Model for Estimation of Time and Cost for Tunnel Projects Based on Risk Evaluation |
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Authors: | T Isaksson H Stille |
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Institution: | (1) Division of Soil and Rock Mechanics, Department of Civil and Architectural Engineering, Royal Institute of Technology, Stockholm, Sweden |
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Abstract: | Summary. In the planning and procurement phases of tunnelling projects, numerous decisions have to be made regarding tender price and
budget. Many case studies have shown that, in practice, the predicted costs and time schedules are often exceeded. This paper
describes a study of the various risk factors in machine tunnelling and their differing impacts on cost and time. It has been
concluded from the study that it is important to make a clear distinction between normal cost and time, and the undesirable events that cause exceptional cost and time. Existing decision-aid estimation models consider variation of the risk factors, but do not consider normal
cost or time separately from undesirable events. Usually, estimations of project cost and time are made in a deterministic
manner, but this does not allow one to consider uncertainty in cost and time variables. However, if the variables are treated
probabilistically, the total cost of tunnelling can be expressed as a distribution curve, and a decision can be made on the
tunnelling method by comparing the respective cost and time distributions. Based on such decisions, the budget and tender
price can be determined separately, both by the client and contractor respectively. To meet the demands placed on decision-making
for tender and procurement for currently favoured construction-contracting methods, a new model for estimating tender price
and budget has been developed, and is described in this paper. This estimating technique has been applied to a case study
of the Grauholz Tunnel. The predictions obtained from the estimation model are shown to be realistic, as the total construction
cost and time obtained from the model correspond fairly well to the actual construction cost and time. The separate estimation
of normal cost and time and exceptional cost and time contribute to the clarity of the results. The use of the proposed model
also shows that the tunnelling method most suitable for the actual geological and hydrogeological conditions can be selected
by this method. |
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Keywords: | : Risk estimation cost time Monte Carlo simulation tunnelling |
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