Underground Contstruction

Service Focus Areas

Underground Construction

Management, design, procurement and construction of complex, urban underground projects – in particular those contacts involving sophisticated equipment such as fully mechanized tunnel boring machines (TBMs) – are subject to many complex and inter-related variables. These include national and local politics, public policy, legal requirements, community involvement, media attention and, strict environmental compliance.

underground construction

Chronic problems include the time available to adequately investigate underground conditions and construction methodologies – including those construction means and methods best suitable for the specific geotechnical and environmental conditions. The latter are often poorly understood.

Techniques such as value engineering and risk mitigation – which are essential quality, cost and schedule control processes – have been underutilized by the construction industry. They need to be better understood and utilized on more projects.

We can improve the way underground projects are managed. This requires changes to some traditional forms of management design, procurement and construction. Changes in the responsibilities and working relationships between owner, engineer and contractor are also necessary.

DISCUSSION AND OVERVIEW

Who is responsible? It is difficult to decide how specific the owner or engineer should be about details of underground construction – for example the configuration and operating characteristics of a tunnel boring machine – before the tender/bid phase. This is the subject of debate and controversy.

The owner is ultimately responsible for the conception, planning, financing, design, construction and commissioning of underground works. In exercising this responsibility, the owner with the engineer, will make critical decisions which directly affect the ultimate success of the tunneling work.

Owner involvement. All agencies, through the environmental and design process attempt to define or "bound" those construction techniques which they believe will be successful for their project – with its specific geotechnical and environmental conditions. They usually try to increase competition by using a "low-bid fixed-price" procurement.

In a "low-bid" environment owners have found that contractors will generally not use complex technology – for example a fully mechanized tunneling machine – which the owner might believe is necessary. Contractors will tend to use the cheapest machine that they believe will work and then they look for chances to use the "changed condition" clause in the contract should problems arise.

The final result is, frequently, a machine that is barely adequate, or inadequate, for the work to be accomplished. This leads to disputes, claims and litigation.

The challenge, for owners and engineers is to use the contract documents to define the appropriate level of machine type and characteristics, with associated tunneling procedures, which are essential to achieve proper ground control and tunneling productivity. We need an environment which:

  1. Maximize contractor competitiveness and flexibility
  2. Provides the necessary safeguards, such as adequate face and settlement control
  3. Avoid unnecessary settlements and damage to adjacent buildings
  4. Requires contractor performance and ground control measures, which can be measured accurately and paid for reasonably
  5. Incorporates all essential design and geotechnical requirements
  6. Safeguards the interests of the owner and project "stakeholders"

As an example, the following discussion, by Wolfgang Roth, an associate, considers how detailed the owner should be in defining tunnel boring machine or underground construction "means and methods". It is extracted from John Reilly’s paper presented at the ITA Conference, Vienna, April 1997. "Owner Responsibilities in the Selection of Tunnel Boring Machines."

    "Successful tunneling requires a careful balance between the cost and effort spent on excavation equipment and techniques versus the cost of ground modification. For example, "the price to pay" for employing an open-face digger shield in coarse alluvium is extensive ground modification including dewatering and/or grouting. Investing in a full-face Tunnel Boring Machine (TBM), on the other hand, reduces grouting costs; and employing Earth Pressure Balance (EPB) or Slurry Shields could even eliminate the need for dewatering. Hence, the choice of tunneling approach strongly depends on economic and investment decisions. Unfortunately, performance specifications allow such decisions to be made by low-bid contractors willing to take the risk of "getting by" with less on tunneling equipment and techniques, without having to pay the price for ground modification.

    Based on recent experience, many multi-million dollar construction claims are traceable to undue reliance on contractors’ engineering judgment in the choice of tunneling methods and equipment. More often than not, these claims are successful. That is, owners end up paying for the downside risks which contractors are willing to take in order to produce the lowest bids. With a better than even chance of recovering ground modification or dewatering costs by way of changed-conditions claims, there is little incentive for contractors to invest in refined tunneling methods and/or sophisticated equipment. The results are frequent construction mishaps, delays, cost overruns, and loss of political and public support on highly visible projects. Improving this situation in the low-bidder environment of public works, which lacks the possibility of meaningful contractor pre-qualification, is not an easy task.

    One solution to the above dilemma is to shift from performance – to prescription-based specifications. Instead of simply requiring a contractor to "tunnel from A to B". Some owners recently have gone so far as to provide pre-purchased tunneling equipment of their choice. Some may regard this approach to be in utter violation of conventional wisdom (i.e. "never tell a contractor how to do his work"). However, with today’s rapidly advancing technologies, this traditional piece of advice may have outlived its usefulness.

    Particularly in the U.S., where contractors seem to be reluctant to apply new technologies on their own, the impetus for progress may well have to come from the owner’s side. Prescription specifications are the only viable means of achieving this goal."

Relevant references follow. See also the listing of references on our "PUBLICATIONS" page.

Reilly, J J, 1996, ‘Introduction; management, Policy and Contractual Considerations for Major Urban Underground Design and Construction Programs’ North American Tunnelling Vol 2, pp 533-540, Washington DC, AA Balkema.

Reilly, J J, 1997. ‘Owner Responsibilities in the Selection of Tunnel Boring Machines with reference to Contractual Requirements and Construction Conditions’ Tunnels for People, Vienna, April, Proc v012, pp 749-756, AA Balkema.

Reilly, J J, 1998. ‘Delegates Forum – What’s Working, What’s Not, What Remains to be Done?’ North American Tunneling Conference ’98, Newport Beach California, February. Reported in the Journal of the American Underground Construction Association, Vol 13 No 1 p 9.

Reilly, J J, Anderson, J & Isaksson, T, 1999. ‘Tunnel Procurement Process – Management Issues and Risk Mitigation’, presented at the 10th Australian Tunneling conference, March, Melbourne.

Reilly, J J, 2000. ‘The Management Process for Complex Underground and Tunneling Projects; Tunneling & Underground Space Technology, Vol. 15, No. 1 2000, pp 31 – 44, Elsevier Science.