The shear strength of soil indicators should be using direct shear consolidation of fast shear strength index or consolidation determined by triaxial tests undrained shear indicators (fast), without specifying select the applicable state (groundwater bit or more, or less) for supporting and retaining design in the technical specification for retaining and protection of building foundation excavations. Chenggong New Area is located in the hilly area of the basin, the lower water table, soil that has a weak expansion (free swelling ratio<40%, does not belong to the expansive soil, but with the characteristics of the water softening), in the slope pit can easily ignore the role of water in the design, engineering accidents. In this paper, based on the accident of a project in the area as an example,according to limit equilibrium theory,by inversion of the indicators of soil analysis, the main draw of deformation of soil indicators improper access. It puts that the soil in the region should adopt after flooding consolidation fast shear indicators or reduction consolidation fast shear indicators.%现行规范[1~5]用于支挡设计时规定，土体抗剪强度指标宜采用直剪固结快剪强度指标或按三轴试验确定的固结不排水（快）剪指标，而未明确选取时的适用状态（地下水位以上、以下）。呈贡新区地处昆明盆地的丘陵区，地下水位较低，土体具有一定的弱膨胀性（自由膨胀率约40%，不属于膨胀土，但具有遇水软化的特点），在边坡、基坑设计时极易忽视水的作用，从而出现工程事故。本文以该地区某一工程事故为例，根据极限平衡理论，通过对土体指标进行反演分析，得出变形的主要原因为土体指标取用不当。提出该区域土体宜采用浸水后的固结快剪指标或采用折减后的固结快剪指标。
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