Abstract: 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.

Key words: anhydrite rock, pressured water, swelling test, water- bearing state, mechanical performance