【作者】 黄炳香；

【导师】 刘长友；

【作者基本信息】 中国矿业大学 ， 采矿工程， 2009， 博士

【摘要】 煤岩体水力致裂弱化技术是改善坚硬厚（高瓦斯）顶煤冒放性、处理坚硬顶板、防治冲击矿压、改善煤层透气性和防治煤与瓦斯突出等的有效技术途径,是一项煤矿安全高效开采的保障技术。本文以煤岩体强度弱化（结构改造）为工程背景,采用实验研究、理论分析、数值模拟和现场试验等研究方法对煤岩体水力致裂弱化的理论和技术进行了较为系统的研究,具有重要理论意义和广泛工程应用前景。研制了4000kN真三轴岩体水力致裂模拟实验系统。能实现试块尺寸最大为500×500×500mm的真三轴地应力场模拟。设计了具有增压功能的油水加载转换器。实验分析了煤岩力学性质及含水量的影响。基于与煤岩体的全应力应变曲线形态等相似,确定了型煤（煤∶水泥∶石膏）和水泥砂浆的材料配比。应用大尺寸真三轴水力致裂模拟实验系统开展了煤岩体水力致裂裂缝扩展规律研究。实验结果表明,水力致裂裂缝的前沿为椭圆形态,且以钻孔致裂段为中心;水压裂缝前沿椭圆曲线方程（x²）/（a²）+ （y²）/（b²） = 1的长短轴之比a/b保持不变。水力致裂裂缝垂直于最小主应力方向扩展。当中间主应力越接近最小主应力,则钻孔孔底水压裂缝越易向垂直于中间主应力的方向偏转;且其扩展方向平行于σ₂和σ₃确定的矢量面。发现了孔底水压裂缝存在分叉现象,分叉后水压裂缝破裂面的走向与σ₃、σ₂均垂直。煤岩体水力致裂除了水压主裂缝形成主破裂面外,渗透水压力对主裂缝两侧煤体形成渗透水楔作用,裂隙和层理面等发生了张开和扩展。同时,由于节理裂隙等缺陷的存在,煤体水力致裂破裂面的粗糙度明显比一般岩石材料要大。考虑水力致裂过程水向岩石内的渗透滤失引起的孔隙水压力（水力梯度）作用,使水压裂缝尖端扩张的净水压力等于缝尖水压力减去滤失水压力和原岩孔隙流体压力。采用流体力学分析得出了钻孔和水压裂缝内的水力衰减规律。当原生裂隙与最小主应力夹角大于一定值,且水压翼型裂纹与水压主裂缝间的岩桥较短时,水压裂缝沿原生裂隙及其翼型分支裂纹继续向前扩展。固液耦合作用下裂隙煤岩体细观结构破坏研究。在调查煤层裂隙分布规律的基础上,基于断裂力学得出了煤岩体内水压裂隙起裂的最小裂隙水压力与水压翼型分支裂纹的扩展长度。采用RFPA软件模拟了成组原生裂隙条件下,水力致裂弱化的结构改造形态。在岩块为各向同性的前提下,基于能量耗散损伤得出了裂隙煤岩体细观结构破坏与宏观力学性能弱化的关系。煤岩体水力致裂弱化的控制技术研究。结合水力割缝和水力致裂的优势,提出预先水力割缝定向致裂技术。基于钻孔及钻孔水压力的叠加影响,通过多钻孔及其注液方式的组合来控制水压裂缝的扩展方向。结合水压爆破和水力致裂的优点,采用水压爆破致裂对煤岩体的结构进行改造,使裂隙煤岩体形成多个水压主裂缝和沿水压主破裂面的致裂裂缝带。在爆生压力作用下,煤岩体节理裂隙张开扩展,导致结构面的粘结力降低,煤岩体切割加剧,弱化了煤岩体的整体力学性能。实验证明是一种增加水压裂缝数目和改善煤层透气性的有效方法。采动煤岩体水力致裂弱化的时空关系研究。实验研究了煤体自然吸水湿润与时间的关系,分析了干燥煤样和自然煤样的吸水湿润差异。依据渗流的起始水力坡度和水力致裂径向水力坡度衰减规律,得出了水力致裂弱化注水的渗透半径。水力致裂弱化水压主裂缝扩展阶段必须超前支承压力峰值区完成。高瓦斯坚硬厚顶煤弱化的现场试验表明,水力致裂弱化了煤体的整体力学性能,顶煤破碎块度明显降低,工作面回收率提高了23%;预先释放瓦斯,降低了工作面瓦斯浓度,粉尘浓度降低21%,抑制了煤自然发火。更多还原

【Abstract】 Hydraulic fracture weakening technology for coal-rock mass is an efficient means to improve hard thickness top coal（high gas） caving property,deal with hard roof,prevent rook burst,increase coal seam permeability and avoid coal-gas outburst,which is safeguard technology for safety and high efficiency mining of coal mine. Based on the engineering background of coal-rock mass strength weakening （stucture reform） , research methods including experiment research,theory analysis,numerical simulation and test on site have been used to study hydraulic fracture weakening theory and technology of coal-rock mass systematically,which has important theoretic meaning and widespread engineering application prospect.True triaxial hydraulic fracture experiment system with 4000kN anchorage force was developed,which can perform the stress field simulation in-situ with the greatest size 500×500×500mm in true triaxial test. Designed boil-water loading converter has increasing pressure function. Coal mechanical property and influence of water content have been analyzed. For similar form with complete stress-strain curve of （coal） rock mass,material mixture ratio of analogue coal（coal: cement: plaster） and sanded cement grout has been obtained.Crack propagation law of hydraulic fracture in coal-rock mass has been studied. Hydraulic fracture simulation experiment with greatest size in true triaxial test indicates that front hydraulic fracture shape is elliptic and its center is the part of drillhole fracture. Ratio a/b of major axis to minor axis in hydraulic fracture front elliptic curve equation （x²）/（a²）+ （y²）/（b²） = 1 keeps unchanged. Hydraulic fracture crack is expands vertically to the direction of minimum principal stress. The closer medium principal stress is to minimum principal stress,the more prone drill hole bottom hydraulic fracture is to deflect vertically to the direction of medium principal stress;its propagating direction is parallel to vector surface ofσ₂ andσ₃. Bifurcation phenomenon has been found in the hydraulic fracture of drillhole bottom. Strike of hydraulic fracture failure surface is vertical of bothσ₂ andσ₃ after bifurcation.Besides hydraulic fracture technology for coal-rock mass leads to main hydraulic crack to produce main failure surface, the seepage water pressure forms seepage water wedge in coal both sides of main hydraulic crack. Then, fissure and bedding plane will open and propagate. Meanwhile, because of shortcoming of fissure in coal mass, hydraulic fracture failure surface roughness of coal mass is larger than common rock material obviously. Consideration of pore water pressure （hydraulic gradient）caused by seepage filtration from water to rock in the process of hydraulic fracture, expansion net water pressure in crack-tip is equal to crack-tip water pressure subtract filtration water pressure and original rock pore water pressure. Hydraulic decay laws between drillhole and hydraulic crack have been analyzed by fluid mechanics.When the angle between initial fissure and minimum principal stress is more than some value and rock bridge between hydraulic wing crack and hydraulic main crack is shorter,hydraulic crack along the direction of initial fissure and wing crack will keep on propagating constantly.Research on microscopic structure destroy of fissured rock mass has been made under solid and liquid coupling condition. According to coal seam crack distribution laws, minimum fissure water pressure and hydraulic wing crack propagation length of initial fissure in the rock mass have been gained by fracture mechanics. Structure reformation form of hydraulic fracture weakening has been simulated by RFPA software under the condition of a group of initial fissure. According to energy dissipation damage theory,relation between microscopic structure failure of fissured rock mass and macroscopic mechanical property weaken has been obtained under the precondition of rock block isotropy.Control technology of rock mass hydraulic fracture weakening has been made in this paper. With the advantages both hydraulic slotting and hydraulic fracture, guide orientation technology of beforehand hydraulic slotting has been put forward. Because of superposed influence of drillhole and its water pressure, propagating direction of hydraulic fracture is controlled by combination multi drillholes with its liquid injection mode. Combining the advantage of hydraulic blasting and hydraulic fracture,structure reforming technology of hydraulic blasting fracture for coal-rock mass has been presented. The experiment result shows that crack coal-rock mass will generate multiple water pressure main fracture and fracture zone along the water pressure failure surface. Under pressure of explosion,coal joint fissure will open and propagate so that structure plane cohesion stress decreases. As a result, coal cutting becomes serious and whole mechanical property of rock mass has been weakened. It has been proved to be a useful method to increase water pressure crack numbers and coal seam permeability.Research has been made on temporal spatial relation of hydraulic fracture weakening for mining coal-rock mass. Tests have been carried out to study the relation between coal natural water absorption and time,and to analyze the water absorption difference between dry coal sample and natural one. By seepage initial hydraulic slope degree and radial hydraulic fracture slope degree decay laws, seepage radius of injecting water has been acquired by hydraulic fracture weakening. Base on moving abutment pressure distribution and failure character of surrounding rock, rational distance advancing wall of hydraulic fracture weakening has been obtained.Weakening tests of hard thickness top coal with high gas in situ have shown that,hydraulic fracture weakens the whole mechanical property of coal mass and reduces the size of top coal broken and increases recovery ratio of top coal by 23%. It can release gas in advance , reduce gas concentration, reduce 21 % of dust concentration,and suppress coal spontaneous combustion.更多还原