Static And Dynamic Strength Properties Of Municipal Solid Waste And Stability Analysis Of Landfill

Recently Municipal Solid Waste(MSW) aggrandized rapidly in China. Landfill has become the main means to deal with MSW in this country and it will be existed as the final disposal method in the long run. For the rational stability evaluation of landfills, This thesis focuses on the static and dynamic shear strength characteristics, stability analysis of landfills.To investigate the shear strength and deformation characteristics of MSW, UU and CD shear tests were conducted using large-scale triaxial apparatus on MSW samples(30x60cm) simulating the compositions of MSW from Hangzhou Tianziling landfill. The important mechanisms that contribute to the shear strength of MSW are studied, the physical meanings of shear strength parameters c and φ are ascertained. Although MSW is composed of many different materials, based on the strain hardening behavior of MSW, the stress-strain behavior of MSW was simulated using the elastic-nonlinear hyperbolic model.To investigate the dynamic properties of MSW, dynamic triaxial tests are conducted using moderate-scale triaxial apparatus on MSW samples simulating the compositions of MSW from Hangzhou Tianziling Landfill. It is concluded that the relationships of dynamic shear modulus and damping ratio versus dynamic shear strain are similar to those of peaty soil. Because of the high compressure property of MSW, the influence of initial void ratio on the dynamic properties of MSW is very little. The formula for evaluating the maximum dynamic shear modulus is proposed on the basis of experimental results of shear wave velocity measured. The varying ranges and average curves of the normalized dynamic shear modulus and damping ratio versus dynamic shear strain are proposed, which are compared with those of OII landfill .It is found that the composition of MSW affects significantly its dynamic properties. In addition, the MSW dynamic strain, dynamic pore pressure and dynamic strength were investigated by dynamic triaxial tests. The dynamic stress-strain behavior of MSW was studied too.Because of the strain hardening behavior of MSW, the mobilized shear strengthparameters tend to increase with the strain in a process. The factor of safety for the waste mass is evaluated by the limit equilibrium method, which can not relate stability to deformation for the waste mass. So the finite element method is used in this paper to analyze the stability and deformation of the waste mass. The minimum factor of safety is 1.5. In the front slope of the waste mass, the whole lateral deformation can not happen, and the local lateral deformation should not exceed 5%. Detailed calculations were conducted for the waste mass with different front slope grade, height of waste mass, constitutive model parameters, and water level. The factor of safety for the waste mass is 1.5 when the failure strain is 10%, the deformation of the waste mass is satisfied too. So, the factor of safety for the waste mass is rational when the criterion of the failure strain is 10%A three-part wedge analysis is used to calculate the factor of safety for the waste mass against possible translational failure with the base liner sliding faces.The waste mass can be divided into three discrete parts: an active wedge,a passive wedge and landfill retaining wall.Because the direction of interwedge force is undetermined, the value of true factor of safety FStrue can not be calculated accurately, which is between an maximum factor of safety FSmax and an minimum factor of safety FSmjn. If an average value of FSmjn and FSmax is used as a solution of this method to replace the true value of factor of safety FS^e, the difference between FS^e and FSave is no more than 5%.In order to analyze the results from the new method, detailed calculations were conducted for a landfill cell with different configuration and material parameters, which indicates that landfill retaining wall has positive effects on the stability of waste mass. The method that takes no account of landfill retaining wall tends to underestimate the factor of safety.