Investigation On Geotechnical Properties Of Stabilized MSWI Fly Ash And Engineering Applications

Stabilized fly ash is a product of chelation stabilization of waste incineration fly ash.The stabilized fly ash of pharmaceuticals has small capacity,low cost and relatively mature technology.It has been widely used in China in recent years.After the waste incineration fly ash is stabilized,it can enter the sanitary landfill for landfill disposal.However,the construction of domestic stabilized fly ash landfills has just started,lacking special design standards and specifications,mainly referring to relevant standards and norms of domestic waste landfills.There may be some deficiencies in this approach,and further research is needed on the geotechnical characteristics of stabilized fly ash to better guide the design,operation and management of stabilized fly ash landfills.In this paper,the geotechnical properties of stabilized fly ash at different ages in Nanjing stabilized fly ash landfill were tested.The water quality characteristics of leachate in landfill were also tested.Finally,based on the experimental data,the landfill leachate production evaluation,the drainage layer blocking research and the slope stability analysis were carried out.The main research results are as follows:?1?Drilling sampling and static penetration test of stabilized fly ash landfill,the results showed that the stabilized fly ash's color became deeper and deeper with the increase of the buried depth,and there were individual blocks.The static penetration test index q_c of the stabilized fly ash in the landfill was mainly between 1-4 MPa,fs was mainly between 10 and 80kPa,and fs/q_c was mainly between 1%and 4%.The results are similar to silt.?2?The concentration of heavy metals in the leachate of stabilized fly ash landfill is lower than the pollution control standard of domestic waste landfill?GB 16889-2008?.The Cl concentration was as high as 52700 mg L^-1,which seriously affect the effectiveness of the water treatment process.In addition,the Ca²⁺concentration in the leachate was 6585 mg L^-1,and the COD concentration was 1150 mg L^-1,which will cause a certain degree of biochemical clogging.?3?Laboratory tests were conducted to investigate the geotechnical properties of chemically stabilized municipal solid waste incineration?MSWI?fly ash.The measurements involved grain-size distribution,relative density,water content,moisture retention capacity,permeability coefficient,compression property,shear strength,etc.The mean diameter was in the range of0.8-3.1 mm,which was closed to coarse sand or fine gravel;the non-uniform coefficient and curvature coefficient were in the ranges of 4.56-10.33 and 0.32-0.43,respectively.Hence,the stabilized fly ash was poorly graded.The values of relative density were obtained as 1.68-2.56.The moisture content and moisture retention capacity were in the ranges of 16.6%-46.4%and23.9%-56.7%,respectively.Hence,there is water absorbing capacity for the stabilized fly ash.The permeability coefficient was obtained as 9.1×10^-5-4.5×10^-3 cm/s,which decreased with increasing stress.The primary compression ratio and compression coefficient a_v1-21-2 were in the ranges of 0.13-0.18 and 1.21-1.93 MPa^-1,respectively.Hence,the stabilized fly ash has the property of high compressibility.The cohesive force and friction angle were in the ranges of14.0-19.5 kPa and 32.9-34.2°,respectively.The cohesion is mainly contributed by the cementing properties of the stabilized fly ash.The cementitious structure of the stabilized fly ash might be deteriorated with increasing fill age,which resulted in decreases in grain size,relative density,permeability coefficient and shear strength,and an increase in moisture retention capacity.Comparison analysis was conducted between the present results and the references'data for MSW.Based on the above findings,engineering comments were put forward for the design,operation and management of the stabilized MSWI fly ash landfills.?4?A method was proposed for the prediction of leachate production for the stabilized fly ash landfills,in which the landfill process,rainfall infiltration,preferential flow and moisture absorption property of fly ash were considered.The model parameters were calibrated by using the filed investigating data.The calculated results indicated that the leachate was mainly produced from the rainfall infiltration and waste water for transport vehicles cleaning,accounting for about 48%and 52%,respectively.The results also indicated that the ratio of leachate produced from the preferential flow to the total amount was 34.1%when the volumetric ratio of the macro void to the total void was 20%.Therefore,it is suggested that the stabilized fly ash should be fully compacted in order to reduce the macro void,and the water saving system is also recommended for vehicle cleaning,in order to reduce the total leachate production.?5?A prediction model for the drainage layer of the drainage layer considering the distribution law of the clogging material was established.The model simulation results showed that the COD concentration and leachate flux of leachate were the key controlling factors for the development of the blockage of the drainage layer in the stabilized fly ash landfill.The normal service life of the drainage layer increases with the initial permeability coefficient of the drainage layer and the total opening area of the perforated tube,but the growth trend was gradually flat,and the total volume of the blind trench was linear with the normal service life of the drainage layer.?6?Using geostudio software to simulate the effects of rainfall infiltration,slope ratio,landfill height,platform width,leachate water level and other factors on the stability of stabilized fly ash pile slope.The results showed that the effect of rainfall infiltration on the stability of the slope of the pile was not significant;the safety factor of slope stability decreased significantly with the increase of slope ratio,landfill height and leachate water level;with the increase of platform width,the safety factor of slope stability increased linearly.Among them,1:1.5 slope ratio met the safety requirements,but also achieved a relatively high landfill capacity.It is recommended to set the slope ratio of stabilized fly ash to 1:1.5.