Abstract:Baozhen tunnel is the only soft rock tunnel and the key project in the Yichang—Wanzhou Railway. The very complex geological environments,such as high earth stress,deep-buried rich groundwater,very weak and cracked rock masses and asymmetric pressure along the rock strata,make self-stability of the tunnel unfavorable. During tunnel construction,the high deformation rate,intense and long-time deformation are the basic characteristics. At the same time,the deformation shows asymmetrical features and uniformities. Through analyzing the causes of large deformation,it is deemed that groundwater and high earth stress are the critical factors causing large deformation. So using XTR01–01 microcomputer electro-hydraulic servo-controlled triaxial test instrument to study the change law of soft rock strength under different saturated time and confining pressure is significant to assure the design, construction and operation safety of tunnel. The mechanical behaviors of black macker that is widely distributed in Baozhen tunnel are discussed by designing a series of triaxial compressive tests under different saturated times;and research on variation laws of mechanical properties under different confining pressures and saturated times is carried out,describing complete stress-strain curve of macker(saturated time is 1 month) with different confining pressures. The variation laws along with confining pressure and saturated time are analyzed. In addition,the mechanism and relationship between confining pressure,saturated time and strength are researched. Finally,according to dynamic evolution law of adjacent rock,the supporting principles for large deformation in weak rock and high earth stress are put forward.