ROOF-RIPPING CONSTRUCTION TECHNOLOGY FOR LARGE CROSS-SECTIONAL TUNNEL IN SOFT AND WATER-RICH STRATUM

Roof-ripping construction for a large cross-sectional tunnel is a dangerous procedure under complex geological conditions. The spatial structure of the intersection is complex, the stress transformation is frequent, and the support strength is difficult to effectively restrain the surrounding rock deformation, which results in collapse accidents and threatens the construction safety. This paper aims to improve the safety of roof-lifting construction of large cross-sectional tunnel in soft and water-rich stratum. It is based on the construction of the inclined shaft into the main tunnel in Xi Shanying tunnel of Sanqing expressway. It develops a new structure of the combined support of the upper arch of portal frame and the strengthened portal frame at the intersection. It optimizes the supporting structure strength of the strengthened portal frame and roof-ripping construction technology. It studies the construction scheme, construction process and key points of vertical roof-lifting. The results show that the combined supporting structure reduces the over-excavation area and deformation of the surrounding rock, and strengthens the support strength and stability of the stress concentration area. The construction schedule of the proposed method takes only 20 days, which saves nearly one time compared with the traditional construction method, and the construction progress of the intersection from the inclined shaft into the main tunnel is accelerated by the rational organization of the process. The results of tunnel field monitoring show that the convergence deformation and stability control of the surrounding rock at the intersection of the tunnel during the roof-ripping construction meet the construction requirements. In summary, the technical principle of this method is simple and practical. The method can provide experience reference and technical guidance for the construction of large cross-sectional tunnels under similar engineering geological conditions.