The water softening of argillaceous sandstone in complex stress state will seriously reduce the bearing capacity of surrounding rock

resulting in the increase of failure range and deformation pressure of surrounding rock

and finally seriously threaten the safety of water tunnel during operation. To solve this problem

triaxial tests under different immersion time are carried out to investigate by using argillaceous sandstone from water delivery tunnel of Lanzhou water source project. The results are as follows. As the immersion time prolongs

the sensitivity of peak strength and residual strength to confining pressure decreases gradually. This may be attributed to the fact that the water reduces the sensitivity of peak strength and residual strength to confining pressure to a certain extent. In the early stage of immersion

the decreasing rate of residual strength with immersion time is significantly less than that of peak strength with immersion time

and the softening effect of water on the peak strength of argillaceous sandstone is more remarkable. The peak strength

residual strength and elastic modulus of argillaceous sandstone samples decrease with the increase of immersion time in a negative exponential relationship. With the increase of confining pressure

the influence of immersion time on elastic modulus gradually weakens

and the increase of confining pressure reduces the softening effect of water on the elastic modulus of argillaceous sandstone to a certain extent.