Instrumentation of large scale direct shear test to study the progressive failure of concrete/rock interface

Abstract

The shear strength of concrete/rock interface must be clearly assessed to design the rock foundations. However, the concrete/rock interface has different failure modes which depend on the mechanical characteristics of the materials and the morphology of the rock surface. Consequently, to study thoroughly the shear behavior of concrete/rock interface and to define the cracking mechanisms and debonding propagation along the interface, different instrumentation devices were applied during a large scale direct shear test. A large sample formed by pouring concrete over a large rock surface (shear surface of 1.5 m2), was instrumented using the following techniques: strain gauges, acoustic emission and distributed optical fiber sensor. The different observations made during the test were combined to determine the successive stages of interface failure. The strain gauges, which measure local strains within the materials, showed their ability to detect the crack propagation in the materials and the debonding at the interface. The acoustic emission technique was able to detect the damages in the materials and at their interface. The optical fiber sensor measured strains evolution of the concrete near the interface showing the crack propagation during the test and the progressive debonding at the interface.