空心包体式钻孔应力解除法数值模拟研究

Numerical Simulation of Borehole Stress Relief Method with Hollow Inclusion for In⁃Situ Stress Measurement

以岩石力学与工程中普遍使用的空心包体式钻孔应变计为例,采用有限元法对套芯应力解除法地应力测量过程进行了数值模拟研究。采用实体单元对围岩体、应变计胶筒、胶水层进行了模拟,获得了应力解除全过程曲线。详细分析了实测孔壁变形经过不同介质的传递过程,讨论了修正系数K_(n)及其对地应力计算结果的影响,在此基础上分析了胶水材料与应变计胶筒材料的力学性质差异对地应力测量结果造成的影响。结果表明:采用空心包体式钻孔应变计测量地应力存在轴向应力偏大的问题,在计算中考虑修正系数K_(n)可以得到接近真实值的最大以及中间主应力值;而忽略修正系数K_(n)会使计算出的主应力值大于真实值,且当应变计胶筒和岩体弹性模量接近时误差较小。胶水层的力学性能变化也会对地应力测量结果造成一定的影响。

Taking the example of hollow inclusion strain gauge commonly used in rock mechanics and engineering,this article numerically studied the in⁃situ stress measurement process in over coring method with finite element method.The solid element was used to simulate the surrounding rock mass,rubber tube and glue layer,and the stress relief curve was obtained.The transfer process of measured drilling wall deformation through different media was analyzed in detail,and correction coefficients K_(n) and its effects on the insitu stress calculation were discussed.On this basis,the error of insitu stress measurement caused by the differences in mechanical properties between glue material and rubber tube was analyzed.The results show that the calculated axial stress is larger than the actual value by using hollow inclusion strain gauge.The correction factors K_(n) should be taken into calculation model to achieve accurate maximum and intermediate principal stresses.Otherwise,principal stresses are larger than true values and the error is comparatively small when the elastic modulus of strain gauge cylinder and rock are close.Besides,the change of mechanical properties of the glue layer also has effects on measurement results.