软弱地层中深开挖产生隆起的迷思

The puzzle of heave due to deep excavation in soft soil layer

一个位於台湾台北市软弱地层之深开挖基地，依据防止隆起规范及公式分析均合乎安全要求，仍然产生全面性破坏的实例检讨中，发现目前部分土壤力学理论与软弱地层的实际应力应变行为不一致的迷思。并确定软弱地层於国际间尚是一种地层的模糊名词，至今未有明确“定性”的定义与适当“定量”的方法确认，亦缺少完整理论基础。软弱地层基本上是沿用由过压密粘土发展之“弹塑性理论”，於实际开挖的原型量测中发现甚多不能合理解释的矛盾点，必须另建立较合乎软弱地层实际力学特性、具有三线性之“弹变塑性理论”。

A deep excavation projects is located on the Taipei soft deposit. The penetration depth of the retaining system that was evaluated by the building codes showed that the safety factors against heaving are satisfied with the requirement of the codes. But a serious damage still occurred. In the re evaluating works of the project, the authors find that the traditional soil mechanics is inconsistent with the real stressstrain behavior of the soft deposit. Soft ground is always a fuzzy term in geotechnical engineering field. There is no clear qualitative definition on it till now and is short of complete theoretical basis. The traditional concept on the soft ground is based on the elasto plastic model of the overconsolidated clay. From the monitored results in practical deep excavation cases, it is found that there exists many unreasonable contradictions. A tri linear stress-strain model is necessary to simulate the real behavior of the soft deposit.