Technique research and parameter optimization of bolt-shotcrete support for semi-hard or soft rock tunnel

By the relation of Q value to tunnel support parameter, tunnel reinforcement type is initially designed as shotcrete-bolt support with the thickness of 20~30mm for good rock, 50~60mm for fair rock and 60~65mm for broken rock. Based on classification manner of broken zone and optimizing method of support parameter, applicable minimum bolt length for fair rock and broken rock are respectively determined-2.1 m and 2.6m.According to the analysis of punching failure and bond failure, thickness should be no less than 4.71 mm. Design parameter id proved to accord with project practice through stability analysis. After industrial experiment carried out, shotcrete mix proportion and bolt installing technice are finally brought forward aiming at soft broken rock tunnel.