Road drainage design featuresAbstract: With China's rapid economic and social development, road construction has entered a rapid development period. However, increasing traffic and load cases, the use of traditional materials and construction techniques into the road pavement in use revealed many problems, especially in the southern rain-fed areas, roads, water and surface water damage to the phenomenon of performance was very prominent. This has become so foreign road construction of a major difficulty. Therefore, the conventional asphalt concrete pavement in both the design and construction process needs to be improved on. The porous asphalt concrete pavement is adapted to the needs and developed a new type of pavement structure, is particularly suitable for wet areas. This paper briefly studied.Keywords:porous asphalt concrete, pavement, mix design, construction techniques, quality control1 BackgroundWith China's rapid economic and social progress, and infrastructure are also at an unprecedented pace, highway construction is the construction of infrastructure facilities one of the key. As of the end of 2005, highway mileage has more than 41,000 km. Although with the new materials and construction process optimization, continuous improvement of the quality of asphalt pavement, but there is still a considerable part of the asphalt concrete pavement in the process of using a certain degree of damage occurring phenomenon, especially because of a combination of factors caused the early ( with 3 years or so) damage, resulting in the use of asphalt pavement performance and life often achieve their design level, has a serious impact on road transport normal functioning, causing huge economic losses, but also to some extent hampered the development of highway. Past road damage in the form mainly as rutting, low temperature cracking and fatigue cracking, while the use of a semi-rigid pavement structure and the quality of the asphalt mixture has been effectively mitigated. But the damage in the form of water damage is replaced, a troubled company developed a new issue of highway. Especially in the rainy areas in southern China, the highway in the spring melt season, the rainy season and the rainy season, the road will appear Ma surface, loose, and even out the grain pits, this dramatic early destruction, is that people anticipated.2 of water damageWater damage to asphalt pavement problems, the first thing comes to highway drainage system. In order to ensure the stability of roadbed, good road safety performance and driving, highway drainage facilities are set up well to rule out road sector within the scope of surface water and groundwater. Highway drainage from the road sector, the general surface drainage, surface drainage and underground drainage within three parts. Road surface drainage sector, including road surface drainage, drainage and slope the median drainage. Within the porous pavement surface drainage, including drainage,road drainage and permeable edge primary drainage. Underground drainage including sewer, ditches, underground drain or underground pipe. Research shows that setting a good drainage system, can improve the life of asphalt up to 30% or more. In contrast, poor drainage asphalt pavement, which is usually caused by premature destruction of the surface layer of pavement structure in water-saturated state, and traffic caused by heavy vehicles. Any layer of pavement layer, or soaked in a saturated state, will lead to lower structural layer strength, speed up the road the emergence and development of various diseases. Water damage to asphalt pavement from water, surface water infiltration is possible only lead to stripping of asphalt film and aggregate, resulting in road damage. Therefore, the seepage of asphalt pavement will produce key indicators of water damage. It should be said to increase the seepage coefficient index for improving the quality of construction of asphalt pavement, preventing water damage is important. The porous asphalt road surface drainage system is based on the above characteristics and developed a new type of road pavement structure. Drainage asphalt pavement, also known as permeable asphalt pavement, the surface layer is also known for porous asphalt wearing course; refers to the compacted porosity of 20%, the mixture can form a drainage channel within the new asphalt concrete surface layer, its real mechanism for the formation of the skeleton in accordance with embedded crowded - gap structure of open-graded asphalt mixture. Its characteristics are: first, the rain can prevent the formation of road surface water film, sliding performance, improve road roughness, vehicle slip resistance; to eliminate or reduce the rear water flowers, and raise the driver's line of sight of the definition to improve traffic safety; second, high temperature stability, resistance to rutting ability; third, with light and glare to reduce traffic noise and other functions. Seen with both environmentally friendly road drainage, and many characteristics conducive to traffic safety, in line with current technological developments and social trends.3 research statusSince the 1960s, some European countries such as Germany, France, Britain and Italy have proposed a porous asphalt pavement concept, and started research on the asphalt material, made a lot of useful results, thus contributing to the technology the application. European research and development is a first porosity as high as 20% to 25%, a thickness of 4 ~ 5cm of the wear layer. As porosity, water can penetrate into the road, connected by a road in the discharge gap to the edge of the road. There is no rain so thick water film, to avoid the "hydroplaning" generation, but also no longer appears splashing, and effectively to ensure traffic safety. Because of this multi-gap can quickly drain the road, so called porous asphalt pavement. So far European countries porous asphalt pavement research and the use of more than 30 years, part of the state asphalt pavement drainage area of about road accounted for 10% or more. European countries the choice of the asphalt material to reach a basic consensus is to use the modified asphalt, and mainly consider the following requirements: have a good high temperature stability, low temperaturecracking resistance and oxidation resistance. Notify the United States in 1973 recommend the use of open-graded the country sliding wear layer surface, significantly reduce the rainy day "hydroplaning" phenomenon, have achieved good results. Into the late twentieth century, countries on the application of porous asphalt pavement technology research entered a new phase of highway projects in the U.S. long-term performance of road projects there is a special porous asphalt material for the large experimental study of sub-surface ; in the United States in 1990 TRB Annual Meeting held in Washington, the main issue is the drainage of the asphalt material in road engineering experience. In the same year, the U.S. Federal Highway Administration has developed. Sliding surface of open-graded asphalt mixture design method was surface porosity, thickness and major functions are described. The United Kingdom since 1984 in various trials around the country paved the way, the purpose is to verify the porous asphalt pavement noise reduction and durability. Austria for environmental protection needs, in many towns on the road after the drainage of paved road, 10 years ago, has accumulated 6.5 million m2, and plans to permeable pavement for urban roads. The country has been on the road to develop a type of porous drainage design specifications. Netherlands, 2.5 million a year laying permeable pavement m2, the Netherlands has 15.4% of the car lane paved this road. France uses the drainage of the road very quickly, has been paved a few years ago 20 million m2, but also an annual 4 million m2 annually.4 layer of porous asphalt concrete surface design features4.1 Determination of displacementNew elements of the internal structure of asphalt concrete pavement and drainage design still need to calculate the area under normal circumstances, require the discharge of displacement, the formula has been built with cement concrete pavement structures within the displacement formula.4.2 Determination of the drainage structureDrainage structures within the pavement structure divided into three: the first one is the central reserve drainage for wet areas separatedWith no paved highway; second is the edge of the road drainage; third is to set primary drainage. The choice of these types of structure, according to road class, pavement type and local rainfall and other specific circumstances calculated to determine. For rain-fed areas of the highway, under the conditions permit, the above three structures can also use the best.Central reserve drainage sewer mapNew road edges and primary drainage plans4.3 new asphalt concrete pavement structure drainage system materials and construction requirements4.1 Main materials and requirementsDue to drainage of the asphalt mixture porosity, by sunlight, air, water demands a greater influence bitumen viscosity, anti-aging performance, designed to use high viscosity modified asphalt, asphalt and aggregate toincrease the bond force, to prevent the aggregate in the flying wheel loads, improve mixture durability. The main features of high viscosity asphalt softening point is high, 60 ℃high viscosity, high toughness and adhesive toughness. High viscosity modified asphalt properties required in Table 4.1. Segregation, softening point of difference is less4.2 Construction of drainage system requirements of the medianDumping within the median of the horizontal gradient of the infiltration of rainwater with a central low-flow split cavity, and flow through the discharge port or longitudinal row of circles across the road bridge and culvert waterways. Median transverse slope not steep at 1:6; median longitudinal drainage slope, no pavement in the cross section shall not be slow to 0.25%, with pavement shall not slow to 0.12%. When the flow rate exceeds the maximum allowable flow rate of the ground soil, should be in the cross section width of the range map on the ground for anti-erosion process, made of triangular or "U" shaped cross-section of the ditch. Anti-erosion layer of lime or cement stabilized soil can be used, or the use of mortar rubble paving, thickness 10cm ~ 15cm. Around the sewerParcel filtration fabric (geotextile) to prevent infiltration of water to carry the fine will be sewer blockage. Sewer backfill and pavement on the structure of the interface at the laying of asphalt coated double layer of geotextile fabric across the seepage. 70mm ~ 150mm diameter pipes can be used in PVC plastic pipe.4.3 the edge of the road drainage system materials and construction requirementsFilling by the cement pavement edge drain Treatment of open-graded coarse aggregate components, materials and construction methods and drainage have been completed and the road edge fill the same, but set the minimum width of the ditch bottom should not be less than 30cm.4.4 Primary drainage material and construction requirementsPrimary drainage set directly under the concrete pavement. Drainage from the cement or asphalt Treatment of primary non-small particle size, or with fine 4.75mm the following open-graded material composed of crushed stone aggregate, or by a combination of materials without the Treatment of open-graded crushed stone aggregate form. Aggregate should be used clean, hard, durable gravel, crushed its value should not exceed 30%. Maximum size for 20cm or 25cm, and thickness of no more than 2 / 3. The following particle size 4.75mm fine material content should not exceed 10%. Aggregate gradation shall meet the permeability requirements (permeability coefficient of not less than 300m / d), can often head or variable head permeability test after test to determine the distribution. Cement Treatment of gravel aggregate amount of cement should not be less than 160kg/m3, the compressive strength of not less than 7d immersion 3MPa ~ 4MPa. Treatment of gravel aggregate asphalt asphalt aggregate amount of the dry weight of about 2.5% to 4.5%. The thickness of the primary drainage shall be required to discharge water and base material by hydraulic calculations to determine thepermeability coefficient, usually 8cm ~ 15cm range to choose from, but the minimum thickness of not less than 6cm (Treatment of gravel asphalt) or 8cm (Treatment of broken cement stone). The width of the surface layer of construction should be considered beyond the surface layer of the width of the needs of 30cm ~ 90cm. Drainage mat lying under the grass-roots level should be used impermeable or low permeability of dense-graded mixture, in order to block the infiltration of free water and fine material in the soil of the roadbed on the move.Sections in the high water table, to intercept groundwater, water or spring water into the road stranded structure, or excluded because of the negative temperature effect and the accumulation of free water in the top of the embankment can be set directly on the top surface of the roadbed permeable drainage blanket, and, where appropriate Configuration vertical gullies.5 SummaryAnd infiltration of water into the road surface water, is caused by premature or accelerated pavement damage to one of the main structure, new materials, waterproof, both from an economic point of view, or for the construction process, can effectively improve pavement performance, extending its use life. Construction for road construction to provide effective protection.References[1] supported military school. Porous asphalt pavement research, Hebei University master's degree thesis, 2002[2] Feng Jie. Water and solutes in soils with large pore transport mechanism. Hohai University Ph.D. dissertation .2001.10[3] Ji green grams. Road within the drainage system design. Tongji University Ph.D. thesis, 2002.03[4] cold reality. Porous asphalt mixture design and performance grading of the composition, Southeast University master's degree thesis 2003.03[5] Liu Song, Cao Lintao. Asphalt pavement causes and prevention of water damage, road materials and the Sixth National Conference on New TechnologyCollected Works, 2005[6] Guode Dong, Guo Xiaohong the traditional construction process under the asphalt pavement because of water damage analysis and solutions. Highway TrafficTechnology, 2006 (1)[7] Zhu Yongning. Drainage performance of porous asphalt pavement research and design of drainage facilities. Southeast University, Wen, 2003.03[8] Liu Zhaohui. Research permeable asphalt, Petroleum bitumen, 1997.09[9] Wang Zhi music. Porous asphalt pavement research, Taizhou Vocational and Technical College, 2006 (3)[10] Zhang heavens, Gao Qi, etc. Water damage to asphalt pavement and its preventive measures, Beijing Construction Engineering College, 2003 (3).路面排水设计要点摘要：随着我国经济和社会的高速发展，公路建设也进入了快速发展时期。
