A grouting device and construction method for a steel pipe socketed pile

Abstract

This invention discloses a grouting device and construction method for steel pipe nested piles, belonging to the field of geotechnical engineering support and construction technology. This device can solve the problems of blockage and slow grouting speed in cast-in-place piles. The technical solution is as follows: it includes a grouting cylinder, a grouting funnel at the top of the grouting cylinder, a grouting pad at the bottom of the grouting cylinder, and a sleeve fixing structure at the bottom of the grouting pad; the sleeve fixing structure includes multiple locking teeth, which are set at the bottom of the grouting pad and are inclined downward.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering support and construction technology, specifically relating to a grouting device and construction method for steel pipe nested piles. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] In domestic foundation pit engineering, many projects choose pile support as the support method. This involves combining large-diameter cast-in-place piles with prestressed anchor cables, internal bracing, and water-stop curtains to form a composite support structure, solving many deep foundation pit support problems. The advantages of large-diameter cast-in-place piles include: mechanized operation and simple construction; centralized processing and delivery of reinforcing cages and concrete, on-site processing, convenient operation, mature technology, reliable bearing capacity, and strong adaptability to geological formations. However, large-diameter cast-in-place piles present several problems in hard rock strata. For example, in the construction process of soil-rock binary strata where the upper layer is Quaternary and the lower layer is hard rock, the drilling machinery encounters difficulties drilling into the hard rock and the pile body cannot penetrate the rock (or the penetration depth does not meet requirements).

[0004] In recent years, micro-steel pipe piles, as a new type of advanced support structure, have been widely used in geotechnical engineering due to their advantages such as light weight, high bearing capacity, strong adaptability to strata, flexible pile location, small construction machinery requirements, minimal disturbance to the reinforced strata, low construction vibration, fast construction speed, and large foundation pit support depth. In actual engineering projects, a down-the-hole drilling rig or geological drilling rig is generally used to pre-drill the hole, and then seamless steel pipes are driven in as the pile body material, followed by the injection of cement mortar or pure cement grout into the pile hole. This advanced support structure can effectively embed the pile body into hard rock strata without easily damaging the pile body, and achieve a large single pile bearing capacity. Therefore, the use of micro-steel pipe piles can effectively solve the problem of difficulty in driving large-diameter cast-in-place piles into rock.

[0005] In some areas, the upper layer is Quaternary with low strength, while the lower bedrock has high strength, making it a typical soil-rock binary foundation. Combining the advantages of large-diameter cast-in-place piles and micro steel pipe piles, a composite support system for deep foundation pits has emerged, using large-diameter cast-in-place piles in the upper layer and embedded micro steel pipe piles in the lower layer. This system is called "steel pipe nested piles," which means using large-diameter cast-in-place piles in the upper soil layer and embedding micro steel pipe piles in the lower hard rock strata.

[0006] However, during the construction of nested steel pipe piles, the steel pipe piles need to be installed after grouting. A pre-tied positioning sleeve for the steel pipe pile is placed at the center of the reinforcing cage before grouting. This results in less space for grouting compared to ordinary cast-in-place piles, leading to problems such as blockage and slow grouting speed during the reinforcing cage grouting process. Furthermore, in binary strata with soil above rock, the upper fill soil is often unstable during borehole formation and prone to collapse, significantly limiting the pile driving process.

[0007] Chinese patent application CN202210189896.7 discloses a construction method to improve the rock embedment depth of large-diameter steel pipe nested piles, achieving precise positioning of large-diameter cast-in-place piles, ensuring rock embedment depth, and reducing disturbance to surrounding buildings in the overlying soil layer. However, this technology does not solve the problem of easy cross-hole movement of the built-in micro-steel pipe piles during construction. Chinese patent application CN201010127499.4 discloses a systematic implementation method for constructing large-diameter inclined rock-embedded piles, studying the drilling pressure determination method for inclined rock-embedded pile hole formation and improving the placement of the reinforcing cage and concrete pouring process, but this technology does not solve the problem of easy hole collapse of the upper large-diameter cast-in-place pile. Combined with existing construction technologies, none of the above technologies have solved the problems of difficulty in grouting steel pipe nested piles and difficulty in lowering built-in micro-steel pipe piles. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this invention is to provide a grouting device and construction method for steel pipe nested piles, which can solve the problems of pile blockage and slow grouting speed.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0010] In a first aspect, the present invention provides a grouting device for a steel pipe nested pile, including a grouting cylinder, a grouting funnel at the top of the grouting cylinder, a grouting pad at the bottom of the grouting cylinder, and a sleeve fixing structure at the bottom of the grouting pad; the sleeve fixing structure includes multiple locking teeth, which are arranged at the bottom of the grouting pad and are inclined downward.

[0011] As a further technical solution, the grouting pad includes an upper pad and a lower pad, with a support plate disposed between the upper pad and the lower pad.

[0012] As a further technical solution, both the upper and lower pads have through holes in their centers; the through holes in the upper and lower pads are used to insert grouting cylinders, which pass through the through holes in the upper and lower pads.

[0013] As a further technical solution, multiple locking teeth are set at the bottom of the lower pad, and the multiple locking teeth form a circle, with the center of the circle being the center of the through hole in the lower pad. The multiple locking teeth are evenly spaced.

[0014] As a further technical solution, the tilting direction of the locking teeth is tilted from the connection point with the lower pad to the axis of the through hole in the lower pad.

[0015] As a further technical solution, the locking teeth are triangular structures; the bottom of the lower pad of the grouting pad is provided with multiple sliding grooves along the radial direction of the through hole, the locking teeth are connected to the sliding grooves and can move along the sliding grooves, and can be fixed at different positions of the sliding grooves; the cylinder of the grouting cylinder is a multi-section telescopic structure, and adjacent cylinder sections can be tightened and fixed by threads.

[0016] Secondly, the present invention also provides a construction method for steel pipe nested piles, which uses the grouting device described above for grouting; the specific steps are as follows:

[0017] Fabricate a large-diameter cast-in-place pile reinforcement cage, and tie steel pipe pile positioning sleeves to the large-diameter cast-in-place pile reinforcement cage. The two steel pipe pile positioning sleeves are arranged symmetrically.

[0018] The pile hole layout is carried out to determine the drilling location, the sleeve drilling work is carried out, the drilling rig is positioned after the sleeve is lowered and drilling is carried out;

[0019] Lower the large-diameter cast-in-place pile reinforcement cage and fix the large-diameter cast-in-place pile reinforcement cage to the sleeve;

[0020] Place the grouting pad on top of the sleeve, and fix the sleeve to the grouting pad using the sleeve fixing structure. Tighten multiple sections of the grouting cylinder in sequence and insert them between the two steel pipe pile positioning sleeves at the height of one section above the bottom of the large-diameter cast-in-place pile reinforcement cage. Place a grouting funnel on top of the grouting cylinder for grouting.

[0021] After the concrete is poured, it is cured. Once the concrete strength of the pile body reaches the set strength, the drilling of the micro steel pipe pile is carried out to complete the construction process of the steel pipe nested pile.

[0022] As a further technical solution, the axis connecting the two steel pipe pile positioning sleeves is perpendicular to the edge line of the foundation pit excavation, so that the micro steel pipe piles corresponding to the steel pipe pile positioning sleeve close to the foundation pit are the front row piles, and the micro steel pipe piles corresponding to the other steel pipe pile positioning sleeve outside the foundation pit are the rear row piles.

[0023] When constructing miniature steel pipe piles, the front row of miniature steel pipe piles is constructed first, and cement mortar is injected into the miniature steel pipe piles. After the front row of miniature steel pipe piles has been drilled, lowered, grouted, and cured, the rear row of miniature steel pipe piles is constructed.

[0024] As a further technical solution, the construction process of micro steel pipe piles is as follows:

[0025] Drill holes for the positioning sleeve of the steel pipe pile; lift one end of the micro steel pipe pile and vertically lower it into the pile hole. If the micro steel pipe pile cannot be lowered, lift it out and drill again. Use the pipe-following drilling method to bring the micro steel pipe pile into the pile hole along with the drill rod.

[0026] After all the front row of micro steel pipe piles inside the foundation pit are inserted into the hole, grouting is carried out. Pressure grouting is used to inject cement mortar into the micro steel pipe piles until the positioning sleeve of the steel pipe pile is filled, and then curing is carried out.

[0027] After all the front row of micro steel pipe piles has been cured, the construction of the rear row of micro steel pipe piles on the outside of the foundation pit will be carried out. The construction process is the same as that of the micro steel pipe piles on the inside of the foundation pit.

[0028] As a further technical solution, an intermittent pile construction procedure is adopted during the drilling process; during the grouting process, grouting is paused when the poured concrete reaches the height of one section of the grouting cylinder, the entire grouting cylinder is pulled up one section and one section of the cylinder is removed before grouting continues. This process is repeated to pull up the grouting cylinder until the grouting is completed. After the concrete has cured, the sleeve is pulled out.

[0029] The beneficial effects of the present invention are as follows:

[0030] The grouting device of this invention is fixed to the sleeve by a sleeve fixing structure at the bottom of the grouting pad. A grouting funnel is placed on top of the grouting cylinder to supply grout for injection. During grouting, the grouting cylinder is lowered to the bottom of the pile hole of the cast-in-place pile reinforcement cage, thereby directly delivering the concrete into the bottom of the pile reinforcement cage. The grouting cylinder continuously moves upward as the pouring process progresses, thus accurately delivering the concrete to the grouting position throughout the entire grouting process. This solves the grouting problems of partial blockage and slow grouting speed in cast-in-place piles. This grouting device avoids the problem of grouting difficulties and has the advantage of improving construction efficiency.

[0031] The construction method of the present invention involves lowering a sleeve using a driving and pulling machine before the pile hole is formed. The sleeve is used to reinforce the large-diameter pile hole, thus avoiding the problem of hole wall collapse caused by disturbance to the pile hole during subsequent construction.

[0032] The construction method of the present invention distinguishes the positions of the two steel pipe piles in the cast-in-place pile and divides the two steel pipe piles into front and rear rows of piles. When the steel pipe pile is drilled, the front and rear rows of piles are constructed alternately, that is, the front row of piles is constructed first, and the rear row of piles is constructed after the front row of piles is completed. This construction method can prevent cross-hole between piles in the micro steel pipe pile.

[0033] The construction method of this invention uses casing drilling technology to construct the lower micro steel pipe piles. When encountering hole blockage during the lowering of the steel pipe piles, the construction method of using the drill rod of a down-the-hole drilling rig to bring in the steel pipe piles solves the problem of difficulty in lowering micro steel pipe piles.

[0034] The construction method of the present invention solves the problem of difficulty in embedding large-diameter cast-in-place piles into rock by nesting steel pipe piles in large-diameter cast-in-place piles and using steel pipe piles for rock embedding. Attached Figure Description

[0035] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0036] Figure 1 This is a schematic diagram of the grouting device for the steel pipe nested pile of the present invention;

[0037] Figure 2 This is a schematic diagram of the installation of the grouting device for the steel pipe nested pile of the present invention during construction.

[0038] Figure 3 This is a cross-sectional view of the grouting device for the steel pipe nested pile of the present invention after installation;

[0039] Figure 4 This is a schematic diagram of the steel pipe nested pile reinforcement cage and the steel pipe pile positioning sleeve of the present invention;

[0040] Figure 5 This is a schematic diagram of the steel pipe nested pile reinforcement cage sleeve of the present invention;

[0041] Figure 6 This is a schematic diagram of the miniature steel pipe pile of the present invention;

[0042] Figure 7 This is a schematic diagram of the steel cage hoisting process of the present invention;

[0043] In the diagram: the spacing or dimensions between parts have been exaggerated to show their positions; the diagram is for illustrative purposes only.

[0044] Among them, 1 is the longitudinal reinforcement of the steel cage, 2 is the positioning sleeve of the steel pipe pile, 3 is the outer stiffening reinforcement, 4 is the welding point of the steel reinforcement, 5 is the fixed reinforcement, 6 is the micro steel pipe pile, 7 is the sleeve, 8 is the sleeve fixing structure, 9 is the poured concrete, 10 is the cement mortar, 11 is the grouting pad, 11-1 is the upper pad, 11-2 is the lower pad, 11-3 is the support plate, 12 is the grouting cylinder, 13 is the grouting funnel, 14 is the hoisting hole, 15 is the grouting hole, 16 is the steel pipe nested pile, 17 is the large diameter cast-in-place pile, and 18 is the steel cage of the large diameter cast-in-place pile. Detailed Implementation

[0045] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0046] As described in the background section, the existing technology has shortcomings. In order to solve the above-mentioned technical problems, the present invention proposes a grouting device and construction method for steel pipe nested piles, which can effectively solve the problems of difficulty in driving and grouting steel pipe nested piles, inter-pile cross-holes in micro steel pipe piles, and difficulty in lowering micro steel pipe piles.

[0047] In a typical embodiment of the present invention, such as Figure 1 As shown, a grouting device for steel pipe nested piles is proposed, including a sleeve fixing structure 8, a grouting pad 11, a grouting cylinder 12, and a grouting funnel 13.

[0048] A grouting funnel 13 is provided at the top of the grouting cylinder 12, a grouting pad 11 is provided at the bottom of the grouting cylinder 12, and a sleeve fixing structure 8 is provided at the bottom of the grouting pad 11.

[0049] Among them, the grouting pad 11 is a double-layer steel pad, which includes an upper pad 11-1 and a lower pad 11-2. A support plate 11-3 is set between the upper pad 11-1 and the lower pad 11-2, and the upper and lower pads and the support plate form an integral structure.

[0050] During grouting, the bottom of the grouting pad 11 is placed on top of the sleeve 7. Both the upper pad 11-1 and the lower pad 11-2 have through holes in their centers; the through holes of the upper pad 11-1 and the lower pad 11-2 match the diameter of the grouting cylinder 12 for insertion into the grouting cylinder 12, which passes through the through holes of the upper pad 11-1 and the lower pad 11-2.

[0051] The sleeve fixing structure 8 includes multiple locking teeth, which are set at the bottom of the grouting pad 11. Specifically, the multiple locking teeth are set at the bottom of the lower pad 11-2, and the multiple locking teeth form a circle. The center of the circle is the center of the through hole of the lower pad. The multiple locking teeth are evenly spaced and used to fix the sleeve 7 located at the bottom during grouting. It has the advantages of convenient use and tight fixation.

[0052] The locking teeth are tilted downwards, with the tilt direction being from the connection point with the lower pad to the axis of the through hole in the lower pad. That is, the angle between the locking teeth and the diameter of the through hole in the lower pad is an acute angle. Multiple locking teeth form an inward-clamping shape, which can lock the fixed sleeve.

[0053] In this embodiment, the locking teeth are triangular in structure, made of steel, and four locking teeth are arranged in a circle.

[0054] In other preferred embodiments, the bottom of the lower pad 11-2 of the grouting pad 11 is provided with multiple grooves along the radial direction of the through hole. Clamping teeth are connected to the grooves and can move along them, and are fixed in different positions by screws. The clamping teeth can be adjusted and fixed along the center direction of the lower pad of the grouting pad, thereby adapting to clamping sleeves of different sizes.

[0055] The bottom of the grouting cylinder 12 is inserted into the grouting pad 11. The grouting cylinder 12 is cylindrical and has a multi-section telescopic structure. Adjacent sections of the cylinder can be tightened together by threads. During grouting, it can be continuously pulled up and disassembled as the concrete height rises.

[0056] The grouting funnel 13 has a funnel-shaped structure and is inserted into the top of the grouting cylinder 12. During construction, the grouting funnel 13 is placed on top of the grouting cylinder 12, and the concrete 9 is poured into the grouting cylinder 12 through the grouting funnel 13. The grouting cylinder 12 is then filled with the large-diameter cast-in-place pile reinforcement cage 18 through the grouting pad 11 for grouting.

[0057] In this embodiment, both the grouting cylinder 12 and the grouting funnel 13 are made of steel-plastic composite material, which has the advantages of being lightweight, easy to handle and disassemble, and having high strength.

[0058] The dimensions of each part of the grouting device are determined according to the design requirements. Taking the grouting device in an actual project as an example, the sleeve fixing device 8 is a straight triangular prism with a bottom diameter of 20mm and a height of 20mm; the grouting pad 11 is 1500mm long, 1200mm wide, and 500mm high, with a 780mm opening in the middle; the grouting cylinder 12 has a diameter of 750mm and a wall thickness of 5mm; the grouting funnel 13 has a diameter of 700mm, a top funnel diameter of 1000mm, and a wall thickness of 5mm.

[0059] This grouting device is used for grouting the steel pipe nested pile 16, which is composed of two miniature steel pipe piles 6 nested inside a large-diameter cast-in-place pile 17. A positioning sleeve 2 for the steel pipe pile is pre-placed inside the large-diameter cast-in-place pile 17 and then poured, combining the advantages of both the large-diameter cast-in-place pile 17 and the miniature steel pipe piles 6. The function of the positioning sleeve 2 is to reserve holes for the positioning and placement of the miniature steel pipe piles 6 after the large-diameter cast-in-place pile 17 is poured. After the concrete 9 is cured, holes are drilled in the positioning sleeve 2 and the miniature steel pipe piles 6 are lowered to the design elevation, after which cement mortar 10 is injected.

[0060] The large-diameter cast-in-place pile 17 is formed by pouring concrete into a large-diameter cast-in-place pile reinforcement cage 18. The large-diameter cast-in-place pile reinforcement cage 18 consists of longitudinal reinforcement bars 1 and outer stiffening bars 3. The longitudinal reinforcement bars 1 are fixed to the outer stiffening bars 3 by welding. Each reinforcement cage has 10 longitudinal reinforcement bars, which are arranged in a circular pattern at intervals. The specific steel bar type can be determined according to different design requirements. Taking the steel bar in a certain project as an example, the specification is 22mm diameter steel bar with HRB400 type.

[0061] The outer stiffener 3 is a circular hoop, with 6 bars arranged at a spacing of 2m. The outer stiffener 3 is set horizontally. After binding, the longitudinal bar 1 of the steel cage, the outer stiffener 3 and the fixed bar 5 are welded and fixed at the steel bar welding point 4. The specific steel bar type can be determined according to different design requirements. Taking the steel bar in a certain project as an example, the specification is steel bar with a diameter of 22mm and the type is HRB400.

[0062] The fixing reinforcing bar 5 is fixed to the outer stiffening bar 3 by welding. After bending, it is directly tied to and welded to the steel pipe pile positioning sleeve 2 to fix the steel pipe pile positioning sleeve 2. The fixing reinforcing bar 5 is fixed to the outer wall of the steel pipe pile positioning sleeve 2 in a circular shape and welded to the outer stiffening bar 3. The specific reinforcing bar type can be determined according to different design requirements. Taking the reinforcing bar in a certain project as an example, the specification is a 22mm diameter HRB400 reinforcing bar.

[0063] Sleeve 7 is a single-section steel sleeve placed inside the large-diameter cast-in-place pile hole. During grouting, the aforementioned grouting device is placed on top, and the grouting pad 11 is placed on top of sleeve 7 for grouting. Before the reinforcing cage is lowered, a driving and pulling machine is used to drive the pile into position to protect the pile hole and prevent collapse. The large-diameter cast-in-place pile reinforcing cage 18 is fitted inside sleeve 7. After grouting, grouting concrete 9 is formed in sleeve 7 and the large-diameter cast-in-place pile reinforcing cage 18. The specific sleeve diameter and sleeve length are determined according to design requirements. Taking a cast-in-place pile sleeve in a certain project as an example, the length is 11.2m, the pile diameter is 1050mm, and the wall thickness is 10mm.

[0064] The positioning sleeve 2 for the steel pipe pile is made of seamless steel pipe and is fixed inside the reinforcing cage 18 of the large-diameter cast-in-place pile by fixing reinforcing bars 5. It is used to reserve holes for the micro steel pipe pile 6 during the pouring of the large-diameter cast-in-place pile 17. The specific pipe diameter and length are determined according to the design requirements. Taking the dimensions of the built-in steel pipe pile in an actual project as an example, the pipe diameter is 168mm, the length is 3.5m, and the wall thickness is 5mm.

[0065] The miniature steel pipe piles 6 are made of seamless steel pipes, and the holes are drilled using a down-the-hole drill. The hole diameter must be slightly larger than the designed pile diameter of the miniature steel pipe pile 6 and slightly smaller than the designed pile diameter of the steel pipe pile positioning sleeve 2. The miniature steel pipe piles 6 are divided into front and rear rows according to their distance from the foundation pit. The miniature steel pipe piles 6 closer to the foundation pit are the front rows, and those further away are the rear rows. The miniature steel pipe piles 6 are located inside the steel pipe pile positioning sleeve 2, used to support the foundation pit and embed into the rock strata under the soil-rock dual foundation. They have the advantages of light weight and high bearing capacity. When encountering difficulties in lowering the piles, a casing drilling method is used. The specific pile diameter and length are determined according to the design requirements. Taking the dimensions of an actual project's embedded steel pipe pile as an example, the pile length is 5m, the pile diameter is 108mm, and the wall thickness is 5mm.

[0066] Lifting holes 14 are symmetrically welded to both sides of the top of the micro-steel pipe pile 6 to allow steel wires to pass through, facilitating the hoisting of the micro-steel pipe pile 6 into the positioning sleeve 2. Grouting holes 15 are symmetrically welded to both sides of the bottom of the micro-steel pipe pile 6 to allow cement mortar to pass through the micro-steel pipe pile during grouting, thus bonding with the rock on the borehole wall. The specific hole diameters are determined according to design requirements. Taking the borehole diameter of a micro-steel pipe pile in an actual project as an example, both lifting holes 14 and grouting holes 15 are 30mm diameter circular holes.

[0067] The large-diameter cast-in-place piles 17 are mechanically drilled using a rotary drilling rig, with intermittent pile construction to reduce damage to already poured cast-in-place piles. Together with the internal micro-steel pipe piles 6, they form a steel pipe nested pile 16 for supporting the foundation pit, offering advantages such as convenient construction and high bearing capacity. The specific pile diameter and length are determined according to design requirements. Taking a large-diameter cast-in-place pile in a certain project as an example, the diameter is 1000mm, the pile spacing is 1500mm, and the effective pile length is 11.20m.

[0068] The specific concrete and mortar grades are determined according to design requirements. Taking the concrete and cement mortar of a cast-in-place pile in an actual project as an example, C30 concrete is used for the cast-in-place concrete 9, and the concrete cover thickness of the reinforcement is 50mm. Cement mortar 10 uses pure cement slurry with a water-cement ratio of 0.5, and pressure grouting is used during construction.

[0069] In another typical embodiment of the present invention, a construction method for steel pipe nested piles is proposed, which uses the grouting device described above for grouting; the specific steps are as follows:

[0070] (1) Determine the engineering geological conditions and hydrogeological conditions around the pile hole;

[0071] (2) Reinforcing cage binding and welding:

[0072] Fabricate a large-diameter cast-in-place pile reinforcement cage 18 according to the design drawings. The length of the reinforcement cage should meet the design requirements. The cage body is tied and formed on the support. First, fix the outer stiffening rib 3 on the operating platform, mark the welding position of the longitudinal reinforcement 1 of the reinforcement cage and the position of the outer stiffening rib 3, and then weld the longitudinal reinforcement 1 of the reinforcement cage and the outer stiffening rib 3.

[0073] (3) After the large-diameter cast-in-place pile reinforcement cage 18 is made, the steel pipe pile positioning sleeve 2 is tied, the completed reinforcement cage is laid flat, the steel pipe pile positioning sleeve 2 is lifted horizontally by an excavator, and the large-diameter cast-in-place pile reinforcement cage 18 is put in manually. The steel pipe pile positioning sleeve 2 is tied and welded with the fixing steel bar 5, and the two steel pipe pile positioning sleeves are arranged symmetrically.

[0074] (4) After the site is leveled, the pile hole is laid out to determine the drilling position; a vibratory drilling machine is used to drill the sleeve 7. An angle ruler is used to measure and correct the angle before and during drilling to ensure that the verticality of the lowering meets the pile body deviation requirements.

[0075] (5) After the sleeve 7 is lowered, the drilling rig is positioned and drilling begins. The base and top seat of the drilling rig should be installed stably. After the center is checked and positioned, pre-drilling is performed. The cylindrical drill bit is installed in the rotary drilling rig and drilled to the predetermined depth. The gravel and soil around the drill bit are squeezed into the drill cylinder. After the gravel and soil fill the drill bit, the drilling rig is operated to rotate the drill bit in the opposite direction. The bottom of the drill bit is sealed and it is pulled out of the hole for slag removal. Here, the sleeve 7 serves to prevent the hole wall from collapsing during construction.

[0076] (6) After the drilling is completed, the hole is inspected with a pile foundation hole inspection instrument. The hole diameter, hole verticality and hole depth are qualified. The hole is cleaned by slag removal method. Drilling is stopped and the hole is cleaned. During the construction of the large diameter cast-in-place pile 17, the intermittent pile construction process is required to reduce the damage to the already poured large diameter cast-in-place pile 17.

[0077] (7) When lowering the steel cage 18 of the large-diameter cast-in-place pile, use a crane to vertically lift the steel cage 18 of the large-diameter cast-in-place pile. The steel cage 18 of the large-diameter cast-in-place pile is lifted at 3 points. The lifting points are evenly distributed along the length of the steel cage 18 of the large-diameter cast-in-place pile, with three points in total: the two ends and the middle point. The stiffening hoops at the lifting points are reinforced by welding to ensure that the lifting is stable.

[0078] During hoisting, first adjust the large-diameter cast-in-place pile reinforcement cage 18 to be perpendicular to the site, and manually stabilize the bottom of the reinforcement cage to ensure that the large-diameter cast-in-place pile reinforcement cage 18 does not bend or twist, and hoist it to the design elevation.

[0079] (8) Fix the large-diameter cast-in-place pile reinforcement cage 18 to the sleeve 7 to prevent it from floating or falling off during the concrete pouring process; when lowering it, make sure that the axis of the two micro steel pipe piles 6 is perpendicular to the edge line of the foundation pit excavation, that is, one micro steel pipe pile 6 is close to one side of the foundation pit as the front row of piles, and the other is on the outside of the foundation pit as the rear row of piles; after the reinforcement cage is lowered and positioned, perform the second hole cleaning.

[0080] (9) The above-mentioned grouting device is used for grouting during construction to solve the problem of grouting difficulties during injection;

[0081] Before grouting, the grouting pad 11 is placed on the sleeve 7 that has been completed below. The sleeve 7 is fixed to the grouting pad 11 using the sleeve fixing device 8. Then, the multiple sections of the grouting cylinder 12 are tightened in sequence and passed through the through hole of the grouting pad 11 between the two steel pipe pile positioning sleeves. The cylinder is inserted to the height of one section above the bottom of the large-diameter cast-in-place pile reinforcement cage 18. A grouting funnel 13 is placed on the top of the grouting cylinder 12.

[0082] (10) After the preparation work is completed, start pumping the concrete 9 to the grouting funnel 13 so that it falls naturally. At the same time, the workers use hammers and other tools to strike the grouting cylinder 12 to prevent the concrete 9 from getting blocked. During the grouting process, the workers estimate the height of the large-diameter cast-in-place pile 17 based on the volume of the concrete 9 being pumped. When the concrete 9 reaches the height of one section of the grouting cylinder 12, stop grouting. Use a crane to pull the grouting cylinder 12 up one section and remove one section of the cylinder before continuing grouting. Follow this process to pull the grouting cylinder 12 up until the grouting is finished. After the concrete has cured for 3 hours, pull out the sleeve 7.

[0083] During this process, the grouting cylinder 12 is pulled up over time to deliver concrete to the grouting position. As time goes on, the volume of concrete poured increases and the accumulated height increases. Therefore, pulling up the grouting cylinder 12 can ensure that the poured concrete reaches the corresponding grouting position.

[0084] (11) After the concrete is poured, it is cured. After the concrete strength of the pile body reaches 75% of the design strength, the drilling construction of the micro steel pipe pile 6 is carried out to complete the construction process of the steel pipe nested pile 16. During construction, the front row of micro steel pipe piles 6 is constructed first. Cement mortar 10 is injected into the micro steel pipe piles 6. After the front row of micro steel pipe piles 6 is drilled, lowered, grouted and cured, the rear row of micro steel pipe piles 6 is constructed. In this way, the front row of micro steel pipe piles 6 is embedded in the rock at the bottom and the injected cement mortar 10 has generated strength, which can prevent the occurrence of cross-hole problems.

[0085] The construction process of miniature steel pipe piles is as follows:

[0086] A tracked hydraulic down-the-hole drill was used to drill the steel pipe pile positioning sleeve 2 that was left in the borehole after the pile body was poured. The hole depth was the length of the micro steel pipe pile minus the overlap length between the cast-in-place pile and the steel pipe pile (usually 2.0m).

[0087] After drilling is completed, a crane is used to lift one end of the micro steel pipe pile 6 and vertically lower it into the pile hole. If the micro steel pipe pile 6 cannot be lowered due to blockage or other reasons, the micro steel pipe pile 6 is lifted out and a down-the-hole drill is used to drill again. The micro steel pipe pile 6 is brought into the pile hole along with the drill rod by the method of pipe-following drilling.

[0088] After all the front row of micro steel pipe piles 6 inside the foundation pit are inserted into the hole, grouting is carried out. Pressure grouting is used, and cement mortar 10 is injected into the micro steel pipe piles 6 using pressure grouting equipment until the steel pipe pile positioning sleeve 2 is filled. Then curing is carried out.

[0089] After all the front row of micro steel pipe piles 6 have been cured, the construction of the rear row of micro steel pipe piles 6 on the outside of the foundation pit will be carried out. The construction process is the same as that of the micro steel pipe piles 6 on the inside of the foundation pit. After the construction of the rear row of micro steel pipe piles 6 on the outside of the foundation pit is completed, the construction process of the steel pipe nested piles 16 is completed.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A construction method for steel pipe nested piles, the specific steps of which are as follows: Fabricate a large-diameter cast-in-place pile reinforcement cage, and tie steel pipe pile positioning sleeves to the large-diameter cast-in-place pile reinforcement cage. The two steel pipe pile positioning sleeves are arranged symmetrically, and the axis connecting the two steel pipe pile positioning sleeves is perpendicular to the edge line of the foundation pit excavation. This makes the micro steel pipe piles corresponding to the steel pipe pile positioning sleeves close to the foundation pit the front row of piles, and the micro steel pipe piles corresponding to the other steel pipe pile positioning sleeves outside the foundation pit the rear row of piles. The pile hole layout is carried out to determine the drilling location, the sleeve drilling work is carried out, the drilling rig is positioned after the sleeve is lowered and drilling is carried out; Lower the large-diameter cast-in-place pile reinforcement cage and fix the large-diameter cast-in-place pile reinforcement cage to the sleeve; Place the grouting pad on top of the sleeve, and fix the sleeve to the grouting pad using the sleeve fixing structure. Tighten multiple sections of the grouting cylinder in sequence and insert them between the two steel pipe pile positioning sleeves at the height of one section above the bottom of the large-diameter cast-in-place pile reinforcement cage. Place a grouting funnel on top of the grouting cylinder for grouting. After the concrete is poured, it is cured. Once the concrete strength of the pile body reaches the set strength, the drilling of the micro steel pipe piles is carried out to complete the construction process of the steel pipe nested pile. When constructing the micro steel pipe piles, the front row of micro steel pipe piles is constructed first. Cement mortar is injected into the micro steel pipe piles. After the drilling, lowering, grouting and curing of the front row of micro steel pipe piles are completed, the rear row of micro steel pipe piles is constructed. The grouting device used in this method includes a grouting cylinder, a grouting funnel at the top of the grouting cylinder, a grouting pad at the bottom of the grouting cylinder, and a sleeve fixing structure at the bottom of the grouting pad; the sleeve fixing structure includes multiple locking teeth, which are located at the bottom of the grouting pad and are inclined downwards.

2. The construction method as described in claim 1, characterized in that the construction process of the micro steel pipe piles is as follows: Drill holes for the positioning sleeve of the steel pipe pile; lift one end of the micro steel pipe pile and vertically lower it into the pile hole. If the micro steel pipe pile cannot be lowered, lift it out and drill again. Use the pipe-following drilling method to bring the micro steel pipe pile into the pile hole along with the drill rod. After all the front row of micro steel pipe piles inside the foundation pit are inserted into the hole, grouting is carried out. Pressure grouting is used to inject cement mortar into the micro steel pipe piles until the positioning sleeve of the steel pipe pile is filled, and then curing is carried out. After all the front row of micro steel pipe piles has been cured, the construction of the rear row of micro steel pipe piles on the outside of the foundation pit will be carried out. The construction process is the same as that of the micro steel pipe piles on the inside of the foundation pit.

3. The construction method according to claim 1, wherein During the drilling process, an intermittent pile construction procedure is adopted; during the grouting process, when the poured concrete reaches the height of one section of the grouting cylinder, grouting is paused, the entire grouting cylinder is pulled up one section and one section of the cylinder is removed before grouting continues. This process is repeated until the grouting is completed. After the concrete has cured, the sleeve is pulled out.

4. The construction method of steel pipe nested piles as described in claim 1, characterized in that, The grouting pad includes an upper pad and a lower pad, with a support plate disposed between the upper and lower pads.

5. The construction method of steel pipe nested piles as described in claim 4, characterized in that, Both the upper and lower pads have through holes in their centers; the through holes in the upper and lower pads are used to insert grouting cylinders, which pass through the through holes in the upper and lower pads.

6. The construction method of steel pipe nested piles as described in claim 5, characterized in that, Multiple locking teeth are located at the bottom of the lower pad, forming a circle. The center of the circle is the center of the through hole in the lower pad, and the multiple locking teeth are evenly spaced.

7. The construction method of steel pipe nested piles as described in claim 6, characterized in that, The cleat is inclined from the connection point with the lower pad to the axis of the through hole in the lower pad.

8. The construction method of steel pipe nested piles as described in claim 1, characterized in that, The locking teeth have a triangular structure; the bottom of the lower pad of the grouting pad is provided with multiple sliding grooves along the radial direction of the through hole, the locking teeth are connected to the sliding grooves and can move along the sliding grooves, and can be fixed in different positions of the sliding grooves; the cylinder of the grouting cylinder has a multi-section telescopic structure, and adjacent cylinder sections are fixed by screwing together.

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