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%.