Failure analysis and zoning control of water gushing in foundation pit

Abstract

A water gushing failure of foundation pit in sand layers and deep confined aquifer in Nanjing, China, is presented in this study. During foundation pit excavation, the water gushing through the waste pile hole below the pit bottom caused local collapse failure and crown beam fracture in the southeast corner of the foundation pit. A series of urgent remedial measures were adopted to prevent the gushing from further developing, however, none of them worked until artificial recharge was proposed. The reasons for the water gushing and the effect of the urgent remedial measures are analyzed and discussed in this work. The gushing channel along the waste pile without effective plugging was established by the high level of confined water head from deep confined aquifer to pit bottom, which was the main reason for the gushing. Based on site reinvestigation and monitoring results, the soil around the foundation pit was divided into three disturbed areas: mild disturbance zone (MDZ), severe disturbance zone (SDZ), and collapse zone (CZ). The reinforcement and dewatering measures were proposed for different disturbance zones after rechecking the original design scheme with the disturbed soil parameters. Finally, the lessons learnt are summarized from the incident and provides practical experience and guidance for similar foundation pit projects.