Experimental Study On Reinforcement Of Yangtze River Floodplain Soft Foundation Using Vacuum Combined Surcharge Preloading

Huadian Power International Corp plans to build a coal storage and transportation wharf with an annual throughput of 15 million tons along the Yangtze River in Jurong,Zhenjiang,Jiangsu.The compressibility of natural foundation is high,ground bearing capacity is insufficient and poor foundation stability are due to deep Yangtze River floodplain silty clay in the field.It is designed to reinforce the natural foundation by drainage consolidation.In this paper,some field tests were taken during vacuum combined surcharge preloading.Then the factors affecting the ground consolidation were analysed by comparing field data with numerical solution.The main works and achievements are as follows:(1)The properties of soil layer were obtained by laboratory tests,then the engineering performance of soft soil was evaluated.The results show that the soft soil layer(1)-1 and(2)have poor engineering performance,the value of natural water content is higher than liquid limit,and I_L>1.0,which is in plastic-flow state.(2)The monitoring instruments were installed in the field to obtain the variation of vacuum degree,settlement,pore water pressure and the horizontal displacement of deep soil at the edge of the reinforced area during the foundation reinforcement using vacuum preloading and vacuum combined surcharge preloading.With field data,the factors affecting the foundation reinforcement were analyzed to ensure the ground treatment continuous and effective.(3)The foundation reinforcement effect was evaluated by comparing the properties of soil and in suit vane shear test before and after vacuum preloading or vacuum combined surcharge preloading.Then the in suit shallow plate load test was carried out to get the bearing capacity of the foundation after reinforcement.(4)An improved analytical solution of sand-drained ground consolidation was proposed considering the vacuum pressure decay along the depth and load applied in stages.With the improved analytical solution,the influence of vacuum pressure decay rate and the smear zone permeability coefficient on sand-drained ground consolidation was discussed based on the field data.