长壁工作面开采上行裂隙混合型裂纹扩展机理

Mechanism of upward mixed crack propagation in long wall working face

为揭示长壁工作面开采的上行裂隙发育机理,得到其发育高度的确定方法;基于断裂力学混合型裂纹扩展理论,运用断裂力学分析了上行裂隙发育顶端岩层受力状态,分析了上行裂隙发育的判据,提出了上行裂隙发育高度的确定方法;基于混合型裂纹σ(θ)_(max)理论,建立了上行裂隙岩层裂纹扩展理论模型,提出了裂纹扩展与上行裂隙发育的判据。研究表明:随长壁工作面推进,上行裂隙发育可以分为上行裂隙产生段、发育延伸段和稳定段3个阶段,裂纹的扩展表现为混合型裂纹;工作面充分采动后,岩层顶面产生的裂纹在拉应力的作用下沿裂隙带方向向下扩展,若与上行裂隙贯通,导致该岩层完全破断;若外力作用不足以使裂纹扩展贯通该岩层,则上行裂隙不再发育。

In order to reveal the development mechanism of upward fracture in longwall face mining,based on mixed mode fracture extension theory in fracture mechanics,fracture mechanics is applied to analyze the stress state of strata on the top of the upward fracture,the criterion of upward fracture extension is analyzed,and the development height of upward fracture is determined.Results show that with the working face advances,the development of upward fracture can divided into three stages:generation stage,development and extension stage,and stable stage,and the fracture extension is mixed mode fracture.Based onσ(θ)_(max) theory,the fracture extension theoretical model of upward fracture is established,and the criterion of upward fracture extension is proposed.After full mining,under the action of tensile stress,the crack generated on the top of the rock layer expands downward along the direction of the fracture zone.If it is connected with the upward fracture,the rock layer will be completely broken.Otherwise,if the fracture does not extend and cut-through the strata,the upward fracture does not develop,therefore,the development height of the upward fracture is the distance from top of the seam to the bottom of the strata.