Method and system for quickly restoring bearing capacity of large-diameter steel cylinder, and implementation method thereof

Abstract

Provided are a method and a system for quickly restoring bearing capacity of a large-diameter steel cylinder or caisson 1. When the caisson is vibrated and lowered to a design depth through a linkage

Description

TECHNICAL FIELD The present invention relates to the marine and deep-water foundation engineering, and particularly relates to a method and a system for quickly restoring bearing capacity of a large-diameter steel cylinder, and an implementation method thereof. BACKGROUND A large-diameter steel cylinder has a simple structure, without complex nodes or connectors, but features strong adaptability to geological conditions and self-stabilization performance. In addition, the large-diameter steel cylinder has a large cross-sectional area and moment of inertia, a cross-section thereof has excellent bending resistance. Moreover, due to a large diameter, a contact area between an outer wall of a steel cylinder and surrounding soil is also large, making the large-diameter steel cylinder have strong horizontal resistance. Based on these advantages, the large-diameter steel cylinder is widely used as an island and cofferdam construction structure for an artificial island, a large-diameter foundation construction enclosure structure for a seacrossing bridge, a riser protective structure for a deep-sea oil drilling platform, and the like. Since the large-diameter steel cylinder has a huge size (with a diameter exceeding 20 m), traditional small-size impact hammers are unsuitable for sinking construction of the large-diameter steel cylinder. At present, vibratory sinking of the large-diameter steel cylinder is realized through a vibration hammer in a multi-hammer linkage manner, featuring convenient and fast construction process, examples include the sinking construction of large-diameter steel cylinders in island construction projects, such as Hong Kong-Zhuhai-Macao Bridge, and Shenzhen-Zhongshan Bridge. However, in the process of the sinking of the large-diameter steel cylinder by a linkage manner, high-frequency vibratory force will weaken soil surrounding the steel cylinder, and diminish the load-bearing capacity of the steel cylinder while accelerating its sinking. The foundation soil needs a long period (usually more than 1 year) to remold and restore its load-bearing capacity, this is why the large-diameter steel cylinder is mainly used as a temporary enclosure support structure rather than directly as a load-bearing structure to withstand external loads. With the gradual increase in scale and volume of marine infrastructure across China, wind, wave and current, as well as superstructure loads have witnessed a sharp increase, imposing severe challenges to its foundation support structure, and resulting in sharp increase in costs of traditional large-diameter pile foundations, large-diameter suction cylinder foundations, and the like. Theoretically, large-diameter steel cylinders have high vertical and horizontal load-bearing capacities. When their load-bearing capacities can be rapidly restored after the vibration sinking construction by a linkage hammer, making the large-diameter steel cylinders have the structural bearing capacities, they cannot only provide a safe and stable deep construction foundation solution for existing marine infrastructure construction and operation, but also promote the development of larger-scale marine infrastructure, yielding significant social and economic benefits. SUMMARY Objectives of the present invention: a first objective of the present invention is to provide a method for quickly restoring bearing capacity of a large-diameter steel cylinder to solve the problem that weakened foundation soil around a cylinder body needs has a long restoration period and cannot withstand the main load-bearing structural function after the vibration sinking construction by a linkage hammer; a second objective of the present invention is to provide a system for quickly restoring bearing capacity of a large-diameter steel cylinder; and a third objective of the present invention is to provide an implementation method of the system for quickly restoring bearing capacity of a large-diameter steel cylinder. Technical solution: the present invention provides a method for quickly restoring bearing capacity of a large-diameter steel cylinder, when the large-diameter steel cylinder is vibrated and lowered to a design depth through a linkage hammer, and water in a weakened foundation of an outer side wall of the large-diameter steel cylinder is discharged, such that foundation soil around a cylinder body is reshaped and consolidated, and quickly restoring the bearing capacity of the large-diameter steel cylinder is accordingly achieved. Further, the foundation soil around the large-diameter steel cylinder is drained in layers in an axial direction of the cylinder body, and drained at a plurality of points in a circumferential direction of the cylinder body, so as to accelerate remolding and consolidation of the foundation soil around the cylinder body uniformly. The system for quickly restoring bearing capacity of a large-diameter steel cylinder provided in the present invention includes: distributed drainage channels installed on the outer side wall of the large-diameter steel cylinder in a longitudinal direction, and a plurality of the distributed drainage channels being uniformly distributed in a circumferential direction of the large-diameter steel cylinder; a plurality of annular directional blocking devices installed on the outer side wall of the large-diameter steel cylinder in the longitudinal direction and configured to facilitate layered isolation of the foundation soil around the large-diameter steel cylinder; and mobile self-sealing water pumping devices installed inside each of the distributed drainage channels and configured for drainage in layers of the foundation soil around the large-diameter steel cylinder. Further, the number of the distributed drainage channels is three. Further, the distributed drainage channels each includes a negative-pressure water pumping pipe and inclined strut steel plates symmetrically disposed on both sides of the negative-pressure water pumping pipe, where the negative-pressure water pumping pipe, the inclined strut steel plates and the outer side wall of the large-diameter steel cylinder form an outer side cavity; the negative-pressure pumping pipe is open at an upper end, and is sealed at a lower end, and has opening sections and non-opening sections alternately arranged from bottom to top, holes communicating with the outer side cavity are form on the opening sections, water permeable holes communicating with the outer side cavity are formed on each of the inclined strut steel plates at positions corresponding to the opening sections, and the holes and the water permeable holes are blocked by a filter screen; and the annular directional blocking devices are disposed at positions corresponding to the non-opening sections, positions of the outer side cavity corresponding to the non-opening sections are blocked, and the mobile self-sealing water pumping devices are disposed inside the negative-pressure water pumping pipe. Further, the mobile self-sealing water pumping devices each includes a hollow shunt tube, a negative-pressure drainage tube, an upper fastening end and a lower fastening end, an outer diameter of the fastening end is slightly smaller than that of the negative-pressure water pumping pipe, an outer rubber bladder and an inner rubber bladder are disposed between the two fastening ends, and a space between the inner rubber bladder and the outer rubber bladder is filled with liquid; the hollow shunt tube passes through the upper fastening end, the inner rubber bladder and the lower fastening end, one end of the negative-pressure drainage tube is connected to the hollow shunt tube, and the other end thereof is connected to a vacuum pump device; pressurizing one-way valves are installed on the hollow shunt tube, a baffle plate downwardly inclined is installed on each pressurizing one-way valve for intercepting water flow after the vacuum pump device is started, such that part of high-speed water flow is allowed to enter the inner rubber bladder through the pressurizing one-way valves, and the outer rubber bladder squeezes an inner wall of the negative-pressure water pumping pipe to achieve sealing; and a pressure relief valve is disposed on the upper fastening end, and the pressure relief valve is connected to a ground surface through a pressure relief valve wire for releasing pressure of the inner rubber bladder, such that the sealing of the negative-pressure water pumping pipe by the outer rubber bladder is released, allowing the mobile self-sealing water pumping device to move inside the negativepressure water pumping pipe. Further, four pressurizing one-way valves are vertically and symmetrically installed at a central position of the hollow shunt tube, and one baffle plate is installed at an upper position of each pressurizing one-way valve. Further, the annular directional blocking devices each includes a groove-shaped base with an opening facing outwards, a bottom plate of the groove-shaped base is connected to the outer side wall of the large-diameter steel cylinder and an outer side wall of the distributed drainage channel, and wing plates on both sides of the groove-shaped base are connected to the outer side wall of the large-diameter steel cylinder through inclined strut transition plates; a grouting bag is placed inside the groove-shaped base; a grouting pipe is disposed on the outer side cavity, one end of the grouting pipe is connected to one one-way grouting valve disposed at a joint of the groove-shaped base and the inclined strut steel plate, and the other end thereof is connected to a grouting device; and an opening of the groove-shaped base is covered by a protective cover plate connected to the inclined strut transition plate at a lower side, and the protective cover plate can be pushed and opened after the grouting bag is filled with grout. Further, the one-way grouting valves of all grouting bags are disposed on the inclined strut steel plate on the same side, each grouting pipe is only connected to one one-way grouting valve, and grouting amount of each grouting bag is not less than 0.9 times of a maximum grouting volume thereof; and all the grouting bags can be grouted at the same time, or can be grouted sequentially from bottom to top. The implementation method for the system for quickly restoring bearing capacity of a large-diameter steel cylinder provided in the present invention includes: 1) after the large-diameter steel cylinder is vibrated and lowered to the design depth, each of the distributed drainage channels is inserted with one mobile self-sealing water pumping device, which is simultaneously lowered down to a position of the non-opening section; 2) the grouting device is started, the grouting bag is filled with cement grout to achieve layered isolation of the foundation soil around the large-diameter steel cylinder; 3) the vacuum pump device is started, the baffle plate starts to intercept the water flow, part of the high-speed water flow is allowed to enter the inner rubber bladder through the pressurizing one-way valves, and the outer rubber bladder expands and squeezes the inner wall of the negative-pressure water pumping pipe to form a vacuum environment; 4) the vacuum pump device continuously works until water output of the negative-pressure drainage tube reduces and becomes in a stable state, or working time is not less than 2 h; 5) the vacuum pump device is closed, the pressure relief valve wire is pulled, the liquid inside the inner rubber bladder flows out through the pressure relief valve, and the outer rubber bladder retracts; and all the mobile self-sealing water pumping devices are pulled up to a position of the non-opening section at an upper layer; and 6) the steps 3)-5) above are repeated until the negative-pressure drainage operation at a top layer is completed, the mobile self-sealing water pumping devices are recovered, and the distributed drainage channels are filled with the cement grout. Beneficial effects: compared with the prior art, the present invention has the following advantages: (1) In view of slow restoration of the bearing capacity of the large-diameter steel cylinder, the present invention suggests draining water from the surrounding weakened soil by using a linkage hammer, so as to accelerate remolding and consolidation of the foundation soil, and enable the large-diameter steel cylinder to exert its bearing capacity within a short period of time. Furthermore, compared with the traditional grouting methods for reinforcing the foundation, the method of consolidation through drainage to accelerate the restoration of bearing capacity is more economical and environmentally friendly. (2) The present invention further provides a distributed system for quickly restoring bearing capacity of a large-diameter steel cylinder, which can accelerate remolding and consolidation of the foundation soil around the cylinder body uniformly, significantly speed up the restoration time of bearing capacity and improve restoration effects of the bearing capacity. The implementation process of the system is simple, fast and easy to operate; and the mobile selfsealing water pumping devices are reusable and economical. The present invention effectively overcomes the problem that the large-diameter steel cylinder is incapable of providing higher bearing capacity within a short period of time due to weakened foundation soil, providing a new technical path for using the large-diameter steel cylinders directly as load-bearing foundation, which is of significance to the development of ocean engineering projects such as ultra-large-diameter single pile foundations for offshore wind power and large-diameter fastening foundations for floating wind power. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a system for quickly restoring bearing capacity provided by an embodiment of the present invention installed on a large-diameter steel cylinder. FIG. 2 is a cross-sectional view of a distributed drainage channel installed on an outer wall of a large-diameter steel cylinder in an embodiment according to the present invention. FIG. 3 is a schematic diagram of connection points between inclined strut steel plates and a negative-pressure pumping pipe in an embodiment according to the present invention, FIG. 3(a) shows lowest points of connection thereof; and FIG. 3(b) shows highest points of connection. FIG. 4 is a structural schematic diagram of a negative-pressure pumping pipe in an embodiment according to the present invention. FIG. 5 is a schematic diagram of the arrangement of an annular directional blocking device on the large-diameter steel cylinder in an embodiment according to the present invention, FIG. 5(a) shows connection to an outer side of a distributed drainage channel; and FIG. 5(b) shows connection to an outer side wall of a large-diameter steel cylinder. FIG. 6 is a schematic diagram of a mobile self-sealing water pumping device disposed inside a negative-pressure pumping pipe in an embodiment according to the present invention. Reference numerals in FIGs. 1-6 are as follows: 1. large-diameter steel cylinder; 2. distributed drainage channel; 21. negative-pressure water pumping pipe; 211. non-opening section; 212. opening section; 213. filter screen; 22. inclined strut steel plate; 3. annular directional blocking device; 31. groove-shaped base; 311. bottom plate; 312. wing plate; 32. inclined strut transition plate; 33. protective cover plate; 34. grouting bag; 35. grouting pipe; 36. one-way grouting valve; 37. grouting device; 4. mobile self-sealing water pumping device; 41. upper fastening end; 42. lower fastening end; 43. hollow shunt tube; 431. pressurizing one-way valve; 432. baffle plate; 44. outer rubber bladder; 45. inner rubber bladder; 46. pressure relief valve; 47. pressure relief valve wire; 48. negative-pressure drainage tube; and 49. vacuum pump device. DETAILED DESCRIPTION OF EMBODIMENTS The present invention will be further described below with reference to the accompanying drawings. A core idea of the present invention is to provide a method for quickly restoring bearing capacity of a large-diameter steel cylinder, that is, when the large-diameter steel cylinder 1 is vibrated and lowered to a design depth through a linkage hammer, and water in a weakened foundation of an outer side wall of the large-diameter steel cylinder 1 is discharged, such that foundation soil around a cylinder body is reshaped and consolidated, and a purpose of quickly restoring the bearing capacity of the large-diameter steel cylinder 1 is achieved. In order to accelerate remolding and consolidation of the foundation soil around the cylinder body uniformly, the foundation soil around the large-diameter steel cylinder 1 is drained in layers in an axial direction of the cylinder body, and drained at a plurality of points in a circumferential direction of the cylinder body. Based on the above core idea, this embodiment of the present invention provides a system for quickly restoring bearing capacity of a large-diameter steel cylinder, as shown in FIG. 1, the system is a distributed transverse negative-pressure consolidation system, including distributed drainage channels 2 installed on the outer side wall of the large-diameter steel cylinder 1 in a longitudinal direction, annular directional blocking devices 3 installed thereon in a transverse direction, and mobile self-sealing water pumping devices 4 installed inside the distributed drainage channel 2. With reference to FIG. 2, in this embodiment, the number of the annular directional blocking devices 3 is three. The number of the distributed drainage channels 2 is five, and they are uniformly distributed in a circumferential direction of the large-diameter steel cylinder 1. Relative positions of plane arrangement points of the distributed drainage channels 2 are determined by dividing a circumferential angle of a cross section of the large-diameter steel cylinder 1 into a number n of the distributed drainage channels 2 to obtain equally divided positions of an angle a. The distributed drainage channels 2 each includes a negative-pressure water pumping pipe 21 connected to the outer side wall of the large-diameter steel cylinder 1 and inclined strut steel plates 22 symmetrically disposed on both sides of the negative-pressure water pumping pipe 21, and the negative-pressure water pumping pipe 21, the inclined strut steel plates 22 and the outer side wall of the large-diameter steel cylinder 1 form an outer side cavity. As shown in FIG. 3, lowest points of connection between the inclined strut steel plates 22 and the negative-pressure pumping pipe 21 are at a horizontal axis of the negative-pressure pumping pipe 21, and highest points thereof are tangent points between the inclined strut steel plates 22 and the negativepressure pumping pipe 21. With reference to FIG. 4, the negative-pressure pumping pipe 21 is open at an upper end, and is sealed at a lower end, and has opening sections 212 and non-opening sections 211 alternately arranged from bottom to top, a series of holes communicating with the outer side cavity are form at equal intervals on the opening sections 212 in a length direction, and an outer surface of the opening section 212 is wrapped with a layer of a filter screen 213. A series of water permeable holes communicating with the outer side cavity are formed on each of the inclined strut steel plates 22 at positions corresponding to the opening sections 212, and the water permeable holes are blocked by the filter screen 213. Positions of the outer side cavity corresponding to the nonopening sections 211 are blocked, for example, by using a welded steel plate or injecting glue. With reference to FIG. 5, the annular directional blocking devices 3 are disposed at positions corresponding to the non-opening sections 211, each includes a groove-shaped base 31 with an opening facing outwards, a bottom plate 311 of the groove-shaped base 31 is connected to the outer side wall of the large-diameter steel cylinder 1 and an outer side wall of the distributed drainage channel 2, and a height of a horizontal central axis of the groove-shaped base 31 is the same as that of a center of the non-opening section 211. Wing plates 312 on both sides of the groove-shaped base 31 are connected to the outer side wall of the large-diameter steel cylinder 1 through an inclined strut transition plate 32. A folded grouting bag 34 is placed inside the groove-shaped base 31. A grouting pipe 35 is disposed on an inner wall of the outer side cavity close to the inclined strut steel plates 22, one end of the grouting pipe is connected to one oneway grouting valve 36 disposed at a joint of the groove-shaped base 31 and the inclined strut steel plate 22, and the other end thereof is connected to a grouting device 37 on a ground surface. An opening of the groove-shaped base 31 is covered by a protective cover plate 33 connected to the inclined strut transition plate 32 at a lower side, and the protective cover plate 33 can be pushed and opened after the grouting bags 34 are filled with grout. The one-way grouting valves 36 of all grouting bags 34 are disposed on the inclined strut steel plate 22 on the same side, each grouting pipe 35 is only connected to one one-way grouting valve 36, and grouting amount of each grouting bag 34 is not less than 0.9 times of a maximum grouting volume thereof; and all the grouting bags 34 can be grouted at the same time, or can be grouted sequentially from bottom to top. With reference to FIG. 6, the mobile self-sealing water pumping devices 4 are disposed inside the negative-pressure water pumping pipe 21, including a hollow shunt tube 43, a negativepressure drainage tube 48, an upper fastening end 41 and a lower fastening end 42, where the upper fastening end 41 and the lower fastening end 42 are annular structural members with the same size, an outer diameter thereof is slightly smaller than that of the negative-pressure water pumping pipe 21, and an inner diameter thereof can simply allow one hollow shunt tube 43 to be passed through. An outer rubber bladder 44 and an inner rubber bladder 45 are disposed between the two fastening ends, where a connection position of the outer rubber bladder 44 is at an outer diameter of a ring of the fastening end, and a connection position of the inner rubber bladder 45 is at a 1 / 4 width of the ring of the fastening end. The hollow shunt tube 43 passes through the upper fastening end 41, the inner rubber bladder 45 and the lower fastening end 42, an upper port thereof is in sealed connection to an annular opening on an upper surface of the upper fastening end 41, and a lower port thereof is in sealed connection to an annular opening on a lower surface the lower fastening end 42. One end of the negative-pressure drainage tube 48 is connected to the hollow shunt tube 43, and the other end thereof is connected to a vacuum pump device 49. Four pressurizing one-way valves 431 are vertically and symmetrically installed at a central position of the hollow shunt tube 43, one baffle plate 432 downwardly inclined is installed at an upper position of each pressurizing one-way valve 431, the baffle plate 432 is configured to intercept water flow after the vacuum pump device 49 is started, such that part of high-speed water flow is allowed to enter the inner rubber bladder 45 through the pressurizing one-way valves 431, and the outer rubber bladder 44 squeezes an inner wall of the negative-pressure water pumping pipe 21 to achieve sealing. A pressure relief valve 46 is disposed at a 1 / 8 width of the upper fastening end 41, and the pressure relief valve 46 is connected to an operating console at the ground surface through a pressure relief valve wire 47 for releasing pressure of the inner rubber bladder 45, such that the sealing of the negative-pressure water pumping pipe 21 by the outer rubber bladder 44 is released, allowing the mobile self-sealing water pumping device 4 to move inside the negative-pressure water pumping pipe 21. When the system is used for the first time, a space between the inner rubber bladder and the outer rubber bladder is filled with liquid, and gas inside the inner rubber bladder 45 is evacuated. An embodiment of the present invention further provides an implementation method of the system for quickly restoring bearing capacity of a large-diameter steel cylinder, including the following steps: 1) after the large-diameter steel cylinder 1 is vibrated and lowered to the design depth, each of the distributed drainage channels 2 is inserted with one mobile self-sealing water pumping device 4, which is simultaneously lowered down to a position of the non-opening section 211; 2) the grouting device 37 is started, the grouting bags 34 are filled with cement grout according to the requirements to achieve layered isolation of the foundation soil around the large-diameter steel cylinder 1; 3) the vacuum pump device 49 is started, the baffle plate 432 starts to intercept the water flow, part of the high-speed water flow is allowed to enter the inner rubber bladder 45 through the pressurizing one-way valves 431, and the outer rubber bladder 44 expands and squeezes the inner wall of the negative-pressure water pumping pipe 21 to form a vacuum environment; 4) the vacuum pump device 49 continuously works until water output of the negative-pressure drainage tube 48 reduces and becomes in a stable state, or working time is not less than 2 h; 5) the vacuum pump device 49 is closed, the pressure relief valve wire 47 is pulled, the liquid inside the inner rubber bladder 45 flows out through the pressure relief valve 46, and the outer rubber bladder 44 retracts; and all the mobile self-sealing water pumping devices 4 are pulled up to a position of the non-opening section 211 at an upper layer; and 5 6) the steps 3)-5) above are repeated until the negative-pressure drainage operation at a top layer is completed, the mobile self-sealing water pumping devices 4 are recovered, and the distributed drainage channels 2 are filled with the cement grout. io

Claims

1. A system for improving the bearing capacity of the ground around a steel cylinder, the system comprising:a steel cylinder (1) with distributed drainage channels (2) installed on the outer side wall of the steel cylinder (1) in a longitudinal direction, and a plurality of the distributed drainage channels (2) being uniformly distributed in a circumferential direction of the steel cylinder (1);a plurality of annular directional blocking devices (3) installed on the outer side wall of the steel cylinder (1) in the longitudinal direction and configured to facilitate layered isolation of the foundation soil around the steel cylinder (1);mobile water pumping devices (4) installed inside each of the distributed drainage channels (2) and configured for draining layers of the foundation soil around the steel cylinder (1);wherein the steel cylinder (1) can be vibrated and lowered to a design depth through a linkage hammer, and water in the foundation soil around the steel cylinder (1) can be discharged through the distributed drainage channels (2) using the mobile water pumping devices (4), such that foundation soil around a cylinder body is reshaped and consolidated, and improving the bearing capacity of the steel cylinder (1) is accordingly achieved.

2. The system for restoring bearing capacity of a steel cylinder according to claim 1, characterized in that the number of the distributed drainage channels (2) is three.

3. The system for restoring bearing capacity of a steel cylinder according to claim 1, characterized in that the distributed drainage channels (2) each comprises a negative-pressure water pumping pipe (21) and inclined strut steel plates (22) symmetrically disposed on both sides of the negative-pressure water pumping pipe (21), and the negative-pressure water pumping pipe (21), the inclined strut steel plates (22) and the outer side wall of the steel cylinder (1) form an outer side cavity; the negative-pressure pumping pipe is open at an upper end, and is sealed at a lower end, and has opening sections (212) and non-opening sections (211) alternately arranged from bottom to top, holes communicating with the outer side cavity are form on the opening sections (212), water permeable holes communicating with the outer side cavity are formed on each of the inclined strut steel plates (22) at positions corresponding to the opening sections (212), and the holes and the water permeable holes are blocked by a filter screen (213); and the annular directional blocking devices (3) are disposed at positions corresponding to the nonopening sections (211), positions of the outer side cavity corresponding to the non-opening sections (211) are blocked, and the mobile water pumping devices (4) are disposed inside the negative-pressure water pumping pipe (21).

4. The system for restoring bearing capacity of a steel cylinder according to claim 3,characterized in that the mobile water pumping devices (4) each comprises a hollow shunt tube (43), a negative-pressure drainage tube (48), an upper fastening end (41) and a lower fastening end (42), an outer diameter of the fastening end is slightly smaller than that of the negativepressure water pumping pipe (21), an outer rubber bladder (44) and an inner rubber bladder (45) are disposed between the two fastening ends, and a space between the inner rubber bladder and the outer rubber bladder is filled with liquid; the hollow shunt tube (43) passes through the upper fastening end (41), the inner rubber bladder (45) and the lower fastening end (42), one end of the negative-pressure drainage tube (48) is connected to the hollow shunt tube (43), and the other end thereof is connected to a vacuum pump device (49); pressurizing one-way valves (431) are installed on the hollow shunt tube (43), a baffle plate (432) downwardly inclined is installed on each pressurizing one-way valve (431) for intercepting water flow after the vacuum pump device (49) is started, such that part of high-speed water flow is allowed to enter the inner rubber bladder (45) through the pressurizing one-way valves (431), and the outer rubber bladder (44) squeezes an inner wall of the negative-pressure water pumping pipe (21) to achieve sealing; and a pressure relief valve (46) is disposed on the upper fastening end (41), and the pressure relief valve (46) is connected to a ground surface through a pressure relief valve wire (47) for releasing pressure of the inner rubber bladder (45), such that the sealing of the negative-pressure water pumping pipe (21) by the outer rubber bladder (44) is released, allowing the mobile water pumping device (4) to move inside the negative-pressure water pumping pipe (21).

5. The system for restoring bearing capacity of a steel cylinder according to claim 4, characterized in that four pressurizing one-way valves (431) are vertically and symmetrically installed at a central position of the hollow shunt tube (43), and one baffle plate (432) is installed at an upper position of each pressurizing one-way valve (431).

6. The system for restoring bearing capacity of a steel cylinder according to claim 3, characterized in that the annular directional blocking devices (3) each comprises a grooveshaped base (31) with an opening facing outwards, a bottom plate (311) of the groove-shaped base (31) is connected to the outer side wall of the steel cylinder (1) and an outer side wall of the distributed drainage channel, and wing plates (312) on both sides of the groove-shaped base (31) are connected to the outer side wall of the steel cylinder (1) through an inclined strut transition plate (32); a grouting bag (34) is placed inside the groove-shaped base (31); a grouting pipe (35) is disposed on the outer side cavity, one end of the grouting pipe (35) is connected to one oneway grouting valve (36) disposed at a joint of the groove-shaped base (31) and the inclined strut steel plate, and the other end thereof is connected to a grouting device (37); and an opening of the groove-shaped base (31) is covered by a protective cover plate (33) connected to the inclinedstrut transition plate (32) at a lower side, and the protective cover plate (33) can be pushed and opened after the grouting bag (34) is filled with grout.

7. The system for restoring bearing capacity of a steel cylinder according to claim 6, characterized in that the one-way grouting valves (36) of all grouting bags (34) are disposed on the inclined strut steel plate (22) on the same side, each grouting pipe (35) is only connected to one one-way grouting valve (36), and grouting amount of each grouting bag (34) is not less than 0.9 times of a maximum grouting volume thereof; and all the grouting bags (34) can be grouted at the same time, or can be grouted sequentially from bottom to top.

8. An implementation method for the system of claims 1-7 for restoring bearing capacity of a steel cylinder, characterized by comprising:1) after the steel cylinder (1) is vibrated and lowered to the design depth, each of the distributed drainage channels (2) is inserted with one mobile water pumping device (4), which is simultaneously lowered down to a position of the non-opening section (211);2) the grouting device (37) is started, the grouting bags (34) are filled with cement grout to achieve layered isolation of the foundation soil around the steel cylinder (1);3) the vacuum pump device (49) is started, the baffle plate (432) starts to intercept the water flow, part of the high-speed water flow is allowed to enter the inner rubber bladder (45) through the pressurizing one-way valves (431), and the outer rubber bladder (44) expands and squeezes the inner wall of the negative-pressure water pumping pipe (21) to form a vacuum environment;4) the vacuum pump device (49) continuously works until water output of the negative-pressure drainage tube (48) reduces and becomes in a stable state, or working time is not less than 2 h;5) the vacuum pump device (49) is closed, the pressure relief valve wire (47) is pulled, the liquid inside the inner rubber bladder (45) flows out through the pressure relief valve (46), and the outer rubber bladder (44) retracts; and all the mobile water pumping devices (4) are pulled up to a position of the non-opening section (211) at an upper layer; and6) the steps 3)-5) above are repeated until the negative-pressure drainage operation at a top layer is completed, the mobile water pumping devices (4) are recovered, and the distributed drainage channels (2) are filled with the cement grout.

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