1. Difficulty in dredging hard plastic soil

For non-inertia grab, the construction efficiency of hard plastic soil is not reduced to a great extent, But for the cutter suction, bucket wheel and inertia grab dredger, excavation and transport capacity is obviously insufficient. Pipe blockage often occurs in the construction of cutter suction dredger or bucket wheel dredger relying on pipeline transfer.


  1. Difficulty of abnormal soil dredging

No matter which construction method is adopted, the soft and hard degree of soil has a great influence on construction efficiency, especially for the construction of iron and manganese nodules. Exploration departments usually distinguish soil types after removing iron and manganese nodule particles, and the soil types are of lower grade. In response to the tender, the bidding unit can only compile the tender price according to the determined soil grade and apply the corresponding quota. Due to the hardness and high density of iron and manganese nodule particles, iron and manganese nodule particles deposit in the transportation process and slide along the bottom wall of the pipe at a low speed. Its sliding speed is only about 1.5m/s, much lower than the normal movement speed of 3.5m/s in the suspended or semi-suspended soil. Once the velocity in the pipe changes slightly, the direction of the pipe changes, the soil collapses during excavation, the excavation speed is slightly fast, or the operation is improper, etc., iron and manganese nodule particles will accumulate in the pipe, resulting in pipe blockage. Therefore, depending on the pipeline transfer of the cutter suction or bucket wheel dredger construction, construction efficiency will be seriously reduced, and lead to serious wear of mechanical equipment, transport capacity is seriously inadequate.


  1. Difficulty in dredging plate sand layer and medium-coarse sand

The plate sand layer is usually located in the inland area near the seaside, and the sand grains are extremely fine, which are usually mixed and precipitated with a small amount of clay particles. the consolidation degree of fine sand and clay particles is promoted, and the plate like mortar is formed, and the particle structure is unusually tight. In the process of transportation, the collision, friction and impact of water flow with pipelines are easy to be broken, and the wear degree of pipelines is equivalent to that of grade 5 soil of transportation dredging soil. The biggest difficulty is the excavation difficulty. However, due to the large particle size of medium and coarse sand, water sand stratification occurs in the transportation process. The main difficulties are the insufficient transportation capacity of equipment and abnormal wear of equipment.