Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

Hanoi Metro Pilot Line Project: Some aspects of risk management and subsidence Nguyen Duc Toan1, M.Eng; Luu Xuan Hung2, Ph.D

INTRODUCTORY REMARKS The Vietnamese engineers have gained fairly extensive degree of expertise in conventional tunnelling over the past decades. But the experience in mechanized tunnelling, particularly in urban areas, is not yet equivalent. Meanwhile, the world tunnelling industry in general has made great pace of developments. The major issues of durability, serviceability, technical feasibility and constructability have been steadily addressed. The technological achievements also permit great advance rates and very long headings. Especially, the latest breakthroughs could be attributed to the full-face mechanized tunnelling technology. If modern shielded Tunnel Boring Machines (TBM) are properly evaluated and chosen, tunnel drives through almost any types of ground can be possible. Also, if high elaborated technical measures are well understood and applied, significant settlements can be almost entirely avoided. Therefore, the developing countries (e.g. Vietnam) can no longer stand apart from all that technological evolvement and economic movement accounting for the globalization, as far as the countries' development demands are concerned. Vietnam has hundreds of urban centers with more than twenty millions inhabitants approaching 26 percent of the total population of over 83 million of the country. The biggest cities such as Ho Chi Minh City, Hanoi, and Danang have recently shown a rapid expansion. These cities are suffering heavily traffic congestion and its side-effects and substantially reduction of the quality of life. In fact, the efforts to invest in a surface traffic system improvement seem to be inadequate. We believe there needs to be alternatives in the future. In order to solve the problems by relieving congestion and overcrowding and to ensure sustainable development, it is necessary to build more efficient transport systems. The mass transit networks will be a solution for urban areas, which shall incorporate the new underground metro systems (subway). Hanoi and Ho Chi Minh City is implementing their first metro systems as such. This paper presents the most general issues related to the surface settlement or subsidence caused by tunnelling operations, as well as some aspects of risk management for the construction of the Hanoi Light Rail Transit (LRT/Metro) Pilot

1

Hanoi Metropolitan Rail Transport Project Board (HRB). Address: No. 8, Ho Xuan Huong Str., Hanoi, Vietnam. Tel: +84-4-943.51.27; Fax: +84-4-943.51.26; Mobile: +84-90-513.13.23. Email: [email protected] 2 Hanoi Metropolitan Rail Transport Project Board (HRB). Address: No. 8, Ho Xuan Huong Str., Hanoi, Vietnam. Tel: +84-4-943.51.27; Fax: +84-4-943.51.26. Email: [email protected]

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Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

Line Project's underground section, initially mentioning the Urban Mass Rail Transit No. 2 (UMRT-2) Line1, with special consideration to the TBM application option.

1. Introduction to the Project

The Owner of the Hanoi Metro Pilot Line Project is The Hanoi Metropolitan Rail Transport Project Board (HRB)2, under the Hanoi People's Committee (HPC). The Hanoi Metro Pilot Line Project lies in the main east-west traffic axis of Hanoi city. The peak hour traffic volume reaches to 37,600 pax/two directions/hour, which already exceeds the capacity of the road. Congestion will become very serious in the coming years since the number of private cars is ever more increasing. It is anticipated that the peak hour traffic volume will reach 50,000 to 60,000 pax/two directions/hour in 2010. Therefore, the operation of the Hanoi Metro Pilot Line after the year 2010 will be crucial, in terms of solving the traffic jams due to overcrowded situation and the pollution due to exhaust fumes, especially ensuring high safety for the people who participate in the traffic circulation. The total length of the double track metro line is 12.5 km plus 0.2 km of access road to the depot complex at Nhon town. The main line from Nhon depot to the Central Railway Station consists of an elevated bridge section of 9.8 km long and an underground tunnel section of 2.9 km which involves 4 underground stations. A second phase of the project will include more 2.5 km of underground tunnel in the inner city area from the Central Railway Station to the Hanoi Opera House. The construction of the project's depot had been started on 27 December 2006. The project's main line is expected to complete its detailed design stage soon and start construction within the year 2007, in order to accomplish in 2010 in commemoration of 1000th anniversary of the Hanoi city founding.

2. Risk management

In general, a comprehensive network of Project Management, Commercial and Contract Management services is required for every transportation, infrastructure, engineering, or construction project. Benefits for the Owners must be maximized whilst their downside risks must be minimized. Through many stages of a project cycle, these professional services may include: • • • • • • • 1 2

Pre-contract commercial advice and risk assessment; Project management; Commercial and contract management; Quantity surveying; Dispute resolution; Construction management; and Personnel management, training and recruitment. Also namely "Hanoi City Urban Railway Construction Project (Line 2)". Formerly The Hanoi Authority for Tram and Public Transport Development Management (HATD)

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Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

The HRB is striving to acquire experiences in all these professional services for all the elevated bridges, at grade and underground tunnel sections of the planned urban rail transport projects. Concerning the quantity surveying, it would be good to examine/develop a guidance for cost estimation practice and cost estimation management during planning, programming, and preconstruction, to aim at achieving greater consistency and accuracy between planning, programming and preliminary design, and final design. The guidance, if any, must explore/provide appropriate strategies, methods, and tools to develop, track, and document realistic cost estimates during each phase of the process. For the tunnels construction of the Hanoi Metro Pilot Line Project, priority is being given to the selection of a suitable TBM, either through refurbishment or outsourcing ways. Risk management for TBM application will be specifically considered in the paragraphs below. 2.1

Critical cases of TBM tunnelling in soil

The TBM performance is influenced by the rock mass quality, the selected machine type and the tunnel diameter. Advances in TBM technology and reliability have resulted in bored tunnels being successfully driven through ground conditions historically considered difficult. However, critical cases of TBM excavation from which risks emanate do not disappear. During excavation, the situation can become critical at any minute, meter, and under any circumstance. According to Kovari (2004), high risk factors of tunnelling in urban areas include: • •

• •

•

•

Low overburden: In case of large tunnel diameter may create ground deformations (settlements) and collapse up to surface. Existing structures in the vicinity: The sensitivity of these structures to ground settlements and the potential damage to ground collapse may vary within extremely wide ranges. Apart from surface monitoring to control the effects and the potential damages on pre-existing buildings, utilities and infrastructures, it is needed to adopt relevant damage risk categories. Unknown obstacles in the ground: The presence of frequently hidden subterranean obstacles causes specific difficulties for urban tunnelling using TBMs. Constraints of alignment: Selection of both horizontal and vertical alignment generally meets with constraints. Land acquisition costs would be very high and the foundations of the existing buildings would create complications during construction. Access difficulties: For example, selecting places of attack (launching shaft, access to TBM) and planning material transport from and to the construction site; restrictions in sinking drill holes for explorations, for ground water control or ground consolidation. Public opposition: The loss of public confidence in the TBM technology, and the strong resistance to further underground projects in towns due to damage to buildings and roads.

The main features that permit safe and economic tunnelling in soft ground under urban conditions using TBM´s with slurry or EPB type of face support include:

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Report at the Meeting between ITA and ITST on Tunnelling

• • • • •

Hanoi, 12 March 2007

Efficient TBM technology Reliable design procedure Improved methods of conditioning Advanced grouting technology Reliable risk management

2.2

Risk management for tunnels

Tunnelling is not a risk-free technology. The “right” construction method with the “right” experience parties involved are crucial for the success. The construction of tunnels and underground works are affected by potential risks not only for the different active Parties (Owner, Consulting Engineers, Contractor, Supplier), but also for the Public, especially in urban areas. Tunnelling projects must now consider numerous underlying political and environmental factors which add to the overall complexity of a given project. This calls for the need of risk management. According to its definition risk has two components: probability of occurrence w and amount of damage D. In a quantitative appraisal the product of these two factors defines the risk: R = w x D. An initial risk can be reduced by reducing its probability and its impact. It is clear that residual risks are unavoidable and they should be shared among the Parties and systematically controlled by the countermeasures. Several kinds of risks include (ITA, 2004): -

significant cost overrun risk work delay risk environmental risks risk of spectacular tunnel collapses and other disasters (potential for large scale accidents during tunnelling work) risk of damage to a range of third party persons and property in urban areas, (a particular concern with heritage designated buildings) risk of public protests, caused by the problems of tunnelling projects

“Risk management” is the overall term which includes risk identification, risk assessment, risk analysis, risk elimination and risk mitigation and control. Risk management for tunnels is now routine for major projects worldwide. A Systematic Risk Management Techniques is recommended for risk management. Through the use of a robust and transparent Risk Management Plan (RMP) adopted from the early design stages to the construction and operation phases, most risks can be effectively managed. Risk management tools may include (ITA, 2004): -

Fault tree analysis Event tree analysis Decision tree analysis Multirisk Monte Carlo simulation

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Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

A Code of Practice for Risk Management of Tunnel Works, with its project stage basis, could be good to face the more demanding challenge of future tunnelling projects. It is hoped that the risks will be fairly shared between the Parties involved. In the construction contract procurement stage suggested in the above Code, three points could be highlighted: i) the use of FIDIC, ICE, National or Proven Form of Contract; ii) including of Geotechnical Baseline Report in Contract Documents, and also in Subcontract Documents; and iii) including risk clauses in contract. The risk of unforeseen ground conditions (differing site conditions) and contractual claims cannot be overlooked; these can be administered fairly with the help of a Disputes Review Board (DRB). Another useful tools include a cost-risk estimating procedure (CEVP - Cost Estimate Validation Process), and a decision making tool in tunnelling (DAT - Decision Aids in Tunnelling). CEVP develops a probabilistic cost and schedule model to comprehensively and consistently define the probable ranges of cost and schedule required to complete each project, by incorporating uncertainty (uncertainty includes both risk and opportunity) (Reilly, 2005). DAT helps to make more rational, informed, and effective decisions in tunnel design and construction. The most important element of DAT is the possibility to consider diverse sources of geotechnical and construction uncertainties and variabilities. Both RMP and DAT have been successfully applied in recent years to a series of important deep and long tunnel projects like the California high-speed rail, the Pajares and Guadarrama high-speed railway tunnels in Spain, the new Lyon-Turin high-speed railway link (Grasso, 2001). Following experience with risk management can be learned from the Copenhagen Metro in Denmark (opening in turn 2002, 2003 and 2007): ◊ The Contract defined the construction risk assessment work to be carried out by the Contractor. There were general requirements for all the construction risk assessments to be carried out for all construction sites and some further requirements to the construction risk assessment for the TBMs. ◊ The TBM construction risk assessment had to start immediately after signing of the Contract with an assessment of the conceptual design followed by an assessment of the detailed design with the purpose to contribute to the design of the TBMs. Furthermore, risk assessment of the TBM operation was carried out providing input to the operation procedures. ◊ Risk identification and management: • • • • • • •

Installation risk resulting from TBM rotation TBM advance pressure Twisted thrust shoes Rigid erector hydraulics Transport conditions Sequence of installation Eccentricity of thrusters

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Report at the Meeting between ITA and ITST on Tunnelling

• 2.3

Hanoi, 12 March 2007

Sectional tension forces

Concluding remarks on risk management

In order to meet the complex requirements of a tunnelling project, the geotechnical design should be based on adequate geotechnical investigation, then data evaluation provided, and monitoring program elaborated. High performance TBMs are essential for the successful construction of tunnel projects. The TBMs will be purpose built machines using proven “state of the art” technology and designed specifically for the project to a minimum specification to ensure their reliability in terms of performance and settlement control. They should be designed to cater for the range of ground conditions anticipated. Risk management procedures should be provided for to cover all the possible risks; prepare measures to deal with that risks including corresponding cost estimate. Risks have to be considered from the first steps of the tunnel project, through installation process to its operation. Budget for risk management should be allocated and defined in tender documents and contract requirements.

3. Subsidence induced by tunnelling

3.1

General

All sub-surface excavations give rise to ground movement. In other words, ground movements are an inevitable consequence of constructing a tunnel. These movements manifest themselves, in particular, as settlement. The extra volume of ground excavated larger than the finished void occupied by the tunnel is called the "volume loss" or "ground loss" (VL). It is usually expressed a percentage fraction of the excavated area of the tunnel. A proportion of these losses will develop to the surface (VS). The volume loss at the tunnel VL will be approximately equal to the net volume of the surface settlement trough VS in most ground conditions. If the ground response is at constant volume (i.e. undrained), the relationship will be exact. The hypothesis will be checked especially if the ground is clayish and the overburden is thin. Otherwise, relationship between the displacement in the tunnel crown (Urcrown) and the middle surface settlement (Smax) can be different. The magnitude of the volume loss VL depends on many different factors: • • • • •

soil type tunnelling method rate of tunnel advance tunnel size form of temporary and primary support

Before the magnitude of ground movements can be predicted, it is necessary to estimate the expected ground loss. This estimate will be based on case histories data and should include an engineering appraisal that takes into account the proposed tunnelling method and site conditions. 6

Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

Two settlement prediction approaches exist: (1) well-tested semi-empirical approach, based on empirical formulas derived from past observations; and (2) numerical method, principally the finite element method, which is now rather popular method. 3.2

Settlement Control Approaches

The presence of a surface structure usually changes the settlement profile, due to the interaction between the ground and the building. If differential settlements are significant they may damage the building. Here is the order of considerations to minimize settlement affecting buildings above: ¾ ¾ ¾ ¾ ¾

Settlement prediction Monitoring; Protective works; Defects surveys; and Repairs

Tunnelling-induced subsidence can be mitigated and controlled by means of the following protective measures [2]: • Good tunnelling practice (including continuous working, erecting linings immediately after excavation and providing tight control of the tunnelling process to reduce the magnitude of settlement); • At-source measures (including all actions taken from within the tunnel during its construction to reduce the magnitude of ground movements generated at source, such as face stability, backfill grouting at shield tail, etc.); • Ground treatment measures (including compensation grouting, permeation or jet grouting, control of ground water, etc.); • Structural measures (to reduce the impact of ground movements by increasing the capacity of a building or structure, typically including underpinning or jacking/shoring). Defect surveys should be undertaken long enough before construction starts in the area to capture the condition of all properties immediately prior to tunnel construction. It is necessary to use a reliable damage classification system for masonry structures with the concept of limiting tensile strain. A staged process of assessing risk may be adopted, including preliminary assessment, second stage assessment, and detailed evaluation. In this process, buildings are eliminated from further stages depending on the potential degree of damage predicted. 3.3

Settlement Calculation

Surface settlement will be calculated based on tunnel geometry, ground conditions, shield machine characteristics, lining ring division, and lining material, etc. For the Hanoi Metro Pilot Line Project, these data will be elaborated from the additional geotechnical investigation results that will be carried out by the Owner soon, and the concurrent detailed design process. Calculations can be performed by empirical/analytical method or by numerical estimation, or by both methods.

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Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

With regard to the empirical methods, Peck (1969), O’Reilly and New (1982) presented a Gaussian curve to approximate the short-term transverse settlement trough of a single tunnel in the "green-field" (Figure 1) as ⎛ − y2 ⎞ S = S max exp ⎜ 2 ⎟ ⎝ 2i ⎠

i = K zo

(O’Reilly and New, 1982) Distance to tunnel center-line, y

-y Surface Settlement, S

y i

Smax

Figure 1: Surface settlement trough (after Peck, 1969) where, S = theoretical surface settlement (the Gauss error function, or normal probability curve) Smax = maximum surface settlement (over tunnel axis, i.e. the settlement trough depth) exp = the exponential function written as exp(x) or ex, where e equals approximately 2.718 and is the base of the natural logarithm y = transverse horizontal distance from the tunnel centerline i = standard deviation of the curve (point of inflexion of the curve), or a trough width parameter K = dimensionless empirical constant, depending on the soil type z0 = tunnel axis depth Smax, K and i are given by the following expressions, among others: Smax =

VS 2π i

= VL (%).

π .D 2 4

.

1 0.313VL (%) D 2 = i 2π i

(New and O'Reilly, 1991 / Mair et al, 1996) where D is the tunnel diameter. i = K zo

i = 0.43z0 + 1.1 [m]; K = 0.4 ÷ 0.5

(for cohesive soils)

i = 0.28z0 - 0.1 [m]; K = 0.25 ÷ 0.35

(for non-cohesive soils)

VL can be estimated according to the construction methods as follows: NATM: 8

Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

London Clay → VL = 0.5% - 1.5% which compares favourably with controlled shield tunnelling Open face tunnelling Stiff clay → VL = 1% and 2% Closed face tunnelling (EPB or slurry shields): A high degree of settlement control can be achieved. Sands → VL < 0.5% (0.35% can be achieved with slurry shield and EPB TBM tunneling). Soft clays → VL = 1% - 2% (excluding consolidation settlements) On the other hand, the structural behaviour of the liner and the ground loss can be considered in a numerical model of tunnelling. In modelling and predicting the development of surface settlements by a professional geomechanical program, the following input are needed: geometry, material properties of support system. The output, except from the surface settlements, also include the lining forces (normal force and bending moment that are used to design the reinforcement for the lining), and stress paths.

In summary, surface settlements can be predicted for the urban tunnel drives using both empirical and numerical prediction methods. The two methods can be used in combination to cross-check one another. The FEM is a strong tool but it still depends on the qualification of the users, not including specific adaptations or approximations. And it is vital that the output from the numerical analysis is checked carefully. The semi-empirical methods must be applied with caution, and FE analysis with geomechanical software must be used toward an effective way. Settlement analysis logically indicates the necessity of a clear presentation of the effects of tunnelling on the overlying structures.

4. Estimate of Damage to the Existing Structures

It is known that, different forms of structure will be affected in different ways by the settlement trough. As said above, a strategy to minimize damages to the adjacent existing buildings due to tunneling-induced ground settlements include: Settlement prediction; Monitoring; Protective works; Defects surveys; and Repairs. A detailed investigation into and an application guidance for the assessment methods of tunnelling-induced building damage is not the subject of this paper. However, as a first idea, it has been known that, design philosophies have employed techniques of classifying buildings according to the probability of a certain threshold of damage being experienced. This leads to a Staged Assessment Process. Buildings under consideration are eliminated when they are shown, by progressively more complex analyses, to lie within acceptable risk levels (Chiriotti, 2006). Below are some information that will be useful for the actual assessment process in the near future during the actual implementation of the urban rail projects in Hanoi.

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Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

Impact of tunnelling operations to the existing pile foundations in Hanoi: A lot of high-rise building (e.g. over 10 storeys) have recently appeared in Hanoi in recent (within 15 years to date). The number of the 12 to 27-storey buildings is about 50. Various types of footings/foundation used in Hanoi are presented in the Table 1 below. Most of the low-rise buildings in Hanoi that have been built before the 1980s utilized the bamboo pile driving or bricklaying foundations setting on the alluvial soil or silt clay strata. Therefore, these buildings are sensitively influenced, affected and damaged by the excavating works, tunnelling or by the high vibration from the nearby construction sites. The recently-built high-rise buildings have incorporated the bored piles with the pile toes founded in the gravel or cobble layers at great depths; these buildings are difficult to be impacted by the excavation and vibration from the adjacent construction sites. Table 1: Various types of footings/foundations used in Hanoi Footings/ foundation types

Description

Bamboo piles

Manually driven, highly dense, common depth of 3 m to 5 m; nowadays still often being used

Brick/masonry foundation

Nature and depth, extent not clear

Wooden piles

Driven, unclear depth. The wooden piles of the Hanoi Opera House with a diameter of 200 - 300 mm that had been driven by the French in early time(?)

Driven piles

concrete Used in the years 1970s, but the driving work caused substantial damage to the adjacent buildings. At present this kind of pile driving is prohibited.

Press/Jack piles

Rectangular concrete piles with a diameter from 150 - 300 mm, the length of each pile section is about 1.5 m; piles are driven into the ground by the hydraulic pressing/jack frames. Pile sections are equipped with pile caps, welded together and pressed into the ground until refusal. Depth may reach to 20 m. Usually combined with concrete base slab with integral beams. Had been used from the 1980s.

Bored piles/ Drilled shafts

Presently widespread used in the high-rise buildings. Bored piles may have diameters up to 1.2 m; the depths to many dozens of meter; steel casings may be used for the first 5 m, and the remaining deep part of pile shaft obtains its bearing capacity by cement concrete.

All these information will have to be taken into account when conducting the detailed design for the Hanoi Metro Pilot Line Project, and when preparing studies for the similar projects, especially the 15 km underground section of the UMRT2 Line which in part passes beneath the ancient quarter.

CONCLUSIONS This paper has as a first setp reviewed some aspects of risks in tunnelling, in particular the subsidence issue in urbans areas, since these are the important and often encountered problems. The article aims, to a qualitative extent, at applying appropriate 10

Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

risk and settlement management as well as building damage assessement techniques for the actual metro projects in Vietnam. The next development of this article will be to quantify these techniques. Prospect of the execution of the Hanoi Metro Pilot Line Project and others This kind of metro project is executed for the first time in Vietnam. The selection of conventional or mechanized tunnelling methods for the underground section of the Hanoi Metro Pilot Line is still left open. In either case, risk management and project management shall not be overlooked. For the TBM potential option, the optimization of segmental lining design and construction, in close relation with proper selection and operation of the tunnel boring machine (TBM), are the two among major concerns for the owners, designers and contractors; and the following shall be considered: A comprehensive and interdisciplinary consideration is required to achieve the attractive and effective mechanized tunnelling alternatives in saving both time and cost. The Parties involved should be aware of the proper approaches in adopting the mechanized tunnelling technology for this tunnel project. The TBM option must prove to be feasible from both operational and engineering points of view, environmentally acceptable and value for money. Difficult or critical cases of excavation in various mechanized tunnelling techniques (with certain kinds of TBMs) should be analysed in connection with face stability and ground reinforcement issues. Both the technical aspects and the economic impact of the critical interaction between the TBM and the tunnel lining (as well as the interaction between the soil and the TBM tunnelling process) will have to be identified and described in order to comprehend the lining behaviour, the risk of ground failure and the risk of surface subsidence. All the involved parties will need to join their hands to make this metro pilot line project successful. The smooth execution of this pilot line will pave the way for the success of the second line with an even much longer underground section i.e. UMRT-2 line with 15 km of tunnels. The HRB is steadily improving its capacity to efficiently manage these two challenging projects, that in a near future will actively serve for the benefit of the people of Hanoi City./.

References [1]

Chiriotti E. & Romano M. 2006. Ground and surface monitoring in urban environment. PART 3 & 7 - Methods for predicting settlements and deformations due to tunnelling. Turin-based GEODATA Spa. Lectures at Master Course in Tunnelling and TBMs, Edition V, Politecnico di Torino, Italia.

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Report at the Meeting between ITA and ITST on Tunnelling

Hanoi, 12 March 2007

[2]

Cross London Rail Links Ltd. 2005. D12 - Ground Settlement. Crossrail Bill supporting documents. Available on the websites http://www.crossrail.co.uk/; http://billdocuments.crossrail.co.uk/

[3]

Grasso P. 2001. Risk analysis for long tunnels at great depth - Works Planning & Financing Engineering - Design of the Safety and Smoke Control System. ITAWG17.

[4]

Hanoi Authority for Tram and Public Transport Development Management (HATD), 2006. Hanoi Pilot LRT Line - Feasibility Study Report, Hanoi, November 2006.

[5]

ITA-WG2. 2004. Guidelines for tunnelling risk management. International Tunnelling Association, Working Group No. 2 - Research.

[6]

Japan International Cooperation Agency (JICA), Hanoi People's Committee (HPC), 2006. The Comprehensive Urban Development Program in Hanoi Capital City (HAIDEP). Draft Final Report - Prefeasibility Study B: The UMRT 2 Line. Almec Co., Nippon Koei Co. Ltd., Yachiyo Engineering Co.. Hanoi, November 2006.

[7]

Kovari K., Ramoni M. 2004. Urban tunnelling in soft ground using TBM's. Key note lecture at International Congress on Mechanized Tunnelling: Challenging Case Histories. Politecnico di Torino, Italy - 16-19 November 2004.

[8]

Mair R.J., Taylor R.N. and Burland J.B. (1996). Prediction of ground movements and assessment of risk of building damage due to bored tunnelling. In: Proc. of the Int. Symp. on Geotech. Aspects of Underground Construction in Soft Ground, 713-718, Balkema, Rotterdam.

[9]

New B.M, O'Reilly M.P. 1991. Tunnelling induced ground movements; predicting their magnitude and effects. J.D. Geddes Ground movements and structures, Proc. of 4th International Conference, University of Wales College of Cardiff 1991, London. Pentech Press, 1992. pp. 671-697.

[10] Peck R.B. (1969). Deep excavations and tunneling in soft ground. Proceedings 7th International Conference. Soil Mechanics and Foundation Engineering, Mexico, State-of-the-Art Volume, pp. 225-290. [11] Reilly J.J. 2005. Cost estimating and risk management for underground projects. Proc. International Tunneling Association Conference, Istanbul, May 2005.

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