1.The maximum digging width of the steel pile dredger:
the maximum digging width is limited by the length of the ship, generally, it is the total horizontal length of the ship during the construction (please remember that the vertical distance between the steel pile and the cutter head is 1.1~1.2 times). When the dredger swings laterally and laterally, the swing angle formed with the center line of the dredging tank is limited to about 40° (that is, the full width of the left and right swing is about 80°). When the width of the dredger exceeds the maximum dredging width of the dredger, the construction must be carried out in sections.
2. Construction methods of downstream and upstream cutter suction vessels:
This method is mostly used for inland river dredging; it is suitable for projects with long trenches and a large amount of work; it is more suitable for dredging silt or projects with high-quality requirements; It is more advantageous for us to choose the tidal direction with a long downstream duration in the tidal reaches. The disadvantage is that it is more difficult to set up the floating pipe, so many pipe anchors need to be lowered. It is often necessary to check the pipeline and loosen the cable properly at any time. With regard to the areas with high flow velocity or a large angle between the flow direction and the excavation groove, that is to say, that the ship should move around, If the operation is slightly inappropriate, the sludge discharge pipeline should become a “dead bend”.
It is more suitable for these areas with advection or small flow velocity (slow flow).
Water pipelines are easy to set up, fewer anchors are used for pipelines, the pipelines can be bent evenly, it is not easy to cause “dead bends”, and it is easy to operate and manage. Another is that you can control the position of the boat and swing flexibly.
It is easy to produce back silt in the dug trench, so to ensure the construction quality, the super-depth should be appropriately increased.
3. Slitting, sectional and layered construction method of cutter suction dredger:
the width of the area to be excavated should be greater than the maximum width of the dredger at one time. The method for determining the maximum excavation width at one time: the steel pile is positioned at 1.1~1.2 times the length of the ship or the left and right swing width of the ship is 80 degrees.
when the trench length of the project is greater than the effective extension length of the buoy pipeline; when the trench turning section needs to be divided into several straight sections for construction; In addition, on the same shoal channel, if there are two or more separated shallow sections, the construction shall be carried out in sections， too.
First, the project needs to excavate the earthwork above the waterline. The second is that the quality of the trench slope is higher or the project requires the excavation of a compound (step) slope. The third is that the thickness of the engineering mud layer is greater than the thickness of one dredging or the excavated soil is hard. Fourth, in areas affected by tidewater, for example, the water depth of the trench at high tide exceeds the maximum excavation depth of the dredger, or the water depth at low tide is not enough for the draft of the dredger. Therefore, it is necessary to use the construction method of digging the upper layer of the high tide tile and the lower layer at low tide according to the change in tide level. The control of the ditch slope mostly occurs in the dredging works of infrastructure and excavation with a thick mud layer (layered excavation). The most commonly used method is to use the step method for dredging. The more steps are divided, the closer the excavation line is to the actual design slope. The determination of each step is to be determined according to the method of layer thickness for cutter suction ships. If there are many excavation steps, the mud layer of the non-slope part can be excavated first. Then focus on excavating the layered steps, the purpose is to ensure the quality of the project.
4. Construction methods of different soil qualities during construction:
Excavation of hard clay:
Generally, the water content of hard clay is low, and the cohesion is large. The reamer rotates in a clockwise direction, and the “hob” phenomenon occurs when the reamer moves laterally to the right. In addition to properly controlling the braking pressure of the left anchor. In addition, at the same time, it is necessary to appropriately reduce the speed of the reamer, the speed of the traverse, and the distance of the forward movement. If necessary, the lowering depth of the reamer can be increased(On the principle of not putting the reamer on the reamer).
Generally, the particles of sand are coarse and should be deposited. In order to prevent clogging of the suction port and mud discharge pipe, the thickness of the excavated mud layer and the forward movement distance should not be too large. , the pressure gauge condition maintains the proper concentration.When it is found that there are signs of pipe blockage, the lateral movement should be stopped, and the reamer frame should be raised to blow clean water. If the vehicle is parked or suddenly stopped for some reason, then when the vehicle resumes driving, water must be dredged to dredge the pipes. When excavating loose sandy soil, the reamer can use low speed, and the fixed point and fixed suction operation method can be used according to the suction distance of the suction port and the thickness of the sand layer.
Excavation plastic or hard plastic operation method:
generally, the clod is easy to stick between the blades, which reduces the speed of the reamer and even loses the kinetic energy of the reamer.We should take the reamer out of the water (the suction port is still under the water) every once in a while to clear the blockage. It is also possible to install high-pressure flushing equipment on the reamer head for flushing.
If excavating the silt, quicksand operation:
generally control the vacuum gauge with the optimum mud concentration, and use the pressure gauge to operate. If the mud layer is thin, the forward movement distance and the lateral movement speed can be increased.