同沉积作用下地裂缝破裂扩展机理及效应研究

The syndepositional ground fissure belongs to tectonic fissure with "growth" characteristics. The Xi'an ground fissure is a syndepositional fissure and a well-known urban geological disaster, which significantly limits the development and utilization of the deep underground space in this city. This project takes Xi'an fissure as an example. The study is oriented from the development process of geological history and the dynamic characteristics of the basin, based on the structure-sequence-sediment analysis method, through similar physical model tests. A series of synthetic studies will be carried out to investigate the sedimentary phase transition effect of the rupture propagation, the effect of compaction and consolidation of soil layers, the effect of ground fissure activity rate, the dip effect of ground fissures, the sedimentary environment effect and its comprehensive effect under the same deposition effect. Its controlling manner and sensitivity factors will be analyzed. The project will summarize the process and mode of crack propagation syndepositional ground fissures through the observation of stress, deformation monitoring and rupture phenomena, as well the field investigation, exploration and numerical simulations. Based on the theory of nonlinear fracture mechanics, soil mechanics and dislocation, the project will analyze the mechanism of the expansion, closure and penetration of the fractures in different depositional stages. The fracture width and the influence zone of the hanging wall and footwall at different depths of ground fissure will be studied to determine their maximum ranges. Based on that, a three-dimensional fracture-expansion model will be established. This research provides geological parameters and theoretical basis for the development and utilization of deep urban underground space in the ground fissure section as well as for disaster prevention and control. Therefore, it has significant theoretical and practical engineering meanings.

同沉积地裂缝属于构造地裂缝，具有“生长”特点。西安地裂缝是典型的同沉积地裂缝和著名城市地质灾害，并严重制约西安城市深层地下空间的开发利用。本项目以西安地裂缝为例，从地质历史发展过程和盆地动力特点出发，基于构造-层序-沉积分析方法，通过物理模型试验，开展同沉积作用下地裂缝破裂扩展的沉积相变效应、土层压密固结效应、地裂缝活动速率效应、地裂缝倾角效应、沉积环境效应及其综合效应研究，分析其控制性和敏感性因素；通过应力、变形监测和破裂现象观察，结合地裂缝的野外调查、勘探和数值模拟结果，总结同沉积地裂缝的破裂扩展过程和模式；基于非线性断裂力学、土力学和位错理论，分析不同沉积阶段破裂的扩展、闭合和贯通机制，解析地裂缝不同深度上、下盘的破裂宽度和影响带范围，确定其最大范围值，建立三维破裂扩展结构模型，为地裂缝地段城市深层地下空间开发利用和灾害防治提供地质参数和理论依据，从而具有重要的理论和实际工程意义。

同沉积地裂缝属于构造地裂缝，具有“生长”特点。项目以同沉积地裂缝为对象，通过野外调查、综合勘探和理论分析，开展了汾渭盆地典型同沉积地裂缝的发育特征和成因机理研究，总结了中国地裂缝的空间分布规律和成因机制；进行了黄土地区地裂缝带大型试坑浸水试验和地裂缝带表水入渗及沉降变形过程阶段的划分；开展了6组同沉积地裂缝破裂扩展物理模拟试验和11组数值模拟分析，确定了考虑沉积相、土层压密固结、活动速率、倾角、沉积环境及其综合效应和破裂不同力学行为，总结了同沉积地裂缝破裂扩展演化过程和破坏模式；分析了同沉积地裂缝破裂扩展力学机制和湿陷地裂缝的开裂和形成机制；提出了通水调压控裂法（CABHP）。研究结果显示：汾渭盆地同沉积地裂缝较发育，特征典型；同沉积地裂缝的破裂过程分为9个阶段：开始活动，端部拉裂，端部反倾和地表竖向裂缝产生，竖向裂缝向下发展和反倾裂缝变宽，新地层沉积下竖向裂缝填充和反倾裂缝趋于闭合，老地层形成的竖向裂缝端部拉裂，竖向裂缝端部形成反倾裂缝和地表竖向裂缝产生，新地层竖向裂缝向下发展和反倾裂缝延伸变宽，以及竖直裂缝相互贯通阶段；同沉积过程对土体地裂缝破裂扩展范围有一定削弱作用，但总体地表破裂规模变大；地裂缝区风积同沉积有利于黄土梁洼形成；快速同沉积活动以主裂缝破裂扩展为主，裂缝位置更集中；预设裂缝倾角越小，影响带宽度越大；水下同沉积裂缝破裂扩展响应受阻、发育能力减弱，影响带范围减小；随着变角度预设裂缝角度的变缓，影响带范围增大；压密同沉积下裂缝影响带范围减小，但裂缝在后续同沉积过程中不易闭合。表水入渗是地裂缝活动的重要诱因，黄土湿陷地裂缝的形成机制、分布位置、开裂深度及最大影响范围可以用悬臂梁理论解析；采用定向钻井打通被错断含水层可以避免或减缓地裂缝活动。研究结果对同沉积地裂缝致灾机理认识，地裂缝地段城市深层地下空间开发利用及地裂缝灾害综合防治具有重要的理论和现实意义。