Study On The Characteristics Of The Mixture Of River Sand And Construction Waste In Filling Subgrade

In recent years,with the rapid development of urbanization,large construction waste emerges in the procedure of the reconstruction of old city,city village and shantytown,most of which are shipped to the suburbs or rural areas without any treatment and then are stacked in the open air or buried simply.The traditional treatment measure causes destruction to the urban environment and pollution to groundwater.What's more,failing to reuse the construction waste is of a great waste because construction waste can be treated as renewable resources.On the other hand,the shortage of the landfill material for subgrade continues to grow.In the past,river sand can be treated as appropriate landfill material for subgrade.However,with the increase of mining depth,the river sand becomes too fine to satisfy the requirement of engineering.In order to solve the two problems above,the mixture of river sand and construction waste with different proportions are treated as subgrade landfill material.Laboratory tests and numerical simulation are carried out to study the engineering performance of the mixture.In this paper the construction waste is taken from the engineering of the old village reformation of Liuzhiyuan village in Ji'nan.The construction waste after being smashed is mainly composed of brick and concrete and the proportion of the brick and concrete is about 7:3.The specific gravity value of the construction waste is about 2.72.The water absorption value is 5.35%.The crushing value is 38.07%.The specific gravity value of the river sand tested in this paper is 2.66 while the mud content is about 3.2%.The mixture of river sand and construction waste are divided into five kinds.Each kind is set up into different ratio with 10:0,8:2,6:4,4:6,2:8 and respectively named Sample A,Sample B,Sample C,Sample D and Sample E.To study the physical and mechanical properties and road performance of the mixture,laboratory tests are carried out.With the help of finite difference software FLAC3D,the anti-liquefaction performance and settlement deformation characteristics of the mixture are studied by numerical simulation.The results are shown as following:(1)Through laboratory tests,the physical and mechanical properties of the mixture are studied.The main tests contain the screen test,the specific gravity test,the compaction test,the permeability test,the capillary rise test and the direct shear test.According to the test results,the physical and mechanical properties of the mixture can be sorted as following:Sample C?Sample D>Sample E>Sample B>>Sample A.(2)To study the road performance of mixture,the compaction characteristic,the bearing capacity characteristic and the dynamic strength characteristic of the mixture with different ratio are discussed by carrying out compaction test,CBR test and dynamic triaxial test.The test results show that the road performance of different samples can be sorted as following:Sample C>Sample D>Sample B?Sample E>>Sample A.According to ranking of both physical and mechanical properties and road performance,the engineering performance can be sorted as following:Sample C>Sample D>Sample B?Sample E>>Sample A.(3)The liquefaction reaction of the mixture with different ratio under the designed seismic in the eight degree seismic area(Linyi,Shandong,China)is simulated by the finite difference software FLAC3D.The simulation results show that the subgrade backfilled with only river sand has the highest liquefaction risk and fastest liquefaction speed.As the proportion of construction waste rises,the liquefaction risk of the mixture declines and there is little liquefaction risk when the ratio of river sand and construction waste is 6:4.The anti-liquefaction performance can be sorted as following:Sample E?Sample D>Sample C>Sample B>Sample A.(4)The construction procedure of subgrade filling is simulated using the finite difference software FLAC3D.According to the simulation result,the construction speed of the mixture with ratio of 10:0 and 2:8 should better not fast than 0.25 m/day.For the mixture with ratio of 8:2,6:4 and 4:6,the maximum filling height should be less than 0.20 meter per day.The results of laboratory tests and numerical simulation show that adding certain construction waste into the river sand can improve the engineering performance of the river sand.The improvement of the performance reach the peak when the proportion of construction waste is about 40%-60%.The mixture of river sand and construction waste has good prospects for application.