Experimental and numerical study of shear behavior of concrete–soft rock interface: with approach of concrete penetration in rock cavities

Abstract

In this study, the shear behavior of the concrete-soft rock interface was simulated using PFC3D software and the results were compared with physical tests. While the interface between concrete and rocks has different geometries, concrete also penetrates the voids of the rock. The concrete and gypsum had tensile strengths of 1.2 MPa and 0.51 MPa, respectively. Samples with dimensions of 15 cm × 15 cm × 5 cm containing plaster and concrete layers were made. Concrete is located in the middle part of the sample, and its two sides are surrounded by plaster so that the concrete can penetrate the plaster. Nine different geometries for the concrete–rock interface were chosen i.e., the asymmetric zigzag interface, non-asymmetric zigzag interface, and planar interface. Nine different geometries for the concrete–rock interface were obtained by changing the concrete teeth height, concrete teeth base, and teeth angles. At the fixed interface, concrete penetrated into plaster in one, two, and three channels from each side. Twenty-seven different models are prepared. Samples using special templates, have been replaced in the UCS device and were tested under punch shear loading. Simultaneously by conducting experiments, numerical simulation was done. In such a way that the model and PFC software are calibrated and then numerical modeling of common shear behavior of concrete and rock takes place. The results showed that the fracture pattern of the rock-concrete interface was affected by concrete teeth geometry. In the samples without concrete teeth, a tensile fracture occurs at the interface; but with increasing roughness angle, in addition to tensile fracture, tensile cracks are formed at the tip of the roughness in the sample. By increasing the angle from 0 to 30, the number of tensile cracks in the sample increases. By increasing the concrete injection channels in the rock, the final fracture pattern does not change but crack initiation stress, shear stiffness, and final stress were increased. There is a good match between the experimental and numerical results.