地面井层面拉剪破坏模型及极限分析判识方法

A surface borehole interface model and the limit analysis estimation method

为了有效解决地面瓦斯抽采钻井破坏机理不清、工程防护措施难以有效发挥作用的工程难题,本文基于采场上覆岩层组合划分规律建立了地面钻井变形破坏的层面拉剪变形破坏模型.结果表明:地面钻井的变形破坏可以分为剪切、挤压、拉剪综合等形式,在采场不同的岩层层位,钻井套管的变形形式不同,对钻井工程防护措施也因此具有不同要求;同时,引入极限分析的思想建立了钻井套管变形破坏的判识准则:钻井套管拉伸或剪切安全系数小于阈值、套管壁监测点位移出现突变且塑性破坏区贯通时,可以判定钻井套管破坏.最后,将建立的方法应用到了晋城矿区地面钻井试验中,通过与钻井试验结果的对比分析证明了理论方法的正确性.

Borehole fracture mechanisms and ways to effect engineering controls of them are serious problems in surface borehole engineering. A tension-shear deformation model was used to predict surface borehole fracture modes. The model was based on division of the rock strata into different classes. Shear, squeezing, and tension-shear fracture appear as the surface bore- hole fracture modes. The nature of the strata favor one or the other of these modes and the engineering controls used should be different in the different cases. A limit analysis approach was used to establish criteria to distinguish case fracture. This Suggested that a surface borehole shear or tension safety factor less than some threshold value risks case displacement. If the plastic region penetrates the case the surface borehole will be destroyed. This technique was used on a surface borehole in the Jincheng coal mine with good results.