With respect to the swelling of anhydrite rock surrounding the tunnel under the effect of pressured water

a multifunctional swelling test apparatus was designed and manufactured. Axial swelling strains and the lateral swelling stresses of anhydrite samples under different hydraulic pressures were tested by this test apparatus and the MTS815 rock mechanics testing system. Then the water-bearing state and mechanical performance of these samples were tested. The test results showed that when the hydraulic pressure became higher

the maximal axial swelling strain and lateral swelling stress became higher

meanwhile the activation time of swelling became shorter. With the increase of hydraulic pressure

water absorption by anhydrite increased

and the water in crystalline anhydrite phase gradually increased to maximum water absorption

while the free water gradually decreased and finally dropped to near zero. The elasticity modulus and peak strength increased with the increase of water hydraulic pressure. These indicated that the hydraulic pressure was able to increase the swelling behavior

promote the activation of swelling

influence the water conditions

and strengthen the mechanical performance. Based on the test results

the water absorption function with consideration of pressured water was established

and the swelling constitutive model in humidity stress field theory was improved.