The Research Of Road Retention Band Based On Sponge City Concept

During the construction of traditional urban road,the control concept of road runoff is to quick eliminating and concentrating at end.When heavy rain occurs,it is easy to cause urban waterlogging disasters,and deterioration of water quality of receiving water.Transforming road green band to road retention band is the most promising prospect of low impact development(LID)facilities in Sponge city,its control concept of road runoff is to slow discharge and separation at beginning.It has the function of reducting the road runoff and removing the pollutant of road runoff.This paper presents a design process of road retention band facility,then simulating and analyizing its runoff reduction performance and pollutant removal performance.Using the main skeleton void volume filling method to design the grading of filling soil in the retention Band,getting its soil characteristic parameters,and using empirical formula to predict its saturated permeability coefficient with the test of permeation experiment.Using the soil column infiltration experiments to get filling soil's BMPs efficiency of various pollutants.Then,simulating the rainfall infiltration process of unsaturated filling soil by the ABAQUS soft,to analyizing changing situation of its saturation and porewater pressure under the steady rainfall intensity,getting its average matric suction on the wetted front.Integrating the soil characteristic parameters from the design,experiment and simulation above,modelling single road retention band in SWMM,analyzing the change conditions of its runoff soil infiltration rates,overflow rates,closed drainage rates of the model on different runoff design flow.Then,summarizing the transfer mode between road retention band and its affiliated facilities,as well as its transverse section and plane layout form.Finally combining with practical engineering cases to modelling the retention facilities on actual road area,to the retention facilities with different permeability,simulating its total runoff volume,peak runoff rate,peak time of the entire model under different repetition period of rainfall,and the pollutants concentration changes of NTU,COD,TN,TP.The results show that road retention has slow-releasing and purifying water quality to road runoff,the permeability of packing soil is the the key factors of its runoff reduction and pollution removal performance.Increasing the permeability of the soil,which is beneficial to improve the runoff reduction performance,but it will reduce the pollution removal performance,so to the design,it has to combine the actual engineering situation to coordinatt of these two factors.Considering this article research result,when it is to design the gradation of packing soil,it is recommended that its saturated permeability coefficient should be between 6-10 mm/min.In conclusion,for the design of road retention band in sponge city,this paper proposes its design model,the design method of packing soil gradation,and the evaluation method of the road retention,analyzing and summarizing the influence of filling soil permeability on the water quantity and water quality problem,the aim of the paper is to provide a reference for materials and structural design of sponge city road Retention Band Facility.