基于不同岩石抗拉强度值确定最大水平主应力的对比分析

Comparative Analysis of Determinating the Maximum Horizontal Principal Stress Based on Different Tensile Strength of Rocks

水压致裂原地应力测量系统的柔性对最大水平主应力的结果会产生很大的影响,提高最大水平主应力的测量精度对各种地下等工程设计都具有重要意义。通过进行直接拉伸试验、"垫条加载"和"角锥荷载"形式的圆盘劈裂实验、弯曲拉伸实验获得岩石抗拉强度,结合实测破坏压力、孔隙压力数据及相关理论计算出最大水平主应力,并与利用经典水压致裂公式计算得到的最大水平主应力进行数据对比分析。结果表明:通过"角锥荷载"圆盘劈裂实验、直接拉伸试验、"垫条加载"圆盘劈裂实验、三点弯曲实验所获得的最大水平主应力均大于经典水压致裂公式计算得到的最大水平主应力,且偏差依次增大,由此也说明测试系统的柔性会导致利用经典公式计算的最大水平主应力偏小。4种实验中,通过"角锥荷载"圆盘劈裂实验所获得的数据较其他3种方法更接近经典公式计算得到的最大水平主应力,且偏差较小,可以作为估算最大水平主应力的一种替代方法。在未来的工作研究中,可以为避开系统柔性对实测最大水平主应力的影响、提高测量精度提供方法参考。

The compliance of the hydraulic fracturing in-situ stress measuring system produces a great influence on the results of the maximum horizontal principal stress,and improving the measurement accuracy of the maximum horizontal principal stress has important significances on various underground engineering design. The tensile strength of rock was obtained from direct tensile tests,disk split tests with strip loading and pyramid loading and bending tensile tests. Combined with the actual measured data of failure pressure and pore pressure,based on related theories,the horizontal principal stress were calculated,and they were compared with those of classical hydrofracturing formula.The results show that the maximum horizontal principal stress obtained from disk split tests with pyramid loading,the direct tensile tests,disk split tests with strip loading,three point bending tests is larger than that calculated by using the classical hydrofracturing formula and the deviation increases respectively. It also shows that the compliance of the testing system can lead to the results of classical formula relatively smaller. In the four kinds of tests,the data obtained from disk split test with pyramid loading is closer to that of the classical formula than the other three tests and the deviation is smaller,thus it can be an alternative method to estimate the maximum horizontal principal stress. In the future studies,the paper can provide a method reference for avoiding the influence of the system compliance on the actual measured maximum horizontal principal stress to improve the measurement accuracy.