Conventional constitutive model is not good at simulating the failure range and depth for hard rock under high geostress. The complicated evolvement of stress load

which produced by excavating underground engineering under high geostress in Laxiwa

is simulated through true triaxial experiment.Based on analysis of Mohr-Coulomb strength criterion

Griffith strength criterion

Drucker-Prager strength criterion

twin shear theory and Hoek-Brown strength criterion

a new three shear strength criterion is proposed for hard rock. The effect of three principal shear stress and three normal stress acting on the dodecahedral element and average principal stress are taken into account in the establishment of strength criterion. Based on the experimental result about Laxiwa new granite

the parameters of three shear strength criterion are searched using the global optimum features of genetic algorithm. The results of predicting samples and comparing with Mohr-Coulomb strength criterion

Drucker-Prager strength criterion

twin shear theory show that three shear strength criterion agrees with the experiment and is the same with hard rock. Based on the stress-strain relation curve obtained by experiment

three shear strength criterion and strain softening law

the elastic-brittle-plastic constitutive model is established

which is implanted in FLAC3D through UDM. The parameters of elastic-brittle-plastic constitutive model are searched using genetic algorithm- FLAC method. Calculating results agree with the fact and show that the elastic-brittle- plastic constitutive model can be used in the safety and stability analysis of hard rock underground engineering under high geostresses.