| With the increase of urban population,the scale of municipal solid waste landfill is becoming larger and larger,which leads to the urgent need to expand the capacity of landfills.Geotextile reinforced earth dam is used as the retaining structure in Dameishan(pseudonym)Municipal Solid Waste(MSW)Landfill.The height of the dam is raised from 20 m to 35 m,and the downstream slope of the dam reaches 42.3 °(vertical: horizontal: 1:1.1).Compared with the domestic and foreign waste dam engineering examples,the dam has the characteristics of high height,steep slope,full section geotextile reinforcement,especially the use of cohesionless gravel as dam material.Because there are few similar projects in the past,and the understanding of its deformation characteristics and stability is not deep,the design of this project has great challenges.Combined with the follow-up consultation of the project’s stability evaluation,this paper studies the deformation characteristics and stability characteristics of the retaining dam,deeply discusses and summarizes its internal mechanism,so as to provide certain scientific basis for the design and construction of this project and similar projects in the future.The specific research work of this paper includes centrifugal model test,monitoring data analysis,static and dynamic finite element numerical simulation,slope limit equilibrium analysis.The main research results are as follows:(1)The dam with high steep reinforced graded crushed stone is adopted for the first time in Dameishan landfill,which is successful in practice.It shows that it is technically feasible to dam with reinforced graded crushed stone for retaining the waste dump.This project provides a new technical means for the construction of retaining dam in the future.The follow-up study and consultation work of this paper play an important role in the smooth construction of the project.(2)According to the analysis of monitoring data,the displacement of reinforced graded broken stone dam mainly occurs in the filling construction period.During the construction period,the maximum horizontal displacement of the dam body is 74.3mm,which occurs below about 1 / 3 of the dam height,and the maximum vertical displacement(settlement)of the dam body is 34.4mm,which occurs above 2 / 3 of the dam height.(3)The overall stability of the reinforced gravel dam is closely related to the strength of the reinforced materials and the leachate level of the landfill.For this project,when the strength of the reinforced material is not less than 70%(that is,70% of the long-term design strength of134 kn / m,and the long-term design strength is reduced by 1.91 times from the short-term ultimate strength of 256 kn / M),the integrity of the reinforced retaining dam is good,the safety factor is greater than 1.35 required by the specification,and the most dangerous potential sliding surface is located at the interface between the new and old dam(the reinforced area is not easy to be damaged).When the strength of geotextile is less than 70% and the leachate level is too high,the stability coefficient is slightly lower than 1.35,and the most dangerous potential sliding surface is located in the reinforced dam.During the construction period,the tightness of geotextile should be controlled.During the operation period,attention should be paid to ensure the drainage of leachate in the garbage body and prevent the water level of leachate from being too high.(4)Based on the field monitoring data,it is found that another failure mode of reinforced retaining dam is horizontal sliding between layers of geotextile.When the waste pile behind the dam is unstable and sliding,excessive horizontal thrust will act on the upper part of the retaining dam,which may cause horizontal sliding in the upper part of the retaining dam.At this time,the layer between geotextile and soil(gravel)becomes a weak surface,which is the most dangerous form of destruction.For this kind of gravel reinforced dam,special attention should be paid to prevent the large slip of the landfill itself during the operation of the landfill.In the design of reinforced gravel dam,the horizontal sliding of the upper part of the dam under the action of garbage heap should be taken as a working condition for stability checking.(5)Under the horizontal earthquake,the peak acceleration of the dam crest is about 2.03 times of the peak acceleration of the dam foundation input earthquake,showing an obvious "whiplash effect";when the seismic wave propagates upward,the time lag of the peak acceleration of the dam crest is smaller than that of the peak acceleration of the dam foundation input earthquake;the horizontal vibration of the dam body presents a first-order horizontal bending vibration,and the acceleration and acceleration of the dam body are smaller than that of the dam foundation input earthquake The results show that the displacement increases monotonously along the dam height,and the horizontal reinforced geotextile can improve the overall stiffness of the dam,which makes the deformation of the middle and upper parts of the dam smaller and more evenly distributed.The anti sliding stability coefficient of the dam under7 degree earthquake is about 10% lower than that under static force. |
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