Asymmetric loading effects and reinforcement strategies for double-arch tunnels in probabilistic jointed rock masses

Abstract

Double-arch tunnels constructed in randomly jointed rock masses are subjected to complex asymmetric loading, the induced mechanical behavior is not clearly understood, and the need for a comprehensive investigation is urgent. In this study, 3DEC discrete element modeling of a highway double-arch tunnel project was performed to reveal the effect of random joint parameters on tunnel mechanical behavior. The probabilistic jointed rock masses were modeled via Monte Carlo simulation and a discrete fracture network (DFN) model. The orthogonal experimental method was used to design a simulation scheme for evaluating the effects of key joint parameters (dip angle, trace length, density, strike, and set number) on the differential displacement of the surrounding rock mass, middle partition wall stability, and induced asymmetric stress. The joint dip angle and set number are the primary controlling parameters for surrounding rock mass displacement. The joint density most significantly affected the middle partition wall stability and overall asymmetric loading behavior, with the maximum difference in the asymmetric stress ratio reaching 7.7. A non-bias side tunnel first bench method combined with bias side unilateral extended rock bolt support can effectively reduce asymmetric surrounding rock displacement (by up to 80.0%) and middle partition wall displacement differences (by up to 24.4%). The results provide critical theoretical insights and practical guidance for optimizing the design and construction of double-arch tunnels in complex jointed rock mass conditions.