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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. [ABSTRACT FROM AUTHOR]

Under weak geological conditions, soil deformation and surface settlement are the key factors affecting the success of shallow-buried rectangular excavation. To investigate this issue, an underpass of Zhongxiao East Road in Taipei City was used as a case study. The surface settlement and lateral deformation of an underground diaphragm wall caused by the excavation of a rectangular pedestrian underpass using the pipe-roof preconstruction method (PPM) were investigated by 3D finite element analysis. The numerical analysis results showed that the constructed numerical analysis model had considerable accuracy. The use of PPM combined with a box culvert structure to form a pedestrian underpass could effectively control the surface displacement above the box culvert. Under the condition of the same sectional area, the smaller the width of the pipe-roof structure, the more the impact on the ground surface was reduced. The maximum positive bending moment and maximum negative bending moment on the pipe roof produced by excavation at each stage were roughly inversely related to the height per the width of the cross-section of the pipe diaphragm structure. The results showed that the pipe-roof structure was suitable for underground excavation with shallow-buried depth in the soft soil of the Taipei Basin. Moreover, the shallow-buried box culvert was more sensitive to the subsidence caused by construction than the deep-buried box culvert. [ABSTRACT FROM AUTHOR]

Bermed excavation (deep excavation supported by an excavation wall and a berm) can be an economical method for basement construction in urban areas if ground movement around the excavation is not the primary concern and the excavation site is large and (or) irregular in shape. This paper reviews three bermed excavation projects carried out in the Taipei Basin. One project was successful, one was successful after near failure, and one was a failure. Ironically, extensive ground improvement work had been done for the near-failure and failure cases; but no ground improvement was done for the successful case. It is of interest to find the similarities and differences among these bermed excavation projects. The causes of instability that result in unsuccessful bermed excavation projects and the applications of limit equilibrium analysis to the stability of bermed excavation are also discussed here. These three cases show that the existence of grout columns does not help to effectively increase the stability of the berm if the original safety factor against sliding of a berm slope is less than 1.0 and the improvement ratio of grout columns is low (say <20%). [ABSTRACT FROM AUTHOR]

Presents a discussion on a study which observed large cantilever-shaped lateral wall deflections following jet-grout treatment on adjacent ground and structures in excavation sites in Taipei, Taiwan. Factors resulting to large lateral movements in structures; Background on jet grouting; Results of net lateral wall deflections.