Robust Geotechnical Design of Shield-Driven Tunnels Using Fuzzy Sets

Abstract

This paper presents a new geotechnical design concept - robust geotechnical design (RGD) - which seeks to minimize the variation of the tunnel circumferential performance to the uncertainty of geotechnical parameters (which is a measure of design robustness) in addition to meeting the requirements of safety and cost efficiency. To this end, uncertain geotechnical parameters are represented as fuzzy sets (or more specifically, fuzzy numbers) to copy with the scarcity of data, which provides an adequate measure of the uncertainties when the knowledge is incomplete or data is limited. Given fuzzy input parameters, the circumferential performance of a shield-driven tunnel is uncertain and logically expressed as a fuzzy factor of safety, Based upon which the failure probabilities and robustness of the tunnel circumferential performance can be computed in the RGD framework. Finally, to aid in the selection of the optimal design that maximizes robustness and minimizes cost simultaneously while the safety is brought to the target level, non-dominated optimization is performed and a Pareto front is obtained. the knee point located on the Pareto front is further identified and recommended as the optimal design, showing the best compromise between robustness and cost. The proposed RGD methodology of shield-driven tunnels is deterministic in nature. Through an illustrative design example presented, the effectiveness and significance of the proposed RGD methodology in the design of shield-driven tunnels for the circumferential performance is demonstrated.