Displacement ratio dichotomy back analysis of surrounding rock-initial support system of weathered rock tunnel
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ORIGINAL PAPER
Displacement ratio dichotomy back analysis of surrounding rock-initial support system of weathered rock tunnel Jiancong Xu 1,2
&
Yedi Ni 2
Received: 25 July 2018 / Accepted: 6 February 2019 # Saudi Society for Geosciences 2019
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. Keywords Tunnel . Displacement ratio . Dichotomy . Back analysis . Surrounding rock . Initial support
Introduction In the past few decades, the studies on the calculation theories of geotechnical engineering had been made obvious progress. Furthermore, the numerical calculation methods based on the constitutive relation of geotechnical materials have also rapidly been developed. However, because of many uncertainties in exploration, test and theory, and the inaccuracy of input parameters in numerical calculation, there is often obvious difference between numerical calculation value and in situ measured value, having hindered numerical calculation methods from being applied in practice. The main reason of
Editor handling: Pinnaduwa Kulatilake * Jiancong Xu [email protected] 1
Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, People’s Republic of China
2
Department of Geotechnical Engineering, Tongji University, Shanghai 200092, People’s Republic of China
this problem is that the required input parameters in the numerical calculation are very difficult to obtain accurately. The mechanical design parameters of surrounding rock and primary support of weathered rock tunnel are difficult to obtain by experiments. We usually use the back analysis methods to solve this problem. The back analysis methods have been widely used in the research, design, and construction of underground engineering. The surrounding rock deformation represents macroscopically the most direct and synthetic force-bearing variation
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