坚硬顶板水压致裂控制理论与成套技术

Theory and technology of controlling hard roof with hydraulic fracturing in underground mining

煤矿坚硬顶板具有硬度大、整体性好、分层厚度大等特点,导致诸多围岩控制与安全难题。水压致裂可改造顶板岩体结构,控制工作面顶板的冒落;提出坚硬顶板水压致裂控制的理论与成套技术框架。采用真三轴实验系统等研究揭示水压裂缝的扁椭球体典型形态和空间转向扩展形态,给出围压主应力差、排量、层面与原生裂隙等对水压裂缝扩展的影响规律,考虑围岩的应力应变状态与控顶效果,阐明定向压裂临空坚硬悬顶的断顶线位置适当内错煤柱的原理。给出采动岩体水压致裂的时空关系及确定方法。针对裂缝形态的控制要求,提出定向水力割缝致裂等系统的控制致裂方法,在此基础上研制煤矿井下高压(60 MPa)水压致裂的成套装备。针对不同类型工程特点,控制水压主裂缝扩展、翼型裂纹扩展和吸水湿润作用,使顶板及时充分冒落,实现围岩弱化、应力转移、诱导矿压破煤等功能。研发了工作面端头悬顶、切眼及中部坚硬顶板、坚硬顶煤弱化、综放面初采瓦斯、临空巷道冲击地压和大变形等控制成套工艺技术。成套技术与装备已在大同矿区、神东矿区等推广应用。与传统爆破弱化顶板相比,水压致裂弱化顶板管理简单、扰动小、安全性高、工程量少、作用范围大、控制距离远,且经济成本不到其1/10,在深部开采中更具有优势。

The presence of hard roof in underground coal mine is usually accompanied by the characteristics of high hardness,good integrity and huge thickness,which results in numerous problems in ground control and safety. Hydraulic fracturing transforms the roof structure and controls the roof caving above the working face. A framework of theory and technology for controlling hard roof by hydraulic fracturing were put forward. The typical oblate spheroidal morphology and spatial reorientation propagation morphology of hydraulic fractures were revealed. Additionally,the influence of the differences of principal stresses,water injection rates,bedding plane and pre-existing fissures on the propagation of hydraulic fractures were presented by using the experimental system of true triaxial hydraulic fracturing. The principle of the breaking location of overhanging hard roof for directional hydraulic fracturing was identified according to the stress and strain conditions of the surrounding rock and the effect of roof control. The time-space relationship and the determination method of directional hydraulic fracturing for rock mass affected by the mining were presented. The systematic methods of controlled fracturing such as the directional water jet slotting fracturing was suggested to control the crack morphology. On this basis,a complete set of equipment for high pressure（60 MPa） hydraulic fracturing have been developed to implement in underground coal mine. The hard roof caved timely and fully by controlling the extension of the main hydraulic fractures and wing cracks and the wetting effect due to water absorption. It also achieves the weakening of surrounding rock,the stress transformation,and the coal crushing by inducing ground pressure. A complete set of techniques was developed to solve the problems caused by hard roof,including the control of hanging roof in the face end,hanging roof in the opening cut,hanging roof in the central section of working face,hard top coal weakening,gas ultralimit in the initial mining stage of longwall mining with top coal caving,rock burst and large deformation in gob-side entry. The complete set of technology and equipment has been adopted in Datong coal mining area and Shendong coal mining area. Compared to the traditional methods of weakening the hard roof by blasting,the hydraulic fracturing is more advantageous. It is easy to manage,has less disturbance to the surrounding rock,requires less engineering work. It also works at large scale,long-distance control,and costs 10% less than the cost of explosive blasting.