What is the diversion mode of tunnel diversion? Briefly explain its application conditions and characteristics.

The tunnel diversion adopts running water construction technology, including full-face cofferdam method and segmented cofferdam method respectively.

Applicable conditions and characteristics:

Open channel diversion method: Open channel diversion is suitable for plain rivers with wide beach or slow bank. Ditches are usually dug on the beach or on the river bank, and transverse cofferdams are built upstream and downstream of the foundation pit to make the river flow down through the channels.

Applicable conditions of open channel diversion: If the riverbed overburden is deep, it is difficult to divert by stages, or the riverbed at the dam site is narrow, and one of the following four conditions is met, the open channel diversion scheme can be considered.

First, the construction period is short, and there is a lack of professional equipment and related experience for digging holes.

Second, the diversion flow is large, and the geological conditions are not suitable for excavating diversion tunnels.

Third, during the construction period, there were logging, navigation and ice discharge.

Fourth, there are shoulder-wide platforms, ancient rivers or dumb mouths along the river bank.

Open channel diversion layout should consider:

First, the position of the guide shaft. Try to arrange in dumb mouth, ancient river or wide platform; When arranging, avoid deep excavation and shorten the length of the channel; Try to avoid areas with poor geology and avoid landslides and collapses; In order to make the water flow smooth, the angle between the axis and the mainstream is less than 30 degrees; The turning radius of the open channel should not be less than 5 times the width of the channel bottom.

Second, the elevation of import and export. The elevation of import and export shall be determined according to the navigation, flow, wood crossing and ice release during the construction period. Considering the entry factor, in order to reduce the total amount of excavation, it is best to increase the height.

Tunnel diversion:

Applicable area For this diversion project, it is more suitable for those times when the terrain on both sides is steep or the diversion flow is not very large. In order to save money, it is best to combine tunnel diversion with permanent tunnel.

In the specific layout, it shall be carried out in accordance with the following provisions. First of all, with the help of terrain, we should lay out in a straight line. If you need to turn, the front and rear sides should be set in a straight line, the turning radius should be more than 5 times the width of the tunnel, and the turning angle should be less than 60 degrees.

Choose the area with good geological conditions to arrange the tunnel axis. The tunnel axis should not be parallel to faults, rock strata and fracture zones, and the inclination angle between the tunnel axis and rock strata should be greater than 45 degrees, and the included angle should be greater than 45 degrees.

The included angle between the tunnel entrance and exit and the mainstream direction of the river bed should not be too large; Fourthly, the distance between the entrance and exit of the tunnel and the toe of the upstream and downstream cofferdam should be more than 50m.