The situation in the intersections, squares, parking lots, downpasses, expressways, and highways in the city's major cities is quite special. After the accumulation of water, the impact is greater. The road drainage is of greater importance and must be properly handled and promptly eliminated. run-off. Squares, parking lots, descending interchanges, expressways, highways, etc., where conditions permit the formation of an independent drainage system, may use a design heavy rain return period larger than that of the surrounding area. The gullies at intersections shall be laid out in a vertical design; the gutters in the squares and parking lots may be laid out in one-way, two-way, three-way, radial, and other forms of drainage slopes according to the plane requirements and the surrounding environment. M-type or W-type can be used as a last resort, but it is not conducive to driving. In the drainage of the downstream interchange, it is advisable to set reverse slopes or interception facilities at the slopes of the roads at both ends of the road to limit or reduce the catchment area. The layout, size and number of gutters on the downhill ramp should be designed and calculated. When the runoff collected on the downpass surface cannot be discharged by gravity, it is necessary to set up a pumping station with sufficient energy to drain rainwater during rainfall.
When the groundwater level is too high and affects the stability and strength of the roadbed, and in the cold regions, it may cause road freezing damage. If the roadbed is restricted and cannot be improved, engineering measures to reduce the groundwater level must be taken and stable pavement composition must be considered. Reducing the groundwater level can use different forms of seepage ditch, or use large pore materials such as sand and slag to build the drainage layer and set up vertical and horizontal drainage blind ditch. The elimination of lateral permeate water can use lateral intercepting ditch and drainage facilities. The subgrade is affected by groundwater capillary soaking. Generally, a separation layer can be built under the top of the subgrade. The barrier layer can be made of coarse materials, geotextiles and reverse filter layers, or impermeable layers.