Experimental Study Of Vacuum Preloading Combined With Vacuum Well Point Dewatering Method

The development of the world economy and the rapid increase in world population has resulted in an expansion of urban construction activities, especially in the congested coastal regions and river alluvial plain sediments regions of many countries. The soft soil possess very low bearing capacity, high water content and high compressibility so its physical and mechanical properties are not sufficient to meet the needs of engineering construction activities. Surcharge preloading, vacuum preloading, vacuum pressure combined with surcharge preloading method have emerged at the right moment and developed rapidly. In recent years, a system of vacuum well point combined with vacuum pressure and surcharge preloading has become an attractive ground improvement alternative method in terms of cost and effectiveness and environmental friendliness. However, the mechanism of this method has not yet be clearly researched and documented. Thus it is the main reason for the lagging behind of theoretical research compared to the more advanced practical activities which causes a limited popularization of this method.This paper considers the correlative mechanism of vacuum and surcharge preloading combining with the characteristic of the vacuum well point dewatering. This research aimed to investigate the variation of the vacuum distribution, pore water pressure, effective pressure, soil parameters(permeability, void ratio, water content) and based on the means of analysis, model test, numerical modeling(Geostudio) comparing with measured data, hence the main research achievements are as follows:(1) A successful development of the vacuum well point dewatering combined with surcharge device physical simulation and testing systems. The device adopts sealing air pressure to simulate surcharge load, which yielded perfect experimental results. Through laboratory experiments, research on the vacuum pressure distribution, variation of pore water pressure, settlement, moisture, and void ratio, horizontal permeability obtained the latter engineering characteristics as well as the technology application of vacuum well point dewatering combined with surcharge method.(2) Based on analytical model method and Biot model method(Geostudio) a numerical prediction model for the experiment test was created. By comparing the model results with the measured data verification on the reliability of experimental results was undertaken. At the same time a prediction model for the sand drain preloading was created. The difference between the sand drain preloading method and the vacuum preloading combined with well point dewatering was obtained, and the important influence of the permeability coefficient on the vacuum consolidation process was revealed.(3) Based on the characteristics of vacuum well point dewatering combined with surcharge method and the variation of permeability coefficient with the variation of void ratio in consolidation process an improved Biot consolidation model which considers the variation of soil permeability coefficient was established. A comparison with the measured data was carried out as a validation control process which showed that the new improve numerical Biot model directly improves the prediction accuracy of the results.