A construction method for rigid pipe piles using double-wall steel pipe devices to guide holes

Abstract

This application discloses a construction method for reinforced pipe piles using a double-walled steel pipe device for borehole drilling. The steps are as follows: at a designated location, a pile driver is used to drive the double-walled steel pipe device to drill a pile hole. During drilling, the pile driver is clamped on the outer steel pipe, causing the double-walled steel pipe device to rotate and sink. Simultaneously, cement slurry is sprayed outward through an external grouting nozzle, mixing with the underground soil to form a cement-soil annular structure. When the double-walled steel pipe device sinks to a designated height, the hollow prestressed pipe pile is lowered into the annular cavity. The inner steel pipe is pulled upward, leaving the soil inside the inner steel pipe underground. The outer steel pipe is then rotated upward and pulled out, simultaneously spraying cement slurry outward to mix the cement-soil annular structure, forming a cement-soil mixing pile. This application utilizes the annular cavity of the double-walled steel pipe device to sink the hollow prestressed pipe pile, ensuring the coaxiality of the cement-soil mixing pile and the hollow prestressed pipe pile. Furthermore, since no hole cleaning is required within the annular cavity, construction efficiency is improved, and the soil squeezing effect is reduced.

Description

Technical Field

[0001] This invention relates to a construction method for rigid pipe piles using a double-walled steel pipe device for pre-drilling. Background Technology

[0002] Reinforced composite piles are a new type of pile foundation. The implementation of reinforced composite piles begins with the construction of cement-soil piles, followed by the driving of concrete core piles. This creates a new pile type where the concrete core pile and cement-soil work together to bear the load from the superstructure. Due to the increased pile-soil expansion interface, reinforced composite piles improve load transfer paths, exhibiting characteristics of friction piles. This results in cement-soil piles having significantly higher lateral resistance than concrete piles, while the concrete core piles have significantly higher pile strength than cement-soil piles. The combination of these two types offers a higher cost-performance ratio than traditional pile types.

[0003] The main problems in the construction of reinforced composite pile foundations are as follows: The driving of cement-soil piles and concrete core piles involves two completely different processes, requiring multiple pieces of equipment to operate simultaneously. This results in numerous and complex construction procedures, leading to long construction periods and high costs. During the insertion of the concrete core pile, soil displacement can easily occur, causing damage to adjacent piles and adjacent buildings. It is difficult to ensure that the concrete core pile is inserted from the core of the cement-soil pile, resulting in misalignment between the concrete core pile and the cement-soil pile, significantly reducing the bearing capacity of the reinforced composite pile. Furthermore, if the upper part is an empty pile, the subsequent insertion of pipe piles is extremely difficult because the pile positions of the cement-soil piles are difficult to pinpoint after construction. In addition, for offshore operations, the presence of seawater makes it difficult to locate the pile positions of the previously constructed cement-soil piles, making core pile implantation difficult. These factors limit the use of reinforced composite piles.

[0004] Therefore, simplifying the construction process to shorten the construction cycle, improve construction efficiency, and reduce the soil squeezing effect during construction remain problems that need to be solved for reinforced composite piles. Additionally, when the upper part is an empty pile, accurately positioning the completed cement-soil pile to improve the coaxiality between the cement-soil pile and the core pile is also one of the problems that need to be solved during the construction of reinforced composite piles. Summary of the Invention

[0005] To address at least one of the aforementioned problems, this application proposes a construction method for rigid pipe piles using a double-walled steel pipe device for pre-drilling. The double-walled steel pipe device includes an inner steel pipe, an outer steel pipe, and a precast pile tip. The precast pile tip is a steel structural component, comprising an inner connecting pipe and an outer connecting pipe coaxially fitted together, with the inner connecting pipe located inside the outer connecting pipe. Both the inner and outer connecting pipes are welded to the upper side of an annular plate, and the annular plate has a downwardly protruding, conical pile tip on its lower side. A through-hole is provided within the precast pile tip, coaxially arranged with the inner connecting pipe. The outer steel pipe is detachably held in place on the outer connecting pipe, and the inner steel pipe is detachably held in place on the inner connecting pipe, forming an annular cavity between the inner and outer steel pipes. The core hole communicates with the inner cavity of the inner steel pipe via the inner connecting pipe.

[0006] An external grouting nozzle for spraying grout into the outside of the outer steel pipe is provided at the bottom of the outer steel pipe, and the external grouting pipe is fixedly connected to the external grouting nozzle.

[0007] The construction method includes the following steps:

[0008] (1) At the set position, the pile driver drives the double-walled steel pipe device to drill the pile hole. When drilling the pile hole, the pile driver is clamped on the outer steel pipe, and the double-walled steel pipe device rotates and sinks under the drive of the pile driver. At the same time, cement slurry is sprayed outward through the external grout nozzle. The cement slurry mixes with the underground soil to form a cement-soil ring structure.

[0009] (2) When the double-walled steel pipe device sinks to the set height, the hollow prestressed pipe pile is sunk into the annular cavity;

[0010] (3) First, pull the inner steel pipe upwards so that the soil inside the inner steel pipe remains underground;

[0011] Then the outer steel pipe is rotated upward and pulled out, and cement slurry is simultaneously sprayed outward through the external grout nozzle to mix the cement-soil ring structure and form a cement-soil mixing pile.

[0012] During the specific construction process, after the inner steel pipe is pulled out, a ring-shaped channel will be left. In order to prevent the soil inside the inner steel pipe from sinking and causing the formation of settlement holes in the inner cavity at the upper end of the hollow prestressed pipe, cement grout can be added to the inner side of the hollow prestressed pipe pile to reduce or eliminate the formation of the aforementioned settlement holes.

[0013] In this application, a core hole is set on the precast pile tip, connecting to the inner steel pipe. When the double-walled steel pipe device is sunk into the ground, underground soil can enter the inner steel pipe through the core hole, forming a soil core. When the inner steel pipe is pulled out, the soil core will remain underground, reducing the amount of underground soil backfill and transportation, and lowering construction costs. Furthermore, since no underground soil is excavated to the surface during construction, there is no mud pollution throughout the process, meeting environmental protection requirements.

[0014] The inner cavity of the inner steel pipe is used to accommodate part of the underground soil, reducing the soil squeezing effect and minimizing or eliminating the threat to the completed underground piles and surrounding buildings. The core hole also reduces the end resistance of the double-walled steel pipe device during sinking, making it more conducive to the sinking of the device and enabling the formation of larger diameter pile holes. The outer diameter of the rigid pipe pile formed in this application can reach over 1m.

[0015] After the double-walled steel pipe device is lowered, it forms an annular cavity with an upward opening to accommodate the hollow prestressed pipe pile. This solves the problem of difficulty in positioning the already constructed cement-soil mixing pile when the upper part is an empty pile. It also eliminates the problem of residual underground soil, eliminating the need for multiple hole cleanings, thus allowing the hollow prestressed pipe pile to be lowered into the ground in one go. Since both the inner and outer steel pipes remain underground during the lowering of the hollow prestressed pipe pile, they effectively protect the walls, preventing hole collapse or shrinkage. This makes the application widely adaptable, allowing construction in areas with coarse and fine sand, silt, soft soil, and even pebble layers. Using an annular cavity to accommodate the hollow prestressed pipe pile effectively improves the coaxiality of the cement-soil mixing pile and the hollow prestressed pipe pile.

[0016] Furthermore, to reduce the frictional resistance between the soil core and the inner steel pipe, and to decrease the amount of soil carried during the extraction of the inner steel pipe, an internal grouting nozzle is installed at the bottom of the inner steel pipe. An internal grouting pipe is fixedly connected to the internal grouting nozzle. As the double-walled steel pipe assembly sinks, cement grout is injected into the interior of the inner steel pipe through the internal grouting nozzle, forming a cement grout isolation layer on the inner wall of the inner steel pipe. This cement grout isolation layer effectively reduces the frictional resistance between the soil core and the inner steel pipe.

[0017] Furthermore, to reduce the resistance during the extraction of the inner steel pipe, it is pulled out by rotating it while simultaneously lifting it upwards; or simply by lifting it upwards. Using the rotating-upward lifting method not only reduces resistance and the pulling force during extraction, but also breaks the bond between the soil core and the inner steel pipe, ensuring the soil core remains underground.

[0018] Specifically, a first slot is provided on the inner tube. The first slot is L-shaped and includes a first vertical groove extending in a vertical direction and a first horizontal groove connected to the bottom of the first vertical groove. In the opposite direction of the rotation direction of the double-walled steel pipe device, the first horizontal groove extends from the bottom of the first vertical groove away from the first vertical groove. A first protrusion is fixed on the outside of the bottom of the inner steel pipe. The first protrusion enters the first horizontal groove through the first vertical groove, so that the inner steel pipe is held on the inner tube and the inner steel pipe is lined inside the inner tube. Rotating the inner steel pipe in the rotation direction of the double-walled steel pipe device allows the first protrusion to enter the first vertical groove through the first horizontal groove, and when the inner steel pipe is lifted upward, it can disengage from the inner tube.

[0019] A second slot is provided on the outer pipe. The second slot is L-shaped and includes a second vertical groove extending in a vertical direction and a second horizontal groove connected to the bottom of the second vertical groove. Along the rotation direction of the double-walled steel pipe device, the second horizontal groove extends from the bottom of the second vertical groove in a direction away from the second vertical groove. A second protrusion is fixed on the inner side of the bottom of the outer steel pipe. The second protrusion enters the second horizontal groove through the second vertical groove, so that the outer steel pipe is held on the outer pipe and is sleeved on the outside of the outer pipe. Rotating the outer steel pipe in the opposite direction of the rotation direction of the double-walled steel pipe device allows the second protrusion to enter the second vertical groove through the second horizontal groove, and when the outer steel pipe is lifted upward, it can disengage from the outer pipe.

[0020] This design allows the inner and outer steel pipes to be easily disengaged from the connected inner and outer pipes for recycling. Since the inner steel pipe is lined inside the inner pipe and the outer steel pipe is sleeved on the outside of the outer pipe, it can effectively prevent underground soil from entering the gap between the inner and outer steel pipes and the inner pipe, as well as the gap between the outer and outer steel pipes, causing blockage of the first or second slot and affecting the recycling of the inner or outer steel pipe.

[0021] Furthermore, an outer retaining ring is installed on the outer wall of the outer connecting pipe. When the outer steel pipe is held onto the outer connecting pipe, the outer steel pipe presses against the outer retaining ring, or there is a gap of no more than 5mm between the outer steel pipe and the outer retaining ring. An inner retaining ring is installed on the inner wall of the core hole. When the inner steel pipe is held onto the inner connecting pipe, the inner steel pipe presses against the inner retaining ring, or there is a gap of no more than 5mm between the inner steel pipe and the inner retaining ring. After the inner retaining ring is installed, underground soil will at most enter the gap between the inner steel pipe and the inner retaining ring, but will not enter the gap between the inner connecting pipe and the inner steel pipe. Similarly, with the outer retaining ring installed, underground soil will at most enter the gap between the outer steel pipe and the outer retaining ring, but will not enter the gap between the outer connecting pipe and the outer steel pipe. To prevent underground soil from entering the gaps between the inner steel pipe and the inner retaining ring, as well as the gaps between the outer pipe and the outer steel pipe, a sealing ring can be placed between the outer steel pipe and the outer retaining ring during construction if sealing between them is difficult. Similarly, if sealing between the inner steel pipe and the inner retaining ring is difficult, a sealing ring can be placed between them to close the gap.

[0022] Furthermore, in the radial direction, the outer circumferential surface of the outer retaining ring does not extend beyond the outer circumferential surface of the outer steel pipe; and in the radial direction, the inner circumferential surface of the inner retaining ring extends inward beyond the inner circumferential surface of the inner steel pipe. That is, the outer diameter of the outer retaining ring is not greater than the outer diameter of the outer steel pipe, and the inner diameter of the inner retaining ring is smaller than the inner diameter of the inner steel pipe.

[0023] When the outer circumference of the outer retaining ring does not extend beyond the outer circumference of the outer steel pipe, the radial outer diameter of the double-walled steel pipe assembly can be reduced, thus decreasing the resistance of the underground soil to the sinking of the double-walled steel pipe assembly. When the inner circumference of the inner retaining ring extends inward beyond the inner circumference of the inner steel pipe, the underground soil is compressed when it enters the inner steel pipe through the core hole, resulting in a soil core with an outer diameter smaller than the inner diameter of the inner steel pipe. Although the soil core will still contact the inner wall of the inner steel pipe due to deformation after entering it, the frictional resistance between the soil core and the inner steel pipe is still reduced, making it easier to keep the soil core underground when pulling out the inner steel pipe. Preferably, the inner diameter of the inner retaining ring is 5-10 mm smaller than the inner diameter of the inner steel pipe.

[0024] Furthermore, to improve the uniformity of mixing between the cement slurry and the underground soil, a mixing blade is installed at the bottom of the outer steel pipe, located on the outside of the outer steel pipe. Preferably, the outer diameter of the mixing blade is 1.5-2.5 times the outer diameter of the hollow prestressed pipe pile. This application does not have special requirements for the structure of the mixing blade; existing mixing blades for mixing piles can be used in this application, such as spiral type and plate type mixing blades.

[0025] Furthermore, to improve the torque transmission between the inner and outer steel pipes, an inner groove is provided on the outer wall of the inner steel pipe, and an outer groove is provided on the inner wall of the outer steel pipe. A synchronizing plate is inserted vertically into the annular cavity, with its opposite sides inserted into the inner and outer grooves respectively. Utilizing the synchronizing plate as a torque transmission component between the inner and outer steel pipes allows the outer steel pipe to evenly transmit the torque generated by external forces to the inner steel pipe. Preferably, the synchronizing plate is only located at the top of the inner and outer steel pipes, and its height is controlled between 0.3 and 2 meters.

[0026] Furthermore, in order to successfully pull the inner and outer steel pipes out of the ground, both the inner and outer steel pipes need to be pulled out before the cement-soil mixing piles have completed their initial setting. Attached Figure Description

[0027] Figure 1 This is a structural schematic diagram of an embodiment of a double-walled steel pipe device.

[0028] Figure 2 This is a diagram showing the state of the precast pile tip after it has separated from the inner and outer steel pipes in a double-walled steel pipe assembly.

[0029] Figure 3 yes Figure 2 A magnified view along the AA direction.

[0030] Figure 4 yes Figure 3 Enlarged view of section B.

[0031] Figure 5 This is a structural schematic diagram of a precast pile tip.

[0032] Figure 6 It is a three-dimensional structural diagram of the precast pile tip.

[0033] Figure 7 This is a construction flowchart for rigid pipe piles using a double-walled steel pipe device for borehole preparation. Detailed Implementation

[0034] The structure of the double-walled steel pipe device is described below. Please refer to [link / reference]. Figures 1-6 The double-walled steel pipe device includes an inner steel pipe 12, an outer steel pipe 11, and a precast pile tip 20. The precast pile tip 20 is a steel structural component. The precast pile tip 20 includes an annular plate 23 and an inner pipe 22 and an outer pipe 21 welded to the upper side of the annular plate. The inner pipe 22 and the outer pipe 21 are coaxially sleeved together, wherein the inner pipe is located inside the outer pipe.

[0035] A downwardly protruding, conical pile tip is welded to the lower side of the annular plate. The pile tip includes a cylindrical core tube 25 extending vertically and a conical tube 24 welded to the outside of the core tube 25. The small end of the conical tube faces downward. The inner cavity of the core tube is formed as a core hole 28. The core hole is a through hole that penetrates the conical tube downward. The core hole is coaxially arranged with the inner tube and communicates with the inner cavity of the inner tube.

[0036] The outer steel pipe is detachably held onto the outer connecting pipe, and the inner steel pipe is detachably held onto the inner connecting pipe, forming an annular cavity 17 between the inner and outer steel pipes. An upward-opening annular pile tip cavity 29 is formed between the inner and outer connecting pipes, and the annular cavity 17 connects to this pile tip cavity 29. The core hole connects to the inner cavity of the inner steel pipe via the inner connecting pipe; when the double-walled steel pipe device is in operation, underground soil can enter the inner steel pipe through the core hole, forming a soil core 33.

[0037] Specifically, in this embodiment, three first slots 221 are provided on the inner tube 22. The three first slots are evenly arranged circumferentially. The first slots 221 are L-shaped. Each first slot 221 includes a first vertical groove 222 extending in the vertical direction and a first horizontal groove 223 connected to the bottom of the first vertical groove. In the opposite direction of the rotation direction of the double-walled steel pipe device, the first horizontal groove extends from the bottom of the first vertical groove in a direction away from the first vertical groove. Figure 6 The direction of arrow S in the diagram indicates the rotation direction of the double-walled steel pipe device.

[0038] Three first protrusions 121 are welded to the outer side of the bottom of the inner steel pipe. Each first protrusion 121 can enter the first horizontal groove through the first vertical groove of the first slot, so that the inner steel pipe is held on the inner connecting pipe and the inner steel pipe is lined inside the inner connecting pipe. Rotating the inner steel pipe in the rotation direction of the double-walled steel pipe device allows the first protrusions to enter the first vertical groove through the first horizontal groove, and when the inner steel pipe is lifted upward, it can disengage from the inner connecting pipe.

[0039] Three second slots 211 are provided on the outer pipe 21. The three second slots are evenly arranged in the circumferential direction. The second slots 211 are L-shaped. Each second slot 211 includes a second vertical groove 212 extending in the vertical direction and a second horizontal groove 213 connected to the bottom of the second vertical groove. Along the rotation direction of the double-walled steel pipe device, the second horizontal groove extends from the bottom of the second vertical groove in a direction away from the second vertical groove.

[0040] Three second protrusions 111 are welded to the inner side of the bottom of the outer steel pipe. Each second protrusion 111 can enter the second horizontal groove through the second vertical groove of a second slot, so that the outer steel pipe is held on the outer connecting pipe and sleeved on the outside of the outer connecting pipe. Rotating the outer steel pipe in the opposite direction of the rotation direction of the double-walled steel pipe device allows the second protrusions to enter the second vertical groove through the second horizontal groove, and when the outer steel pipe is lifted upward, it can disengage from the outer connecting pipe.

[0041] In this embodiment, three first slots and three second slots are provided. The number of first and second slots is not strictly required in this application, but to facilitate the rotation of the double-walled steel pipe guide hole device along its central axis, at least two first slots and two second slots are required. When only two first slots and two second slots are provided, the two first slots and two second slots must be positioned opposite each other. The number of first and second slots can be controlled within 2-10.

[0042] To prevent underground soil from entering the first or second clamping slot and obstructing the rotation of the inner or outer steel pipe, thus preventing the inner or outer steel pipe from detaching from the inner or outer connecting pipe, in this embodiment, the outer circumference of the annular plate 23 extends outward beyond the outer circumference of the outer connecting pipe, forming an annular outer retaining ring 231. When the outer steel pipe is clamped onto the outer connecting pipe, the outer steel pipe presses tightly against the outer retaining ring, sealing the gap between the outer steel pipe and the outer connecting pipe. Of course, in other embodiments, the outer retaining ring can be set separately. It is understood that in other embodiments, there can be a gap of no more than 5mm between the outer steel pipe and the outer retaining ring, and a sealing ring can be placed in this gap to seal the gap between the outer steel pipe and the outer connecting pipe.

[0043] In the radial direction, the outer circumferential surface of the annular plate 23 does not extend beyond the outer circumferential surface of the outer steel pipe; that is, in the radial direction, the outer circumferential surface of the outer retaining ring does not extend beyond the outer circumferential surface of the outer steel pipe, so as to reduce resistance.

[0044] In this embodiment, in the radial direction, the inner diameter of the core tube 25 is smaller than the inner diameter of the inner tube 22, so that the core tube also acts as an inner retaining ring. When the inner steel tube is held onto the inner tube, the inner steel tube tightly presses against the top surface 251 of the core tube 25, sealing the gap between the inner steel tube and the top surface of the core tube 25. Of course, in other embodiments, an inner retaining ring can also be set separately. It can be understood that in other embodiments, there can also be a gap of no more than 5mm between the inner steel tube and the top surface of the core tube 25, and a sealing ring can be placed in this gap to seal the gap between the outer steel tube and the top surface of the core tube 25.

[0045] In this embodiment, the inner diameter of the core tube 25 is smaller than the inner diameter of the inner steel tube, such that in the radial direction, the inner circumferential surface of the core tube 25 extends inward beyond the inner circumferential surface of the inner steel tube; that is, in the radial direction, the inner circumferential surface of the inner retaining ring extends inward beyond the inner circumferential surface of the inner steel tube. During construction, underground soil will enter the inner steel tube, forming a soil core 33. When the underground soil passes through the core hole, it will be compressed, making the outer diameter of the formed soil core smaller than the inner diameter of the inner steel tube. Although the soil core will still contact the inner wall of the inner steel tube due to deformation after entering the inner steel tube, it will reduce the frictional resistance between the soil core and the inner steel tube, making it easier to keep the soil core underground when pulling out the inner steel tube.

[0046] The inner diameter of the core tube 25 should preferably be 5-10 mm smaller than the inner diameter of the inner steel tube. Specifically, in this embodiment, the inner diameter of the core tube 25 is 8 mm smaller than the inner diameter of the inner steel tube. That is, the inner diameter of the inner retaining ring is 8 mm smaller than the inner diameter of the inner steel tube.

[0047] An inner grouting pipe 272 and an outer grouting pipe 271 are installed inside the annular cavity. Both the inner and outer grouting pipes are connected to the grouting equipment via rotary joints.

[0048] An inner grouting ring pipe 274 is welded to the bottom of the inner grouting pipe. Three inner grouting nozzles 262 are installed at the bottom of the inner steel pipe. The three inner grouting nozzles 262 are evenly spaced along the circumference of the inner steel pipe, and each inner grouting nozzle penetrates the pipe wall of the inner steel pipe and connects to the inner cavity of the inner steel pipe. The inner grouting ring pipe extends around the outer wall of the inner steel pipe and fits against the outer wall of the inner steel pipe. The inner grouting pipe fits against the outer wall of the inner steel pipe and extends vertically upward into the annular cavity.

[0049] An external grouting ring pipe 273 is welded to the bottom of the external grouting pipe. Three external grouting nozzles 261 are installed at the bottom of the outer steel pipe. The three external grouting nozzles 261 are evenly spaced along the circumference of the outer steel pipe, and each external grouting nozzle penetrates the pipe wall of the outer steel pipe and connects to the outside of the outer steel pipe. The external grouting ring pipe extends around the inner wall of the outer steel pipe and fits against the inner wall of the outer steel pipe. The external grouting pipe fits against the inner wall of the outer steel pipe and extends vertically upward into the annular cavity.

[0050] To improve the uniformity of torque transmission between the outer and inner steel pipes, three inner clamping parts are welded on the outer wall of the inner steel pipe. Each inner clamping part group includes five inner clamping parts 11 spaced apart in the vertical direction. Each inner clamping part has an inner clamping groove that faces outward in the radial direction and penetrates the upper and lower end faces of the inner clamping part in the vertical direction.

[0051] Three outer clamping member assemblies are welded to the inner wall of the outer steel pipe. Each outer clamping member assembly includes five outer clamping members 152 spaced vertically. Each outer clamping member has an outer clamping groove facing inward radially, which extends vertically through the upper and lower end faces of the outer clamping member. Each inner clamping member assembly is radially opposite to one of the outer clamping member assemblies. The oppositely arranged inner and outer clamping member assemblies together form a clamping member combination. Corresponding to each clamping member combination, a synchronization plate 16 is provided. The synchronization plate 16 is inserted vertically into the annular cavity 17, and its opposite sides are inserted into the inner and outer clamping grooves of the corresponding clamping member combination, respectively. The synchronization plate enables the outer steel pipe to evenly transmit the torque generated by the external force to the inner steel pipe.

[0052] Since the bottoms of both the inner and outer steel pipes are connected to the precast pile tip, torque can be transmitted between them via the precast pile tip. Therefore, in another embodiment, each inner clamping member group can have only one inner clamping member located at the top of the inner steel pipe, and each outer clamping member group can have only one outer clamping member located at the top of the outer steel pipe. The height of the synchronizing plate is also shortened, so that the synchronizing plate is only located at the top of the inner and outer steel pipes. When the synchronizing plate is only located at the top of the inner and outer steel pipes, the height of the synchronizing plate can be controlled between 0.3 and 2 meters, specifically 0.3 meters, 0.5 meters, 1 meter, 1.5 meters, or 2 meters, or other values ​​between 0.3 and 2 meters.

[0053] In this embodiment, both the inner and outer retaining components are made of channel steel, and the grooves of the channel steel extend vertically, using the grooves of the channel steel as the inner and outer retaining slots.

[0054] To enhance the mixing of cement grout and underground soil, a mixing blade 13 is installed at the bottom of the outer steel pipe. This mixing blade is located on the outside of the outer steel pipe, and its outer diameter is twice the outer diameter of the hollow prestressed concrete pipe pile. It is understood that in other embodiments, the outer diameter of the mixing blade 13 is 1.5, 1.8, 2.2, or 2.5 times the outer diameter of the hollow prestressed concrete pipe pile, or any other multiple between 1.5 and 2.5 times.

[0055] The following describes the construction method for reinforced pipe piles using a double-walled steel pipe device for pre-drilling. Please refer to [link / reference needed]. Figure 7 The construction method includes the following steps:

[0056] (1) Please refer to Figure 7 In steps (a) and (b), at the designated location, a pile driver is used to drive the double-walled steel pipe device to drill a pile hole. During the drilling, the power head of the pile driver is clamped onto the outer steel pipe, and the double-walled steel pipe device rotates and sinks under the drive of the pile driver. During the rotation and sinking process of the double-walled steel pipe device, underground soil enters the inner cavity of the inner steel pipe through the core hole 28, forming a soil core 33. Figure 7 In the diagram, 100 represents the ground.

[0057] During the rotation and descent of the double-walled steel pipe device, cement grout is sprayed outward through the outer nozzle. The cement grout sprayed onto the outside of the outer steel pipe mixes with the underground soil under the agitation of the mixing blades, forming a cement-soil ring structure 31. Simultaneously, cement grout is injected into the inner steel pipe through the inner nozzle, forming a cement grout isolation layer on the inner wall of the inner steel pipe. This cement grout isolation layer is located between the soil core and the inner steel pipe, reducing the frictional resistance between the soil core and the inner steel pipe.

[0058] (2) Please refer to Figure 7 In step (c), when the double-walled steel pipe device sinks to the set height, the synchronous plate is first pulled out, and then the hollow prestressed pipe pile 32 is sunk into the annular cavity.

[0059] (3) Please refer to Figure 7 In steps (d) and (e), before the cement-soil mixing pile has completed its initial setting, the inner and outer steel pipes are pulled out in sequence, so that the soil core inside the inner steel pipe remains underground.

[0060] When pulling out the inner steel pipe, first rotate the inner steel pipe in the rotation direction of the double-walled steel pipe device, so that the first protrusion enters the first vertical groove from the first horizontal groove. Then, lift the inner steel pipe upward to detach it from the inner connecting pipe. Finally, pull the inner steel pipe completely out of the ground by simply lifting it upward. It can be understood that, in another embodiment, after the inner steel pipe is detached from the inner connecting pipe, it can also be completely pulled out of the ground by rotating and lifting simultaneously.

[0061] When pulling out the outer steel pipe, first rotate the outer steel pipe in the opposite direction of rotation of the double-walled steel pipe device, so that the second protrusion enters the second vertical groove from the second horizontal groove. Then, lift the outer steel pipe upward to detach it from the outer connecting pipe. Then, rotate the outer steel pipe upward and pull it out, while simultaneously spraying cement slurry through the external grout nozzle to mix the cement-soil ring structure, forming a cement-soil mixing pile 34. After the outer steel pipe is completely pulled out, the construction of the reinforced pipe pile is completed.

Claims

1. A construction method for reinforced pipe piles using a double-walled steel pipe device for pre-drilling, characterized in that, The double-walled steel pipe device includes an inner steel pipe, an outer steel pipe, and a precast pile tip. The precast pile tip is a steel structural component, comprising an inner connecting pipe and an outer connecting pipe coaxially sleeved together, with the inner connecting pipe located inside the outer connecting pipe. Both the inner and outer connecting pipes are welded to the upper side of an annular plate, and the lower side of the annular plate has a downwardly protruding, conical pile tip. A through-hole is provided inside the precast pile tip, and the through-hole is coaxially arranged with the inner connecting pipe. The outer steel pipe is detachably clamped onto the outer connecting pipe, and the inner steel pipe is detachably clamped onto the inner connecting pipe, forming an annular cavity between the inner and outer steel pipes. The through-hole communicates with the inner cavity of the inner steel pipe through the inner connecting pipe. An external grouting nozzle for spraying grout into the outside of the outer steel pipe is provided at the bottom of the outer steel pipe, and the external grouting pipe is fixedly connected to the external grouting nozzle. The construction method includes the following steps: (1) At the set position, the pile driver drives the double-walled steel pipe device to drill the pile hole. When drilling the pile hole, the pile driver is clamped on the outer steel pipe, and the double-walled steel pipe device rotates and sinks under the drive of the pile driver. At the same time, cement slurry is sprayed outward through the external grout nozzle. The cement slurry mixes with the underground soil to form a cement-soil ring structure. (2) When the double-walled steel pipe device sinks to the set height, the hollow prestressed pipe pile is sunk into the annular cavity; (3) First, pull the inner steel pipe upwards so that the soil inside the inner steel pipe remains underground; Then the outer steel pipe is rotated upward and pulled out, and cement slurry is simultaneously sprayed outward through the external grout nozzle to mix the cement-soil ring structure and form a cement-soil mixing pile.

2. The construction method according to claim 1, characterized in that, An internal grouting nozzle is installed at the bottom of the inner steel pipe, and the internal grouting pipe is fixedly connected to the internal grouting nozzle. When the double-walled steel pipe device sinks, cement grout is injected into the interior of the inner steel pipe through the internal grouting nozzle, forming a cement grout isolation layer on the inner wall of the inner steel pipe.

3. The construction method according to claim 1, characterized in that, When pulling out the inner steel pipe, the inner steel pipe can be pulled out by rotating it while lifting it upwards; or the inner steel pipe can be pulled out by simply lifting it upwards.

4. The construction method according to claim 1, characterized in that, A first slot is provided on the inner tube. The first slot is L-shaped and includes a first vertical groove extending in a vertical direction and a first horizontal groove connected to the bottom of the first vertical groove. In the opposite direction of the rotation direction of the double-walled steel pipe device, the first horizontal groove extends from the bottom of the first vertical groove in a direction away from the first vertical groove. A first protrusion is fixed on the outside of the bottom of the inner steel pipe. The first protrusion enters the first horizontal groove through the first vertical groove, so that the inner steel pipe is held on the inner tube and the inner steel pipe is lined inside the inner tube. Rotating the inner steel pipe along the rotation direction of the double-walled steel pipe device allows the first protrusion to enter the first vertical groove from the first horizontal groove, and when the inner steel pipe is lifted upward, it can disengage from the inner connecting pipe. A second slot is provided on the outer pipe. The second slot is L-shaped and includes a second vertical groove extending vertically and a second horizontal groove connected to the bottom of the second vertical groove. Along the rotation direction of the double-walled steel pipe device, the second horizontal groove extends from the bottom of the second vertical groove away from the second vertical groove. A second protrusion is fixed on the inner side of the bottom of the outer steel pipe. The second protrusion enters the second horizontal groove through the second vertical groove, so that the outer steel pipe is held on the outer pipe and sleeved on the outside of the outer pipe. Rotating the outer steel pipe in the opposite direction of the rotation direction of the double-walled steel pipe device allows the second protrusion to enter the second vertical groove through the second horizontal groove, and when the outer steel pipe is lifted upward, it can disengage from the outer pipe.

5. The construction method according to claim 4, characterized in that, An outer retaining ring is provided on the outer wall of the outer pipe. When the outer steel pipe is clamped on the outer pipe, the outer steel pipe presses against the outer retaining ring, or there is a gap of no more than 5mm between the outer steel pipe and the outer retaining ring. An inner retaining ring is provided on the inner wall of the core hole. When the inner steel pipe is held on the inner connecting pipe, the inner steel pipe presses against the inner retaining ring, or there is a gap of no more than 5mm between the inner steel pipe and the inner retaining ring.

6. The construction method according to claim 5, characterized in that, In the radial direction, the outer circumferential surface of the outer retaining ring does not extend outward beyond the outer circumferential surface of the outer steel pipe; and in the radial direction, the inner circumferential surface of the inner retaining ring extends inward beyond the inner circumferential surface of the inner steel pipe.

7. The construction method according to claim 1, characterized in that, An agitator is installed at the bottom of the outer steel pipe, and the agitator is located on the outside of the outer steel pipe.

8. The construction method according to claim 7, characterized in that, The outer diameter of the mixing blade is 1.5-2.5 times the outer diameter of the hollow prestressed pipe pile.

9. The construction method according to claim 1, characterized in that, An inner groove is provided on the outer wall of the inner steel pipe, and an outer groove is provided on the inner wall of the outer steel pipe. The synchronizing plate is inserted vertically into the annular cavity, and the opposite sides of the synchronizing plate are inserted into the inner groove and the outer groove respectively.

10. The construction method according to claim 1, characterized in that, Both the inner and outer steel pipes need to be pulled out before the cement-soil mixing pile has completed its initial setting.

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