Dynamically loaded young shotcrete linings

摘要

A criteria for how close, in time and distance, to young shotcrete blasting can take place would be an important tool in planning for safe and economical tunnelling projects. As a first step, field tests with shotcrete at ages of 1 to 25 hours, sprayed on tunnel walls, have been conducted in a Swedish mine. The shot-creted areas were subjected to vibrations from explosive charges detonated inside the rock. The acceleration measurements showed that the shotcrete had withstood high particle velocity vibrations without being seriously damaged. Drumminess of shotcrete appeared, indicating that the major failure mechanism was sudden loss of adhesion to the rock. Elastic wave propagation theory has been implemented numerically to further study the failure mechanism. Due to the changes in shotcrete-rock impedance ratio as the shotcrete cures, the stresses at the interface between shotcrete and rock experience a maximum during a short period within the first 24 hours of shotcrete age.