Tunnelling & Underground Projects Sharing Risks & Responsibilities

Rakesh Kumar Khali, Project Director-Hydro, Hindustan Construction Company Limited, Mumbai, describes the type of risks involved in underground construction projects, gives important guidelines to the tendering authorities and contractors on the preparation and acceptance of contracts, and the possible consequences of major risk factors viz. financial, environmental, and managerial, that all the stakeholders must consider.

Underground space utilization is a rapidly growing trend in India as a number of underground projects are under execution and an equal number of them are in the pipeline awaiting their turn for tendering. These projects demand a particular type of construction and thus need extensive planning right from the tender stage until the final commissioning. Most of the risk factors are inherent in the construction and contract process and are indispensably relevant to tunnelling. Several vital risk factors, which are liable to influence the safety, quality, work schedule and ultimately the overall success of the project, have to be considered and analyzed.

Risk Factors in Tunnelling and Underground Projects
  • Difficult geotechnical and environmental conditions and constraints
  • Improper selection of the design, construction and monitoring methods and the equipment
  • Construction hazards implicit in dangerous underground environments
  • Contractual and commercial conditions related to the above risk factors
As stated above, these risk factors are central to the preparation or acceptance of contracts, and should seriously be thought over by the contractors or the tendering authorities. Other stakeholders should also put their heads together to foresee potential dividends or losses. They should, accordingly, provide for an efficient financial budget, safe environmental management, and speedy implementation of the schedule, in order to achieve balanced and mutually beneficial project targets.

Geological and Environmental Risks
Geotechnical and Hydrological Exploration and Analysis: Availability of detailed and reliable data on soil and rock characteristics, groundwater and gas conditions in the work area are fundamental to proper planning of underground operations and for reducing the risk to a minimum level.

Systematic and Detailed Exploration: The geotechnical data of the construction area leads to the assemblage of an exploration plan which includes the number and location of bore holes, test pits, pilot tunnels, pilot shafts, piezometers, and pump tests etc, and also the type and frequency of investigation and samples taken. The plan must cover the different site conditions. If required, more detailed or alternative types of investigation methods and samples can be added.

Laboratory Testing, Examination and Analysis of Field Samples: Risk of carelessness are implicit in the laboratory works which provide detailed data about the physical and chemical properties, special characteristics and contaminations of the soil and rock layers, and also about the ground water and the gases found during soil exploration.

Analysis of Geology: Hydrology and potential chemical, organic and gaseous contamination of the area, based upon previous explorations, and investigation of recent or past land use.

Comprehensive Interpretation of all Data Obtained: Usually, several reports are made on the geographical areas, or on the special features explored during site investigations, laboratory examinations and analysis, or on the data collected during excavation of pilot tunnels.

Geotechnical Baseline Report (GBR): This comprehensive report is a project-specific handbook, in fact, it is a compilation of the findings of all the site investigations, laboratory tests, research works, and other reports cited above. The GBR presents descriptions, illustrations by 3D models, profiles and sections, and provides for the recommendations and basic parameters of design and methods for monitoring and analysis. It also summarizes the potential risks involved in the construction planning.

Urban and Natural Environmental Factors: Investigation and the resultant understanding of the hydrological, topographical, and urban constraints and potential impacts of the same on the environment are crucial to the design and selection of the construction and monitoring methods. To minimize the adverse environmental impacts, the following analysis and recommendations to mitigate the negative impact should be included in the EIA:
  • Prevention of damage to surface settlements like buildings, pavements, and transportation routes in the vicinity of the underground works and avoidance of displacements has to be the prime concern of the planning process.
  • Prevention of lateral movements in the subsoil layers and subsurface structures and objects as a result of improper excavation support or deficient compensatory grouting.
  • Disruptions in the operation of urban infrastructure like underground pipelines, cables, manholes and chambers must be avoided.
  • Maintenance of roads, railways and pedestrian traffic by the site of the work area by way of safe and protected temporary roads, tracks, sidewalks, driveways, accesses and covered walkways.
  • Quality of life in the city should be achieved by smooth transportation, utility services, infrastructure, air quality, accessibility for emergency vehicles, and maintenance or expansion of public information systems in various forms of communication and media.
  • Protection of archaeological sites which may be encountered underground and the impact on such sites has to be kept to a bare minimum.
  • Protection of natural surface waters, thermal waters, and underground water tables from pollution and loss should be taken care of. Minimum loss has to be done to topography, trees, shrubs and landscapes.
  • Protection of flora and fauna, rock phenomena, and rare soil structures should be insured.
  • Impact of vibration and noise pollution should be minimized in nearby habitats.
Selection of Design, Construction and Monitoring Methods
The essential prerequisites for the selection of design tunnelling and monitoring methods are based on the correct interpretation of the environmental assessment, the GBR, and related data.

Selection of Design Method: There are several design methods for calculating and modeling the soil behavior and also for the effects and forces that will be carried by the underground structures. Selection of the proper input, the most realistic and practical assumptions, and rational safety factors can reduce the risk of underground construction and prevent structural or soil failure.

Planning of Construction Methods, Equipment, Technology and Techniques: After selection and pre-planning of these key methods, the applied equipment and logistic elements that are most compatible to the various site and soil conditions become paramount for avoiding or minimizing problems and risks during the construction of tunnels and subsurface structures.

The basic methods can be:
  • Tunnelling with various techniques
  • Mining in the deeper subsurface soil layers
  • Construction with cut and cover methods when the underground space is created down the surface and covered with a load bearing structural slab.
Tunnelling with Various Tunnel Boring Machines & Selection of the Best Equipment
When the geological, topographical, functional, or urban conditions require a deep tunnel alignment under the surface, various tunnelling methods can be considered. For tunnelling in variable soils, usually, the applications of tunnel boring machine (TBM), which provides the parameters required by the soil and groundwater conditions, can reduce drastically the risk of tunnelling. Closed, open or mixed face shields can provide the necessary support for the excavation and protect the erection of permanent tunnel walls.

Tunnel Boring Machines
Over the last few decades, the following significant changes have been made in the TBM design:
  • The diameter can be over 10-20 and can work in hard and soft ground under 10-20 bars of water pressure.
  • Behind the high-powered cutter heads, the closed face can be supported by earth-pressure balance (EPB shields) or slurry pressure (slurry shields).
  • The cutter rotation motor drives the cutter head and the thrust jacks and the articulation jacks are moving and steering the TBM.
  • For long tunnels, custom-made TBMs are procured, based on the particular requirements of the soft soil or the rock. Double shields are more productive.
  • Hydraulic grippers, front and side shoes, and tail shield relief assemblies etc. can make the tunnelling operation more adaptable.
Trailing Gear: The trailing gear is designed to provide all the supporting functions including transport and supply lines for following TBM operations:
  • Removal of excavated material by conveyors or hydraulic (slurry mixed)technique.
  • Removal of excavated material by conveyors or hydraulic (slurry mixed) technique segment conveyor, hoist and automated segment erector.
Risk Assessment for Tunnelling with TBMs
Although the modern, computer-controlled, high-powered, flexible and protected EPB or slurry shields have proved successful in many large tunnelling projects, there still are the following risk factors:
  • Unforeseen changes in geotechnical conditions (for which the TBM was not designed) can slow down or stop advancement of the TBM.
  • Design or material failures can cause similar problems.
  • Repairing or changing major parts of machinery of the TBM in the deep tunnel, far from access shafts, can be very difficult.
  • Human error or computer failure can also happen at the operation of the complex, computerized TBM, and in certain unexpected situations the computer cannot replace the experienced TBM operator.
  • The vision being hindered by the cutter head, the crew cannot immediately realize the problems, natural cavity, cave-ins, gaps or escaping grouting material.
Tunnelling & Underground Projects Sharing Risks & Responsibilities

Miscellaneous Tunnelling and Mining Methods
Drilling & Blasting: When the proposed tunnel is through a solid rock, the excavation can be executed by drilling and blasting the rock face. Special sophisticated drilling equipment and blasting techniques make this operation safe and accurate. When the rock quality allows, after scaling of the surface of the blasted tunnel, the natural rock surface becomes the final wall. If required, the rock and the roof can get protection by rock bolts and shotcrete layers. This method allows the creation of horseshoe shape or half circle shaped cross sections with a horizontal surface for transporting the muck and materials.

NATM - New Austrian Tunnelling Method: When the soil characteristics make it possible to excavate the tunnel without shield protection using temporary supports only, shotcrete and steel mesh liner with soil anchors or soil nailing support can create a reliable liner for the tunnel. Most of the time, this liner is temporary, and construction of cast-in-place reinforced concrete tunnel wall follows as final protection.

Various Mining Techniques: The underground space can be built with special traditional mining methods or by using modern and sophisticated small equipment, hand tools and safety gears, when other more mechanized methods cannot be applied.

Miscellaneous Tunnelling Methods: Compared to the potential risk factors involved in working with TBMs, there are considerably more risk factors in the case of the less protected drilling/blasting or shotcrete (NATM) methods and mining techniques. Unforeseen fractures or seams, underwater pressure, highly permeable of faulty, weathered, swelling or squeezing soil or rock layers, can represent major hazards. They may cause water and soil burst-in to the tunnel, and sizeable cave-ins can create craters on the surface.

Cut and Cover: This method usually does not require special tunnelling techniques. It can be implemented with common construction equipment. Especially at heavily built-in urban environment, the cut-and-cover construction requires removal, relocation, temporary and staging detour of transportation routes and utility service lines to provide access to the construction area.

A variety of traditional excavators, trenchers, demolition and paving equipment, pipes, cables, cast-in-place or pre-cast elements can be used. Furthermore, slurry walls, secant pile walls, soil treatments, and jet grouting etc. can create an enclosure for the subsurface structures.

Risk Assessment for Cut-and-Cover Tunnels & Structures: The risk factors are similar to those of the general construction methods. The risk assessment would cover selection of proper construction sequences, techniques and equipment, and their impact on the urban and natural environment. The process includes excavation, excavation support, groundwater retention, types and construction of final structures; logistics for handling transportation, and disposal of excavated and construction material.

Selection & Design, Monitoring & Data Analysis: One of the most important steps to control and mitigate risks in subsurface construction is selection of the best systems for real-time monitoring and prompt analysis of data received. Very sophisticated monitoring systems (sensitive instrument, fast data processing and computer system/software capable of real-time analysis and activating built-in indicator signals and alarms), are developed and made available for underground construction. However, the best results can be achieved if the selection of the type and allocation of instrumentation to the levels and technique of signal and alarms are custom designed, not only for the tunnelling equipment, but also for the overall project operation and its environmental conditions.

Benefits of Real-Time Monitoring: The purpose and benefits of real time monitoring are twofold: risk prevention and continuous improvements. The system can monitor all the events and conditions as the tunnel construction progresses, with various indicators and alarms levels. This helps prevent simple errors, failures, or catastrophic/disastrous events. This is a very effective tool for risk prevention.

At the same time, the monitoring system is able to provide continuous real-time analysis of soil, rock and environmental conditions and also the effectiveness of the operation (e.g. earth pressure on the face, power and torque of cutters, pressure and mix of grouting, directions of tunnel, circularity and geometry of the segment rings and shield plates, etc). It makes possible immediate evaluation of the data and, if required, modification of operating parameters to match the actual environmental and soil/rock conditions.

There can be a minor adjustment to the grout mix or modification to the articulation jacks. However, if deemed necessary, it can improve the quality and progress of the tunnelling by significant changes made to the design and set parameters or methods of operation.

Construction in Underground Workplace and Safety Hazards
The work of miners in confined underground spaces has always been very dangerous. Underground tunnelling works today – with regulated safety processes, modern equipment, and protection devices – still have numerous safety hazards. In the case of cut-and-cover construction, the workplace hazards are entirely different. Issues related to the safety of public and urban environment should have more implications in the risk analysis process.

At the planning stage, the contractor should prepare a thorough risk assessment and identify the major safety hazards associated with the selected construction methods and the confined space. The safety regulation from most of the governments and their authorities make it mandatory for the project to have specific safety and emergency plans. The same should be followed by the supervisors and workers at the construction sites. The safety of workers and the public must be the number one priority for contractors, consultants, and all other stakeholders in projects requiring underground construction.

Tendering Requirements & Contract Conditions
The processes aforesaid for reducing the risks of unclear and difficult soil and environmental conditions; improper design, construction, and monitoring methods, as well as workplace and public safety hazards at a manageable level is necessary. But this would not be enough without a clear and mutually satisfactory legal approach for handling the potential risks in the tender and contract document.

In this regard, the tender and request for proposal (RFQ) documents, including the specifications, design drawings, geotechnical and environmental reports, and the client’s requirements are equally important for the strictly legal and commercial conditions in the contract agreement. Often, the presence or absence of a technical note or instruction, ignorance, or perhaps an oversight of it, can cause a damage of millions of dollars, along with lawsuits.

Review of Project Delivery Methods & Potential Risks
For underground and tunnelling projects in a majority of cases, the standard “traditional” Bid/Build or the Design/Build delivery methods and contracts are used.

Traditional Tenders
Traditional or BB (Bid/Build) tenders are based upon complete technical documents prepared by the prime consultants for the client. The potential contractors must submit their tender price (either a stipulated lumpsum price, or summary of unit rate items based on a bill of quantities issued in the tender). The required completion time is provided in the tender documents, or the contractor is required to indicate it in the tender form. The tender documents include the scope of work, drawings and specifications, and other technical conditions.

This is a well-proven project delivery method. Allocation of potential risks has clearly been stated. The consultants are responsible for the correct technical design; the contractor is responsible for interpretation, understanding, and piecing together the designed project – and if they are selected – to build it in time and within the price accepted. The client’s responsibility and risk is practically limited to the selection of the consultant and the contractor, based on the tender results; albeit the risks (e.g. unforeseen underground conditions) cannot be passed on as the liability of the contactor. Typically, the contractor must provide a Bond or Letter of Credit as security for the contract performance.

This traditional tendering method can bring into effect the most cost-effective bid, but only in a highly competitive market. To get the award, some contractors do not consider or understand the full implication of the term risks (incomplete design, unclear conditions, price escalations, etc) and bid with a low margin. According to the contact, the control regime is strict on cost, schedule alternatives, and changes or potential shortcuts. In case of incomplete adherence to the norms, there is hardly any room for the contractor to recover the losses. An unharmonious relationship among the stakeholders will bring a negative impact on the project.

Since the project has to be built as per the design provided, there are chances of lesser success. When the design and specifications are correct, it works. However, in complex projects, when the client is dependent on the contractor for constructability issues, innovative approaches and cost savings, a more flexible approach would be advantageous.

For all the reasons cited above, the general opinion in the international market is that the traditional delivery method is not flexible enough for underground construction projects which involve high complexity and substantial risks.

Design-Built Proposals
The Request for Proposal (RFP) contains conceptual information based on the client’s needs. It can be very concise or detailed (guidelines, specifications, conceptual drawings, etc. prepared by the client’s consultant).

Usually, pre-qualified contractors submit the price proposal for the complete design and construction, based on the RFP requirements, and, if requested, also submit conceptual drawings and description of the facility. The client – after reviewing the submissions, the prices and other conditions, selects one proponent and awards the design-build contract to him. Allocation of the potential risk is simple: the Design-Built contractor is responsible for the project design and implementation according to the contents of the RFP. The risk of the client and the client’s consultant is limited to those items that require a deviation from the RFP.

In general, the Design–Build project delivery method provides more opportunities to the contractors to work out innovative approaches and to secure cost savings through the design process for the contractor and the client’s benefit. However, for underground construction projects, usually, the client’s consultants prepare the soil exploration, the Geotechnical Baseline Report (GBR), the environmental assessment, and conceptual design with horizontal and vertical alignments of tunnels. The contractor’s input is limited only to the detailed design.

In this kind of project, with high complexity and substantial risks related to difficult or unclear geotechnical and environmental constraints during the preparation of proposal, usually, there is no time and opportunity to work out alternative solutions. There is no concession to be given to the contractor if the client’s consultants advise contingent changes in the conceptual design provided. Although the tendering used in complex Design/Build situations is the sole domain of the consultant, the client and the contractor have to mutually agree on the assumption in the GBR.

Delivery Methods with Extra Services
Traditional Bid-Built and Design-Build contracts may be delivered with Guaranteed Maximum Price (GMP). If certain price factors are not available at the time of signing the contract, the contractor accepts and guarantees a limit to the total contract price for the client’s protection.

The Design-Built contracts are sometimes delivered with a financing option called Design Built Financing (DBF) and with the costs of operation of the new facility known as Design Built Operation (DBO) or Design Built Finance Operation (DBFO) contracts. The Bid-Built contracts may also be financed, but they are more frequently combined with operations: Built-Own-Operate-Transfer (BOOT). The contactor will recoup its costs and profit from the operation income.

The delivery methods presented have limited potential for mitigating the risks and managing anomalies and disputes during the contract. The following examples show some alternative project delivery methods which attempt to avoid these anomalies and put the focus on collaboration for avoiding and managing the potential risks.

Proposal from Joint Ventures
This approach is followed when a project is sizable and complex and requires significant resources (e.g. containing complex and large tunnelling or underground structures, subway lines stations etc). Such projects need special expertise, qualified contractors, and a highly trained staff.

The method of delivery is the same as described above, but the contractor is a part of the Joint Venture (JV). The contractor’s or the Design-Build contractor’s risk and responsibility is allocated between the JV partners according to their JV Agreement. The partners are jointly and severally responsible for the contract to the client. However, the gain and risks are shared between the partners, which can help to keep the potential financial consequences under a manageable level for the individual contractors.

For the project and for the JV partners, the real benefit is that at the time of tendering they may do individual risk assessment, method selection, and cost estimates. Before the final submission, the JV partners compare and evaluate each proposal. Each one represents different aspects and various ideas for risk control, which the JV can use in the best combination in the bid. They can also take this beneficial approach during the construction.

In large and complex underground projects, the concept of joint venturing of contractors is very popular. Sharing the potential financial risks between the partners and comparing, discussing multiple risk assessments, and exchanging innovative ideas, have proven to be valuable and effective.

Incentive Contract Delivery Method – Alliancing
In the last decade, the concept of alliancing in construction has gained growing interest in the USA, the UK, Australia, and Hong Kong. This alternative approach to contracting is also attracting Indian entrepreneurs who see positive outcome both for the client and contractor in this method.

Defining Alliancing and Partnering
Partnering is about relationships; it enhances collaboration between parties to an existing contract by improving communication, trust and fair dealing between them. It creates an environment where parties have the confidence that they can express what they want and can expect full and an open-minded consideration of their positions. The partnering arrangement is usually formalized through a partnering workshop, held soon after the contract is signed. The workshop is attended by the senior management of each party as well as contractors, subcontractors, consultants, and suppliers.

Concept of Incentive Contract
The concept of alliancing in construction has two main contents: the first group contains hard (contractual) elements, and the second group contains soft (relationship-based) elements. In construction alliancing, two important elements are, the formal contract and a real gain/pain sharing arrangement. The three essential soft (relationship-based) elements are trust, long–term commitment, and cooperation/communication. A number of different elements can be added to constitute a specific variant of alliancing.

Project alliancing is a legally enforceable relationship entered into between the project sponsor (client) and the various participants selected for their competence and commitment to achieving outstanding results. The parties sign an alliancing agreement which is designed to create an opportunity for the participants to actively seek innovation in all the aspects of the project in a ‘no fault-no-blame’ environment. The basic idea is that if each participant works to achieve outstanding project outcomes, it will lead to increasing levels of commercial profits. In other words, a win–win situation for all.

All parties contribute by their share of effective project management: problems are recognized early and resolved amicably. The result is that the project is completed within scope and within time. A shared clear Project Mission will be established. Incentive for sharing gains and sharing risk–profile is apportioned to the parties.

Risk Sharing – Risk Management – Significant Savings
This approach is more suited to an already existing client/contractor relationship. It requires the contractor to step into the project early on and become part of the project development and design team from the beginning. Using the open-book method means that duplication of cost is identified, misconceptions can be corrected, and as a result, overheads and contingencies can be reduced. The focus is more on the total project and not limited to each participant’s own scope. It boils down to relationships and a commitment and willingness from all the parties to be involved in the collaborative approach.

Contract Conditions & Onerous Contract Requirements
The three most important terms of any tender/proposal or any construction contract are:

Scope: The scope begins with the question “what is the work or subject of the construction services that the client shall receive? How much price shall be paid for the contractor’s services? When shall the project complete, or be available for client’s use?” Answers to these questions must be clear, precise, and indisputable. If any one of these terms is missing, deficient or unclear, the proposal/tender will be declared incomplete, or the contract is invalid. In underground or tunnelling projects, all the three basic elements can be influenced by the major risk factors discussed above, and must therefore be subject to thorough risk assessment.

General and Supplementary Contract Conditions
Besides the three basic terms and conditions in the contract, several other conditions also occur. These can be commercial, legal or technical terms which have to be spelled out in the General Conditions (standard documents set-up used by the client or by all industry stakeholders) and also in the Supplementary Conditions (which are specific to the project, standard for the jurisdiction or to the client).

Some of them can be very useful while clarifying processes, commercial and legal terms and technical requirements and parameters. However, some hidden or obvious intent can bring along unknown risks to the contractor. Such undesired conditions result in avoidable adverse relationships and shake the trust between the parties before the project starts.

Financial Conditions, Price Breakdown, Cash Flow Payment Conditions, Evaluation of Changes
These items are to be regulated in the contract according to the local industry practices or rules. When the modification in the supplementary condition tightens the control on the contractor or puts unnecessary financial burden on him, the price of the project increases.

Preselected, Prepurchased Equipment, Materials and Services
The client can independently order, purchase or select items to be used or built into the project when the quality or compatibility of these items are very important, or the long delivery time of the items requires early steps to assure the availability of the items for the contractor in time to meet the scheduled completion date. It can decrease the schedule related risk and increase the client’s responsibility related to the quality and compatibility of the items. As a prudent practice, often, the most crucial equipment including the TBMs are selected and purchased by the client.

Claims and penalties, disputes and resolution methods are always associated with schedule-related claims. When contractors are over-assessing their capabilities or underestimating the difficulties of the ground conditions, or the client cannot provide the condition as stipulated in the contract, delay claims and counterclaims are presented and disputed by the parties.

Roles and Responsibilities of the Parties
The contract conditions specify the roles and responsibilities of stakeholders: the clients, consultants, contractors and sub-contractors and the co-operation required for successful implementation of the project. Recent contracts require holding partnering workshops for enhancing the relationship and improving communication and trust between the contracting parties. Taken seriously, this concept can improve co-operation and contribute to the success of the traditional Built-Bid or Design-Built contract. However, the best result can be achieved when the partnering concept is added to the incentive contract methods, where the gain from the amicable behavior can be shard between the parties in the form of financial reward (i.e. the extra profit).

Joint Risk Sharing: Balanced and Unbalanced Risk Sharing
In the joint risk sharing and risk control between parties forming a joint venture to tender and build an underground project, the client follows the risk-sharing concept. Usually, every type of contract has risk sharing elements. The traditional DBB and Design-Build contracts (when using typical contract forms established by organizations of industry stakeholders), are based on consensus and on the balanced risk sharing concept.

Unfortunately, several clients, after any negative experience with a failed contract or an abusive contractor, introduce onerous supplementary conditions intending to take more control and less risk (on the advice of lawyers). These attempts can have an adverse effect on the project. Good contractors stay away from any tender or contract with onerous conditions and unbalanced risks or build large contingencies into their price. Only desperate or uniformed contractors are bidding aggressively on the tender, ignoring, or not understanding the risks. The failure is predictable.

In underground projects, where the risk factors are more sizable and the proper risk assessment and prevention are more difficult, it is very important that all the stakeholders review, understand, and strive to establish a balanced risk in the contract.

Summarizing Risks, Problems, Consequences, and Learnings from Case Studies
After reviewing several tunnelling and various underground-construction case studies, the root of the problems and losses can be found in the lack of adequate information. The following is a random list of reasons and consequences:

  • Insufficient geotechnical exploration laboratory evaluation and data reports.
  • Underestimated or misinterpreted difficulties from the (sufficient/correct) geotechnical reports.
  • Overestimated capabilities and capacities of the selected tunnelling method.
  • Insufficient exploration and assessment of the environmental constraints and risks.
  • Underestimated impacts or misinterpreted environmental assessment.
  • Overestimated environmental pre-eminence of the tunnelling/construction method/equipment.
Consequences Affecting the Environment
  • Excessive damage to city infrastructure, broken utilities, eroded rail roads
  • Tunnel cave-ins, surface craters, damaged vehicles, sinking/collapsed buildings
  • Excessive damage to the topography and landscape
  • Loss of surface water from lakes and creeks above the tunnel route
  • Contamination and/or loss of groundwater and thermal water sources
  • Loss of water from the intake of water treatment plants, wells and public supplies
  • Costs to be paid for repairing or finding remedies for the damaged environment.
Consequences in Underground Construction Sites
  • Loss or damage of construction equipment, tools, materials, and services due to mudslide in the caved-in tunnels
  • Damages due to flood surface water or groundwater discharged into the tunnel
  • Costs and schedule impacts resulting from the extra measures taken to stabilize groundwater conditions and to improve soil conditions in order to clean and protect the excavated space, which otherwise may jeopardize the safety of the staff and the public.
The evaluation of these case studies reveals that the problems and losses vary, depending on the contractual methods, stipulations, and relationships. The range of actual problems and consequences are unlimited. Several of them (claims, disputes, unbalanced risk sharing, etc) have been discussed above under the contractual conditions and risk assessments. However, the main source of the problems are always traced back to relationships and commitments. Understanding and willingness by all parties to co-operate for a common goal will lead to successful completion of complex tunnelling or underground projects.

Recommendations for All Stakeholders
Contractors: They should shy away from making onerous tender and contract conditions and imbalanced risks. They should show a high degree of commitment to their business and reputation. They should do a thorough risk assessment and implement constructible and safe solutions. They should behave like reliable partners of their clients and consultants.

Consultants: The quality of information in the technical documents: environmental and geotechnical conditions, functional and structural requirements, and clear communication of them, are extremely important for proper implementation. They should be a good advisor to their clients and function like a partner of the contractor in risk assessment and help find best solutions for construction.

Clients: Before awarding the contract to the lowest price and shortest schedule bid, the clients should be aware of all the risks involved in the risk assessment and act accordingly. They should be responsible for the success of the project and be a partner in reasonable risk sharing.

Rakesh Kumar Khali, Project Director-Hydro, Hindustan Construction Company Limited, Mumbai
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In India, coal is still the primary source of energy; over the past few years, there has been quantum jump in coal production level, but it was mostly due to the high percentage share from the opencast sector. The country is witnessing a fast

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CRCHI emerges as provider of total underground engineering equipment and solutions
China Railway Construction Heavy Industry Corporation Limited (CRCHI) showcased its comprehensive range of equipment and products at bauma that included solutions for the whole industry chain in the field of

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Herrenknecht AG wins bauma Innovation Award 2022 for development of continuous tunnelling
Herrenknecht AG won the highly coveted award bauma Innovation Award 2022 in the category “Machine Technology” for the new development of continuous tunnelling. The award was given for the next innovation boost in the mechanized

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The Genesis of Underground Engineering
Regardless of the tunnelling technology used, tunnel designers decide the future success or failure at an early project stage. In fact, designers are the real managers of tunnel construction. The choice of design together with selected contract model is

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Managing Geological Complexity in BVC and PAC of Tehri PSP, India - A case study
Tehri hydroelectric project is located on the left bank of River Bhagirathi in the state of Uttarakhand. Tehri Pumped Storage Project (PSP) comprising 4 Nos of reversible pump-turbine units of 250 MW each, involves construction of an underground Machine Hall

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TBM driving under low overburden by adopting innovative methodology
TBM mining in urban areas particularly under low overburden (less than 0.5D, D = tunnel Dia) is a big challenge to design team as well as execution team. While working in a Lucknow metro project, the metro authorities encountered a stretch where TBM had to cross

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Tunnel Ventilation System Basic Concepts and Designing Principles
The term ventilation combines several functions such as smoke extraction, pollution ventilation, and ventilation for environmental purpose. The design of a ventilation system is usually based on three scenarios: During construction: to provide external

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