Fig.9.In?uence of support conditions (sti?ness,installation time frame)on convergence.

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–settlements associated with the stability at the face;

–settlements associated with the characteristics and conditions of installation of a temporary support system;

–settlements associated with the cross-sectional staging (sequencing)of the excavation works;

–settlements associated with the?nal lining installation and response.

3.1.1.In?uence of tunnel face stability

Controlling the face stability is essential.Review of the latest developments on tunnel face stability clearly indi-cates a direct relationship between the control of face

stability and the settlements induced ahead of the tunnel face.

3.1.2.In?uence of the temporary support

The selection of an appropriate temporary support system is a key outcome of the project feasibility studies. This involves a compromise to be made between theoret-ical requirements and those imposed by construction methods considerations,and leads to assessing two fun-damental parameters:

–the nominal sti?ness of the support system which must account for its mechanical characteristics and installa-tion methods.

–the time required for installing the support system which depends on the installation distance to the face.

These two parameters are used to evaluate the overall ability of the support system to resist ground conver-gence(Fig.9)and,subsequently,limit construction in-duced settlements at the surface.Once the theoretical support requirements are determined,it is necessary to ensure that they can be achieved given the actual work-site conditions.

3.1.3.In?uence of construction staging

Construction staging may strongly in?uence ground deformations around the opening:

–at the face,in proportion to the face area;

–at some distance from the face;this is dependent upon the ability to rapidly secure the tunnel liner,the staging of face excavation and length of unsupported tunnel walls behind the face;

–ground movement at some distance behind the face is further in?uenced by the distance of?nal liner installa-tion to the face,as this structure is usually signi?cantly sti?er than the initial liner and subject to less deforma-tions;its early installation may also contribute to a more uniform longitudinal distribution of liner loads thereby limiting ground deformations.3.1.4.In?uence of the lining

The in?uence of liner deformations on ground move-ments must be taken into account,particularly in the case of large tunnel spans with limited cover.

3.2.Case of shield-driven tunnels

Settlements induced by shield tunneling can be broken down into four contributions(Fig.10):

–settlements ahead and above the face;

–settlements along the shield;

–settlements at the shield tail skin;

–settlements due to liner deformations.

3.2.1.Settlements ahead and above the face

Settlements at the face are due to ground displacements ahead of(face loss)and above the shield towards the opening.Displacements depend on the level of con?ning support at the tunnel face(within the spoils chamber),the ground conditions and hydraulic conditions.

3.2.2.Settlements along the shield

Measurements taken above shield driven tunnels indi-cate that ground movements are rarely stabilized at the tail skin,and that the response time of the surrounding ground tends to decrease as the cover increases.The few existing observations of such phenomena tend to show that tunnel displacements propagate towards the ground surface at a constant speed for a given ground(Pantet, 1991).

Settlements along the shield may principally be caused by the following:

–overcutting induced by peripheral cutters intended to produce a slightly larger diameter to that of the shield, and thus reduce skin friction and facilitate guidance especially in tight radius curves;

–shield guidance di?culties,particularly in relation to its tendency to plough(dive),which usually requires the shield to be driven with an upward angle so that pitch-ing can be prevented.Similarly,the tendency for the shield to yaw results in an excavated transverse

section Fig.10.Evolution of settlements along a shield.

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which is wider than the shield section,thus contributing to widening the gap between the excavated and theoret-ical tunnel diameter;

–tapering(if any)of the shield;

–roughness of the cutting wheel that may,by friction and ground shear,induce crown settlements and ground movements ahead of the shield.

3.2.3.Settlements at the shield tail

At the shield tail,a gap develops between the ground and the outer face of the liner segments due to:

–the gap generated along the shield;

–the thickness of the tail-skin that varies according to the type(single/double)of shield and tunnel diameter;

–the clearance between the inner face of the tail-skin and outer face of the liner segment,to house the tail seal.

The magnitude of surface settlements depends on whether the tail gap is properly grouted.

It should be noted that these considerations typically refer to the case of segment installation within the tail-skin,and do not account for techniques such as the ex-panded liner segment method.This latter method may be of limited use for settlement control due to the level of stress release they produce within the ground.

3.2.

4.Settlements due to lining deformation

Precast concrete segments installed within the tail-skin must be of su?cient strength to sustain the thrust of the shield jacks.As a result,the radial deformation of the liner rings is likely to be acceptable provided the tail gap is properly grouted.

3.3E?ect of groundwater

Numerous examples can be found of di?culties and accidents in underground works that were caused by groundwater.It must be emphasized that groundwater control is a prerequisite for the successful completion of underground works.

Settlements induced by groundwater typically fall under two categories.

The?rst category refers to the occurrence of settlements almost concurrently with construction.

Lowering of the groundwater table,prior to excavation (through drainage)or as a consequence of tunneling,may cause immediate settlements to occur in layers or lenses of compressible soils,as well as in weathered rocky materials. The impact of such lowering of the groundwater table varies in proportion to its magnitude and radius of in?u-ence:

–when localized,induced deformations are often prone to generate large di?erential settlements that can be damaging to the surrounding buildings;–when widely spread,their consequences are generally less severe(Auber station,line A of the Re′seau Ex-press Regional(RER)–Paris express railway network, St Lazare railway station in Paris,Est-Ouest Liai-son Express(EOLE)–Paris East-West underground link).

The occurrence of groundwater at the tunnel face may induce settlements as a result of:

–the hydraulic gradient weakening the mechanical condi-tions at the face and on the tunnel walls thereby increasing ground deformations;

–worsening e?ects on preexisting mechanical instabilities (washed out karsts,etc);

–worsening of the mechanical properties of the ground in the invert,particularly when the sequential method is used,with the risk for punching of the foundation ground by the temporary support due to loss of con-?nement.

The second category refers to delayed settlements that are typically observed in soft compressible grounds.As a result of the tunneling works,the ground can be locally subjected to stress increase and subsequently excess pore pressures.Similar mechanisms can develop at a larger scale with fully pressurized shield tunneling.Moreover,as a result of seepage towards the tunnel walls that inevitably occurs during and/or after construction,either along the more pervious materials present around the opening or through the tunnel liner,consolidation will take place within the entire ground mass.The magnitude of consol-idation settlements will be larger in areas experiencing higher reductions in pore pressures.

3.4.E?ect of worksite conditions

This includes the settlements induced by the general worksite conditions,especially vibrations induced by boring whether with the sequential or shielded method and muck removal operations.Settlements of this type have been observed in soft ground conditions,or in good ground with poor surface back?ll material.

4.Evaluation of ground movements

https://www.doczj.com/doc/0c13574965.html,putation methods for the evaluation of ground movements around the opening

To date,the theoretical determination of the displace-ment?eld around a tunnel opening remains di?cult, particularly when it comes to achieving a mathematical representation of the complex phenomena observed dur-ing tunneling,due to the large number of parameters to be

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taken into account and to the three-dimensional pattern of the ground motion around the opening.

The resolution of this mechanics problem requires the determination of the constitutive laws representing the fundamental behavior of the materials involved(soil,lin-ing material and,when appropriate,grouting products). The in?uence of the soil’s constitutive model on the determination of the ground movements around the opening has been demonstrated by numerous theoretical studies.

In France,the analysis of the convergence of the tunnel walls is completed using the Convergence-Con?nement method(Panet,1995).This method provides a two-dimensional representation of the three-dimensional deformation pattern around the opening by introducing a ?ctitious tunnel support pressure,the magnitude of which is adjusted in proportion to the stress release coe?cient,k. The magnitude of this coe?cient is varied to account for the behavior of the ground at the tunnel face,the distance of installation of the support system behind the face,the construction method and quality of workmanship.The most recent developments also allow for the in?uence of the support sti?ness to be taken into account.

The equilibrium reached within the ground mass,after it has been disturbed by the excavation works,can be analyzed using two conventional techniques(with the ground being modeled as a continuous medium subjected to external loads):

–analytical methods;

–the?nite element method(FEM).

Analytical methods are based on simplifying assump-tions in terms of geometry,ground layering(single homogeneous layer),selection of constitutive models and de?nition of boundary and initial conditions.Scienti?c literature provides numerous analytical formulations (Clough and Schmidt,1981;Dormieux et al.,199;Rowe and Lee,1992;Sagaseta,1987;Yi et al.,1993).In most cases,the authors focused on de?ning the new stress?eld generated by the excavation;fewer works have been de-voted to the evaluation of the distribution of ground movements around the opening and time e?ects,due to the complexity of such analyses.

On the other hand,numerical techniques such as the FEM take account of heterogeneous ground layers with more sophisticated constitutive models,as well as initial and boundary conditions similar to the actual?eld conditions,and time dependent e?ects.They are partic-ularly e?ective for the study of tunnels excavated in grounds that can be modeled as continuous media,with due account of non-linear behaviors,as well as complex staging and geometrical conditions.However,three-dimensional analyses remain complex and the recourse to a simpli?ed two-dimensional approach may be nec-essary,thus reducing the modeling potential of this technique.4.2.Evaluation methods for surface settlements

With the exception of scale models that are essentially used for research works,two main methods are available for the evaluation of surface settlements.

4.2.1.Empirical and semi-empirical methods

These simpli?ed methods consist in estimating surface settlements based on a limited number of parameters, which allow taking account of:

–the excavation size and depth;

–the ground conditions;

–the volume of ground loss or convergence induced by tunneling.

The simplest method consists in making a pseudo-elastic analysis,which allows to express the maximum surface settlement s max as:

s max?K:k:c R2

where K is the dependent on the ground stresses,ground conditions and tunnel geometry;k the stress release coef-?cient;R the excavated radius;c the average unit weight of the ground;and E the Young’s modulus of the ground.

This approach is usually found to be oversimplifying for the following reasons:

–it cannot strictly speaking be applied to a shallow underground structure(given that the stress?eld around the opening can only be considered uniform when H P3D);

–it does not explicitly take account of the tunnel depth;–it establishes a proportional relationship between the magnitude of maximum surface settlement and the amount of stress release,which is often far from being backed by experience(Section4.3.3).

However,this approach has some merit in that in allows identi?cation of the fundamental parameters involved in the determination of surface settlements:

–tunnel cross section(R2);

–ground deformation(E);

–construction method and workmanship(k);

–experience factor(k).

In practice,empirical methods are most commonly used;these are more or less combined with analytical methods or?nite element computations,and calibrated with data from case histories.

These methods are usually simple and allow parametric studies to be performed on the in?uence of the structure on surface settlements to be carried out.They are therefore particularly useful at the preliminary design stage and may be su?cient to ful?ll all design requirements when site

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conditions are well known and design parameters cali-brated accordingly.

This pragmatic approach was introduced by Schmidt (1969)and Peck(1969)and further developed in the United Kingdom,primarily on the basis of numerous studies related to tunneling in homogeneous ground in London Clay(Attewell et al.,1986;Kimura and Mair, 1981;Mair et al.,1981;O’Reilly,1988;O’Reilly and New, 1982;New and Bowers,1994).

4.2.2.Numerical methods

These methods aim at computing the ground displace-ments at every point within the ground around the open-ing.They take account of the characteristics of both construction and ground conditions(geometry,initial stresses,ground behavior,excavation stages,etc.).The most widely used approach is by means of two-dimensional FEM analyses in a plane perpendicular to the tunnel axis,which is consistent with the analytical ap-proach and the Convergence-Con?nement concept.

It should be noted that this approach can also be used to obtain an evaluation of the loads carried by the tunnel liner,and provides a powerful means for tunnel design, but its implementation remains relatively complex.As a result,although these techniques allow for a comprehen-sive determination of all design parameters,they are pri-marily used as simpli?ed preliminary models,with the most re?ned models(accounting for all geotechnical, geometric and construction speci?cities)being restricted to a selection of key design cross-sections.

For shallow structures,these methods may lead to an erroneous representation of the impact of tunneling at the ground surface,particularly if failure mechanisms are involved.In particular,in cohesionless grounds,two-dimensional FEM models tend to distribute tunneling in-duced deformations over a wider area than that derived from?eld observations.This may result in overestimating the lateral spread of deformations and width of settlement trough,and subsequently underestimating the magnitude of maximum surface settlements.Research currently under way(soil behavior,initial stress conditions,full three-dimensional models,size of?nite elements)should allow further modeling improvements in the future.

It must be kept in mind that large discrepancies exist between the apparent accuracy of the results derived from such powerful models and the poor level of appreciation of design assumptions,particularly as regards ground sti?-ness and construction staging.Hence,it is absolutely necessary to test the model’s sensitivity to a variety of design assumptions so that(potentially serious)erroneous representations and subsequent disputes can be prevented.

As an example,the highest care must be exercised when introducing secondary constitutive soil parameters,such as dilatancy.It is further believed that,until a commonly accepted method of determination of such parameters is developed,and in view of the sensitivity of computational models to these parameters,adverse e?ects should be ex-pected from their introduction.These e?ects can be ex-pected to be enhanced by the excessive importance such parameters may be given as a result of the apparent accuracy provided by the elaborate numerical tools they are used with.

It must be noted that numerical methods allow,when necessary,to fully model the interaction between the ground,the construction works and the existing overlying buildings.The use of these theoretical models in the back-analysis of real case data can prove very useful in deter-mining geomechanical parameters,calibrating empirical methods and interpreting data obtained from in situ monitoring.

4.3.Basic methodology for estimating surface settlements

The proposed approach consists of three main chro-nological stages:

(1)evaluation of the volume of ground loss generated at

the opening(V e);

(2)evaluation of the proportion of ground loss reaching

the ground surface(V s);

(3)determination of the settlement trough shape:

determination of the trough width(2B),

evaluation of the trough depth,i.e.the maximum

surface settlement(s max).

4.3.1.Evaluation of volume losses around the face

With the Convergence-Con?nement method,the determination of the volume of ground loss at the opening (V e)can be achieved by evaluating the convergence of the tunnel walls.Several analytical approaches are available for the case of a circular tunnel driven in a homogeneous isotropic material.These approaches also provide a rea-sonable evaluation of the volume of ground loss around non-circular tunnels using the equivalent radius concept.

With this approach,the key parameter is the stress re-lease coe?cient,k,which accounts for the volume of ground loss developed at and next to the face.

In the case of the sequential method,this coe?cient is varied as a function of the excavation and subsequent support installation stages.

In the case of a shield-driven tunnel,although a single overall value of the stress release coe?cient may be su?-cient for determining the lining thickness,a series of stress release coe?cients should be applied to take account of the di?erent sources of ground loss in the evaluation of surface settlements(Section3.2).This is a delicate process, which requires su?cient feed-back from experience in or-der to calibrate the break down of ground losses on the basis of their incidence on observed settlements.Based on current knowledge,the following distribution of settle-ment contributions can be proposed:

–10–20%caused by the face intake;

–40–50%produced along the shield;

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–30–40%observed at the tail-skin.

In view of current advances in construction techniques and methods,and based on observations made on recent work-sites in di?cult geometric and geotechnical conditions(extension to Vaise of Line D of the Lyon metro;Line2of the Cairo metro),it can also be estab-lished that:

–the magnitude of observed settlements clearly tends to decrease(10–20mm);

–the above percentages of contribution to surface settle-ments tend to vary,with settlements at the tail skin now accounting for a smaller portion of the overall settle-ment due to advances in grouting technologies(Section

6.5.3).Recent experience from earth pressure balance

machine(EPBM)driven tunnels also shows that the proportion of ground lost at the face may be greatly re-duced.In some cases heave ahead of the tunnel face may be experienced.

4.3.2.Propagation of displacements towards the surface

The second stage of evaluation consists in determining the volume of settlement trough(V s)induced at the sur-

face or a given depth.

The simplest assumption consists in considering the ground as incompressible.In this case,the volume of settlement trough equals the volume of ground loss at the opening.This assumption is actually highly depen-dent on the nature and cover of ground above the tunnel.It is typically valid for shallow tunnels in cohe-sive grounds.

Whilst there exists few cases of increase in settlement volume,several factors can contribute to lower volumes of settlement being observed at the surface than those pro-duced at tunnel level.These may include:

–large depth of cover resulting in up to80%deforma-tion dampening;

–the presence of a sti?er layer over the tunnel(bridging e?ect);

–the presence of a layer of dilating material in the tunnel cover(dense sand).

It is clear that each case history is speci?c and,as a result,it is di?cult to provide a general relationship be-tween the volume of settlement trough and the volume of ground loss produced at the opening.One can refer for more details to the abundant literature on this matter. Fig.11provides an example of such observation,derived from measurements made on a few French case histories of tunnels excavated with closed-face shields.

The time required for tunneling induced settlements to reach the ground surface and stabilize is extremely dependent upon project conditions.It is advisable for an appreciation of such phenomena to refer to the existing literature on case history data.4.3.3.Transverse settlements and displacements

The shape of the subsidence trough above mining excavations was examined by Martos(1958)and he pro-posed that it could be well represented by a Gaussian or Normal distribution curve(Fig.12).Later,Schmidt(1969) and Peck(1969)showed that the surface settlement trough above tunnels took a similar form.

O’Reilly and New(1982)developed the Gaussian model by making the assumptions that the ground loss could be represented by a radial?ow of material toward the tunnel and that the trough could be related to the ground con-ditions through an empirical‘‘trough width parameter’’(K).The model was guided by an analysis of case history data.These assumptions allowed them to

develop Fig.11.Dampening coe?cient vs.

C/D.

Fig.12.Idealized transverse settlement trough.

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equations for vertical and horizontal ground movements that were also presented in terms of ground strain,slope and curvature(both at,and below,the ground surface). The equations have since become widely used particularly to assess the potential impact of tunneling works during the design process.

The base equations are given as

S(y,z)=S(max,z)exp–y2/2(Kz)2

V s=(2B)1/2KzS(max,z)

and H(y,z)=S(y,z)y/z

where:

–S(y,z)and H(y,z)are the vertical and horizontal compo-nents of displacement respectively at the transverse distance y,and the vertical distance z from the tunnel axis;

–S(max,z)is the maximum surface settlement(at y=0) and vertical distance z from the tunnel axis;

–K is an empirical constant related to the ground condi-tions(e.g.0.5for sti?clay and sandy clay to0.25for less sti?sands and gravels);

–V s is the settlement volume per unit advance.

Note that the product Kz de?nes the width of the trough and corresponds to the value of y at the point of in?exion of the curve;for most practical purposes the total trough width can be taken as6Kz.

4.3.4.Relationship between crown displacement and surface settlement

The use of the above described procedure,as well as computations of displacement?elds around the excava-tion or use of an empirical approach,may lead to a direct relationship between the displacement in the tun-nel crown(U rcrown)and the middle surface settlement (S max).

Several researchers have proposed formulas to calculate S max/U rcrown according to H/R and a parameter varying with the ground condition(Sagaseta,1987).Each formula has been designed for speci?c cases.In particular,the choice of the parameter associated with the ground de-serves attention because it can incorporate many other factors.

It should be remembered that another method of evaluating surface settlement can be carried out from a typical pseudo-elastic computation(Section4.2.1).

4.3.

5.Back calculation

It may prove useful to start from what is admissible at the surface(cf.Section5)and go back to the volume loss that can be tolerated above the tunnel alignment.By back calculating,we can envisage di?erent settlement troughs meeting the requirements of surface buildings.In this case, a method similar to that applied for a feedback analysis shall be adopted.4.3.6.The settlement trough in three dimensions

The equations given above(in Section4.3.3)describe the form of the ground movements in two dimensions normal to the tunnel axis.In practice the settlement trough also proceeds in advance of the tunnel face.It is a natural consequence of the assumption of a Gaussian transverse pro?le that this trough should take the form of a cumu-lative probability distribution and this has been demon-strated by Attewell and Woodman(1982).

Tunneling works commonly comprise a variety of intersecting excavations where tunnels change in diameter and where cross connecting adits and other openings oc-cur.New and O’Reilly(1991)incorporated the radial?ow and trough width parameter assumptions into the cumu-lative probability distribution model to provide a three dimensional model and demonstrated its application to a relatively complex excavation.

New and Bowers(1994)further developed the cumu-lative probability distribution model by re?ning assump-tions regarding the location of ground loss and giving a full array of equations for the prediction of ground movements in three dimensions.The method is straight-forward to apply as the only inputs required are the geometry of the tunnel/site,the predicted percentage ground loss volume(V s)and the empirical trough width parameter(K)described above.The equations give the vertical and horizontal ground movements,and associated strains and ground curvatures.In particular,this approach gives signi?cantly improved predictions in the vicinity of the tunnels.This model was validated by extensive?eld measurements taken during the construction of the Hea-throw Express trial tunnel at London Airport and else-where.Also suggested is a method for the prediction of movements caused by shaft sinking.

Settlement predictions are usually carried out using empirically based procedures without speci?c regard to the method of construction.However,the proposed con-struction method will in?uence the value taken to repre-sent the volume of the settlement trough and thereby the predicted ground movements.Where ground movements are considered important,every e?ort must be made to control the ground as early and e?ectively as possible at each stage of the excavation and support process.

The convenience of the Gaussian/cumulative probabil-ity distribution curves leads to a series of straightforward mathematical transformations and an apparent precision that may not always be apparent in?eld data.In practice unexpected ground conditions or poor tunneling tech-nique can lead to signi?cantly larger than predicted ground movements.The considerable strength of this ap-proach lies in its ease of use and in its general validation by ?eld measurements from many sources over many years.

It is of little practical consequence to the ground movements whether the ground loss occurs at the tunnel face or at the periphery of the shield or lining.The con-struction method will not usually in?uence the?nal shape

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of the ground movement pro?le but construction sequence can alter the maximum angular distortions experienced in a direction parallel to the tunnel axis.

4.3.7.Volume loss –current EPBM performance

The choice of the volume loss parameter V s is of considerable importance and the value chosen will be related to experience of the tunneling technique and ground conditions at the particular project for which predictions are required.In this respect,good case history data is vital.

In recent years TBM performance has improved con-siderably and in particular the reduced volume losses now possible using earth pressure balance machines (EPBM)has signi?cantly reduced ground movements.A very extensive database of ground movement information has been obtained during tunneling works in the UK for the London tunnels of the channel tunnel rail link (CTRL).Fig.13shows the volume losses for approximately 34km of 8.15m outer diameter tunnels bored through a variety of soils (Bowers and Moss,Personal communica-tions).The results from the eight EPBM are provided as an example of current achievements in controlling ground movements.

4.3.7.1.C220Stratford to St Pancras.The Kawasaki EPBM were driven over almost the whole contract length in closed (i.e.pressurized face)mode.

Between chainage 7+000and chainage 4+500the tun-nels were predominantly driven in dewatered sands.In this area typical volume losses recorded were 0.2–0.4%.It should be noted that this section was driven with contin-uous bentonite support around the shield in addition to maintaining the face pressure and tail-skin grouting.

Between chainage 4+500and chainage 4+000the tunnel boring machines re-entered the Woolwich and Reading clays,progress reduced and settlement increased.Once the settlement exceeded 1%the TBM was stopped and rec-on?gured to mine clay (i.e.number of picks reduced).When tunneling recommenced,the TBM e?ciency im-proved and volume loss averaged a little over 0.5%for the remainder of the drive though the Woolwich &Reading and London Clays,except at Caledonian Road where special control measures reduced the volume loss to 0.15%under critical utilities.

4.3.7.2.C240Stratford to Barrington Road.The Wirth EPBM were driven in closed mode through dewatered sand over much of the contract length.Volume Loss

was

Fig.13.Volume losses observed on the CTRL.

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typically around0.5%.The majority of the drive was driven without the injection of supporting?uid around the TBM skin.Various problems were encountered in the?rst 500m resulting in larger movements at some points, localized surface disruption and damage to property. Nonetheless close control enabled volume losses of around 0.25%to be achieved under critical structures close to the start of the drive.

4.3.7.3.C250Dagenham to Barrington Road.The?rst300 m or so was driven in closed mode with the tunnel crown in alluvium and peat.Considerable problems were encountered here,resulting in variable ground movements and local surface disruption.

After this initial section,the Lovat EPBM were mainly driven in closed mode through London Clay until chai-nage17+000.Thereafter the drives passed down through clay into the underlying sands.

It should be noted that,between chainages18+200and 17+500,signi?cant settlement e?ects from local dewater-ing of the Harwich Formation sands is included in the apparent volume loss graph.

The results from the CTRL project show that,where the EPBM operations were carefully managed,volume losses of0.25–0.5%were readily achieved.This successful control of the ground should give encouragement to promoters of other works that require tunneling beneath urban areas.

5.Incidence of ground displacements on existing structures

Regardless of the method of construction used,the excavation of a tunnel will generate displacements around the opening that may propagate towards the ground sur-face.These displacements may di?er in their magnitude, spread,as well as direction and speed of propagation and may cause damages to structures located in the vicinity of the tunnel(buildings,structures,carriageways,under-ground networks,subways,etc.).

It should also be recognized that the displacements of the building and the ground interact with each other,and that the sti?ness of existing structures will contribute to reducing the magnitude of tunneling induced displace-ments.

5.1.Movements induced on existing structures

Experience shows that old masonry structures are subjected to the same deformation as the ground they are founded upon.This is also the case of most constructions founded on footings or isolated shafts.

Conversely,more recent structures(e.g.made of reinforced concrete)which are heavily reinforced will undergo smaller lateral displacements than the founda-tion ground.The?exural sti?ness of these structures results in reduced distortions in comparison to those experienced by the ground,particularly when continu-ous foundation supports are used(long strip footings, raft).

Sti?structures exhibit a high level of shear resistance and tend to be subject to tilt rather than distortion.This response pattern depends on the building height(number of?oors),the number of openings and type of structure (concrete walls,beams and pillars,etc.).

The location of the structure with respect to the set-tlement trough strongly in?uences the movements it experiences(extension and hogging over the convex parts of the settlement trough;compression and sagging over the concave parts).This is illustrated in Fig.14where some idealized response patterns have been sketched for typical building con?gurations,either narrow or long,and in relation to their location with respect to the settlement trough.

In summary,it can be expected that a structure located in the vicinity of a tunnel under construction will experi-ence the following movements:

–uniform settlement(or heave);

–di?erential settlement(or heave)between supports;

–overall or di?erential rotation;

–overall horizontal displacement;

–di?erential horizontal displacement in compression or extension.

The main parameters involved in the vertical movement of the structure are described in Fig.15.

where:

Fig.14.Typical idealized building response,after(Attewell et al.,1986).

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–L:construction(or element)length in the direction of the settlement trough

–q va:absolute settlement at point A

–q vmax:maximum absolute settlement

–d q VAB:di?erential settlement between A and B

–d q Vmax:maximum di?erential settlement

–x:tilt.

–U BC:rotation of segment BC

–b BC:relative rotation(or angular distortion)of segment BC(b BC=U BC-x)

–a c:angular deformation at point C

–D AD:relative de?ection=maximum displacement relative to the line joining points A and D.

–D AD/L AD:rate of de?ection.

Note:the relative rotation provides an indication of the shear distortion of the structure;the relative de?ection is often correlated to bending distortions.

The main parameters involved in the horizontal movement of the structure are described in Fig.16.

In this?gure:

–q ha:horizontal displacement at point A

–q hb:horizontal displacement at point B

–e hAB:horizontal deformation between points A and B;

ee hAB?q haàq hb

L AB T

5.2.Designation of damages to existing structures

Damages to existing structures fall into three categories:

–architectural damages that a?ect the visual appearance

of the structure;

–functional damages that may be disruptive to the oper-

ation.

–structural damages that a?ect the structural stability.

Damages to structures are caused by cracking of

materials with poor tensile strength such as concrete,

mortar,plaster and coating(the case of materials involved

in underground ducts is analyzed in a separate section).

Failure of supporting structures may occur directly as a

result of excessive cracking or excessive load transfer onto

the reinforcements.To a lesser extent,cracking is harmful

to the structure’s durability by promoting,for example,

steel corrosion.

Crack width therefore appears to be an essential

parameter in assessing building damage.Table1which is

the transcription of the British guidelines can be used in

this evaluation of masonry structures(Burland et al.,1977;

Burland,1995;Mair et al.,1996;Burland).

This classi?cation is primarily intended for practical

purposes and,as a result,is partially based on repair cri-

teria.

Type1:Internal cracks can be easily treated during

routine renovation works,with some rare external cracks

being only noticeable through in depth inspection;

Type2:Internal cracks can be easily?lled but require

the masonry to be rehabilitated to ensure su?cient tight-

ness;doors and windows may be slightly malfunctioning;

Type3:Internal cracks must be opened before?lling;

external cracks may a?ect the quality and durability of

water-tightness,as well as insulation;cracks may cause

signi?cant inconvenience to residents(Serviceability Limit

State)such as deformations of door frames,possible pipe

breakages,

etc.; Fig.15.Vertical movements undergone by the

structure. Fig.16.Horizontal movements undergone by the structure.Table1

Classification of visible damage that may affect standard structures Damage

Type

Damage degree Damage

description

Crack width in

mm(1)

0Negligible

damage

Micro-cracks<0.1

1Very slight

damage

Architectural<1

2Slight damage Architectural,

to be treated

<5

3Moderate damage Functional5–15,or several

cracks>3mm

4Severe damage Structural15–25(2)

5Very severe

damage

Structural>25(2)

Note:(1)crack width is only one aspect of the damaged and cannot be used as a direct measurement.

(2)the number of cracks is also to be considered.

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Type4:Cracking may jeopardize residents’safety (Ultimate Limit State)and structural stability;signi?cant repair works are necessary and may even involve the replacement of wall sections,especially above the opening; doors and windows are twisted,?oors are no longer hor-izontal,supporting beams may be damaged,utilities are broken;

Type5:The structure may become unstable;it should be partially or totally rebuilt.

This empirical classi?cation applies to classical brick and other masonry structures,rather than modern highly rigid reinforced concrete buildings;

–it does not account for speci?c structures where crack-ing may have dramatic consequences,e.g.reservoirs and structures in water-bearing grounds,etc;

–the evolution of damage in types4and5widely de-pends on the structural design(https://www.doczj.com/doc/0c13574965.html,ttice steel struc-tures can be considered particularly resistant);

–it does not take into account of damages that may not be induced by cracking(e.g.deformation or failure of service mains running through the structure).

However it does provide a good assessment for old city buildings which prove the most sensitive and geographi-cally the most likely to be a?ected by a metro or under-ground road project.

5.3.Relationships between the displacements of the struc-ture and cracking

The above classi?cation is based on post movement observations and does not relate to the causes of damages. Some correlation can be achieved by introducing the concept of maximum internal extension or critical exten-sion,e crit(Burland and Wroth,1975)undergone by the structure(or a component of it)prior to cracking becoming visible.This internal extension may either be due to bending(lateral extension,e1)or shear(diagonal extension,e d).Fig.17illustrates this concept using a comparison of the structure with a thick beam model.

Works(Boscardin and Cording,1989)based on a simi-lar approach have allowed a relationship to be established between the critical extension(e crit),on the one hand,and

the distortion(b)and horizontal extension(e h)induced by ground movements,on the other hand.The results of this correlation,as applied to standard structures,are sum-marized in Table2.

This critical extension parameter cannot be directly measured and,from this point of view,it could be useful to provide similar ranges of the other two parameters in-volved in this correlation.Given the number of parameters in?uencing the behavior of a structure located in the vicinity of underground works,it was decided not to provide such corresponding ranges,due to the risk that particular values get generalized.It is recommended to read carefully reference Boscardin and Cording(1989)for further information.

5.4.Relationship between the deformations of the structure and ground movements

A structure subject to the in?uence of a neighboring excavation,either underground or in open cut,appears to be more sensitive to di?erential settlements than if subject to its own weight only.This is due to additional defor-mations imposed by ground movements within the foun-dation strata.It should be noted that deep foundations

too

Fig.17.Thick beam model.

Table2

Relationship between critical extension and cracking

Damage

type

01234&5

e crit(%)60.0500.050<

60.075

0.075<

60.150

0.150<

60.300

0.300

<

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close to the tunnel alignment may result in higher defor-mations in the structure.

Therefore,the response of the structure strongly de-pends on its location with respect to the transverse set-tlement trough(Fig.14).This will determine the extension to which it is subjected,in particular:

–in the case of a building located above the tunnel align-

ment,the diagonal extension,e d prevails on the longitu-dinal extension,e1which is generally compressive.In the particular case of a low,sti?building located above

a narrow trough(sinkhole),e l may however reach high

values at the base;

–in the case of a building located away from the tunnel,

e l prevails;

–if the building is in the vicinity of the point of in?ection of the settlement trough,the deformations are often complex and severe(hogging).

In view of the practical di?culties experienced in achieving an accurate determination of the distribution of ground movements at the surface and modeling of the actual mechanical characteristics of the structures(see Section5.7.4),some relationships have been proposed to correlate the structural damage criterion(e crit)with the average slope of the settlement trough(b aver)underneath the structure.Such a relationship must however be used with care,and is not reproduced in this paper.Details on a more comprehensive method of linking tunneling e?ects to their consequences are described in Section 5.7.4.

5.5.Limits of structural movements for use in preliminary analyses

It is clear that an absolute settlement criterion is insu?cient to solely describe the sensitivity of the overly-ing building to underground movements,unless a very low limit is imposed.

As a?rst approach,reference can be made to article 2.4.6–par.7of EUROCODE7–Part1(ENV.1997-1:1994)(Eurocode7),as quoted hereafter,given its nov-elty at the time of writing this recommendation:

–it is unlikely that the maximum admissible relative rota-tions for open frames,empty frames and bearing walls or continuous masonry walls be the same but they probably range from0.5&to3.33&to avoid a limit state to be reached within the structure.A2&maxi-mum relative rotation is acceptable for many struc-tures.The relative rotation for which an ultimate limit state is likely to be reached is about6.67&;

–for standard structures on isolated foundations,total settlements of50mm and di?erential settlements of 20mm between adjacent columns are often acceptable.

Larger total and di?erential settlements may be admit-

ted if the relative rotations remain within acceptable limits and if total settlements do not cause damages to utilities,or hogging,etc.

–the above indications on limit settlements apply to com-mon routine constructions.They should not be applied to unusual structures or buildings or those for which the load intensity is highly non-uniform.

Numerous indications dealing with less common con-structions or structures can be found in the literature.In addition,tilt(x)of a tall building is visible for values of 4&and above.

Caution:It must be kept in mind that the impact of tilt on building functionality must be carefully examined,gi-ven that a serviceable limit state may be exceeded even without cracking(lift,etc.).

Table3provides some correlation between the above de?ned damage types according to the EUROCODE and British practices(Rankin,1988).

5.6.Tensile deformations admissible by underground utilities

The term‘‘underground utilities’’includes service mains such as drinking water,sewerage,energy(gas,power,oil, etc.)and public or private underground transport infra-structure.This involves various structures in size,design and depth.However,these structures are all characterized by their large length in relation to their transverse size, which is roughly circular.

The response of utilities to undergoing movements is a di?cult soil/structure interaction problem.

Large diameter utilities(>2m)are less numerous, which justi?es case-by-case studies to be performed by means of sophisticated modeling techniques to assess the impact of adjacent underground works in such cases.This can in turn lead to an evaluation of the magnitude of admissible movements.

A similar approach cannot be used for a great number of highly sensitive service mains.The sensitivity of these structures to ground movements(horizontal and vertical) widely depends on their lining material(concrete,cast iron,steel,ductile cast iron,PVC,PE,etc.)and gasket characteristics.In comparison with the values displayed in Table2,the tensile strain criteria respectively associated to the‘Serviceability Limit State’and the‘Ultimate Limit State’of service mains are of the order of0.03%and0.1% for cast iron and lining concrete,0.05%and0.1%for steel, 0.1%and0.2%for ductile cast iron and0.7%and2.0%for plastic materials.

Table3

Range of Serviceability Limit State for standard structures

Damage type Average slope of

settlement trough

under building(%)

Maximum settlement of

the building(mm)

1<2<10

22(410(20

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In fact,the large length of ducts,in comparison to their transverse size and to the width of settlement trough, makes the inner expansion induced by di?erential settle-ments relatively limited,typically1/10th the average duct slope.In addition,the strong longitudinal sti?ness of lin-ings,which are generally made of precast pipes connected with or without?exible gaskets and,results in the mag-nitude of additional deformation caused by horizontal ground displacements remaining limited.It can therefore be concluded that,in most of the cases,only ducts made of brittle materials(cast iron,clayware or concrete)will need to be considered in the determination of admissible ground settlements.

Other than the response of the service main per say, particular attention should be paid to the consequences of di?erential displacements occurring at joints between the duct and other structures located in the area a?ected by the underground works.

Additional consideration should be made in the anal-ysis to the fact that maintenance or replacement of some duct sections may generate relatively moderate costs, particularly when these are scheduled concurrently with the tunneling works.

5.7.Design methodology

The proposed approach to study the e?ects of under-ground works on existing structures can be broken down into six stages,with geotechnical investigations being dealt with separately.

5.7.1.Phase1:investigation of existing buildings

This stage consists in surveying and data collection on the nature,con?guration and condition of the buildings and utilities together with topographic measurements and technical expert reviews.

It is recommended to properly evaluate the actual condition(zero condition)of each structure prior to the start of the construction works and,when possible,to review the history of the building,particularly in terms of movements already experienced.This task is not easy, but it is essential.In this respect,the use of standard classi?cations based on cracking levels should contribute to making this investigation task less subjective.It is recommended that a preventive assessment be included at this stage to provide a strong legal base to the re-cords.

5.7.2.Phase2:information summary

This phase comprises producing a typological classi?-cation of the building and utilities according to the nature, function,value,size,design,age and current condition of its individual components.When possible,a zoning will be developed to identify areas of homogeneous characteris-tics and incorporate geotechnical data collected during the survey.5.7.3.Phase3:selection of damage criteria

This phase aims at determining the objectives to be achieved in terms of damage limitation and converting these objectives into straightforward criteria to be used by the designer.

If the preliminary expert review has led to the produc-tion of data on the condition of the building prior to construction and cracking reports,it is recommended to use the strains involved in the production of the initial reference condition as evaluation criteria.In this case,the initial recorded strain will deducted from the value of allowable extension induced by construction.

The selection of such criteria should also account for the physical possibility to make measurements at the worksite.Except for particular cases,it is often easier to base the evaluation on an average slope of settlement trough,the geometry of which will be determined on site from surveying records taken on carriageways and build-ings.

5.7.4.Phase4:modeling

Modeling works are intended to correlate the building displacements induced by ground movements to its structural deformations.The deformations of the building are assessed,most of the time,by subjecting its founda-tions to the excavation induced ground movements with no account of any in?uence of the structure’s sti?ness. This simplifying and conservative approach also re?ects relatively well the rapid development of settlements in the short term before any adjustment response can be devel-oped within the structure.

Settlement studies conducted during the design phase should enable the engineer and the client to assess the tunneling risks involved in the project.They should therefore make extensive use parametric studies,to eval-uate the in?uence of geotechnical,building,as well as excavation technique parameters.

For given predictions of ground movements,it will often be necessary to quantify their potential e?ects on brick and masonry buildings and this problem has been considered by Burland(1995)and Mair et al.(1996). Broadly speaking their approach is to calculate the tensile strains in the building and to interpret these in terms of damage‘‘degrees of severity’’which are expressed in six categories ranging from‘‘negligible’’to‘‘very severe’’. Each category of damage is described and its ease of repair indicated.

For tunneling works they suggest a three-stage ap-proach:

(1)Preliminary assessment:Ground surface settlement contours are drawn(using the empirical predictive methods given above)and if the predicted settlement of a building is less than10mm it is assumed to have a negligible risk of damage and the assessment process terminated.This is subject to an additional check that no building experiences a slope in excess of1in 500(Note that,for a given settlement,a small shallow

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tunnel will be more damaging than a large deep one because the structural distortion will be greater for the former).

(2)Second stage assessment:The maximum tensile strain in the building is calculated and a‘‘possible’’dam-age category assigned.Note that this will be a conservative assessment because the building strains are based on ‘‘green?eld’’ground movement predictions whereas,in practice,the actual movements may be reduced by the sti?ness of the building.This e?ect could give rise to problems where services enter buildings because of the di?erential movement of the building and the adjacent ground.

(3)Detailed evaluation:This stage is undertaken for buildings where a‘‘moderate’’level of damage has been predicted in stage two.It considers the tunneling se-quence,three-dimensional aspects,speci?c building de-tails and soil/structure interaction.The assistance provided by numerical methods may be valuable at this stage and a hybrid(Gaussian/Finite element)approach has been suggested by Potts and Addenbrooke(1997). Protective measures would then be considered for buildings remaining in the‘‘moderate’’or higher damage categories.

The e?ect of tunneling on pipelines has been considered by Bracegirdle et al.(1996).They addressed the important problem of cast iron pipelines,which are particularly vulnerable because of their brittle nature.Again the ground movements are estimated following the equations given by O’Reilly and New(1982)and the tensile strains in the pipe calculated assuming either?exible or rigid join-ting of the pipe sections.These strains are compared with various acceptability criteria.

Tunneling works at depth usually produce relatively smooth settlement trough shapes and the angular distor-tions occurring at the foundations of structures are rea-sonably predicted by the methods described above. However consideration must sometimes be given to unu-sual geological conditions which may result in localized di?erential settlements and unexpected damage to struc-tures.An example of such an occurrence is reported by Friedman(2003).

Settlements caused by longer-term consolidation may tend to be less damaging than the short term movements but should not be overlooked.

5.7.5.Phase5:determination of the allowable displacement thresholds

The purpose of this stage is to determine the contrac-tual threshold requirements that will have to be met during construction.

The concept of acceptable damages and required ancillary works(preventive or remedial)involves the consideration of non project oriented constraints(human, cultural and legal environment)and economic criteria. These aspects will drive the determination of admissible threshold values.It is not always possible to limit the threshold parameters to a single criterion of admissible movement,unless very stringent requirements are imposed to this criterion.The summary prepared as part of Phase2 is essential to allow developing contractual criteria that are well adapted to the actual needs in terms of building protection.

Threshold values must never be taken as constant;they should primarily be considered as alarm indicators and should be continuously adjusted in view of the observed response of the building subject to tunneling induced ground movements(it is advisable to allow some tolerance on the threshold values,and preclude the development of solutions with0.1&accuracy!).

In a similar manner,one should develop for each pro-ject an alarm(caution)threshold and a stopping thresh-old.

5.7.

6.Phase6:back analysis and calibration of models with observed data

It is clear that the development of settlement esti-mates is not an exact science,and that measurements should be made to monitor the construction works and their e?ects on the surrounding ground and structures (see Section7).

It is absolutely essential,as part of this process,to check model predictions against data obtained from in situ observations.This process of validating the design assumptions should be a routine part of the construction management plan.

6.Settlement control

It would obviously be more satisfactory to plan before construction starts all the measures required to minimize the impact of the tunneling works.However,this optimal situation is hardly feasible both technically and economi-cally due to the uncertainties that remain at the design stage on the ground response to tunneling and the actual condition of the buildings.

Based on past experience,it is recommended to plan, at the design stage,a reasonable set of preventive measures to be used before and during construction, as well develop contingent remedial solutions to be used in case di?culties are encountered during con-struction.

A number of techniques developed for limiting settle-ments or their cause,are described below.The following section focuses on the solutions principles and limitations. One should refer to the relevant specialized literature for further information.

These techniques can be of the preventative or remedial type,and it is generally di?cult to really di?erentiate be-tween the two categories;in fact this distinction is mostly subjective and depends mainly on when the decision is made to implement them.

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6.1.Improvement of the overall project conditions

At the preliminary design stage,one should aim at selecting an alignment that o?ers the most favorable conditions for settlement control.This can be achieved by selecting;

–the largest depth of cover,provided that this does not cause the tunnel drive to encounter ground layers of poorer characteristics;

–ground layers of good mechanical properties for the alignment,provided they are of su?cient thickness (at least one tunnel diameter above the crown).

Should this not be the case,it is better to excavate the tunnel underneath a sti?er layer,and rely on the bridging e?ect this can produce,rather than tak-ing the risk of disturbing its mechanical stability by cutting through it;

–the smallest excavated cross section.This recommenda-tion often leads,for a transportation project,to choos-ing between a single or twin-tube tunnel.The decision is generally made on the basis of the nature of the grounds to be encountered,the advances in con?nement technologies and economical opportunities(e.g.avail-ability of used Tunnel Boring Machines).Although the twin-tube option is often preferable,attention should be paid in that case to ensuring that the distance between both tubes is su?cient to avoid cumulative settlements;–an as-straight-as-possible alignment if a shield is used.

One should also keep in mind,when selecting the con-struction method,that increased settlements are often associated with stoppages or reduced rates of face ad-vance.

6.2.Improvement of ground characteristics

Ground improvement can be achieved by altering its mechanical and/or hydraulic characteristics.The following sections are limited to providing some general background on technologies that can be assumed to be well known to practitioners.

6.2.1.Conventional grouting

Grouting of the ground mass can be used to increase its cohesion(consolidation grouting)and reduce its perme-ability(water-tightness grouting).The e?ectiveness of the techniques relies on the groutability of the ground[see AFTES recommendation(AFTES,1988)]and their ease of implementation.

It can be carried out from the ground surface,when permitted by site conditions,or from the tunnel which,in turn,results in reduced rates of advance.In the particular case of shield driven tunnels,this would require speci?c provisions when manufacturing the machine.

This technique may induce ground heave if uncon-trolled fracture is allowed to develop within the ground,which may be the case with shallow urban tunnels where the magnitude of in situ stresses do not allow high gro-uting pressures to be sustained.Interestingly,there ap-pears to be less concern for the risks associated with heave rather than settlement,although both phenomena can cause damages of the same nature,with cumulative e?ects when they occur concurrently.

One should be careful with the medium term e?ciency of grouting works.In the case of gel grouting performed several months prior to tunneling,some loss of mechanical performance may be experienced as a result of grout deterioration with time(synaeresis).

It must also be remembered that the risk of polluting the water table should be assessed for each product type to be used.

https://www.doczj.com/doc/0c13574965.html,paction grouting

In the case of pervious grounds,such as?lls,for which conventional grouting would lead to using large quantities of grout without any guaranteed e?ciency,or in some loose grounds,considerable improvement of the overall sti?ness can be achieved by injecting a dry mortar from boreholes.

This technique allows an overall improvement of the mechanical characteristics of the ground to be obtained. It may be implemented from the surface as part of an underpinning process.Its e?ciency must be controlled by means of careful topographic surveying,with adjustments being made on the basis of observed surface heave.

The implementation of grouting works(conventional or compaction)performed concurrently with the tunneling process,is referred to as compensation grouting(Baker et al.,1983;Harris et al.,1994).

6.2.3.Jet grouting

This technique consists in high speed injection of grout into the ground through pre-installed drill pipes.The injection of grout,with various speed levels depending on the technique used(single,double or triple jet with or without pre-washing),de-structures the ground at a dis-tance which varies with the compactness of the ground. The grout mixes with the ground to form a column of stabilized soil.The diameter of the column varies in the range0.30–1.20m depending on the technique used and the consistency and nature of the ground.

Ground treatment can be performed through vertical, inclined or sub-horizontal borings.The last option(with single jet)can be implemented from the tunnel face. Particular attention must be paid,when using this ap-proach in?ne soil grounds,to potential adverse e?ects associated with unexpected pressure build up within the ground being excavated at the face(sudden fracture and large heave).

When ground improvement is required,this technique may be used in lieu of grouting in very?ne grounds.The e?ciency of this technique is well proven,and can lead,

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when used with a?ne drilling mesh,to total ground substitution.There are,however,a number of imple-mentation constraints(power consumption,spoil pro-cessing and removal,instantaneous loss of bearing capacity before the grout has set)which require a thor-ough evaluation to be made before this technique is used.

6.2.4.Ground freezing

The principle of this technique is to build a shell or vault of frozen ground around the area to be excavated. The whole tunnel cross section may also be frozen if the capacity of the system is su?cient.The technique may be used in almost any grounds with permeabilities lower than 10)3m/s.

Freezing can be carried out from the surface or the working face.In both cases,the main di?culty lies both in the control of drilling deviations during the installa-tion of the freezing pipes(which length is limited to50 m)and of the circulation of large quantities of under-ground water.

Although this technique can allow ground stability to be improved dramatically,it also requires very tight con-trol because of the potential detrimental e?ects it can cause within the ground,with heave being generated by seepage of groundwater towards the cold source during freezing and subsequent settlement–and alteration of the ground properties while thawing–at the end of the freezing process.

6.2.5.Drainage

The control of hydraulic gradients that may a?ect the stability of the tunnel face may be achieved by lowering the groundwater table from the surface or through drainage at the face.This should be implemented as far ahead of the face as possible.

When the ground is likely to undergo consolidation settlements,or could be made unstable as a result of dewatering(karst?ling),a risk assessment of the possi-ble consequences of the implementation or lack thereof of drainage must be undertaken prior to using this technique.

https://www.doczj.com/doc/0c13574965.html,pensation grouting

Compensation grouting is most commonly carried out in association with new excavation,which may be adjacent or beneath existing tunnels.The grouting may be intended to protect overlying structures or the existing tunnels.The e?ects of excavation and compensation grouting will de-pend largely on the position of each in relation to the existing structures and the sequence of grouting and excavation employed.Grouting either in advance of or following completion of excavation may reduce these ef-fects.

Compensation grouting can,when carried out in close proximity to existing tunnels,induce modes of deforma-tion in linings that are far more damaging than the ellip-tical deformation,which usually accompanies the general loading and unloading of tunnels.When carrying out monitoring of tunnel linings during grouting,therefore,it is not su?cient simply to measure diametric change.It is necessary to determine the mode of deformation and,in the case of bolted segmental cast iron linings,determine tensile strains at critical locations.Damage to cast iron linings arising from compensation grouting is usually in the form of tensile cracking of the?anges at bolt positions. Damage in the form of linear cracks along the long axis of the pans of segments may also be seen.Linings where adjacent rings have been‘rolled’are particularly suscep-tible to damage.Where damage is expected,it may be prudent to release bolts and allow some articulation of the linings.

Damage may also occur where tunnels are lifted by compensation grouting beneath them.In this case,damage may occur as the tunnel linings articulate in the longitu-dinal direction,and may be concentrated at changes in section,headwalls,etc.

The process of compensation grouting involves the injection of grout into the ground at high pressure.The process is essentially a jacking operation which produces movement of the ground regardless of whether the grout injected is concurrent with tunnel construction or acti-vated afterwards.Thus a reaction force is necessary in order to generate the required(upwards)movement and, consequently,there is unquestionably the potential for loading and deformations to be generated in any tunnel lining or temporary works situated below an area of grout injection.

The controlling factors can be divided into those determined by the design of the grouting facilities and those which relate to the implementation of injections for a given situation.

Design of the grouting system:

–the vertical total stress at the grouting horizon which has a strong in?uence on the grout pressure in the ground;

–the vertical spacing between the grouting horizon and the tunnel or excavation which in?uences the spread of load;

–combination with other factors causing loading to a tunnel e.g.close proximity tunnels;

–the properties of the tunnel lining(sti?ness,strength, joints).

Implementation of injections is a?ected by:

–the timing of injections relative to excavation;

–the volume of individual injections;

–the plan location of injections relative to the excava-tion;

–the properties of the grout particularly with respect to the shape and extent of the grout bulb/fracture formed;–the quantities of grouting undertaken.

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近义词和反义词

一、近义词和反义词 近义词（同义词） 读音不同而意思相同或相近的词叫近义词。 恰当地运用近义词，可以表现不同的感情和风格，这就需要我们了解近义词之间的细微的差别。

二、常见句式 按不同的作用，句子可以分为基本类型：陈述句、疑问句、祈使句、感叹句、肯定句、否定句、设问句、反问句、“把”字句和“被”字句。 1、陈述句 只要意思是在告诉别人一件事，都可以上视作陈述句。（陈述句的语调一般是平的，句末用句号。）例：我交上了作业。 2、疑问句 当我们对某一件事不明白或不理解时，就要用一句话去问别人，这句话就叫做疑问句。（疑问句的语调一般是上扬的，句末用问号。）例：你吃饭了吗？ 3、祈使句 是用来要求别人做某件事或不做某件事的句子叫祈使句。（句子末尾的语调一般向下降，句末用句号，语气较强的用感叹号。）例：请你赶快把书送回去。 4、感叹句 带有喜欢、厌恶、痛恨、悲伤、快乐、惊讶、愤怒、恐惧等强烈感情的这类句子叫做感叹句。（末尾的语调一般是下降的，句末大都用感叹号。） 例：昨天是我的眼睛骗了我，那“鸟的天堂”的却是鸟的天堂。 5、肯定句 肯定一件事的句子叫肯定句。（肯定句中往往没有明确表示肯定的词语。）例：他是我妈妈。

6、否定句 否定一件事的句子叫否定句。（否定句中常用“不”“没”“没有”“否认”等词来表示否定。）例：他不是我妈妈。 7、设问句 说话或写文章时，为了强调自己的看法和结论，先提出一个问题，然后紧跟着把自己的看法说出来，也就是自问自答，这就叫设问句。例：是谁创造了人类世界？是我们劳动群众。 8、反问句 反问句提出问题，只问不答把答案巧妙地藏在问话里，读者可以从中体会到明确的答案。（反问句中一般都有明显的反问词语出现，如：“难道”“不是…..吗”等。） 例：万里长城难道不是劳动人民智慧和汗水的结晶吗？ 9、“把”字句 在句子中“把”字来表示处置关系，这样的句子叫做“把”字句。“把”字没有什么实在的含义，只表示一种“处置”与“被处置的关系。”“把”字常用在两种事物的名称之间，表示前者处置了后者。 10、“被”字句 在句子中“被”字来表示处置关系，这样的句子叫做“被”字句。表示一种“处置”与“被处置”的关系，只不过他所表示的关系与“把”字恰恰相反。例：我被老师批评了

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小学语文必考近义词和反义词

近义词和反义词是小学语文学习的重点和难点，也是必考题型之一。 另外学好近义词和反义词还有助于孩子在作文时的遣词造句，对准确表达文意起到至关重要的作用。（收藏了，没事儿就考考孩子） 1.单字类 观──看 寒──冷 舟──船 暖──热 鸣──叫 入──进 归──回 遥──远 瞅──看 藏──躲 绝──尽 叫──喊 望──看 看──瞧 铺──展 去──往 2.词语类 来回──往返 立刻──马上 赶快──赶紧 突然──忽然 寒冷──严寒 坚决──果断 恐惊──恐惧 暗香──幽香 荒芜──荒凉 得意──自得 听见──闻声 农夫──农民 慈祥──慈爱 飞翔──翱翔 详细──具体 每天──天天 赛过──胜过 好像──似乎 闻名──著名 满意──满足 新居──新房 捕获──捕捉 海疆──海域 天涯──天边 结实──坚固 遇到──碰到 轻巧──轻便 整齐──整洁 证明──证实 评比──评选 注意──注重 供应──供给 辛苦──辛劳 认识──熟悉 预报──预告 舒畅──愉快 立刻──连忙 突然──忽然 四周──四面 精彩──出色 笨重──粗笨 直立──竖立 听从──服从 绝技──特技 附近──四周 惊叹──赞叹 柔美──优美 洒脱──潇洒

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小学英语近义词_反义词_同音词辨析和练习 一、小学英语同音词 B—bee—be no—know C—see—sea hi—high I—eye for—four R—are son—sun T—tea our—hour U—you pair—pear Y—why here—hear to—two—too there—their aunt father—farther who’s—whose by—bye—buy right—write aren’t— c-see(看见)-sea(海洋) b-be(是；成为)-bee(蜜蜂) y-why(为什么) for(为)-four hi(喂)-high(高) no(不)-know(知道) by(通过)-bye(再见) son(儿子)-sun(太阳) our(我们的)-hour(小时) right(对的)-write(写) meet(遇见)-meat(肉) hear(听见)-here(这儿) there(在那里)-their(他/她/它们的) dear(亲爱的)-deer(鹿）pear(梨)-pair(一双/副……) father(父亲)-farther(较远地) weight(重量)-wait(等待) it's(它是)-its(它的) who's(谁是)-whose(谁的) 二、小学英语近义词 toilet — WC listen —hear class —lesson everyone —everybody glass —cup large —big glad —happy like —love little —small photo —picture purse— wallet start —begin home—house learn—study beautiful—pretty usually —often look —see cycle —bike near —beside hi —hello quick —fast garden —park desk —table speak —say —talk river —lake go home — a moment ago— just now a lot of —lots of — many be good at —do well in of course —sure be from ——go for a walk take a bus —by bus would like —want look for— find 三、小学英语反义词 big（大的）----- small（小的）bad（坏的）----- good（好的） bright（明亮的）----- dark（黑暗的）black（黑的）----- white（白的） beautiful（美的）----- ugly（丑的）cold（冷的）----- hot（热的） cool（凉爽的）----- warm（温暖的）e（来）----- go（去） cry（哭）----- laugh（笑）clever（聪明的）----- stupid（笨的） different（不同的）----- same （相同的）difficult（难的）----- easy（容易的） dirty（脏的）----- clean（干净的）day（白天）----- night（夜晚） early（早的）----- late（迟的）fast（快的）----- slow（慢的） glad（高兴的）----- sad（悲伤的）inside（里面的）----- outside（外面的） in（里面）----- out（外面）large（大的）----- little（小的） left（左）----- right（右）quiet（安静的）----- noisy（吵闹的） new（新的）----- old（旧的）loose（松的）----- tight（紧的）

消息与通讯的特点与区别

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近义词和反义词

A 爱慕—喜爱安然—安稳遨游—游览奥秘—神秘懊悔—后悔 B 报酬—酬劳悲哀—悲伤崩塌—倒塌必然—必定避免—幸免便宜—廉价哺育—培育 C 猜测—推测才干—才能采用—采纳诧异—惊诧颤动—抖动沉浸—沉醉 惩罚—惩处迟延—拖延耻笑—讥笑炽热—酷热憧憬—向往酬谢—答谢 啜泣—抽泣创造—制造绰号—外号慈悲—慈善慈祥—慈爱葱茏—葱郁 聪明—聪慧催促—督促璀璨—明亮 D 打扮—装扮打搅—打扰胆怯—害怕淡忘—忘却调皮—淘气叮嘱—嘱咐 陡崖—悬崖妒忌—嫉妒对付—应付对照—对比 E 恩赐—赏赐 F 发布—公布发誓—宣誓发展—进展繁殖—生殖反抗—抵抗防御—防备 妨碍—阻碍分量—重量分外—格外愤怒—愤慨锋利—锐利服侍—侍侯 浮现—出现赋予—给予 G 告别—告辞恭敬—尊敬估计—估量鼓励—鼓舞固然—当然故意—有意 关心—关怀管理—治理贯通—贯穿瑰宝—珍宝 H 含糊—模糊寒冷—严寒和蔼—和气宏伟—雄伟欢跃—喜悦环绕—围绕 荒芜—荒凉回顾—回忆汇集—汇合获取—猎取祸患—祸害 J 机灵—灵巧积累—积存即将—马上疾驰—飞奔寄托—寄予讥笑—嘲笑 坚固—牢固坚毅—坚强艰苦—艰难艰难—困难建造—建筑交织—

娇嫩—柔嫩节制—克制竭力—尽力解救—拯救谨防—防备谨慎—慎重 惊险—危险精密—周密精致—精巧敬仰—仰慕境界—境地居然—竟然 绝望—无望 K 开辟—开发开辟—开拓慷慨—大方可惜—惋惜空暇—空闲恐怖—恐惧 控制—操纵款待—招待愧疚—内疚 L 劳苦—劳累冷艳—艳丽黎明—拂晓立即—马上灵便—灵活领略—领会 浏览—扫瞄隆重—盛大沦陷—沦落罗列—排列 M 满意—中意漫步—闲逛茂密—茂盛朦胧—模糊弥漫—布满密切—紧密 勉励—鼓励勉强—牵强藐视—轻视泯灭—消灭明丽—明媚明艳—鲜艳 摹仿—模仿蓦地—突然模范—榜样 N 鸟瞰—俯视凝结—凝聚凝视—注视挪移—移动 O 偶尔—间或 P 判断—推断批评—批判疲惫—疲乏疲倦—疲乏僻静—偏僻漂亮—美丽 飘荡—漂浮飘拂—漂动品格—品行平生—终生平庸—平凡平整—平坦 普通—一般 Q 欺凌—凌辱奇妙—奇异歧视—卑视气魄—气势气势—气概启示—启发 清晰—清楚乾坤—天地潜伏—埋伏谴责—责备惬意—满意亲密—亲热 轻蔑—轻视轻盈—轻快清澈—清亮清纯—纯洁清晰—清楚驱赶

[试论秘书工作的性质和特点] 性质和特点的区别

[试论秘书工作的性质和特点] 性质和特点 的区别 秘书工作的性质、特点和作用是个旧题。自秘书学诞生以来，接连问世的论著几乎都要论及，相关的单篇论文亦屡见不鲜。但时至今日，旧题缘何新做呢？首先，是性质同特点两个概念重叠混淆，它们的关系没有作出科学的阐释。 再者，性质、特点与作用相关的提法，也有重叠之感。 出现上述现象的原因何在呢？1．用日常概念或直观感性经验来代替科学的理论概念。 2．从秘书部门的单项任务去相应地提出单个的性。这是一种就事论事的思想方法，缺乏必要的概括和抽象，其结果，秘书工作的性自然很多了。3．对性质、特点的联系和区别及其相互关系缺乏科学的理解，甚至出现了本末倒置的现象。这里有两个问题，其一，是性质决定特点，还是特点决定性质？其二，承办事务是秘书工作的基本性质吗？4．作者的主观随意性，移植管理科学的有关概念，缺乏必要的正确的阐释。 二、旧题新做的基本依据1．考察秘书工作的性质、特点和作用要以行政组织法为指导。 2．从国家行政机关的系统性宏观地考察秘书工作的性质、特点和作用。3．要把日常观念或直观经验概念提炼上升为科学的理论概念。 三、旧题新做之我见秘书工作的性质、特点和作用属

于秘书学的基本概念，而基本概念正是奠定概念体系的理论基础。 本质和特点是既有联系又有区别的两个概念：本质概括了事物特点的主要方面，而特点是事物某一方面的本质表现。是本质决定特点而不是特点决定本质，对于秘书工作的特点，我以为提以下四个就可以了： 1．政策性。2．综合性。3．服务性。 4．机要性。上述四个主要特点，都是从辅助性那个主要的东西派生出来，既与本质相通，又是某一方面的本质反映。

辨析近义词的方法

辨析近义词的方法 1．词义轻重程度不同：希望──期望──渴望（轻、重） 2．词义范围大小不同：事情──事件──事故（从大到小） 3．具体与概括不同：船──船只（具体、概括） 4．词义着重点不同：化装──化妆（装扮──打扮）；才能──才华（做事能力──文艺特长）；陡峭──峻峭（坡度大而陡直──高而险） 5．搭配对象不同：交流（思想、经验）──交换（礼物、意见） 6．适用对象不同：爱戴（对上）──爱护（对下） 7．词性和功能不同：突然（形，作状、谓、定语）──猛然（副词，作状语） 8．感情色彩不同：果断──决断──武断（褒──中──贬） 9．语体色彩不同：吓唬──恐吓（口语──书面语） 反义词是词性相同、词义相反的词。 1 反义词：凉爽(闷热)、欢乐（痛苦） 2 反义词：理解（误解）、强烈（微弱） 4 反义词：整体（部分）、茁壮（瘦弱）、奉献（索取）、同（异）、整（零）、 美（丑） 5 反义词：赞美（嘲笑）、燃烧（熄灭）、透明（浑浊） 6 反义词：天堂（地狱）、秀美（粗陋） 7 反义词：吸引（排斥）、纯净（污浊） 8 反义词：迷惑（清醒）、可爱（可憎）、得意（失意） 9 反义词：憨厚（狡诈）、神秘（普通）、保存（销毁） 10 反义词：机灵（迟钝） 11 反义词：失败（成功）、信心（灰心）、招集（解散）、抵抗（投降） 12 反义词：屈辱（荣誉、荣耀）、免除（任命） 13 反义词：异常（正常）、分析（综合） 14 反义词：聚集（分散）、舒服（难受）、精彩（低劣、粗糙）、举世闻名（默 默无闻） 15 反义词：俊俏（丑陋）、格外（一般、普通）、出现（消失、隐没）、光彩 （羞耻、耻辱）、告别（欢聚、团聚）、生机勃勃（死气沉沉）16 反义词：活泼（严肃、呆板）、甜津津（苦巴巴）、成熟（幼稚、稚嫩）、 热闹（冷清） 17 反义词：奇怪（正常、平常）、聚精会神（心不在焉）

产品特性与过程特性的区别

产品特性和过程特性的区别如果说产品特性从安全、法规、性能、尺寸、外观、装配等方面考虑，过程特性仅从产品形成过程中的参数（温度、压力、电压、电流）等考虑是不是很准确呢？ 欢迎大家讨论，敬请指教！ 简单的讲, 产品特性是随着产品走,如过程加工中产品的尺寸.材料等, 过程特性是在过程上不随产品走的东西,如工艺参数温度.压力等. 我一般是作这样的区分. 产品特性能做spc, 过程特性不能产品特性一般是指产品工程规范的要求；过程特性可以指工艺（过程）参数过程特性保证产品特性 虽然大家说的都对，但是怎样确定产品和过程的特殊特性呢？是不是特殊特性都要采用SPC 控制或100% 控制或防差错系统？ 通过fmea 来确定的！根据过程的风险以及顾客的呼声来确定控制方法！ 特性矩阵分析-初始特殊特性清单-FMEA- 控制计划？ 还是：特性矩阵分析-FMEA- 初始特殊特性清单--控制计划？ 第一阶段: 确定初始过程特殊特性清单FMA 分析 第二阶段 样件控制计划产品和过程特殊特性 第三阶段 特性矩阵图试生产控制计划PFMEA 第四阶段: 控制计划产品特性，随着产品走，是在过程中形成的，而过程特性不随产品走，我们只有通过过程特性来控制产品特性。而控 制产品特性包括人、机、法、环、测和过程规范，故这些都是过程特性；产品特性可以从料、技术要求、技术规范进行考虑。 谁有更深层次的讨论，请指教。 更正一下。 初始特殊特性清单-特性矩阵分析-PFMEA- 控制计划先有特殊特性，才有特性矩阵分析。体现特性和过程之间的相互关系及特性之间的影响。产品特性和过程特性的区别：用过程特性去保证产品特性啊！产品特性是要带到最总顾客的手里啊！而过程特性是在过程中为保证产品的特性而对过程设置的特性，过程控制主要控制“过程特性啊” 特殊特性释义 以下是我对特殊特性的一些见解，希望能够得到大家的评论！也是为了“特殊特性清单是越来越长还是越来越短”的 讨论而作 特殊特性是APQP 的核心。无论是QS9000 还是TS16949 ，其实对于特殊特性的解释和理解是一样的。不同的是 QS9000 着重阐明了通用、福特、克莱斯勒三大车厂的特殊要求。如对特性的等级分类以及特性符号标记。而TS16949 则体现的是大众化的，灵活的，可根据顾客而定的特性要求。 现在就以TS16949 体系中对于特殊特性的理解来展开说明，一直推广到QS9000 中的特殊要求。 TS16949 中特殊特性的出处说明！ TS16949 有两处地方出现过特殊特性。 第一处： 7.2.1.1 顾客指定的特殊特性组织必须在特殊特性的指定、文件化、和控制方面符合客户的所有要求。 解释：也就是说凡是客户指定的特殊特性，应在相关文件中体现。 相关文件有：设计FMEA、过程FMEA、控制计划、作业指导书、检验规范等在上述文件中应作特殊特性符号的标记。 第二处： 7.3.2.3 特殊特性组织必须应用适当的方法确定特殊特性。

服务和商品的四个特性区别

服务与商品的区别在于下面所讲的四个服务特征： [服务无形性] 指服务在被购买之前是看不见、尝不到、抓不着、听不到也闻不出的。例如，人们在做美容手术之前是看不见成效的，航空公司的乘客除了一张飞机票和安全到达目的地的承诺之外什么也没有。 为了降低不确定性，购买者纷纷寻找服务质量的“标志”。他们的结论得自于他们所能看到的场所、人员、设备和通信状况。因此，服务提供者的任务是使服务在一个或几个方面有形化。与产品营销人员努力在增加有形产品的无形成分正好相反，服务营销人员努力增加的是无形产品的有形成分。 有形产品通过生产，然后存储、销售，最终被消费掉。与此形成对比的是，服务是先被销售，然后同时被生产和消费。 [服务不可分性] 指服务不能与服务提供者分离，不管这些提供者是人还是机器。如果服务人员提供了服务，那么这位服务人员便是服务的一部分。由于顾客在服务进行时也在场，所以提供者和顾客之间的相互作用成为服务营销的一大特色。提供者和顾客都会影响到服务的结果。 [服务可变性（或不一致性、易变性）] 指服务的质量取服务的人员，以及时间、地点和方式。例如一些饭店，比如香格里拉饭店，因提供较好的服务而著称。还有，即使是在同一家香格里拉饭店中，一位登记台服务人员可能笑容可掬、效率很高，而离他几英尺远的一位服务人员可能正心情不佳，效率也很低。甚至同一个香格里拉服务人员的服务也会因他或她在接待顾客时心情的好坏而导致服务质量大不相同。 [服务没有存货性] 因为服务是一行动或一次表演，而不是顾客可以保留的一件有形的物品，所以它是“易腐的”和不能被储存的。当然，必要的场地、设备和劳动能够被事先准备好以创造服务，但这些仅仅代表生产能力，而不是产品本身。 在服务企业中拥有未被使用的能力就像水流进水槽却没有塞子：除非顾客（或需要服务的物体）在那里接水，否则水就被浪费了。当需求超过能力时，顾客会失望地离开，因为没有存货提供支持。因此，服务营销人员的一项重要任务就是要找到平衡需求水平的方法，以适应服务的供应能力

产品特性与过程特性的区别

产品特性和过程特性的区别 如果说产品特性从安全、法规、性能、尺寸、外观、装配等方面考虑，过程特性仅从产品形成过程中的参数（温度、压力、电压、电流）等考虑是不是很准确呢？ 欢迎大家讨论，敬请指教！ 简单的讲,产品特性是随着产品走,如过程加工中产品的尺寸.材料等, 过程特性是在过程上不随产品走的东西,如工艺参数温度.压力等. 我一般是作这样的区分. 产品特性能做spc,过程特性不能 产品特性一般是指产品工程规范的要求；过程特性可以指工艺（过程）参数 过程特性保证产品特性 虽然大家说的都对，但是怎样确定产品和过程的特殊特性呢？是不是特殊特性都要采用SPC控制或100%控制或防差错系统？ 通过fmea来确定的！根据过程的风险以及顾客的呼声来确定控制方法！ 特性矩阵分析-初始特殊特性清单-FMEA-控制计划？ 还是：特性矩阵分析-FMEA-初始特殊特性清单--控制计划？ 第一阶段: 确定初始过程特殊特性清单FMA分析 第二阶段 样件控制计划产品和过程特殊特性 第三阶段 特性矩阵图试生产控制计划PFMEA 第四阶段: 控制计划 产品特性，随着产品走，是在过程中形成的，而过程特性不随产品走，我们只有通过过程特性来控制产品特性。而控制产品特性包括人、机、法、环、测和过程规范，故这些都是过程特性；产品特性可以从料、技术要求、技术规范进行考虑。 谁有更深层次的讨论，请指教。 更正一下。 初始特殊特性清单-特性矩阵分析-PFMEA-控制计划先有特殊特性，才有特性矩阵分析。体现特性和过程之间的相互关系及特性之间的影响。 产品特性和过程特性的区别：用过程特性去保证产品特性啊！产品特性是要带到最总顾客的手里啊！而过程特性是在过程中为保证产品的特性而对过程设置的特性，过程控制主要控制“过程特性啊” 特殊特性释义 以下是我对特殊特性的一些见解，希望能够得到大家的评论！也是为了“特殊特性清单是越来越长还是越来越短”的讨论而作 特殊特性是APQP的核心。无论是QS9000还是TS16949，其实对于特殊特性的解释和理解是一样的。不同的是QS9000着重阐明了通用、福特、克莱斯勒三大车厂的特殊要求。如对特性的等级分类以及特性符号标记。而TS16949则体现的是大众化的，灵活的，可根据顾客而定的特性要求。 现在就以TS16949体系中对于特殊特性的理解来展开说明，一直推广到QS9000中的特殊要求。 TS16949中特殊特性的出处说明！ TS16949有两处地方出现过特殊特性。

反义词辨析——教(学)案

教学过程 一、导语 词语是语言的基础，现代汉语的词语浩如烟海、丰富多彩，其中有为数不少的词语，它们在意义上相近，它们叫同义词。那么，你们知道与同义词相反的是什么词吗？它就是反义词。这节课我们要讲的容就是——辨析反义词 二、知识点讲解 1.什么是反义词 意义相反或相对的一组词叫做反义词。如：“上”和“下”，“前进”和“后退”，“好”和“坏”就各是一组反义词。反义词是客观事物互相对立、互相矛盾的关系在语言词

汇中的反映。但有的反义词反映的事物本身，孤立地看来并不互相矛盾对立，如“手和脚”，“冬和夏”等，它们构成反义关系，主要是由社会习惯决定的。构成反义词的两个或两个以上的词，必须是属于同一意义的，如“长和短”都属于度量的，“早和晚”、“古和今”都属于时间的，“快和慢”都属于速度的。不同畴的词，如“浅”和“大”就不能构成反义词。因此，反义词既是相互对立的，又是相互联系的。 反义词是就词与词的关系说的，不是词与词组关系说的，所以，“好”与“不好”，“干净”与“不干净”等虽有反义关系，但都不是一组反义词，因为“不好”、“不干净”是词组。 由于词的多义和同义现象存在，一个词可能有几个反义词。如“老”是多义词，它的本义是年纪大，引申义有“旧”、“长过头”等意义，这些引申义的相反意义，就都成了“老”的反义词——“幼”、“新”、“嫩”。又如“开”的反义词是“关”，由于“关”的同义词有“闭合”、“封”、“盖”等词，这些词就都成了“开”的反义词了。 2.反义词的分类 反义词的类型大致分为两类： 1）绝对反义词。两个意义绝对相反的词，肯定甲，就必须否定乙。这类反义词，不依靠语言环境（上下文）就可以指出来。如“生和死”、“动和静”、“有和无”“赞成和反对”等。 2）相对反义词。两个意义相反的词，肯定甲就否定乙，但否定甲，不一定就肯定乙，因为还有丙、丁等其他意义。如“白”和“黑”相反，但是，不“白”，却不一定是“黑”；不“黑”也不一定就是“白”，它们中间还有很多颜色存在。 正因为是相对的反义，所以哪个词跟哪个词构成反义关系，并不是固定不变的。在特