【作者】 王哲成；

【导师】 张云；

【作者基本信息】 南京大学 ， 地质工程， 2012， 硕士

【摘要】 虽然地裂缝已经成为一种重要的城市地质灾害,但由于地裂缝难以直接观察的特点以及土体变形的复杂性,使得人们对地裂缝的研究大多还停留在对已知地裂缝进行定性的现场勘察和灾害评估。破坏力学的发展使人们很自然的想到利用已有的破坏力学对地裂缝进行模拟和预测,并已取得一定的成果。本文遵循这一思路,引入了破坏力学数值模拟的理论和方法,摈弃了传统的连续体力学分析方法、材料强度理论以及土体脆性破坏的假设,在常规有限单元法的基础上加入基于弥散裂缝模型的钝化断裂带模型,结合裂缝开展的张开度COD和能量释放率作为单元的断裂判据,对土体中拉张型裂缝的动态发展进行模拟,所建立的模型通过已有实验研究成果进行了验证,并对三种常见地质条件下拉张型地裂缝的形成和发展进行了模拟和分析,讨论了不同条件下拉张型地裂缝的形成机制、分布特点及其对土体变形的进一一步影响。本文的研究表明,利用钝化断裂带模型的方法对土体Ⅰ型开裂过程进行数值模拟是可行的,对实验尺度土样的模拟结果以及对拉张型地裂缝的模拟结果都与实际观测基本相符：模拟过程中,拉张型地裂缝大多形成于浅部土体并竖直向下发展,大多数情况下地裂缝处通常形成明显的水平位移差和相对较小的竖直位移差,说明地裂缝两侧产生了较大的水平张开度和较小的垂向错动,然而在有先期断层存在的情况下,断裂面的重新开裂会产生较为显著的垂向错动,虽然由此带来的剪应力影响有待进一步研究,但也由此可推测随着裂缝开展深度的增加,拉张型地裂缝也有可能产生与先期断层相似的作用,使得其破坏模式从早期的拉张型逐渐向拉张-剪切型转变。更多还原

【Abstract】 Earth fissures have already become a kind of significant urban geo-hazards. Due to the difficulties in observing soil fissuring and the complexity of soil deformation, current researches on earth fissures are still largely limited to qualitative field surveys and hazard evaluation to some existing fissures. With the development of failure mechanics, it naturally occurs for people to use failure mechanics to simulate earth fissures, and some achievements have been reached. Based on the previous studies, this paper did not use the method and strength theory of traditional continuum mechanics and the assumption of brittle failure of soil, but applied theories and methods of failure mechanics to the simulation of soil cracking, Based on a conventional finite element method program, Crack Band Model, which is developed from Smeared Crack Model, is built to simulate the whole process of soil cracking, with the Crack Opening Displacement (COD) and energy release rate used as the fracture criterion to describe the dynamic propagation of fissures. Then the model has been preliminarily validated by comparing the simulation results to the data acquired from an existing experiment. Finally, tensile-induced earth fissures triggered by groundwater extraction under three kinds of geological conditions have been simulated and analyzed. For each geological condition, the mechanism and the distribution of tensile earth fissuring and the influence of the occurred fissures on further soil deformation are explained.It is shown that the CBM is a feasible approach for simulating model I crack initiation and propagation in soil, which has been examined by the data from laboratory tests and the field observations of initiation and propagation of tensile-induced earth fissures. Most simulated fissures are initiated at the ground surface and propagate downwards, with significant horizontal and relatively small vertical displacement gradient, which means a great fissure aperture and a rather small vertical offset. However, a greater vertical offset is observed on a fissure formed at a pre-fault. Although the influence of shear strain on earth fissures is currently ignored, it can also be inferred that with the depth of fissure growing greater, the tensile-induce fissure may play a similar role as a pre-fault in the soil layer, which may lead to a change of failure model from pure tension to tension-shear.更多还原