Offshore pipeline laying method for crossing existing high-speed bridge

Abstract

The invention relates to the field of offshore pipeline laying, and particularly discloses a method for laying an offshore pipeline crossing an existing high-speed bridge, which mainly comprises the following steps: construction method pile and platform construction, trench excavation construction, foundation treatment, main pipeline assembly welding, splicing and sinking, gravelly soil backfilling, low-strength self-compaction flow state filling material construction, and pile and platform dismantling construction. According to the construction method, the outer side of the pile foundation penetrating through the lower portion of the expressway is subjected to pile enclosure excavation through the PLC construction method, the pile foundation can be protected, disturbance of the excavated groove soil body is reduced, and then safe use of the pier and the temporary trestle bridge is guaranteed.

Description

Technical Field

[0001] The invention relates to the field of offshore pipeline laying, in particular to a method for laying offshore pipelines crossing existing high-speed bridges. Background Art

[0002] Offshore pipeline laying is a crucial part of construction in the oil and gas industry, including tailwater and deepwater operations. It is typically used for pipeline landing or landing sections, in shallow waters, or for short distances. For example, in shallow waters close to shore, pipelines can be pulled directly onto land using a winch or laid using a dedicated pipe-laying vessel. Currently, this is one of the primary methods for offshore pipeline laying.

[0003] However, laying large-diameter pipelines offshore usually requires the manufacture of prefabricated parts, but when it is necessary to lay them at the lower end of a highway bridge, the construction process cannot be carried out well. Summary of the Invention

[0004] In response to the existing problems, the present invention provides a method for laying offshore pipelines across existing high-speed bridges. The device used in conjunction with the method can effectively solve the problems raised in the background technology.

[0005] In order to solve the above problems, the present invention adopts the following technical solutions:

[0006] A method for laying an offshore pipeline across an existing high-speed bridge comprises the following steps:

[0007] Step S1: PLC method pile and platform construction:

[0008] Piling equipment combined with high-frequency vibratory hammers is used to sink piles. PLC piles are driven according to the designed dimensions. In addition to installing the designed steel purlins and steel pipe braces, double H-shaped steel is laid on the top of the piles as a load-bearing beam. Prefabricated bridge decks are installed on the load-bearing beams to complete the construction platform.

[0009] Step S2: trench excavation construction:

[0010] The trench is excavated strictly in accordance with the design and construction drawings. The excavation is completed by an amphibious excavator combined with a ship-mounted mud pump, supplemented by manual hydraulic flushing. During the excavation process, a symmetrical and balanced soil unloading method is used to ensure soil pressure balance.

[0011] Step S3: foundation treatment and construction:

[0012] Amphibious excavators and dredgers are used in conjunction with divers to carry out paving and backfilling. The cushion backfill materials are transported by small transport ships combined with truck unloading at the pier.

[0013] Step S4: Main pipeline assembly welding, splicing and sinking construction:

[0014] First, prefabricate and sink pipe sections at the embankment and cofferdam. Amphibious excavators in the mudflat section assist crawler cranes and winches in prefabrication and delivery of the pipe sections. Once prefabrication is complete, the entire pipe is delivered to the excavated trench for sinking, completing the pipeline installation work in the mudflat section.

[0015] Step S5: gravel soil backfill construction:

[0016] Use a small excavator on a PLC pile platform combined with a small transport ship for backfilling operations;

[0017] Step S6: Construction of low-strength self-compacting fluid filling material:

[0018] Low-strength self-compacting fluid filling material is prepared by a mixer and pumped and transported backfilled through a ground pump with an extended conduit;

[0019] Step S7: Pile and platform removal construction:

[0020] The pile driving equipment is combined with high-frequency vibration hammer to pull out the piles and the dismantling platform. When the PLC method piles are removed, the soil inside the steel pipe piles is grouting reinforced.

[0021] As a further solution of the present invention: in step S1, the PLC method piles are composed of steel pipe piles and Larsen steel sheet piles through a locking combination.

[0022] As a further solution of the present invention: the purlin and the steel sheet pile are connected by means of a corbel stiffener, the construction platform is used for construction machinery and equipment, pumping low-strength self-compacting fluid filling materials, grouting equipment, temporary stacking and parking of construction materials, and the paving is carried out as the paving is carried out and advanced in real time to ensure that sufficient working space is provided for the construction machinery and equipment.

[0023] As a further solution of the present invention: in the step S1, the PLC method piles are driven by piling equipment combined with a high-frequency vibration hammer, and the method piles are pushed from the side of the trestle toward the pier. The PLC method piles on one side are driven first, and the method piles are staggered on both sides. The support system of the construction platform is assisted by piling equipment, and the construction personnel perform full welding operations at the designed position.

[0024] As a further solution of the present invention: in the step S2, two amphibious excavators are used in conjunction with a ship group mud pump to carry out upper construction. The amphibious excavators are responsible for excavating and shoveling the earth in the mudflat section. The ship group mud pump is responsible for draining the earth excavated and shoveled into the ship to the mud barge transport ship and then abandoning it. The earth in the ship is discharged by diluting the water in the drainage ditch of the drainage pump station to form mud, which is then transported to the mud barge transport ship through a delivery pipe by the mud pump in the hull. The hydraulic excavation trench construction adopts a set of high-pressure water guns and mud pumps, supplemented by manual excavation to the bottom of the trench.

[0025] As a further solution of the present invention: in the step S2, the hydraulic flushing trough consists of three parts: a clean water mud flushing system, a mud delivery system and a power distribution system. The assembly, disassembly and transportation are completed manually, and the construction work of the earthwork project involving the high-speed double-track section is completed with the help of hydraulic force. The water flow is pressured by a high-pressure water pump, transported through a water hose, and sprayed out through a water gun head to cut and crush the soil to be excavated, so that it is moistened and disintegrated to form a mixture of mud and mud blocks, which is then transported to a mud barge transport ship for storage by a mud pump and a mud delivery pipe, completing the various construction processes of excavation, loading, transportation and unloading of the high-speed double-track pipeline trench earthwork project.

[0026] As a further solution of the present invention: in step S3, the dredger digs a trench in parallel to the axis of the DN1800 pipeline to prevent the ship from running aground on the seabed due to insufficient draft. The surveyor uses the instrument axis to control the berthing position of the dredger on the ship, so that the dredger is as close to the axis as possible.

[0027] As a further solution of the present invention: in step 5, gravel is backfilled around the pipeline, and then a layer of membrane bag concrete is covered on the gravel soil. When all the gravel soil is backfilled, the pipe cavities on both sides of the pipeline are first backfilled layer by layer in a symmetrical, spaced, and round-trip manner.

[0028] As a further solution of the present invention: in step S5, the gravel soil backfill section of the high-speed double-track section trench gravel soil backfill is a trapezoidal structure, the filling stone is a pebble mixture, the content of particles with a particle size greater than 20 mm exceeds 50% of the total weight, and the content of particles with a particle size greater than 2 mm exceeds 40% of the total weight, and it must not contain pollutants dissolved in the ocean.

[0029] As a further solution of the present invention: in step S6, the low-strength self-compacting fluid filling material is prepared by first weighing the mud and building stone powder and pouring them on a mixing board and stirring them evenly, then weighing out the silica-alumina active minerals, admixtures, and additives and mixing them together, splitting the center of the pile, pouring half of the required water, stirring evenly, and then pouring the remaining water, continuing to stir until uniform, and transporting or pumping through a pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A construction flow chart for a method of laying an offshore pipeline across an existing high-speed bridge;

[0031] Figure 2 A schematic diagram of the structure of a construction platform in a method for laying an offshore pipeline across an existing high-speed bridge;

[0032] Figure 3 This is a plan view of the pile layout of the PLC method used in a method of laying an offshore pipeline across an existing high-speed bridge;

[0033] Figure 4 A diagram of the PLC pile structure used in a method for laying offshore pipelines across an existing high-speed bridge.

[0034] Figure 5 This is a cross-sectional view of the backfill section in a method of laying an offshore pipeline across an existing high-speed bridge. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with specific inventions, and the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] In the description of this specification, the reference terms "this embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples.

[0037] like Figure 1 As shown, this embodiment provides a method for laying an offshore pipeline across an existing high-speed bridge, including the following steps: Step S1, PLC method pile and platform construction:

[0038] Piling equipment combined with high-frequency vibratory hammers was used to sink piles to minimize the impact on the surrounding environment. PLC piles were driven according to the designed dimensions to ensure the construction of PLC piles, backfill, pile extraction, grouting, and to strengthen the protection of the permanent piers of the high-speed double-track bridge. In addition to the designed steel purlins and steel pipe braces, double-piece H-shaped steel was laid at the top of the piles as a load-bearing beam to match the PLC piles. The prefabricated bridge deck was installed on the load-bearing beam to complete the processing of the construction platform.

[0039] Step S2: trench excavation construction:

[0040] The trench is excavated strictly in accordance with the design and construction drawings. The excavation is completed by an amphibious excavator combined with a ship-mounted mud pump, supplemented by manual hydraulic flushing. During the excavation process, a symmetrical and balanced soil unloading method is used to ensure soil pressure balance.

[0041] Step S3: foundation treatment and construction:

[0042] Amphibious excavators and dredgers are used in conjunction with divers to carry out paving and backfilling. The cushion backfill materials are transported by small transport ships combined with truck unloading at the pier.

[0043] Step S4: Main pipeline assembly welding, splicing and sinking construction:

[0044] First, prefabricate and sink pipe sections at the embankment and cofferdam. Amphibious excavators in the mudflat section assist crawler cranes and winches in prefabricating and delivering the pipe sections. Once prefabricated, the entire pipe is delivered to the excavated trench for sinking, completing the pipeline installation work in the mudflat section (high-speed double-track section).

[0045] Step S5: gravel soil backfill construction:

[0046] Use a small excavator on a PLC pile platform combined with a small transport ship for backfilling operations;

[0047] Step S6: Construction of low-strength self-compacting fluid filling material:

[0048] Prepared by a specific mixer, it is pumped and transported backfilled using a ground pump with an extended conduit;

[0049] Step S7: Pile and platform removal construction:

[0050] The pile driving equipment is combined with high-frequency vibration hammer to pull out the piles and the dismantling platform. When the PLC method piles are removed, the soil inside the steel pipe piles is grouting reinforced.

[0051] like Figure 2-5 As shown in this embodiment, the PLC method piles are composed of steel pipe piles and Larsen steel sheet piles through a lock joint combination, wherein the steel pipe piles are made of Q235 material with specifications (Φ: 820mm, δ: 14mm), and the Larsen steel sheet piles are made of Q345 material with specifications (δ: 15.5mm, steel sheet pile cross-sectional area: 96.99cm 2), the steel purlin adopts double-piece form model (HM500*300*11*18), flange connection plate: 650*400*14 (L*W*δ), stiffening rib: 464*140*14 (A*B*δ), the purlin and steel sheet pile are connected by bracket stiffening plate, the construction platform is mainly used for temporary stacking and parking of construction machinery and equipment, pumping low-strength self-compacting fluid filling materials, grouting equipment, construction materials, etc., the laying adopts the method of laying as the driving progresses and real-time advancement to ensure that sufficient working space is provided for construction machinery and equipment, the PLC method pile adopts pile driving equipment combined with high-frequency vibration hammer to vibrate and sink piles to reduce the impact on the surrounding environment, the method piles are pushed and driven from the side of the trestle to the pier direction, and the PLC method piles on one side are driven first, The construction piles are staggered on both sides, and the support system of the construction platform is assisted by pile driving equipment. In order to ensure that each pile is accurately driven, the first pile is located upstream, and a limit device is set on the guide frame before driving. The size is 1cm larger than each side of the pile. When driving, the back of the pile is close to the guide frame, and the hook is slowly lowered while driving. To ensure the verticality of the pile, a total station is used to observe in two perpendicular directions to ensure that the pile is inserted correctly and straight. After the first pile is qualified through testing, each pile is driven to the designed position on the offshore side based on the first pile. During the entire construction process, the total station should be used to always control the verticality of each pile within 0.5%. When deviation occurs, it should be adjusted in time, and the construction personnel will make adjustments at the designed position. During full welding operation, there is upward extrusion at the lower end of the pile during the insertion and driving process. The gap between the pile lock buckle and the lock buckle is large, and the upper end will always tilt away from the first pile. Therefore, a plumb bob must be used for every four or five piles to control the inclination of the pile within 0.5%. If the inclination exceeds the limit, it should be corrected. When the pile deflects too much, multiple corrections are used to gradually reduce the offset. If the soil is too hard to correct, a fall chain group is used to correct the deviation. Combined with the actual situation, characteristics and surrounding construction restrictions of the project, two amphibious excavators are used in conjunction with a ship group mud pump for upper construction (i.e., depth 0-4m). The amphibious excavator is responsible for excavation and shoveling of earth in the mudflat section, and the ship group mud pump is responsible for discharging the earth excavated and shoveled into the ship by the excavator to the mud barge transport ship. , and then discarded. The earthwork transportation in the ship is mainly carried out by diluting the water in the drainage ditch of the drainage pump station to form mud, which is then transported to the mud barge transport ship through the delivery pipe by the mud pump in the hull. The hydraulic flushing trench construction adopts a set of high-pressure water guns and mud pumps, supplemented by manual excavation (i.e. depth 4m-trench bottom). The hydraulic flushing trench consists of three parts: clean water mud flushing system, mud delivery system and power distribution system. The assembly, disassembly and transportation can be completed manually. The construction work of the earthwork project involving the high-speed double-track section is completed with the help of water power. The water flow generates pressure from the high-pressure water pump, is transported through the water hose, and a dense high-pressure, high-speed columnar water flow is ejected through the water gun head to cut and crush the soil to be excavated, make it wet and disintegrate, and form a mixture of mud and mud blocks.The slurry is then transported to the mud barge for storage by the mud pump and mud pipe, thus completing the excavation, loading, transportation and unloading of the high-speed double-track pipeline trench earthwork project. In order to avoid the ship from being stranded on the seabed due to insufficient draft when the dredger excavates the trench, the excavation operation is carried out parallel to the DN1800 pipeline axis. The surveying personnel use the instrument axis to control the berthing position of the dredger on the ship, so that the dredger is as close to the axis as possible. Before the construction of the sunken pipe, a positioning pile is set every 50m. The positioning piles of the floating sunken pipe construction section are φ500×10 steel pipe piles with a length of 15m. The mudflat section is assisted by piling equipment; the sea-land junction section is assisted by the dredger. The pipeline section (high-speed double-track section) is sent to float on the excavation of the mudflat section, and after the positioning piles are completed, When the pipe section is being laid, the water inlet valve is installed in the middle and upper part of the blind plate at the end of the pipe, and the exhaust valve is installed on the upper part of the blind plate at the head of the pipe. After positioning, the pipe is laid for the first time. The pipe section is located on the mudflat, and the tail of the outer pipe section is held and positioned by a crane vessel, and small boats and positioning piles are arranged at a certain interval in the pipe to control the expected sinking position of the pipe section. When the pipe section is being laid, the shape and stress of the pipe section are controlled, and lightweight floats are arranged along the pipeline to cooperate with crane vessels and small boats for construction. After the pipe section is in place, the position of the pipe section is adjusted again under the control of the measuring instrument to make the pipe section accurately match the installation axis position. After the position of the pipe section is accurately adjusted, the head of one end of the pipe is slightly raised by 10 cm. When the pipe is being laid, the blind plate at the end of the pipe can be opened to let water in and sink it. According to the sinking situation of the pipe section, the pipe section position is adjusted again. The speed of water inflow should be controlled, and the pipe section should maintain an appropriate position and shape so that water can be taken in at one end and the other end can be exhausted smoothly to prevent water hammer. When the pipe section is full of water and sinks automatically, the axial position of the pipe section should be checked and verified during the pipe sinking process to ensure that the pipe section is accurately sunk into place. After the pipe section sinks, the divers on the diving work boat will go into the water to conduct underwater inspection of the pipe section, check the condition of the entire pipe section, apply sand and flushing treatment to the local overhead and high starting point to complete the pipe sinking work. When the underwater pipeline is installed strictly, the stress condition of the pipe section during the sinking process is calculated to ensure that the stress is within the control range. When sinking the pipeline in the mudflat section, it is slowly lifted and the sinking speed is controlled to prevent the mudflat section pipeline from colliding with the hull. Before sinking, divers are arranged to explore the underwater foundation trench. Prevent large foreign objects (or sharp stones) from falling into the foundation trench to avoid damage caused by the sinking of the mudflat section pipeline. After the completion of the sinking of the mudflat section pipe section (high-speed double-track section), the diver will go into the water to check the immersed pipe at the junction of the mudflat section and the sea section. The diver should check the mud adhesion and position of the section of the pipeline, and carry out paving and mud suction treatment on the local overhead and high starting point to ensure that the pipe section is adhered to the mud. If the force is good, you can prepare to enter the trench backfill process. The pipeline is mainly backfilled with crushed stones, and then a layer of membrane bag concrete is covered on the crushed stone soil. When all the crushed stone soil is backfilled, the pipe cavity on both sides of the pipeline is first backfilled in layers, symmetrically, at intervals, and back and forth layer by layer. The gravel soil backfill section of the high-speed double-track section trench gravel soil backfill is a trapezoidal structure, and the filling stone is a pebble mixture.The content of particles with a diameter greater than 20mm exceeds 50% of the total weight, and the content of particles with a diameter greater than 2mm exceeds 40% of the total weight. The backfill material shall meet environmental protection requirements and shall not contain pollutants dissolved in the ocean. The gravel soil backfill on the pier side adopts the PLC method pile excavator combined with a small transport ship and divers to carry out the backfill operation. The gravel soil backfill on the trestle side is carried out by borrowing the highway construction platform and temporary bridge. The gravel soil backfill trench is carried out on the platform and temporary bridge with a crane and a loading and unloading hopper. For the backfill on the trestle side, the raw materials are transported to the corresponding position of the trestle and poured into the mudflat. The excavator is then used to turn it into the foundation trench. After backfilling to the designed elevation, divers go into the water to level the slope. The earth and stone backfill of the pipeline under the highway temporary bridge can be carried out at the highway construction platform and temporary bridge on the steel temporary bridge under construction. The gravel soil backfill trench is carried out on the platform and temporary bridge with a crane and a loading and unloading hopper. Backfill, after transporting the raw materials to the corresponding position of the trestle, pour them into the mudflat, and then use the excavator to turn them into the foundation trench. The concrete bags can also be lifted from the platform to the trench, and then the divers will level the slope to complete the construction. The divers will go into the water to install the geotextile bags according to the designed position and fix them in preparation for underwater concrete pouring. This section of the pipeline trench is close to the steel temporary bridge. On the temporary bridge, the concrete pump truck will directly pump the concrete into the bags for pouring. The low-strength self-compacting fluidized fill material is prepared by first weighing the mud and building stone powder and pouring them on the mixing board to mix them evenly. Then, the silicon-aluminum active minerals, admixtures, and additives are weighed out and mixed together. The center of the pile is opened and half of the required water is poured in. After careful mixing, the remaining water is poured in and the mixing is continued until uniform. The low-strength self-compacting fluidized fill material is a filling material with the characteristics of self-leveling, self-compacting, and self-hardening. It is transported through pipelines or pumped to achieve the effects of self-leveling, self-compacting, and self-hardening.

[0052] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying 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 limiting the present invention.

[0053] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0054] The above is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for laying an offshore pipeline across an existing high-speed bridge, characterized in that: The steps include: Step S1: PLC method pile and platform construction: Piling equipment combined with high-frequency vibratory hammers is used to sink piles. PLC piles are driven according to the designed dimensions. In addition to installing the designed steel purlins and steel pipe braces, double H-shaped steel is laid on the top of the piles as a load-bearing beam. Prefabricated bridge decks are installed on the load-bearing beams to complete the construction platform. Step S2: trench excavation construction: The trench is excavated strictly in accordance with the design and construction drawings. The excavation is completed by an amphibious excavator combined with a ship-mounted mud pump, supplemented by manual hydraulic flushing. During the excavation process, a symmetrical and balanced soil unloading method is used to ensure soil pressure balance. Step S3: foundation treatment and construction: Amphibious excavators and dredgers are used in conjunction with divers to carry out paving and backfilling. The cushion backfill materials are transported by small transport ships combined with truck unloading at the pier. Step S4: Main pipeline assembly welding, splicing and sinking construction: First, prefabricate and sink pipe sections at the embankment and cofferdam. Amphibious excavators in the mudflat section assist crawler cranes and winches in prefabrication and delivery of the pipe sections. Once prefabrication is complete, the entire pipe is delivered to the excavated trench for sinking, completing the pipeline installation work in the mudflat section. Step S5: gravel soil backfill construction: Use a small excavator on a PLC pile platform combined with a small transport ship for backfilling operations; Step S6: Construction of low-strength self-compacting fluid filling material: Prepare low-strength self-compacting fluid filling materials and use ground pumps with extended conduits for pumping and transporting backfill; Step S7: Pile and platform removal construction: The pile driving equipment is combined with high-frequency vibration hammer to pull out the piles and the dismantling platform. When the PLC method piles are removed, the soil inside the steel pipe piles is grouting reinforced.

2. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 1, characterized in that: In step S1, the PLC method piles are formed by combining steel pipe piles and Larsen steel sheet piles through locking joints.

3. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 2, characterized in that: The connection between the purlin and the steel sheet pile is made by means of corbel stiffeners. The construction platform is used for temporary stacking and parking of construction machinery and equipment, pumping of low-strength self-compacting fluid filling materials, grouting equipment, and construction materials. The laying is carried out in real time.

4. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 1, characterized in that: In step S1, the PLC method piles are driven by piling equipment combined with a high-frequency vibration hammer. The method piles are pushed forward from the side of the trestle toward the pier. The PLC method piles on one side are driven first. The method piles are staggered on both sides. The support system of the construction platform is assisted by piling equipment, and the construction personnel perform full welding operations at the designed position.

5. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 1, characterized in that: In step S2, two amphibious excavators are used in conjunction with a ship-mounted mud pump to carry out upper construction. The amphibious excavators are responsible for excavating and shoveling the earth in the mudflat section. The ship-mounted mud pump is responsible for draining the earth excavated and shoveled into the ship to the mud barge transport ship and then discarding it. The earth in the ship is discharged by diluting the water in the drainage ditch of the drainage pump station to form mud, which is then transported to the mud barge transport ship through a delivery pipe by the mud pump in the ship body. The hydraulic excavation trench construction uses a set of high-pressure water guns and mud pumps, supplemented by manual excavation to the bottom of the trench.

6. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 1, characterized in that: In step S2, the hydraulic scouring trench is composed of three parts: a clean water mud flushing system, a mud delivery system and a power distribution system. The assembly, disassembly and transportation are completed manually, and the construction work of the earthwork project involving the high-speed double-track section is completed with the help of hydraulic power. The water flow is pressurized by a high-pressure water pump, transported through a water hose, and sprayed out through a water gun head to cut and crush the soil to be excavated, so that it is moistened and disintegrated to form a mixture of mud and mud blocks. The slurry is then transported to a mud barge for storage by a mud pump and a mud delivery pipe, completing the various construction processes of excavation, loading, transportation and unloading of the high-speed double-track pipeline trench earthwork project.

7. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 1, characterized in that: In step S3, the dredger digs a trench parallel to the pipeline axis, and the surveyor on the ship uses the instrument axis to control the berthing position of the dredger so that the dredger is as close to the axis as possible.

8. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 1, characterized in that: In step S5, gravel is backfilled around the pipeline, and then a layer of membrane bag concrete is covered on the gravel soil. When all the gravel soil is backfilled, the pipeline cavities on both sides are first backfilled layer by layer in a symmetrical, staggered, and round-trip manner.

9. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 1, characterized in that: In step S5, the gravel soil backfill section of the high-speed double-track section trench gravel soil backfill is a trapezoidal structure, the filling stone is a pebble mixture, the content of particles with a particle size greater than 20 mm exceeds 50% of the total weight, and the content of particles with a particle size greater than 2 mm exceeds 40% of the total weight. The backfill material must not contain pollutants dissolved in the ocean.

10. The method for laying an offshore pipeline across an existing high-speed bridge according to claim 1, characterized in that: In step S6, the low-strength self-compacting fluidized filling material is prepared by first weighing the mud and building stone powder and pouring them onto a mixing board and stirring them evenly, then weighing out the silicon-aluminum active minerals, admixtures, and additives and mixing them together, splitting the center of the pile, pouring in half of the required water, stirring evenly, and then pouring in the remaining water, and continuing to stir until uniform. The low-strength self-compacting fluidized filling material is transported through a pipeline or pumped.

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