In the construction of cutter suction dredger, if the excavation volume is greater than the suction volume, the mud layer is easy to collapse and produce residual layer. If there is a large back siltation in the construction area, it is easy to produce the phenomenon of pre excavation and post siltation. What are the causes of the residual layer.
(1) The main reason is that the excavation volume is larger than the suction volume, and the flow field caused by the rotation of the cutter.
(2) It is left after the mud surface is broken and scattered, and it is caused by water flushing or soil landslide. Therefore, a certain depth of excavation should be increased, which should also be determined according to the length of the construction period and the amount of siltation in the period.
The above is the reason for the residual layer. In operation, if the residual layer is encountered, the following treatment methods can be adopted:
(1) In general, because the amount of back silting is proportional to the length of construction period, the control measures of "first deep then shallow" should be taken into consideration when increasing the depth of excavation and preparation for silting. When the back siltation is small, it should be over deep to ensure the quality.
(2) When the thickness of sand is several times the diameter of cutter and the soil is loose sand, the slope collapse can be used to increase the concentration. However, the operation should be careful to avoid the collapse of the soil layer pressing on the bridge.
(3) In order to ensure personal safety, drinking is forbidden before work. All operations are forbidden after drinking, and those who are seasick are forbidden to operate.
(4) People under 18 and over 50 years old are not allowed to operate the dredger.
(5) Try not to work at night. Under special circumstances, the dredger detection equipment should be fully used and the personnel should be arranged in place.