Abstract: The construction of the underground continuous wall through the water-rich soft stratum is easy to induce the local instability of the weak stratum. In order to study its local instability mechanism theoretically, the local instability stress model is set up and various influence factors such as the cover load, soil strength and groundwater seepage are taken into account. The limit equilibrium of the theoretical model is analyzed to obtain the ultimate support pressure and the minimum height of the mud level of the local instability of the groove wall. Through the parameter sensitivity analysis, the influences of trench length, soil strength, thickness and permeability on the stability of the water-rich soft layer are studied. The results show that the ultimate support pressure is mainly affected by trench length, weak stratum strength and covering thickness, while the confined water seepage in weak stratum has only a slight influence on the support pressure. The theoretical model is applied in the ulta-deep wall of Suzhou and it is found that a good agreement is found between the field monitoring and the study results, which indicates the applicability of the current solution on the local failure evaluation.

Key words: diaphragm wall, trenching construction, water-rich weak stratum, local failure, limit equilibrium analysis