STUDY ON PRE-REINFORCED HALF-TUNNEL STRUCTURE IN HIGH CUT SLOPE

The pre-reinforced half-tunnel has been proposed as a new construction method to protect the environments in highway 306 of Tibet. This method combines pre-reinforcement of the high slopes with prestressed cables and half tunnel excavation. With this method,it is possible to reduce much excavation earthwork,and at the same time,to keep the whole slope stable. The behaviors of the pre-reinforced cables, however,have not been investigated extensively. An assessment is therefore needed for the effectiveness of various reinforcement designs of the half-tunnel with pre-reinforced structure. In this paper,the background and objective of this study are first presented. Then,a numerical method and the analysis procedure are briefly described. The numerical simulation include:(1) an unreinforced case;(2) one role of pre-reinforced cables in the top rock mass; (3) two roles of cables in the side wall;(4) one role of cables in top rock mass and one role in side wall;and (5) one role in the top rock mass and two roles in side wall rock mass. The commercial code FLAC2D is adopted to execute the numerical analysis,in which the behavior of rock mass is described by Mohr-Coulomb constitutive model and the prestressed cables are simulated by an internal structural element of FLAC2D code. Finally,the effectiveness of the pre-reinforcement for the half-tunnel excavation and design of pre-reinforcement are discussed based on the numerical results and suitable retaining scheme is presented.