Design and research on drainage measures for subgrade and pavement of municipal engineering?

Subgrade and pavement drainage, as an indispensable medium for vehicles and people to travel, directly affects the life of roads, traffic safety and the appearance of cities. According to the experience of highway construction and subgrade and pavement drainage treatment in recent years, the measures of drainage design are discussed.

1 Importance of subgrade and pavement drainage

In rainy areas, a perfect road drainage system is very important. When it rains, the sources entering the rainwater pipe network are road water, water not absorbed by the green belt and road water. If the road drainage is not smooth, the water on the road surface and the water not absorbed by the green belt will gather on the road. By analyzing its harmfulness, it also reflects the importance of subgrade and pavement drainage from the side.

1. 1 easy to cause traffic accidents.

If the road surface is not well drained and the vehicle runs at high speed on the water surface, the water film on the road surface will affect the contact between the wheel and the road surface, which will easily cause the wheel to slip on the liquid surface, and braking will cause the tire to slip, which will affect the driver's driving safety. Therefore, in order to ensure traffic safety, reasonable road drainage design is the key, and the importance of design is self-evident.

1.2 road hazards

If the road surface water is not discharged smoothly, the road surface will be soaked by water. With the extension of time, water will soak the materials of each structural layer and subgrade soil, forming unbonded and granular materials, which will reduce the strength of subgrade soil. Where the freezing depth is greater than the pavement thickness, the high groundwater level will cause frost heaving, and the frost heaving soil will produce uneven frost heaving, which will reduce the bearing capacity during ice melting. On the ground covered with cement, the water entering the cracks will form a water flow with high pore water pressure and high velocity under the action of vehicle load, which will make the fine particles of the pavement base turn over and lose support. After a long time, the platform will stagger and crack, and finally the whole shoulder will be damaged. On the asphalt pavement, long-term contact with water will make the asphalt mixture peel off, which will affect the durability of asphalt concrete and produce cracks.

1.3 Affect the city appearance

If the road surface is not well drained, some roads will be soaked in water. After the rain stops, under the rolling action of vehicles, silt will form, and the urban roads look muddy. With the development of economy and society and the improvement of people's quality, people are most concerned about the image quality of the city. The environmental problems of municipal roads are not handled well, which has a great impact on the overall image of the city and affects the appearance of the city.

2 principles of subgrade and pavement drainage in municipal road construction

The basic principle of drainage design is to make full use of topographic advantages and natural water system, make comprehensive planning, pay attention to economic development, and achieve the goal of comprehensive management.

2. 1 subgrade drainage principle

(1) The amount of water infiltrated into the pavement structure in the internal drainage system is less than the drainage capacity of various drainage facilities, and the drainage capacity of the upstream drainage facilities cannot exceed that of the downstream drainage facilities; ② The maximum water seepage time of pavement structure should not exceed 1h in frozen area, 2h in heavy traffic flow and 4h in non-frozen area. The seepage path length of seepage water in pavement structure should not exceed 45 m ~ 60 m; (3) The drainage facilities can't be blocked by fine materials that penetrate into the pavement structure, subgrade or shoulder, so as to ensure that the drainage capacity of the system will not be lost quickly with the passage of time. In case of poor drainage area, it is necessary to strengthen subgrade protection, reinforce subgrade and carry out special design when necessary; (4) In special areas, drain ditches shall be buried on the ground and underground, and the length of trench lines shall be determined according to the actual situation, so that there will be no water accumulation somewhere underground.

2.2 the principle of pavement drainage

(1) Rain and snow that have fallen on the road surface should be discharged to both sides through the cross slope of the road surface to avoid water accumulation in the lane surface; (2) When the longitudinal slope of the route is gentle, the catchment is not large, and the slope will not be washed away, the road surface water will be discharged by crossing the embankment slope; (3) The longitudinal slope of the route is steep and the catchment is large. A longitudinal drainage ditch is arranged at the outer side of the leading edge belt at a certain distance from the inner center, and water is discharged from the boundary through a transverse drainage pipe. It can reduce the amount of water at low points, so as not to form stagnant water and freeze in winter.

Design and research of drainage measures for subgrade and pavement

Municipal road drainage is mainly to discharge the water falling from the ground and the water melted by snow from the roadbed at the fastest speed, so as to minimize the surface and underwater leakage caused by poor drainage. Water is mainly introduced into the urban rainwater pipeline system from the aspects of roadbed drainage, pavement drainage and pavement structure drainage. On the other hand, reduce the amount of rainwater entering urban rainwater pipes, and reduce the amount of water by laying permeable bricks on non-load-bearing roads and sinking green belts.

3. 1 subgrade drainage measures

Subgrade is the foundation of the road, and the road should realize the function of vehicle running. Subgrade foundation must achieve high strength, high hardness and good stability. The subgrade is located under the pavement structure, and water is very destructive to the subgrade, so it is very important to properly handle the drainage of the subgrade for the overall quality of the road. Before subgrade design, the following aspects need to be considered: first, investigate the climate of the city where the road is located, especially the temperature and rainfall in winter, which directly determine the pretreatment before construction. Secondly, investigate the topography, road conditions and conditions on both sides of the repaired road section, and according to these, focus on designing the junction of road section changes. In order to facilitate drainage, the design scheme of gentle slope and sloping road foundation is determined. The specific design methods are as follows: ① For wet subgrade, the water content is not too high. Before construction, longitudinal drainage ditches can be dug on both sides of subgrade, and some transverse drainage ditches can be dug at regular intervals to collect subgrade water into the drainage ditches and pump it away with submersible pump; (2) If the wet subgrade can't be dried by rolling, it can be treated by replacement, such as riprap to squeeze silt, replacement of soil, replacement of granular materials with good water permeability, etc. (3) Drainage design in pavement structure: In addition to most of the surface water discharged from the rain outlets through the longitudinal and transverse slopes of the road, there are certain pores on the pavement surface, and a small amount of surface water penetrates into the pavement structure through the pores and cracks of the road. If this part cannot be drained, the strength of subgrade will be reduced over time, so certain measures must be taken to drain the surface water that may penetrate into subgrade in advance. Permeable water passes through the permeable layer longitudinally, penetrates into the longitudinal water collecting ditch and water collecting pipe transversely, and then flows out of the foundation through the transverse pipeline; (4) In the area with more groundwater, the pavement is designed with seepage ditch and gravel cushion, and the water is introduced into the seepage ditch and discharged from the subgrade through the pipeline, thus reducing the groundwater level and keeping the subgrade in a relatively dry state.

3.2 Road drainage measures

In order to facilitate the drainage of pavement water, the slope of the sidewalk is set to face the roadway, and the rainwater falling on the sidewalk is discharged into the rainwater manhole beside the road through the cross slope. Roads are places for digging. Various forms of retaining walls are often set on both sides of the road. Interception ditches are set above the retaining walls on both sides of the road to intercept the surface water that will flow into the sidewalk, and the intercepted water will enter the urban rainwater pipeline system. For the ground with slope, the water flows to the lowest point of slope, and is collected and led to the collection pool, and the water in the collection pool is discharged by setting a drainage pump station.

3.3 reduce the water entering the motor vehicle lane.

(1) Non-load-bearing pavement is paved with water-permeable bricks. Laying permeable concrete bricks on non-load-bearing sidewalks, this kind of permeable concrete brick has a larger gap and stronger water permeability, and can penetrate into the underground part through the permeable bricks when it rains, reducing the water flow to the highway. (2) Construction of sunken green space with green belt facilities. The green landscape belt is still separated from the road surface by kerbs, and the water inlet is installed below the kerbs. The green belt is 20cm lower than the road surface, and a green belt is divided every 30m, so the rainwater overflow must be higher than the green belt. With this design, when the rainfall is small, the water in the green belt will penetrate into the ground, and the water will not overflow the overflow and flow onto the road. When the rainfall is heavy, it will flow into the rainwater pipeline through the overflow, which can reduce the amount of water flowing to the road surface.

4 conclusion

Drainage design of municipal engineering subgrade and pavement is a complex and professional work. Drawing lessons from the experience of municipal engineering road design at home and abroad, this paper summarizes some experiences of different sections with China characteristics, which is convenient to ensure the engineering quality and add luster to the urban infrastructure.

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