Experimental study on normal fault rupture propagation in loose strata and its impact on mountain tunnels

Understanding earthquake fault rupture propagation is important in building and lifeline engineering, especially in the construction of mountain tunnels. Thus, studying rupture propagation in strata and tunnel failure with fault displacement is significant. For this purpose, an experiment has been designed to simulate normal fault displacements with different dip angles. The influence of normal faults on tunnels has been observed by examining the rupture and strata deformation and analyzing the shear zone, tunnel stain, position, and forms of tunnel cracks. The results show that more than one strata rupture appears when the normal fault moves, and at least one rupture reaches the ground surface as the vertical fault dislocation is approximately 4.4% of the covering depth. In general, those ruptures form an inverted triangle zone in which strata deform significantly. The range of the rupture shear zone increases as the fault dip angle decreases. Strata-tunnel -fault can be considered as a beam on an elastic foundation. The lining of the tunnel in the hanging wall and shear zones is subjected to sagging, and that in the foot wall zone is subjected to hogging. Failure modes appear to change with fault dip angle. The lining damage form is flexure failure occurring mainly in the foot wall with the circumferential cracks, when the dip angle is 75 degrees. When the dip angle is 60 degrees and 45 degrees, the failures are caused by a combination of flexure and shear both in the shear and foot wall zones with a lot of circumferential and diagonal cracks. Furthermore, to guide design work reasonably, the calculation method in determining the weak parts of the tunnel and feasible reinforcement measures are discussed. (C) 2015 Published by Elsevier Ltd.