An Enhanced Ubiquitous-Joint Model for a Rock Mass With Conjugate Joints and Its Application on Excavation Simulation of Large Underground Caverns

Xianlun Leng,Qian Sheng,Jian Chen,Chuan Wang,Hailun Li

doi:10.3389/feart.2021.744900

Abstract

A conjugate jointed rock mass (CJRM) is a rock mass with two sets of intersecting joints formed from intact rock under shear. Its mechanical properties and excavation-induced hazards of large underground caverns are different from those of common rock masses because of the unique geological origin thereof. To demonstrate numerically the excavation responses of CJRM, the ubiquitous-joint model is enhanced by consideration of the specific mechanical behaviors of the rock mass. In the enhanced model, CJRM is considered as the composite of columns of rock and two sets of weak planes of joints. The local coordinates, failure modes, and failure sequences of the rock columns and joints are redefined based on the composite characteristics of CJRM, and the failure criteria and plastic potential functions are accordingly modified. The enhanced model is verified numerically by triaxial compression tests and then employed to simulate the excavation of large underground caverns of a pumped storage power station in China. Results show that the modification of the local coordinate system, failure modes, and failure sequences made in the enhanced model is suited to the simulation of the mechanical behaviors of CJRM. Compared with the original ubiquitous-joint model, the enhanced model allows better predictions of the distribution of plastic zones and magnitudes of deformations in simulating underground excavations in CJRM and helps to assess the excavation-triggered hazards more accurately.

Highlights

Joints are often found in rock masses around underground caverns and usually occur in one or more sets in different directions, cutting the rock mass into blocky structures (Bandis et al, 1983; Jaeger et al, 2007; Wu et al, 2018)
conjugate jointed rock mass (CJRM) or the similar rock masses often appear in engineering practice, but their specific mechanical performance is much less explored in numerical simulation (Wang and Huang, 2014; Yang et al, 2019; Zhao et al, 2020)
This study enhanced U-J model by consideration of the particular mechanical behaviors of CJRM based on an equivalent continuum method and used the enhanced model to study the excavation responses of the large underground caverns in CJRM

Summary

Introduction

Joints are often found in rock masses around underground caverns and usually occur in one or more sets in different directions, cutting the rock mass into blocky structures (Bandis et al, 1983; Jaeger et al, 2007; Wu et al, 2018). Numerical-analysis-based researches investigated the effects of the distribution properties (such as the orientation and spacing) and mechanical parameters of layered joints on the failure mode, plastic zones, and deformation of the surrounding rock masses (Adhikary and Dyskin, 1997; Park and Adachi, 2002; Wang and Huang, 2014; Zhou et al, 2016; Sainsbury and Sainsbury, 2017; Zhou et al, 2019; Yang et al, 2019; Zhou et al, 2021) as well as the internal forces and failure modes of the reinforcements (Hatzor et al, 2015; Gao et al, 2019) of underground caverns.

Results

Discussion

Conclusion