Numerical Simulation of Mining-Induced Damage in Adjacent Tunnels Based on FLAC3D

Guorui Wang,Peixian Li,Ximin Cui,Qiang Wu,Zhixiang Tan,Loke Foong

doi:10.1155/2021/9855067

Abstract

The Bayueshan (BYS) tunnels are adjacent tunnels which comprise key engineering structures important for Yurong highway from Chongqing to Sichuan, China. The tunnels were established crossing over the old goafs of a coal mine. The tunnels have been damaged three times between 2014 and 2016. To evaluate the reasons for the damage, fast Lagrangian analysis of continua in three dimensions ( FLAC 3 D ) was used to simulate the underground coal-mine excavation yearly from 2012 to 2015. The simulation results show that the subsidence of the ground surface increased annually. The maximum subsidence of the left tunnel was 505 mm and that of the right tunnel was 512 mm. The excavation led to increase in the tunnels’ stress concentration. The simulations further show that uneven horizontal displacement and subsidence were the major factors in inducing tunnel construction defects. Poor geological conditions, water, and vehicle dynamic loads were also important factors that induced damage. Several engineering suggestions for ways to maintain the tunnels are given in this paper, and the research provides a reference for safety evaluation for tunnels crossing over an old goaf.

Highlights

Underground mining can change rock’s original stress condition, and the rock mass will move to achieve a new balance [1, 2]
Chongqing Bayueshan (BYS) tunnel is an important length of highway engineering from Chongqing to Sichuan, China. e BYS tunnel was established over a coal mine, and some parts extend through the mine’s old goaf. e coal mine is still in production, and the underground mining and old goaf have caused the tunnels to crack, beginning in 2014
FLAC3D is a finite-difference program developed by Itasca Co. e software can simulate different materials with mechanical behavior of failure and plastic flow

Summary

Introduction

Underground mining can change rock’s original stress condition, and the rock mass will move to achieve a new balance [1, 2]. E first is based on the model of stochastic medium theory [9, 10], the second on the theory of the elastic-plastic medium theory [11, 12], and the third and most used is numerical simulation [13,14,15]. E elastic-plastic medium theory is often based on a hypothesis and simplified model, but it cannot reflect the actual geological and mining conditions, and its results are often significantly different from actual ones [16, 17]. Numerical simulation is currently the method that is used mostly in tunnel damage analysis [18,19,20]. E coal mine is still in production, and the underground mining and old goaf have caused the tunnels to crack, beginning in 2014. E research results are used as a basis for BYS tunnel maintenance design engineers

Geological Conditions

Simulation Model

Results