MECHANICAL CHARACTERISTICS AND TREATMENT METHOD OF COLLAPSE OF TUNNEL WITH HALF-HARD AND HALF-SOFT ROCKS ALONG ITS TRANSVERSE SECTION

The Jiaoling tunnel in construction encountered two types of rocks along its transverse section. Half of the tunnel section is hard-rock while the other half is soft rock. The hard rock is intact and has a 40 MPa compressive strength. The soft rock is weathered and fractured and has a compressive strength 5MPa. Collapse at the side of soft rock took place during the construction. Mechanical characteristics for the hard and soft rocks and the collapse reasons were analyzed at the portal of the left tunnel line. . Then counterpart collapse treatments were employed. For example, surface with grouting reinforcement and tube-grouting frame were explained. Strength of the treated soft rock was almost equal to that of hard rock. Bearing loop was made up of treated soft rock and hard rock. At last the treated zone was monitored. It was judged from monitoring data that the zone was stable quickly. So, this treatment method is reasonable and effective. The bearing loop theory can be used to the half-hard and half-soft rock transverse-section tunnel. New idea in the paper is the suspension theory applicable to bolting and grouting-tube treatment of soft rock tunnel. This theory can improve the effectiveness of bolt reinforcing soft rock tunnel. This conclusion in the paper is useful for design and construction of tunnel in half-hard and half-soft rock. 