TUNNELING
X.J. Li (lixiaojun@https://www.doczj.com/doc/135864460.html,)
Department of geotechnical engineering, Tongji University
TEXTBOOKS
?Dimitrious Kolymbas, Tunnelling and Tunnel Mechanics — A Rational Approach to Tunnelling.
Springer, 2008. (https://www.doczj.com/doc/135864460.html,/book/10.1007/3-540-28500-8/page/1) ?U.S. Department of Transportation Federal Highway Administration, Technical Manual for Design and Construction of Road Tunnels — Civil Elements. American Association of State
Highway and Transportation, 2009.
(https://www.doczj.com/doc/135864460.html,/bridge/tunnel/pubs/nhi09010/index.cfm)
1. INTRODUCTION
1.1 DEFINITIONS
Tunnel- underground passage for transportation of passengers, freight, water, sewage, excavated minerals, gas, coal etc.)
Tunneling- the construction (by any method) of a covered cavity of predesigned geometry whose final location and use is under the surface (this includes cut and cover and sunken tubes)
1.2 BRIEF HISTORY OF TUNNELING
See the “world’s longest tunnel” page at: https://www.doczj.com/doc/135864460.html,/
for a listing of the most historically significant tunnels.
40,000 B.C. Hematite mined in Africa for ritual paint
* tunneling one of oldest engineering disciplines?
3,000 B.C. Egyptians construct tunnels leading to tombs.
* extensive use of slave labor
* cracking rock by thermal stresses induced by heating rock then cooling with water or vinegar| * wooden wedges inserted into cracks and wetted causing swelling of the wood and further
cracking
https://www.doczj.com/doc/135864460.html,.eg/2009/970/he1.htm
2,180 B.C. Pedestrian tunnel constructed under Euphrates River by “cut & cover”.
about 0 A.D. Romans construct tunnels for transportation, water supply and drainage.
Major contribution was improved alignment of tunnels by drilling shafts from the surface and connecting them with tunnels. Previously, alignment was achieved by following noises at the
surface.
1300's Black powder invented (but holes drilled by hand until about 1850)
1550 Lift pumps with pistons operating in cylinders were used for drainage. Previously, soaked rags or hollow balls on chains were raised to the surface by horse or manpower.
1700's Steam engine invented and used to power pumps
1681 157 m Malpas Canal tunnel in France marked beginning of era of tunnels for transportation.
1824 First U.S. transportation tunnel: 450 ft. (137 m) tunnel on Schuylkill Canal near Auburn, PA. It was the 1st canal tunnel in the world and was constructed as a novelty to attract tourists. Removed in 1857.
1825 First usage of tunneling shield on Thames tunnel (patented by Brunnel).
Numerous delays were encountered due to poor ground conditions. Brunnel recei ved 100’s of letters offering advice on which he commented: "In every case they made the ground to suit the plan, not the plan to suit the ground."
1851-1875 First "tunneling machine" (power drills driven by compressed air) used at Hoosac Tunnel in North Adams, MA but failed after 10 feet. Nitroglycerine was also first used at Hoosac;
compressed air drills bored the holes. See:
https://www.doczj.com/doc/135864460.html,/wgbh/buildingbig/wonder/structure/hoosac.html
Early 1900's Golden Age of Tunneling:
20-km Simplon railroad tunnel between Italy and Switzerland (Alps)
https://www.doczj.com/doc/135864460.html,/wiki/Simplon_Tunnel
9.6 km Moffat rail tunnel (Rockies) See construction photos at:
https://www.doczj.com/doc/135864460.html,/rg/mainline/moffat%20route/moffat%20tunnel.htm
Description of construction at: https://www.doczj.com/doc/135864460.html,/byways/ptp_building.html
1920-1927 Holland Tunnel (Clifford Holland) under Hudson
First major use of compressed air and first tunnel for automobile traffic.
Fans provided ventilation of CO for first time.
https://www.doczj.com/doc/135864460.html,/wgbh/buildingbig/wonder/structure/holland.html
https://www.doczj.com/doc/135864460.html,/crossings/holland/
1952 Modern TBM1 era begins (James Robbins)
soft shale at Oahe Dam in South Dakota excavated
1980’s 211 km Chicago Tunnel and Reservoir2 Plan (TARP)
1971-1988 Longest rail tunnel – Seikan tunnel 53.6km (Japan)
1988-1994 Channel tunnel – 50.5km (UK-France)
2000 Longest roadway tunnel constructed in Norway (Laerdal Tunnel) – 24 km
2007 Longest roadway tunnel in China, Zhongnanshan tunnel3 – 18km
1.3 TUNNEL RECORDS
CURRENT VEHICLE TRANSPORTATION TUNNEL RECORD HOLDERS
World: Laerdal 24.0 km 2000
Asia: Zhongnanshan 18.0 km 2007
USA: Ted Williams/I90 extension 4.2 km 2003 LONGEST TRAIN TUNNEL
Japan: Seikan Tunnel 53.6 km 1988 LONGEST CONTINUOUS TUNNEL FOR ANY PURPOSE:
USA: Delaware Aqueduct System Tunnel 137.0 km(?) 1937-1962 HISTORICAL RATES OF ADVANCE IN ROCK
Excavation Method Average rate of Advance
30,000 slaves 0.07 m per week
hand drilling & black powder 3 m per week
power drilling and gelatine powder 60 m per week
1 tunnel boring machine 345 m per week
1.4 TUNNEL COSTS
A. Initial capital expenditures and materials
* TBM is major capital expenditure
* Liners may constitute up to 30% of the total tunnel cost.
B. The rate of advance, which in turn depends on:
1. Length of an individual shift (8 to 10 hrs)
2. Number of shifts per day (1 to 3)
3. Number of working days per week
4. Overall duration or length of the contract
(such that the "learning curve" for machine operations becomes a minor factor)
5. Size of tunnel
6. Materials handling system
7. Geologic medium and any associated problems.
C. COST ESTIMATING
* Construction costs are difficult to predict based on previous experience (unlike building construction) because:
1. Ground conditions will vary from project to project, and they will control the selection of the
construction system.
2. Relatively few projects have been constructed in one geographic area.
3. The use of tunnels has varied from transit to water supply to sewage so that the final finish
and design tolerances vary.
4. Technological improvements have occurred between successive contracts for tunnels in
similar soils but which are constructed at different times.
5. The interrelationships between excavation methods, lining methods, shape and tunnel length
are difficult to break down into component factors.
Table 1. Costs of recent metro extensions
City Duration (years)Length (km)Stations Costs (m $)Costs / km (m $) London 9 16 11 6,000 375
Athens 12 18 21 2,800 156
Paris 8 7 7 1,090 155
Lisbon 8 12.1 20 1,430 118
Madrid 4 56 37 1,760 30 Shanghai L13 33.6 31 3,150 94
Table 2. Approximate costs for 1 m tunnel excavation and support
Case Costs in US $ /m
Estimated minimum costs worldwide 1,000 + 600 (d – 6 m)
Good ground requiring minimum support 3,000 + 800 (d – 6 m)
Average tunneling costs 5,000 + 1,000 (d – 6 m)
Poor ground requiring extensive support 7,000 + 1,200 (d – 6 m)
Faulted ground with severe squeezing 9,000 + 1,400 (d – 6 m)
1.5 PLANNING
Planning of tunnels is staged and addresses many aspects such as:
? Route studies
? Financial studies
? Types of tunnels
? Geotechnical investigation
? Environmental and community issues
? Sustainability
? Design
? Construction
? Operation
? Maintenance
? Risk analysis and management
A. ROUTE STUDIES
A road tunnel is an alternative vehicular transportation system to a surface road, a bridge or a
viaduct. Road tunnels are considered to shorten the travel time and distance or to add extra travel capacity through barriers such as mountains or open waters. They are also considered to avoid surface congestion, improve air quality, reduce noise, or minimize surface disturbance.
Often, a tunnel is proposed as a sustainable alternative to a bridge or a surface road. In a tunnel route study, the following issues should be considered:
? Subsurface, geological, and geo-hydraulic conditions
? Constructability
? Long-term environmental impact
? Seismicity
? Land use restrictions
? Potential air right developments
? Li fe expectancy
? Economical benefits and life cycle cost
? Operation and maintenance
? Security
? Sustainability
B. FINANCIAL STUDIES
The financial viability of a tunnel depends on its life cycle cost analysis. Traditionally, tunnels are designed for a life of 100 to 125 years. However, existing old tunnels (over 100 years old) still operate successfully throughout the world. Recent trends have been to design tunnels for 150 years life. To facilitate comparison with a surface facility or a bridge, all costs should be expressed in terms of lifecycle costs. In evaluating the life cycle cost of a tunnel, costs should include construction, operation and maintenance, and financing (if any) using Net Present Value.
In addition, a cost-benefit analysis should be performed with considerations given to intangibles such as environmental benefits, aesthetics, noise and vibration, air quality, right of way, real estate, potential air right developments, etc.
The financial evaluation should also take into account construction and operation risks. These risks are often expressed as financial contingencies or provisional cost items. The level of contingencies would be decreased as the project design level advances. The risks are then better quantified and provisions to reduce or manage them are identified.
C. TYPES OF TUNNELS
Selection of the type of tunnel is an iterative process taking into account many factors, including:
? Depth of tunnel
? Number of traffic lanes
? Type of ground traversed
? Available construction methodologies.
For example, a two-lane tunnel can fit easily into a circular tunnel that can be constructed by a tunnel boring machine (TBM). However, for four lanes, the mined tunnel would require a larger tunnel, two bores or another method of construction such as cut and cover or SEM methods.
General Description of Various Tunnel Types
?Cut-and-cover tunnels are built by excavating a trench, constructing the concrete structure in the trench, and covering it with soil.
?Bored or mined tunnels are built without excavating the ground surface. These tunnels are usually labeled according to the type of material being excavated.
?Rock tunnels are excavated through the rock by drilled and blasting, by mechanized excavators in softer rock, or by using rock tunnel boring machines (TBM). In certain conditions, Sequential Excavation Method (SEM) is used.
?Soft ground tunnels are excavated in soil using a shield or pressurized face TBM or by sequential excavation method (SEM).
?Immersed tunnels are made from very large prec ast concrete or concrete-filled steel elements that are fabricated in the dry, floated to the site, placed in a prepared trench below water, and connected to the previous elements, and then covered up with backfill.
?Jacked box tunnels are prefabricated bo x structures jacked horizontally through the soil using methods to reduce surface friction; jacked tunnels are often used where they are very shallow but the surface must not be disturbed, for example beneath runways or railroads embankments.
The maximum size of a circular TBM existing today is about 51 ft (15.43 m) for the construction of Chongming Tunnel, a 5.6 mile (9-kilometer) long tunnel under Yangtze River in Shanghai.
When larger and deeper tunnels are needed, either different type of construction methods, or multiple tunnels are usually used. For example, if the ground is suitable, SEM in which the tunnel cross section can be made to accommodate multiple lanes can be used.
Shallow tunnels would most likely be constructed using cut-and-cover techniques.
In special circumstances where existing surface traffic cannot be disrupted, jacked precast tunnels are sometimes used.
Pipe roofing – jacked box tunnel
D. ENVIRONMENTAL AND COMMUNITY ISSUES
*Tunnels are more environmentally friendly than other surface facilities
? Traffic congestion reduced
? Air quality improved
? Noise reduced
? Visual aesthetic and land use improved
? Property values be improved
? Communities less impacted in the long term
*The construction impact on the community and the environment is important and must be addressed.
*Construction noise, dust, vibration, water quality, aesthetic, and traffic congestion are important issues to be addressed and any potentially adverse impact should be mitigated.
*Excavation may encounter contaminated soils or ground water. Such soils may need to be processed or disposed in a contained disposal facility, which may also have to be capped to meet the
environmental regulations. Provisions would need to address public health and safety and meet regulatory requirements.
E. OPERATIONAL ISSUES
In planning a tunnel, provisions should be made to address the operational and maintenance aspects of the tunnel and its facilities. Issues such as traffic control, ventilation, lighting, life safety systems, equipment maintenance, tunnel cleaning, and the like, should be identified and provisions made for them during the initial planning phases. For example, items requiring more frequent maintenance, such as light fixtures, should be arranged to be accessible with minimal interruption to traffic.
F. SUSTAINABILITY
Tunnels by definition are sustainable features. They typically have longer life expectancy than a surface facility (125 versus 75 years). Tunnels also provide opportunities for land development for residential, commercial, or recreational facilities. They enhance the area and potentially increase property valu es. An example is the “Park on the Lid” in Mercer Island, Seattle, Washington where a park with recreational facilities was developed over I-90. Tunnels also enhance communities connections and adhesion and protect residents and sensitive receptors from traffic pollutants and noise.
“Park on the Lid” in Mercer Island, Seattle, Washington, USA
1.6 CONTRACTING
Generally, two categories of delivery methods have been used in the past for underground construction,with various levels of success. They are:
? Design-Bid-Build
? Design-Build
A. DESIGN-BID-BUILD
This is the traditional (or conventional) type of contract. The Owner is responsible for the design.
He contracts with designers to develop feasibility studies, environmental impact statements, preliminary design, and final design. In several iteration steps, the design undergoes reviews and many of the problems and issues of a project are revealed during the various stages of design.
B. DESIGN-BUILD
The Contractor is responsible not only for the construction but also for the design. The owner’s engineer develops a preliminary design that incorporates the essential project requirements, owner’s pre ferences for design and configurations and sufficient assessment of ground conditions and third-party impacts. The Contractor has increased opportunities to apply innovative solutions and his design can interact closely with the construction process. Partly overlapping design and construction (’design as you go’) speeds up the total time for the project.
? The Owner looses (at least partly) control of the process.
? The Contractor is mainly interested in the least expensive construction approach but not in the long-term performance.
? Unifying Designer and Contractor reduces the traditional checks, balances and monitoring, which help to avoid flaws. The amount of design and construction documentation is minimized. ? The description of underground conditions, provided by the Owner, is not adapted to a particular method of construction.
? The preparation of a Design-Build proposal is much more costly for the Contractor.
Risk should by no means lead to an antagonism between the involved parties. This would deprive them of the benefits of synergy and cause additional costs. MUIR-WOOD writes:
The most dominant philosophical basis of bad management is the notion of the zero-sum game, a defect which springs from the dominance of lawyers . . . Where lawyers earn more from the failure of projects than do the most skilled engineers from success, clearly there are fundamental systemic faults.
Dispute Review Boards (DRB), consisting of independent specialists, can help to resolve controversies without costly litigations. A DRB typically consists of three experts —one appointed by the Owner, one by the Contractor and the third appointed on the recommendation of the first two experts.
To be successful, a DRB should develop a good understanding of the project and its participants. This is best accomplished through regular on-site meetings and site visits, whether or not there is a dispute to be heard. Hearings can be made more efficient if the parties provide a short written statement of position in advance.28 A DRB is most effective when a well defined set of contract documents and a Geotechnical Baseline Report (see Section 3.7) are available.
Opting for the cheapest offer often results in financial loss. Quality may cost more, but makes a much better long term option than having to commit to significant repair and refurbishment work in the short term. In the future, assignment criteria in the construction industry will increasingly have to relate to initial quality, longevity, low maintenance and operational costs.
Glossary