What Is Surface Drainage?

Subgrade surface drainage refers to the removal of surface runoff formed by precipitation within the road boundary, and the surface runoff of adjacent areas that may enter the road boundary affect the stable surface water of the roadbed.

Subgrade ground drainage

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Subgrade surface drainage refers to the removal of surface runoff formed by precipitation within the road boundary, and the surface runoff of adjacent areas that may enter the road boundary affect the stable ground surface of the roadbed.

Water is one of the main external causes of various diseases and deformations of roads, which should be given full attention in the design of roads, and various drainage measures should be adopted in accordance with local conditions, and these facilities must be combined into a complete

The general principles to be followed for ground drainage can be summarized as follows: ^[1]

Subgrade ground drainage can use side ditch, intercepting ditch, drainage ditch, downwater and rapids, water blocking zone, evaporation pond and other facilities. The following is a brief overview of the installation locations and requirements of each facility: ^[2]

Side ditch

(1) Side ditch setting: Generally, side ditch should be set at the fill section where the filling height is less than the side ditch depth and the lower slope foot of the embankment section. The side ditch is generally set to have water outlets in sections, because the water outlets not only lead the water out of the roadbed in one click, but also need to be set according to the local meteorological and hydrological conditions to ensure that the roadbed must be excluded in time.

(2) Construction requirements: Appropriately deepen the outer side ditch of the curve so that the added value is equal to the super high value. Construction of side ditch at a flat curve requires that the longitudinal slope at the bottom of the ditch should be smoothly connected with the longitudinal slope at the bottom of the ditch before and after the curve. Water accumulation or overflow on the inside of the curve must not occur. In the soil side ditch section, when the longitudinal slope at the bottom of the ditch is greater than 4%, measures should be taken to reinforce the side ditch in time. Generally, the paving side ditch should be made of mortar and stones, and the stones should meet the requirements of the specification. When using trowel bottom, it should be smooth and smooth.

Intercepting ditch

(1) Setting of intercepting ditch: In the absence of earthwork compression, the problem of ground pressure may not be considered. The setting of the intercepting ditch and the distance from the top of the excavated subgrade are determined by the soil quality, but it should be determined without affecting the stability of the slope. Prerequisites. For general soil quality, the interception ditch is not less than 5m from the subgrade slope top, and the distance to the collapsible loess area should not be less than 10m. Moreover, the interception ditch should be reinforced at the same time as the interception ditch to prevent seepage. leak. The soil excavated in the intercepting ditch should be piled between the road cutting and the intercepting ditch to form a T-shape as a whole, and then compacted to make a cross slope with a top surface inclined to the intercepting ditch, the inclination angle is 1.5% 2%. When there is idle earthwork on the subgrade, the intercepting ditch should be a certain distance from the idle earthwork, generally 2-6 meters, and the slope of the spoil pile should not be less than 5m from the top of the excavation slope of the subgrade, and it should also be set on the top of the spoil pile. 1.5% to 2% tend to the cross slope of the intercepting ditch. The intercepting ditch on the embankment on the hillside is slightly different from the previous one, and it must be at least 2.0 to 5 from the foot of the embankment slope. Om, and the excavated soil is filled between the embankment and the interception ditch, and a slope protection slope with a slope of 1.5% to 2% is built to ensure the smooth drainage of the ground water inside the embankment.

(2) Construction requirements: When the length of the intercepting ditch exceeds a certain distance, an appropriate outlet should be selected to direct water to the natural ditch or the bridge culvert inlet. The intercepting ditch must have a fixed outlet, and drainage must be provided if necessary. Ditch, falling water or rapids. The outlet of the intercepting ditch must be smoothly connected with other drainage facilities. To prevent water from seeping down and scouring. The intercepting ditch should be tightly impervious and reinforced. Poor geological sites and rocky sections with soft soil, large water permeability or fissures should be used. For the soil intercepting ditch with large vertical slope at the bottom of the ditch and the outlet of the intercepting ditch Reinforcement measures shall be adopted to prevent leakage and scouring and trench walls.

3. Ditch

(1) The linear shape of the drainage ditch is required to be smooth. If possible, use a straight line. Turns should be made into arcs. The radius should not be less than 10m. The length of the drainage ditch depends on actual needs.

(2) When the drainage ditch is laid along the route, it should be as far away from the roadbed as possible, and it should not be less than 3 to 4m from the foot of the roadbed. When the velocity of the water flow is greater than the permissible scouring velocity, the surface of the trench bottom and trench wall shall be strengthened.

4. Water fall and rapids

(1) The falling and rapids troughs must adopt the mortar structure or concrete structure. The height of the falling steps can be determined according to the conditions of terrain and geology. The heights of the various steps of the multi-stage steps can be different. The slope of the ground is adapted.

(2) The longitudinal slope of the rapid trough should not exceed 1: 1.5, and it should be matched with the natural ground slope. When the rapids trough is long, several longitudinal slopes can be used at the bottom of the trough. Generally, the upper section is steeper and slows down gradually.

(3) When the rapid flume is very long, it should be built in sections, each section should not exceed 10m, and the joints should be filled with waterproof materials, and there should be no gaps.

(4) The masonry of the rapid flume should form a transition between the natural water flow and the entrance and exit of the culvert. The foundation should be embedded below the ground. The base requires a smooth platform and an end retaining wall. The embankment slope rapid groove shall be constructed to provide a smooth channel for water to flow into the drainage ditch. The kerb opening and the transition section of flowing water entering the embankment slope rapid groove shall be smoothly connected.

5.Evaporation pond

When the water on the pavement cannot lead outside the roadbed, we can set an evaporation pond near the roadbed. When using a soil pit as the evaporation pond, the distance from the foot of the roadbed should not be less than 5 ~ 10m. The distance from the large evaporation pond to the foot of the embankment shall not be less than 20m, and the water level in the pit shall be at least 1m below the edge of the embankment. The bottom of the pit should be a horizontal slope inclined from the sides to the center by 0.5% to 1%. The population from the earth pit shall be smoothly connected with the connected drainage ditch or drainage channel.

6. Blocking edge stone

In order to avoid the high embankment slope from being washed by the pavement water, it is necessary to set a water blocking edge on the road shoulder, intercept the water flow to the drainage ditch or set up a rapid groove at the opening of the water barrier to lead away from the subgrade. . The shoulders of road sections with water blocking edges should be appropriately reinforced.