Research On Consolidation Of Complex Drain System

In real ground treatment projects, the ground within the depth of PVD forms a multi-layer ground with vertical drains. The course obtaining final answer of the degree of consolidation of multi-layer ground with vertical drains is very complex. The continuity condition of the pore pressure and flow between two continuous layers should be met. And the continuity condition of the pore pressure and flow inside PVD between tow continuous layers should be met. Infinite series in the expression of pore pressure leads to convergent problems of the final answer, which makes the solving process even harder. For the existing answer for the degree of consolidation of multi-layer ground with vertical drains, either the impact of factors that affect the degree of consolidation (well resistance, smear effect) has not been fully considered, or the theory can not be extended to more layers. This paper obtains answer for three-layer ground with vertical drains and multi-layer ground with vertical drains, and makes research on convergence of the answer.Rocks and giant stones are the main filling material in the traditional construction project of sea wall and dams. National policy restrictions and the long-term consumption, have led to a serious shortage of conventional debris resources, so soilbag filled with mud soil has emerged as a new filling material. At present, domestic and foreign research on soilbags concentrates in the force analysis, filling characteristics and permeability characteristics, while consolidation problems of the soilbags are rarely studied and no one has ever made research on consolidation of soilbag set by vertical drains filled with mudsoil. The consolidation solution of ground with vertical drains considering the actual square construction pattern of the vertical drains is obtained. After the extra consideration of the permeability of the influence area boundary, the solution is applied to estimate the degree of the soilbag system. The calculation result is proved to be consistent with results of FEM and lab experiments.This paper follows the specific work:1. The consolidation theory of three-layer ground with non-ideal vertical drains is proposed. Orthogonal relation of multiple-layered system is proved. Convergence problem exists during getting the final answer of degree of consolidation. When GPA/MPA situation is serious, the consolidating result is not convergent, otherwise, a two-step-control method can be applied to improve the accuracy of the final answer. This paper studies application range of application of the two-step method and addresses the application of the method. The two-step method is applied to improve the result accuracy of a calculation case of the Yueqing Bay, and the calculation result coinsides with the real measure data.2. Two methods are applied to calculate the degree of consolidation of multilayer-ground with non-ideal vertical drains. Calculation result of the method using a recurrence relation shows, hyperbolic functions, complex expression of the transfer matrix and matrix multiplication make the divergence of the transfer matrix enlarged. Also, the control matrix is not stable in calculating the parameter βm.All of the above reason leads to the non-convergent answer. Otherwise, the method expanding the continuous-matrix can obtain a convergent result of the multilayer-ground with non-ideal vertical drains. The key point is to expand the size of the continuous matrix.3. The general expression of the multi-layer ground with vertical drains is obtained by the expanding-continuous-matrix method. The consolidation of the four-layer ground is studied. The result has been compared with the result from the consolidation theory of the double-layer ground with vertical drains. After confirmation of the correctness of the results, the theory is applied to make analysis of the four-layer ground system.4. The expression of degree of consolidation of ground with vertical drains considering the actual square construction pattern of the vertical drains is obtained. This paper draws on the consolidation theory considering the hexagonal affected zone, and introduces concept of the permeable boundaries. The error between the square pattern and the circular pattern is clarified after a comparison is made among different patterns. After the consideration of the permeability of the influence area boundary, this paper uses the theory to estimate the degree of consolidation of soilbag filled with mudsoil set by vertical drains system, and the estimation result gives a good conincidence with the lab experiment and the FEM result. The FEM and the calculating theory are used to compare consolidation results of soilbag with/not with vertical drains. FEM is applied to study the influence of the aspect ratio and the influence of the height to the consolidation speed of the soilbag system.4:1is supposed to be the best aspect raio of the soilbag.5. This paper furtherly considers the distribution pattern of the permeability coefficient and some nonlinear factors and obtains the final expression of degree of consolidation. Analysis of the calculation considering the nonlinear factors shows that the load applied upon soil surface and property of the soil will affect the consolidating speed. The study makes more factors can be considered in the consolidation problem to compare with in-situ data of real projects.