Characteristis Values of Tip Resistance on the Rock for the Weak Underlying Stratum

From the point of punching damage mode of rock tensile strength, a mathematic model of punching safety indices and punching tip resistance value coefficient was established based on the analysis of rock characteristics and rock mechanical strength. Stretch and compression strength, punching safety indices and tip resistance coefficient of sedimentary rock were calculated by use of the empirical data of mechanical property of rock, and their characteristics were analyzed respectively.It is concluded that it tends to be unsafe that the relative standard provides 3d thickness of hard rock which has high compression strength and low stretch strength overlying weak subsoil bearing strata based on the use of uniaxial saturated compress strength as tip resistance value. The punching tip resistance coefficient of rock with different lithology, integrity and safety classes was calculated by tip resistance mathematic model and rock mechanical empirical data.The proposed value of tip resistance coefficient of the rock overlying weak bearing strata is given after comparing the calculation outcomes with resisting compression tip resistance values from references.