Abstract:To discuss the difference of mechanical behavior of marble buried deeply in high stress caused by different stress paths and reveal the influence of unloading on rocks’mechanical properties,a series of triaxial tests under loading and unloading conditions were carried out on the marble samples from the tunnel of Jinping Secondary Hydropower Project.The results showed that when marble is broken,the vertical and horizontal strain under unloading condition are smaller than that under triaxial compression tests,and the brittle features of rocks are more conspicuous under unloading condition.The secant modulus and Poisson ratio have good linear relationship with confining pressure in different stress paths.The secant modulus under unloading condition is smaller than that under triaxial compression test,but Poisson ratio is on the contrary.The failure face of marble is more rough under unloading condition,and the cohesion cdecreases 36.4% while the internal friction angle φincreases 35.4% relatively with the loading tests.The shear strength in unloading condition is lower than that in loading condition when normal stress is below 45 MPa,and damage occurs more.These results showed that the influence of unloading should be considered fully during the excavation of deep underground engineering.