Study On The Instability Of Municipal Solid Waste And The Mechanism Of Shear Strength Under Reinforcement

Municipal solid waste(MSW)is a kind of non-homogeneous and complex component.It will also produce leachate and landfill gas due to biodegradation,which leads to the special function of landfill,extreme service environment,and prone to environmental disasters.No matter precipitation or local high pressure,the effective stress in landfill will be reduced,like the second failure mode of soil slope.The stress-strain intensity response of MSW is of great significance to the design and operation of landfill,as well as the characteristics and reuse of landfill after closure.It is generally believed that municipal solid waste is a kind of material with high strength due to the reinforcement of fiber materials.Therefore,it is very important to study the instability of garbage and the shear strength mechanism of reinforced garbage.In this paper,the undisturbed waste samples on site were compared with the indoor samples,and the angle of structural solid phase in garbage was described by using CT scanning and image processing technology.The constant deviating stress path test and ring shear test were carried out for garbage of different components to study the instability of garbage and clarify the role of fiber reinforcement in garbage.Based on the above,the two-dimensional and three-dimensional shear strength models of reinforced soil were deduced.This paper completed the following research works:1.A kind of sampler for different depth of original sample in landfill has been designed and made.The structural solid phase was identified by ParaView 5.8 after the image data of each section of the sample were obtained by CT scanning,and the probability density distribution function and the density distribution function of structural solid phase angle are obtained.At the same time,it is found that the influence of overlying load on structural solid phase is limited,and the average angle of structural solid phase is mainly about 30°?32°.2.Based on the test data of constant deviator stress path,it is found that the above instability occurs in MSW,it is shown as follows:the axial strain and volume strain change abruptly with the decrease of effective average stress,that is,the volume of sample expands rapidly,the axial strain increases suddenly,and the radial strain increases suddenly.The results show that the sample will not lose its stability under the condition of undrained,but only under the condition of drained.At the same time,when the effective confining pressure decreases and the effective stress ratio reaches a certain value,the garbage will become unstable.The slope of instability line will decrease with the increase of void ratio after consolidation3.It is found that in the ring shear test the shear displacement required to reach the peak strength increases with the increase of normal stress,however,with the increase of shear rate,the shear displacement required to reach the peak strength decreases.In the whole process of ring shear test,the simplified garbage shows strain hardening characteristics.Reinforcement can improve the shear strength of garbage by 8%?14%.The shear strength parameters of refuse are very important for the overall stability evaluation of landfill(whether it is a landfill or a refuse dam).4.Based on the two failure modes of reinforced soil,namely pull-out failure and pull-out failure,the two-dimensional and three-dimensional theoretical models of shear strength of reinforced soil are derived respectively.The shear strength of reinforced soil is a function of fiber geometry,fiber volume content,reinforcement angle,shear band width,fiber tensile strength and soil shear strength.The influence of shear band width on the shear strength of the increased part will not exceed 13%.It is generally considered that the influence of shear band width on the shear strength of the increased part is 3-5%.The model can be applied to two kinds of materials,garbage and reinforced soil.