Three-Dimensional Discrete Element Analysis on Tunnel Face Instability in Cobbles Using Ellipsoidal Particles.

Zheng Duan,Xiangying Ji,Hai Liu,Chao Liu,Fei Wang,Zixin Zhang,Jie Cui,Liufeng Pan

doi:10.3390/ma12203347

Abstract

Soil disturbance has always been the major concern in shield tunneling activity. This paper presents the investigation on the micro-scale responses of the soils during shield tunnel excavation in sandy-cobble stratum. The code paraEllip3d is employed in discrete element method (DEM) analysis in which the soils are mimicked as an assembly of ellipsoids. Triaxial tests on the micro-scale responses of cobbles are carried out using the materials sampled from the tunnel face during construction period, and corresponding DEM simulations are performed to calibrate the micro parameters for the ellipsoids. On this basis, the face instability process during the shield tunneling in cobbles is studied using 1 g model test as well as corresponding DEM simulation. The micro-scale responses of cobbles are investigated by triaxial test as well as corresponding DEM simulations. Multiple material responses are discussed in the DEM simulations, including the stress–strain relationship, the contact distribution, and the force chain evolution in the elementary and model test. Finally, the mechanism of tunnel face instability in cobbles are discussed on the basis of aforementioned investigations.

Highlights

Shield tunneling is widely adopted for underground construction due to its gentle impact on surrounding environment and high excavation efficiency
A series of discrete element method (DEM) simulations using three-dimensional ellipsoids were performed on the triaxial compression tests of Beijing cobbles and the 1 g model test on Beijing Underground Cross City Railway (BJUCR) Tunnel project in Beijing
The micro-parameters were calibrated by the comparison between discrete element modeling and triaxial compression test conducted in the lab, and the evolution of micro-structure was investigated simultaneously

Summary

Introduction

Shield tunneling is widely adopted for underground construction due to its gentle impact on surrounding environment and high excavation efficiency. Benefitting from the urbanization and its associated development in China, a surging number of shield tunnels with large diameters are emerging in recent decades. According to previous research [1,2], the increase of the shield tunnel diameter results in rising excavated volume, the decrease of tunnel face stability. For shield tunneling in clay and sand, multiple studies have been performed from the perspective of macro-scale [2,3,4] and micro-scale [5,6,7] responses of surrounding soils. The research on soil material responses in micro-scale during tunneling in cobbles is scarce. Different from fine-grained soil, the coarse-grained soil in tunneling is characterized by its lagging effect in face instability induced by tunneling activity

Results

Discussion

Conclusion