Abstract: The aim of this study is to investigate and evaluate the distribution of initial in-situ stress field of the deep buried diversion tunnel of a hydropower station in northeastern Nepal. By constructing a regression equation and fitting the initial in-situ stress data measured by hydraulic fracturing technique, we obtained the distribution law of initial in-situ stress field of the project area via 3D finite element regression analysis. The inversion results of stress field suggest that the regression calculation results highly fit the measured values, verifying the rationality of regression results. The area where the axis of the tunnel located is dominated by horizontal tectonic stress field, and the in-situ stress level is generally medium and low; but at the location where buried depth is large, the in-situ stress is high and extremely high, and rock burst is highly possible. The intersection angle between maximum horizontal principal stress and tunnel axis is large near the tunnel exit, which is unfavorable to the stability of surrounding rocks. The research findings offer effective data support for engineering construction.

Key words: diversion tunnel, initial in-situ stress field, finite element regression analysis, horizontal principal stress, Nepal