A New Combined Vacuum Preloading with Pneumatic Fracturing Method for Soft Ground Improvement

AbstractA combined vacuum preloading with pneumatic fracturing method (VPF) was developed to overcome some shortcomings of the conventional vacuum preloading for soft soil improvement. In this method, high pressure air is injected into the soil before and during vacuum pressure exerting, which causes pneumatically fractures when the air pressure exceeds a critical threshold value. These fractures can increase significantly the soft soil mass permeability and accelerate the pore water pressure dissipating. Hence the VPF method can reduce preloading time and enhance the improvement efficiency of deep soft soil layers. A field project in a highway engineering located in Jiangsu Province of China was conducted to compare the performance of the VPF method and the conventional vacuum preloading. The vacuum degree, pore water pressure, groundwater level, surface settlement and horizontal displacements were monitored during the field test. The effectiveness of soft ground improvement was demonstrated by the comparison of piezocone penetration tests and soil property tests before and after ground improvement. The results showed the high efficiency of the VPF method, especially for deeper soft soil layers. It is a promising method in soft ground improvement engineering practice