This paper presents a few case histories where excessive settlements were reported following ground improvement of a number of soft soil sites. The case histories involved different ground improvement techniques such as preloading and surcharging with and without prefabricated vertical drains (PVD), deep soil mixing, concrete injected columns and vacuum consolidation. The ground conditions and the adopted ground improvement designs are discussed. The observed post-construction settlements for the various cases are also presented. Further, the back-analysis works are detailed in order to provide some insight into the possible contributing factors to the measured excessive settlements.
It is clear from these case histories that observational approach by monitoring the ground behaviour during and after ground treatment and construction should be adopted to ensure that the post-construction performance is consistent with design expectation. In addition, the paper demonstrates that selection and design of the ground improvement techniques should be conducted with clear understanding of the theoretical background and limitation of the improvement techniques, regardless of the system adopted. Consideration of construction activities and staging is also important in order to capture the impact of various construction loading on soft soil consolidation and settlement.
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