美兰机场明挖隧道基坑围护支撑体系优化及实施

针对海南东环铁路美兰机场明挖隧道基坑围护结构方案存在的问题，建立了优化设计思路，研究采用了拉力分散型预应力锚索与钢支撑联合运用的混合支撑体系，给出了锚索结构、布置型式及主要技术参数；针对锚索孔和旋喷桩桩间漏水、漏砂问题，采取了止水、堵漏技术，有效解决了锚索施工成孔和基坑漏水问题。采用该混合支撑体系，不但可以大量节省钢材，而且能改善施工条件，加快施工进度。

Optimization and Practice of Bracing System for Open Cut Tunnel Excavation near Meilan Airfield

Aiming at the existing problems of retaining and protecting scheme for cut and cover tunnel excavation near Meilan airfield in Hainan East-circling Railway, an idea for optimum design is developed. A combined bracing system consisted of pull decentralization pre-stressed anchors and steel tube braces is adopted. The structure, arrangement and main technique parameters of the anchors are presented. Aiming at the problem of surging water and sand between spinning piles or in boring holes, the technique of cutting and preventing water leakage are developed so that the problem of difficult to bore holes for anchors and to prevent water leakage are solved availably. Because of application of the combined bracing system, not only a great deal of steel will be saved, but also construction conditions will be improved greatly and construction schedule will quicken.