Harbor dredging construction methods

Abstract

The present invention discloses a harbor dredging construction method, including: construction preparation: laying anti-fouling curtains outside the construction water area; using a total station to measure the construction area; harbor dredging: using a grab dredger to excavate in layers, and using a mud barge to transport the mud to the mud unloading point for disposal; excavation of the foundation trench and the sea side of the soil between piles: extending the pipe head of a sand pumping ship to the sea side of the area between piles to pump mud and sand to form a sea side dredging section; excavation of soil between piles: using a long-arm excavator to excavate and dredge the soil between piles; excavation of the shore side of the soil between piles: using a long-arm excavator to excavate to form a shore side dredging section; harbor shallowing: conducting a full-topographic survey to determine the shallow point and shallowing route, and shallowing the harbor according to the shallow point and shallowing route to ensure the dredging depth. The construction method of the present invention solves the problem of continuous movement of mud and sand and its deposition in the excavated trench, causing siltation and loss or reduction of dredging results, thereby ensuring dredging effectiveness and saving dredging construction time.

Description

Technical Field

[0001] The present invention relates to the field of dredging construction, and more particularly to a harbor dredging construction method. Background Art

[0002] Dredging projects are widely used to excavate new waterways, ports, and canals, as well as to excavate foundation pits for hydraulic structures such as docks, shipyards, and locks. In recent years, with increasing demands for environmental standards, preventing and reducing pollution to water and land caused by dredging has become a critical issue that must be considered in dredging projects. Existing harbor dredging construction methods often involve excavating underwater silt, transporting silt, and dumping silt throughout the construction process. However, due to the limitations of these construction methods, silt is constantly moving and depositing in the excavated trenches, causing back-silting, resulting in the loss or reduction of dredging results, poor dredging effectiveness, and prolonged dredging construction time. Summary of the Invention

[0003] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0004] Another object of the present invention is to provide a harbor dredging construction method, which performs anti-pollution pretreatment before construction to reduce pollution to surrounding waters caused by subsequent dredging. A stepped slope is excavated in layers in front of the wharf, and the area between the piles is excavated on the sea side and the shore side to form a sea side dredging section and a shore side dredging section. This solves the problem of continuous movement of sediment and its deposition in the excavated trench, causing siltation and resulting in loss or reduction of dredging results, thereby ensuring dredging effectiveness and saving dredging construction time.

[0005] In order to achieve these purposes and other advantages according to the present invention, a harbor dredging construction method is provided, comprising the following steps:

[0006] Step 1: Construction preparation: Deploy anti-fouling curtains outside the construction area; use a total station to measure the construction area;

[0007] Step 2: Harbor Dredging: The grab dredger is towed from the cruise ship to the construction area. DGPS is used to locate the vessel, and the bow and stern are pushed by an anchor boat to adjust the vessel's position to the set location. The grab dredger is used to excavate the dredged material in layers, and a mud barge is used to transport the mud to the unloading point for disposal.

[0008] Step 3: Excavation of the foundation trench and the sea side of the soil between the piles: The sand pumping vessel is moored near the front of the wharf and anchored with a cable. The pipe head is extended to the sea side of the area between the piles. Mud and sand are pumped out to form a sea side dredging section. The silt is directly pumped to the mud barge, and the sand is transported to the storage area through a pre-set pipeline.

[0009] Step 4: Excavation of soil between piles: After the pile foundation and cross beams are completed and before the longitudinal beam construction begins, a long-arm excavator is used to excavate and dredge the soil between piles;

[0010] Step 5: Excavation of the soil bank between piles: Rock dumping is performed on the bank wall to form a rock dumping platform, and a long-arm excavator is used to excavate on the rock dumping platform to form a bank dredging section;

[0011] Step 6: Shallowing of harbor basin: Conduct full terrain survey to determine shallow points and shallowing routes, and shallowing of harbor basin according to shallow points and shallowing routes to ensure dredging depth.

[0012] Preferably, in said step 2, after adjusting the ship position to the set position, the step further includes: after the ship stops, lowering a positioning pile, throwing two side anchors at the bow, gradually adjusting the ship position to the center line of the trench, and installing the transverse ground anchor of the grab dredger; wherein, when constructing upstream, the leading angle of the ground anchor is not greater than 20°, and the lagging angle is not greater than 10°.

[0013] Preferably, in step 2, the layer thickness of the layered excavation is 1.5m, and the layered excavation is carried out until the designed bottom elevation is reached. During the dredging process, the next grab of the grab dredger is controlled to overlap with the previous grab within the range of 1 / 4 to 1 / 3 of the grab to control the elevation and flatness of the harbor bottom.

[0014] Preferably, in step 2, each layer of excavation is carried out using the method of "lateral excavation for width and longitudinal excavation for length", with longitudinal construction first and then transverse construction; the longitudinal movement length of the grab dredger is equal to the grab opening length minus 1m, and the transverse movement width of the grab dredger is determined by the width of the grab dredger used. The specific method is: before excavating each dredging area, the number of transverse excavations of the harbor should be calculated based on the width of the harbor to be excavated and the width of the grab dredger, wherein the calculation formula for the number of transverse excavations is:

[0015] n=b / (a-2)

[0016] Where n is the number of horizontal excavations, b is the dredging width in m, and a is the grab dredger width in m.

[0017] Preferably, in step three and step four, when the soil between the piles is excavated and dredged, a long-arm excavator ship is used to enter the pile rack, loosen the soil between the piles, and throw soil and mud to the sea side of the soil between the piles; wherein the long-arm excavator ship is towed to the construction site by an anchor boat, fixed by two anchor piles behind the long-arm excavator ship, and tires are arranged around the ship to cushion minor collisions.

[0018] Preferably, the slope of the harbor dredging area is excavated in steps, and a stable slope is formed by utilizing natural landslides. The dredging is carried out in strips with a width of 15m. Each trench overlaps the adjacent trench by 2 to 3m.

[0019] Preferably, the step six further includes the step of post-dredging measurement, wherein the selection of post-dredging measurement instruments is the same as the measurement instruments used in construction preparation.

[0020] Preferably, in step five, the top elevation of the riprap platform is +2.15 mCD.

[0021] The present invention has at least the following beneficial effects:

[0022] First, the harbor dredging construction method of the present invention arranges anti-pollution curtains outside the construction water area to prevent and reduce pollution of the water area and land area caused by the dredging construction.

[0023] Second, the harbor dredging construction method of the present invention optimizes the dredging construction process, excavates a stepped slope in layers at the front of the wharf, and excavates the area between the piles on the sea side and the shore side to form a sea side dredging section and a shore side dredging section, thereby solving the problem of continuous movement of sediment and its deposition in the excavation groove, causing siltation, and resulting in loss or reduction of dredging results, ensuring dredging effectiveness and saving dredging construction time.

[0024] Other advantages, objectives and features of the present invention will be reflected in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the harbor dredging construction method of the present invention;

[0026] Figure 2 This is a flow chart of the harbor dredging process in the harbor dredging construction method of the present invention;

[0027] Figure 3 The present invention provides a flow chart of the harbor dredging process for shallowing the harbor. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to the embodiments so that those skilled in the art can implement the invention with reference to the description.

[0029] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0030] It should be understood that terms such as “having,” “including,” and “comprising” used herein do not prescribe the existence or addition of one or more other elements or combinations thereof.

[0031] It should be noted that, in the description of the present invention, the terms "horizontal", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like to indicate directions or positional relationships are the directions or positional relationships shown, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0032] like Figures 1 to 3 As shown, the present invention provides a harbor dredging construction method, comprising the following steps:

[0033] Step 1: Construction preparation: Deploy anti-fouling curtains outside the construction area; use a total station to measure the construction area;

[0034] Step 2: Harbor Dredging: The grab dredger is towed from the cruise ship to the construction area. DGPS is used to locate the vessel, and the bow and stern are pushed by an anchor boat to adjust the vessel's position to the set location. The grab dredger is used to excavate the dredged material in layers, and a mud barge is used to transport the mud to the unloading point for disposal.

[0035] Step 3: Excavation of the foundation trench and the sea side of the soil between the piles: The sand pumping vessel is moored near the front of the wharf and anchored with a cable. The pipe head is extended to the sea side of the area between the piles. Mud and sand are pumped out to form a sea side dredging section. The silt is directly pumped to the mud barge, and the sand is transported to the storage area through a pre-set pipeline.

[0036] Step 4: Excavation of soil between piles: After the pile foundation and cross beams are completed and before the longitudinal beam construction begins, a long-arm excavator is used to excavate and dredge the soil between piles;

[0037] Step 5: Excavation of the soil bank between piles: Rock dumping is performed on the bank wall to form a rock dumping platform, and a long-arm excavator is used to excavate on the rock dumping platform to form a bank dredging section;

[0038] Step 6: Shallowing of harbor basin: Conduct full terrain survey to determine shallow points and shallowing routes, and shallowing of harbor basin according to shallow points and shallowing routes to ensure dredging depth.

[0039] In the above technical solution, anti-pollution curtains were deployed outside the construction area before construction to prevent and reduce pollution to the water and land areas caused by dredging. By optimizing the dredging construction process, a stepped slope was excavated in layers in front of the wharf. The area between the piles was excavated on the sea side and the shore side to form the seaside dredging section and the shoreside dredging section. This solved the problem of continuous movement of sediment and its accumulation in the excavated trench, causing siltation and loss or reduction of dredging results, ensuring dredging effectiveness and saving dredging construction time.

[0040] In one of the technical solutions of the present invention, in step 2, after adjusting the ship position to the set position, the step also includes: after the ship stops, lowering a positioning pile, throwing two side anchors at the bow, gradually adjusting the ship position to the center line of the trench, and installing the transverse anchor of the grab dredger; wherein, when constructing upstream, the leading angle of the anchor is not greater than 20°, and the lagging angle is not greater than 10°.

[0041] In the above technical solution, after the grab dredger is towed to the construction area by a tugboat, it is positioned using DGPS and the bow and stern are pushed by an anchor boat, gradually adjusting the ship's position to the desired location. After the ship stops, a positioning pile is lowered, two side anchors are set at the bow, and the ship's position is gradually adjusted to the centerline of the trench. Placing piles while the ship is moving is strictly prohibited. The grab dredger's transverse anchor should be securely installed. When constructing upstream, the lead angle of the anchor should generally not exceed 20°, and the trailing angle should not exceed 10°. When anchoring, the grab dredger should generally drop the upper wind anchor first, followed by the lower wind anchor. When reeling in the anchor, the lower wind anchor should be reeled in first, followed by the upper wind anchor. This achieves the positioning and anchoring of the grab dredger.

[0042] In one of the technical solutions of the present invention, in step 2, the layer thickness of the layered excavation is 1.5m, and the layered excavation is carried out until the designed bottom elevation is reached. During the dredging process, the next grab of the grab dredger is controlled to overlap with the previous grab within the range of 1 / 4 to 1 / 3 of the grab to control the elevation and flatness of the harbor bottom.

[0043] In the above technical solution, in order to properly control the elevation and flatness of the harbor bottom, the grab bucket's drop depth must be controlled during dredging. This is done by using the existing control point elevations and marking control marks on the wire rope. The grab bucket's excavation spacing is also controlled. During excavation, there is a certain height difference between the mud surface that has been grabbed and the original mud surface that has not been grabbed. The grab bucket will "turn over" in this area, which will be reflected in the tilt of the wire rope. Therefore, the overlap between the next grab bucket and the previous grab bucket can be controlled to within 1 / 4-1 / 3 of the grab bucket. In areas with poor geology, the overlap range can be appropriately increased.

[0044] In one of the technical solutions of the present invention, in step 2, each layer of excavation is carried out using the method of "lateral excavation for width and longitudinal excavation for length", with longitudinal construction first and then transverse construction; the longitudinal movement length of the grab dredger is equal to the grab opening length minus 1m, and the transverse movement width of the grab dredger is determined by the width of the grab dredger used. The specific method is: before excavating each dredging area, the number of transverse excavations of the harbor should be calculated based on the width of the harbor to be excavated and the width of the grab dredger, wherein the calculation formula for the number of transverse excavations is:

[0045] n=b / (a-2)

[0046] Where n is the number of horizontal excavations, b is the dredging width in m, and a is the grab dredger width in m.

[0047] In the above technical solution, the longitudinal and transverse travel lengths of the grab dredger are determined based on the principle of preventing missed excavations. After the grab dredger completes longitudinal excavation of a harbor section, it should anchor and advance a certain distance to begin excavating the next section. This advance (i.e., longitudinal travel) distance is equal to the extended length of the grab dredger. The actual length of the grab dredger used is the longitudinal travel length of the grab dredger per operation.

[0048] In one of the technical solutions of the present invention, in step three and step four, when the soil between the piles is excavated and dredged, a long-arm excavator ship is used to enter the racks between the piles, loosen the soil between the piles, and throw soil and mud to the sea side of the soil between the piles; wherein the long-arm excavator ship is towed to the construction site by an anchor boat, fixed by two anchor piles behind the long-arm excavator ship, and tires are arranged around the ship to cushion minor collisions.

[0049] In the above technical solution, the long-arm excavator vessel is positioned by two anchor piles, and possible minor collisions are cushioned by arranging tires around the vessel.

[0050] In one of the technical solutions of the present invention, the slopes in the harbor dredging area are excavated in steps, and natural landslides are used to form stable slopes. The dredging is carried out in strips with a width of 15m. Each trench overlaps the adjacent trench by 2 to 3m.

[0051] In this technical solution, the slopes in the dredged area are excavated in steps, with the overall undercutting and undercutting being achieved, utilizing natural landslides to create stable slopes. Dredging is carried out in strips, each 15m wide. To prevent missed cuts, each trench overlaps the adjacent trench by 2-3m.

[0052] In one of the technical solutions of the present invention, the step six further includes the step of post-dredging measurement, wherein the selection of post-dredging measurement instruments is the same as the measurement instruments in construction preparation.

[0053] In the above technical solution, the setting of section spacing and measuring point spacing for completion measurement, as well as the selection of measuring instruments are the same as those for pre-dredging measurement. The measurement results will be checked in detail with the design requirements and engineering quality standards until they meet the project completion requirements.

[0054] In one technical solution of the present invention, in step 5, the top elevation of the riprap platform is +2.15 mCD. A long-arm excavator is used to dump rocks into the excavation site to form a temporary riprap platform. The riprap platform is extended parallel to the wharf in its length.

[0055] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following embodiments are provided for illustration:

[0056] Take, for example, the dredging work involved in the Phase II Terminal Expansion and Reconstruction Project at Tanga Port in Tanzania. The project is located in Tanga, northeastern Tanzania. Tanga is situated in the Gulf of Tanga on the northeastern coast of Tanzania, west of the Pemba Strait. It is Tanzania's second-largest port. It is approximately 190 km (320 km by land, a 5-6 hour drive) away from the port and 130 km from Mombasa, Kenya.

[0057] Project Overview:

[0058] The new wharf is 450 meters long and 50 to 92 meters wide. The hydraulic pile foundation platform is 38.5 meters wide. The entire wharf comprises two berths and is divided into four sections, with lengths of 103 meters, 87 meters, 110 meters, and 150 meters, respectively. The wharf's hydraulic structure utilizes a high-pile beam-slab construction. The pile foundation utilizes 1.1-meter-diameter, fully vertical cast-in-place piles, with six piles per bent and 8.05 to 8.2 meters between the bents. Land is located behind the pile foundation platform. Sandy foundation areas are primarily treated with backfilling with rock and localized shallow high-pressure jet grouting. Muddy foundation areas are primarily treated with backfilling with sand and deep DCM.

[0059] The dredged bottom mark for the harbor basin is -13m CD, and the dredged bottom mark for the berth 1 foundation channel is -16m CD. The dredged bottom mark for the wave barrier at berth 1 is -3m CD, and the dredged bottom marks for the steps above and below the jet grouting piles at berth 2 are -6.5m CD and -9.6m CD, respectively.

[0060] Weather conditions:

[0061] The port has a tropical savanna climate, with northeasterly winds prevailing from December to February and southwesterly winds from April to October. Temperatures fluctuate slightly throughout the year, and the average annual rainfall is around 1,300 mm. Precipitation occurs year-round, with higher precipitation in April and May.

[0062] Geological conditions: The project site is mainly composed of very soft organic silt, very loose / loose / medium dense / dense / very dense gravel sand mixed clay soil and soft plastic / hard plastic / hard plastic / hard clay / sand mixed clay soil.

[0063] The wharf for this project is 450 meters long. The overall deployment plan proposes to divide the wharf into three operating sections (150m + 150m + 150m) along the shore from east to west. To meet the owner's requirement to ensure the normal operation of the 150m old wharf during the construction period, the overall construction adopts a segmented, flow-through operation method from east to west. The specific dredging plan is as follows:

[0064] A harbor dredging construction method comprises the following steps:

[0065] Step 1: Construction preparation: Deploy anti-fouling curtains outside the construction area; use a total station to measure the construction area;

[0066] Step 2: Harbor dredging (including Berth 1 and Berth 2 basins and berth waters):

[0067] 1) Positioning and anchoring of grab dredger

[0068] The grab dredger is towed from the cruise ship to the construction area, positioned using DGPS and using an anchor boat (specification: 300 HP) to push the bow and stern, and adjust the ship's position to the set position. After the ship stops, a positioning pile is lowered, and two side anchors are dropped at the bow. The ship's position is gradually adjusted to the center line of the trench, and the grab dredger's transverse ground anchor is installed. When working against the current, the lead angle of the ground anchor is not greater than 20°, and the trailing angle is not greater than 10°. When the grab dredger drops anchor, it is generally necessary to drop the upper wind anchor first and then the lower wind anchor. When reeling in the anchor, it is necessary to reel in the lower wind anchor first and then the upper wind anchor.

[0069] 2) Dredging

[0070] Grab dredgers are used for layered excavation, with each layer being 1.5m thick. Each layer is excavated using a "lateral excavation for width, longitudinal excavation for length" approach, with longitudinal construction first followed by transverse construction. Each backward movement of the grab dredger, i.e., the longitudinal length of the dredger, is equal to the grab bucket's open length minus 1m (0.5m for both front and rear). After longitudinal construction is complete, the lateral width of the grab dredger is determined by the grab dredger's width minus 2m. These longitudinal and transverse movement lengths are determined based on the principle of preventing missed excavations.

[0071] The lateral width of the grab dredger operation is determined by the width of the grab dredger used. Specific method: Before excavating each dredging area, the number of lateral excavations of the harbor should be calculated based on the width of the harbor to be excavated and the width of the grab dredger. The calculation formula for the number of lateral excavations is:

[0072] n=b / (a-2)

[0073] Where n is the number of horizontal excavations, b is the dredging width in m, and a is the grab dredger width in m.

[0074] After a grab dredger completes longitudinal excavation of a harbor section, it must anchor and advance a certain distance to begin excavating the next section. This distance is equal to the length of the grab dredger's extended reach. The actual length of the grab dredger used is the length of its longitudinal movement.

[0075] Among them, the grab dredger (8m3, Zhuhai Doumen District Shipyard) has a length of 36.80m, full load waterline length of 36.8m, beam of 12.5m, maximum beam of 12.70m, depth of 2.80m, maximum height of 8.50m, light load draft of 1.280m, full load draft of 1.800m, full load displacement of 740.870t, light load displacement of 575.050t, structural type: longitudinal frame type, navigation area: Class A, hull material: steel, number of watertight transverse bulkheads: 5.

[0076] 3) Dredging bottom elevation and flatness control

[0077] This project uses 8m 3 Grab dredgers excavate in layers, with a layer thickness of 1.5m, until the designed bottom elevation is reached. To control the elevation and flatness of the harbor bottom, the grab's drop depth must be controlled during dredging. This is done by using existing control point elevations and marking control marks on the wire rope. The grab's excavation spacing is also controlled. During excavation, there is a certain height difference between the mud surface that has been grabbed and the original mud surface that has not been grabbed. The grab will "turn over" in this area, which will be reflected by a tilt on the wire rope. Therefore, the overlap between the next grab and the previous grab can be controlled to within 1 / 4-1 / 3 of the grab range. In areas with poor geology, the overlap range can be appropriately increased.

[0078] 4) Dredging and abandoning soil:

[0079] The GPS positioning system on the mud barge is used to move the mud barge to the designated location for slag disposal. The mud barge is an open bottom mud barge (500m 3 , Qingxin County Shantang Town Shipyard), specific parameters include: total length: 50.55m, ship length: 47.20m, full load waterline length: 48.98m, ship width: 11.50m, maximum ship width: 11.80m, molded depth: 3.60m, maximum ship height: 15.35m, light load draft: 1.127m, full load draft: 3.000m, full load displacement: 1465.207t, light load displacement: 492.470t, structure type: longitudinal frame type, navigation area: Class A, hull material: steel, number of watertight transverse bulkheads: 7.

[0080] Step 3: Excavation of foundation trench and soil between piles on the sea side (Berth 1, Berth 2): Sand pumping ship (Specification: 300m 3 / h) Anchoring and laying mooring cables near the front of the wharf, with the pipe head extended to the sea side of the area between the piles, and mud and sand are pumped out to form a sea side dredging section. The mud is directly pumped to the mud barge, and the sand is transported to the storage area through the pre-set pipeline;

[0081] Step 4: Excavation of soil between piles (Berth 1, Berth 2): After the pile foundation and cross beams are completed and before the longitudinal beam construction begins, a long-arm excavator (18m long) is used to excavate and dredge the soil between the piles.

[0082] Step 5: Excavation of soil bank between piles (Berth 1 only): Rock dumping is done on the quayside to form a riprap platform. A long-arm excavator (specification: 320) is used to excavate on the riprap platform to form a bank dredging section.

[0083] Excavation and dredging of the soil between the piles must be completed after the pile foundations and transverse beams are completed, but before longitudinal beam construction begins. Excavation within the grouting pile construction area must not begin until the grouting piles reach their designed strength. For Berth No. 2, excavation between the piles cannot begin until the steel sheet piles are complete and the grouting and mixing piles reach their designed strength. A small, custom-built sand pumping vessel dispatched from China can pump mud and sand at the front edge of the wharf. A stepped slope is excavated layer by layer at the front edge of the wharf to create a natural slope. A long-arm excavator then enters the area between the piles to excavate, gradually forming the designed excavation section on the seaward side. For landward excavation, a platform is constructed from boulders at the front edge of the old wharf. From this platform, the long-arm excavator gradually excavates the designed landward section. Any hard clay layers within the dredging area can be removed with the long-arm excavator, assisted by a water jet. Larger boulders can also be removed with the long-arm excavator.

[0084] During harbor dredging, the soil between the piles collapses toward the harbor basin under the influence of gravity, forming a natural collapse surface. A grab dredger continues excavating this collapsed area in the harbor basin until no further collapse is observed. A sand pumping vessel anchors near the pier, drops anchor, and extends its pipe head to the seaward side of the area between the piles to begin pumping mud and sand. The silt is pumped directly onto a mud barge for disposal, while the sand is transported to a stockpile via a pre-installed pipeline. The excavated cross-section is regularly measured, and the pumping vessel's pipe head is gradually advanced from the seaward side toward the landward side until it reaches the maximum length of the mud pipe head. A long-arm excavator then enters the pile-to-pile arrangement, loosens the soil between the piles, and dumps the soil and mud to the seaward side. The long-arm excavator is towed to the construction site by an anchor boat. It is secured to the work site using two anchor piles at the rear of the long-arm excavator, and tires are placed around the vessel to cushion any minor impacts. Afterward, a long-reach excavator was positioned near the edge of the old wharf and began removing silt from the designed retaining wall to the edge of the old wharf. Excavation continued below the designed excavation line, and the long-reach excavator then dumped rocks into the excavated area to form a temporary rock platform. The platform was extended parallel to the wharf along its length, with the top elevation of the platform at +2.15 mCD.

[0085] The long-arm excavator has a hull length of 16.8 meters, an 18-meter boom, and a width of 6 meters. The anchor piles are 12 meters x 2. A commander should be stationed on the platform during long-arm excavator operation, communicating via walkie-talkie. Early warnings should be issued promptly to prevent the long-arm excavator from operating too close to the beams and causing them to rub against them. Minimize lateral movement of the long-arm during excavation; when the grab bucket is raised, lateral movement of the long-arm should only be performed after it reaches a height above the beams. Any beams accidentally impacting the surface should be promptly chiseled away to expose the aggregate and then filled with concrete of the same grade. Regularly measure the shape of the excavated section and, if no significant changes are observed, measure the stability of the rock platform. Once the rock platform is stable, move the long-arm excavator onto it. When excavating the bank side of the soil between the piles on the platform, ensure the safety of the equipment and operators and excavate at a constant speed. If significant collapse of the excavated section is observed, the excavator should be moved to another section and backfilled with rock to stabilize the platform. According to the above method, the excavation section of the soil between the piles is gradually formed from both the sea side and the land side.

[0086] Step 6: Shallowing of harbor basin: Conduct full terrain survey to determine shallow points and shallowing routes, and shallowing of harbor basin according to shallow points and shallowing routes to ensure dredging depth.

[0087] During construction with grab vessels, shallow spots can be accidentally left behind. Natural slopes between piles can also impact the surrounding areas of the harbor basin. Therefore, prior to completion, this project will conduct a harbor dredging exercise to ensure the dredging depth meets design requirements. First, a full-scale topographic survey will be conducted to identify shallow spots. A rational dredging route will be planned to improve construction efficiency.

[0088] Use a sand pump ship to remove shallow spots near the front of the wharf, and use a grab ship to remove shallow spots in the harbor area. Since the ship moves slowly during construction, the influence of wind and current should be fully considered to ensure that the ship is on the planned route and that the shallow spots are removed accurately. This method can effectively remove the ridges and shallow stalks that have formed in the construction area and reduce the time for shallowing. Step 7, post-dredging measurement: The section spacing and measuring point spacing of the completion measurement, as well as the selection of measuring instruments are the same as those for the pre-dredging measurement. Check the measurement results in detail with the design requirements and engineering quality standards until they meet the project completion requirements.

[0089] The harbor dredging construction method of the present invention has achieved good results in the dredging construction of the Tanga Port Phase II Terminal Expansion and Reconstruction Project in Tanzania. Compared with the existing harbor dredging construction method (dredging underwater silt, transporting silt, and throwing silt), the harbor dredging construction method of the present invention performs anti-pollution pretreatment before construction to reduce the pollution of the surrounding waters by subsequent dredging. The area between the piles is divided into the sea side and the shore side for excavation to form a sea side dredging section and a shore side dredging section, which reduces the continuous movement of silt and its deposition in the excavated groove, causing siltation, resulting in the loss or reduction of dredging results, and ensuring the dredging effectiveness. The dredging construction method of the present invention takes 175 days, while the existing dredging construction method takes 235 days. By adopting the dredging construction method of the present invention, the dredging construction time is shortened by 60 days.

[0090] The number of modules and processing scales described herein are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be apparent to those skilled in the art.

[0091] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A harbor dredging construction method, characterized in that: The following steps are involved: Step 1: Construction preparation: Deploy anti-fouling curtains outside the construction area; use a total station to measure the construction area; Step 2: Harbor Dredging: A grab dredger is towed from the cruise ship to the construction area. Using DGPS for positioning and using an anchor boat to push the bow and stern, the vessel is adjusted to the designated location. The grab dredger excavates the dredged material in layers, and a mud barge transports the mud to the unloading point for disposal. The slopes of the harbor dredging area are excavated in steps, utilizing natural landslides to create stable slopes. Dredging is carried out in strips, each 15 m wide, with each trench overlapping the adjacent trench by 2-3 m. Step 3: Excavation of the foundation trench and the sea side of the soil between the piles: The sand pumping vessel is moored near the front of the wharf and anchored with a cable. The pipe head is extended to the sea side of the area between the piles. Mud and sand are pumped out to form a sea side dredging section. The silt is directly pumped to the mud barge, and the sand is transported to the storage area through a pre-set pipeline. Step 4: Excavation of soil between piles: After the pile foundation and cross beams are completed and before the longitudinal beam construction begins, a long-arm excavator is used to excavate and dredge the soil between piles; Step 5: Excavation of the soil bank between piles: Rock dumping is performed on the bank wall to form a rock dumping platform, and a long-arm excavator is used to excavate on the rock dumping platform to form a bank dredging section; Step 6: Shallowing of harbor basin: Conduct full terrain survey to determine shallow points and shallowing routes, and shallowing of harbor basin according to shallow points and shallowing routes to ensure dredging depth.

2. The harbor dredging construction method according to claim 1, characterized in that: In the step 2, after adjusting the ship's position to the set position, the following steps are also included: after the ship stops, lowering a positioning pile, dropping two side anchors at the bow, gradually adjusting the ship's position to the center line of the trench, and installing the grab dredger's transverse ground anchor; wherein, when constructing upstream, the leading angle of the ground anchor is not greater than 20°, and the lagging angle is not greater than 10°.

3. The harbor dredging construction method according to claim 1, characterized in that: In the step 2, the layer thickness of the layered excavation is 1.5 m, and the layered excavation is carried out until the designed bottom elevation is reached. During the dredging process, the next grab of the grab dredger is controlled to overlap with the previous grab within the range of 1 / 4 to 1 / 3 of the grab to control the elevation and flatness of the harbor bottom.

4. The harbor dredging construction method according to claim 3, characterized in that: In step 2, each layer of excavation is carried out using the method of "lateral excavation for width and longitudinal excavation for length", with longitudinal construction first and then transverse construction; the longitudinal movement length of the grab dredger is equal to the grab opening length minus 1 m, and the transverse movement width of the grab dredger is determined by the width of the grab dredger used. The specific method is: before excavating each dredging area, the number of transverse excavations of the harbor should be calculated based on the width of the harbor to be excavated and the width of the grab dredger. The calculation formula for the number of transverse excavations is: n=b / (a-2) Where n is the number of horizontal excavations, b is the dredging width in m, and a is the grab dredger width in m.

5. The harbor dredging construction method according to claim 1, characterized in that: In step three and step four, when the soil between the piles is excavated and dredged, a long-arm excavator is used to enter the pile rack, loosen the soil between the piles, and throw soil and mud to the sea side of the soil between the piles; wherein the long-arm excavator is towed to the construction site by an anchor boat, fixed by two anchor piles behind the long-arm excavator, and tires are arranged around the ship to cushion minor collisions.

6. The harbor dredging construction method according to claim 1, characterized in that: The step six also includes the step of post-dredging measurement, wherein the selection of post-dredging measurement instruments is the same as the measurement instruments in construction preparation.

7. The harbor dredging construction method according to claim 1, characterized in that: In step 5, the top elevation of the riprap platform is +2.15 mCD.

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