【作者】 梅海；

【导师】 苏生瑞；

【作者基本信息】 长安大学 ， 环境工程， 2010， 博士

【摘要】 2008年5月12日发生的汶川8.0级强烈地震震撼了全中国,引起了全世界的共同关注。此次地震不仅暴露了我国地震地质工作存在的薄弱环节,同时也给地震工程地质研究提供了了一系列急待解决的新课题。开展对龙门山地区构造应力场及灾害效应的数值模拟不仅是具有重大的现实意义,而且可为研究龙门山活动断裂动力学机制和汶川地震灾害效应提供一定的依据,同时对其他类似地区的地震活动和工程规划具有重要的借鉴意义。本文在现场调查和分析的基础上,进行了龙门山构造带的构造应力场、小鱼洞新生断裂形成机理、断裂带附近地表建筑物的灾害效应的数值模拟分析。通过上述模拟,得到了如下认识：(1)在全面收集已有区域资料和现场调查的基础上,通过对研究区内断裂附近在地震前、地震时和地震后的构造应力场的模拟分析,初步揭示了研究区在地震前→地震时→地震后的最大主应力和剪应力在量值和方向上的变化规律。(2)通过试验模拟,分别考虑三种可能的情况进行模拟,即小鱼洞破裂带的形成是受两侧断裂共同作用的结果、小鱼洞破裂形成区本身是一个软弱带和小鱼洞破裂形成区有先存的隐伏断裂,初步揭示了小鱼洞断裂形成的应力机制。小鱼洞地表破裂的产生的机理可概括为：在该区域有先存隐伏断裂的条件下,受区域构造应力场的作用,在地震时隐伏断裂发生活动,切穿浅层岩土体,形成地表破裂带。二维和三维数值模拟结果均表明,小鱼洞新生断裂的产生与龙门山中央断裂和前山断裂的应力分布规律有密切关系,而且龙门山中央断裂对小鱼洞断裂产生的影响大于龙门山前山断裂。(3)对位于断层上盘的水磨镇硅业公司主楼的地震动响应的数值模拟分析结果表明：①地震时厂房所受的轴向应力在底部最大,向上逐渐减小,与厂房底部柱体发生挤压破坏的特征相对应。厂房所受的剪应力值和剪切方向与柱体剪切破坏特征相对应。地震对楼体主梁的破坏是轴向应力和剪应力同时作用造成的。②靠近断层一侧应力、应变和位移值大于远离断层一侧,断层面刚度和断层距建筑物的距离对于建筑物所受到的最大主应力、剪应力、最大剪应变和加速度有明显的影响。③断层上盘建筑物的地震灾害效应比断层下盘表现更为明显,破坏程度也更大。同时,通过模拟,阐述了位于断层上盘的楼房发生差异性破坏的机理,并得到了地震作用时间、断层力学性质和断层位置对断层灾害效应的影响规律。(4)对小鱼洞镇主街道和虹口乡八角庙疗养院进行的数值模拟得到的地面综合位移方向和量值,与实地调查结果吻合,应力分布规律也能很好地解释地面破裂的形成机制和建筑物破坏的形式。根据对模拟结果的分析,得出了场地的位移和应力的分布规律。更多还原

【Abstract】 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.更多还原