Back analysis and prediction for displacement of surrounding rock around model tunnel of a powerstation

Zhanghewan Pumped Storage Station was provided with four sets of pump-turbine units with a total capacity of 1000 MW,and its underground powerhouse was 151.1 m,23.4 m and 48.3 m in length,width and height,respectively.In order to further study the stability of the surrounding rock around powerhouse cavern and to optimize the design parameters,observation and experimental study were carried out for the surrounding rock around a model tunnel near the underground powerhouse.And,back analysis was done on the basis of the observed results of convergence,multi-point displacement and anchorage bar stress,and the calculated results were as follows: horizontal stress 2.52～2.88 MPa,stress ratio 0.7～0.8 and elastic modulus 26.0 GPa.According to the initial geostatic stress and deformation parameters obtained by the back analysis,a prediction for displacement and stress distribution of the surrounding rock around the machine hall and the main transformer chamber was conducted,and it was indicated that the deformations of the surrounding rock were smaller and coincident with the measured values of displacement.