重力式挡土墙抗滑稳定容许安全系数取值标准初探

A preliminary study of allowable factor of safety in gravity retaining wall stability analysis

我国水工挡土墙设计规范中规定稳定性验算采用以安全系数为度量指标,给定的安全系数允许值范围在1.20~1.35之间,低于国外规范的取值。采用可靠度分析方法,建立目标可靠指标与安全系数之间的定量关系。通过分析计算确认安全系数满足对数正态分布。对一个目标可靠指标为3.2的特例获得其安全系数在1.43~1.55之间的结论。根据前期提出的相对安全率指标判据提出了安全系数满足对数正态条件下的计算公式。使用这一判据,论证了将这一特例扩展到不同墙体几何参数和强度指标参数情况时这一可靠指标和安全系数关系的普遍适用性。提出的安全系数取值标定方法和相应成果可供规范修订工作参考。

The design specification for Chinese hydraulic retaining wall （SL_379-2007） uses the safety factor criterion in stability analysis, whose allowable values are stipulated in a range of 1.20 to 1.35, which is much smaller than those specified in the overseas design regulations. In this paper, a probabilistic analysis approach is used to establish the relationship between the target reliability index and safety factor. Results show that the factors of safety follow a log-normal distribution relationship. The related criterion for the ＇Safety Margin Ratio （SMR）＇ has been updated. The study uses a target Case that has a reliability ir^dex of 3~2. Ithas been found that the allowable factor of safety is in a range between 1.43 and 1.55. Using the SMR approach, the authors further demonstrate that the calibrated allowable factor of safety is equally allocable to the extended target cases that involve different geometric and shear strength values of this retaining wall. The method and analytical results described in this paper are useful for regulation makers.