Optimization Study In The Consolidation Theory Of Ground With Vertical Distributed Arrangement Of Horizontal Drains

For soft soil treated by preloading and drainage method,horizontal drains serve as horizontal drainage channels,which play an important role in accelerating the consolidation process of foundation.At present,the study on horizontal drains mainly focuses on its horizontal permeability coefficient,paving thickness and the drainage materials used.In some land reclamation projects,the scheme of hydraulically filling dredged clays with multiple horizontal drains is often adopted to shorten the drainage distance for seepage flow of pore-water under the drift or self-weight load.Some studies have designed layered clay-sand foundation according to drainage efficiency of horizontal drains,but the optimization design of the thickness,layout number and position of horizontal drains is insufficient.Aiming at the consolidation of foundation with the horizontal drains,onedimensional foundation with horizontal drains under the non-uniform distribution of initial excess pore water pressure,two-dimensional foundation with horizontal drains and two-dimensional layered clay-sand foundation consolidation model were established.Using the analytical and numerical methods to optimum design of horizontal drains.The main research results are as follows:(1)For one-dimensional foundation with horizontal drains under the nonuniform distribution of initial excess pore water pressure,horizontal drains should be installed at the depth of soil layer with great excess pore pressure at the early stage of consolidation,and turn to 2H/3(PTIB)or H/2 of soil(PTPB)at the later stage of consolidation(H is the depth of foundation).(2)For two-dimensional consolidation of foundation with horizontal drains,the consolidation rate of foundation is related to the geometric and physical parameters at the interface between drainage layer and soft soil.The consolidation rate increases with the increase of horizontal permeability coefficient,but decreases with the increase of foundation width for the soft soil.For horizontal drains,the consolidation rate increases with the increase of horizontal drains thickness and horizontal permeability coefficient.Moreover,the influence of horizontal permeability coefficient and thickness on the permeability of the horizontal drains was considered comprehensively.When the boundary condition of the interface of horizontal drains and soil foundation is close to the full drainage boundary condition,the parameters required were different for different soil width.In addition,the horizontal permeability coefficient of soil had little effect on the parameters when the boundary condition of the interface of horizontal drains and soil foundation is close to the full drainage boundary condition.(3)For layered clay-sand foundation,there must be an optimal spatially layout of drainage layer which makes the degree of consolidation of foundation reach the maximum under the fixed time.The optimal layout position of all horizontal drains moves gradually towards the bottom of foundation with the increase of consolidation time under the PTIB condition(single drainage condition).It is worth noting that the optimal thickness of each sand layer does not vary significantly(i.e.,increases slightly)with the increase of time factor.For the PIPB condition(double drainage condition),horizontal drains always distributes symmetrically in the middle of the soil and the optimal location layout position of all horizontal drains moves gradually towards the middle of the soil with the increase of consolidation time.Moreover,the drainage layer located in the middle of the foundation has the largest thickness.Considering the ease of construction,the layout number of horizontal drainage layer should be limited as much as possible.Engineers are encouraged to combine factors in terms of optimization design and feasibility of construction to determine the optimal layout number of horizontal drains.