Effects Of Subsidence On Geosynthetic Liner System Of Landfill And Anti-subsidence Design Methods

With the rapid economic development and urbanization, the generated quantity of Municipal Solid Waste (MSW) increased at a high speed in China. The construction of landfill is still the main measures to deal with MSW. Local subsidence often occurs in landfill due to the complexity, high compressibility of components of MSW and its non-uniformity distribution. Large internal force and deformation would be induced along geosynthetic liner system in subsidence areas subjected to the local subsidence, which would destroy the liner system and lead to leakage of leachate. Moreover, the high leachate level resulted by the leakage of the liner system may cause the instability of the MSW fill. Until recently, research on the liner system subjected to the local subsidence only based on the engineering experience, it is necessary to study its mechanism and proposed a reasonable design method for this problem.Firstly, based on model tests and numerical analyses, the lateral coefficient of earth pressure expression in Terzaghi loosen earth pressure formulate is modified, and its calculated results are in good agreement with the model tests and numerical simulations. Also, displacement-related vertical earth pressure expression is proposed considering arch effect.Secondly, based on tensile cable and large strain circle membrane theory, the analytical models of the liner systems considering the plane strain and axial symmetry local subsidence are presented respectively. The models can take into account the effects of large deformation of liner system, sliding of the liner system near by the subsidence area and the displacement-related vertical earth pressure. Good agreement between the computed results by the proposed MATLAB programs and the FLAC numerical analyses results validates the present analytical models. Parametric studies are also given.Finally, associate with Giroud (1990) resisting local subsistence design method, a new engineering design method of the liner system resisting local subsistence in landfill is proposed based on displacement-related vertical earth pressure theory, it is applied to a design case in practice. If the thickness of the MSW overlying on the liner system is smaller than 30 m, the Giroud (1990) design method is conservatively, otherwise, its predicted allowable tensile force of the liner system will be smaller than the true one due to it cannot taken into accout the displacement-related vertical earth pressure.