基于侧压力系数的岩爆区初始地应力场二次反演分析

Two-stage back analysis of initial geostress field in rockburst area based on lateral pressure coefficient

为准确获得桑珠岭隧址区初始地应力场分布规律,提出在岩爆区初始地应力场的二次反演方法。采用最小二乘法寻优准则对隧址区初始地应力场进行多元线性回归分析,利用叠加原理得到在一次反演下的初始地应力场;采用表面应力解除法测量隧道开挖后的洞壁二次应力,记录发生岩爆的部位并据此判断侧压力系数的大小,与在一次反演下相应位置的侧压力系数进行对比,如果两者都大于或者等于或者小于1,则以在一次反演下计算得到的侧压力系数为基准,以其大小不变作为约束条件对初始地应力进行修正,当采用修正后的初始地应力作为应力边界条件,计算得到隧道开挖后的洞壁二次应力与实测洞壁二次应力最接近时,以此时修正后的初始地应力和原位地应力进行回归得到在二次反演下的地应力场。结果表明:当测量原位地应力的钻孔较少且计算区域较大时,一次反演回归得到离钻孔较远位置的应力计算值与实测值存在一定的误差;二次反演在原位地应力的基础上增加实测洞壁二次应力进行修正,得到离钻孔较远位置的应力计算值与实测值吻合更好,所提出的二次反演方法可为类似工程的研究提供参考。

In order to accurately obtain the distribution rule of initial geostress field of Sangzhuling tunnel site, a two-stage back method to calculate initial geostress in rockburst area is presented. Based on the least square method, multiple linear regression is used to analyze the initial geostress field and with superposition principle, the initial geostress field is obtained. The wall stress after tunnel excavation is measured through stress relief method. According to the site of rockburst, the lateral pressure coefficient is acquired and then compared with its equivalent value from the primary inversion in the corresponding position. If both values are larger than or equal to or less than one, then the lateral pressure coefficient is assumed to be the calculated value of primary inversion and the value is taken as the constraint condition to modify the initial geostress. When the calculated secondary wall stress acquired from the modified initial geostress is close to the measured one, the secondary geostress is obtained through the regression analysis with the modified initial geostress and in-situ geostress. The conclusions show that when a small number of boreholes are used for in-situ geostress and with a large computational domain, there are some errors between the measured stress and the calculated stress from the primary inversion in positions far from the boreholes. Furthermore, based on in-situ geostress, the secondary inversion modifies results by using measured secondary wall stress as a complement, and then the calculated stress in positions far from the boreholes shows better agreement with the measured stress, which can be presented as an inversion method to provide reference for similar research projects.