Boiling Failure and Resumption of Deep Excavation

Boiling failure that results from drilling for installation of a new pneumatic piezometer in the final grade of a deep excavation in Taipei, Taiwan, is presented in this case study. The extent of the damage includes the boils of a mixture of soil and water entering the bottom of the excavation, heave of the center posts, inclination of internally horizontal struts, subsidence and excessive lateral inward deformation of the diaphragm wall, and significant ground settlement. The corresponding emergency efforts to minimize the loss are addressed. In addition, the paper focuses on two remedial schemes to resume excavation following the incident. One is the grouting measure adopted by the contractor, and the other is a dewatering scheme proposed by the writers. Constructibility, safety, schedule, and cost of the two schemes are compared. It is demonstrated that a dewatering scheme should be considered where applicable to mitigate against similar incidents in the Taipei metropolitan area in the future.