高压气体致裂煤岩孔壁应变响应特征研究

Study on the strain response characteristics of coal and rock borehole walls under high-pressure gas fracturing

目前缺乏对空气致裂全过程进行精准监测和评价的手段,而应变监测能够实时记录裂纹萌生和扩展的过程。通过研究高压气体冲击全过程中孔壁的应变响应,可明确致裂过程裂纹与应变响应之间的关系,获得最优致裂角度。为了探寻高压气体致裂煤岩体过程中裂纹和与应变之间的关系,利用高压气体冲击致裂煤岩体真三轴实验系统,开展了5种冲击角度(0,30,45,60,90°)下的高压气体致裂实验,研究了气体致裂过程中煤岩体裂缝形态、气压曲线与孔壁应变响应特征。实验结果表明:(1)随着冲击角度增加,煤岩体裂缝形态呈现先复杂后单一的分布特征。(2)致裂过程中气压呈现上升、陡降、聚集、稳定释放4个阶段。(3)孔壁应变数据主要由拉应变组成,应变曲线出现2个明显峰值,第1个峰值在气压曲线达到峰值0.1 s后出现并伴随主裂纹产生,第2个峰值常伴随着主裂纹的衍生与扩展。(4)当冲击角度为45°时,试件内部容易萌生复杂裂纹网络,致裂效果最佳。

There has been a lack of precise methods for monitoring and evaluating the entire process of gas fracturing.However,strain monitoring can effectively record the real-time initiation and propagation of cracks.By studying the strain response of borehole walls during high-pressure gas impact,the relationship between crack formation and strain response during the fracturing process can be clarified,enabling the identification of the optimal fracturing angle.A true triaxial experimental system for high-pressure gas fracturing of coal and rock was used,and experiments were conducted at five different impact angles(0,30,45,60,90°) to investigate crack morphology,pressure curves,and strain response characteristics of the borehole walls.The experimental results revealed that:(1) As the impact angle increased,the crack morphology of coal and rock exhibited a pattern that was initially complex but later became simpler.(2) The gas pressure during the fracturing process passed through four stages:an increase,a sharp drop,accumulation,and steady release.(3) The strain data for the borehole walls were predominantly tensile,and the strain curve displayed two distinct peaks:the first peak occurred 0.1 seconds after the pressure curve reached its peak,coinciding with the formation of the main crack;the second peak was generally associated with the propagation and expansion of the main crack.(4) When the impact angle was 45°,a more complex crack network tended to form within the specimen,resulting in the most effective fracturing.