Research On The Effect Of Consolidation Drainage System Of Soft Ground Under Static And Dynamic Loadings

The Static-Dynamic Drainage Consolidation Method (SDDCM) can be used to reinforce the ultra-soft soil (silt, silty soil) foundation, and the design Optimization of drainage system is the determinants. How much is the thickness of sand cushion? What is the spacing of plastic drain board? What is the inserted depth of plastic drain board? The answers of these questions are the key factors of SDDCM. Effects of different drainage systems can be described by the change of pore water pressure and soil deformation, scholars have done a great deal of indoor experiments about this, but there always exists a problem that the impact load is not high enough so that the physical and mechanical properties of soil couldn’t be inspired. In order to explore the effect of different drainage system, indoor model tests under impact loadings of high energy level were carried on to study the variation of pore water pressure, soil pressure and soil deformation.In this paper, based on an ultra-soft ground treatment project in Guangzhou, model tests were designed in accordance with the similarity theory strictly (geometric similarity ratio of1:30). With the use of self-designed impact loading system of high-energy and high-speed, model tests were taken on the soft clay (w=70.48%, e=1.96), to study on accumulation and dissipation of pore water pressure and soil pressure under impact loading with different drainage systems as well as deformation of the soil.The main research contents and results in this paper are as follows:(1) Under impact loading, settlement is proportional to the change amplitude of pore pressure, the larger variation of pore pressure is, the greater amount of the settlement would be.(2) Settlement is inversely proportional to plastic drain spacing, namely, a smaller plastic drain spacing result in a greater settlement. On the basis of a large number of model test data, the following curve between plastic drain spacing and settlement is obtained by curve fitting: (3) The rationality of the test results were verified by comparing the data of pore water pressure, earth pressure and settlement obtained from model test with that from site project.(4) According to the Nansha field data, the model of reasonable drainage spacing L of silt foundation under impact loads was obtained as follows:Also the following phenomena were verification in the course of this study: a larger drainage spacing leads to larger pore pressure variation in the moment of impact, and the smaller drainage spacing is, the faster pore pressure dissipation would be after unloading.The results of this study will provide some reference for the model test theory、the design of indoor model test、the effect of drainage system under impact loading、the generation of residual stress、the site construction of Static-Dynamic Drainage Consolidation Method.