Method for targeted reinforcement of super-deep and thick overburden layer foundation by super-high pressure jet grouting pile

Abstract

This invention discloses a method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles, relating to the field of pile foundations, and solving the problems of high construction difficulty and poor reinforcement effect in high-pressure jet grouting reinforcement of ultra-deep overburden foundations. The technical solution adopted in this invention is as follows: First, the drilling point is determined and construction equipment is arranged. Then, a pilot hole is drilled, with its lower end located within or at the bottom of the weak layer. The diameter of the pilot hole is the minimum value required to meet the subsequent water-air-grout segmented cutting jet grouting construction requirements. Next, the high-pressure jet grouting pipe is lowered to the bottom of the pilot hole, and water-air-grout segmented cutting jet grouting is performed on the weak layer. Then, the loose surface layer of the foundation is reinforced against liquefaction. The completed high-pressure jet grouting pile is cured. Finally, the next drilling point is determined, and the process is repeated. This invention is used for targeted reinforcement of ultra-deep overburden layers.

Description

Technical Field

[0001] This invention relates to the field of pile foundations, specifically a method for targeted reinforcement of foundations with ultra-high pressure jet grouting piles and ultra-thick overburden layers. Background Technology

[0002] With the increasing improvement of infrastructure in the east, my country’s large-scale infrastructure construction is moving towards the west. The western region is located in my country’s strong earthquake zone, with complex geological conditions and significant dynamic disasters, especially in the river valleys. In the field of water conservancy construction, heavy-load structures have high requirements for the deformation and stability of the foundation. However, the thickness of the overburden layer in many construction sites exceeds 100m. The overburden layer is an ultra-deep overburden layer, which contains soft soil, silt, silt, sand and other weak layers. These overburden layers have the following characteristics: (1) The soil is distributed in layers, and each layer has different properties and varying strengths. There are weak layers in the deep foundation, and the foundation treatment needs to target the weak layers for reinforcement; (2) The upper load is large, and it is necessary to improve the stiffness of the entire foundation in order to control the long-term deformation of the foundation under the action of the upper load; (3) The surface of the foundation in the river valley often contains liquefiable soil layers, such as saturated sand and gravel, which are prone to liquefaction and instability under strong earthquake action.

[0003] Strengthening foundations with ultra-deep overburden requires addressing the issues of targeted reinforcement of weak layers, overall improvement of foundation stiffness, and surface soil liquefaction simultaneously. High-pressure jet grouting is a foundation reinforcement technology that injects cement grout into the soil under high pressure, allowing the grout to fully mix with the soil and then harden to form a high-strength pile. Current high-pressure jet grouting systems employ a "full-section grouting" method, resulting in a significant amount of returned grout that is not effectively utilized during construction and is typically discharged or discarded, leading to substantial waste of cement grout and a significant increase in material costs. For foundations with extremely deep overburden layers, which contain not only soft layers but also hard soil layers, the pilot holes for high-pressure jet grouting piles are cylindrical, posing construction difficulties as the pilot holes penetrate the hard soil layers. In addition, the effective reinforcement depth of high-pressure jet grouting piles is shallow, making it impossible to target and reinforce the deep soft layers. Coupled with insufficient jetting pressure and unstable jetting conditions, problems such as small pile diameter, large grout consumption, and low grout utilization rate are very likely to occur, resulting in ineffective grout consumption in the hard soil layer section and insufficient reinforcement effect in the soft layer, thus causing insufficient pile strength or unsatisfactory reinforcement effect. Summary of the Invention

[0004] This invention provides a method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles, solving the problems of high construction difficulty and poor reinforcement effect in ultra-deep overburden foundations reinforced by high pressure jet grouting.

[0005] The technical solution adopted in this invention is: a method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles, comprising the following steps: S1. Determine the drilling site and arrange construction equipment around it, including positioning the high-pressure jet grouting pile main unit at the drilling site, and installing high-pressure grout pumps, high-pressure water pumps and air compressors.

[0006] To facilitate subsequent construction, step S1 further includes arranging an electrical control cabinet, slurry storage tank, slurry mixing tank, silo, and water tank around the high-pressure jet grouting pile host, and also configuring a crane around the high-pressure jet grouting pile host.

[0007] To further reduce the length of the pipelines for the high-pressure grout pump and the high-pressure water pump, in step S1, the distance between the high-pressure grout pump and the high-pressure jet grouting pile host is 3-5m, and the distance between the high-pressure water pump and the high-pressure jet grouting pile host is 3-5m.

[0008] S2. Drill a hole at the drilling point to the design elevation. The pilot hole obtained from the drilling is arranged vertically and penetrates the loose strata of the foundation surface. The lower end of the pilot hole is located in the weak layer or at the bottom of the weak layer. The diameter of the pilot hole is the minimum value that meets the construction requirements of step S3.

[0009] To ensure the quality of the pilot hole and prevent hole collapse, a further step is taken: during drilling in step S2, a casing is used to protect the loose strata on the surface of the foundation. The casing has holes in its wall. For example, in step S2, the holes in the casing are distributed in a quincunx pattern, with a diameter of 150-200 mm and a spacing of 2-5 m.

[0010] S3. Lower the high-pressure jet grouting pipe to the bottom of the pilot hole, and then perform water-air-grout segmented cutting jet grouting on the weak layer from bottom to top. Among them, the lower end of the high-pressure jet grouting pipe is provided with a first nozzle and a second nozzle in the vertical downward direction. When performing water-air-grout segmented cutting jet grouting, high-pressure water is first jetted into the weak layer through the first nozzle, and then grout and compressed air are jetted into the weak layer simultaneously through the second nozzle to form a gas-liquid mixture. Part of the gas-liquid mixture mixes with the soil of the weak layer and forms an enlarged diameter pile. The remaining gas-liquid mixture naturally returns to the ground through the air lift effect. Part of the returned grout fills the pilot hole and forms a pilot hole pile. Part of the returned grout enters the loose strata around the pilot hole, and the remaining returned grout is discharged from the opening of the pilot hole.

[0011] S3-1. Use a high-pressure jet grouting pipe to perform water-air-grout segmented cutting jet grouting on the weak layer. During the jet grouting process, raise the high-pressure jet grouting pipe. When the second nozzle of the high-pressure jet grouting pipe is raised to the top surface of the weak layer being treated, stop the jet grouting.

[0012] S3-2. Increase the pressure of the swirl nozzle until the first nozzle enters the bottom surface of the untreated weak layer above. Repeat step S3-1 until all weak layers have been treated.

[0013] S3-3. Stop the jet grouting and pull the high-pressure jet grouting pipe out of the pilot hole.

[0014] Step S3 involves segmented water-air-grout cutting jet grouting to form enlarged-diameter piles in the weak layer, achieving targeted reinforcement of the weak layer. Specifically, to ensure sufficient reinforcement of the weak layer, in step S3, the diameter of the enlarged-diameter piles is not less than 2.0m, the pressure of the high-pressure water is ≥20MPa, the pressure of the grout is ≥40MPa, and the pressure of the compressed air is 1~2MPa.

[0015] S4. Reinforce the loose strata on the surface of the foundation to prevent liquefaction.

[0016] To fully utilize the slurry discharged from the borehole opening, further steps include: in step S1, constructing a slurry collection trench and a waste slurry pool around the drilling site; in step S3, the slurry discharged from the borehole via the ground is collected in the waste slurry pool through the slurry collection trench to form waste slurry; and in step S4, the waste slurry is reinjected into the loose strata of the foundation surface. For example, in step S4, a grid-like grouting trench is excavated on the ground, or a grid-like grouting pipe is laid on the ground to reinject the waste slurry into the loose strata.

[0017] S5. Perform maintenance on the completed high-pressure jet grouting piles.

[0018] S6. Determine the next drilling point and repeat steps S1 to S5 until all high-pressure jet grouting piles are completed.

[0019] There are usually multiple drilling sites arranged in rows and columns, with the distance between adjacent drilling sites being relatively close. To avoid cross-grouting caused by water-air-grout segmented cutting jet grouting at adjacent drilling sites, a further step is taken: when determining the next drilling site in step S6, a staggered drilling method is adopted.

[0020] The beneficial effects of this invention are as follows: This invention employs ultra-high pressure jet grouting piles for targeted reinforcement of ultra-deep overburden foundations. It reinforces weak layers through segmented water-air-grout cutting jet grouting, and can be used to reinforce ultra-deep overburden foundations, with reinforcement depths reaching 50-100m, and even exceeding 100m. This invention involves drilling at the drilling point; the borehole diameter only needs to meet the requirements of segmented water-air-grout cutting jet grouting construction. The small borehole diameter reduces the construction difficulty in ultra-deep overburden foundations. This invention forms enlarged-diameter piles in weak layers, and does not perform jet grouting in hard soil layers that do not require reinforcement, achieving the effect of "targeted reinforcement" and resulting in high material utilization. During water-air-grout segmented cutting jet grouting, some of the returned grout fills the pilot hole and enters the loose strata surrounding it. This not only reinforces the loose strata around the pilot hole but also forms small-diameter piles within the pilot hole, effectively creating a small-diameter pile composite foundation. This increases the stiffness of the loose strata on the foundation surface, enhancing its deformation resistance. This invention also reinforces the loose strata on the foundation surface against liquefaction, solving the problem of insufficient liquefaction resistance in these strata. This invention simultaneously addresses the issues of reinforcing deep, weak soil layers, increasing the stiffness of the upper soil layer, and improving the liquefaction resistance of shallow soil layers, achieving a triple reinforcement effect with high material utilization and superior economic efficiency. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the planar layout of the construction equipment and facilities around the drilling site in step S1 of the present invention.

[0022] Figure 2 This is a schematic diagram of the water-air-slurry segmented cutting jet grouting in step S3 of the present invention.

[0023] Figure 3 This is a schematic diagram of the high-pressure jet grouting pile obtained by the present invention in a vertical section, and a schematic diagram of the waste slurry being reinjected into the loose strata of the foundation surface.

[0024] Figure 4 This is a schematic diagram of the present invention, which collects the returned slurry in a slurry collection trench and then reinjects the waste slurry into the loose strata.

[0025] Attached reference numerals: 1. Drilling point; 2-1. High-pressure jet grouting machine; 2-2. High-pressure grout pump; 2-3. High-pressure water pump; 2-4. Air compressor; 2-5. Electrical control cabinet; 2-6. Grout storage tank; 2-7. Grout mixing tank; 2-8. Silo; 2-9. Water tank; 2-10. Crane; 2-11. Grout collection ditch; 2-12. Waste grout pool; 3-1. Loose stratum; 3-2. Weak layer; 3-3. Gravel layer; 4. High-pressure jet grouting pipe; 4-1. First jet hole; 4-2. Second jet hole; 5-1. Expanded diameter pile; 5-2. Pilot pile; 6. Casing; 7. Grouting pipe. Detailed Implementation

[0026] The invention will now be further described with reference to the accompanying drawings.

[0027] This invention is used to treat foundations with complex geological conditions, deep soil layers, and difficulties in direct treatment, with the aim of improving the stability and bearing capacity of the foundation. The method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles of this invention includes the following steps S1 to S6.

[0028] S1. Determine the drilling point 1 and arrange the construction equipment around the drilling point 1, including positioning the high-pressure jet grouting pile host 2-1 to the drilling point 1, and installing the high-pressure grout pump 2-2, the high-pressure water pump 2-3 and the air compressor 2-4.

[0029] Step S1 involves precisely positioning the high-pressure jet grouting pile host 2-1 to the location corresponding to drilling point 1. This is the starting point and foundation of the entire construction process. The high-pressure jet grouting pile host 2-1 is the core equipment for construction, and its location directly affects the accuracy and efficiency of subsequent construction. To ensure the stability and efficiency of grout supply, the high-pressure grout pump 2-2 and high-pressure water pump 2-3 are generally placed 3 to 5 meters away from the high-pressure jet grouting pile host 2-1. This distance ensures a suitable pipeline length, reduces pressure loss, and guarantees timely and sufficient grout supply to the construction area. The air compressor 2-4 is used to provide compressed air. To ensure the stability and efficiency of compressed air supply, the distance between the air compressor 2-4 and the high-pressure jet grouting pile host 2-1 is generally 10 to 15 meters.

[0030] To facilitate subsequent construction, step S1 typically includes arranging an electrical control cabinet 2-5, a slurry storage tank 2-6, a slurry mixing tank 2-7, a material silo 2-8, and a water tank 2-9 around the high-pressure jet grouting pile main unit 2-1. Figure 1 As shown. The silo 2-8 and water tank 2-9 are used to supply material to the slurry mixing tank 2-7. The slurry mixed in the mixing tank 2-7 is temporarily stored in the slurry storage tank 2-6. In addition, step S1 also involves equipping the high-pressure jet grouting pile host 2-1 with a crane 2-10. During construction, the crane 2-10 is used to lift and move various equipment and materials, such as drill rods and cement slurry buckets, improving the flexibility and efficiency of construction.

[0031] In order to promptly remove the mud and waste soil generated during construction and avoid pollution and obstruction to the construction area, a mud drainage ditch is also set at the location corresponding to the high-pressure jet grouting pile host 2-1. The mud drainage ditch is generally set on the downwind side of the construction area, and the ditch path is kept to the shortest possible.

[0032] S2. Drill a hole at drilling point 1 to the design elevation. The pilot hole obtained from the drilling is arranged vertically and penetrates the loose stratum 3-1 on the surface of the foundation. The lower end of the pilot hole is located in the weak layer 3-2 or at the bottom surface of the weak layer 3-2. The diameter of the pilot hole is the minimum value that meets the construction requirements of step S3.

[0033] During drilling operations, the hole position deviation is generally controlled to be less than 5 cm, and the hole bottom deviation rate is generally controlled to be within 1% to ensure the accuracy and stability of the drilling. If hole collapse occurs during drilling, a casing (6-inch) is used for wall protection. (See [link to relevant documentation]). Figure 2 The casing 6 is generally made of PVC pipe, and its wall has holes. The casing 6 is typically placed within the loose stratum 3-1 on the surface of the foundation. The holes in the casing 6 allow grout to enter the loose stratum surrounding the pilot hole. For example, the holes in the casing 6 are arranged in a quincunx pattern, with a diameter of 150–200 mm and a spacing of 2–5 m. The lower end of the pilot hole is located within the weak layer 3-2 or at its bottom surface. When the thickness of the weak layer 3-2 is too great, and the borehole cannot reach its bottom surface, the lower end of the pilot hole is located within the weak layer 3-2 after drilling to the design elevation. See, for example... Figure 3 The borehole penetrates the loose stratum 3-1 and the weak stratum 3-2 from top to bottom. The lower end of the pilot hole is located on the bottom surface of the weak stratum 3-2, and the lower end of the pilot hole is also located on the top surface of the hard stratum, such as the gravel layer 3-3.

[0034] The drill rod used for drilling has a hollow circular tube structure. The inner cavity of the drill rod is a mud discharge pipe. The end face of the drill rod is provided with connection holes. For example, four connection holes are provided at equal central angles. Multiple through holes are provided along the axial direction in the body of the drill rod. Each through hole forms a high-pressure slurry pipeline, a compressed air pipeline, a high-pressure water pipeline, a pressure sensor circuit pipe, as well as a back-suction cement pipeline, a back-suction air pipeline, a hydraulic pipeline for controlling the mud discharge valve, and a pressure sensor circuit pipe.

[0035] S3. Lower the high-pressure jet grouting pipe 4 to the bottom of the pilot hole, and then perform water-air-grout segmented cutting jet grouting on the weak layer 3-2 from bottom to top. Step S3 includes the following steps S3-1 to S3-3.

[0036] S3-1. High-pressure jet grouting pipe 4 is used to perform water-air-slurry segmented cutting jet grouting on the weak layer 3-2.

[0037] The lower end of the high-pressure rotary nozzle 4 is provided with a first nozzle 4-1 and a second nozzle 4-2 in a vertically downward direction. (See attached image) Figure 2The first nozzle 4-1 and the second nozzle 4-2 are both arranged circumferentially around the high-pressure jet grouting pipe 4. During water-air-grout segmented cutting jet grouting, high-pressure water is first jetted into the weak layer 3-2 through the first nozzle 4-1, and then grout and compressed air are simultaneously jetted into the weak layer 3-2 through the second nozzle 4-2. Generally, the grout and compressed air are introduced 30 seconds later than the high-pressure water. The high-pressure water forms a high-pressure water jet to cut the soil in the weak layer 3-2. The pressure of the high-pressure water is generally not less than 20 MPa to ensure effective cutting and breaking of the soil by the water jet. To fully reinforce the weak layer 3-2, the pressure of the grout is generally ≥40 MPa, and the pressure of the compressed air is generally 1–2 MPa to ensure the sufficiency and uniformity of the grouting, and to improve the quality and stability of the reinforcement.

[0038] The second nozzle 4-2 simultaneously injects grout and compressed air into the weak layer 3-2, forming a gas-liquid mixture. This mixture further breaks down and fractures the weak layer 3-2, while simultaneously injecting grout into the soil. The grout mixes with the broken soil, thus reinforcing the weak layer 3-2. The grout used for soil reinforcement is generally cement-based. Each second nozzle 4-2 can simultaneously inject compressed air and grout. The grout is ejected from the center of the nozzle 4-2 in a columnar shape, while the compressed air is ejected from around the grout, with both distributed concentrically. Part of the gas-liquid mixture mixes with the soil in the weak layer 3-2 to form an enlarged diameter pile 5-1, typically with a diameter not less than 2.0m. The remaining gas-liquid mixture naturally returns to the soil through the air lift effect. Part of the returned grout fills the pilot hole and eventually forms the pilot pile 5-2, achieving the initial recycling of excess grout; part of the returned grout enters the loose stratum 3-1 around the pilot hole, reinforcing the loose stratum 3-1 and achieving the further recycling of excess grout; the remaining returned grout is discharged from the opening of the pilot hole. The casing 6 has holes, allowing some of the returned grout to enter the loose stratum 3-1 around the pilot hole through the holes in the casing 6.

[0039] To ensure the uniformity and continuity of jet grouting, the high-pressure jet grouting pipe 4 is raised upwards during the jet grouting process, generally at a uniform speed. When the second nozzle 4-2 of the high-pressure jet grouting pipe 4 reaches the top surface of the weak layer 3-2 being treated, the jet grouting is stopped, and the treatment of the weak layer 3-2 is completed.

[0040] High-pressure water, compressed air, and grout are sprayed into the pilot hole. The air pressure inside the pilot hole is greater than atmospheric pressure, and the air pressure at the bottom of the pilot hole is relatively higher, while the air pressure at the top of the pilot hole is relatively lower. Therefore, the cut soil and grout are sent to the ground and discharged as the drill rod is lifted by the upward airflow.

[0041] S3-2, raise the pressure swirl nozzle 4 until the first nozzle 4-1 enters the bottom surface of the untreated weak layer 3-2 above, and repeat step S3-1 until all weak layers 3-2 are treated.

[0042] The weak layer 3-2 in the ultra-deep overburden foundation consists of one or more layers. When the weak layer 3-2 consists of multiple layers, water-air-grout segmented cutting jet grouting is performed on each layer from bottom to top according to step S3-2 until all weak layers 3-2 are treated.

[0043] S3-3. Stop the jet grouting and pull the high-pressure jet grouting pipe 4 out of the pilot hole.

[0044] After jet grouting is completed, the ducts are sealed to prevent grout leakage and environmental pollution, while also ensuring the stability and bearing capacity of the pilot pile 5-2. Specialized sealing materials and equipment, such as cement grout and expansion plugs, can be used to effectively seal the ducts.

[0045] S4. Reinforce the loose strata 3-1 on the surface of the foundation to resist liquefaction.

[0046] To fully utilize the slurry discharged from the borehole opening, it can be used to reinforce the loose stratum 3-1 against liquefaction. Specifically, in step S1, a slurry collection trench 2-11 and a waste slurry pool 2-12 are constructed around the drilling point 1. For example, the mud discharge trench can be cleaned or modified and then used as the slurry collection trench 2-11. In step S3, the slurry discharged from the borehole through the ground is collected in the waste slurry pool 2-12 via the slurry collection trench 2-11 to form waste slurry. In step S4, the waste slurry is reinjected into the loose stratum 3-1 on the surface of the foundation. For example, in step S4, a grid-like grouting trench is excavated on the ground, or a grid-like grouting pipe 7 is laid on the ground to reinject the waste slurry into the loose stratum 3-1. Waste slurry is generally reinjected into loose stratum 3-1 under normal pressure. The grouting tank and grouting pipe 7 are generally arranged in a square grid so that excess slurry can be injected evenly into loose stratum 3-1, effectively improving the liquefaction resistance of shallow foundation and reducing slurry waste, while also reducing the pollution of the natural environment by excess engineering materials.

[0047] S5. Perform maintenance on the completed high-pressure jet grouting piles.

[0048] S6. Determine the next drilling point 1, and repeat steps S1 to S5 until all high-pressure jet grouting piles are completed.

[0049] Steps S5 and S6 can be performed simultaneously. There are generally multiple drilling points 1, arranged in rows and columns, with adjacent drilling points 1 being relatively close together. To avoid cross-grouting issues that may occur when water-air-grout segmented cutting jet grouting is performed sequentially at adjacent drilling points 1, step S6 uses a staggered drilling method when determining the next drilling point 1. That is, the next drilling point 1 is not adjacent to the current drilling point 1. The next drilling point 1 is generally separated from the current drilling point 1 by one drilling point 1, but it can also be separated by two or more drilling points 1. In step S6, the construction equipment needs to be moved to the next drilling point 1, for example, using a crane 2-10 for hoisting and moving the equipment. The staggered drilling method can avoid cross-grouting issues between adjacent drilling points 1, improve construction quality and safety, reduce mutual influence and interference during construction, and improve overall construction efficiency.

[0050] This invention is used to reinforce weak layers in ultra-deep overburden layers, effectively solving problems related to anti-sliding stability and deformation control. It enables the construction of ultra-high pressure jet grouting piles at depths of 50mm to 100m underground. During construction, the jetting process is stable, with efficient slag removal and borehole cleaning, and minimal grout waste. This invention can also be used for targeted reinforcement of soft soil foundations such as cohesive soil and sandy soil, reinforcement of various soft foundations in complex environments, reinforcement of various soft foundations under complex construction site conditions with limited space, reinforcement of water-stop curtains in deep soil layers, reinforcement of water-stop curtains at the external joints of ultra-deep ground walls, and repair of various damaged water-stop curtains.

Claims

1. A method for targeted reinforcement of a super-deep and thick overburden layer foundation by using super-high pressure jet grouting piles, characterized in that, Includes the following steps: S1. Determine the drilling construction point (1) and arrange construction equipment around the drilling construction point (1), including positioning the high-pressure jet grouting pile host (2-1) to the drilling construction point (1), and installing the high-pressure grout pump (2-2), high-pressure water pump (2-3) and air compressor (2-4). S2. Drill to the design elevation at the drilling construction point (1). The pilot hole obtained from the drilling is arranged vertically and penetrates the loose stratum (3-1) of the foundation surface. The front end of the pilot hole is located in the weak layer (3-2) or at the bottom surface of the weak layer (3-2). The diameter of the pilot hole is the minimum value that meets the construction requirements of step S3. S3. Lower the high-pressure jet grouting pipe (4) to the bottom of the pilot hole, and then perform water-air-grout segmented cutting jet grouting on the weak layer (3-2) from bottom to top. Among them, the lower end of the high-pressure jet grouting pipe (4) is provided with a first nozzle (4-1) and a second nozzle (4-2) in the vertical downward direction. When performing water-air-grout segmented cutting jet grouting, high-pressure water is first jetted into the weak layer (3-2) through the first nozzle (4-1), and then grout and compressed air are simultaneously jetted into the weak layer (3-2) through the second nozzle (4-2) to form a gas-liquid mixture. Part of the gas-liquid mixture mixes with the soil of the weak layer (3-2) and forms an enlarged diameter pile (5-1). The remaining gas-liquid mixture returns to the ground naturally through the air lift effect. Part of the returned grout fills the pilot hole and forms a pilot hole pile. Part of the returned grout enters the loose stratum (3-1) around the pilot hole. The remaining returned grout is discharged from the opening of the pilot hole. S3-1. Use a high-pressure jet grouting pipe (4) to perform water-air-slurry segmented cutting jet grouting on the weak layer (3-2). During the jet grouting process, raise the high-pressure jet grouting pipe (4). When the second nozzle (4-2) of the high-pressure jet grouting pipe (4) is raised to the top surface of the weak layer (3-2) being treated, stop the jet grouting. S3-2, raise the pressure swirl nozzle (4) until the first nozzle (4-1) enters the bottom surface of the untreated weak layer (3-2) above, and repeat step S3-1 until all weak layers (3-2) are treated. S3-3, Stop the jet grouting and pull the high-pressure jet grouting pipe (4) out of the pilot hole; S4. Reinforce the loose strata (3-1) on the surface of the foundation to resist liquefaction; S5. Curing of the completed high-pressure jet grouting piles; S6. Determine the next drilling point (1) and repeat steps S1 to S5 until all high-pressure jet grouting piles are completed.

2. The method of claim 1, wherein the method is characterized by: Step S1 also arranges an electrical control cabinet (2-5), a slurry storage tank (2-6), a slurry mixing tank (2-7), a silo (2-8), and a water tank (2-9) around the high-pressure jet grouting pile host (2-1), and also sets up a crane (2-10) around the high-pressure jet grouting pile host (2-1).

3. The method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles as described in claim 1, characterized in that: In step S1, the distance between the high-pressure grout pump (2-2) and the high-pressure jet grouting pile host (2-1) is 3-5m, and the distance between the high-pressure water pump (2-3) and the high-pressure jet grouting pile host (2-1) is 3-5m.

4. The method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles as described in claim 1, characterized in that: In step S2, when drilling, a casing (6) is used to protect the wall of the loose stratum (3-1) on the surface of the foundation. The casing (6) has holes in its wall.

5. The method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles as described in claim 4, characterized in that: In step S2, the holes in the casing (6) are distributed in a plum blossom shape, with a hole diameter of 150-200 mm and a hole spacing of 2-5 m.

6. The method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles as described in claim 1, characterized in that: In step S3, the diameter of the expanded diameter pile (5-1) is not less than 2.0m, the pressure of the high-pressure water is ≥20MPa, the pressure of the grout is ≥40MPa, and the pressure of the compressed air is 1~2MPa.

7. The method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles as described in any one of claims 1 to 6, characterized in that: In step S1, a slurry collection ditch (2-11) and a waste slurry pool (2-12) are constructed around the drilling point (1). In step S3, the slurry discharged from the ground through the pilot hole is collected in the waste slurry pool (2-12) through the slurry collection ditch (2-11) to form waste slurry. In step S4, the waste slurry is reinjected into the loose strata (3-1) of the foundation surface.

8. The method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles as described in claim 7, characterized in that: Step S4 involves excavating a grid-shaped grouting trench on the ground or laying a grid-shaped grouting pipe (7) on the ground to reinject the waste grout into the loose stratum (3-1).

9. The method for targeted reinforcement of ultra-deep overburden foundations using ultra-high pressure jet grouting piles as described in any one of claims 1 to 6, characterized in that: When determining the next drilling point (1) in step S6, the alternate-hole drilling method is adopted.

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