Initial geostress field is a basic index for underground engineering design. According to geological data of Jiangbian hydropower station diversion tunnel area

a numerical model of this area is established by fast Lagrangian analysis of continua in three dimensions (FLAC3D). The mixed boundary conditions and lateral pressure coefficients which change with depth are applied to simulate different kinds of rocks

fault fracture zone and alteration zone along the diversion tunnel

so as to conduct positive analysis. According to the measured principal stress data of the engineering site

based on the principle of radial basis function (RBF) neural network

back analyses of rock mechanical parameters and initial stress field are made. The calculated results are consistent well with the measured results and meet accuracy requirements. The results show that the back analysis results are in line with the actual project; and back analysis method is reasonable.