What Are the Different Types of Drainage Design?

Pavement drainage design refers to a type of drainage design that combines roadbed, bridge and culvert structures according to factors such as highway grade, precipitation, and longitudinal slope of the route. In the design of pavement drainage, a drainage plan should be reasonably selected, and drainage facilities should be arranged to ensure the stability of the roadbed and pavement.

According to the different water sources, the water flow affecting the road surface can be divided into two types: surface water and groundwater. The corresponding road drainage is divided into road surface drainage and road internal drainage. Pavement surface drainage includes pavement surface drainage and central partition drainage. Pavement surface drainage refers to the removal of surface water from the pavement and shoulders. Drainage of the center divider refers to the removal of surface water in the area of the center divider. Pavement internal drainage refers to the exclusion or dredging of water that penetrates into the pavement structure (surface layer, base layer and cushion layer) through cracks, joints or surface voids, or floods the inside of the pavement structure with groundwater and stagnant water on both sides of the road .

The purpose of pavement drainage is to require all levels of highways and urban roads to set up necessary drainage facilities according to the specific conditions of local precipitation and pavement, and to properly select the spatial layout and structure of the pavement, timely discharge precipitation to the pavement, and prevent road surface water Infiltrate into the road surface and even the roadbed to ensure driving safety. Water on high-grade roads with high driving speed should be quickly removed to prevent water film from forming on the road to affect driving safety.

Pavement drainage design should be based on highway grade, precipitation, route longitudinal slope and other factors, combined with drainage design of subgrade, bridge and culvert structure, reasonable selection of drainage schemes, layout of drainage facilities, and formation of a complete and unblocked drainage system to ensure the stability of the subgrade and pavement. The return period of pavement drainage design should be 5 years for expressways and first-grade highways; 3 years for second-grade highways and below; for highways or special sections in rainy areas, it can be appropriately increased. ^[1]

According to

Pavement drainage design

(1) Design principles for pavement surface drainage

Rainwater falling on the pavement should be drained to both sides of the road through the lateral slope of the pavement to avoid stagnant water in the pavement range of the driving road.

In the case that the amount of water on the longitudinal slope of the route is not large, the embankment is low, and the slope surface will not be washed away, the water on the pavement surface should be drained by means of lateral flooding on the embankment slope.

When the embankment is high and the slope is not protected and is easily washed away by the water on the pavement surface, or if the slope is protected, it is still possible to be washed away. A water blocking belt should be set up along the outside edge of the shoulder to collect the road Surface water is then discharged from the embankment through drains and rapids.

When a water blocking belt is set up to collect the water on the surface of the pavement, the water surface within the water blocking section of the water blocking belt shall not flow over the outer edge of the right lane on the expressway and first-grade highway, and on the second-grade highway or below. Cross the right lane centerline.

(2) Pavement surface drainage design scheme

When the cross section of the roadbed is a road cutting, the laterally drained surface water collects in the side ditch. When the embankment cross section is an embankment, there are two ways to exclude the water on the pavement surface: one is to let the water on the pavement surface diffusely discharge to the embankment slope in the form of a lateral diffuse flow; the other is to set a water blocking belt on the outer edge of the shoulder to The water on the pavement surface is collected in a shallow triangular cross-section of water passing through the shoulder of the road, and then drained out of the embankment slope through drain holes and rapids located at a certain distance.

In the case of small water catchment, low embankment, different longitudinal slopes of the route, and strong erosion resistance of the slope surface, the lateral diffuse dispersion method should be preferentially adopted; when the surface water is likely to wash the embankment slope surface, it should be used The water on the pavement surface is collected in the catchment belt and discharged through the drain and the rapids.

Pavement drainage design

When the width is less than 3 and the surface is drained by a pavement-enclosed central divider, the surface water falling on the divider is drained to the driveways on both sides, the slope of which is the same as the cross slope of the road surface; An edge stone or a water drain is set at the upper edge of the partition, or a gap-shaped circular water collection pipe or a dish-shaped concrete shallow trench and a drain are not arranged in the partition to intercept and drain the surface water of the upper half of the pavement. The outlet of the cross section of the edge stone can be open, grille or combination, and the drain of the dish-shaped concrete shallow trench is grille.

When the width is greater than 3 m and the surface is not drained by the central partition that is closed by pavement, the surface water that has landed on the partition is collected at the central depression of the partition. And drained through the longitudinal slope to the water outlet or bridge and culvert water channel crossing the road boundary. The horizontal steep slope of the separation zone shall not be steeper than 1: 6; the vertical drainage slope of the separation zone. It shall not be less than 0.25% when there is no surfacing in the cross section, and it shall not be less than 0.12% when there is surfacing in the cross section.

The central partition with no pavement surface and no surface drainage measures, the surface falling on the partition seeps underwater and is excluded by the underground drainage facilities in the partition.

Pavement drainage design

(1) Setting conditions

In humid and rainy areas with an annual precipitation of more than 600 mm, the roadbed is composed of expressways, first-grade highways and important second-grade highways composed of fine-grained soil with poor permeability (the permeability coefficient is not greater than 5-10 cm / s). .

There is stagnant water on both sides of the roadbed, which may penetrate into the pavement structure.

In severely frozen areas, the roadbed is wet and over-wet sections composed of silty soil.

For existing pavement reconstruction or improvement projects, it is necessary to exclude the moisture accumulated in the pavement structure.

(2) Setting requirements

The drainage capacity of various drainage facilities in the internal drainage system of the pavement should be greater than the amount of water seeping into the pavement structure, and the drainage capacity of the downstream drainage facility should exceed the drainage capacity of the upstream drainage facility.

The maximum seepage time of infiltration water in the pavement structure should not exceed 1 h in frozen areas, and should not exceed 2 (heavy traffic) to 4 h (light traffic) in other areas. The length of the seepage path of the infiltration water in the pavement structure should not exceed 45-60 m.

The drainage facilities should not be blocked by the fines brought by the seepage flow from the pavement structure, the roadbed or the shoulder, so as to ensure that the drainage capacity of the system will not be quickly lost over time. ^[3]