Keywords: deep excavation, building foundation, safety, fuzzy AHP, decision-making.

The demands of deep excavation construction are increasing with the increasing numbers of high-rise building projects in Taiwan in recent years. The commonly used construction methods for deep foundation excavations in Taiwan include slurry wall, boring pile, sheet pile and guid pile and horizontal board construction. These methods are inherently dangerous and often cause construction accidents that bring about substantial fatalities or injuries of workers, property losses, and competition delay. Therefore, determining an appropriate construction method from these alternatives under given site conditions is fundamental to the success of the construction.

Although safety is a primary consideration in selecting an appropriate construction alternative, numerous decision criteria including cost, duration, and quality, etc, are also important and need to be considered. Moreover, since the importance or preference of alternatives and their associated decision criteria are usually evaluated by domain experts, the assessment results are vague or imprecise. Thus the process of determining a suitable alternative involves a great deal of complexity and difficulty.

Initiated by Saaty [1], Analytical Hierarchy Process (AHP), a pairwise comparison procedure for analyzing relative weights of alternative criteria, has become an effective technique in helping decision makers evaluate a wide range of decision problems [2]. However, AHP is incapable of dealing with the information or evaluation results that are vague or imprecise in nature [3].

To deal with the limitation of AHP, this paper proposes a fuzzy Analytical Hierarchy Process (Fuzzy AHP), an integration of AHP and fuzzy set theory, to characterize the relative importance or weights of the decision criteria considered in the process of determining a desirable construction method for deep excavation. This model aims to assist contractors in alleviating the complex analysis process and ensuring accuracy of selection, To better capture uncertainty and vague information in evaluating relative importance or weights of paired criteria, this model utilizes fuzzy numbers and a-cut operation to represent a variety of degrees of believe.

A case study is performed to show the capability of this model. In this case study, the above four excavation alternatives are evaluated based on the pairwise comparison of safety, cost and duration that is disaggregated by several sub-criteria including geological conditions, underground water conditions, excavation depth, constructability, weather, sub-groundwater, adverse effect on the surrounding building, construction cost and failure cost. The results of the case study demonstrate the effectiveness and practicality of this model.

1

T.L. Saaty, "A scaling method for priorities in hierarchical structure", Journal of Mathematical Psychology, Vol.15, pp. 274-81, 1997. doi:10.1016/0022-2496(77)90033-5

2

C.L. Hwang, and K. Yoon, "Multiple Attribute Decision Making:Methods and Applications, A State-of-Art Survey", Springer-Verlag, New York, 1981.

3

B.L. Golden, E.A. Wasil, and P.T. Harker (Eds), "The analytic hierarchy process", Springer-Verlag, New York, 1989.

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