Lecture 3 soil water characteristic curve

不同干密度下非饱和土土-水特征曲线陈宇龙;内村太郎【摘要】对吸湿与脱湿过程中引起非饱和土土-水特征曲线进行分析,观察不同密度土样的土-水特征曲线与滞后现象.利用Fredlund and Xing的土-水特征曲线模型对试验数据进行拟合,得到模型拟合参数与土-水特征曲线参数的定量关系.研究结果表明:进气值随着参数a的增大而线性增大,残余基质吸力随着参数m的增大而呈幂函数减小,减湿率随着参数n的增大而呈指数减小.干密度对土-水特征曲线有显著影响.随着干密度增大,残余基质吸力与进气值及进水值增大,减湿率减小,滞后现象的显著程度降低.瓶颈效应、不同的接触角和空气体积是造成滞后效应的主要因素.%Drying and wetting soil-water characteristic curves (SWCCs) for two sandy soils were investigated to research the effects of dry density on the SWCCs and hysteretic behaviors. Drying and wetting SWCCs were obtained for two sandy soils with different dry densities. The test data were best-fitted using the Fredlund and Xing equation. The results show that the fitting parametera increases linearly with the increase of the air-entry value of the SWCC, the fitting parameterm decreases with the increase of the residual suction of the SWCC and the fitting parametern also decreases with the increase of the slope of the SWCC. With the increase of parametera, the air-entry value increases linearly; with the increase of parameterm, the residual suction decreases in power function, and with the increase of parameter n, the slope of drying SWCC decreases in exponential function. The dry density has significant effects on the soil-water characteristic curve. With the increase of dry density, the residualsuction, air-entry value and water-entry value increase, and both the slope of drying SWCC and the hysteresis decrease. The hysteresis is mainly attributed to the ink-bottle effect, the contact angle effect and entrapped air.【期刊名称】《中南大学学报（自然科学版）》【年(卷),期】2017(048)003【总页数】7页(P813-819)【关键词】非饱和土;土-水特征曲线;干密度;滞后现象【作者】陈宇龙;内村太郎【作者单位】东京大学土木工程系,日本东京,113-8656;东京大学土木工程系,日本东京,113-8656【正文语种】中文【中图分类】TU441土−水特征曲线(soil-water characteristic curve，SWCC)是描述非饱和土中吸力与饱和度或体积含水率之间关系的曲线[1−2]，它能够反映非饱和土的众多性质如渗透性、强度、应变、应力状态等[3−6]。

Nature of Soil–Water Characteristic Curve for Plastic SoilsFernando A.M.Marinho 1Abstract:Determinations of unsaturated soil parameters using experimental procedures are time consuming and difficult.In recent years,the soil–water characteristic curve ͑SWCC ͒has become an important tool in the interpretation of the engineering behavior of unsaturated soils.Difficulties associated with determining such parameters have justified the use of indirect determination.This paper presents the general behavior of the SWCC for plastic soils,in terms of gravimetric water content versus soil suction,according to the soil type,and also the stress history of the soil.In order to investigate possible relationships between the liquid limit ͑w 1͒,suction capacity and SWCC,data from the literature were collected and analyzed.The present study examined 49SWCCs from 18soils.The objectives of the paper were twofold:to contribute to the interpretation and use of the SWCC and to present a simple method for inferring the SWCC for plastic soils,taking into account the stress history of the soil.DOI:10.1061/͑ASCE ͒1090-0241͑2005͒131:5͑654͒CE Database subject headings:Unsaturated soils;Soil water storage;Soil suction;Liquid limit;Stress history .IntroductionThe soil-water characteristic curve ͑SWCC ͒has been used as a tool for predicting the mechanical and hydraulic properties of unsaturated soils.The indirect determination of these parameters may be justified not only by the difficulties involved in such tests but also by the costs associated with determinations of these pa-rameters ͑e.g.,Fredlund 1998͒.The proliferation of SWCC use for indirect determination of unsaturated soil properties is un-avoidable and in some cases desirable.The volume change with increased suction will depend on the initial void ratio and/or the stress history.The shape of the SWCC reflects the influence of stress history on the soil.For this reason,models used for pre-dicting unsaturated soil parameters should consider the influence of the stress history of the soil via the SWCC.An understanding of the phenomena involved in the relationship between water con-tent and suction is paramount for adequate interpretation of the SWCC.One of the objectives of this paper was to contribute to the interpretation and use of the SWCC,which in turn would help in understanding the engineering behavior of unsaturated soils.The SWCC was analyzed in terms of gravimetric water content versus soil suction,according to the soil type and taking into account the stress history of the soil.A further objective was to present a simple method for deducing the SWCC for plastic soils using one water content/suction determination and the liquid limit of the soil.Background to Soil–Water Characteristic Curve The shape of the SWCC depends on the pore size distribution and compressibility of the soil in relation to suction.These two char-acteristics of porous materials are affected by the initial water content,soil structure,mineralogy,and the stress history ͑e.g.,Lapierre et al.1990;Vanapalli et al.1999;Simms and Yanful 2000͒.Most SWCCs are S shaped and the curve shapes are a response to the pore size distribution of the material.For a rigid porous material of single pore size ͑i.e.,uniform pore size distri-bution ͒,whether it is a soil or not,the SWCC should be similar to curve ͑a ͒shown in Fig.1.However,complete water loss with suction increasing beyond the air entry value is not usual.In other words,it is difficult to remove all the water from a porous mate-rial by means of a small increase in suction.Even in a porous material with uniform pore size distribution,some water would still be present in the material due to surface phenomena.The SWCC shape for a material of single pore size could be more appropriately represented by curve ͑b ͒in Fig.1.Nevertheless,for this material even after air entry suction,some water still remains in the soil and for the removal of the residual water higher energy are required.Curve ͑c ͒in Fig.1represents an example of material with two pore sizes.Each of the sizes is associated with one suction value via the capillary phenomenon ͑e.g.,Fredlund and Rahardjo 1993͒.Material with great numbers of pore sizes should present a more gradual reduction in water content with an in-crease in suction,as shown in curve ͑d ͒in Fig.1.By applying the capillary model,the equivalent pore size for the material can be deduced ͑i.e.,from 0.0146to 0.0000146mm ͒.Clay soils typically have nonuniform grain size and pore size distributions ͑e.g.,Delage and Lefebvre 1983͒.As a consequence,linear and less steeply sloping SWCCs ͑using a semilog plot ͒are normally obtained for clays.Clays may experience shrinkage that reduces pore size.Fine-grained soils with a liquid limit greater than 25%typically exhibit significant shrinkage characteristics when dried.This can be observed in Fig.2,in which the liquid limit and shrinkage limit for some soils are presented.This figure also illustrates that the shrinkage limit by itself is not a sufficient parameter for identifying soil behavior.Shrinkage phenomena in1Associate Professor,Dept.of Foundation and Engineering.,Univ.of São Paulo,CED 04318-002Sao Paulo,Brazil.E-mail:fmarinho@usp.br Note.Discussion open until October 1,2005.Separate discussions must be submitted for individual papers.To extend the closing date by one month,a written request must be filed with the ASCE Managing Editor.The manuscript for this paper was submitted for review and pos-sible publication on May 31,2000;approved on September 23,2004.This paper is part of the Journal of Geotechnical and Geoenvironmental Engineering ,V ol.131,No.5,May 1,2005.©ASCE,ISSN 1090-0241/2005/5-654–661/$25.00.654/JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ©ASCE /MAY 2005D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .clays due to increased suction can play an important role in shap-ing the SWCC.During shrinkage the emptying of pores is accom-panied by reduction in pore size,which keeps the spaces filled with water and increases the air entry value.A reduction in pore size in clays may also occur due to me-chanical overconsolidation.In this case,the air entry value is higher than for the normally consolidated soil,and the SWCC shape for this type of material is relatively flat.Various methods are commonly used when defining the SWCC for a soil from lower to higher suction levels ͑e.g.,McQueen and Miller 1974;Blight and Roussev 1995;Barbour 1998͒.The reason for this is that not all methods used to measure suction can cover all suction ranges.Depending on the method used,total or matric suction is obtained.When a combination of methods is used without paying attention to the type of suction that is being measured,the SWCC shape may be affected if the value of osmotic suction is significant.For suctions up to 30kPa,the pressure plate method with the hanging column is usually convenient.For suctions between 30and 1,500kPa,the pressure plate ͑i.e.,axis-translation technique ͒or filter paper methods can be used.In most high suction range ͑i.e.,greater than 1,500kPa ͒the suction measured is the total suction,regardless of the method used for measurement.Marinho and Chandler ͑1993͒drew attention to the fact that the filter paper,even when in con-tact with the soil,may not have adequate contact with the soil–water and hence this method may measure a combination of total and matric suction.Effect of Soil Plasticity on Soil–Water Characteristic CurveThe influence of soil plasticity on the SWCC has been demon-strated in the literature ͑e.g.,Black 1962;Mitchell and Avalle 1984;Fleureau et al.1990,among others ͒.Results obtained by Marinho and Chandler ͑1993͒showed a relationship between liq-uid limit and suction capacity ͑C ͒for compacted soils.Suction capacity is defined as the reduction in water content ͑expressed in percent ͒over one logarithmic cycle.It has also been suggested that soils prepared from slurries should represent the upper limit of suction capacity for a given soil.There is a unique relationship between soil suction and water content normalized by the suction capacity C ͑i.e.w /C ͒,for dynamically compacted soils.The value of C could be reduced in accordance with the stress history.Har-rison and Blight ͑2000͒emphasized the relationship between C and some soil properties such as plasticity index,clay fraction and linear shrinkage.Harrison and Bligh ͑2000͒observed that,for residual soils,the relationship did not present good correlation.The effect of soil plasticity on the SWCC is displayed sche-matically in Fig.3͑a ͒,showing that the slope of the SWCC changes with the liquid limit when a log scale is used for repre-senting suction.This effect can be compared to the relationship between void ratio and effective overburden pressure for saturated soils presented by Skempton ͑1970͒.The general behavior of clay samples with different stress histories or different preparation pro-cedures is schematically shown in Fig.3͑b ͒.The behavior ob-served is also in agreement with data presented by Croney and Coleman ͑1954͒and Toll ͑1988͒.The SWCC for most soils with a liquid limit of more than 25%can be assumed to be a straight line between suctions of 100and 10,000kPa,on a semilog plot,regardless of the suction method used ͑McQueen and Miller 1974;Marinho and Chandler 1993͒.Some soils,such as residual soils,may present some predomi-nance of void size that induces a change in suction capacity at suction levels within the interval mentioned above.The soil state at the liquid limit has been used for relating soil properties.Burland ͑1990͒introduced the concept of intrinsic properties for saturated clays,which was based on the voidratioFig.1.General shape of soil–water characteristic curve according to pore sizedistributionFig.2.Relation between liquid limit and shrinkage limit for some soils ͓Holtz ͑1959͒;Fleureau et al.͑1993͒;Tuncer ͑1988͔͒Fig.3.Plasticity chartJOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ©ASCE /MAY 2005/655D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .of samples prepared between the liquid limit ͑w L ͒and 1.5w L .The relationship between water content and stress during isotropic consolidation can be obtained provided the specific gravity of the soil is known.The results obtained from drying saturated clay are equivalent to the isotropic consolidation,provided the soil re-mains saturated ͑e.g.,Blight 1965͒.Reddi and Poduri ͑1997͒pre-sented a study in which the void ratio at the liquid limit was used to obtain the water retention properties of the soil at other states.Marinho and Pinto ͑1997͒,in discussing the work presented by Reddi and Poduri ͑1997͒,presented data showing the relationship between w L and the pore size distribution index ͑␭͒,based on the Brooks and Corey ͑1966͒model for undisturbed soils and soils prepared at the w L .Effect of Stress History on Soil–Water Characteristic CurveCroney and Coleman ͑1954͒were among the first investigators to study the effect of the stress history of the sample on the SWCC.It is clear from the findings of this study that,for the same water content,overconsolidation induces a reduction in suction and as a consequence in suction capacity.The degree of saturation of an overconsolidated sample is always higher than that of a normally consolidated soil,provided the suction is higher than the air entry value of the normally consolidated sample.Toll ͑1988͒performed a series of tests and described the soil behavior during desatura-tion,presenting a framework for examining the relationship be-tween water content and volume change with suction.Toll ͑1988͒also presented the concept of a virgin desaturation line ͑VDL ͒,which is the line where,for some value of suction,the relation-ship between water content and logarithm of suction is unique ͓see Fig.3͑b ͔͒.The point at which soils in different initial states reach the VDL is associated with the air entry value.Delage and Lefebvre ͑1983͒used mercury intrusion porosimetry to show the effect of the stress history on the air entry value of plastic soils.Tests were performed on St.Marcel clay,consolidated at different stress levels,including dried samples.The results clearly indi-cated that the air entry value increases with the consolidationpressure and is even higher for samples previously dried.It should be pointed out that the air entry value increases with the overconsolidation of the soil but,as for saturated soils,the stress required to reach the same water content is lower.Vanapalli et al.͑1999͒performed a series of tests using a sandy clay till ͑Indian Head till ͒to deduce the effect of soil struc-ture and stress history on the SWCC.The samples were statically compacted,placed in an oedometer cell,soaked under constant volume,and mechanically loaded to different values of net nor-mal stress.After the required stress was reached,the samples were unloaded under drained conditions.The loading and unload-ing of the sample induced additional overconsolidation in the sample.The samples were then removed from the oedometer cell and the SWCC was obtained from a pressure plate.No correction for volume change was made when the degree of saturation was used to represent the SWCC.A negligible volume change of the soil during drying was observed.Vanapalli et al.͑1999͒observed a significant difference in the SWCC ͑represented as degree of saturation versus suction ͒,particularly at the beginning of the curve ͑low suctions ͒,thus reflecting the macrostructure of the soil.The results also suggested that the increase in stress after compaction reduced the differences observed in the SWCC at low suctions.Relationship between Suction Capacity and Liquid LimitThere seems to be an upper limit for the suction capacity C ,and this is related to the samples prepared and tested from slurry.The upper limit for C also agrees well with the data for saturated clays presented by Burland ͑1990͒and shown by Marinho and Chan-dler ͑1993͒in terms of suction capacity.There also seems to be a lower limit for the suction capacity related to overconsolidated clays.The stress history of the sample plays an important role in its suction capacity.Hence,a compacted soil may be near the upper limit or near the lower limit for the C value.It depends on the level of stress to which the sample was subjected.For differentTable 1.Soils Analyzed Soil w 1͑%͒w p ͑%͒I p ͑%͒Reference1London clay 78.026.052Croney and Coleman ͑1954͒2Silty clay41.520.521Croney and Coleman ͑1954͒3Red clay from Kenya 95.035.060Coleman et al.͑1964͒4London clay70.024.046Marinho ͑1994͒5Taplow Terrace Brickearth 36.019.017Dumbleton and West ͑1968͒6Kaolinite 61.030.031Biarez et al.͑1987͒7Yellow clay 40.020.020Fleureau et al.͑1990͒8Residual soil48.029.019Marinho and Stuermer ͑1998͒9Residual of gneiss ͑from 1.6m depth ͒50.031.01910Residual of gneiss ͑from 3.0m depth ͒50.034.01611Residual of gneiss ͑from 4.4m depth ͒53.033.02012Residual of gneiss ͑from 6.0m depth ͒51.039.01213London clay77.029.048Marinho ͑1994͒1490%London clay/10%sand 69.024.045Marinho ͑1994͒1570%London clay/30%sand 54.019.035Marinho ͑1994͒1650%London clay/50%sand 40.017.023Marinho ͑1994͒1730%London clay/70%sand 24.018.06Marinho ͑1994͒18Carsington63.031.032Marinho ͑1994͒656/JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ©ASCE /MAY 2005D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .samples of a soil compacted with the same energy but different water contents,little difference is observed in the suction capacity ͑e.g.,Marinho and Stuermer 2000͒.The SWCC determined by Marinho and Stuermer ͑2000͒started from the compaction water content,thus implying that only the micropores are controlling behavior.Simms and Yanful ͑2000͒observed that the pore size distributions of the micropores are similar,regardless of the com-paction water content.Even for nonplastic materials,such as the till tested by Watabe et al.͑2000͒,the effect of the compaction water content can be detected.Watabe et al.͑2000͒tested samples compacted at differ-ent initial water contents.The samples were dynamically com-pacted and saturated using backpressure.The results showed that the higher the degree of saturation after compaction,the higher the suction at the air entry value is.The SWCC shape obtained differed significantly up to 300kPa,thereby showing the effect of the compaction water content on the initial portion ͑i.e.,macropores ͒of the SWCC.The effect of the stress history from a particular initial structure on the SWCC was not investigated by Watabe et al.͑2000͒.It should be pointed out that,although the till tested by Watabe et al.͑2000͒was a nonplastic material,it was a well-graded soil with clay content ͑%Ͻ2␮m ͒of 7%,silt con-tent of approximately 36%,and fine sand content of about 30%.The clay content and grain size distribution of the nonplastic por-tion may be an important factor in the observed behavior.Normalization of Using Suction CapacityMarinho and Chandler ͑1993͒proposed the normalization of water content on the SWCC.It was found that the normalization of the SWCC applied to dynamically compacted soils gives a unique relationship for the soils analyzed.Models for Predicting Soil–Water Characteristic CurvesThere are several models available in the literature for predicting the SWCC using a limited quantity of data ͑e.g.,Black 1962;McQueen and Miller 1974;Gupta and Larson 1979͒.None of the suggested methods take into account the stress history of the soil.In order to obtain the complete SWCC,most of the available models divide the SWCC into segments.The geometrical and mathematical aspects of the fitting method may justify the proce-dure of dividing the SWCC into segments.The models are also aimed at characterizing the physical meaning of the holding forces that are present at different levels of suction.McQueen and Miller ͑1974͒presented a procedure for defining the SWCC based on one suction/water content measurement.A straight line on a semilog plot can,according to McQueen and Miller ͑1974͒,rep-resent the SWCC in the range between 30kPa and 10Mpa.It should be pointed out that this suction range can still be associ-ated with capillary water provided the pore sizes are equivalent to the suction.McQueen and Miller’s ͑1974͒method makes no ref-erence to the history of the soil specimen.Black ͑1962͒presented a method that correlates the plasticity index,water content and soil suction.The method was to be used for remolded soils and was based on results obtained using British clays.All data analyzed by Black ͑1962͒were above the A line on the plasticity chart and the relationship between soil suction and water content presented a well-defined correlation with the plas-ticity index.In order to investigate possible relationships between theliq-Fig. 4.Schematic representation of relationship between water content and suction for:͑a ͒different soils in similar states and ͑b ͒same soil in differentstatesFig. 5.Soil–water characteristic curves for soil starting drying process fromslurry Fig.6.Soil–water characteristic curves for stiff soils upondryingFig.7.Soil–water characteristic curves for dynamically compacted samples upon dryingD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .uid limit,suction capacity and SWCC,previously reported data were collected and analyzed.The results presented in this paper show a consistent relation-ship between the slope of the SWCC ͑with suction in log scale ͒and the rigidity of the soil in relation to suction increase.This peculiar behavior suggests the possibility of adopting a simple model for deducing the SWCC.Soils Considered in AnalysisData from 42SWCCs from 18soils were analyzed.The Atterberg limits and the reference sources for the soils analyzed are shown in Table 1.Fig.4presents soils analyzed in this paper on a plas-ticity chart.It can be seen that most of the soils are located above the “A line.”Only the residual soils ͑8,9,10,11,and 12͒lie below the A line.Figs.5–8present the relationship between water content and soil suction for samples at initial state ranging from slurry to stiff material,including dynamically compacted and statically com-pacted,respectively.Even for the same type of sample ͑prepared from slurry,with dynamic compaction,etc.͒,the behavior can vary widely according to the soil type.In some cases slurry samples have low water content values,thereby indicating a low value for suction capacity,particularly at low suction levels.This behavior is associated with the storage capacity of the soil,and in this case it is more directly associated with soil mineralogy.This paper shows that the liquid limit can adequately reflect the rela-tionship between storage capacity and the stress history of the soil.The soil state that represents the association between water content and suction at failure conditions is called the “continu-ously disturbed state”͑e.g.,Croney and Coleman 1954;Brady 1988͒.After each suction measurement the sample is deliberately mixed or disturbed,to simulate a failure condition.The continu-ously disturbed state can also be identified as a critical state line for the SWCC ͑e.g.,Croney and Coleman 1954;Brady 1988͒.Fig.9presents the SWCC for continuously disturbed samples obtained from results presented by Croney and Coleman ͑1954͒,Dumbleton and West ͑1968͒,and Marinho ͑1994͒.Fig.10presents the relationship between suction capacity and liquid limit obtained from tests with samples at four different initial conditions.In addition to the data related to the soils pre-sented in Table 1,Fig.10also presents some data from the litera-ture,in which it was not possible to obtain the SWCC,but the suction capacity could be deduced ͑e.g.,Holmes 1955;Blight 1961;Matyas,1963;Olson and Langfelder 1965;Cepeda-Diaz 1987;Jucá1990;Ho et al.1992;Ridley 1995;Clarke and Neves,Jr.1996͒.From the analysis of the data collected from the literature,it was observed that the normalization with the suction capacitywasFig.8.Soil–water characteristic curves for statically compacted samples upondryingFig.9.Soil–water characteristic curves for continuously disturbedsamples Fig.10.Relationship between suction capacity and liquid limit for different samplehistoriesFig.11.Soil–water characteristic curve normalization using the suction capacityD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .not universal.The suction capacity alone cannot represent the SWCC of the soils.Some discrepancies were observed in the data used.The differences in the position of the SWCC can be ob-served in Fig.11,where the normalized water content is plotted against soil suction on a logarithmic scale.One important observation related to Fig.11is that most of the normalized data lay along parallel lines.This empirical behavior can be used to indirectly estimate the SWCC for plastic soils using only one suction/water content measurement and the soil–liquid limit,and using the empirical relation between the liquid limit and suction capacity ͑Fig.10͒.Deducing Soil–Water Characteristic Curve Using One Set of Data and Liquid LimitThe steps to be followed for obtaining the SWCC for soils with a liquid limit of more than 25%are described as follows:The At-terberg limits for the soil must be determined in order to certify that the soil lies above the A line on the plasticity ing the liquid limit and observing the soil state,the suction capacity can be determined using Fig.10.At least one value of water content ͑w i ͒and suction ͑suction i ͒needs to be obtained.Any method for suction measured can be used for determining the necessary suc-tion ing the filter paper method at least 7days is neces-sary for equilibrium.If a high capacity tensiometer ͑e.g.,Marinho and Pinto 1997͒is used,just few minutes are necessary.With the water content ͑w i ͒of the sample,Fig.12can be used to estimate the line related to the suction capacity obtained ing the interception point as a reference,a horizontal line is then traced.A vertical line is drawn at the value of the suction mea-sured ͑suction i ͒that is associated with the water content ͑w i ͒.The intersection between that vertical line and the horizontal traced line is a point on the line that relates the normalized water content͑w /C ͒and the soil suction.In order to convert the relationship between the normalized water content ͑w /C ͒and suction into the SWCC,the suction capacity ͑C ͒previously obtained is used.Applying MethodThree examples of the use of the method are presented using data from Bao and Ng ͑2000͒,Ridley ͑1995͒,and Vaunat and Romero ͑2000͒.However,experimental results obtained by Vaunat and Romero were not included in the data used for the development of the method.The data taken from the above references were the liquid limit and one suction/water content measurement,as shown in Table 2.Table 2also presents the parameters obtained from the method.A guide to the use of the method is presented for the soil shown by Bao and Ng ͑2000͒:1.The liquid limit of the soil is 63.5%and its plastic limit is27.3%͑Ng,personal communication,May 2001͒.2.The soil is above the A line in the plasticity chart.3.Since the soil is an undisturbed expansive soil,it is assumedthat the soil is heavily overconsolidated.From Fig.10,the suction capacity ͑C ͒is 5%.4.The values of water content and suction were obtained di-rectly from the reference,as shown in Table 2͑Bao and Ng 2000͒.5.By entering the water content in Fig.12,the intercept withthe dotted line corresponding to the C value is obtained in Fig.10.6.The interception point corresponds to a normalized watercontent ͑w /C ͒of 5.9.ing the suction value from Table 2,the line showing therelationship between normalized water content and suction is obtained.8.Assuming that C =5%,the value of the water content can beobtained for some points.Considering this is a graphical method,the linear relationship may not be accurately obtained.Fig.13presents the experimental data from Bao and Ng ͑2000͒,Ridley ͑1995͒,and Vaunat and Romero ͑2000͒,and a line representing the results obtained using the method.The results obtained when using the method for the soils presented by Bao and Ng ͑2000͒and Ridley ͑1995͒was reasonably good.The SWCC prediction for the soil presented by Vaunat and Romero ͑2000͒was also reasonable,although a small discrepancy was observed.This discrepancy obtained may be as-sociated with the interpretation of the stress history of the soil.ConclusionsFrom the analysis of data from 42SWCCs from 18soils obtained from the literature,it was possible to classify the behavior of the soil according to its nature ͑associated parameter w 1͒and its stress history ͑associated parameter C ͒.It was observed that soilsTable 2.Data from Literature and Parameters of Method ReferenceSample type w 1͑%͒Water content ͑%͒Suction ͑kPa ͒C ͑%͒w /C Bao and Ng ͑2000͒Undisturbed 63.5281005 5.9Ridley ͑1995͒Compacted643057012 2.5Vaunat and Romero ͑2000͒Compacted high density562245054.5Fig.12.Diagram for soil–water characteristic curve approximation using one data set and liquid limitJOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ©ASCE /MAY 2005/659D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .。

Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated GeotechnicsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Advances in Unsaturated Geotechnics D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/16/13. C o p y r i g h t A S C E . F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .。

SOIL MECHANICSLECTURE NOTESLECTURE # 1SOIL AND SOIL ENGINEERING* The term Soil has various meanings, depending upon the general field in which it is being considered.*To a Pedologist ... Soil is the substance existing on the earth's surface, which grows and develops plant life.*To a Geologist ..... Soil is the material in the relative thin surface zone within which roots occur, and all the rest of the crust is grouped under the term ROCK irrespective of its hardness.*To an Engineer .... Soil is the un-aggregated or un-cemented deposits of mineral and/or organic particles or fragments covering large portion of the earth's crust.* Soil Mechanics is one of the youngest disciplines of Civil Engineering involving the study of soil, its behavior and application as an engineering material.*According to Terzaghi (1948): "Soil Mechanics is the application of laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by the mechanical and chemical disintegration of rocks regardless of whether or not they contain an admixture of organic constituent."* Geotechnical Engineering ..... Is a broader term for Soil Mechanics.* Geotechnical Engineering contains:- Soil Mechanics (Soil Properties and Behavior)- Soil Dynamics (Dynamic Properties of Soils, Earthquake Engineering, Machine Foundation)- Foundation Engineering (Deep & Shallow Foundation)- Pavement Engineering (Flexible & Rigid Pavement)- Rock Mechanics (Rock Stability and Tunneling)- Geosynthetics (Soil Improvement)Soil Formation* Soil material is the product of rock* The geological process that produce soil isWEATHERING (Chemical and Physical).* Variation in Particle size and shape depends on:- Weathering Process- Transportation Process* Variation in Soil Structure Depends on:- Soil Minerals- Deposition Process* Transportation and DepositionFour forces are usually cause the transportation and deposition of soils1- Water ----- Alluvial Soil 1- Fluvial2- Estuarine3- Lacustrine4- Coastal5- Marine2- Ice ---------- Glacial Soils 1- Hard Pan2- Terminal Moraine3- Esker4- Kettles3- Wind -------- Aeolin Soils 1- Sand Dunes2- Loess4- Gravity ----- Colluvial Soil 1- TalusWhat type of soils are usually produced by the different weathering & transportation process?- Boulders- Gravel Cohesionless- Sand (Physical)- Silt Cohesive- Clay (Chemical)* These soils can be- Dry- Saturated - Fully- Partially* Also they have different shapes and texturesLECTURE # 2SOIL PROPERTIESPHYSICAL AND INDEX PROPERTIES1- Soil Composition- Solids- Water-Air2- Soil Phases- Dry- Saturated * Fully Saturated* Partially Saturated- Submerged3- Analytical Representation of Soil:For the purpose of defining the physical and index properties of soil it is more convenient to represent the soil skeleton by a block diagram or phase diagram. 4- Weight - Volume Relationships:WeightW t = W w + W sVolumeV t = V v + V s = V a + V w + V s 1- Unit Weight - Density* Also known as- Bulk Density- Soil Density-Unit Weight-Wet DensityRelationships Between Basic Properties:Examples:________________________________________________________________________Index PropertiesRefers to those properties of a soil that indicate the type and conditions of the soil, and provide a relationship to structural properties such as strength, compressibility, per meability, swelling potential, etc.________________________________________________________________________1- PARTICLE SIZE DISTRIBUTION* It is a screening process in which coarse fractions of soil are separated by means of series of sieves.* Particle sizes larger than 0.074 mm (U.S. No. 200 sieve) are usually analyzed by means of sieving. Soil materials finer than 0.074 mm (-200 material) are analyzed by means of sedimentation of soil particles by gravity (hydrometer analysis).1-1 MECHANICAL METHODU.S. Standard Sieve:Sieve No. 4 10 20 40 60 100 140 200 -200Opening in mm 4.76 2.00 0.84 0.42 0.25 0.149 0.105 0.074 -Cumulative Curve:* A linear scale is not convenient to use to size all the soil particles (opening from 200 mm to 0.002 mm).* Logarithmic Scale is usually used to draw the relationship between the % Passing and the Particle size.Example:Parameters Obtained From Grain Size Distribution Curve:1- Uniformity Coefficient C u (measure of the particle size range)Cu is also called Hazen CoefficientCu = D60/D10C u < 5 ----- Very UniformC u = 5 ----- Medium UniformC u > 5 ----- Nonuniform2- Coefficient of Gradation or Coefficient of Curvature C g(measure of the shape of the particle size curve)C g = (D30)2/ D60 x D10C g from 1 to 3 ------- well graded3- Coefficient of Permeabilityk = C k (D10)2 m/secConsistency Limits or Atterberg Limits:- State of Consistency of cohesive soil1- Determination of Liquid Limit:2- Determination of Plastic Limit:3- Determination of Plasticity IndexP.I. = L.L. - P.L. 4- Determination of Shrinkage Limit5- Liquidity Index:6- Activity:SOIL CLASSIFICATION SYSTEMS* Why do we need to classify soils ?To describe various soil types encountered in the nature in a systematic way and gathering soils that have distinct physical properties in groups and units.* General Requirements of a soil Classification System:1- Based on a scientific method2- Simple3- Permit classification by visual and manual tests.4- Describe certain engineering properties5- Should be accepted to all engineers* Various Soil Classification Systems:1- Geologic Soil Classification System2- Agronomic Soil Classification System3- Textural Soil Classification System (USDA)4-American Association of State Highway Transportation Officials System (AASHTO) 5- Unified Soil Classification System (USCS)6- American Society for Testing and Materials System (ASTM)7- Federal Aviation Agency System (FAA)8- Others1- Unified Soil Classification (USC) System:The main Groups:G = GravelS = Sand.........................M = SiltC = Clay........................O = Organic........................* For Cohesionless Soil (Gravel and Sand), the soil can be Poorly Graded or Well GradedPoorly Graded = PWell Graded = W* For Cohesive Soil (Silt & Clay), the soil can be Low Plastic or High Plastic Low Plastic = LHigh Plastic = HTherefore, we can have several combinations of soils such as:GW = Well Graded GravelGP = Poorly Graded GravelGM = Silty GravelGC = Clayey GravelPassing Sieve # 4SW = Well Graded SandSP = Poorly Graded SandSM = Silty SandSC = Clayey SandPassing Sieve # 200ML = Low Plastic SiltCL = Low Plastic ClayMH = High Plastic SiltCH = High Plastic ClayTo conclud if the soil is low plastic or high plastic use Gassagrande's Chart________________________________________________________________________ 2- American Association of State Highway Transportation Officials System (AASHTO):- Soils are classified into 7 major groups A-1 to A-7Granular A-1 {A-1-a - A-1-b}(Gravel & Sand) A-2 {A-2-4 - A-2-5 - A-2-6 - A-2-6}A-3More than 35% pass # 200A-4Fine A-5(Silt & Clay) A-6A-7Group Index:_________________________________________________ ___3- Textural Soil Classification System (USDA)* USDA considers only:SandSiltClayNo. Gravel in the System* If you encounter gravel in the soil ------- Subtract the % of gravel from the 100%.* 12 Subgroups in the systemExample: ********MOISTURE DENSITY RELATIONSHIPS(SOIL COMPACTION)INTRODUCTION:* In the construction of highway embankments, earth dams, and many other engineering projects, loose soils must be compacted to increase their unit weight.* Compaction improves characteristics of soils:1- Increases Strength2- Decreases permeability3- Reduces settlement of foundation4- Increases slope stability of embankments* Soil Compaction can be achieved either by static or dynamic loading:1- Smooth-wheel rollers2- Sheepfoot rollers3- Rubber-tired rollers4- Vibratory Rollers5- Vibroflotation_____________________________________________________________________________________________General Principles:* The degree of compaction of soil is measured by its unit weight, , and optimum moisture content, w c.* The process of soil compaction is simply expelling the air from the voids.or reducing air voids* Reducing the water from the voids means consolidation.Mechanism of Soil Compaction:* By reducing the air voids, more soil can be added to the block. When moisture is added to the block (water content, w c, is increasing) the soil particles will slip more oneach other causing more reduction in the total volume, which will result in adding moresoil and, hence, the dry density will increase, accordingly.* Increasing W c will increaseUp to a certain limit (Optimum moister Content, OMC)After this limitIncreasing W c will decreaseDensity-Moisture RelationshipKnowing the wet unit weight and the moisture content, the dry unit weight can be determined from:The theoretical maximum dry unit weight assuming zero air voids is:I- Laboratory Compaction:* Two Tests are usually performed in the laboratory to determine the maximum dry unit weight and the OMC.1- Standard Proctor Test2- Modified Proctor TestIn both tests the compaction energy is:1- Standard Proctor TestFactors Affecting Compaction:1- Effect of Soil Type2- Effect of Energy on Compaction3- Effect of Compaction on Soil Structure4- Effect of Compaction on Cohesive Soil PropertiesII- Field CompactionFlow of Water in SoilsPermeability and Seepage* Soil is a three phase medium -------- solids, water, and air* Water in soils occur in various conditions* Water can flow through the voids in a soil from a point of high energy to a point of low energy.* Why studying flow of water in porous media ???????1- To estimate the quantity of underground seepage2- To determine the quantity of water that can be discharged form a soil3- To determine the pore water pressure/effective geostatic stresses, and to analyze earth structures subjected to water flow.4- To determine the volume change in soil layers (soil consolidation) and settlement of foundation.* Flow of Water in Soils depends on:1- Porosity of the soil2- Type of the soil - particle size- particle shape- degree of packing3- Viscosity of the fluid - Temperature- Chemical Components4- Total head (difference in energy) - Pressure head- Velocity head- Elevation headThe degree of compressibility of a soil is expressed by the coefficient of permeability of the soil "k."k cm/sec, ft/sec, m/sec, ........Hydraulic GradientBernouli's Equation:For soilsFlow of Water in Soils1- Hydraulic Head in SoilTotal Head = Pressure head + Elevation Headh t = h p + h e- Elevation head at a point = Extent of that point from the datum- Pressure head at a point = Height of which the water rises in the piezometer above the point.- Pore Water pressure at a point = P.W.P. = g water . h p*How to measure the Pressure Head or the Piezometric Head???????Tips1- Assume that you do not have seepage in the system (Before Seepage)2- Assume that you have piezometer at the point under consideration3- Get the measurement of the piezometric head (Water column in the Piezometer before seepage) = h p(Before Seepage)4- Now consider the problem during seepage5- Measure the amount of the head loss in the piezometer (Dh) or the drop in the piezometric head.6- The piezometric head during seepage = h p(during seepage) = h p(Before Seepage) - DhGEOSTATIC STRESSES&STRESS DISTRIBUTIONStresses at a point in a soil mass are divided into two main types:I- Geostatic Stresses ------ Due to the self weight of the soil mass.II- Excess Stresses ------ From structuresI. Geostatic stressesI.A. Vertical StressVertical geostatic stresses increase with depth, There are three 3 types of geostatic stresses1-a Total Stress, s total1-b. Effective Stress, s eff, or s'1-c Pore Water Pressure, uTotal Stress = Effective stress + Pore Water Pressures total = s eff + uGeostatic Stress with SeepageWhen the Seepage Force = H g sub -- Effective Stress s eff = 0 This case is referred asBoiling or Quick ConditonI.B. Horizontal Stress or Lateral Stresss h = k o s'vk o = Lateral Earth Pressure Coefficients h is always associated with the vertical effective stress, s'v.never use total vertical stress to determine s h.II. Stress Distribution in Soil Mass:When applying a load on a half space medium the excess stresses in the soil will decrease with depth.Like in the geostatic stresses, there are vertical and lateral excess stresses.1. For Point LoadThe excess vertical stress is according to Boussinesq (1883):- I p = Influence factor for the point load- Knowing r/z ----- I1 can be obtained from tablesAccording to Westergaard (1938)where h = s (1-2m / 2-2m) m = Poisson's Ratio2. For Line LoadUsing q/unit length on the surface of a semi infinite soil mass, the vertical stress is:3. For a Strip Load (Finite Width and Infinite Length): The excess vertical stress due to load/unit area, q, is:Where I l = Influence factor for a line load3. For a Circular Loaded Area:The excess vertical stress due to q is:。

Soil and Water Management in Responseto Extreme WeatherPaula MisiewiczHarper Adams UniversityOptions for Soil Management in 2012-2013:Tillage and DrainageOutlineFundamentalsThe problem and the penaltiesS&W Management Options Short termMedium termLong termConclusionsTypical problemsA less common sceneWaterlogging treatment Grain Yield (g/m²)Straw Yield (g/m 2)Free draining 937942From 19 Nov for 25 daysWater table @ 5 cm837*879***From 19 Nov for 25 daysSurface water table850*827***From 19 Nov for 120 daysSurface water table876847***LSD (5%)8510.7% reduction Effect of winter waterlogging on Winter wheat yield (Letcombe)Sandy loam 1976-7 & 1977-812.2% reductionSource: Belford (1981), J. Agric. Sci, 97Waterlogging treatment Grain Yield (g/m²)Straw yield (g/m²)1. Free draining 12818612. From 1 Nov for 42 days 11958753. From 25Jan for 42 days 12358574. From 2 May for 21 days 11318022 &3 & 41044**782LSD (5%)1679119 % reductionThe Role of Drainage onMechanisationIncreasing water table depth:o Increases soil strength &trafficabilityo Less soil damage orcompaction.o Easier& more effective fieldoperations.o Increased number of availablework days, improvedtimeliness and establishment.From :ProfiLand drainage and crop yieldCrop failure –during growth, in this case ~25% lossSoya beans, Illinois -July 2008Effect on crop growth –Denchworth SoilFDEU studies at Drayton 1970 -74 Winter WheatYield ~4.5 t/haDrains & Moles + 1.0 t/haDrains No moles & subsoiling+ 0.6 t/haStudies at Brooksby showed + 0.5t/ha from molingBirds Eye lost 40% of pea yield in summer of2007 due to poor trafficabilityFDEU Annual Report 1975Water budgetPrincipal types of drainage problem1.Surface water control (perched water table or top water)2.Groundwater table control (bottom water)Impermeable layerImpermeable layerSaturated zoneRelationship betweencompaction and infiltration rateAfter: Chyba, 20121.42 1.58 1.62 1.62Soil Density g/ccInfiltrationrate(mm/Effect of organic matter•Silt loam soils in Missouri:organic matter decline from 3.9% to 2.6% over 60 years.•This corresponded to a change in plastic limit moisture content from 27% to 22% and a less ideal working range.After: Baver et. al., 1972Hard Friable Plastic Liquid HardFriablePlasticLiquid3.9%2.6%Soil moisture contentIdeal working rangeDryWetShort term measures•Study “Old Drainage Plans”•Walk ditch drains•Check that tile drains, plastic pipes and mole drains are flowing•Clean blocked ditch and open drains•Flush pipe drains•Ensure outfalls are functioning•Install “short term” mole drains if appropriate•Map damaged areas for repair later in the season/next opportunityClean ditchesDrainage Maintenance:Pipe Jetting for Blockages13Mole drain/pipe from the ditchFit duals and reduce inflation pressureShallow, i.e.12-15” deep, mini-mole with 2’’ diameter foot.No -Expander+ 2nd tractor &chains or winch Herringbone cracksMole plough draught forces 1/3 of the force at 0.6m “Mini mole” depthConventional mole depthAfter: Godwin, Spoor & Leeds Harrison, 1982Medium term•Mole drain clay soils with perched water tables to connect with gravel backfill of existing tile/plastic drains•Subsoil (with wings) damaged areas after next harvest •Improve existing drainage systemsLong term measures•Install pipe/ditch drains (probably targeted)•Mole drain clay soils with perched water tables to connect with gravel backfill•Install grass waterways•Grade low spots in flat lands•Improve existing drainage systems•Reduce surface compaction by reducing traffic density and intensity (CTF and LGP)•Improve soil organic matter content (a very long term effect)Grass waterways/USDALand smoothing of low spotsAfter: Schwab et al 1993Random Traffic ProblemsExtensive areas of the field are exposed to trafficking•Random Traffic + plough = 85% covered•Minimum Tillage= 65% covered•Direct Drilling= 45% covered Kroulik et al, 2011grain cartingstraw carting straw baling Wheat Czech RepublicPotatoesShropshireKroulik , Misiewicz, White and Godwin, 2012After: Tullberg et al. 2003Reduced pressure/axle weight and central tyre inflation pressurecontrol systemsOptions for compaction reductionControlled trafficSource: CTF EuropeControlled Traffic Farming (CTF)•Area exposed to wheels < 30-40% & could be <20%•Improved soil structure•Reduced input costs: time; fuel; machinery by 22%•Operating profit up 8% (£75/ha without yield addition)•Increased crop yields from non trafficked soils + 9 to16%•Infiltration increased by circa 400% in UKSource: Chamen, 2011Lower Ground Pressure (LGP)+ Simple+ Cheap-Pressure is applied+ Less working time and improved fuel economy, trafficability andmanoeuvrabilityCombine: + £3 to 4/ha for 5 -7 year lifePrice offset by improved trafficability and narrower operatingwidthsTyrell, Claas UKExtra costsTractor -280 hp : Ultraflex tyres extra = £1/haCombine: Ultraflex = £0.50/haPrice offset by fuel savings (c.20%)Mozziconacci, MichelinEffect of infiltration rate on runoffParrett and Tone Catchment, Dorset/Somerset@ Haselbury Plucknet/ChiselboroughRainfallRainfallRainfallRainfallRainfallandrunoffrates(mmh-1)23rd December25th December24th Decemberq poor=0.72q good-Infiltration Rate 4-8 mm/hrq poor=1.6q poor=3.3q good =1.23q good=2.6q goodq poor=0.89q poor=1.7q good=1.35^^^^^^^^^^||||25%23% 21%19%% Reduction in peak flow After: Godwin and Dresser, 2003From: Schwab et al., 1993Infiltration Rate1-4 mm/hr25Regular inspections of drainage systems are needed.Restoration of an old system is cheaper than a new system.Improved soil and water management is achieved by:•Considering the short, medium and longer term actions •Checking, maintaining and improving drainage infrastructure •Reducing traffic intensity & contact pressurePrevention is better than cureConclusionsThank You!pmisiewicz@。