Recycling In Subgrade And Dynamic Behavior Of Construction Waste And Silt Mixture

Infrastructure construction and urbanization are often accompanied with the demolition of old buildings,along with a large number of construction waste which is difficult to dispose of.In order to solve the problem of construction waste,the General Office of the State Council issued”the Circular on Issuing the Work Program for the Pilot Project of‘Waste-free Cities'Construction”.By2020,the construction index system of"Waste-free Cities"will be established systematically,and the comprehensive management system and technical system of"Waste-free Cities"construction will be explored and established.In the Dajiangdong industrial agglomeration area of Hangzhou City,Zhejiang Province,road construction projects are mainly facing two problems:difficult disposal of demolished construction wastes along the road and shortage of traditional road construction materials.Dajiangdong area is located in the Qiantang River estuary,where Holocene alluvial silt widely distributed.The silt shows the regional characteristics of"high silty and low viscous",which is not suitable to be directly used as roadbed filling material.In order to effectively utilize the resource attributes of construction waste,a new material called“cement-treated silt-construction waste mixture”is proposed in this paper,which aims to substitute the traditional slag material for road embankment filling.As a new road-building material,the mixture must meet the physical and mechanical requirements of road-building materials in relevant codes,meanwhile,it should be able to maintain stability under long-term overload traffic loads.Therefore,this paper takes the mixture material as the research object,systematically explores the road performance and dynamic response of the mixture material under different construction waste proportion?CWP?and cement content ratio.Then the long-term deformation of the mixture material under traffic load is predicted by numerical method.The main research contents are as follows:?1?The maximum dry density,unconfined compressive strength and CBR value of mixed filler with different proportions were determined with cement content and CWP as variables?cement content is 0%,2%,3%,4%,5%,waste content is 0%,30%,50%,70%?.The changing rules of each index under different cement content,CWP and curing age are discussed.The test results show that the mixed filler reaches the optimum proportion when the CWP is 50%and the cement content is 5%.At this proportion,the maximum dry density is 2.00 g/cm3,the unconfined compressive strength of 28 d is 0.66 MPa,and the CBR value is 439.70%,which meets the requirements of embankment materials in the code.The mechanical properties of composites increase with the increase of cement content,shows the trend of first increasing and then decreasing with the increase of CWP.?2?The dynamic properties of composite materials with 5%cement stabilized silt,50%waste and 5%cement content under field conditions are studied through dynamic triaxial tests.The test results show that the dynamic strength of mixture is better than that of cement-treated silt.According to the critical dynamic stress?corresponding failure dynamic stress at 2000 cycles?,when the overload rate of standard truck reaches 169%and 200%respectively,the stable silt and composite materials will be damaged under long-term overload traffic load.The Monismith cumulative plastic strain index model is used to fit the cumulative plastic strain-vibration curves under various amplitudes,obtain a good fitting effect.The variation rule of the model parameters with the waste mixing ratio is given in this chapter.?3?Uniaxial compression test platform and biaxial servo test platform are developed to simulate unconfined compressive strength test and dynamic triaxial test by using PFC^2D particle flow software.By adjusting the contact parameters and the proportion of particle groups,the variation of strength and dynamic strength of composites under different CWP is discussed.From the simulation results,the mixed filler has the best static properties when the CWP is 50%,and the mixture has the best dynamic properties when CWP is 50%?70%.?4?in order to correctly relect the dynamic properties of materials,a dynamic constitutive model is established by UMAT in ABAQUS.The deformation of mixed fillers under different vehicle loads and different layers of use also been simulated.From the simulation results,the cumulative deformation of the mixed filler shows a stable development law after rapid accumulation with the number of cycles.When it is used as embankment filling material,the maximum cumulative deformation of standard truck,50%overloaded and 100%overloaded is 5.74mm,7.07mm and7.90mm respectively at the top of the embankment;when it is used as roadbed filling material,the maximum cumulative deformation of standard,50% overloaded and 100% overloaded is 16.40mm,20.60mm and 24.70mm respectively at the top of the roadbed.