Laboratory test on foamed concrete-rock joints in direct shear

Foamed concrete has been widely used in tunnels where foamed concrete-rock joints are usually encountered. However, few studies have been conducted on the mechanical properties of the joint. To investigate the shear behaviors of the joint, compressive properties of foamed concrete were first studied by compression tests, and a series of direct shear tests under constant normal load condition were then conducted. Three failure types were identified during the tests: interface failure, foamed concrete failure and the mixed type. Both the normal stress and dry density of the foamed concrete can significantly influence the shear behaviors of the joint, but have little effect on the friction coefficient of the joint. Based on the results, a model was proposed for the joint, which can successfully describe the shear behaviors of the joint. The model can easily be implemented in numerical codes, and then be used to investigate the mechanical behaviors of tunnels in practical cases.