基于Hoek-Brown准则的流-固-应力耦合作用下软煤钻孔失稳机理

It is well known that the deep hole drilling in high gas soft coal seam, hard and soft compound coal seam and outburst coal seam which has Ⅲ~Ⅴ structures is a worldwide problem, it has become the bottleneck restricts gas control effect of some high gas and outburst coal mines. Although numerous fruitful studies about drilling construction equipment and process have been carried out at home and abroad, there are hardly any reports about instability mechanism of borehole in soft coal seam under fluid-solid-stress coupling effect, the difficult problem of deep hole drilling has not been solved yet..This project will introduce mechanics theory of granular media, Hoek-Brown failure criterion and geological strength index into gas control field, mechanics property research methods of raw coal specimen containing fluid which has Ⅲ~Ⅴ structures and coal body containing fluid will be founded. Based on above research results, mechanical analysis of distribution law of stress field and displacement field around borehole in soft coal seam will be carried out, crushing zone radius and plastic zone radius of borehole will be acquired, instability & failure form of hole-bottom and borehole wall will be discussed, and mechanical criterion about instability of borehole in soft coal seam will be searched. Secondly, instability model of borehole in soft coal seam under fluid-solid-stress coupling effect will be built and solved, gradual change process of instability, instability & failure form and its controlling factors of borehole in coal seam which has Ⅲ~Ⅴ structures will be discussed in the condition of different stress & gas pressure & water saturation, instability mechanism and failure scope of borehole will be acquired. Finally, above research findings will be modified and perfected according to drill experiment in simulation coal seam.

高瓦斯松软煤层、软硬复合煤层和突出煤层深孔钻进是公认的世界性难题，已成为制约部分高瓦斯和突出矿井瓦斯治理效果的瓶颈。尽管众多研究者在钻孔施工装备及工艺的改进方面开展了大量工作，但因流-固-应力耦合作用下的软煤钻孔失稳机理至今少人问津，软煤深孔钻进难题仍未破解。.本项目旨在引入散体力学理论，建立Ⅲ~Ⅴ类含流体原煤试样力学特性研究方法；引入Hoek-Brown准则及GSI，建立含流体煤体力学特性研究方法。基于此，对软煤钻孔周围应力场、位移场分布进行力学分析，理论确定钻孔破碎区、塑性区半径，探讨孔底、孔壁的失稳破坏形式，探求软煤钻孔失稳的力学判据；其次，建立流-固-应力耦合作用下的钻孔失稳模型并解算，探讨Ⅲ~Ⅴ类煤层钻孔在不同应力、不同瓦斯压力、不同含水饱和度条件下的失稳渐变过程、失稳破坏形式及其控制因素，阐明其失稳机理，查明其失稳影响范围；最后，通过煤层模拟钻进试验，修正、完善理论研究成果。

高瓦斯松软煤层、软硬复合煤层和突出煤层深孔钻进是公认的世界性难题，已成为制约部分高瓦斯和突出矿井瓦斯治理效果的瓶颈。众多研究者在钻孔施工装备及工艺的改进方面开展了大量卓有成效的工作，少数研究者分析了软煤钻孔施工过程中发生的某些现象，但软煤深孔钻进难题并未得到根本解决。本项目以散体力学理论、H-B准则及GSI为基础，进行了流-固-应力耦合作用下的软煤钻孔失稳机理研究。. 基于散体煤样的直接剪切、三轴剪切实验，结合常规单、三轴实验，对比研究了原煤与型煤试样的变形及破坏特征，探讨了含水率、孔隙压力对型煤试样力学特征的影响机制；基于H-B准则及GSI，建立了煤体力学参数估算方法，对比研究了煤样与煤体的力学特性。探讨了煤层钻孔孔壁失稳的力学判据与条件，分析了钻孔周围“三带”内的孔壁稳定性。建立了含瓦斯煤流固耦合动态模型并解算，研究了钻孔周围应力、瓦斯压力及渗透率变化规律，探讨了不同侧压系数条件下煤层钻孔周围塑性区分布特征、钻孔失稳破坏过程中的成拱特性，厘清了钻孔失稳破坏类型及其控制因素。最后，构建了钻孔动态失稳监测系统及方法，试验探讨了模拟煤层钻进过程中钻孔动态失稳特征。. 研究表明：对于III~V类煤，可利用型煤来代替原煤估算煤体的粘聚力与内摩擦角。H-B准则可作为判定Ⅰ类煤层钻孔孔壁是否发生失稳破坏的准则；Ⅱ~Ⅳ类煤层钻孔孔壁需同时满足3个条件，即煤体发生强度破坏、裂纹在应力作用下逐步扩展和裂纹在瓦斯压力作用下继续扩展直至相互贯通，才会发生失稳破坏。孔周塑性区分布范围随GSI值的增大而减小，两者遵循幂函数关系；塑性区分布形状因侧压系数、GSI值不同而差别较大；钻孔失稳破坏类型分为应力控制型破坏、结构面控制型破坏、软煤中的喷孔破坏。煤体所受应力及吸附气体压力越大，钻孔破坏程度、卸压范围及峰值应力越大，两者为钻孔失稳的主要控制因素。. 通过本项目研究，初步揭示了流-固-应力耦合作用下软煤钻孔失稳机理，为钻孔成孔工艺提供了理论支撑。