Abstract: 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.

Key words: lateral pressure coefficient, rockburst, geostress field, back analysis, surface stress relief method