Research On Mechanical Behavior Of Mountain Tunnel Under Stick-slip Behavior And Near-fault Ground Motions

Vast majority of earquakes happened in China resulted from complicated and frequent intra-plate tectonic activities.Trigger mechanism of these earquakes is stick-slip behavior of seismogenic fault in crust.After main shock,serval non-causative faults and fracture zones emerge in near-field area.Surface ground rupture is the main effect created by earthquake,principally resulting in more or less severe damage to buildings and other rigid structures.Besides,previous studies of earthquake damage and seismic engineering have found the characters,for near-fault ground motions,of velocity pulse and possibility,that vertical peak accerlation lager than horizontal one.With construction planning implementation,tunnels,inevitably,may pass through seismogenic faults zone,which would cause nonnegligible safety hazards.Therefore,the main objective of this dissertation is to investigate the effect of stick-slip behavior of seismogenic fault and near-fault ground motions on mountain tunnel.The main research works are as follows:(1)Numerial calculations,taking Longmenshan Fault as an example,are performed to simulate the progress of slick-slip on the normal fault,reverse fault and strike slip fault under tensional and compressed stresses between plates in different velocities,with slip rate-weakening frition constitutive employed in the contact of plates,and Burgers viscoelasticity model adopt to represent rheological attribute of lithosphere.Under the circumstances,characteristic curves of key parameters in three kinds of faults are acquired,as the basis of subsequent studies.(2)Three-dimensional finite element model is built to study the influence of normal seismogenic fault with 60° dip angle stick-slip dislocation on mountain tunnel,in which the dislocation load curves come from(1).After extended finite element calculation,failure mechanisms of tunnelling structure,undertaking slick-slip on the normal fault,reverse fault and strike slip fault,are analyzed.(3)Three-dimensional finite element model is built to study the seismic response of mountain tunnel through near-field non-causative faults and fracture zones,with concrete elastic-plastic constitutive.Influences of velocity pulse on tunneling structure are studied in four seismic waves,which are in the same peak acceleration but collected from different epicentral distances.And influences of vertical peak accerlation lager than horizontal one on tunneling structure are studied in different ?,representing the ratio of vertical peak accerlation to horizontal one.