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

• Main Authors: Jen-Chin Wang, 王仁志
• Other Authors: Ta-Teh Chang
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/81268781865708922821

碩士 === 中原大學 === 土木工程研究所 === 98 === Dynamic compaction is applicable for granular and loose sandy soil. With the fines content at a high level, it become difficult for the pore water pressure to dissipate and for the energy to transfer. In such situation stage, vertical drainage method such as wick drains, somehow be useful to solve the problem. But, it requires pre-loading, process to build up excess pore water pressure. For the pre-loading stage, large amount of soil mass to used and may encounter difficulties in move in and out. One of the old traditional technique, the vacuum method, which requires no pre-loading soil mass, but its subsequent drainage effectiveness gradually decreases. Therefore, a combination of the dynamic compaction and vacuum method is applied for the improvement of saturated soft foundation. Repeated vacuum dewatering and compaction cycles, can achieve rapid effectiveness enhancing of soft deposit . In this study, a combination of the high vacuum and dynamic compaction method (hereafter called the “HV+DC” method) is simultaneously employed for the improvement of saturated soft foundation. HV and DC are applied alternately and repeatedly to achieve the required level of ground improvement. The current study presents an in-depth investigation 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 are identified and optimized so as to provide the construction parameters, such as compaction energy, spacing, drop number, vacuum dewatering number and location, 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, has rapid stabilization effects, and low construction cost, but also holds significant promise as an innovative ground improvement method whenever soft soils are encountered. The application of the “HV+DC” method increased the cone penetration tip resistance, qt of the pond fly ash layer at the Ningbo site to over 2.5 times, and that of the clay mud layer to over 1.5 times (compared to 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 over 40% of total cost, and about 50% of construction time from the original design of soil cement mixing method.