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Developments in excavation bracing systems
1. Introduction
Nearly all civil engineering construction projects (e.g. buildings,roads, tunnels, bridges, water treatment plants, pipelines, sewers)involve some amount of soil excavation. Often due to space limita-tions caused by adjacent structures, property lines, or easements,an earth retention system is needed to allow soil to be excavated to the required depth. Historically, many excavation bracing sys-tems have been developed. Of them, several methods are now more common; these include soldier beams and lagging, sheet pil-ing, bored pile walls, and slurry walls.
The choice of earth retention system for use in any particular context is limited by technical performance requirements and con-struction feasibility (e.g. means, methods) including reliability of execution, with cost considered only after these other issues have been addressed. Environmental consequences (e.g. regulatory requirements for handling of waste slurries and drilling fluids) are also typically of great concern (Yau and Yang, 1998).
The earth retention system is usually just one component of a larger construction project. Since timely completion of the project,greatly affecting the total cost, is ultimately a critical project goal,bracing systems that can be completed quickly or that can be constructed in parallel with other site operations are referred.In many cases, a temporary bracing system is used to support the excavation in order to allow continuous progress to be made,until a permanent system is constructed. The temporary system may be removed or left in place.
开挖工程支撑体系的发展
1.引言
几乎所有土木工程建设项目（如建筑物，道路，隧道，桥梁，污水处理厂，管道，下水道）都涉及泥土挖掘的一些工程量。往往由于由相邻的结构，特性线，或使用权空间的限制，必须要一个土地固定系统，以允许土壤被挖掘到所需的深度。历史上，许多挖掘支撑系统已经开发出来。其中，现在比较常见的几种方法是：板桩，钻孔桩墙，泥浆墙。
土地固定系统的选择是由技术性能要求和施工可行性（例如手段，方法）决定的，包括执行的可靠性，而成本考虑了这些之后，其他问题也得到解决。通常环境后果（用于处理废泥浆和钻井液如监管要求）也非常被关注（邱阳、1998）。
土地固定系统通常是建设项目的较大的一个组成部分。如果不能按时完成项目，将极大地影响总成本。通常首先建造支撑，在许多情况下，临时支撑系统是用于支持在挖掘以允许进行不断施工，直到永久系统被构造。临时系统可以被去除或留在原处。
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