Based on existing test information in engineering

statistic mechanical model for deep overlying strata reinforced by rotary-type jet grouting is put forward. In this model

the reinforced deep overlying strata is divided into core-shaped and core-unshaped concretion in order to consider the effects of core recovery rate in drill test on the prediction of the macromechanical properties for the reinforced deep overlying strata . By use of stochastic simulation theory

sampling methods of the spatial location and micromechanical parameters of core-shaped and core-unshaped concretion in the mass covering strata are deduced. And then a computer simulation method of determining the macromechanical properties of jet grouting concretion is developed by combining the elastoplastic FEM with stochastic simulation techniques. Finally the macromechanical parameters of the deep overlying strata reinforced by jet grouting at Xiangjiaba hydropower station are investigated by the method proposed above.