Study on Shear Strength Characteristics of Basalt-Concrete Bonding Interface Based on in-situ Direct Shear Test

In rock engineering, the shear strength of the basalt-concrete bonding interface is a key factor affecting the shear performance of hydroelectric dam foundations, embedded rock piles and rock bolts. In this study, 30 sets of in-situ direct shear tests were conducted on the basalt-concrete bond interface in the Baihetan dam area to investigate the shear strength characteristics of the basalt-concrete bonding interface. The bonding interface contains two states, i.e., the bonding interface is not sheared, termed as s_e (symbolic meaning see Table 1); the bonding interface is sheared with rupture surface, termed as s_i. The effects of lithology, Joints structure, rock type grade and concrete compressive strength on the shear strength of the concrete-basalt contact surface were investigated. The test results show that the shear strength of the bonding interface (s_e & s_i) of columnar jointed basalt with concrete is greater than that of the bonding interface (s_e & s_i) of non-columnar jointed one with the same rock type grade. When the rock type grade is III₂, f_col is 1.22 times higher than f_ncol and c_col is 1.13 times greater than c_ncol. The shear strength parameters of the basalt-concrete bonding interface differ significantly for different lithologies. The cohesion of the bonding interface (s_i) of cryptocrystalline basalt with concrete is 2.05 times higher than that of the bonding interface (s_i) of breccia lava with concrete under the same rock type grade condition. Rock type grade has a large influence on the shear strength of the non-columnar jointed basalt-concrete bonding interface (s_e & s_i). c_nol increases by 33% when the grade of rock type rises from III₁ to II₁. the rock type grade has a greater effect on bonding interface (s_i) cohesion than the coefficient of friction. When the rock type grade is reduced from III₂ to III₁, f^′_ncol increases by 2% and c^′_ncol improves by 44%. The shear strength of the non-columnar jointed basalt-concrete bonding interface (s_e & s_i) increases with the increase of the compressive strength of concrete. When concrete compressive strength rises from 22.2 to 27.6 MPa, the cohesion increases by 94%.