Study On Vertical Expansion Of Municipal Solid Waste Landfill

With the development of Chinese society and economy and the expansion of urban population,municipal solid waste(MSW)has increased substantially,and landfills in many cities are overwhelmed,facing the dilemma of filling up soon and having nowhere to fill the garbage.However,due to urban land scarcity,especially in densely populated cities,land is extremely limited.It is challenging to construct a new landfill to handle increased MSW.Expanding existing landfills is one of the most economical and effective means to solve the shortage of landfill capacity.In this paper,the vertical expansion of the existing landfill is carried out,and it is believed that the settlement and stability of the landfill are important factors that affect the success of the vertical expansion of landfill.The settlement model of the landfill is summarized,and the settlement calculation method of the vertical expansion landfill is proposed.The instability mode and the cause of instability of the vertically expanded landfill are analyzed,and the stability of the vertically expanded landfill is analyzed through Geo-Studio numerical simulation software.Finally,taking Xi’an Jiangcungou landfill as an example,combined with the monitoring projects,the stability control effect of a drainage layer applied in vertical expansion landfill is evaluated.The following conclusions are obtained:(1)Considering that the existing landfill waste is underconsolidated,the settlement of the landfill is divided into two parts:self-weight settlement and additional settlement.The self-weight settlement calculation is based on the main compression model proposed by Sowers,and the leachate level factor is considered.The additional settlement calculation adopts the Gourc model considering the secondary compression caused by mechanical creep and the secondary compression caused by biodegradation.The landfill storage capacity is divided into theoretical storage capacity without considering waste compression and actual storage capacity considering waste compression.The increased storage capacity of landfill is calculated quantitatively,and the definition of capacity increase rate is proposed.(2)According to the position of the slip surface of the vertical expansion landfill,four slope instability modes in the vertical expansion of the landfill are put forward:shallow slippage of the existing landfill,shallow slippage of the expanding landfill,the interface slip between the existing and the expanding landfill,and deep slippage passes through the foundation soil.The analysis shows that the reasons for the instability and destruction of the vertical expansion are:the leachate level in the existing landfill is high;the height of the expanding landfill is too high;the shear strength of the interface liner is low;and the foundation bearing capacity is insufficient.(3)The stability of the vertical expansion landfill is analyzed by Geo-Studio numerical simulation software,and the relationship between the safety factor and the leachate water level height and the vertical expansion height is analyzed.The results show that the safety factor of the landfill,the height of the leachate water level and the height of the vertical expansion can be fitted to a nonlinear curved surface equation,and the correlation coefficient R~2 is 0.988.The safety factor of landfill decreases as the height of leachate level increases,and the relationship between the landfill safety factor and height of leachate level can be fitted to a logarithmic relationship.The safety factor of the landfill decreases as the vertical expansion height increases,and the relationship between the landfill safety factor and the vertical expansion height can be fitted to a linear relationship.(4)Taking the Xi’an Jiangcungou Landfill as an example,the self-weight settlement is 16.24 m,the additional settlement is 13.38 m,the total settlement is29.62 m,the actual monitoring settlement is 27.5 m,the error height is 2.12 m,and the error ratio is 0.76%.The capacity increase rate is 26.44%.Considering the influence of leachate water level height and vertical expansion landfill height,the overall safety factor of landfill is calculated to be 0.94～1.58.After laying the leachate drainage layer,the surface displacement rate did not exceed the warning value,and the maximum daily displacement was 33%～50%of the non-drainage layer,and the leachate level was effectively reduced,thus improving the stability if the vertical expansion landfill.This paper takes the Xi’an Jiangcungou Landfill as an example.On the basis of the existing landfill,the vertical expansion of 30 m landfill can increase the storage capacity 28.8 million tons.When the leachate water level is 15 m from the surface,the safety factor of the 30 m vertical expansion of landfill is 1.45,and the landfill is in a stable state.The calculation and analysis of this case can provide reference for similar vertical expansion projects.