Research on Environmental Dredging and Technical Key Points

Ecological environment protection is the theme of social development and construction in recent years. The concept of environmental protection is reasonably applied in dredging projects of ports and waterways. It can not only meet people’s requirements for the protection of the ecological environment but also enable dredging engineering enterprises to keep up with the needs of the times, so as to realize the sustainable development of ecological environment and social economy in modern life in China. Based on this, according to the characteristics of environmental dredging construction, this paper analyzes several factors of environmental impact caused by dredging construction of port-channel, so as to realize the purpose of environmental protection construction by strengthening the effective control of dredging construction technology.

1. Environmental dredging effect in ports and waterways

 1.1 Diffusion of pollutants in sludge substratum

Industrial wastewater, domestic sewage and dead biological debris discharged from the area near the port are discharged into the port with the help of surface runoff, and gradually accumulate sediments in the port channel. These sediments often contain nutritive salts, which tend to produce eutrophication when their content exceeds a certain level. This is not only easy to cause the body of water odor, aquatic life death, and damage to the water environment, but also easy to affect the normal operation near the port. Under normal conditions, the water body itself has a purification effect, as long as the content of nutrients in the water within a certain range, there will be no eutrophication phenomenon. However, if the sludge layer in the channel is not well treated before the port dredging project, the sludge will be stirred during the dredging process, which will aggravate the diffusion of pollutants in the sediment, release the nutrient salts in the pollutants, and easily produce eutrophication.

 1.2 Damage of inorganic suspended matter to the aquatic ecosystem

In the dredging project of the harbor channel, the inorganic suspended matter is the most common pollutant and the main pollution source in the water area. The dredging project will stir up the inorganic suspended matter in the water, and the closer it is to the dredging vessel, the higher the concentration of inorganic suspended matter will be, which will reduce the light transmittance, increase the turbidity of the water, and have an adverse impact on the aquatic ecosystem.

 1.3 Noise pollution and pollution of dredging vessels and dredging equipment

Dredging vessels will produce noise pollution during dredging and dredging construction, which will affect the surrounding ecological environment. And the dredging vessels and dredging equipment used in the port dredging project will also have an adverse effect on the ecological environment. For example, vessels and equipment may leak oil during construction, causing pollution to water bodies. At the same time, construction vessels will also discharge a certain amount of domestic sewage to the water body, which will adversely affect the water body.

2. The construction characteristics of the environmental dredging project

 2.1 Improve the precision of engineering construction

According to previous experience, the pollution blockage layer in waterway waters is generally between 10cm and 15cm. The positioning accuracy and excavation accuracy of engineering construction should be constantly improved during actual construction. Before excavation, a detailed field survey should be carried out to draw the corresponding schematic diagram of river excavation, and the size, depth, and width of the trench should be designed, so as to ensure that no leakage excavation, no over-excavation, and at the same time to prevent the production of greater pollution and damage to the balance of the surrounding ecological environment.

 2.2 Effectively reduce re-pollution during dredging

It is easy to cause sediment suspension during dredging and sediment leakage may occur during sediment transport. After the sediment deposition, attached to the above pollutants will be suspended and water, leading to insufficient sunlight, biological growth, and reproduction hindered. Therefore, special facilities are needed to treat the bottom sludge to prevent the pollutants from contaminating the water again.

 2.3 Professional monitoring of pollution sources

The pollution elements in the construction project are closely monitored to ensure that the water quality changes or pollution problems can be solved in time. In the channel dredging project, the common pollution factors that need to be monitored and analyzed usually include: mud diffusion degree, mud concentration, backwater concentration, suspended pollutant particle quantity, etc. While monitoring, the tailwater concentration in the discharge field should be strictly controlled.

 2.4 Cleaning of polluted sediments

Dredged sediment can also have a serious impact on the surrounding ecological environment, so appropriate measures should be taken to deal with the sediment. In order to prevent these sediments from polluting the accumulation site or nearby waters, it is necessary to adopt effective purification measures such as chemical decomposition or physical decomposition to avoid secondary pollution. At the same time, measures should be taken to control the concentration of polluted sediments to prevent polluting the ambient air.

3. Analysis of technical control points of dredging construction of harbor channel

 3.1 Port channel dredging construction control

Technical control of dredging construction is the most important prerequisite for the development of technology. In terms of construction control, the following points should be done:

First, technical agitation should be carried out on the bottom contaminated sediment of the channel, but the number of agitation should be controlled within a certain range (generally the agitation range is 4~8m), which is also to prevent further diffusion and aggravation of pollutants, affecting the ecological environment in other areas of the water. At the same time, certain non-proliferation construction technology measures should be taken to ensure that a high concentration of pollutants can be removed quickly, so as to avoid the transformation of pollutants into a suspended state and minimize the pollution level of surrounding water bodies.

Second, accurate positioning should be carried out for the dredging construction of port-channel, which should not only include the enhancement of the excavation accuracy (control the bottom layer of pollutants in the depth of 15cm~1m) but also should clarify the scope of dredging and excavation. If it is a waste polluted sediment, its dredging control should also be planned within the standard range. The general idea is to raise the technical standards of dredging significantly above those of ordinary dredging. Thirdly, the noise of large equipment such as diesel engines should be reduced as far as possible. During the dredging operation, the engine room door of the ship should be closed to ensure that the dredging operation will not disturb the construction and affect the construction quality due to too much noise. Due to the large pollution caused by the dredging of the harbor channel, the direct discharge of sewage and garbage from dredgers should be strictly controlled during the dredging operation, especially for some sensitive waters, the real-time monitoring of the pollution level should be strengthened to ensure that the water quality is always within the qualified standard range.

 3.2 Environmental technology analysis of dredging construction

As described in the paper, the dredging construction of port-channel must focus on avoiding sensitive areas of water, and prevent the diffusion of suspended substances, so as to do good real-time monitoring. Of course, the construction technology and progress should also be adjusted according to these monitoring conditions, so as to give a reasonable play to the technical content. Specifically, the following two technical points are given.

(1) Reasonable arrangement of mud discharge pipeline

In the construction area of the port channel, the layout of the mud discharge pipeline on the water should take the lead to investigate the flow and wind direction, and according to them, the mud discharge pipeline should be set into an arc shape and anchored at the same time. At the same time, connect the waterway pipeline with the underwater pipeline, set a two-way pipe anchor for the channel, and fix it with a three-way pipe anchor. In the construction process, it is generally selected to install the night light display for the water pipeline, and at the same time set the pipe anchor drift. Finally, when considering the floor-suction dredging vessel, consideration should be given to whether the dredging pipeline is too long. If it is too long, it may lead to the fracture of the dredging pipeline when the wind waves or the flow velocity is too high. Generally speaking, the length design of the dredging pipeline should be controlled within the range of 300~500m. In addition, during the construction process, the tightness of the mud conveying pipe should be ensured to avoid any leakage during mud conveying. The mud is mainly sprayed from the interface, so it should be well checked and maintained on a daily basis to avoid large-scale environmental pollution caused by the break and leakage of the mud pipeline.

(2) Environmental protection construction treatment of blowing-fill overflow in the blowing-fill area

Environmental protection countermeasures for the blowing-filling overflow in the blowing-filling area of the port-channel should be carried out based on three points. Firstly, the flow direction of the spilled mud should be strictly controlled during the blowing-filling process to prevent a large amount of mud from flowing into the water and causing serious water pollution and even affecting the water quality outside the blowing-filling area. Therefore, we should try our best to control the discharge sludge concentration of the overflow port, so we can consider setting separate cofferdam, increase the distance of the overflow port of the blow filling point, increase the flow rate of mud in the blow filling area, but reduce the flow rate at the same time, so as to improve the settlement effect of suspended solids and effectively control the actual concentration of suspended solids. Second, technological transformation should be carried out on the basis of the traditional dredger, and environmental protection measures should be set for dredging construction. For example, the anti-mud curtain can be set in the construction area for the grab dredger, with the purpose of preventing a large number of sediment pollutants from spreading. At the same time, it can set the antifouling cover on the reamer head of the cutter suction dredger, and realize effective control of suspended matter pollution in waterway waters with reamer head. Third, in the process of land reclamation work, should be regularly to the exhaust pipe and dredge the maintenance inspections on the connection between the two points, the first time found between pipeline there may be a bad connection or damage problem, actively adopt corresponding remedial measures, and in order to effectively avoid the happening of mudflow pollution accident.