Study On Permeability And Water Storage Performance Of Recycled Graded Gravel Layer

With the advancement of urbanization in China,some places have entered the peak period of construction and development,and the amount of construction waste generated has also increased significantly.At the same time,the unrestricted hardening in the process of urban construction has caused cities to "not absorb water and store water," exacerbating the urban heat island effect.The construction of a sponge city can absorb and store water when it rains,and "release" and use the stored water when needed.This requires a large amount of graded crushed stone as a permeable layer,and the application of high-absorbent construction waste in the construction of sponge cities can realize the recycling of urban resources and is of great significance.This article focuses on the study of the water permeability and water storage performance of the recycled graded gravel layer for sponge cities.Using the self-designed test device and test method,the permeable water storage state of the gravel layer at different times during simulated precipitation was studied.By changing the aggregate type,aggregate grading,and initial state of the aggregate(dry or wet),the effect of aggregate properties on the overall water storage and permeability of the aggregate is studied;By changing the thickness,compaction degree,packing method(layered or mixed according to particle size)of the crushed stone layer,the influence of the crushed stone layer structural parameters on the overall water storage and permeability of the crushed stone layer was studied.;Based on the above experimental results,the relationship between the water storage capacity of the gravel layer and the void structure,and the relationship between the water permeability and water storage capacity were discussed.The main conclusions are as follows:(1)In the case of simulated precipitation,the change of water storage in the gravel layer can be summarized as follows: the initial precipitation is absorbed by the gravel layer,and the water storage volume rises at a uniform rate.As the amount of precipitation increases,the gravel layer begins to permeate and the rate of permeation gradually increases,and the amount of water storage begins to decelerate and rise.When the water penetration rate is equal to the precipitation rate,the precipitation permeation reaches equilibrium,and the water storage capacity is almost unchanged.After the precipitation stopped,the water storage in the gravel layer began to decrease and the rate of decrease gradually slowed down until the water storage stabilized.(2)The volumetric water storage rate of the recycled aggregate crushed stone layer can reach 15% ~ 30%,which is obviously better than that of natural aggregate 2% ~ 15%.This is because the use of recycled aggregate does not affect the void storage between aggregates In the case of water capacity,the aggregate's own water absorption capacity is obviously increased,thereby increasing the water storage rate of the gravel layer;The water-permeable capacity of recycled aggregate is weaker than that of natural aggregate gravel,and the water permeability coefficient decreases with the increase of the recycled aggregate content;After 24 hours of precipitation,the wet reclaimed aggregate gravel layer can still store water for 2% to 4%.(3)The water storage rate of the recycled aggregate layer with a particle size of less than 5 mm can reach 30%,which is 2 to 3 times that of coarse aggregate,and its water permeability is much smaller than that of coarse aggregate crushed stone layer;Diameter layered packing can increase the water storage rate of the crushed stone layer;compaction can reduce the total void rate of the crushed stone layer by 5% ~ 10%,the water storage rate by 3% ~ 5%,and at the same time significantly reduce the permeability coefficient;The layer thickness has little effect on the permeability coefficient and volumetric water storage rate of the gravel layer.(4)The water permeability and water storage capacity of the crushed stone layer are always in a negative correlation,and the permeability coefficient of the crushed stone layer with a particle size of not less than 2.36 mm is sufficient to meet the requirements of the specification for permeable materials.Therefore,according to the existing test and analysis results,it can be preliminarily believed that under other circumstances,the "water permeability" can be reduced within the allowable range by reducing the particle size,changing the gradation,layering the filler and compacting.,In order to maximize the effect of "storing" the gravel layer.