Studies On One-Dimensional Consolidation Theory For Layered Soft Soils Under Continuous Drainage Boundary Conditions

Consolidation theory has always been one of the core problems of soil mechanics,and is the theoretical basis of settlement prediction and control of soft soil foundation.The boundary drainage condition has an important influence on the consolidation behavior.However,the traditional consolidation theory regards the boundary as completely permeable or completely impermeable,which is inconsistent with the engineering practice.The semi-permeable boundary is difficult to apply and it is generally difficult to obtain explicit solutions.The proposed continuous drainage boundary can solve the above boundary problems very well.Soft soil foundation has its own layering and structure,and the stage of foundation treatment and building operation are often accompanied by soil self-weight,external complex load,temperature and so on.However,there is no systematic study on one-dimensional consolidation theory of soft soil under complex external loads,self-weight,stratification,structure and optimization of horizontal drainage sand blanket in foundation treatment under continuous drainage boundary conditions.Therefore,it is necessary to carry out a systematic study of the consolidation theory under continuous drainage boundary conditions to be more perfect and to engineering practice.Based on the continuous drainage boundary conditions,the one-dimensional consolidation of single-layer foundation and layered foundation under complex conditions such as arbitrary external load,self-weight,structural property is studied by using analytical and semi-analytical numerical methods.The consolidation behavior of soft soil and the influence of related soil parameters are analyzed in depth.Finally,the placement of sand blanket in Foundation treatment is discussed.The optimization problem has been studied.The main research contents and innovative achievements are as follows:(1)The dimensionless analytical solution of one-dimensional consolidation theory under continuous drainage boundary conditions is presented.Based on the continuous drainage boundary under instantaneous load,the continuous drainage boundary conditions under arbitrary load are derived.The correctness of the solution is verified by degenerate solution.Convergence analysis of the solution is carried out and the influence of interface parameters on consolidation behavior is discussed.The inversion formulas of interface parameters are proposed,and the existing experimental data are analyzed and compared.(2)Considering the change of load action with time,the one-dimensional consolidation equation under arbitrary load and continuous drainage boundary variable load is established,and the analytical solution is derived by using the finite Fourier sine transformation method.The results of solution degradation and numerical calculation are compared to verify the correctness of the solution.The effects of interface parameters and load parameters on the consolidation behavior of soils under four kinds of variable loads(linear load,exponential load,harmonic load and trapezoidal periodic cyclic load)are discussed.Finally,semi-analytical solutions such as boundary transformation method,Laplace transformation,matrix transfer method and Laplace numerical inverse transformation are used to solve the one-dimensional consolidation problem of layered foundation with continuous drainage boundary under arbitrary loads.The correctness of the solution is verified by solution degradation and numerical comparison.The effects of interface parameters and load parameters on the consolidation behavior of layered foundation are discussed.(3)Considering the influence of self-weight stress,the analytical solution of one-dimensional consolidation of homogeneous foundation under continuous drainage boundary condition is derived by using the Finite Sine Fourier transform method.The correctness of the solution is verified.The influence of interface parameters and self-weight stress coefficient on consolidation behavior of single-layer soil is analyzed.The one-dimensional consolidation equation of layered soil under arbitrary load continuous drainage boundary condition is established.The semi-analytical solutions including boundary transformation method,Laplace transformation,matrix transfer method and Laplace numerical inverse transformation are used to give the solutions.The comparison and verification are made.The effects of interface parameters and self-weight stress coefficient on the one-dimensional consolidation behavior of layered foundation considering self-weight are discussed.(4)Considering the structure of soft soil,using the idea of layered soil,the analytical solution of one-dimensional consolidation of single-layer structural soft soil under continuous drainage boundary condition is given.The correctness of the solution is verified.The influence of interface parameters,soil structure and yield stress on consolidation behavior is discussed.On this basis,the consolidation problem of layered structured soft soil foundation under continuous drainage boundary condition is solved by using the idea of layered foundation,and is verified by comparison of degradation and numerical value.Finally,the influence of interface parameters,permeability and compressibility on consolidation behavior of layered structured soft soil foundation is discussed.(5)Considering the influence of laying position of horizontal drainage sand blanket on consolidation behavior,the one-dimensional consolidation equation of horizontal drainage sand blanket in homogeneous foundation considering soil self-weight under continuous drainage boundary condition is established.The solution of optimal laying position of horizontal drainage sand blanket is given by using Fourier sinusoidal transformation method and numerical method,and the optimal laying of horizontal drainage sand blanket is analyzed.The relationship between the location of sand blanket and the degree of consolidation of foundation is given,and the design diagram of the relationship between the optimal location and time of sand blanket with different interface parameters is given.On this basis,the one-dimensional consolidation equation of laying horizontal drainage sand blanket in layered foundation is established.The semi-analytical solutions such as transfer matrix method,Laplace transform and numerical inversion are used to give the solution of the optimal laying position of horizontal drainage sand blanket in layered foundation,which verifies the reliability of the solution.The influence of consolidation coefficient,soil thickness and permeability coefficient on the optimal placement position of horizontal drainage sand blanket is discussed,and the effect of optimal design of horizontal drainage sand blanket on consolidation degree is analyzed by an example.