正断型隐伏地裂缝破裂扩展的土性效应研究

发布时间：2018-11-15 19:56

【摘要】：地裂缝是长久以来伴随人类社会发展的一种重要的自然灾害,也是一个亟待认识、解决的科学问题。近几个世纪人类文明急速发展,人口快速增长,科技、经济飞速发展及对自然资源大量开采,人类活动对地球环境的影响越来越深远,大规模的资源开采和地质体改造使生态环境恶化,自然灾害频发。地裂缝在许多国家普遍存在,其发育强度和规模有逐年加剧的态势,造成愈来愈大的经济损失,现已成为一种主要的区域性地质灾害。本文主要内容如下:1.通过野外调查及搜集典型地裂缝钻探、槽探资料,总结了地裂缝的部分特征如下:主裂缝的形态在地表下浅层往往是垂直的,主要由张拉应力控制,深部裂缝受剪应力控制;地裂缝断面近地表处近直立,裂缝随深度增加有变缓的趋势,呈现为一条弯向上盘的曲线;岩土层对地裂缝位移有着吸收作用,这一现象使不同深度处土体的位移有差异。2.使用PFC2D离散元软件建立正断型隐伏地裂缝数值模型,通过数值反演法标定颗粒的细观参数。设置颗粒细观参数、模型边界条件,模拟不同工况条件下地裂缝的破裂扩展过程。观察隐伏地裂缝破裂扩展过程,裂缝开启与破裂轨迹,裂缝的破裂特征,并与现场勘察资料进行对比。通过设置不同的土层性质,观察地裂缝破裂扩展过程随土体性质改变而发生的变化。得出以下结论:①土体抗剪强度并非完全等于摩擦力与粘聚力的叠加,在大围压、高应变条件下粘聚力的作用会减弱甚至消失。②土体内摩擦角增大会导致裂缝倾角的增大,粘聚力的增大会使地表产生张拉裂缝,两者作为上盘下降过程中阻力的组成部分,而阻力的增大会使上盘中反倾次级裂缝更易于发生。③土体内摩擦角控制地裂缝的整体倾角,粘聚力会导致主裂缝在上部土体中发展时倾角逐渐增大甚至出现反倾。3.根据现场观测和离散元模拟,基于材料力学理论、摩尔库伦破坏准则,对隐伏地裂缝破裂扩展过程进行了力学分析。研究结果表明,地裂缝的破裂扩展与裂缝尖端上部土体应力变化关系密切,应力状态的变化直接导致裂缝的发生。同时,对破裂角与应力之间的关系进行研究,与数值模拟结果进行对比,结果较为理想。
[Abstract]:Ground fissure is an important natural disaster which has been accompanied by the development of human society for a long time, and it is also a scientific problem that needs to be recognized and solved urgently. In recent centuries, with the rapid development of human civilization, the rapid growth of population, the rapid development of science and technology, the rapid economic development and the massive exploitation of natural resources, the impact of human activities on the earth's environment has become more and more far-reaching. Large-scale exploitation of resources and transformation of geological bodies cause deterioration of ecological environment and frequent natural disasters. Ground fissures are common in many countries, and their development intensity and scale are increasing year by year, resulting in more and more economic losses, which has become a major regional geological disaster. The main contents of this paper are as follows: 1. Through field investigation and collecting data of typical ground fracture drilling and trough exploration, some characteristics of ground fracture are summarized as follows: the shape of main fracture is often vertical in the shallow layer below the surface, mainly controlled by tensile stress, and the deep fracture is controlled by shear stress; The ground fissure section is nearly upright near the ground surface, and the fracture tends to slow down with the increase of depth, which shows a curve of curved upward face, and the earth layer absorbs the displacement of the ground fracture, which makes the displacement of soil in different depth different. 2. PFC2D discrete element software is used to establish the numerical model of the positive fault type concealed ground fissure, and the mesoscopic parameters of the particles are calibrated by numerical inversion method. The fracture propagation process of the ground crack under different working conditions is simulated by setting the particle meso parameters and the boundary condition of the model. The fracture propagation process, crack opening and fracture track and fracture characteristics of the hidden ground fracture are observed and compared with the field investigation data. By setting different soil properties, the fracture propagation process of ground cracks is observed with the change of soil properties. The following conclusions can be drawn: (1) the shear strength of soil is not equal to the superposition of friction and cohesion. Under the condition of large confining pressure and high strain, the effect of cohesive force will weaken or even disappear. 2 the increase of internal friction angle of soil will lead to the increase of crack inclination. The increase of cohesive force will lead to tensile cracks on the surface, both of which are part of the resistance in the process of upper plate descent, and the increase of resistance will make the secondary cracks in the upper plate more prone to occur. 3 the internal friction angle of soil controls the overall dip angle of the earth cracks. The cohesive force will cause the inclination of the main crack in the upper soil to gradually increase or even reverse tilt. Based on the field observation and discrete element simulation, based on the material mechanics theory and the Moore Coulomb failure criterion, the fracture propagation process of the concealed ground fracture is analyzed. The results show that the fracture propagation of the ground fissure is closely related to the stress change of the upper part of the crack tip, and the change of the stress state directly leads to the occurrence of the fracture. At the same time, the relationship between fracture angle and stress is studied, and the results are compared with the results of numerical simulation.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P642.2

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