高切坡半隧道超前支护结构研究

 在山区基础设施建设过程中，经常发生因开挖边坡造成坡体失稳并诱发地质灾害的情况发生，为此，提出高切坡超前支护的思想。以西藏S306线段为依托，提出一种新型的高切坡超前支护结构型式——半隧道超前支护结构：它由普通的半隧道结构与边坡超前支护结构有机组合，以达到稳定边坡、减少开挖量、环保经济的目的。采用数值方法对超前支护半隧道结构的作用机制进行研究，分别模拟无支护开挖和超前支护结构的4种不同组合加固后开挖时的情况，分析高切坡的稳定性、应力分布及塑性区开展的情况，通过比较得出高切坡半隧道超前支护结构的合理组合方式。

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.