| With the continually accelerating urbanization and rapid urban development,there are great changes in cities,and meanwhile,soil,vegetation and other original underlying surfaces of natural land are replaced by lots of urban gray infrastructures made from reinforced concrete.The change in urban underlying surfaces leads to the increase of in permeable surfaces in cities and the increasing runoff coefficients of rainfall,and then rainfall resources cannot penetrate to recharge groundwater timely and efficiently,so it leads to increasing volume of rainfall runoff,increasing peak flow,serious pollution and frequent flood disasters.As one of the main underlying surfaces in cities,urban road system has the characteristics of large area and high use frequency,and road runoff problems must be solved as soon as possible.Low impact development is a new ecological storm water and flood management concept,and the low impact development and construction of urban road systems is feasible and essential to some extent,with many construction advantages and characteristics,so it will become a trend for the ecological and sustainable development and construction of urban road systems.There are not many researches about the low impact development and construction of the road system in Chongqing,and especially,the number of the researches from the perspective of planning,design and application is quite limited.The paper gives a brief introduction about the research and construction background of low impact development for the road system in Chongqing and introduces some storm water and flood management problems in the current urban road systems as well as the development opportunities,feasibility,urgency and necessity of low impact development and construction for road systems;and besides,the paper also summarizes the development and construction of roads and their drainage systems in Chongqing,the basic researches on low impact development concepts and the relevant theoretical and practical studies in China and other countries,to provide references for the low impact development and construction of the road system in Chongqing.The paper regards the characteristics of rainfall and slope in Chongqing as the starting point,selects the facilities of low impact development suitable for the road system in Chongqing including bio retention zone,ecological tree pool,low elevation greenbelt,permeable pavement,grass swales and focuses on studying the structural parameters and adjustment construction according to the characteristics about the roads in Chongqing,determines the thickness of the different structurallayers of the facilities,and proposes suggests from the soil,plants,slope and other aspects of the facilities' construction,to provide some references for the planning,design and applications of low impact development for the road system in Chongqing;In addition,the paper also studies the selection and construction of rainwater regulation and storage devices around the roads in Chongqing,to supplement and perfect the low impact development and construction of the road system in Chongqing.In the research,651 road sections of main urban area in Chongqing are investigated,and expressways,arterial roads,secondary trunk roads and branch ways are divided into different forms through combining the existence of seeded strips and the features of trees on both sides of various roads in Chongqing from the perspective of urban storm water and flood management,to make the planning and design of low impact development for the road system in Chongqing become more suitable for the characteristics and current construction situation of roads in Chongqing,which also can make the research become more targeted;what's more,the paper also divides the road grade of Chongqing into three scopes through combining it with relevant code requirements and status surveys,including 0.5%-3.0%,3.0%-6.0% and >6.0%,and discusses the influence of different grades on the rainfall runoff and low impact development and construction of roads.The increase of slope caused the increase of rainwater runoff,and caused some scouring of the surface of the facilities.The paper sums up and learns from the experience and deficiencies about the low impact development and construction of existing road systems,puts forward a planning and layout pattern suitable for different road forms in Chongqing in accordance with the hydro logical analysis on the roads in Chongqing,makes full use of road sidewalks to plan the permeable pavement,the use of green space to build low impact development facilities,and studies the cohesive relations among different parts in the low impact development and construction for the road system of Chongqing.Among the different parts,rain through the flow,concentrated convergence and appropriate drainage for effective convergence,and a suitable planning and layout pattern can be learnt and applied in the low impact development and construction of road system in Chongqing in future.The paper studies the design scale of the low impact development facilities for the road system in Chongqing,determines a design method combining formula deduction with model simulation for various facilities,applies it in the design calculation for the low impact development facilities of different forms of roads in Chongqing,determines the design scale of low impact development facilities for various roads:sidewalks pavement layout permeable pavement,and other low-impact development facilities are based on the design of rainfall targets and rainwater runoff to determinethe design scale,and simulates their rainfall runoff processing capacity under different rainfall conditions.The combined application of calculation methods provides more rigorous and precise design methods for the study on low impact development facilities,clarifies the design scale of low impact development facilities for the road system in Chongqing and verifies its good rainfall runoff processing capacity and coping capacity for different rainfalls.In addition to that,the paper also introduces the planning background and basic information about Yuelai New District,selects some suitable sections for site analysis,determines construction objectives,the rainwater runoff treatment capacity of the road system in Yuelai New District should reach 80% of the total annual runoff control rate and try to restore the hydrological condition of the natural state.The paper investigates the main roads in the area as well as the current situation about their low impact development and construction,evaluates and summarizes the effects and deficiencies of current construction.If it is allowed under the current construction conditions,the theories about the study on the adjustment construction,planning and layout pattern and design scale of low impact development facilities for the road system in Chongqing shall be applied the low impact development and construction for the road system of Yuelai New District,and relevant simulations and discussions are carried out about its construction effects.In fact,a reasonable planning and design can improve the rainfall runoff processing capacity of the low impact development and construction for the road system in Yuelai New District and provide references for the planning,design and construction of low impact development for the road system in Chongqing,to develop a good pilot construction demonstration area.The research provides rational and correct analysis methods for the planning,design and construction of low impact development for the road system in Chongqing,shows the feasibility of the research and construction,and obtain some conclusions and achievements in basic study,planning,layout and design calculation for the low impact development of road system in Chongqing,which can solve rainfall runoff control problems in the road system of Chongqing effectively and show the comprehensive benefits of road construction in Chongqing,with a broad application prospect and great promotional values. |
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