含X型节理岩体裂隙扩展及水压致裂机理研究

X-type joint is one of the main joint types encountered in rock mechanics and rock engineering applications such as energy exploitation, civil, mining, and tunnel excavation. To date research effort on crack propagation or hydraulic fracturing has been mainly focused on rock with single joint or parallel joints. There exists little literature on how crack propagates in rock with pre-existing X-type joints. In this proposal, firstly, crack propagation and rock bridge failure under uniaxial, biaxial and triaxial tension/compression loading configurations will be experimentally studied in the laboratory. Based on the experimental results, the cracking initiation and crack propagation mechanisms of jointed rock masses with X-type joints under tension/compression loading will be proposed. Secondly, hydraulic fracturing experiments under triaxial loading condition will be performed and the corresponding cracking initiation and crack propagation mechanisms for rocks with X-type joints will be established. Thirdly, for these hydraulic fracturing experiments, the conditions under which the pre-existing X-type joint can be penetrated by hydraulic fracture will be studied, and the initial conditions as well as the methods that favor the hydraulic fracture to propagate deeply in the vicinity of the pre-existing X-type joints will be investigated. The crack propagation computing module for jointed rock masses with X-type joints will be established combining the mechanistic model derived from the experimental results with existing numerical simulation software. The results of this project can provide support for both theoretical and numerical improvements for hydraulic fracturing study in oil and shale gas exploitation.

在能源开发、矿山开采和隧道建设等岩体工程中，X型节理是节理存在的主要形式之一，但目前对岩体裂隙扩展及水压致裂的研究主要以含单一节理或雁形节理岩体为研究对象，对含X型节理岩体的研究尚不多。本项目拟首先研究含X型节理岩体试件在单轴、双轴及三轴拉/压加载下的裂隙扩展及岩桥贯通模式，确立含X型节理岩体在拉/压加载下的裂隙起裂准则及扩展规律；继而通过含X型节理岩体水压致裂三轴实验，研究岩体在水压致裂下的裂隙扩展行为，得到岩体在水压致裂作用下X型节理及水力裂缝的起裂及扩展规律；进而继续通过含X型节理岩体水压致裂实验，研究典型地应力场条件下X型节理被水力裂缝穿透的条件，确立水力裂缝在X型节理存在处深入延伸的实现条件及方法。将实验得到的含X型节理岩体裂隙扩展力学模型与现有计算软件结合，建立含X型节理岩体裂隙扩展专用计算模块。上述成果可以为石油增产、页岩气开采所需的水压致裂提供理论支持与数值模拟手段。

本项目针对岩体工程中大量存在的X型节理，以类岩石材料模拟岩体，研究了含X型节理岩体的拉/压力学性能及在水压致裂下的裂隙扩展规律与机理。本项目首先通过含单组X型节理岩体试件的拉/压加载实验，得到了含X型节理岩体在拉/压加载下的裂隙起裂模式及扩展规律；继而通过含两组X型节理岩体试件的拉/压加载实验，确立了X型节理岩桥贯通准则；进而通过含交叉多裂隙岩体的拉/压加载实验，明确了裂隙数量及位置等对岩体破坏模式的影响规律。在掌握含X型节理岩体拉/压力学性能的基础上，通过含X型节理岩体三轴水压致裂实验，研究了岩体在水压致裂下的裂隙扩展行为，得到了X型节理位置及主次裂隙角度对水力裂缝的起裂及扩展影响规律；进而继续通过含X型节理岩体水压致裂实验，确定了X型节理被水力裂缝穿透的条件，为水力裂缝在X型节理存在处深入延伸找到了实现方法。结合实验得到的含X型节理岩体裂隙扩展结果，用计算软件Abaqus的扩展有限元模块，定量分析了含X型节理岩体在拉/压荷载及水压载荷下的裂隙扩展机理。本项目所得成果可以为岩体加固及页岩气开采所需的水压致裂等工程提供理论支持与数值模拟手段。