Risk assessment of shield construction adjacent to the existing shield tunnel based on improved nonlinear FAHP

To solve the problem that the traditional fuzzy Analytic Hierarchy Process (FAHP) cannot reflect the influence of prominent risk indexes on the evaluation results, a new risk assessment model of shield construction adjacent to the existing shield tunnel was established by introducing nonlinear operators into the traditional FAHP. A risk assessment index system including 5 primary risk indexes and 21 secondary risk indexes and risk assessment criteria were established for shield construction adjacent to the existing shield tunnel. The game theory was used to calculate the combination weights, which comprehensively consider the advantages of subjective and objective weights. The certainty was obtained through cloud model calculation, and then the membership degree vector was obtained to construct the fuzzy relationship matrix. Introducing nonlinear operators to comprehensively analyze the weights and fuzzy relationship matrices. Based on the principle of maximum membership degree, the final risk level result was obtained. The new model was applied to a case study of the risk assessment of shield construction of Changsha Metro Line 2, which is adjacent to Changsha Metro Line 4. The results show that: (a) The risk levels of sample 1 and sample 3 were level Ⅲ and sample 2 was level Ⅱ. The result was consistent with the actual situation which validates the applicability and accuracy of the employed methodology. (b) Compared with the traditional FAHP, the new risk assessment model adequately reflected the prominent impact of adverse risk indexes on risk assessment. Therefore, the new model maximizes the assurance of the rationality of the risk assessment results, which can be feasibly used in applications and guide other similar projects.