Thermo-elastoplastic constitutive model for municipal solid waste (MSW) considering temperature effects and fiber reinforcement

Considering the composition complexity of municipal solid waste (MSW) and the temperature rise caused by degradation of organic matters, according to the triaxial test results of MSW with different fiber contents under different temperatures, it is shown that the temperatures and fiber materials are the key factors affecting the mechanical properties of MSW. Therefore, MSW can be regarded as a composite of soil-like materials and fiber materials, whose mechanical properties depend on the combined interaction of the two materials. It is assumed that the temperatures only affect the volumetric deformation of MSW, and the fiber reinforcement effects are gradually apparent during loading. Based on this, the hardening law of plastic volumetric strain considering the temperature effects and the evolution equation reflecting the reinforcement effects of fiber materials are both proposed. Through the new plastic potential function developed with reflecting the effects of the temperatures and fiber reinforcement, the thermo-elastoplastic constitutive model is derived for MSW using the associated flow rule. Compared with the test results of different MSW, those of the proposed model are in good agreement with the test data. The main features of upward curvature of stress-strain curves and continuously increasing volumetric strain with axial stain are better reproduced by the proposed model as well as other mechanical properties of MSW such as the greater strength under higher confining pressure, greater strength with higher fiber content, and lower strength at higher temperatures. Although the calculations of the proposed model have some deviation from the test results in terms of volume change behaviors, the main volume deformation characteristics of MSW are well captured by the proposed model, including the smaller volumetric strain under higher confining pressure, lager volumetric strain with higher fiber content, and slightly larger volumetric strain at higher temperature. In conclusion, the proposed model can accurately reflect the influences of confining pressure, fiber content and temperature on the stress-strain and volumetric strain behavior of MSW, which effectively verifies the retionality of the constitutive model.