The exploitation of hydrothermal geothermal resources (HGR) in fault zone is one of the most promising technical schemes for geothermal energy development. To understand the hydraulic and mechanical behaviors of rock mass in fault zone, a series of thermal-hydraulic-mechanical (THM) coupling tests of fault rocks were conducted, and the influence of the fault gouge content, water temperature, seepage pressure and stress on the permeability, porosity, secant Young's modulus, cohesion and internal friction angle of fault rocks was investigated. The results show the permeability evolution can be divided into four stages: slight decline stage, slight rise stage, steady increase stage and rapid increase stage. The porosity evolution can be classified into two stages: seepage dominant stage and axial compression dominant stage, and the time-varying law of porosity of cemented rock mass are significantly different. With the increase of content of fault gouge, the secant Young's modulus, cohesion and internal friction angle of fault rocks gradually increase; while the temperature has little significance on the three parameters. With the increase of seepage pressure, the secant Young's modulus, cohesion and internal friction angle decrease; while the three parameters increase accordingly with the increase of the axial and confining pressure. The research results enrich the study of THM coupling properties of fault rocks, and provide a theoretical basis for exploiting HGR by fault.
For a better understanding of the mechanism of the roof cavity in the face-to-tip area and the shield-strata interaction, a roof stability mechanical model was developed based on the Timoshenko beam theory. A new type of canopy load measuring system for a physical shield and the digital image system for measuring strata displacement were also developed and used in the large-scale physical modeling study to reproduce the roof cavity and the massive roof fall in the face area. The deformation of the immediate roof was obtained under different influencing factors including the shield stiffness, the immediate roof elastic modulus, the buried depth of the coal and Poisson’s ratio of the roof strata, as well as the processive development of the roof fall, the strata displacement field and the variation of the shield load. The results show that: the deflection and rotation angle of the immediate roof were significantly improved when the shield stiffness was increased or at a high strata modulus. The deformation, i.e., the deflection and rotation angle of the immediate roof, increased with an increase of the buried depth, though the Poisson’s ratio increases the deformation of the immediate roof in a rather insignificant manner. The development of the physical longwall face was classified into three stages, i.e., the stable stage, the cavity stage and the major fall stage, based on the stability of the roof in the face-to-tip area. In the stable stage, the immediate roof became broken and the roof fall cutting line moved forward to the position above the shield canopy, leading to the head drop of the canopy and incomplete contact between the canopy and the roof. The maximum shield load, therefore, decreased from 2.5 kN to 1.7 kN. During the roof cavity stage, however, the roof cavity occurred 3 times and developed upward. The caved shape evolved from a trapezoid to a triangle, and the shield load saw a further decline to 1.3 kN. During the massive roof fall stage, the entire fall of the roof along the coal wall occurred and the rotation of the massive thick roof to the gob area was also seen. The longwall shield simulated a complete load-increasing stage typically observed in the field, and the shield resistance recovered to 1.7 kN.
为探究不规则煤柱变形破坏机理,为采场煤柱失稳型动力灾害防治提供理论参考,基于不规则煤柱区微震监测数据,利用矩张量反演、应力场反演及波速层析等方法,研究不规则煤柱破裂类型、震源机制、主控因素、应力分布及变形破坏特征,并由此提出不规则煤柱变形破坏机理.结果表明:不规则停采煤柱胶带巷侧发生压缩破坏,辅运巷侧主要表现为拉伸破坏;区域震源机制为左旋斜滑正断层,推断真实断层面为走向214°、倾角55°、滑动角-145°;煤柱变形破坏主要受最大主应力σ1控制,相邻矿井采空区侧向压力是煤柱破坏的主导因素;在最大主应力σ1主控作用下,煤柱发生压缩破坏,并造成应力集中及煤岩体变形破坏向煤柱内部转移.
沿空留巷作为无煤柱开采技术的一种,在提高煤炭回收率、降低开拓掘进量的同时,也给后续留巷巷道的维护带来诸多挑战.以沿空留巷技术的应用为主线,选取Y型通风的后退式留巷工艺(常规留巷工艺)和超前预掘运输巷的前进式留巷工艺(超前预掘留巷工艺)为研究对象,研究2种不同留巷工艺下回采巷道的破坏特征,通过分析回采巷道三维应力场的演化规律,揭示不同留巷工艺下回采巷道差异破坏的力学机理.结果显示,围岩主应力方向的分布与开挖空间的形成密切相关,在开挖空间附近的"应力扰动区"内,岩体的最小主应力总是近似指向开挖空间的几何中心,最大主应力呈椭球形将开挖空间环向包裹;不同留巷工艺下回采巷道围岩应力场的分布规律也不尽相同,巷道主应力的大小和侧压系数的高低在一定程度上共同决定了巷道的破坏形态;采动应力对回采巷道的影响并不总是不利的.应力场是矢量场,具有大小和方向,回采巷道的破坏特征取决于采动应力和原岩应力矢量相加所形成的"复合应力场",而不是两场的代数和.因此,开拓方式的选取和支护参数的确定不仅要考虑原岩应力场的分布规律,还需要考虑采动应力场的影响.在一定条件下,合理利用采动应力可以改善围岩的应力环境,降低回采巷道维护难度.
针对传统采用倾角传感器与测高传感器对液压支架支护姿态、支护高度进行解算存在的诸多问题,提出了基于立柱千斤顶行程、平衡千斤顶行程驱动的液压支架支护姿态与高度解析方法.基于液压支架的骨架结构参数模型,构建了液压支架主体结构件各铰接点的位置关系方程,通过分析液压支架各部件的运动参数关联关系,得出了液压支架支护姿态与支护高度的数学表达.分别采用牛顿-拉夫逊方法、弦割法、布罗伊登法对液压支架支护姿态与高度进行数值求解,开发了基于3种方法的液压支架支护姿态与高度解析算法.通过对比分析发现,牛顿-拉夫逊方法、弦割法的求解精度不受迭代初始参数影响,而布罗伊登法的求解精度则受初始参数影响较大,且牛顿-拉夫逊方法、弦割法的解算精度、解算效率、稳定性均明显高于布罗伊登法.牛顿-拉夫逊方法、弦割法的求解精度基本相同,均能达到角度误差小于1°、高度误差小于0.1m,但牛顿-拉夫逊方法的求解效率显著高于弦割法.通过对40组骨架模型进行求解对比分析,以及多组液压支架现场实测求解对比分析,验证了基于立柱千斤顶行程、平衡千斤顶行程驱动的液压支架支护姿态与高度解析方法的可行性、稳定性与实用性,确定牛顿-拉夫逊方法作为液压支架支护姿态与高度的解析方法.
