Laboratory Study On The Strength Characteristics Of MBT Waste

With the accelerating urbanization process and the continuous improvement of the level of urbanization,more and more people have been moving to cities,and the number of urban population has increased dramatically.The total amount of municipal solid waste has also increased year by year.Most cities have faced or will face the dilemma of garbage siege in the future.Under the background of creating sustainable development and constructing an ecological and civilized society,these huge amounts of municipal solid waste are urgently needed to be reduced,resourced and harmless.Hangzhou is the first city in China to adopt Mechanical-Biological-Treatment(MBT)technology to treat municipal solid waste.Through the treatment in this way,the degree of reduction for municipal solid waste has been greatly improved.Although municipal solid waste has been reduced,however,the final product—MBT waste still needs to be landfilled.There is no research about the shear strength characteristics of MBT waste in China,and there is no design norm and standard for MBT landfills.In the case of increasing landfill heights,MBT landfills may have catastrophic consequences such as landslides,instability,and leachate leakage.In order to provide reasonable advice and guidance for the design,construction and management of MBT landfills,and to prevent and control the collapse of landfills,it is essential to study the shear strength characteristics of MBT waste.In this paper,the direct shear test and the triaxial test were carried out to research and analyze the shear strength characteristics of MBT waste.The shear strength characteristics of MBT waste were studied by direct shear test and considering the factors of 3 void ratios,four-level pressure and pressure compression of each stage for 24 h.The strength characteristics and constitutive model of MBT waste were studied by triaxial test with considering 3 void ratios,four-level confining pressure and drainage conditions.The results of the study are as follows:1.For the direct shear test:(1)The compression amount increases with increasing compression time.The compression amount increases rapidly during the initial stage of compression.As the compression time increases,the compression curve gradually becomes gentle,and the compression amount of 1 h accounts for 85% of the total compression of 24 h;(2)The void ratio decreases with increasing compression time,and the void ratio decreases rapidly during the initial stage of compression.As the compression time increases,the curve of the void ratio gradually becomes gentle;(3)The compression indexes of MBT waste are obtained by the curves of e-p and e-lgp;(4)The shear stress increases with increasing shear displacement,which reflects the characteristics of strain hardening;(5)The relationship between shear strength and pressure is conformed to Coulomb's law;(6)The shear strength parameters are related to shear strain and increase with increasing shear strain.The range of cohesion and internal friction angle is given.2.For the triaxial test:(1)The deviatoric stress gradually increases with increasing axial strain and no peak value is attained even when the axial strain exceeded 30%,indicating a strain hardening behavior;(2)The range of values of shear strength parameters(cohesion,effective cohesion,internal friction angle and effective internal friction angle)of different conditions(UU?CU and CD)are obtained;(3)The relationship between shear strength parameters and axial strain can be fitted to a linear relationship,and a linear relationship expression between shear strength parameters and axial strain is established;(4)The stress-strain relationship of MBT waste in 15% axial strain is conformed to the Duncan-Chang model,and the model parameters are obtained.In this paper,the initial void ratio,vertical pressure,confining pressure,drainage conditions and strain values are considered synthetically.The range of shear strength parameters of MBT waste is studied.And compared with the shear strength parameters MBT waste at abroad,the research results can provide a theoretical basis for the stability analysis of landfills.