Laboratory Assessment Of Mechanical Interface Properties, Interaction And Behaviour Between Rock And Shotcrete

The shear resistance of a joint can be determined by using the concept of mobilised roughness under the applied normal forces. The effect of concrete curing age and roughness of rock surfaces are currently being estimated for the most of design procedures in the ground support system, which results of this study can provide comprehensive information for numerical analysis.

A series of laboratory direct shear tests were performed on cemented shotcrete-rock with different roughness scales (JRC 0-2 and 6-10) over a range of concrete curing ageing. Three concrete age ranges were selected for testing, these included 3-6, 7-11 and +26 days cured. Rock samples were collected from various finalised and ongoing projects in Brisbane City. Brisbane tuff; a volcanic igneous rock, was selected and tested in this study for the sake of the consistency in laboratory results. Samples were prepared from the core specimens and cast within a mortar mixture based on the standard dimensions of the shear testing apparatus; being 150 x 150 mm. All samples were tested under the dry conditions according to the suggested method by the International Society of Rock Mechanics (ISRM).

In addition to the frictional angle and cohesion strength of tested samples, shear and normal stiffnesses of the interface were also determined, which play critical roles in the reliable numerical modelling. An interesting observation was the complex interaction at the interface and the mechanisms that controlled the peak shear strength which depended on the surface roughness, the existence of natural flaws and applied loads. The shear failure mechanism was investigated under a various range of normal forces and shear displacement rates, aiming to provide the required information for Discrete Element Models (DEM) and elastic closed formed solutions in rock mechanics engineering applicable for underground support design.