Briefly describe the cross-sectional forms and characteristics of the channel

Channels commonly used in drainage systems usually have larger diameters. If the inner diameter is greater than 3-4m, they are often cast or built on site. The materials used include concrete pipes, reinforced concrete, masonry, concrete blocks, etc. There are many cross-sectional forms, but generally not circular. The following introduces the commonly used channel cross-sectional forms.

When the soil pressure and load are large, the semi-elliptical cross section can better distribute the pipe wall pressure, thereby reducing the pipe wall thickness. When the sewage flow does not change greatly and the channel diameter is greater than 2m, this type of cross section is more suitable.

The height of the horseshoe section is smaller than the width. This type of section can be used when the geological conditions are poor or the terrain is flat and the burial depth needs to be minimized. Since the lower part of this section is larger, it is suitable for conveying large-volume sewage with little flow change.

The egg-shaped cross section has a smaller bottom, so theoretically, it can maintain a higher flow rate at low flow, thus reducing siltation. In the past, it was widely used in combined sewer systems. However, practice has shown that the channel siltation of this cross section is quite serious, and maintenance and clearing work are relatively difficult.

The rectangular cross section can be deepened as needed to increase the displacement. This cross section is often used in sewage channels of some industrial enterprises, drainage channels in narrow road areas, and flood drainage channels. Based on the rectangular cross section, it can be improved to make a vaulted rectangle, an arc-bottomed rectangle, a concave-bottomed rectangle, etc. to improve the stress and hydraulic conditions. The concave-bottomed rectangular cross section of the pipe channel is suitable for the combined sewer system. On sunny days, the sewage flows in the small rectangular trough to maintain a certain degree of fullness and flow rate and reduce the degree of siltation.

Trapezoidal sections are suitable for open channels, and their slopes depend on the soil properties and paving materials.

In general, when designing the channels of the drainage system, considerations should be given to mechanics, hydraulics, economy and maintenance management requirements.