Innovative Soft Soil Stabilization Using Simultaneous High-Vacuum Dewatering and Dynamic Compaction

Abstract

A combination of the high-vacuum (HV) and dynamic compaction (DC) method (HV+DC method) was used to improve saturated soft foundation. HV and DC were applied alternately and repeatedly to achieve the required level of ground improvement. An in-depth investigation was conducted of the technical requirements, processes, and mechanisms involved in the HV+DC method at the Ningbo Harbor Coal test site near Shanghai, China. Relevant drainage control parameters were identified and optimized to provide the construction parameters, such as compaction energy, spacing, drop number, vacuum dewatering number and location, and wellpoint depth and number, for large area construction. The monitoring during the field trial case study presented here indicates that the method is not only based on sound concepts with rapid stabilization effects and low construction costs but also holds significant promise as an innovative ground improvement method when soft soils are encountered. The application of the HV+DC method increased the cone penetration tip resistance q_t of the pond fly ash layer at the Ningbo site more than 2.5 times and that of the clay mud layer more than 1.5 times (compared with unmodified ground) and improved the characteristic value of the bearing capacity of the foundation up to 135 kPa, all of which adequately met the design requirements. For the total area of 400,000 m² of the main project, this innovative method has saved more than 40% of total cost and approximately 50% of construction time from the original design of the soil cement mixing method.

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