Theory Of Consolidation Of Soft Clay Improved By DJM Combined With PVD Method

DJM combined with PVD method (2D method) is a new soft ground improvement method, which develops from Dry jet mixing column method (DJM). 2D method covers all advantages of DJM and drainage consolidateon method. Compared with traditional DJM, the ground improved by 2D method has a different rule on accumulation and dissipation of excess pore water press in virtue of adding the penetration path of pore water in ground soil. By contrasting with the drainage consolidation method, the presence of DJM affords the pile effect, which makes the ground have an obvious composite behavior. As a new technique, the theory of 2D method still need a further study.Consolidation theory is an important guidance in design and practice for soft ground, there is a direct correlation between soil strength and consolidation degree, so it is significant to reveal the basal consolidation behavior of 2D method. Based on such background, a research on consolidation theory of 2D method.is conducted in the paper.A simplified consolidation calculation model of the ground improved by 2D method after loading is developed based on Barron consolidateion theory;the formulas of pore pressure and consolidation degree are deduced; the simplified consolidation calculation method about composite ground and sub-layer is discussed respectively; Considering both composite ground and sub-layer,a 2D method consolidation calculation program based on the one dimension consolidation theory of double -layers is completed ,which can also consider the continuity of pore water pressure between the two layers; a formula of consolidation degree under multilevel loading condition is recommended by considering the dissipation rule of excess pore water pressure.A numerical simulation method of the ground improved by 2D method under the supposition of plane-strain theory is recommended, which considers both of stress and penetration conditions; a FEM model is founded based on Biot consolidation theory; the consolidation characteristic about a field case after loading is simulated by this method, and also be contrasted with the numerical simulation results of traditional DJM. The conclusion shows that excess pore water pressure of 2D method is lower than DJM at any time because of the addition of drain path,not only in composite ground but also in sub-layer, and the nearer the soils be to the surface, the lower the pore pressure.By the field experiment, a contrast is made between 2D method and DJM, such as consolidation behavior and deformation rule etc, the results shows that the rules of the excess pore water pressure ,the consolidation degree and the settlement-time relationship are consistent with the field dates respectively,which also confirms that the theoretical analysis method and numerical simulation mothed used here are viable.Still by the theoretical analysis and numerical simulation, the contrast about consolidation behavior among 2D method,DJM, PVD and nature ground is carried;the factors which affect the consolidation degree of the ground improved by 2D method are evaluated,such as the module of DJM, the column spacing, the penetration coefficient of PVD, the module and the thickness of cushion and so on.The conclusion shows that DJM has more influence on the pore water pressure of the upper soil, and PVD and DJM both have more influence on the lower soil.At a certain range, the dissipation of pore water pressure can be quickened by increasing the module of DJM and the penetration coefficient of PVD ,or decreasing the column spacing, and the module or the thickness of the cushion only has litter influence on consolidation of the foundation.