Model for estimation of time and cost based on risk evaluation applied on tunnel projects

The objective of this thesis is to improve the quality of the basis for making decisions about tender prices and budgets for tunnel projects by developing a model for the estimation of construction time and cost. In the planning and procurement phases of tunnel projects, numerous decisions have to be made in relation to the tender price and project budget. Literature studies shows that time schedules and costs for tunnelling projects are often exceeded. In this study it has been stated that there are various risk factors with different impacts on cost and time values in tunnelling projects. It has therefore been concluded 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, which handle variations in variables do not consider normal time or cost and undesirable events separately in the estimations. Estimations of project time and cost are normally made in a deterministic manner. There is however, a need to be able to handle variation in cost and time variables in the estimation. If the variables are stochastic, the total cost of a tunnelling method is expressed as a distribution curve, and the decision about which tunnelling method to use involves comparing their respective time- and cost distributions. Based on these decisions, the budget and tender price have to be determined by the client and contractor respectively. In order to respond to the demands placed on the basis for decision-making about tender price and budget, a new model for estimation has been developed. The estimation model described in this thesis has been applied to two case studies—the Grauholz Tunnel in Switzerland, and the South Marginal Zone of the Hallands Ridge tunnel in Sweden. The application on these case studies shows that the results obtained from the estimation model are realistic, as the total construction time and cost obtained from the estimations roughly correspond to the actual construction time and cost. The separate estimation of normal and exceptional time and cost contribute to the clearness of the result. It has been shown that the normal time and cost impact mostly on the construction time and cost, and that estimation of the exceptional time and costs for each undesirable event identified is possible. Application of the proposed estimation model also shows that the tunnelling method most suitable for the actual geological and hydrogeological conditions can be selected using the model. This is possible, as the normal and the exceptional costs that could be expected are shown in the results. Furthermore, the application also shows that it is important to consider different degrees of robustness in the tunnelling methods, as the time and cost of applying these measures often increase the normal cost, but reduce the normal time and the exceptional time and cost.