Displacement ratio dichotomy back analysis of surrounding rock-initial support system of weathered rock tunnel

Abstract

The mechanical design parameters of surrounding rock and primary support of weathered rock tunnel are difficult to obtain by experiments. In this paper, taking the ratio of vault settlement to flank wall horizontal displacement as an investigation variable, we proposed the displacement ratio dichotomy numerical back analysis method (DDNBAM) to calculate the physical–mechanical parameters of tunnel surrounding rock-initial support system. Based on the DDNBAM, we presented a new method to evaluate the rationality of primary support design parameters by the ratio of the equivalent lateral pressure coefficient to the equivalent Young’s modulus with time for weathered rock tunnel in construction. The results are shown as follows: the results calculated by the DDNBAM may reasonably reflect the dynamic variations of tunnel surrounding rock-primary support system using the center cross disphragm (CRD) method; the higher calculation precision may be obtained using the DDNBAM, comparing with the parabolic-apex back analysis method previously proposed by Xu (2012); and adopting the DDNBAM may obtain more reasonable and reliable physical–mechanical parameters of surrounding rock-initial support system.