Methods to improve the efficiency of trailing suction hopper dredgers in excavating fine sand

Abstract

The method for improving the efficiency of trailing suction hopper dredgers in dredging fine sand, as proposed in this invention, includes the following steps: S1. Understanding the soil distribution and quantity of dredged material in the channel through on-site surveys, and analyzing the characteristics of sand layer distribution; S2. Investigating and observing the construction characteristics of the trailing suction hopper dredger and the three stages of the dredging and loading process; S3. Treating the actual soil conditions of the identified sand-bearing areas in the channel, removing surface silt, observing and recording relevant data to form statistical reports for retention, future reference, and comparative analysis; S4. Identifying the factors affecting the efficiency of trailing suction hopper dredging fine sand, and formulating targeted construction countermeasures for each factor; S5. Setting construction goals and achieving the completion deadline. This method greatly improves the construction efficiency of trailing suction hopper dredgers in dredging fine sand, while reducing pollution to the marine environment, ensuring the construction period, improving project quality, expanding the application areas of trailing suction hopper dredgers, and promoting comprehensive economic and social development, achieving good social and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of waterway dredging technology, and in particular to a method for improving the efficiency of dredging fine sand using trailing suction hopper dredgers. Background Technology

[0002] Dredging is the operation of removing underwater sediment from waterways using dredgers or other tools. It is a primary means of developing and maintaining waterways, an important method for port and waterway construction and maintenance, and a necessary technical measure to improve navigation capacity, waterway operating conditions, and thus enhance the economic and social benefits of waterway transportation. The dredging industry has grown alongside the port transportation industry for decades. With my country's sustained rapid economic growth and the high-speed development of its port transportation industry, the throughput capacity of domestic ports has been constantly refreshed. Major ports are constructing deep-water berths, and new artificial island projects, land reclamation projects, and large-scale waterway projects are emerging, leading to a strong demand in the domestic dredging market. Among these projects is the Zhanjiang Port 300,000-tonnage waterway expansion and renovation project. This project is a key construction project planned by the Ministry of Transport and Guangdong Province, and upon completion, it will become the only deep-water waterway in South China capable of accommodating 400,000-tonnage ultra-large vessels. This project involves widening, deepening, and extending the existing 300,000-tonnage waterway. The project area extends from point A30' at the entrance of the Longteng Channel (approximately 9.2 km from the starting point of the 300,000-tonnage waterway project outwards) to point F', 1.027 km south of the turning point F of the Dongtoushan Channel (coinciding with the end point of the 300,000-tonnage waterway project). After the expansion and reconstruction, the total length is 64.1 km. Divided by the Zhanjiang Bay entrance, it consists of an outer channel and an inner channel. The outer channel is 47.435 km long, including the outer and inner sections of the Longteng Channel; the inner channel is 16.665 km long, including the Nansandao West Channel, the Shitoujiao Channel, and the Dongtoushan Channel. The project is implemented in three sections.

[0003] The construction scope of Section I of the Zhanjiang Port 300,000-tonnage waterway reconstruction and expansion project includes dredging, navigation mark construction, and environmental monitoring of the section from A30' (section 0+000) to B' (section 36+200) of the outer section of the Longteng Waterway. The total length of the construction section is 36.2km, with a design bottom elevation of -23.6m to -23.9m and a navigation width of 340m. After the commencement of the Phase I project, construction progressed smoothly overall. However, during construction, in accordance with the requirements of relevant provincial and municipal departments, and to facilitate the construction of the Zhanjiang BASF New Integrated Base Project (hereinafter referred to as the "BASF Project"), the dredged material from this project needed to be changed from being dumped externally to being backfilled into the BASF Project reclamation area. This resulted in significant changes to the project's operating conditions. Firstly, the adjusted dredged material handling method significantly increased the transportation distance and processing time. Secondly, the temporary channel leading to the BASF Project reclamation area was shared by multiple vessels from various units, causing mutual interference, and both the main channel and the temporary channel had speed restrictions. These factors significantly lengthened the construction cycle for each dredging vessel trip, while the optimization space for the transportation and shore-dredging construction links was limited. Therefore, improving the dredging efficiency of the dredging vessels was undoubtedly the key to success.

[0004] The BASF Zhanjiang Integrated Base Project is a key national project with strategic and overall significance. The backfilling work for the BASF project is time-sensitive, demanding, and fraught with challenges and uncertainties. In particular, the backfilling of the land for the BASF Phase I and II projects using dredged material from the navigation channel is crucial to the successful handover of the land and carries significant responsibility. Furthermore, the BASF project has requirements for the bearing capacity of the backfill dredged material, necessitating materials with a high sand content. Only by increasing the sand content of the dredged material loaded onto the suction hopper can the quality requirements for backfill be met. Therefore, given the large workload, short construction time, and heavy schedule pressure, the construction technicians adjusted the project schedule and timeline to adapt to the onshore conditions of the BASF project's reclamation area. However, based on the loading situation, it was found that the existing trailing suction hopper dredging method did not achieve the expected results in dredging fine sand. Fine sand has always been a challenge for trailing suction hopper dredging due to its dense texture and strong sedimentation and aggregation in water. Therefore, based on the current construction methods and efficiency, it is difficult to guarantee the timely completion of the project. The 300,000-tonnage channel of Zhanjiang Port is the "lifeline" of Zhanjiang Port and the lifeline of Zhanjiang's economic development. After completion, the project will become the only deep-water channel in South China capable of navigating 400,000-tonnage ultra-large vessels. The efficiency of the dredging construction of the 300,000-tonnage channel will play a decisive role in whether Zhanjiang Port can quickly receive more large vessels and improve its operational capacity. Therefore, how to improve the efficiency of trailing suction hopper dredging fine sand has become an urgent problem to be solved. How to solve the problem of efficiently dredging fine sand with trailing suction hopper dredgers to meet the dredging volume requirements is a pressing issue for companies whose main business is dredging, and it is also a key direction for further expanding the application fields of trailing suction hopper dredgers.

[0005] Meanwhile, waterway dredging projects require substantial funding and advanced technology, making the application of appropriate technologies crucial during the dredging process. Dredging personnel must conduct a comprehensive analysis based on engineering standards and local planning designs, then determine the optimal dredging implementation plan according to the actual conditions. This effectively reduces risks associated with dredging operations, truly enhancing economic and ecological benefits, improving the surrounding environment, and driving comprehensive economic and social development. Summary of the Invention

[0006] The purpose of this invention is to provide a method to improve the efficiency of trailing suction hopper dredgers in excavating fine sand by investigating, researching, and analyzing the factors affecting the efficiency of trailing suction hopper dredgers in excavating fine sand, and to provide the best construction plan accordingly, so as to solve problems such as tight project time, heavy workload, uncertainties, and difficulty in achieving the expected construction results.

[0007] The method for improving the construction efficiency of trailing suction hopper dredgers in excavating fine sand proposed in this invention includes the following steps: S1. Based on on-site surveys, understand the soil distribution and stock of dredged material in the waterway, focus on investigating the sand source, form survey data, determine the construction area, and analyze the sand layer distribution characteristics;

[0008] S2. Investigate and observe the construction characteristics of the trailing suction hopper dredger and the three stages of the dredging and loading process. In the early stage of excavating the sandy area, conduct trial excavation of the sandy section shown in the survey data, collect relevant construction data, and determine the actual soil conditions of the sandy area of ​​the waterway.

[0009] S3. The actual soil conditions of the identified sandy area of ​​the waterway are treated, the surface silt is removed, and after the conditions for excavation of the lower sand layer are met, engineering technicians are stationed on the ship to track the construction of the trailing suction hopper dredger for fine sand, observe and record relevant data to form statistical reports for retention and future analysis and comparison.

[0010] S4. Based on the above steps, conduct research and analysis to determine the causes affecting the efficiency of trailing suction hopper dredging fine sand. Classify the causes and formulate targeted construction countermeasures for each cause. The construction countermeasures include: reasonably controlling the overflow time; dynamically using the loading hatch; reducing the mud flow rate in the mud tank; and coordinating single and double harrow mixed construction.

[0011] S5. Set construction goals, implement corresponding measures based on the construction strategies in S4, and achieve the completion deadline.

[0012] The S1 includes: First, according to the design geological survey data, the scope of Section I of the Zhanjiang Port 300,000-tonnage waterway reconstruction and expansion project is the waterway section from A30' (section 0+000) to B' (section 36+200) of the outer section of the waterway. Then, a supplementary field survey is conducted on the area near B' of the waterway to determine the construction area as two areas: about 6KM east of B and 9-13KM east of B. The boreholes are arranged on the slopes on both sides of the waterway.

[0013] According to supplementary field surveys, the sand layers in the construction area are mainly fine and medium sand. The sand layers about 6 km east of point B are continuous but unevenly distributed, and the underlying strata are mostly silty clay layers. The surface layer 9-13 km east of point B is silt or silt. The sand layers are discontinuous, appearing as lenses. The layers are relatively thin, with silty soil in the middle and sand at the bottom, showing alternating sand and mud deposition characteristics.

[0014] The S2 includes: According to the investigation, the construction characteristics of the trailing suction hopper dredger are as follows: It is equipped with a rake head excavator and a hydraulic mud suction device. During construction, the rake head is lowered underwater by the rake arms extending from both sides of the ship to loosen and excavate the seabed mud and sand. The mud and sand are pumped by the mud pump and transported through the pipeline to the loading port to enter the mud tank. There are two sets of mud loading ports in the mud tank of the trailing suction hopper dredger, located in the midship and stern respectively. The overflow port is located near the bow. Since the distance between the front and rear assembly hatches and the overflow port is different, the flow path of the mud after entering the mud tank is also different. Based on the on-site observation, it is understood that under normal circumstances, the trailing suction hopper dredger will lower the left and right rake heads to excavate and open the front and rear assembly hatches to load the mud tank during the construction process.

[0015] The dredging and loading process consists of three stages:

[0016] 1.) Begin dredging and loading until the mud reaches overflow height. During this stage, all the mud and sand remain in the mud tank, either suspended or deposited.

[0017] 2.) As loading continues in the overflow state, overflow losses begin to occur. During this stage, some sediment is deposited under gravity, while the rest is lost with the overflow. The deposition ratio depends on the loading flow rate, energy dissipation method, sediment tank structure, overflow facilities, and sediment particle size. As sediment continues to deposit, the deposition surface rises, the flow area decreases, and the flow velocity above the deposition surface begins to increase, causing the deposited sediment to be eroded again, resulting in an increasing tendency for overflow losses.

[0018] 3.) Stop loading when the concentration of the incoming and overflowing soil is basically the same, that is, when the amount of soil loaded into the compartment no longer increases.

[0019] After the trial excavation, the actual soil conditions in the sandy area of ​​the waterway were as follows: the surface layer was covered with silt. Although the supplementary survey data showed that the surface layer was sand, the sand in the lower layer was not reached due to insufficient excavation depth. Therefore, a trailing suction hopper dredger was used to excavate the floating mud on the surface of the sandy area.

[0020] S3 includes: after removing the surface silt, the tracking vessel's dredging operations for silty sand are recorded as follows: dredging was carried out in the sandy section from K29+600 to K32+600, with a total of 18 dredging trips. The soil was mainly silty sand. The average dredging time per trip was approximately 3 hours, the cycle time was approximately 8.5 hours, and the loading volume was approximately 4000 m³. 3 The data shows that construction efficiency is low.

[0021] The S4 includes four categories of factors affecting the efficiency of trailing suction hopper dredging fine sand: overflow duration, loading method, sedimentation rate of mud and sand in the mud tank, and single or double rake usage. Reasonable control of overflow time addresses the overflow duration; dynamic use of the loading hatch addresses the loading method; reducing the mud flow rate in the mud tank addresses the sedimentation rate of mud and sand in the mud tank; and mixed single and double rake usage addresses the single or double rake usage.

[0022] The S5 includes: the set construction target is: the average loading capacity of the trailing suction hopper dredging vessel for fine sand per trip is increased from 4000m³. 3 Increased to 5400m 3 The increase is 35% to ensure the progress and quality of the project construction and to achieve the delivery schedule. The construction countermeasures according to S4 include: 1.) According to the loading effect of the ship, the overflow time is appropriately extended. Specifically, during construction, the overflow time is extended by half an hour to increase the amount of earthwork loaded. The relevant personnel on board closely monitor the changing trend of the earthwork loading curve and control the overflow time according to the changes in the earthwork loading curve. When the earthwork volume does not change significantly with the increase of the overflow time, the rake is started and construction is stopped.

[0023] 2.) Based on geological survey data and actual site conditions, and after determining that the soil was silty fine sand with suitable thickness and good distribution continuity, researchers conducted multiple sets of tests on various loading methods while controlling the overflow time to be the same. The test results showed that: using four-corner loading before overflow shortened the loading time; using rear loading after overflow prolonged the sediment flow and improved the sedimentation effect of silty fine sand.

[0024] 3.) The mud tank structure is optimized by incorporating the principle of hydraulic energy dissipation. An energy dissipation device, a grid baffle, is installed within the mud tank. Two grid baffles are used: one installed in front of the rear loading hatch, and the other between the front loading hatch and the overflow port. Each grid baffle is a rectangular or T-shaped metal plate with several grid bars evenly arranged longitudinally. Several through holes are evenly arranged between adjacent grid bars, serving to dissipate energy, facilitate flow, and prevent clogging. The lower part of the grid baffle is suspended. When using the grid baffle for energy dissipation, the high-speed mud flow forms a hydraulic jump upon passing the grid baffle, creating a cascading energy dissipation; or it impacts the grid baffle wall, directly offsetting some of the energy, increasing the cross-sectional area of ​​the water flow, reducing the flow velocity, and thus ensuring sufficient sedimentation.

[0025] 4.) The construction process adopts a combination of single-rake and double-rake construction. In the early stage, double-rake construction is adopted to ensure the efficiency of the early stage of loading. After the earthwork loading curve slows down, single-rake construction is used to reduce the flow rate of the loading port pipe, reduce the flow velocity of mud and sand into the tank and the scouring of the sediment layer at the bottom of the mud tank, reduce the overflow of mud and sand from the overflow port and improve the loading efficiency.

[0026] The construction data of single-harrow, double-harrow, and mixed single-harrow and double-harrow construction using trailing suction hopper dredgers were recorded, statistically analyzed, and plotted as graphs. The average earthwork loading capacity per dredger for double-harrow construction was statistically determined to be 5115 m³. 3 The average earthwork loading capacity per vessel for mixed single and double rake construction is 5485m³. 3 .

[0027] This includes statistical analysis of construction data, concluding that the above steps significantly improve the efficiency of trailing suction hopper dredgers in handling fine sand, achieving an average loading capacity of 5538m³ per trip when the optimal loading time is reached. 3 This represents a 37.9% increase compared to the previous period, achieving the set construction target.

[0028] The method for improving the efficiency of trailing suction hopper dredgers in dredging fine sand proposed in this invention involves understanding and analyzing the soil distribution and quantity of dredged material in the waterway to identify the factors affecting the efficiency of trailing suction hopper dredgers in dredging fine sand. Effective and targeted countermeasures are then implemented, significantly increasing the loading capacity of the dredged fine sand. This not only effectively promotes project construction progress but also ensures the backfilling needs of related projects. Under optimal loading time conditions, the average loading capacity per dredger reaches 5538 m³. 3The loading capacity increased by 37.9%, improving construction efficiency and playing a crucial role in ensuring the project schedule. At the same time, it promoted the upgrading and development of the port. The dredged material was effectively used for backfilling and utilization, which facilitated the construction of major projects such as BASF. It also reduced marine environmental pollution, improved engineering quality, broadened the application fields of trailing suction hopper dredgers, and drove the comprehensive development of the economy and society. Attached Figure Description

[0029] Appendix Figure 1 This is an overall flowchart of the method for improving the construction efficiency of trailing suction hopper dredgers in excavating fine sand, as proposed in this invention.

[0030] Appendix Figure 2 This is a general plan of the construction area for the method proposed in this invention to improve the efficiency of dredging fine sand using a trailing suction hopper dredger.

[0031] Appendix Figure 3 for Figure 2 A schematic diagram of the supplementary survey location area is provided.

[0032] Appendix Figure 4 This is a comparison chart of the target and the original cargo hold volume for the method proposed in this invention to improve the efficiency of dredging fine sand using a trailing suction hopper dredger.

[0033] Appendix Figure 5 This is a comparison chart of the earthwork loading curves for single-harrow and double-harrow construction of the method for improving the construction efficiency of dredging fine sand by trailing suction hopper dredgers proposed in this invention.

[0034] Appendix Figure 6 This is a comparison chart of overflow time and loading capacity in the method for improving the efficiency of dredging fine sand by trailing suction hopper dredgers proposed in this invention.

[0035] Appendix Figure 7 This is a comparative chart showing the test results of the overflow volume after different loading methods in the method for improving the construction efficiency of trailing suction hopper dredgers in dredging fine sand, as proposed in this invention.

[0036] Appendix Figure 8 This is a schematic diagram of the energy dissipation principle of the grid baffle in the method for improving the construction efficiency of trailing suction hopper dredgers in excavating fine sand proposed in this invention.

[0037] Appendix Figure 9 This is a schematic diagram of the cross-sectional structure of the grid baffle in the method for improving the construction efficiency of trailing suction hopper dredgers in excavating fine sand proposed in this invention. Detailed Implementation

[0038] See Figure 1 The figure shows the overall flowchart of the method for improving the efficiency of dredging fine sand using a trailing suction hopper dredger, as proposed in this invention. The method includes the following steps:

[0039] S1. Based on on-site investigation, understand the soil distribution and quantity of dredged material in the waterway, and focus on investigating the sand source, form survey data, determine the construction area, and analyze the characteristics of sand layer distribution;

[0040] S2. Investigate and observe the construction characteristics of the trailing suction hopper dredger and the three stages of the dredging and loading process. In the early stage of excavating the sandy area, conduct trial excavation of the sandy section shown in the survey data and collect relevant construction data to determine the actual soil conditions of the sandy area of ​​the waterway.

[0041] S3. The actual soil conditions of the identified sandy area of ​​the waterway are treated, the surface silt is removed, and after the conditions for excavation of the lower sand layer are met, engineering technicians are stationed on the ship to track the construction of the trailing suction hopper dredger for fine sand, observe and record relevant data to form statistical reports for retention and future analysis and comparison.

[0042] S4. Based on the above steps, conduct research and analysis to determine the causes affecting the efficiency of trailing suction hopper dredging fine sand. Classify the causes and formulate targeted construction countermeasures for each cause. The construction countermeasures include: reasonably controlling the overflow time; dynamically using the loading hatch; reducing the mud flow rate in the mud tank; and coordinating single and double harrow mixed construction.

[0043] S5. Set construction goals, implement corresponding measures based on the construction strategies in S4, and achieve the completion deadline.

[0044] S1 includes: First, based on the geological survey data, the scope of Section I of the Zhanjiang Port 300,000-tonnage waterway reconstruction and expansion project is determined to be the section from point A30' (section 0+000) of the outer section of the waterway to point B (section 36+200) of the outer section of the waterway. Figure 2 As shown, a supplementary field survey was then conducted on the area near point B of the waterway, determining the construction area to be two regions: approximately 6 km east of point B and 9–13 km east of point B. The boreholes were then deployed on the slopes on both sides of the waterway. Figure 3 The area shown is 9-13 km east of point B;

[0045] Supplementary field investigation revealed that the sand layers in the construction area are mainly fine and medium sand. Approximately 6 km east of point B, the sand layers are continuous but unevenly distributed, with underlying strata primarily consisting of silty clay. 9–13 km east of point B, the surface layer consists of silt or silt, with discontinuous distribution, appearing as lenticular bodies. These layers are relatively thin, with silty soil in the middle and sand at the bottom, exhibiting alternating sand and mud deposition characteristics. (Supplementary investigation area as follows...) Figure 3 As shown;

[0046] According to the investigation, the construction characteristics of the trailing suction hopper dredger in S2 are as follows: It is equipped with a rake head excavator and a hydraulic mud suction device. During construction, the rake head is lowered underwater by the rake arms extending from both sides of the ship to loosen and excavate the seabed mud and sand. The mud and sand are pumped by the mud pump and transported through the pipeline to the loading hatch to enter the mud tank. There are two sets of mud loading hatches in the mud tank of the trailing suction hopper dredger, located in the midship and stern respectively. The overflow port is located near the bow. The distance between the front and rear sets of loading hatches and the overflow port is different, and the flow path of the mud after entering the mud tank is also different. Based on the on-site observation, under normal circumstances, the trailing suction hopper dredger will lower the left and right rake heads to excavate and open the front and rear sets of loading hatches at the same time during the construction process.

[0047] The three stages of the dredging and loading process are as follows:

[0048] 1.) Begin dredging and loading into the silt hopper until the silt reaches overflow height. During this stage, all the silt remains in the hopper, either suspended or deposited. 2.) Continue loading into the hopper while it overflows, at which point overflow losses begin to occur. During this stage, some silt is deposited under gravity, while the rest is lost with the overflow. The deposition ratio depends on the loading flow rate, energy dissipation method, hopper structure, overflow facilities, and silt particle size. As silt continues to deposit, the deposition surface rises, the flow area decreases, and the flow velocity above the deposition surface increases, causing further scouring of the deposited silt and leading to a tendency for increased overflow losses. 3.) When the concentration of silt entering the hopper and the overflow is essentially the same, meaning the volume of silt being loaded no longer increases, loading is stopped.

[0049] After conducting trial excavation, the actual soil conditions of the sandy area of ​​the waterway were found to be as follows: the surface layer was covered with silt. Although the supplementary survey data showed that the surface layer was sand, the sand layer was not reached due to insufficient excavation depth. Therefore, a trailing suction hopper dredger was used to excavate the floating mud on the surface of the sandy area.

[0050] S3 includes: After removing the surface silt, tracking the dredging operations of the vessels on the fine sand section, recorded as follows: 18 dredging trips were carried out on the sandy section from K29+600 to K32+600. The soil was mainly fine sand. The average dredging time per trip was approximately 3 hours, the cycle time was approximately 8.5 hours, and the loading volume was approximately 4000 m³. 3 The data shows that construction efficiency is low. Relevant statistics are shown in Table 1 below:

[0051] Ship number Construction section Soil Dredging time (h) <![CDATA[Loading earthwork (m 3 )]]> 1 29+600-32+600 fine sand 3.13 4051 2 29+600-32+600 fine sand 3.00 4049 3 29+600-32+600 fine sand 3.16 4097 4 29+600-32+600 fine sand 3.20 4178 5 29+600-32+600 fine sand 2.88 3790 6 29+600-32+600 fine sand 3.06 4084 7 29+600-32+600 fine sand 3.13 4136 8 29+600-32+600 fine sand 2.91 3870

[0052] S4 includes: analyzing the reasons affecting the efficiency of trailing suction hopper dredging fine sand, and dividing the reasons into four categories: (1) the cause of overflow time, (2) the cause of loading form, (3) the cause of sedimentation rate of mud and sand in mud tank, and (4) the cause of single-rake and double-rake usage of the rake head; according to the overflow construction principle of trailing suction hopper dredging: the ship will transport the mud sucked from the rake head to the mud tank through the suction action of the mud pump. When the mud tank is full but has not reached the load capacity of the trailing suction hopper dredging, the dredging will continue to be carried out and the overflow will be carried out through the overflow port to increase the amount of soil loaded. Through sampling and observation of the soil in the mud tank, it was confirmed that the soil in the current construction stage is mainly fine sand. Through the observation and recording of the ship, when the overflow time of the single ship construction is not long, the loading volume displayed by the instrument is low, about 4000m. 3 Meanwhile, the loading volume corresponding to different overflow durations varies significantly. The following measures are taken: During construction, the overflow time is appropriately extended, increasing the volume of earthwork loaded. The overflow time is controlled based on the changes in the earthwork loading curve. Construction is stopped when the earthwork volume no longer changes significantly with increasing overflow time. Additionally, before dredging begins, the water in the hopper is drained as much as possible using a pumping method to prevent dilution of the incoming mud, thus shortening the optimal loading overflow time.

[0053] To implement the above measures, the "Junhai 1" vessel was used to construct the cargo hold in the sandy area on the northern slope of the K29+600-K32+600 section. The overflow time was appropriately extended by half an hour, and technicians closely monitored the changing trend of the earthwork loading curve. Construction was stopped when the overflow time increased but the earthwork volume change trend became less significant. By adopting these measures, the earthwork volume loaded by the "Junhai 1" was significantly increased. Therefore, under the premise of the same construction section and soil quality, adopting an appropriate overflow time improved the loading effect of fine sand, increasing the average earthwork volume loaded per vessel by approximately 525 m³. 3 Reasonable control of overflow time is a corresponding measure taken to address the causes of overflow duration; the changes in overflow duration and loading volume during actual construction are shown in Table 2 below:

[0054]

[0055] See the comparison chart of overflow duration and loading volume. Figure 6 ;

[0056] See Figure 7 The dynamic use of the loading hatch is due to the loading method. To further determine the impact of various loading methods on sediment sedimentation, technicians conducted multiple sets of comparative experiments. Specifically, four-corner loading was used before overflow began, and front loading, rear loading, and four-corner loading were used after overflow began. Samples were taken simultaneously near the loading hatch and overflow outlet, and the sand layer thickness was measured after sedimentation to compare the sedimentation effect under different loading methods. Specific experimental results are shown in Table 3 below:

[0057]

[0058] Based on the experimental results, the analytical conclusion is that using a post-loading method after the overflow begins is beneficial for sediment sedimentation and improves the sediment loading effect.

[0059] The reduction of mud flow velocity in the mud tank is due to the sedimentation rate of mud and sand in the mud tank. Specifically, the movement of mud and sand after entering the mud tank mainly includes the following: (1) Suspension and sedimentation: After the mud enters the mud tank from the loading hatch, the mud and sand in the mud will be suspended, and some will be deposited under the action of gravity; (2) Scouring: As the sedimentation increases, the sedimentation surface rises, the flow area decreases, resulting in an increase in flow velocity, which causes scouring of the sedimentation surface and some fine particles to be resuspended; (3) Displacement: The displacement of particle mud and sand along the bottom bed causes adjustment of the bottom bed.

[0060] After the mud enters the mud chamber, if the sediment cannot settle in time during its movement from the loading port to the overflow port, it will flow out through the overflow port, causing significant overflow losses and directly affecting loading efficiency and time. During construction in the sandy area from K29+000 to K32+600, the mud flow rate in the mud chamber was relatively fast, and the mud concentration at the overflow port was high. Analysis of samples taken at both the loading port and the overflow port revealed the presence of fine sand in the construction area. However, the similar sedimentation results at both ports indicated that the sediment failed to settle in time, resulting in poor loading and high overflow losses. Therefore, measures were taken to reduce the mud flow rate in the mud chamber to improve loading volume and efficiency.

[0061] See Figure 5 The figure shows a comparison of earthwork loading curves for single-rake and double-rake construction. The mixed construction of single-rake and double-rake refers to the reasons for using single and double rake heads. Specifically, during the construction of fine sand, technicians found that during the recording of construction data on the "Junhai 6" vessel, a malfunction of the right rake mud pump led to the use of a single left rake. After data comparison, the loading volume of this vessel was relatively higher than that using double-rake construction. According to the loading principle of trailing suction hopper dredgers, single and double rake construction directly affects the flow rate of the loading pipeline and the flow velocity of mud entering the mud tank, thus affecting the loading sedimentation and overflow effects.

[0062] Therefore, single-rake and double-rake construction tests were conducted in the same construction area for comparison and verification. Data analysis and comparison yielded the following results: Figure 5 Analysis of the test results shows that, in the first 195 minutes of construction, double-rake loading was more efficient than single-rake loading. After 225 minutes, single-rake loading became more efficient than double-rake loading. At the end of the construction, the single-rake loading volume was approximately 300m higher than the double-rake loading volume. 3 The cargo capacity has increased significantly.

[0063] See Figure 4S5 includes: setting construction targets: the average loading capacity of trailing suction hopper dredgers for fine sand per trip is increased from 4000m³. 3 Increased to 5400m 3 The increase was 35% to ensure the project's progress and quality, and to meet the delivery deadline. The S4 construction strategies included:

[0064] 1.) Based on the loading effect of the ship, the overflow time should be appropriately extended. Specifically, during construction, the overflow time should be extended by half an hour to increase the amount of earthwork loaded. The relevant personnel on board should closely monitor the changing trend of the earthwork loading curve and control the overflow time according to the changes in the earthwork loading curve. When the earthwork volume does not change significantly with the increase of the overflow time, the rake should be started and construction should be stopped.

[0065] 2.) Based on geological survey data and actual site conditions, and after determining that the soil was silty fine sand with suitable thickness and good distribution continuity, researchers conducted multiple sets of tests on various loading methods while controlling the overflow time to be the same. The test results showed that: using four-corner loading before overflow shortened the loading time; using rear loading after overflow prolonged the sediment flow and improved the sedimentation effect of silty fine sand.

[0066] 3.) The structure of the mud chamber is optimized by using the principle of hydraulic energy dissipation. An energy dissipation device is installed in the mud chamber, which is a metal grid baffle. When the grid baffle is used for energy dissipation, the high-speed mud flow forms a hydraulic jump when passing through the grid baffle, resulting in water drop energy dissipation; or it impacts the grid baffle wall, directly offsetting part of the energy, increasing the cross-sectional area of ​​the water flow, reducing the flow velocity, and thus fully settling the mud and sand.

[0067] 4.) A construction technique combining single-harrow and double-harrow methods was adopted. Double-harrow construction was used in the early stages to ensure efficiency during the initial loading phase. Construction data from single-harrow, double-harrow, and mixed single-harrow methods on the suction hopper vessel were recorded, statistically analyzed, and plotted as graphs. The average earthwork loading capacity per vessel using double-harrow construction was found to be 5115 m³. 3 The average earthwork loading capacity per vessel for mixed single and double rake construction is 5485m³. 3 .

[0068] After the earthwork loading curve slows down, use a single rake to reduce the flow rate of the loading port pipe, reduce the flow velocity of mud and sand into the tank and the scouring of the sediment layer at the bottom of the mud tank, reduce the overflow of mud and sand from the overflow port, and improve loading efficiency.

[0069] See Figure 9The grid baffle consists of two pieces, one installed in front of the rear loading hatch and the other installed between the front loading hatch and the overflow port. The grid baffle is a rectangular or T-shaped metal plate 1, welded together from upper and lower parts. The vertical joints are not welded, while the horizontal joints are welded. Several grid strips are evenly arranged longitudinally on the metal plate, and several through holes 2 are evenly arranged between adjacent grid strips, serving to dissipate energy, allow for flow, and prevent blockage. The energy dissipation principle is described in [reference needed]. Figure 8 A grating baffle, an energy dissipation device, was installed in the mud hold. The grating baffle's structural design utilizes the principle of hydraulic energy dissipation to accelerate the sedimentation of fine sand, reduce overflow losses, and increase the ship's loading efficiency without affecting the loading capacity. When using a grating baffle, the high-speed mud flow easily forms a hydraulic jump as it passes through the grating, resulting in water drop and energy dissipation; or it impacts the grating wall, directly offsetting some of the energy. This causes the water level behind the grating to rise, increasing the cross-sectional area of ​​the flow and reducing the flow velocity, thus allowing for sufficient sedimentation. The lower part of the grating baffle is suspended. After installing the grating baffle, the ship was stationed to observe whether the sedimentation effect of fine sand in the mud hold improved. Observation and comparison revealed a significant decrease in the mud flow velocity in the mud hold, a substantial reduction in the mud concentration at the overflow outlet, and an increase in the amount of fine sand loaded.

[0070] This includes statistical analysis of construction data, concluding that the above steps significantly improve the efficiency of trailing suction hopper dredgers in handling fine sand, achieving an average loading capacity of 5538m³ per trip when the optimal loading time is reached. 3 This represents a 37.9% increase compared to the previous period, and the project's construction goals have been achieved.

[0071] This method, by understanding and analyzing the soil distribution and stock of dredged materials in waterways, identifies the factors affecting the efficiency of trailing suction hopper dredging vessels in excavating fine sand, and takes effective and targeted countermeasures. This has significantly increased the loading capacity of trailing suction hopper dredged fine sand, which not only strongly promotes the project construction progress but also ensures the backfilling needs of related projects. At the same time, it reduces marine environmental pollution, improves project quality, broadens the application fields of trailing suction hopper dredgers, and promotes the comprehensive development of the economy and society.

Claims

1. A method for improving the efficiency of dredging fine sand using a trailing suction hopper dredger, characterized in that, Includes the following steps: S1. Based on on-site investigation, understand the soil distribution and quantity of dredged material in the waterway, focus on investigating the sand source, generate survey data, determine the construction area, and analyze the sand layer distribution characteristics; S2. Investigate and observe the construction characteristics of the trailing suction hopper dredger and the three stages of the dredging and loading process. In the early stage of excavating the sandy area, conduct trial excavation of the sandy section shown in the survey data, collect relevant construction data, and determine the actual soil conditions of the sandy area of ​​the waterway. S3. The actual soil conditions of the identified sandy area of ​​the waterway are treated, the surface silt is removed, and after the conditions for excavation of the lower sand layer are met, engineering technicians are stationed on the ship to track the construction of the trailing suction hopper dredger for fine sand, observe and record relevant data to form statistical reports for retention, backup and comparative analysis. S4. Based on the above steps, conduct research and analysis to determine the causes affecting the efficiency of trailing suction hopper dredging fine sand, classify the causes, and formulate targeted construction countermeasures for each cause. These countermeasures include: rationally controlling overflow time; dynamically using the loading hatch; reducing the mud flow rate in the mud tank; and coordinating single and double harrow operations. S4 includes four categories of causes affecting the efficiency of trailing suction hopper dredging fine sand: overflow duration, loading method, sedimentation rate of mud in the mud tank, and the use of single or double harrows. The construction countermeasures include: rationally controlling overflow time to address the overflow duration; dynamically using the loading hatch to address the loading method; reducing the mud flow rate in the mud tank to address the sedimentation rate of mud in the mud tank; and coordinating single and double harrow operations to address the use of single or double harrows. S5. Set construction goals, implement corresponding measures based on the construction strategies in S4, and achieve the completion deadline.

2. The method for improving the efficiency of dredging fine sand using a trailing suction hopper dredger according to claim 1, characterized in that, The S1 includes: First, based on the design geological survey data, the waterway is determined to be the section of the Zhanjiang Port 300,000-tonnage waterway reconstruction and expansion project, specifically the section from point A30' to point B' outside the waterway. Then, a supplementary field survey is conducted on the area near point B' of the waterway to determine the construction area as two areas: approximately 6 km east of point B and 9–13 km east of point B. The boreholes are arranged on the slopes on both sides of the waterway. According to supplementary field surveys, the sand layers in the construction area are mainly fine and medium sand. The sand layers about 6 km east of point B are continuous but unevenly distributed, and the underlying strata are mostly silty clay layers. The surface layer 9-13 km east of point B is silt or silt. The sand layers are discontinuous, appearing as lenses. The layers are relatively thin, with silty soil in the middle and sand at the bottom, showing alternating sand and mud deposition characteristics.

3. The method for improving the efficiency of dredging fine sand using a trailing suction hopper dredger according to claim 1, characterized in that, The S2 includes: According to the investigation, the construction characteristics of the trailing suction hopper dredger are as follows: It is equipped with a rake head excavator and a hydraulic dredging device. During construction, the rake head is lowered underwater by the rake arms extending from both sides of the ship to loosen and excavate the seabed mud and sand. The mud and sand are pumped by the mud pump and transported through the pipeline to the loading hatch to enter the mud tank. There are two sets of mud loading hatches in the mud tank of the trailing suction hopper dredger, located midway and stern respectively. The overflow port is located near the bow. The distance between the front and rear sets of loading hatches and the overflow port is different, and the flow path of the mud after entering the mud tank is also different. Based on the on-site observation, under normal circumstances, the trailing suction hopper dredger will lower the left and right rake heads to excavate and open the front and rear sets of loading hatches at the same time during the construction process.

4. The method for improving the construction efficiency of a trailing suction hopper dredger in dredging fine sand according to claim 1, characterized in that, The three stages of the dredging and loading process in S2 are as follows: 1.) Begin dredging and loading the mud into the silt tank until the mud reaches overflow height. During this stage, all the mud and sand remain in the silt tank, either suspended or deposited. 2.) As loading continues in the overflow state, overflow loss begins to occur. During this stage, some sediment is deposited under gravity, while the rest is lost with the overflow. The deposition ratio depends on the loading flow rate, energy dissipation method, sediment tank structure, overflow facilities, and sediment particle size. As sediment continues to deposit, the deposition surface rises, the flow area decreases, and the flow velocity above the deposition surface begins to increase, causing the deposited sediment to be eroded again, resulting in an increasing tendency for overflow loss. 3.) Stop loading when the concentration of the incoming and overflowing soil is basically the same, that is, when the amount of soil loaded into the compartment no longer increases; After the trial excavation, the actual soil conditions in the sandy area of ​​the waterway were as follows: the surface layer was covered with silt, and the supplementary survey data showed that the surface layer was sand. Since the excavation depth was insufficient, the lower layer of sand was not reached. Therefore, a trailing suction hopper dredger was used to excavate the floating mud on the surface of the sandy area.

5. The method for improving the construction efficiency of a trailing suction hopper dredger in dredging fine sand according to claim 1, characterized in that, S3 includes: after removing the surface silt, tracking the ship's construction status for fine sand, and recording it as follows: construction was carried out on the sandy section K29+600~K32+600, with a total of 18 ship trips. The soil was mainly fine sand. The average dredging time per ship trip was about 3 hours, the cycle time was about 8.5 hours, and the loading volume was about 4000m³. According to the data, the construction efficiency was low.

6. The method for improving the construction efficiency of a trailing suction hopper dredger in dredging fine sand according to claim 1, characterized in that, S5 includes: the set construction target is to increase the average loading capacity of the trailing suction hopper dredger for fine sand per trip from 4000m³ to 5400m³, an increase of 35%, to ensure the progress and quality of the project construction and achieve the delivery schedule. The corresponding measures implemented according to the construction countermeasures in S4 include: 1.) Based on the loading effect of the ship, the overflow time should be appropriately extended: During construction, the overflow time should be extended by half an hour to increase the amount of earthwork loaded. Technicians should closely monitor the changing trend of the earthwork loading curve and control the overflow time according to the changes in the earthwork loading curve. When the earthwork volume does not change significantly with the increase of the overflow time, the rake should be started and construction should be stopped. 2.) Based on geological survey data and actual site conditions, and assuming the soil was silty fine sand of suitable thickness and good distribution continuity, the technicians conducted multiple tests on various loading methods while controlling the overflow time to be the same. The test results showed that: before overflow, using four-corner loading shortened the loading time; after overflow, using rear loading extended the sediment flow and improved the sedimentation effect of silty fine sand. 3.) The structure of the mud chamber is optimized by using the principle of hydraulic energy dissipation. An energy dissipation device, namely a grid baffle, is installed in the mud chamber. When the grid baffle is used for energy dissipation, the high-speed mud flow forms a hydraulic jump when passing through the grid baffle, resulting in water drop energy dissipation; or it impacts the grid baffle wall, directly offsetting part of the energy, thereby increasing the cross-sectional area of ​​the water flow and reducing the flow velocity, thus allowing the mud and sand to settle fully. 4.) The construction process adopts a combination of single-rake and double-rake construction. In the early stage, double-rake construction is adopted to ensure the efficiency of the early stage of loading. After the earthwork loading curve slows down, single-rake construction is used to reduce the flow rate of the loading port pipe, reduce the flow velocity of mud and sand into the tank and the scouring of the sediment layer at the bottom of the mud tank, reduce the overflow of mud and sand from the overflow port and improve the loading efficiency.

7. The method for improving the construction efficiency of trailing suction hopper dredgers in excavating fine sand according to claim 6, characterized in that, The grating baffle is configured as two pieces, one of which is installed in front of the rear loading hatch and the other is installed between the front loading hatch and the overflow port. The grating baffle is a rectangular or T-shaped metal plate with several grating strips evenly arranged in the longitudinal direction of the metal plate. Several through holes are evenly arranged between adjacent grating strips to dissipate energy, allow flow, and prevent blockage. The lower part of the grating baffle is suspended.

8. The method for improving the construction efficiency of a trailing suction hopper dredger in dredging fine sand according to claim 6, characterized in that, Construction data for single-harrow and double-harrow construction and mixed single-harrow and double-harrow construction using trailing suction hopper dredgers were recorded, statistically analyzed, and plotted as curves. The average earthwork loading capacity per dredger for double-harrow construction and the average earthwork loading capacity per dredger for mixed single-harrow and double-harrow construction were statistically compared to draw conclusions.

9. The method for improving the construction efficiency of a trailing suction hopper dredger in dredging fine sand according to claim 8, characterized in that, The construction data was recorded, statistically analyzed, and concluded that by adopting the above steps, the construction efficiency of the trailing suction hopper dredger for fine sand was significantly improved, and the construction objectives were achieved.

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