Numerical Study On The Tectonic Stress Field Of Longmenshan Region And Its Hazard Effect

Based on the field investigation and analysis, numerical simulation on tectonic stress field of Longmen mountains structural belt, forming mechanism of the Xiaoyudong incipient fault, and hazard effect of surface structures near the fault were carried out, and the results are as follows:(1) According to all the geology data and field investigation, numerical simulation of tectonic stress field near the faults in research area, variation of magnitude and direction of the maximum principal stress and the shear stress before, during and after the earthquake are obtained:(A) the directions of maximum principal stress are regionalization. According to the difference of stress direction before, during and after earthquake, the maximum principal stress zone can be divided into southwest region of back Longmenshan fault, middle part of back Longmenshan fault (the southeast of Wolong Town, the northwest of Sanjiang Village), the region of central Longmenshan fault near Yingxiu Town, the region of Xiaoyudong Town between central Longmenshan fault, the region between Qingping Village on central Longmenshan fault and Guangming Village on back Longmenshan fault, and the region between center range fault of Longmen mountain and back range fault of Longmen mountain in the west of Beichuan County.(B)The shear stress along the Longmenshan fault from before the earthquake, when the earthquake occurred after the change rule and for (a) before the earthquake occurred when the earthquake and local shear stress concentration area near Yingxiu, especially with the most obvious, but after the earthquake, the shear stress distribution, and even after the earthquake, compared with before the earthquake fracture and Longmen mountains of Longmen mountains of central piedmont fault of shear stress value, but the Longmen fault shear stress on the back range of the mountain is increased.(b) the Longmen fault high shear stress on the show to the northeast of migration rule, with the most outstanding near Yingxiu, in a certain extent, it also explains why the aftershock, mainly concentrated in the northeast of the Longmen fault rupture, especially in the north.(2)Through the three groups of numerical simulation, the formation Xiaoyudong fault zone is the result of combined action of both the sides of faults, the formation area of Xiaoyudong fault zone was a weakened zone, and there was a buried fault on the formation area of Xiaoyudong fault zone. The results reveal preliminarily stress mechanism of Xiaoyudong fault formation. (3)The numerical simulation results on seismic response of the main building, located on the hanging wall of the fault, of Silicon Company in Shuimo Town show that:(A)The axial stress to the factory building is the biggest at the bottom and decreases from bottom to up during the earthquake, corresponding to characteristics of damage pillars by extrusion. Shearing strength and its direction of factory building is also corresponding to pillars shear failure characteristics. Girder of the building damaged in the earthquake caused by the shear stress and axial stress simultaneously.(B)Stress, strain and displacement near the fault is greater than those far from the fault and fault stiffness and the distance from fault to building have a significant influence on the maximal principal stress, the shear strain, the maximal shear stress and acceleration of the building.(C)The earthquake hazard effect of the building on the hanging wall of fault is more obvious than that in the foot wall, and destructiveness is greater.(4) Sense of ground comprehensive displacement and its value from numerical simulation on the main street in Xiaoyudong and Bajiaomiao sanatorium in Hongkou are close to on-the-spot investigation results. Regularity of the stress distribution can explain forming mechanisms of rupture ground and failure modes of building. According to the simulation results, displacement and regularity of the stress distribution are obtained.(A)Ground uplifts on the whole under the earthquake. Displacement and stress on the hanging wall of fault are larger than that on the football, and regularity of displacement from up to down is just the opposite to the regularity of stress. After the earthquake, fault intended to move forward to the footwall, which caused strong tensile stress appearing on the hanging wall and was easy to produce tension cracks on the building and ground.(B)Vector directions of the maximum principal stress near faults are heterotrophic and vertical to fault. The maximum principal stress vector is horizontal to the ground, and the maximal principal stress and shear stress appeared near the fault.(C)The simulation results show that major influence range of building is mainly concentrated on the hanging wall of fault and the earthquake hazard effect of the building on the hanging wall of fault is more obvious than that in the foot wall, which are consistent with the actual situation.