ABSTRACT
When inserting detonators into boreholes and when mounting steel arch supports inside tunnels, workers approach a cutting face about 10 minutes after concrete is sprayed. It is still not clear whether such early-age shotcrete could support what size of rock and how shotcrete would deform just before rockfall. In this study, a new punching test equipment is developed which could apply a load of rock mass to the base concrete. Based on the test results, the base concrete with thickness of 40–50 mm and compressive strength of around 0.3 N/mm2 easily fails with a few hundred newtons of resistance and several micrometers of extrusion displacement. However, cracks on the surface of concrete could be captured during post-failure behaviour at around few millimeters of extrusion displacement; thus, if measurement instrument could detect the crack generation and growth, and then it would be possible to warn against rockfall.
