Seabed immersed tunnel variable-section prefabricated pipe pile system and construction method thereof

Abstract

The invention discloses a variable-section prefabricated pipe pile system for a seabed immersed tunnel and a construction method thereof, and the construction method comprises the following steps: a, removing sludge on the surface of a seabed by adopting a dredging ship, delimiting a construction area, and digging a foundation trench in the construction area; b, positioning and guiding underwater sonar to control the pile sinking precision and control the underwater robot formation to carry out combined construction, and carrying out pile sinking preparation at the bottom of the foundation trench according to a preset pile hole position; c, the underwater robot sinks the first-stage spiral prestressed pipe pile, and a reserved grouting hole is synchronously adopted for grouting to reinforce a pile-soil gap; d, special-shaped flanges are installed, and the cross-shaped prestressed pipe piles and the cylindrical prestressed pipe piles are connected in sequence; and e, a cushion layer is laid, the immersed tube tunnel is immersed, and then layered backfilling is conducted. The variable-section prefabricated pipe pile system and foundation soil bear loads together and bear force cooperatively, and the variable-section prefabricated pipe pile system has the advantages that the bearing capacity is improved, sedimentation is reduced, the construction speed is increased, and full-life-cycle health monitoring and pile foundation health diagnosis are conducted.

Description

Technical Field

[0001] This invention belongs to the field of submarine immersed tunnel technology, and in particular relates to a variable cross-section precast pipe pile system for submarine immersed tunnels and its construction method. Background Technology

[0002] With the rapid development of marine transportation facilities, immersed tunnels face multiple challenges in complex marine environments: ① Shallow piles are easily eroded and corroded by seawater, while deep pile-soil interfaces are prone to slippage and uplift; ② Traditional homogeneous pipe piles have a single cross-section, making it difficult to adapt to different geological characteristics, resulting in redundant or insufficient bearing capacity; ③ Vibration / hammer driving pile technology causes seabed liquefaction, and static pressure piles lack interface reinforcement, resulting in a 30%-50% reduction in pile-soil friction; ④ Insufficient positioning accuracy during underwater construction (error > 100mm with traditional methods) easily leads to pipe section misalignment and leakage.

[0003] Existing technologies suffer from three major drawbacks: 1) Homogeneous pipe piles cannot achieve gradient force transmission across tensile (bottom layer), shear (middle layer), and compressive (top layer) layers, resulting in low pile foundation utilization; 2) The lack of synchronous grouting technology leads to a pile-soil interface strength of only 1.2-1.8 MPa, lower than the requirements for marine foundations (≥2.5 MPa); 3) Manual pile driving results in a verticality deviation >1°, exacerbating the risk of uneven settlement. There is an urgent need to develop variable cross-section pipe pile systems and high-precision construction techniques to improve pile foundation durability and bearing capacity. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the prior art by providing a variable cross-section precast pipe pile system for subsea immersed tunnels and its construction method.

[0005] To achieve the above objectives, the invention employs the following technical solution: a construction method for a variable cross-section precast pipe pile system for subsea immersed tunnels, comprising the following steps: a. Use a dredging vessel to remove silt from the seabed surface, delineate the construction area, and excavate foundation trenches within the construction area; b. Positioning and guidance of underwater sonar control for pile driving accuracy control of underwater robot formation for joint construction. At the bottom of the foundation trench, pile driving preparation is carried out according to the preset pile hole position. The joint construction is carried out by at least a joint construction system composed of a mother ship control center, underwater robot cluster and sonar network. The joint construction system can achieve precise positioning and construction control of underwater robot formation through the integration of acoustic and optical technologies, so as to achieve centimeter-level precise sinking of precast piles for immersed tunnel and cluster collaborative operation. c. The underwater robot drives the first-stage spiral prestressed pipe piles, and simultaneously uses the reserved grouting holes to grout and reinforce the gap between the pile and the soil. d. Install the special-shaped flange and connect the cross-shaped prestressed pipe piles and cylindrical prestressed pipe piles in sequence; e. Lay a tensile strength cushion layer, sink the immersed tunnel, and then backfill in layers.

[0006] The aforementioned technical solution employs a variable cross-section precast pipe pile system composed of cylindrical, cross-shaped, and spiral prestressed pipe piles, along with flanges. This system utilizes a layered interface design, integrating the advantages of all three types of piles. It reduces the impact of seawater erosion and corrosion, enhances pile side friction, strengthens the foundation, optimizes the force transmission path, and improves pull-out resistance. Furthermore, the flange-jointing process allows for adjustable pile length combinations, adapting to unevenness along the foundation depth. The solidified grout further strengthens the pile-soil interface, enhancing bearing capacity. Simultaneously, the use of underwater sonar for positioning guidance and underwater robot formations optimizes the construction accuracy of traditional methods, improves the efficiency and safety of underwater construction, and ensures construction stability. Additionally, a real-time monitoring system adjusts construction parameters in real-time during construction to ensure quality. The variable cross-section precast pipe pile system shares the load with the foundation soil, providing advantages such as increased bearing capacity, reduced settlement, faster construction speed, extended service life, and the ability to perform full-life-cycle health monitoring and pile foundation health diagnosis.

[0007] As a further technical solution, the joint construction includes: The first-stage sonar guides the underwater robot to the vicinity of the pile location, and the second-stage forward-looking sonar of the underwater robot is activated to re-determine the pile driving position; An underwater robot arm is used to grip the pile head, and sonar feedback is used to ensure that the tilt angle is less than a first predetermined value. Simultaneously monitor pile driving force, grouting pressure, grout return volume, and pile driving speed, and automatically control pile driving and grouting based on sensor feedback data; The verticality, planar error, and settlement of the soil around the pile after pile driving are checked. The verticality deviation should not exceed the second predetermined value, and the planar error should not exceed the third predetermined value.

[0008] In the above technical solution, the first-level sonar provides wide-range navigation, while the second-level sonar provides precise positioning, effectively reducing the time for the robot to search for the pile. At the same time, by monitoring parameters such as pile driving force and grout return in real time, the pile driving speed and grouting pressure are automatically adjusted to avoid pile tilting or grout loss, thus significantly improving the construction qualification rate.

[0009] As a further technical solution, the joint construction system includes the following steps; The mother ship uses USBL sonar to locate the underwater robot and calculate its relative position. The underwater robot uses multibeam sonar to scan and transmits data to the mother ship to generate point cloud maps and coordinates. The mother ship's signal processing system compares the point cloud map with the real-time and preset coordinates and generates correction commands. The underwater robot's vector thruster adjusts its micro-force through the correction commands. The second-level sonar scan identifies the center hole of the precast pile, the blue-green laser rangefinder measures the distance between the robot and the pile top benchmark to determine the pile driving position, the robotic arm grabs the pile body, and the tilt sensor adjusts the vertical state. The underwater robots work in a coordinated formation. The mother ship makes rough adjustments and then makes precise scheduling, using optical communication to monitor the spacing between the underwater robots. If the spacing is too small, the robots slow down or hover.

[0010] The above technical solution utilizes multi-level sonar positioning, fine scanning, real-time correction, precise grasping, and collaborative scheduling to achieve high-precision positioning, accurate pile driving, and safe and efficient cluster collaborative construction of underwater robots in complex underwater environments.

[0011] As a further technical solution, the grouting is a cement-bentonite-fly ash mixed grout with a mixing ratio of 1:0.2:0.2, a slump of 220-250mm, an initial setting time of ≤4 hours, and a final compressive strength of ≥15MPa. The high slump ensures that the grout fully fills the gap between the pile and the soil, expands the penetration radius to 1.5-2.0m, and reduces the porosity by 15%.

[0012] As a further technical solution, the installation of the non-shaped flange includes: Insert four M30 bolts for initial positioning; Place a double-layer EPDM rubber sealing ring; Tighten the bolts symmetrically in three stages to 30%, 50%, and 70% torque; Epoxy resin is injected into the flange gap to seal it.

[0013] In the above technical solution, a double-layer EPDM sealing ring + epoxy grouting is used to achieve the IP68 standard for underwater sealing performance and improve durability. At the same time, the use of three-fold symmetrical bolt tightening (30%→50%→70% torque) can effectively reduce the risk of flange stress concentration and improve the strength of the connection node.

[0014] As a further technical solution, the method of reinforcing the pile-soil gap by grouting through pre-reserved grouting holes includes: Once the piles are driven to 1 / 3 of the design depth, the first grouting is initiated, and sensors are used to monitor and control the amount of grout return in real time. The grouting pressure is gradually increased as the grout is pressed to a predetermined height to ensure full diffusion of the grout. After grouting, maintain the grouting pressure for the predetermined time to allow the grout to fill the pile-soil interface as much as possible.

[0015] In the above technical solution, the grouting pressure is increased by 1.0m to adapt to different soil permeability coefficients, and the uniformity of grout diffusion is improved by 40%; the pressure is maintained for 10 minutes to ensure that the grout fully fills the micro-cracks, and the shear strength of the pile-soil interface reaches more than 2.5MPa.

[0016] Based on the specification, this invention provides a variable cross-section precast pipe pile system for subsea immersed tunnels, including cylindrical prestressed pipe piles, cross-shaped prestressed pipe piles, and spiral prestressed pipe piles connected in series from top to bottom by irregular flanges; it also includes a static pressure pile driving synchronous grouting system for simultaneous grouting during pile driving, as well as underwater robot formation and positioning guidance underwater sonar.

[0017] In the above technical solution, the spiral piles (bottom layer for pull-out resistance), the cross-shaped piles (middle layer for shear resistance), and the cylindrical piles (top layer for bearing pressure) form a gradient force transmission system, which increases the overall bearing capacity by 50%. The flange connection allows for free combination of pile lengths, which can cope with the unevenness of the strata and reduce pile foundation waste.

[0018] As a further technical solution, the outer diameter of the round end of the special-shaped flange is 200mm larger than the outer diameter of the cylindrical prestressed pipe pile, and the inner diameter is consistent with the inner diameter of the cylindrical prestressed pipe pile, with an error of ≤±2mm to ensure unobstructed grouting channel. The cross-shaped end of the special-shaped flange adopts a gradually changing cross section. The width and thickness of its rib plate are the same as those of the cross-shaped prestressed pipe pile. The center dimension gradually transitions to a circle and a spiral shape. The outer diameter is enlarged to disperse stress. The flange bending strength is ≥800MPa, avoiding the risk of joint breakage.

[0019] As a further technical solution, the cross-shaped prestressed pipe pile has a cross-shaped cross section, including four symmetrical trapezoidal ribs and a central circular core. The thickness of the thinnest part of the rib should be 80~200mm, and the width of the rib should not be more than three times the thickness of the rib. Grouting holes are equally spaced on the side walls of the cylindrical prestressed pipe pile, the cross-shaped prestressed pipe pile, and the spiral prestressed pipe pile.

[0020] As a further technical solution, the spiral prestressed pipe pile has an outer diameter of 1.5~2.5m, an inner diameter of 0.8~1.5m, a pile length of 6~20m, a spiral rib height of 50~80mm, a pitch of 500~800mm, a rib width of 80~150mm, and a single pile bearing capacity greater than 12000kN. The spiral rib increases the pile-soil contact area, and the pull-out bearing capacity is 1.8 times that of traditional piles. It is suitable for high water level buoyancy conditions. The pitch design forms a "soil nail effect" to reduce pile settlement.

[0021] Compared with existing technologies, the beneficial effects of this invention are as follows: The variable cross-section precast pipe pile system composed of cylindrical high-strength prestressed pipe piles, cross-shaped high-strength prestressed pipe piles, spiral high-strength prestressed pipe piles, and flanges adopts a layered interface design, which can integrate the advantages of the three types of piles. It can reduce the impact of seawater erosion and corrosion, enhance the pile side friction resistance, strengthen the foundation, optimize the force transmission path, and improve the pull-out performance. In addition, the flange-jointing process can achieve adjustable pile length combinations, adapt to the unevenness of the foundation along the depth, and the solidified solidified grout can further replace the pile-soil interface strength and improve the bearing capacity. At the same time, the underwater robot formation based on sonar-assisted positioning can optimize the construction accuracy of traditional methods, improve the efficiency and safety of underwater construction, and ensure construction stability. In addition, the real-time monitoring system can adjust the construction parameters in real time during the construction process to ensure quality. The variable cross-section precast pipe pile system shares the load with the foundation soil and works together to bear the force. It has the advantages of improving bearing capacity, reducing settlement, accelerating construction speed, extending service life, and conducting full life cycle health monitoring and pile foundation health diagnosis. It can effectively improve the problem of soft foundation damage in immersed tunnels and improve the construction accuracy of precast pile system and the strength of pile-soil interface. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the construction method provided in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the working principle of the combined sonar and underwater robot construction provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the working principle of the integrated static pressure pile driving and grouting reinforcement construction provided in an embodiment of the present invention. Figure 4 This is a cross-sectional schematic diagram of a variable cross-section precast pipe pile system for an immersed tunnel, provided as an embodiment of the present invention. Figure 5 This is a schematic diagram of a single variable cross-section precast pipe pile provided in an embodiment of the present invention; Figure 6 This is a top view of a flange provided for an embodiment of the present invention.

[0023] In the diagram: 1. Seabed silt layer; 2. Foundation trench; 3. Seabed; 4. Geotextile; 5. Variable cross-section precast pipe pile system; 51. Cylindrical high-strength prestressed pipe pile; 52. Sensor; 53. Flange; 531. Gradual cross-section section; 532. EDPM rubber sealing ring; 533. Flange ring bolt; 54. Cross-shaped high-strength prestressed pipe pile; 55. Spiral high-strength prestressed pipe pile; 56. Grouting hole; 6. Cushion layer; 7. Immersed tunnel; 8. Backfill layer; 9. Underwater robot; 10. Static pressure pile driving synchronous grouting system; 11. Positioning guidance underwater sonar. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, it should be noted that the terms "middle", "upper", "lower", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] like Figure 1 As shown, the specific scheme of the embodiment is as follows: A construction method for a variable cross-section precast pipe pile system for subsea immersed tunnels includes the following steps: a. Use a dredging vessel to remove silt from the seabed surface, delineate the construction area, and excavate foundation trenches within the construction area; b. Positioning and guiding underwater sonar to control pile driving accuracy control underwater robot formation to carry out joint construction, prepare for pile driving at the bottom of the foundation trench according to the preset pile hole position; c. The underwater robot drives the first-stage spiral prestressed pipe piles, and simultaneously uses the reserved grouting holes to grout and reinforce the gap between the pile and the soil. d. Install the special-shaped flange and connect the cross-shaped prestressed pipe piles and cylindrical prestressed pipe piles in sequence; e. Lay a tensile strength cushion layer, sink the immersed tunnel, and then backfill in layers.

[0027] The aforementioned technical solution employs a variable cross-section precast pipe pile system composed of cylindrical, cross-shaped, and spiral prestressed pipe piles, along with flanges. This system utilizes a layered interface design, integrating the advantages of all three types of piles. It reduces the impact of seawater erosion and corrosion, enhances pile side friction, strengthens the foundation, optimizes the force transmission path, and improves pull-out resistance. Furthermore, the flange-jointing process allows for adjustable pile length combinations, adapting to unevenness along the foundation depth. The solidified grout further strengthens the pile-soil interface, enhancing bearing capacity. Simultaneously, the use of underwater sonar for positioning guidance and underwater robot formations optimizes the construction accuracy of traditional methods, improves the efficiency and safety of underwater construction, and ensures construction stability. Additionally, a real-time monitoring system adjusts construction parameters in real-time during construction to ensure quality. The variable cross-section precast pipe pile system shares the load with the foundation soil, providing advantages such as increased bearing capacity, reduced settlement, faster construction speed, extended service life, and the ability to perform full-life-cycle health monitoring and pile foundation health diagnosis.

[0028] In this embodiment, joint construction includes: The first-stage sonar guides the underwater robot to the vicinity of the pile location, and the second-stage forward-looking sonar of the underwater robot is activated to re-determine the pile driving position; An underwater robot arm is used to hold the pile head, and sonar feedback is used to ensure that the inclination is less than the first predetermined value. The pile driving force, grouting pressure, grout return volume and pile driving speed are monitored simultaneously, and the pile driving and grouting are automatically controlled by sensor feedback data. The verticality, planar error, and settlement of the soil around the pile after pile driving are checked. The verticality deviation should not exceed the second predetermined value, and the planar error should not exceed the third predetermined value.

[0029] The specific implementation steps of the joint construction system are as follows: The first-stage sonar uses ultra-short baseline sonar (USBL) for basic global positioning. The first-stage sonar transmitter is installed on the mother ship. The mother ship emits 30kHz sound wave signals through a bottom array. The underwater robot captures the sound wave signals of the mother ship through its onboard transponder and responds. The transponder calculates the relative position of the mother ship and the underwater robot by measuring the round-trip time of the sound waves. When the robot approaches the target pile, the second-stage sonar on the underwater robot uses a multi-beam forward-looking sonar to scan at a high frequency of 1.2MHz to acquire scanning data. The underwater robot transmits the scanning data to the mother ship, and the signal processing system on the mother ship generates a three-dimensional point cloud map of the seabed with a resolution of 5cm and the robot's measured coordinates based on the scanning data. The mothership signal processing system identifies secondary sonar signals, and generates correction commands by comparing point cloud maps, real-time coordinates, and preset coordinates in real time. The correction commands are then transmitted again via sonar to direct the underwater robot to perform positioning correction. The vector thruster mounted on the underwater robot receives correction commands and performs micro-force adjustments (during micro-force adjustments, the thrust control accuracy of the vector thruster is ±10N), so that the planar position deviation between the pile center and the target center is stabilized within 2cm. During the final execution phase, the second-level sonar scan identifies the center hole of the precast pile and acquires the center hole data. The blue-green laser rangefinder mounted on the underwater robot measures the distance parameters between the underwater robot and the pile top reference point (the wavelength of the blue-green laser rangefinder is 532mm). The pile driving position is determined by the center hole data and the distance parameters. The underwater robot uses sensors on its robotic arm to guide the arm to grasp the pile with an accuracy of ±5mm. At the same time, the tilt sensor on the robotic arm controls the verticality of the pile in a closed loop to ensure that the tilt of the pile does not exceed 0.5°. Multiple underwater robots form a robot joint formation, which adopts a master-slave cooperative architecture for comprehensive scheduling. The underwater robots receive control commands transmitted by the first-stage sonar of the mother ship through transponders to make coarse position adjustments. After the coarse position adjustments, the mother ship then precisely schedules the robot joint formation using an adaptive frequency band of 12-18kHz. Within a 10-meter range, the underwater robot uses its onboard blue LED optical communication (transmission rate 2Mbps) to avoid frequency band conflicts with the detection sonar of the second-level sonar. To ensure the safety of cluster operations, each underwater robot constructs a virtual safety cylinder with a diameter equal to its body width plus 2 meters. At the same time, the second-level sonar on each underwater robot monitors the distance between adjacent underwater robots in real time and makes distance determination. When the distance between adjacent underwater robots is 2m-5m, the underwater robot automatically reduces its speed to 0.3m / s and feeds back its position signal to the mother ship through the second-stage sonar, thereby replanning its path. When the distance between adjacent underwater robots is 2m, the underwater robot immediately activates its onboard emergency hovering device.

[0030] The aforementioned technical solution utilizes multi-level sonar positioning, fine scanning, real-time deviation correction, precise grasping, and collaborative scheduling to achieve high-precision positioning, accurate pile driving, and safe and efficient cluster collaborative construction of underwater robots in complex underwater environments. Specific effects include: using USBL sonar and multi-beam forward-looking sonar, combined with micro-force adjustment of the vector thruster, ensuring the deviation between the underwater robot and the target position is controlled within 2cm, guaranteeing construction accuracy; using sonar scanning to identify the center hole position and laser rangefinder to measure distance, the robotic arm precisely grasps the pile and adjusts its vertical state, ensuring the pile inclination does not exceed 0.5°, improving construction quality; multiple underwater robots form a joint formation, adopting a master-slave collaborative architecture, using optical communication and sonar monitoring to determine safe distances and plan paths, ensuring the safety and efficiency of cluster operations; and a real-time data transmission and dynamic adjustment mechanism between the mother ship and the underwater robots ensures the flexibility and adaptability of the construction process, enabling timely responses to changes in the complex underwater environment.

[0031] In this embodiment, the grouting is a cement-bentonite-fly ash mixture with a grout ratio of 1:0.2:0.2, a slump of 220-250mm, an initial setting time of ≤4 hours, and a final compressive strength of ≥15MPa. The high slump ensures that the grout fully fills the gap between the pile and the soil, expands the penetration radius to 1.5-2.0m, and reduces the porosity by 15%.

[0032] In this embodiment, the installation of the irregular flange includes: Insert four M30 bolts for initial positioning; Place a double-layer EPDM rubber sealing ring; Tighten the bolts symmetrically in three stages to 30%, 50%, and 70% torque; Epoxy resin is injected into the flange gap to seal it.

[0033] In the above technical solution, a double-layer EPDM sealing ring + epoxy grouting is used to achieve the IP68 standard for underwater sealing performance and improve durability. At the same time, the use of three-fold symmetrical bolt tightening (30%→50%→70% torque) can effectively reduce the risk of flange stress concentration and improve the strength of the connection node.

[0034] In this embodiment, grouting through pre-reserved grouting holes is used to reinforce the pile-soil gap, including: Once the piles are driven to 1 / 3 of the design depth, the first grouting is initiated, and sensors are used to monitor and control the amount of grout return in real time. The grouting pressure is gradually increased as the grout is pressed to a predetermined height to ensure full diffusion of the grout. After grouting, maintain the grouting pressure for the predetermined time to allow the grout to fill the pile-soil interface as much as possible.

[0035] In the above technical solution, the grouting pressure is increased by 1.0m to adapt to different soil permeability coefficients, and the uniformity of grout diffusion is improved by 40%; the pressure is maintained for 10 minutes to ensure that the grout fully fills the micro-cracks, and the shear strength of the pile-soil interface reaches more than 2.5MPa.

[0036] Based on the specification, this invention provides a variable cross-section precast pipe pile system for subsea immersed tunnels, including cylindrical prestressed pipe piles, cross-shaped prestressed pipe piles, and spiral prestressed pipe piles connected in series from top to bottom by irregular flanges; it also includes a static pressure pile driving synchronous grouting system for simultaneous grouting during pile driving, as well as underwater robot formation and positioning guidance underwater sonar.

[0037] In the above technical solution, the spiral piles (bottom layer for pull-out resistance), the cross-shaped piles (middle layer for shear resistance), and the cylindrical piles (top layer for bearing pressure) form a gradient force transmission system, which increases the overall bearing capacity by 50%. The flange connection allows for free combination of pile lengths, which can cope with the unevenness of the strata and reduce pile foundation waste.

[0038] In this embodiment, the outer diameter of the round end of the special-shaped flange is 200mm larger than the outer diameter of the cylindrical prestressed pipe pile, and the inner diameter is consistent with the inner diameter of the cylindrical prestressed pipe pile, with an error of ≤±2mm to ensure unobstructed grouting channel. The cross-shaped end of the special-shaped flange adopts a gradually changing cross section. The width and thickness of its rib plate are the same as those of the cross-shaped prestressed pipe pile. The center dimension gradually transitions to a circle and a spiral shape. The outer diameter is enlarged to disperse stress. The flange bending strength is ≥800MPa, avoiding the risk of joint breakage.

[0039] In this embodiment, the cross-shaped prestressed pipe pile has a cross-shaped cross section, including four symmetrical trapezoidal ribs and a central circular core. The thickness of the thinnest part of the rib should be 80~200mm, and the width of the rib should not be more than three times the thickness of the rib.

[0040] In this embodiment, the outer diameter of the spiral prestressed pipe pile is 1.5~2.5m, the inner diameter is 0.8~1.5m, the pile length is 6~20m, the spiral rib height is 50~80mm, the pitch is 500~800mm, the rib width is 80~150mm, the single pile bearing capacity is greater than 12000kN, the spiral rib increases the pile-soil contact area, the pull-out bearing capacity is 1.8 times that of traditional piles, and it is suitable for high water level buoyancy conditions. The pitch design forms a "soil nail effect" to reduce the settlement of the pile body.

[0041] In this embodiment, grouting holes are provided at equal intervals on the side walls of cylindrical prestressed pipe piles, cross-shaped prestressed pipe piles, and spiral prestressed pipe piles. Example

[0042] This invention provides a variable cross-section precast pipe pile system for subsea immersed tunnels and its construction method, such as... Figure 1 , Figure 2 as well as Figure 4 As shown, the feature is that it includes cylindrical high-strength prestressed pipe piles 51, flanges 53, cross-shaped high-strength prestressed pipe piles 54, spiral high-strength prestressed pipe piles 55, a cushion layer 6, an immersed tunnel 7, a backfill layer 8, a static pressure pile driving synchronous grouting system 10, an underwater robot for pile driving accuracy control 9, and a positioning and guidance underwater sonar 11. Its construction steps include: ① Geological survey, and use dredging vessel to remove silt from the surface of seabed 3, delineate the construction area, and form a construction surface; ② The seabed was sloped and excavated to form trench 2; ③ The underwater robot formation 9, precisely positioned by sonar 11, enters the site and prepares for the driving of the variable cross-section prefabricated pipe pile system 5 at the bottom of the foundation trench 2 according to the preset pile hole position; ④ The underwater robot 9 drives the first-stage spiral high-strength prestressed pipe pile 55, and simultaneously uses the reserved grouting hole 56 to grout and reinforce the gap between the pile and the soil. ⑤ Install the inter-pile flange 53 and then construct the cross-shaped high-strength prestressed pipe pile 54 and the cylindrical high-strength prestressed pipe pile 51 in sequence. ⑥ Laying of the subbase layer 4, sinking of the immersed tunnel 7 and construction of the backfill layer 8, completing the construction of the immersed tunnel system.

[0043] like Figure 2 As shown, in some embodiments, the cylindrical high-strength prestressed pipe pile 51 is a reinforced concrete structure, prefabricated using the pre-tensioning method. Factory testing requires it to meet requirements for flexural strength, compressive strength, impermeability, and corrosion resistance. The pile's outer diameter is 1.5~2.5m, inner diameter is 0.8~1.5m, and length is 6~20m. Holes 56 with a diameter of 20mm are pre-drilled at equal intervals on the sidewall of the pile pipe to allow the reinforcing grout injected into the pile pipe to pass through during the downward compression and expansion process. The reinforcing steel is prestressed, using high-strength steel strand or prestressed steel bars. The high-strength steel strand is 1860MPa grade, and the prestressed steel bars should be HRB500 grade or higher, with a tension stress preferably 0.6~0.7 times the ultimate tensile strength. The concrete strength grade should be C60~C80, the elastic modulus should be 35GPa, and the impermeability grade should be ≥P12. The prefabricated pipe piles are arranged in a group, forming a square distribution.

[0044] Furthermore, the corrosion protection requirements are divided into steel reinforcement corrosion protection and concrete corrosion protection. Steel reinforcement corrosion protection uses an epoxy coating to protect the prestressed steel bars, and a zinc alloy is applied to the outside of the steel bars using a sacrificial anode cathodic protection method. The concrete corrosion protection scheme adopts a layered structure of internal admixture proportions and external anti-corrosion coatings. The internal admixture proportions use slag powder, silica fume, and fly ash as core admixtures, with the addition of calcium nitrite and organic rust inhibitors. The slag powder content should be 10%~20% of the cement mass to reduce the heat of hydration of cement and reduce concrete porosity to reduce seawater chloride ion penetration. The silica fume content should be 3%~5% of the cement mass to fill the micropores in the concrete. The fly ash is Grade I or II low-calcium fly ash, with an addition of 15% of the cement mass to improve workability and inhibit alkali-aggregate reaction. The calcium nitrite rust inhibitor is added at 1% of the cement mass to passivate the steel bar surface. The organic rust inhibitor can be an amino alcohol rust inhibitor, with an addition of 0.5% of the cement mass. The external coating has a layered structure consisting of an inner layer, a middle layer, and an outer layer. The inner layer uses an epoxy zinc-rich primer with a thickness of 80-120 μm, the middle layer uses a thick-film epoxy glass flake coating with a thickness of 300-500 μm, and the outer layer uses a polyurethane topcoat with a thickness of 80-120 μm.

[0045] like Figure 3 As shown, in some embodiments, the flange 53 is a special-shaped flange to achieve geometric transformation between circular and cross-shaped sections, and between cross-shaped and spiral sections, ensuring effective and uniform load transfer. It is made of Q355B / C low alloy steel, located at the pile end, with an outer diameter matching the outer diameter of the pipe pile, which is 200mm larger than the outer diameter of the pipe pile. The inner diameter is consistent with the inner diameter of the pipe pile, with an error ≤±2mm to ensure unobstructed grouting channels. The thickness can be 40~80mm, and the bending and shear resistance requirements need to be verified based on bending moment and material yield strength. The cross-shaped end 54 adopts a cross-section gradient form 531, with the rib width and thickness being the same as the cross-shaped pipe pile. The center dimension gradually transitions to circular and spiral shapes. The number of flange ring bolts 533 can be 16~32, with a bolt diameter of M30 and a tensile strength of grade 8.8 or 10.9. The bolt center spacing should be greater than three times the bolt diameter, and the bolt preload is 70% of the bolt tensile strength. The gasket uses EDPM rubber sealing rings 532.

[0046] In some embodiments, the underwater pile splicing process of flange 53 includes the following steps: ② Connecting: Guide the upper and lower pipe pile flanges 53 to connect, and insert 4 bolts for initial positioning.

[0047] ② Sealing: Place double-layer EPDM rubber sealing rings 532 in the flange gap.

[0048] ③ Bolt installation: Install all 533 bolts and manually pre-tighten to 30% torque; tighten in stages in a symmetrical order to ensure even force distribution.

[0049] ③ Waterproofing: Apply epoxy grout to the exposed part of flange 53.

[0050] like Figure 2 As shown, in some embodiments, the cruciform high-strength prestressed pipe pile 54 adopts a reinforced concrete structure with a cruciform cross-section, consisting of four symmetrical trapezoidal ribs and a central circular core. The thinnest part of the rib should be 80~200mm thick, and the width of the rib should not exceed three times the thickness. The outer diameter of the core portion of the pile is 1.5~2.5m, the inner diameter is 0.8~1.5m, and the pile length is 6~20m. Holes with a diameter of 20mm are equidistantly reserved on the sidewall of the pile pipe to allow the reinforcing grout injected into the pile pipe to pass through during the downward compression and expansion process from the top of the pile pipe. The reinforcing steel is prestressed, using high-strength steel strand or prestressed steel bars. The high-strength steel strand type is 1860MPa grade, and the prestressed steel bars should be HRB500 grade or above, with a tensile stress preferably 0.6~0.7 times the ultimate tensile strength. The concrete strength grade should be C60~C80, the elastic modulus is 35GPa, and the impermeability grade is ≥P12. The precast pipe piles are arranged in a group in a square pattern. Their anti-seepage and anti-corrosion requirements are the same as those in claim 3.

[0051] Furthermore, the spiral high-strength prestressed pipe pile 55 adopts a reinforced concrete structure, with an outer diameter of 1.5~2.5m, an inner diameter of 0.8~1.5m, a pile length of 6~20m, a spiral rib height of 50~80mm, a pitch of 500~800mm, a rib width of 80~150mm, and a single pile bearing capacity greater than 12000kN. The pile pipe has equidistantly reserved holes of 20mm diameter on its sidewalls to allow the reinforcing grout injected into the pile pipe to pass through during the downward compression and expansion process from the top of the pile pipe. The reinforcing steel is prestressed, using high-strength steel strand or prestressed steel bars. The high-strength steel strand is of grade 1860MPa, and the prestressed steel bars should be grade HRB500 or higher, with a tensile stress preferably 0.6~0.7 times the ultimate tensile strength. The concrete strength grade should be C60~C80, the elastic modulus should be 35GPa, and the impermeability grade ≥P12. The precast pipe piles are arranged in a group in a square pattern. Their anti-seepage and anti-corrosion requirements are the same as those in claim 3.

[0052] like Figure 1As shown, in some embodiments, geotextile 4 is laid under the coarse sand and gravel cushion layer 6; the geotextile cushion layer is laid horizontally on top of the solid waste mixed pile, and the tensile strength of the geotextile used is not less than 30KN / m; the coarse sand and gravel cushion layer is constructed by an underwater paving machine, adopting a non-full strip structure, the immersed tunnel is placed on the coarse sand and gravel platform, multiple trenches are opened in the platform, the coarse sand and gravel particle size is 1~40mm, the leveling error does not exceed ±20mm, and the mud content of the coarse sand and gravel is not greater than 5%, the width of the coarse sand and gravel platform is 4m, the spacing between the trenches is 1.0~1.4m, and the thickness of the coarse sand and gravel cushion layer is 800mm.

[0053] like Figure 1 , Figure 5 As shown, in some embodiments, the static pressure pile driving synchronous grouting system 9 consists of a static pressure pile driver and a high-pressure grouting system. The static pressure pile driver can be a ZYJ-1800 or ZYJ-2400, equipped with an automatic leveling system and a clamping mechanism. The pile driving force should be 1.2 to 2.0 times the vertical bearing capacity of a single pile. The pile driving speed should be coordinated with the properties of the underlying soil layer; it should not exceed 0.5 m / min for conventional soft soil layers and 0.2 m / min for hard soil layers. The high-pressure grouting system includes a grouting pump, a mixing station, grouting pipes, and grouting holes 56. The grouting material is a mixture of cement slurry, bentonite, and fly ash, with a ratio of 1:0.2:0.2. The slump of the slurry can be 220 to 250 mm, and the initial setting time and compressive strength must meet the relevant national standards.

[0054] Furthermore, the synchronous grouting adopts an integrated construction process of static pressure pile driving and grouting reinforcement, and the specific construction steps include: ① Prefabricate pipe piles and embed grouting pipes inside the pipe piles.

[0055] ② Drive the piles to 1 / 3 of the design depth.

[0056] ③ Start the first grouting. The grouting pressure can be 1.0MPa, and the flow rate should not be too large. Use sensors to monitor and control the amount of grout returned in real time.

[0057] ④ Gradually increase the grouting pressure every 1.0m to ensure full diffusion of the grout.

[0058] ⑤ Maintain the grouting pressure for 10 minutes to allow the grout to fill the pile-soil interface as much as possible, thereby improving the reinforcement effect.

[0059] like Figure 4As shown, in some embodiments, the underwater robot 9 for pile driving accuracy control includes a propulsion system, sensors, a robotic arm, a camera, and a positioning system relying on two-stage sonar. It uses a multi-sensor array deployed on the pile body and employs the SLAM positioning algorithm to construct a pile location environment model for pile driving quality control. The underwater robot can be a Schilling UHD III and can be customized for prefabricated pipe piles used in subsea immersed tunnels. The sonar system 11 can be a Kongsberg high-resolution sonar detector. The combined use of sonar and the underwater robot enables millimeter-level accuracy control of pile driving in subsea immersed tunnels.

[0060] Furthermore, the joint construction steps include: ① Positioning: The first-stage sonar 11 guides the underwater robot 9 to the vicinity of the pile location, and the forward-looking second-stage sonar of the underwater robot 9 is activated to accurately determine the pile driving position.

[0061] ② Vertical pile: The pile head is held by an underwater robot with a 9-arm mechanical arm, and the tilt angle is kept less than 0.03° by sonar feedback.

[0062] ③ Pile driving: Simultaneously monitor pile driving force, grouting pressure, grout return volume, and pile driving speed, and automatically control pile driving and grouting by using data feedback from sensor 52.

[0063] ④ Acceptance: Inspect the verticality of the pile, the plane error, and the settlement of the soil around the pile after pile driving. The verticality deviation should not exceed 0.3°, and the plane error should not exceed 30mm.

[0064] like Figure 6 As shown, in some embodiments, the construction steps include: Step S100: Geological survey, and use a dredging vessel to remove silt from the seabed surface, delineate the construction area, and form a construction surface; Step S200: Excavate the seabed slope to form a foundation trench; Step S300: The underwater robot formation, precisely positioned by sonar, enters the site and prepares for the driving of the variable cross-section precast pipe pile system at the bottom of the foundation trench according to the preset pile hole positions; Step S400: The underwater robot performs the first stage of spiral high-strength prestressed pipe pile driving, and simultaneously uses reserved grouting holes to grout and reinforce the pile-soil gap; Step S500: Install the inter-pile flange and then construct the cross-shaped high-strength prestressed pipe piles and cylindrical high-strength prestressed pipe piles in sequence. Step S600: Laying the foundation layer, sinking the immersed tunnel and carrying out the anchoring backfill layer and general backfill layer construction to complete the construction of the immersed tunnel system.

[0065] Furthermore, the mechanical removal of silt from the seabed surface 1 forms a construction face, using a grab dredger with a cleaning width of 100m and a length slightly longer than the immersed tunnel 7. The slope excavation forms a foundation trench 2 with a slope ratio of 1:2. The foundation layer laying includes: laying a geotextile layer 4 at the bottom of the foundation trench 2; laying a coarse sand and gravel layer 6 on top of the geotextile layer, and compacting and leveling the gravel layer; the immersed tunnel 7 is placed by: prefabricating the immersed tunnel in a dry dock, floating the tunnel, and hoisting the immersed tunnel onto the surface of the foundation layer. This provides an ecologically sustainable seismic mitigation and reinforcement system and construction method for immersed tunnels, aiming to achieve seismic protection and mitigation of immersed tunnels under low-carbon conditions, and to solve the problems of seismic resistance and uneven settlement of immersed tunnels.

[0066] Furthermore, before mechanically removing silt from the seabed surface to form a construction surface, the process includes: prefabricating the immersed tube 7 in a dry dock. The immersed tube 7 can be taken as an example of a standard section of the Hong Kong-Zhuhai-Macau Bridge immersed tunnel, with a length of 180m, a width of 37.95m, and a height of 11.4m. The inclined sections on both sides of the immersed tube 7 can have a width of 3.62m and a height of 3.62m.

[0067] This invention utilizes a variable cross-section precast pipe pile system composed of cylindrical high-strength prestressed pipe piles, cross-shaped high-strength prestressed pipe piles, spiral high-strength prestressed pipe piles, and flanges. This system employs a layered interface design, integrating the advantages of the three types of piles. It reduces the impact of seawater erosion and corrosion, enhances pile side friction, strengthens the foundation, optimizes the force transmission path, and improves pull-out resistance. Furthermore, the flange-jointing process allows for adjustable pile length combinations, adapting to the unevenness of the foundation along its depth. The solidified grout further strengthens the pile-soil interface, enhancing bearing capacity. Simultaneously, the sonar-assisted positioning of underwater robot formations optimizes the construction accuracy of traditional methods, improving the efficiency and safety of underwater construction and ensuring construction stability. In addition, a real-time monitoring system adjusts construction parameters in real time during construction to ensure quality. The variable cross-section precast pipe pile system shares the load with the foundation soil, working synergistically to improve bearing capacity, reduce settlement, accelerate construction speed, extend service life, and enable full-life-cycle health monitoring and pile foundation health diagnosis. In summary, this method can effectively improve problems such as the damage to soft foundations in immersed tunnels, and enhance the construction accuracy of precast pile systems and the strength of the pile-soil interface.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A construction method for a variable cross-section precast pipe pile system for subsea immersed tunnels, characterized in that, Includes the following steps: a. Use a dredging vessel to remove silt from the seabed surface, delineate the construction area, and excavate foundation trenches within the construction area; b. Positioning and guidance of underwater sonar control for pile driving accuracy control of underwater robot formation for joint construction. At the bottom of the foundation trench, pile driving preparation is carried out according to the preset pile hole position. The joint construction adopts at least a joint construction system composed of mother ship control center, underwater robot cluster and sonar network. The joint construction system uses the integration of acoustic and optical technologies to accurately position and control the construction of underwater robot formation, so as to achieve centimeter-level accurate sinking of precast piles for immersed tunnel and cluster collaborative operation. c. The underwater robot drives the first-stage spiral prestressed pipe piles, and simultaneously uses the reserved grouting holes to grout and reinforce the gap between the pile and the soil. d. Install the special-shaped flange and connect the cross-shaped prestressed pipe piles and cylindrical prestressed pipe piles in sequence; e. Lay a tensile strength cushion layer, sink the immersed tunnel, and then backfill in layers.

2. The construction method of a variable cross-section precast pipe pile system for an immersed tunnel according to claim 1, characterized in that: The joint construction includes: The first-stage sonar guides the underwater robot to the vicinity of the pile location, and the second-stage forward-looking sonar of the underwater robot is activated to re-determine the pile driving position; An underwater robot arm is used to grip the pile head, and sonar feedback is used to ensure that the tilt angle is less than a first predetermined value. Simultaneously monitor pile driving force, grouting pressure, grout return volume, and pile driving speed, and automatically control pile driving and grouting based on sensor feedback data; The verticality, planar error, and settlement of the soil around the pile after pile driving are checked. The verticality deviation should not exceed the second predetermined value, and the planar error should not exceed the third predetermined value.

3. The construction method of a variable cross-section precast pipe pile system for an immersed tunnel according to claim 1, characterized in that: The joint construction system includes the following steps: The mother ship uses USBL sonar to locate the underwater robot and calculate its relative position. The underwater robot uses multibeam sonar to scan and transmits data to the mother ship to generate point cloud maps and coordinates. The mother ship's signal processing system compares the point cloud map with the real-time and preset coordinates and generates correction commands. The underwater robot's vector thruster adjusts its micro-force through the correction commands. The second-level sonar scan identifies the center hole of the precast pile, the blue-green laser rangefinder measures the distance between the robot and the pile top benchmark to determine the pile driving position, the robotic arm grabs the pile body, and the tilt sensor adjusts the vertical state. The underwater robots work in a coordinated formation. The mother ship makes rough adjustments and then makes precise scheduling, using optical communication to monitor the spacing between the underwater robots. If the spacing is too small, the robots slow down or hover.

4. The construction method of a variable cross-section precast pipe pile system for an immersed tunnel according to claim 1, characterized in that: The grouting is a cement-bentonite-fly ash mixture with a mix ratio of 1:0.2:0.2, a slump of 220-250mm, an initial setting time of ≤4 hours, and a final compressive strength of ≥15MPa.

5. The construction method of a variable cross-section precast pipe pile system for an immersed tunnel according to claim 1, characterized in that: The installation of the non-standard flange includes: Insert four M30 bolts for initial positioning; Place a double-layer EPDM rubber sealing ring; Tighten the bolts symmetrically in three stages to 30%, 50%, and 70% torque; Epoxy resin is injected into the flange gap to seal it.

6. The construction method of a variable cross-section precast pipe pile system for an immersed tunnel according to claim 1, characterized in that: The method of reinforcing the pile-soil gap by grouting through pre-reserved grouting holes includes: Once the piles are driven to 1 / 3 of the design depth, the first grouting is initiated, and sensors are used to monitor and control the amount of grout return in real time. The grouting pressure is gradually increased as the grout is pressed to a predetermined height to ensure full diffusion of the grout. After grouting, maintain the grouting pressure for the predetermined time to allow the grout to fill the pile-soil interface as much as possible.

7. A variable cross-section precast pipe pile system for subsea immersed tunnels, characterized in that, It includes cylindrical prestressed pipe piles, cross-shaped prestressed pipe piles, and spiral prestressed pipe piles connected in series from top to bottom by irregular flanges; it also includes a static pressure pile driving synchronous grouting system that injects grout simultaneously during the pile driving process, as well as underwater robot formation and positioning guidance underwater sonar.

8. A variable cross-section precast pipe pile system for subsea immersed tunnels according to claim 7, characterized in that: The outer diameter of the round end of the special-shaped flange is 200mm larger than the outer diameter of the cylindrical prestressed pipe pile, and the inner diameter is consistent with the inner diameter of the cylindrical prestressed pipe pile, with an error of ≤±2mm to ensure unobstructed grouting channel. The cross-shaped end of the special-shaped flange adopts a gradually changing cross section. The width and thickness of its rib plate are the same as those of the cross-shaped prestressed pipe pile, and the center dimension gradually transitions to a circle and a spiral shape.

9. A precast pipe pile system with variable cross-section for subsea immersed tunnels according to claim 7, characterized in that: The cross-shaped prestressed pipe pile has a cross-shaped cross section, including four symmetrical trapezoidal ribs and a central circular core. The thickness of the thinnest part of the rib should be 80~200mm, and the width of the rib should not be more than three times the thickness of the rib. Grouting holes are equally spaced on the side walls of the cylindrical prestressed pipe pile, the cross-shaped prestressed pipe pile, and the spiral prestressed pipe pile.

10. A variable cross-section precast pipe pile system for subsea immersed tunnels according to claim 7, characterized in that: The spiral prestressed pipe pile has an outer diameter of 1.5~2.5m, an inner diameter of 0.8~1.5m, a pile length of 6~20m, a spiral rib height of 50~80mm, a spiral pitch of 500~800mm, a rib width of 80~150mm, and a single pile bearing capacity greater than 12000kN.

Images