Two Possible New Techniques for Determining the Early-Age Shear Strength of Shotcrete: Auger Penetrometer and Vane Shear Tester

Abstract

Shotcrete or sprayed concrete is widely used as ground support in the construction of tunnels. The early-age strength development of shotcrete is very important because it influences the determination of safe re-entry times beneath the tunnel heading. This study has examined the possible application of a handheld soil vane shear tester and a handheld auger penetrometer for testing the early-age strength of shotcrete. This is achieved by measuring the shear strength because previous research in this area indicates that the shear failure dominates the early-age resistance of shotcrete. The investigation involved testing of three techniques, which resulted in readings of both compressive and shear strengths. Shear testing involved a combination of the vane shear tester and the auger penetrometer, which obtains its readings through auger penetration and rotation. The compression testing involved the use of the Meyco needle penetrometer, which was tested on the same cast specimens as the shear tests and at the same time intervals. In this paper, the term shotcrete has been used for the special normal concrete, with a simple shotcrete mix design, used in this investigation. Strong correlations were found among the vane shear strength, auger penetrometer shear strength, Meyco penetrometer compressive strength, and time after pouring, for up to 4 h of testing. The shear strength results from the auger penetrometer and the vane shear tester are very similar, and there is almost a perfect linear correlation between the results from these two methods.