深埋软弱岩层钻孔围岩应变软化弹塑性分析

Elastoplastic analysis of surrounding rock of drilling with strain softening model in deep soft rock

为解决在软弱岩层中钻孔易塌孔、成孔难的工程问题,认为岩体黏聚力沿塑性区呈线性弱化,得出应变软化条件下钻孔围岩二次应力、位移和塑性区分布表达式。利用FLAC3D内嵌FISH语言,自定义岩体黏聚力,对钻孔围岩弹塑性分布进行数值模拟分析。研究表明,理想弹塑性模型下的塑性区半径公式为文中解黏聚力co=cs时的特解;考虑黏聚力弱化特性后,相同地应力条件下塑性区半径显著扩大,为修正Fenner解的1.4倍,钻孔围岩最大切向应力位于距钻孔中心约2.9倍钻孔半径处,应力集中系数小于2。成果应用于四川某矿井钻孔工程,表明当加固半径约为3倍钻孔半径时,成孔率在90%以上,取得较好技术经济效果。

When drilling in soft and weak rock,the drilling is difficult to form and collapses frequently.To solve this engineering problem,based on the assumption that the rock cohesion weakens linearly along the plastic zone,the elastoplastic analysis of surrounding rock of drilling was completed and the secondary stress,displacement and plastic zone expressions of distribution are obtained.Gained self-defined rock mass cohesion by using FISH language that embedded in FLAC3Dsoftware.The numerical simulation analysis of elastoplastic distribution of rock around drilling was done.Compared to the original ideal M-C standards,the contrast results indicate that the theoretical calculation is correct.Theory and numerical simulation results show that: The plastic zone radius formula(e.g.fixed Fenner solution) that based on ideal elasticplastic model is a special solution when cohesion co equal to cs.After considering the cohesion weakening and residual cohesion,the plastic zone radius is 1.4 times as big as fixed Fenner solution.The numerical simulation shows that the maximum tangential stress in surrounding rock of drilling present to approximately 2.9 times drilling radius from drilling center;the stress concentration factor is less than 2.When under the same in-situ stress conditions,the plastic zone radius expand obviously after considering the cohesion weakening.Through analysis it is gained that the best drilling reinforcement radius is 3 times of the drilling radius;these achievements were applied to a drilling engineering of a certain coal mine in China.