Study On The Numerical Simulation Of Earth Fissure With Buried Bedrock Ridge

Fissures caused by the excessive exploitation of groundwater are a worldwide problem occurred in many countries.Specifically,these fissures above the buried bedrock ridge represent a typical geological hazard in Su-Xi-Chang area,China which cause massive damage to the houses and infrastructure,seriously restricting economic development.Recently,several progresses are achieved on the numerical simulation of ground fissure.A novel numerical simulation method has been proposed to describe the initiation and propagation of single earth fissure.Based on the rupture simulation,multiple regression analysis is developed to determine the relative importance of several factors which contribute to ground fissures.However,the sensitivity analysis of fissure with buried bedrock ridge only considers two parameters which can’t represent all the impacting factors.Moreover,no study is processed on numerical simulation of multi-fissures which are commonly recognized in the field with abrupt bedrock ridge.Thus,it’s necessary to study on the global parametric sensitivity analysis of numerical simulation for rupture with buried bedrock ridge and multi-fissures numerical simulation.These studies develop an understanding of the mechanics leading to earth fissure formulation and evolution.The results provide scientific support for prevention and control on the fissure disaster and have important theoretical significance and practical application value.This paper is focused on the study of ruptures with buried bedrock ridge.The model scenario reproduces the initiation and propagation of single fault.Sobol method and RBD-FAST are used to analyze four factors,including the geometry of bedrock,aquifer thickness,compressibility and pore water pressure change.According to the results from two methods,when the relative opening depth is response variable,bedrock geometry is key factor,pore pressure change is less susceptible while aquifer thickness and compressibility show low sensitivity.The study indicates rupture is more likely to propagate downward when buried depth of the bedrock is shallower with steep slope as well as the pore pressure decreases significantly.An conceptual model with five pairs of contact surfaces is developed to simulate the evolution of five cracks simultaneously.The model outcomes highlight the stress is concentrated mostly on the ground surface above the ridge and nearby the bedrock flanks.From patterns of stress distribution and faults activities,it is concluded that tensile stress only makes rupture open while the shear can trigger the fissures with sliding.Same approach is applied on the case in Wuxi with three parallel fissures.The model results show all three fissures are initiated from the ground surface and propagate downward,the middle one directly above the ridge is induced by tensile stress with obvious opening rather than sliding.The maximum normal displacement and activated depth are 26 cm,12m respectively.On the contrast,due to the shear stress the fissures on both sides are manifested distinct vertical offset amounted to 33 cm and developed to a maximum depth of about 25–40 m,consistent with the magnitude of field observation data.