Tunnelling in the Himalayas: Risk assessment and management for tunnelling in extreme geological conditions

Transcription

1 World Tunnel Congress Underground Facilities for Better Environment and Safety - India Tunnelling in the Himalayas: Risk assessment and management for tunnelling in extreme geological conditions Ian Mcfeat-Smith IMS Tunnel Consultancy Ltd., Hong Kong SYNOPSIS: This paper draws upon experience gained from a series of major tunnel projects undertaken in the Himalayas and several others worldwide that identify specific engineering risks being encountered in extreme geological conditions in developing mountainous terrain. A state of the art Risk Management Plan and Matrix is presented and used to demonstrate appropriate methodology for identification and management of such hazards and risks as well as appropriate mitigation measures to be undertaken for effective control of the works. Experience is drawn from a series incidents encountered in major rock tunnels where severe access constraints, unstable and snow bound portals, large water inflows, silt flows, rock bursts, squeezing ground, wide fault zones, hard abrasive quartzies, schistose metamorphic rocks, soft youthful sandstones have been, and are currently being excavated by drill and blast, roadheader, open type and double shielded TBMs. Means of minimizing such risks and their impact on contracts are identified together with improved practices for the Indian Tunnelling Industry. Indicative international costs for tunnelling in such conditions are also provided. 1. INTRODUCTION The Himalayas, as described by Panthi (2007) covers some 594,400 m 2 with altitudes varying from 100 m up to 8,848 m above sea level and weather conditions varying from alpine snow and ice covered ridges to sub-tropical hot weather in the Southern planes and deep valleys. Increasing population trends and urbanization in India and Nepal are creating enormous pressure in the Siwaliks and lesser Himalayan zones for water related resources including hydro-electric power, irrigation and drinking water, as well as for road transportation. Needless to say modern tunnelling methods, materials and plant are in considerable demand for such infrastructure however the area is subject to tectonic uplifting as well as rapid erosion by several major river systems. Hence the steep mountain slopes and roads are experiencing debris flows, avalanches and rock and soil slope instability particularly during the monsoon season. As a result access is difficult and road closures not uncommon. Also portal works and site camps often need protection from such unstable elements. The rock types are predominantly young sedimentary and metamorphic rocks often giving rise to major tunnel stability hazards by means of: poor rock quality; deep weathering; high schistosity, shearing and faulting; high rock stresses causing rock bursts and deformation; and large water inflows. Overburden cover for tunneling projects can be as high as 2,000m, for the recently tendered Rohtang Road tunnel project for example, but more commonly varies up to 1,200-1,500m for many of the Indian HEP headrace tunnels. Rock tunnelling by means of roadheader is being carried out in soft youthful sedimentary rocks such as the low strength Shivalik Sandstones for the Subansiri HEP project in the Assam Province; whilst drill and blast has been favoured for HEP projects such as the Parbati HEP Project Stage II in the schists, phillites, quartzites and other massive metamorphosed rocks found in the Himachal Pradesh, and Sikkim Povinces as well as for the Lower Marsyangdi HEP Scheme, in Nepal for example. Several attempts at the application of open type TBMs in such conditions have led to abandonment of the works due to severe water inflows and associated problems in the case of the Dulhaste HEP project in Kashmir, and to large delays due to silt flows, rock bursts and associated contractual constraints on the Parbati HEP project. Undeterred, and under pressure to meet huge increases in demands for power, and having gained experience from these challenging conditions, the National Hydroelectric Power Corporation (NHPC) of the Indian Government will soon let a contract to 1748

2 construct the 16km long Kishanganga HEP headrace tunnel to be driven by TBM in similarly extreme conditions. The writer draws from personal experiences gained from most of these projects as well as from worldwide applications of TBM tunneling in similar terrain. 2. RISKS FROM VARIABLE ROCK MASS QUALITY Whist long sections of massive sedimentary rocks occur in the Assam Province for example most tunnels are encountering highly variable and inconsistent rock mass conditions. Goel et al. (1995) describes hazards on the 4.75m diameter Maneri-Uttarkashi tunnel driven by drill and blast in quartzitic and metabasic rocks as including: problems of tunnel face collapse, with or without heavy ingress of water, cavity formation and large tunnel closures leading to buckling of steel ribs on account of squeezing ground. The absence of advance knowledge of the frequently changing rock mass and ground water conditions and, therefore, the inability of the tunnelling engineers to modify the construction method and support system was responsible for these problems. Panthi (2007) identifies the directional behaviour of thin bands of very weak and deformed rocks including sheared mylonites intercalated with stronger, better quality rocks such as gneiss and quartzite i.e. mixed face conditions, as giving rise to severe stability problems. 3. RISKS FROM WEATHERING AND MAJOR FAULT ZONES The combination of active tectonic movement and complex climatic conditions in the Himalayas enhance deep weathering effects along weakness zones and, according to Panthi (2007) triggered tunnel collapse at the pressure shaft on the Khimti Project at a depth of over 100m. Similar effects were found by the writer on Casecnan Project in the Philippines where weathering effects along inclined shear zones promoted the collapse of the raise bore at about 150m depth resulting in the abandonment of the entire surge shaft. Tunnelling across major fault zones is hazardous in terms instability arising from variability of the geological conditions from soft mylonitic materials to hard boulders, the possibilities of encountering squeezing ground; and the continuity of such zones and hence their being linked to large surface water sources. Fault zones expected in the Rohtang Tunnel are expected to be as wide as 600m for example. However they are less likely to be encountered unexpectedly and the opportunity exists to investigate and even drain these by drilling long directionally controlled cored boreholes up to about 1km long. In the writers opinion responsibility for conducting such site investigation (SI) rests fairly and squarely on the shoulders of Clients. Advance open hole probing is not an adequate substitute for such SI. 4. STRESS INDUCED RISKS 4.1 Rock bursts At Parbati cracking sounds followed by spawling and bursting occurred in a zone with overburden cover of 650 to 1000m rather than in areas of maximum cover. Rock bursts occur in areas of high insitu stress suddenly and dramatically posing serious hazard to miners near the tunnel face. The frequency of such incidents in a single drive can vary from or more. Severe injuries and fatalities can be expected in drill and blast tunnels due to the intensity of labour required at the face and some events occur as major rock falls or as large overbreak above the immediate face causing damage to plant such as jumbos, and roadheaders if in use. The main impact of these is the loss of life, demoralizing of tunnel crews, delays and associated costs. The impact on TBM drives is substantially less as the TBM shield takes the impact, although close support (say steel sets at 0.5m intervals) may be required for open TBMs and gripping problems can be expected. 4.2 Squeezing/convergence Convergence, or tunnel strain in terms of the percentage tunnel wall displacement/ tunnel radius (ε %), is related to the ratio of the rock mass strength (σ MPa) relative to the insitu stress (p). Figure 1 shows tunneling problems in terms of squeezing for different levels of strain. Table 1 after Hoek (2001) shows the severity and amount of strain monitored in a series of Indian tunnel projects. Large to severe convergence in drill and blast tunnels is controlled by the installation of pre-reinforcement such as umbrellas of horizontal 1749

3 pipe piles, multiple headings and close face tunnel support systems. For TBM tunnels options include open type TBM with steel sets and other rock reinforcement or purpose designed double shielded TBM s and segmental lining. 5. RISKS FROM LARGE WATER INFLOWS Provided tunnels are driven up-gradient most water inflows in rock have marginal impact but for shallow or downgrade tunnelling silting, ponding, flooding and loco traction become problematic, particularly for high speed tunnelling. However water inflows can result in instability problems in weak and susceptible rock materials. At the Dulhaste project in Kashmir a headrace tunnel driven by an open TBM was inundated with a major water inflows of over 1000l/sec. This inrush occurred at a minor shear zone aquifer (fractured quartzite) within impermeable interbeded phillites and included 4,000m3 of sand and quartzite pebbles. This resulted in an immediate delay of about 280 days, the TBM being abandoned by a bypass and the project delayed for about 50 years. The inflows fell to 150l/sec within 100 days and five years later inflows of 100l/sec were still being recorded. The project has recently been completed by conventional excavation. At the headrace tunnel for Parbati Stage II a similar incident occurred in May 2007 when routine probing ahead of an open TBM tunnel in sheared and faulted quartzite at 900m overburden cover located inflows of over 120l/sec containing about 40% sand and silt. The inflows occurred at high pressures and could not be contained. Eventually over 4000m3 of sand and silt buried the TBM, which has subsequently been recovered. In other drives local water inflows of over 50l/sec at 500m overburden cover have been recorded in association with fractured quartzites. McFeat-Smith et al 1998 provide empirical methodology for predicting water inflows in such terrain. Figure 1. Squeezing problems in terms of levels of strain after Hoek (2001) 1750

4 Table 1. Case histories of squeezing tunnels in India (after Hoek 2001) Tunnel Depth m σ MPa σ/ p Span m Closure m ε % Comments Nathpa Jhakri headrace tunnel (fault zone) Maneri-Uttarkashi power tunnel (metabasics) Severe squeezing controlled by forepole umbrella Severe squeezing damage to sets and concrete lining Giri-Bate tunnel (phillites) Severe squeezing with buckling of steel sets Maneri Bhali Stage 1 (fractured quartzite) Large squeezing with buckling of steel sets Giri-Bate tunnel (slates) Large squeezing with deformation of sets Loktak tunnel (shale) Large squeezing, supported by rockbolts, shotcrete and stets Chibro-Khodri tunnel (crushed red sandstone) Maneri Bhali Stage 2 (sheared metabasics) Maneri Bhali Stage 2 (sheared metabasics) Moderate squeezing, stabilized by circular steel sets Mild squeezing Mild squeezing 6. CASE HISTORY FOR TBM TUNNELLING IN SEVERE CONDITIONS Of particular relevance for tunnelling in the Himalayas are the experiences gained from construction of the 13km long Irrigation and Power Tunnel for the Umiray Angat Scheme in the Philippines (McFeat-Smith, 2000 and Grandori, 2001). This was constructed by GLF/SELI who completed the 13.2km drive by a purpose designed TBM in severe access conditions and extreme geological conditions as listed below: Difficult access in remote mountainous terrain including major river training and site formation works before tunnelling could commence, creating extreme logistical problems A 4.88m diameter, 13.2 km long tunnel with access possible from only one portal Variable geological conditions in rock types such as hard basaltic agglomerates intercalated with siltstones and mudstones Cover up to 1,200m in an earthquake zone with severe convergence and inflows expected. In order to deal with these conditions the contractor elected to: Transport all plant and service the first 5kms of TBM drive and its back up by helicopter. To drive the tunnel by a double shielded TBM from a single portal To use a state of the art double shielded hard rock TBM with hexagonal segmental lining During excavation conditions encountered included: Individual inflows of over 200l/sec and cumulative water inflows of about 850 l/sec Several cave-ins up to 10m high above the TBM cutterhead at major fault gouge zones. This was managed by an arrangement and drill rig for installing 2m long resin grouted bars through the cutterhead to achieved better face stability 1751

5 Jamming of the TBM shield in long sections of tunnel due to high convergence necessitating hand excavation outside shield. Figure 2 shows the area excavated by hand. In spite of this a very high progress rate was achieved on the initial 4km drive and the tunnel was completed and lined in 24months. These project innovations allowed the double shielded TBM to be developed to a high level of maturity and, in expert hands, to be capable of achieving rapid rates of advance in some of the most extreme geological conditions encountered worldwide (McFeat-Smith, 2001). The TBM was designed to provide: The shield diameters were progressively reduced from front to rear to better cope with squeezing and converging ground Short cutterhead (reducing the incidence of stoppages by blocks and boulders and minimizing ground disturbance in poor ground) with rear loading cutters Access for probing and drilling from inside the shield Very high cutterhead power and torque Variable frequency drive Very high main and auxiliary thrust The telescopic shield design introduced the new SELI active articulation system which, in the more extreme conditions, allowed the contractor to completely open the telescopic shield area to access the converging zones for hand mining close to the face area 7. RISK ASSESSMENT AND MANAGEMENT PLAN The proposed system relies upon the involved parties identifying risks for particular projects and helps in the quantification and mitigation of such risks as discussed in the following section of this paper. The risk management system must be implemented as an integral part of the overall project management system, to provide assurance that the project shall be completed on time, on budget and in compliance with the specified contract and statutory requirements for materials and workmanship, environmental protection and health and safety. An appropriate code for Risk Assessment and Management is given by ITI (2006). Figure

6 Throughout the development of tunnel projects the parties involved are required to hold monthly meetings to review risks associated with the various planning, design and construction methodologies and strategies being developed for the project Through these review meetings the parties involved should endeavor to identify risks and quantify all significant risks that have been identified. The typical Himilayan Risks analysed in the following section provide a guide for this purpose that can be developed and structured in accordance with McFeat-Smith, (2006 and 2008) and McFeat-Smith and Harman, (2004). For each risk identified mitigation measures to reduce the risks to a tolerable level need to be defined and priced as part of the estimation process. The proposed solution should represent the optimum solution, with the risks minimised and the mitigation and/or contingency measures priced. Potential risks can be categorised as R4 unacceptably high through to R1 acceptable risks as outlined on Table 2 which indicates the necessary timing and urgency of the action required. Quantification of each risk level is given on Table Scope and objectives of the risk management system The parties should implement a risk management system for the project that covers all elements of the works, with the primary objective of protecting the interests of all parties who may be involved in, or effected by, the project, including the General Public and the Client. Although the risk management process should be basically the same for each type of risk, for ease of reference the risks can be categorised under: Financial, Programme, Safety, Community Relationship and Environmental (Table 3). The risk management system should ensure that: Risks are identified for all aspects of the project; Identified risks are evaluated as a product of their frequency and consequence ; Identified risks are each allocated strategic treatment options from the choices of avoidance, transfer, mitigation or acceptance, then explained in detail; Emergency and Contingency plans are established for all R3 and R4 level risks; Resources are focused on mitigating the most significant risks; Ownership for management of the risk and its related treatment and contingency measures are implemented by more than one staff but supervised and reported on by one manager; Risk status is reviewed on a scheduled basis to identify if changing circumstances alter risk priorities and treatment for alteration of resources; Participating staff are trained in all risk aspects related to their processes; Records of all risk management activities are maintained; Audits of risk management activities are implemented and effective; Senior management must drive risk management activities. Risk level R4 R3 R2 R1 Table 2. Risk levels and general action plans Action and timescale Immediate senior management attention needed. Action plans must be developed, with clear assignment of individual responsibilities and time frames. Risk is unacceptable and must be mitigated to R3 level before works commence. Senior management attention needed. Action plans must be developed, with clear assignment of responsibilities and time frames. Risk must be accepted by the Board or mitigated to R2 level. Risk requires specific monitoring and review to ensure level of risk does not increase. Risk can be accepted and managed with routine or specific procedures and application of resources. Risk can be accepted and managed by routine procedures. Unlikely to need specific application of resources. 1753

7 Table 3. Risk matrix Scope of assessment: Risk matrix for tunnelling in the Himalayas Consequence Insignificant Minor Moderate Major Catastrophic Description C1 C2 C3 C4 C5 Likelihood Rare L1 R1 R1 R1 R2 R3 Unlikely L2 R1 R1 R2 R2 R3 Possible L3 R1 R2 R2 R3 R3 Likely L4 R2 R2 R3 R3 R4 Almost certain L5 R2 R3 R3 R4 R4 Legend: Low risk Moderate risk High risk Extreme risk R1 R2 R3 R4 Level Descriptor Description of Likelihood L1 Rare Event is highly unlikely to occur on this project. L2 Unlikely Event is unlikely to occur on this project. L3 Possible Event could possibly occur on this project. L4 Likely Event is likely to occur on this project. L5 Almost certain Event is almost certain to occur, possibly several times. Level Descriptor Description and example of Consequence C1 Insignificant F: Negligible financial loss (less than 0.005% of contract sum ); P: Loss of less than 1 week; S: First aid injury treated onsite or offsite with no lost time; C: Complaints received and resolved immediately; E: Incident within the works area and rectified with no long term effect. C2 Minor F: Minor financial loss (0.005% to 0.05% of contract sum); P: Loss of 1 week to 2 weeks; S: Medical treatment minor injury resulting in less than 3 days lost time C: Complaints received by hotline and resolved within designated time E: Incident causes minor impact to local community but no long term effect. C3 Moderate F: Moderate financial loss (0.05 to 0.5% of contract sum); P: Loss of 2 weeks to 1 month; S: Medical treatment injury with 3 or more days lost time, reportable injury C: More than 1 complaint on same issue, delay in implementing measures; E: Incident causes complaint, minor impact to local community. C4 Major F: Major financial loss (0.5 to 5% of contract sum); P: Loss of 1 month to 3 months; S: Serious injury or more than 1 month lost time; C: Constant complaints leading to adjustments in working methods; E: Incident causes many complaints and possible prosecution necessitating change in methods or increase in mitigation. C5 Catastrophic F: Huge financial loss (more than 5% of contract sum); P: Loss of more than 3 months; S: Fatality with possible prosecution and suspension of works; C: Complaints cause job to be suspended and change in working methods; E: Incident causes works to be suspended due to public complaints or instruction by Police and prosecution due to breach of Environmental Laws. Descriptor: F: Financial P: Programme S: Safety C: Community Relationship E: Environment 1754

8 7.2 Risk mitigation Measures proposed to mitigate risks should be subject to review by all concerned parties. All mitigation measures need to be adequate to reduce the level of risk to a tolerable residual level. If in the opinion of the reviewers this is not achievable then the proposed methods or sequence of construction should be revised to provide a construction solution for which residual risks are tolerable. The committee should monitor and review the identified risks and their related timeframes, mitigation and implementation actions. The methodology for carrying out the Risk Review Meetings may for larger projects involve decentralization for management purposes. 7.3 Risk register review meeting procedure The Agenda should cover the following items: Identification of New Risks Review of Risk Register to confirm status of mitigation for Active Risks Status of action statements from previous meeting Present for discussion risk management performance indictor statistics Confirm action statements from the current meeting Discuss performance measurement of risk management success Other actions 8. SUMMARY OF TYPICAL RISKS AND MITIGATIONS FOR THE HILMALAYS The following analysis has been prepared taking into account Risk Registers prepared for several Himalayan projects. Risks have been selected to be typical of those that can be anticipated for tunneling in such extreme terrain and geological conditions. Space does not permit publication of the Risk Register and its specific format hence only the Risk Summary Report for high level risks is included in Table TUNNELLING COSTS VS ROCK MASS CONDITIONS Figure 2 after Hoek (2001) give comparable costs for drill and blast tunnel excavation and support (excluding linings and fittings) for different span tunnels in varying geological conditions. When highlights the large impact geological conditions have on costs. It also shows back analysis of costs and rates for excavation and support carried out by the writer for the 1.5km long 16.5m span Cheung Ching Highway tunnels in rock in Hong Kong for different IMS Rock Classes (see McFeat-Smith, 1998). This shows a similar trend illustrating that advance rates/week decrease to about 1/30th and costs increase by a factors of over 10 fold respectively as tunnelling progress from competent hard rock to poor rock to fault gouge materials (IMS classes 1-6). The cost data on both sets of data are compatible. The message to Client bodies in India from these trends is quite clear for tunneling in variable terrain high quality site investigations are a necessity and should be considered as an investment for Clients hoping to complete the works on time, within budget and without years of litigation. Table 4. Summary of typical high level risks for tunnelling in the Himalayas Risk Description Possible Mitigation Measures Insufficient area for temporary and permanent works at portals Anticipated access difficulties to district/works areas due to road blockages from slope/ snow falls Unexpected avalanche directions/ slope instability/ debris flow at portal due to high rainfall 1. Identify potential conflicts 2. Conduct VE workshop with Engineer 3. Redesign as required 1. Plan logistics of supply and camp locations 2. Expect to use additional resources for clearing access to working areas 3. Request support from Client for clearances 1. Review risks of slope instability 2.Carry out additional SI and analysis as required 3. Conduct VE workshops 4. Propose alternative layouts 1755

9 Loss of life at construction camps due to landslides, flooding etc Unexpected low rockhead at portals Extremely hard and abrasive rock causing rapid wear of drill bits/ picks / cutter consumption Unexpected geological conditions eg collapse / failure of tunnel face and roof due to variable rock quality, high schistocity, mixed face conditions, unfavourable orientation Explosion/ Fire Risk Description Ice in roof and on road deck (Transportation Tunnels) Failure of temporary support after installation due to squeezing Excessive geological overbreak Rock bursts; face, roof and wall collapses after blasting due to high insitu stress Table 4 (contd.) 1. Conduct safety review and check of proposed camp areas 2. Ensure emergency safety procedures in place including evacuation plan 1. Carry out site investigation (SI) to international standards by nominating expert drilling contractor capable of drilling 1000m long HDD holes 2. Include pre-reinforcement and face support in temporary support design 3 Ensure close supervision of ground conditions at portal areas 4. Conduct close monitoring of support performance and ground conditions 1. Obtain fresh, unfractured core samples of all rock types to be encountered 2. Conduct appropriate rock cutting and abrasivity testing as part of SI 3. Contractor to employ expert to predict performance of plant 1. Devise method of identifying uncharacteristically low bids for tunneling works, advise authorities in advance then refuse to award contracts to such tenders 2. Conduct more appropriate SI for tunnel by means of deep borehole drilling from surface, horizontally from portals up to 1000m, or tunnel face (cored) 3. Specify and enforce compliance with international codes for safety and risk 4. Ensure contractor has appropriate plant, personnel, time and resources for job 5. Do not rush into tenders - have entire design, contract docs reviewed by experts 6. Devise temporary support for IMS Class 6 using pre-reinforcement etc 7. Ensure close and timely face and roof support to match conditions encountered 8 Close supervision of works by experienced tunnel superintendent 9. Consider application of new generation of double shielded TBMs 10. Conduct partnering, VE workshops etc to enhance co-operation, communication, reduce power difference between Engineer and Contractor 1. Restrict storage and use of dangerous goods/ flammable materials 2. Train workers and supervisors in safe handling of dangerous goods 3. Provide fire protection measures/use hot works permit system 4. Consultation with the appropriate authorities 5. Provide fire fighting systems for jumbos and critical plant 6. Provide dangerous goods stores for oxygen and acetylene 7. Ensure all electrical systems are installed by a qualified electrician 8. Provide magazine for storage of explosives 9. Conduct regular housekeeping inspections 10. Conduct regular plant inspections and maintenance Possible Mitigation Measures Installation of MPS multi-pulse sequencing by electro-osmosis (McFeat-Smith and Stanley, 2008) as opposed to perishable membranes 1. Employ experienced temporary support designer on site. 2. Ensure close monitoring of previous supports and convergence. 3. Add additional support 1. Employ blasting expert engineer to advise 2. Adopt observational methodology 3. Seek advice of specialist engineering geologist 1. Protection and safehavens for workers 2. High awareness of safety issues and control 3. Toolbox talks to workers to ensure close co-operation; 4. Incentive schemes for workers working in dangerous conditions 5. Close attention to monitoring results by senior personnel 6. Application of observational method 7. Face, wall and roof support to suit specific geological conditions 1756

10 Major sections of soft ground tunnelling e.g. fault gouge or weathered zones Collapse between tunnel and portal due to instability at fault zones or high insitu stress zones Tunnel completely silted up. Probe hole encounters silty water inflow at high pressure Extensive downtime to tunnelling operations for grouting Post Excavation Grouting instructed by Engineer prior to installation of tunnel lining Breakdown of stakeholder relations Complete stabilization' of tunnel not achieved by end of contract Insufficient time allowed in ients programme for tunneling in extreme geological conditions i.e. late delivery of project likely Table 4 (contd.) 1. If geology unknown carry out additional SI from face using cored holes 2. Conduct probing to investigate water inflows using facilities for diverting silt flows at pressure 3. Ensure availability of specialist advisers for temporary support and grouting 4. Ensure availability of experienced miners and management with close supervision of works by experienced tunnel superintendent 5. Carry out consolidation grouting as required 6. Carry out pre-reinforcement 7. Ensure close and timely face and roof support to match conditions 8. Use multiple face excavation and closing of invert arch if required 1. Adopt and practice international code of practice for safety in tunnelling 2. Appoint a senior safety officer with appropriate powers 3. Install quality communication system 4. Carry out detailed Risk Assessment and Management Plan 5. Develop an Emergency and Contingency Plan for tunnel collapse 6. Provide First aid stations, and an emergency rations station to be maintained in an area of stable ground as close to face as possible 1. Utilize probing equipment for drilling at high pressures 2. Use state-of the art grouting mixes and plant 3. Draw up Emergency and Contingency plan for management of silt inflows 1. Use services of top class grouting consultant to minimise learning curves 2. Provide detailed Method Statements at tender 3. Utilize state-of the art grouting mixes and plant 4. Draw up Emergency and Contingency plan for management of water inrushes 1. Recognise that this is a waste of time and money 2. Conduct non-contractual partnering to ensure close co-operation on site 3. Conduct VE workshops on grouting techniques using grouting consultant 1. Early consultation between all stakeholders 2. Conduct non-contractual partnering to ensure close communication, co-operation and reduce power difference between all stakeholders 3. Establish clear lines of communication and reporting 4. Conduct workshops for information sharing 1. Employ experienced tunnel consultants as advisors for both tender and construction (e.g. IMS) 2. Employ experienced management team 3. Implement risk management plan 1757

11 Figure 3. Approximate costs in 1999US$ for excavation and support for drill and blast tunneling (Excluding lining and Finishes) Figure 4. Approximate costs in 1997 HK$ for excavation and support for drill and blast tunnelling and advance rates achieved m/week for IMS different rock classes 1758

12 10. CONCLUSIONS The growing need to implement quality Risk Assessment and Management systems is self evident from the cases histories presented in this paper. Clients are well advised not to continue to undertake major tunneling works in such terrain without a major review of their overall strategy and approach to awarding such contracts. The system outlined has been used by the writer for several major tenders and into the construction stage. Feedback indicates that this is a critical activity for tunnelling in the Himalayas extreme geological conditions as an essential step forward for potentially successful, profitable outcome of further tunnelling projects. Likewise, Clients must understand that conducting quality SI works; using VE workshops with advice from international specialists; non-contractual partnering; risk sharing contracts (McFeat-Smith 1986); are all essential mitigation measures for such works. The standards and extent of site investigations and expectations of the return from such investment must improve (McFeat-Smith, 1998). Like all risk assessment systems, without the benefit of exhaustive data on the frequency of occurrences of particular incidents it is at best semi-quantitive and therefore relies strongly upon the degree of engineering experience and judgment of the various engineering teams involved. Hence in order to ensure a degree of objectivity an independent overview by a plain speaking, non-stakeholder in the contract is considered essential. The analysis conducted for a typical but none-the-less likely tunnel project is revealing and quantifies problems and risks that are being encountered on site. It should be borne in mind that, in addition to these, large number of many more apparently minor risks including issues of currency variations and supplier interfaces for example also have to be managed. The types of risks and associated mitigation measures have been clearly identified. This paper also discusses why and how to make changes in the Indian Tunnelling Industry, and in particular, for the need to avoid placing incalculable risks upon Contractors in terms of time and money. The time for action and improvement is now. REFERENCES 1. Anon. A Code of Practice for Risk Management for Tunnelling Works. International Tunnelling Insurance Group.Jan Hoek E. Big Bad tunnels in Rock. The Thirty Sixth Karl Terzaghi Lecture. Journal of Geotech. and Geoenvironmental Engrg, September Grandori R., Manila Aqueduct (Philippines) The Construction of the Umiray-Angat Tunnel Project. RETC Proceedings, San Diego. SME Inc , Goel, R.K., Jethwa, J.L. and Paithankar, A.G. Tunnelling through the young Himalayas-a case history of the Maneri Uttarkashi power tunnel. Engrg Geol., 39, 31-44, McFeat-Smith, I.. The use of ground classification systems for payment purposes in rock tunnelling. Proc. Int. Symp. on Large Rock Caverns, Helsinki, pp , McFeat-Smith I. Mechanised Tunnelling in Asia. Published IMS Tunnel Consultancy Ltd. Hong Kong McFeat-Smith I., MacKean R. and Waldmo O., Water inflows in bored rock tunnels in Hong Kong: Prediction, construction issues and control measures. ICE Conference on Urban Ground Engineering, Hong Kong, McFeat-Smith, I. Breakthrough in the Philippines-GLF/SELI takes on severe mountain tunneling conditions with double shielded TBM. Tunnels and Tunnelling, June and July, McFeat Smith, I. TBM selection for control of water ingress and face stability for tunnelling in the widest range of geological conditions. Proceedings of ICTUS, TUCS, Singapore Nov McFeat-Smith, I.and Harman, K.W. IMS risk evaluation system for financing and insuring tunnel projects ITA AITES Singapore May, McFeat-Smith, I. Risk Assessment and Management For Tunnelling Projects In Hong Kong, HKIE Geotechnical Division, 28th Annual Seminar, May McFeat Smith, I. Risk Assessment And Management for Three Major Transportation Tunnel Projects in S.E.Asia. Beacons, Transport India Conf., New Delhi, May McFeat-Smith, I. and Stanley, C. Electro-osmosis using multi pulse sequencing for removing and repelling water out of buildings and other structures. Joint HKIE/ Henan, China June Panthi, K.K. Underground space for infrastructure development and engineering geological challenges in tunnelling in the Himalayas. Tunnelling and Underground Space Technology. Vol 22, Issue 5, March

13 BIOGRAPHICAL DETAILS OF THE AUTHOR Dr Ian McFeat-Smith is a qualified engineering geologist, mining and civil engineer. He obtained his Ph.D. researching the performance of rock tunnelling machines, and worked as engineering geologist on 28kms of TBM tunnels for the Kielder Water Scheme in UK using a risk sharing contract. As a Director of Haswell then Atkins China Haswell he has been resident in Hong Kong for over 25 years working on all stages of the Hong Kong MTR; on 60 other tunnelling contracts throughout S.E.Asia. In 1998 he published his book on Mechanised Tunnelling for Asia (see He is currently Independent Risk Management Supervisior for the Kowloon Southern Link. He was the TBM Expert on High Level Committee, Parbati, Head Race Tunnel, India. As a Director of IMS Tunnel Consultancy Ltd he provides services for Clients, Contractors and Insurers on TBM applications, water inflow control, engineering risk management for tunnelling and expert witness services. An IBM compatible computer diskette (CD) in conformity with the above is also required to be sent. The electronic copy should be prepared by using MS Word (suitable for windows). 1760