Study On The Failure Modes Of Municipal Solid Waste Landfills

With the acceleration of urbanization and the increase of urban population,the output of municipal solid waste is increasing.How to effectively treat and dispose of municipal solid waste has become a problem for urban development.The advantages of effective garbage separation,large processing volume,convenient operation,and good controllability are widely used in practical projects.However,safety accidents in landfills have occurred frequently in recent years.Based on the existing landfill site stability studies.This study summarized global examples of landfill slope instability over the past 40 years then selected 62 cases from 22 different counties to analyze the primary factors causing landfill instability.The laboratory experiments of municipal solid wastes at different landfill ages were conducted,and the stability analysis models under different conditions were established by Geo-Studio numerical simulation software,and the results of the study are as follows:1.Results of laboratory tests(1)Laboratory tests were conducted on four types of municipal solid waste at different landfill ages of 0.5,1,2 and 2.5 years.The characteristics of field capacity and shear strength under vertical pressure were studied through experiments and theoretical analysis.(2)The initial moisture content of municipal solid waste decreases with the increase of landfill depth and landfill time,the specific gravity of municipal solid waste increases with the increase of landfill depth and landfill time.The initial water content of the municipal solid waste is between 67.25%and 78.71%,and the specific gravity is between 1.632 and 1.945.(3)The field capacity(wet weight and dry weight)of the municipal solid waste decreases with the increase of landfill time.(4)The field capacity of municipal solid waste and the overburden pressure are significantly related.Both the dry weight and wet weight field capacity decrease as the overburden pressure increases,the volume field capacity increases first and then decreases with the increase of overburden pressure.(5)The values of cohesion and internal friction angle of samples with landfill age of 0.5 years are respectively 8.6-11.3 kPa and 7.3-8.5°2;the values of cohesion and internal friction angle of samples with landfill age of 1 year are respectively 9.2-12.4 kPa and 8.5-11.7°;the values of cohesion and internal friction angle of samples with landfill age of 2 years are respectively 10.5-15.4 kPa and 10.4-14.9°;the values of cohesion and internal friction angle of samples with landfill age of 2.5 years are respectively 10.5-15.4 kPa and 10.4-14.9°.The values of cohesion and internal friction ratio are 14.6-19.3 kPa and 12.7-18.5° respectively.2.Analysis of instability failure modes of landfill(1)Slope instability in landfills was categorized into three modes based on the position of the slip surface in the landfill.In Mode 1,the slip surface is generated inside the waste pile,the first instability mode is the most frequent,accounting for 69.4%;in Mode 2,the slip surface passes through the foundation soil,the second mode account for 19.32%;and in Mode 3,the slip surface occurs along the interface between the bottom liner and the waste pile,the third mode account for 11.28%of all case studies.(2)Five main causes of landfill instability were identified that high landfill water level,incomplete compaction of MSW,an insufficiently loaded foundation,low liner interface shear strength or liner system failure,rapid landfill gas release and deflagration.These mechanisms accounted for 40.32,22.58,19.35,11.29,and 6.45%of all case studies,respectively.(3)Geo-studio numerical simulation software was used to establish the geometric model of the landfill,and the factor of safety(Fs)and possible slip surface of the landfill were calculated under different conditions and the corresponding.(4)The increase of water level,continuous rainfall,high landfill height,steep slope and the reduction of shear strength parameters of landfill waste will directly reduce the factor of safety and stability of landfill,increase the risk of instability.(5)According to three different landfill instability modes,three typical landfill cases are selected,i.e.Maoershan landfill in China,meethotamulla landfill in Sri Lanka and Xiaping landfill in China.The causes of instability and the slope factor of safety is calculated by geo-studio numerical simulation softwareThe research results of this paper can provide reference for the study of landfill stability and the estimation of leachate production.