A Note on Deep Seated Failures in Supported Vertical Cuts in Sands below the Groundwater Table by a Coupled Numerical-Analytical Method

摘要

Stability of supported excavations in sands and other granular matters against deep failure is of particular importance as different modes of failure are often probable. Among all, the active/passive earth pressure failures, failure of supports and braces, hydraulic failures due to the ground heaving or piping and the bearing capacity or deep seated failure can be pointed out. In some staged-construction procedures, a sheet-pile may not be previously extended below the final level of the cut or the extended length can be insufficient to prevent such failures. In this research, the stability of vertical cuts against such failures has been studied. In particular, when the sand is below the groundwater table, a rather steady state flow of water will form towards the bottom of the cut and together with the weight of the surcharge in the proximity of the cut, it can cause several kinds of failure. For such a problem, a semi-analytical approach is implemented comprising of the solution of the flow field by complex analysis and the stress field (stability analysis) by the slip lines method. Whereas the first analytical procedure works as a background solution, the foreground numerical solution of the stress field can be used for stability analysis. A number of analyses revealed that the deep seated failure may precede the piping and/or heaving failures. Also, in absence of the groundwater seepage, a deep failure is probable. The results are presented in terms of some measure of stability, defined as a factor of safety.