Fault-Related Instability Problems of Tunnels - The Host Rock Slip Criterion and Characteristics of the Tunneling-Induced Shear Displacements

Abstract

As one of the fault-related instability problems of tunnels, rock slip along fault plane is closely related to the shear strength of a fault, and usually causes irrecoverable and sometimes catastrophic engineering problems. In this paper, based on continuum assumption and Coulomb-slip failure, a criterion to evaluate rock slip along the fault plane was proposed for a circular tunnel in rock masses containing a fault. A mathematical equation that describes the relationship between required shear strength of a fault and horizontal stress ratio, fault spatial extension and location was established. From the equation, the influences of the important parameters on the required shear strength of a fault was analysed after a numerical validation was performed. Besides, the effects of fault spatial extension and location on the tunnelling-induced shear displacements were characterized through numerical models. Characteristics of the tunnelling-induced shear displacements at the excavation wall indicated that fault location with respect to the tunnel dominates the nonuniform rock deformations at excavation wall, and larger fault dip angles could lead to larger shear displacements in some specific pair cases. The presented investigation provides both a deeper insight into the instability problems of tunnels related to a fault and a guideline for tunnel support design.

Mechanical characteristics of large-section tunnel in soft rock based on various rock conditions and excavation footages

“…The stability of tunnel is always the focus of research [1,2], especially for the tunnel in the weak surrounding rock [3,4], and its stability is also closely related to construction method. According to domestic and foreign engineering experience, if the full-section excavation method is not suitable for tunnels, bench method is often used [5].…”

Analysis of Extent of Deformation Range and Failure Characteristics of Rocks Surrounding a Tunnel Crossing Fault Zone Based on FDEM

“…For example, rock mass characteristics within fault zones usually include high susceptibility to fracturing and weathering, poor strength, and signi cant di erences from the surrounding rock. When a tunnel passes through a fault zone, considerable deformation occurs, potentially alongside serious problems such as tunnel face instability, collapsing of the tunnel wall, and supporting structural failure [1][2][3][4][5]. In his study, Terzaghi [6] ascribed the large extrusion deformation in the tunnel to the considerable amount of clay minerals present in the rock, suggesting that the volume of this rock mass slowly increased and then intruded into the tunnel clearance.…”