黏土层基坑工程隆起分析之可靠度评估

Reliability assessment of basal-heave for excavations in clay

评估黏土层基坑底面的隆起稳定性,是基坑工程设计十分重要的工作。截至目前为止,基坑工程设计本质上仍是采用定值性的分析方法,并未考虑材料及计算方法的变异性,亦即分析时土壤等材料参数,均给予一个定值而得到一个单一的安全系数,以评估其安全性。采用Terzaghi、台湾建筑技术规则及上海市基坑设计规程所建议的抗隆起稳定分析方法,进行假设案例的隆起破坏机率分析,结果显示,破坏风险和设计参数的不确定性有关,安全系数和破坏风险的关系并不一致,若地工系统有较大的不确定性,则即使基坑底面具有较大的抗隆起稳定安全系数,亦无法保证基坑工程的破坏风险较低。

Evaluation of basal stability is important in the design of braced excavation in clay.Up to now,approaches to excavation design have always been essentially quantitative,i.e.,with single values assigned of the mechanical properties of soils and with a single factor estimating the safety of the design,regardless of both the uncertainties pertaining to the calculation procedures and/or variability of the soil properties.This study adopts different basal-heave stability analysis methods of Terzaghi,Taiwan's architecture code and Shanghai standard code for design of excavation engineering.The results highlight the inconsistency in the relationship between the factor of safety and the underlying level of risk,depending on the degree of uncertainty of either damage risk or design parameters.Larger factor of safety does not necessarily imply a smaller level of risk.