| With the rapid development of economy and the improvement of urbanization of our country,the amount of municipal solid waste and landfills have increased dramatically.Due to the characteristics of high-pile and large-volume,the complicated components of refuse and the high water level of leachate,environmental pollution and slope stability are easily caused,it is of great significance to study the heterogeneous,seepage field and stability of landfill.Around the landfill "heterogeneous",in this paper,the distribution characteristics of waste properties in time and space domains are statistically analyzed,and the establishment methods of heterogeneous saturated unsaturated seepage model,guide and drainage layer silting and blocking model and heterogeneous stability model considering the landfill process are proposed,and then the flow law of leachate and slope stability are analyzed.The main findings of this paper are as follows:(1)From the statistical point of view,the distribution law of the heterogeneous characteristics of waste pile is studied,and the temporal and spatial distribution of the physical components,unit weight,permeability,cohesion and internal friction angle of waste are revealed,as well as the interaction between various factors.The composition of waste is influenced by national policy,climate,life style,region and time.The content of organic matter in landfills in developing countries is about 75-97%,and the content of kitchen waste is as high as 60%,which directly affects the content of waste water and the level of landfill leachate.With the increase of burial depth,the pressure and degradation degree of garbage increase,which makes the inorganic content increase and the density increase,and the void ratio and saturated permeability coefficient decrease.There is a strong negative correlation between cohesion and internal friction angle of landfill.With the increase of burial depth,organic compounds such as plastics and fibers degrade,which makes cohesion of landfill reduce and internal friction angle increase(2)Based on the principle of saturated-unsaturated seepage of heterogeneous soil,a method of establishing seepage model considering the characteristics of heterogeneous seepage and the process of filling is proposed.At the same time,the model of silting and blocking of the drainage layer is established,which can not only calculate the water level distribution of the seepage liquid in the actual process of silting and blocking of the drainage layer of the landfill,but also be applied to the distribution of the permeability coefficient of the drainage pipe on the sand ground and the drainage of the tailings pond pipe silting and other similar projects.The influence of rainfall intensity,guide layer,middle cover layer and garbage permeability coefficient distribution on the seepage field of landfill unit have studied,and the formation reason of the stagnant water level and the factors affecting the stagnant water level height are obtained.Considering the heterogeneity of waste,it can be regarded as dividing waste pile into infinite layers.The maximum perched water level is large,which is unfavorable to the stability of landfill.Therefore,the selection of permeability coefficient and distribution of landfill permeability is the key to the analysis of landfill seepage field(3)Combined with the distribution law of shear strength of landfill,a method of building heterogeneous finite element model about the unit weight and shear strength of garbage is put forward.Through research,it is found that the distribution of unit weight and shear strength of waste has a great influence on the stability of slope,especially in the early stage of landfill,the unit weight change rate of waste is large.The effects of slope height,ratio of slope thickness to height,ratio of slope thickness to height,unit weight,shear strength and water level of leachate on slope safety coefficient are studied.When the ratio of slope thickness to height is large,three-dimensional slope can be simplified as two-dimensional plane strain problem.Under the same conditions,the safety factor of three-dimensional slope is slightly larger than that of two-dimensional slope.When the water level of leachate increases to a certain height,the difference between the two is small,and the water level has a greater impact on the safety factor than the slope thickness.A series of safety coefficient charts are given through calculation Under the condition that each parameter is determined,the range of safety coefficient of landfill slope can be predicted preliminarily,which provides basis for the early design of landfill(4)Taking the Xi'an Jiangcungou Landfill as the research object,the saturated-unsaturated transient model of heterogeneous waste is applied to practical engineering.Considering the landfill process and heterogeneous permeability,the calculated maximum water level is higher.Compared with the homogeneous material,the difference of the water level of each waste layer is about 0.08?1.88 m,which is not good for the stability of the landfill.At the same time,the development law of the heterogeneous waste unit leachate is verified,which provides a basis for the design of the landfill dewatering and safe operation.In the landfill,the water level of leachate is high and there is multi-layer stagnant water level.The guide and drainage layer can only reduce the stagnant water level of the current garbage layer better,and the stagnant water level drops about 0.52?1.38 m,while the other garbage layers have less impact due to the barrier of covering layer.In the actual landfill,guide and drainage pipes should be set at the bottom of each layer of garbage or vertical wells should be used to reduce the stagnant water level.(5)Combined with the engineering characteristic distribution of Xi'an Jiangcungou Landfil,the heterogeneous stability model is applied to the actual project to study the influence of different unit weight and shear strength distribution on the landfill stability.The model is also applicable to complex terrain,geomembrane or multiple strata.It is found that the mechanical properties of refuse have great influence on the stability of landfill slope,especially the shear strength distribution plays an important role in determining the type of slope instability and the position of sliding surface.Considering the water free condition,the calculation results show that the landfill has no instability under various gravity and shear strength distribution,and the safety factor is 1.363?1.794.Considering the perched water level of the landfill,the downstream waste dam has landslide,and the safety factor is 1.109,which needs to be reinforced.Through the analysis of the slope stability of the three-dimensional landfill,it is found that the slope of the reservoir bank is steep and prone to instability.During the operation and management of the landfill site,the stability of the slope of the reservoir bank should be paid attention to while considering the capacity of the landfill.If necessary,the bank slope should be strengthened or the slope ratio improved. |
PDF Full Text Request