Service Performances Prediction And Pollution Migration Of Subgrade Built With Construction Waste Recycled Material

Building the embankment with recycled aggregates processed from construction and demolition waste(CDW),is not only helpful to consume CDW effectively,but also relieve the problems of environmental pollution caused by mountain quarrying for road construction,and large amount of sources materials for subgrade filling.However,CDW is a kind of mixture with great variability in its compositions.It contains a large amount of brick slags,and easy to break under the impact of traffic load.Thus,it is difficult to estimate the service performance resilient modulus.Furthermore,the construction waste contains pollution sources,which may affect the surrounding environment when used for subgrade filling.Based on the material properties of recycled aggregates,such as particle breakage,water retention,resilient modulus and pollutants migration,some researches of service performances prediction and pollution migration law of subgrade built with construction waste recycled materials were carried out in this paper by laboratory experiments and numerical calculation,the main results are as follows:(1)Construction waste recycled materials with different gradations and components were designed first by investigation.From the perspective of particle breakage and maximum compaction,the matching degree of various laboratory specimen methods,static compressure,compaction and vibration compaction,were analyzed with the actual project,and the optimal specimen forming method was determined.From the view of subgrade application,the relative breakage rate Br was calculated quantitatively by constructing hyperbolic model in the dynamic cyclic loading tests.Based on the fractal theory,the fractal dimension value calculation formula of stable gradation of recycled materials was proposed,and it provided a basis for the calculation of stable gradation of recycled materials.(2)The SWCC of recycled aggregates under multiple working conditions were studied by using soil-water characteristic curve(S WCC)rapid testing equipment,the effects of gradation,composition,compaction degree and overburden stress on the water retention properties of recycled aggregates were analyzed.Then the prediction model of SWCC of recycled materials related to stress was proposed,and it was used in the constitutive equation of the numerical model.Combined with the rewriting method of weak partial differential equation,the calculation of the humidity field of the recycled aggregates subgrade under the condition of stress-humidity coupling was realized,and the evolution law of humidity field inside subgrade during the operation period was analyzed.(3)Based on dynamic triaxial test,the prediction model of resilient modulus of recycled material considering the physical state was established.And the numerical model of the recycled aggregates subgrade was established,and the distribution law of the resilient modulus in the recycled aggregates subgrade was obtained.The influences of different pavement structures,designed speeds and gradations of recycled materials on dynamic resilient modulus were analyzed.Based on the principle of equivalent bending modulus,a method for predicting equivalent structure resilient modulus of recycled aggregates subgrade was proposed.Simultaneously,the prediction model of dynamic elastic modulus considering particle breakage was proposed.According to the distribution law of relative breakage index,the grading dimension value of each layer of subgrade under stable state was obtained,and it supplied a reference for the stable grading design of subgrade materials.(4)By scanning electron microscope(SEM)test after sampling different components of recycled material,three typical pollution elements(cadmium,lead and arsenic)were selected as the research object.In the single and multi-layer soil column leaching test,the precipitation characteristics of pollutants in recycled soil column under different compaction degree,composition and gradation conditions were studied.With the numerical calculation method under the condition of multi-physical field coupling,the migration law of the target pollution elements in the unsaturated subgrade under three gradations was analyzed.Referring to the pollutant distribution at the characteristic interface of the subgrade bottom and the vertical surface of the slope foot,the sensitivity of the dispersion coefficient of subgrade and foundation,the initial pollution concentration in the numerical model were carried out.The research results provide theoretical basis for the migration and prevention of pollutants in recycled materials.