A cast-in-place bored pile construction process

Abstract

The application discloses a bored pile construction process and relates to the field of bored piles, which comprises the following steps: installing a pile casing; drilling a pile hole; placing a reinforcement cage; lowering a grouting pipe and inserting the lower end of the grouting pipe into a pebble layer at the bottom of the pile hole; lowering a guide pipe; pouring concrete; curing the pile body and solidifying the concrete; and high-pressure injecting mortar into the pebble layer through the grouting pipe. The application has the effects of reducing the occurrence of the sinking of the bored pile and improving the stability of the bored pile.

Description

Technical Field

[0001] This application relates to the field of cast-in-place piles, and more particularly to a construction process for bored cast-in-place piles. Background Technology

[0002] Drilled cast-in-place piles are piles made by forming pile holes in the foundation soil through mechanical drilling, steel pipe extrusion, or manual excavation on the engineering site, placing a steel cage inside, and pouring concrete. Depending on the hole-forming method, cast-in-place piles can be divided into driven cast-in-place piles, drilled cast-in-place piles, and excavated cast-in-place piles.

[0003] The existing patent application with publication number CN108978640A discloses a method for constructing cast-in-place piles, including the following steps: (1) leveling the site; (2) drilling, specifically as follows: using drilling equipment to vertically drill holes to form pre-pile holes, the diameter of the pre-pile holes being larger than the outer diameter of the reinforcing cage and smaller than the diameter of the pile holes in the design drawings; (3) enlarging the hole, specifically as follows: placing a hollow cylindrical water bag in the pre-pile hole, the outer diameter of the water bag being consistent with the diameter of the pile holes in the design drawings, the length of the water bag being consistent with the depth of the pile holes in the design drawings, the top of the water bag being flush with the ground and connected to a water injection pipe, injecting water into the water bag until the water pressure is greater than 1MPa, letting it stand for at least 10 minutes, depressurizing and pumping out the water bag to form the final pile hole; (4) sinking the reinforcing cage; (5) pouring concrete; (6) breaking the pile head.

[0004] When constructing cast-in-place piles in plains areas, if the drilling depth is 25-31 meters, the bottom of the drilled pile hole will be in a gravel layer. If the above-mentioned cast-in-place pile construction method is used, the cast-in-place pile is prone to sinking after construction due to the loose gravel layer, resulting in low stability, which urgently needs improvement. Summary of the Invention

[0005] In order to improve the problem that cast-in-place piles easily sink when they encounter a relatively loose gravel layer at the bottom in related technologies, this application provides a construction process for bored cast-in-place piles.

[0006] This application provides a construction process for bored piles, which adopts the following technical solution: A construction process for bored piles includes the following steps: Install casing; Drilling pile holes; Place the steel reinforcement cage; Lower the grouting pipe and insert the lower end of the grouting pipe into the gravel layer at the bottom of the pile hole; Lowering the catheter; Pour concrete; Pile curing, concrete setting; Grout is injected under high pressure into the pebble layer through the grouting pipe.

[0007] By adopting the above technical solution, a grouting pipe is placed in the pile hole before concrete pouring; after the pile body solidifies, it seals the pile hole; at this time, mortar is injected under high pressure into the pebble layer through the grouting pipe, and the mortar seeps into the gaps in the surrounding pebble layer. After completion, the mortar solidifies, and the pebble layer under the cast-in-place pile will solidify into a unified structure, forming a relatively stable structure that can provide better support for the cast-in-place pile. In this way, the occurrence of pile settlement is reduced, and the stability of the cast-in-place pile is improved.

[0008] Preferably, a plug is fixed at the lower end of the grouting pipe, and a grouting hole is provided on the grouting pipe near the plug; During the lowering of the grouting pipe, the grouting hole is located within the pebble layer.

[0009] By adopting the above technical solution, when lowering the grouting pipe, pressure needs to be applied to insert the lower end of the grouting pipe into the pebble layer. At this time, the lower end of the grouting pipe is easily blocked. However, by setting a plug at the lower end of the grouting pipe and opening the grouting hole on the side wall of the grouting pipe, it is helpful to reduce the occurrence of blockage at the lower side of the grouting pipe and to ensure the normal progress of the grout injection work into the pebble layer.

[0010] Preferably, the outer side of the grouting pipe is covered with a fragile layer, which seals the grouting hole.

[0011] By adopting the above technical solution, the grouting hole is blocked by the easily broken layer. When high-pressure mortar is injected into the grouting pipe, the mortar can break through the easily broken layer, which helps to reduce the occurrence of concrete entering the grouting pipe through the grouting hole and blocking the grouting hole, and ensures the normal progress of the mortar injection operation into the pebble layer through the grouting pipe.

[0012] Preferably, the fragile layer includes a rubber strip and an adhesive tape, wherein the rubber strip is spirally wound around the grouting pipe, and the adhesive tape is wrapped around the outside of the rubber strip around the grouting pipe.

[0013] By adopting the above technical solution, the rubber strip is wrapped around the grouting pipe, and the rubber strip is tightly wrapped around the grouting pipe with adhesive tape. After the rubber strip is attached to the grouting pipe, it has a strong supporting capacity, reducing the occurrence of concrete breaking through the vulnerable layer and entering the grouting pipe through the grouting hole.

[0014] When high-pressure mortar is injected into the grouting pipe, the mortar will squeeze the rubber band and tape outward; after the tape breaks, the rubber band will spread outward, and the grouting hole can normally inject mortar into the pebble layer, thus helping to ensure the normal progress of the mortar injection operation into the pebble layer through the grouting pipe.

[0015] Preferably, the lower end of the grouting pipe is provided with a plug, and the upper side of the plug is provided with an embedding part, which is embedded in the lower end of the grouting pipe and has an interference fit with the lower end of the grouting pipe; After lowering the grouting pipe and before injecting the mortar, pull the grouting pipe upward so that the pebble layer is located below the plug to form an unloading space, and keep the lower end of the grouting pipe in the pebble layer.

[0016] By adopting the above technical solution, when high-pressure mortar is introduced into the grouting pipe, the high-pressure mortar can push the plug out of the grouting pipe, and the plug will fall into the unloading space; then, the high-pressure mortar can be injected into the pebble layer through its lower end and the unloading space, thereby ensuring the normal progress of the mortar injection operation into the pebble layer through the grouting pipe.

[0017] Preferably, the lower side of the plug is tapered, and the tip of the plug faces downwards: A spiral plate is fixed to the outer wall of the lower end of the grouting pipe, and the spiral plate is spirally wound around the lower end of the grouting pipe. During the lowering of the grouting pipe, rotate the grouting pipe to allow it to spiral into the pebble layer; After lowering the grouting pipe and before injecting the mortar, rotate the grouting pipe to raise it.

[0018] By adopting the above technical solution, on the one hand, in actual construction, the grouting pipe can be rotated, and the grouting pipe can be easily rotated into the pebble layer through the cone tip of the plug and the rotating plate.

[0019] On the other hand, rotating the grouting pipe allows it to rise through the screw-in plate. Because the screw-in plate advances and retracts within the pebble layer, it contacts and supports the grouting pipe, reducing the likelihood of accidental sinking. Furthermore, the screw-in plate prevents concrete from flowing downwards into the unloading space, reducing the risk of blockage.

[0020] Preferably, the upper end of the grouting pipe is detachably fixed with a support frame; When lowering the grouting pipe, insert the grouting pipe into the reinforcing cage; Before pouring concrete, pull the grouting pipe upwards and install a support frame at the upper end of the grouting pipe, so that the periphery of the support frame abuts against the side wall of the casing.

[0021] By adopting the above technical solution, the periphery of the support frame abuts against the side wall of the casing, thereby supporting the upper end of the grouting pipe, reducing the occurrence of the upper side of the grouting pipe tilting towards the periphery of the casing, and thus ensuring the stability of the grouting pipe.

[0022] Preferably, the support frame includes a mounting sleeve and an abutment bracket disposed on the mounting sleeve. The mounting sleeve is fitted onto the grouting pipe, and a locking bolt is threaded onto the mounting sleeve, with the end of the locking bolt abutting against the grouting pipe.

[0023] By adopting the above technical solution, the installation sleeve is fitted onto the grouting pipe and fixed onto the grouting pipe with locking bolts, which helps to facilitate the installation of the support frame on the grouting pipe.

[0024] Preferably, the abutment bracket includes a support tube and an abutment rod, one end of the support tube is connected to the mounting sleeve, and the other end of the support tube extends to the side away from the mounting sleeve; One end of the abutment rod is coaxially inserted into the support tube. An elastic element is provided inside the support tube. The side of the support tube near the mounting sleeve is in a blocking shape. The elastic element is pressed against the support tube near the mounting sleeve and the abutment rod. The side of the abutment rod away from the elastic element abuts against the inner wall of the protective sleeve.

[0025] By adopting the above technical solution, when lowering the grouting pipe, the abutment rod can be pressed into the support pipe and the elastic element can be compressed. After the lower end of the grouting pipe is inserted into the gravel layer, the pressure on the abutment rod can be released. At this time, the abutment rod can pass through the reinforcing cage under the push of the elastic element and press against the casing. After the casing is pulled out, the elastic element will push the abutment rod against the side wall of the pile hole, which helps to ensure the stability of the upper side of the grouting pipe and facilitates the installation of the support frame.

[0026] Preferably, the end of the support tube near the mounting sleeve is hinged to the mounting sleeve, the hinge axis between the support tube and the mounting sleeve is perpendicular to the axis of the mounting sleeve, a limit block is fixed on the mounting sleeve, the limit block is located on the side of the support tube hinge that is axially upward on the mounting sleeve, and a torsion spring is also provided between the mounting sleeve and the support tube for providing torque to the support tube and pressing the support tube against the limit block.

[0027] By adopting the above technical solution, during the installation of the support frame, each support pipe can be gathered together at the axis of the installation sleeve, which further facilitates the installation of the support frame. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of Example 1, mainly illustrating the pile hole, reinforcing cage, and casing; Figure 2 This is a schematic diagram illustrating the grouting pipe structure, as shown in Example 1. Figure 3 This is an exploded schematic diagram illustrating the easily broken layer structure, as shown in Example 1. Figure 4 This is a schematic diagram illustrating the main components of the steel cage, grouting pipe, and support frame structure in Example 2. Figure 5 This is a schematic diagram illustrating the main structure of the screw-on plate in Example 2; Figure 6 This is an exploded view of the support frame structure, which is the main feature of Example 2.

[0029] Reference numerals: 1. Grouting pipe; 11. Plug; 111. Embedded part; 12. Grouting hole; 13. Easily broken layer; 131. Rubber strip; 132. Adhesive tape; 14. Steel wire; 15. Screw-in plate; 2. Support frame; 21. Mounting sleeve; 211. Locking bolt; 212. Limiting block; 22. Abutment bracket; 221. Support pipe; 2211. Torsion spring; 2212. Elastic element; 222. Abutment rod; 100. Pile hole; 200. Casing; 300. Reinforcing cage. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the accompanying drawings.

[0031] This application discloses a construction process for bored piles.

[0032] Example 1: Reference Figure 1 and Figure 2 The construction process of bored piles includes the following steps: S1. Measurement and layout.

[0033] The ground location and elevation of the cast-in-place piles were determined and laid out using GPS measurements. The center of pile hole 100 was determined using the "cross method," and the line was extended outward from the center of pile hole 100 to the surrounding area. Short steel bars were driven into the ground and tied with lines to mark the center and surrounding area of ​​pile hole 100.

[0034] S2. Install the protective sleeve 200.

[0035] The casing 200 is made of steel. The axial length of the casing 200 is not less than 2m, and the inner diameter is 100-200mm larger than the designed diameter of the pile hole. The casing 200 is driven into the area of ​​the pile hole 100 according to the positioning mark.

[0036] S3, Drill pile holes 100.

[0037] S3.1. Position the drilling rig and align the drill bit with the center of the pile hole 100. In this embodiment, a rotary drilling rig can be used.

[0038] S3.2 During drilling, mud is continuously added into the hole as the drilling depth increases. The drilling depth is controlled by the drilling rig depth controller, and the drilling mud is transported to the mud drying area by a loader.

[0039] S3.3 Remove the mud and debris from the bottom of the hole, and use a measuring hammer to measure the thickness of the sediment in the pile hole 100. The sediment thickness should be less than 50 mm. When cleaning the hole, inject mud into the pile hole 100 in a timely manner to maintain the pressure inside the pile hole 100 greater than the pressure outside the pile hole 100, so as to prevent the pile hole 100 from collapsing.

[0040] S3.4 After the mud and sludge are cleaned up, the depth, position, verticality and deviation of the pile hole 100 shall be checked to ensure the quality of the pile hole 100.

[0041] S3.5 After confirming that there are no problems with the pile hole 100, promptly move the drilling rig out of the safe area of ​​the pile hole 100 to prevent loose soil from falling into the formed hole and affecting the quality of the pile hole 100. S4. Place a 300mm steel reinforcement cage.

[0042] When placing the reinforcing cage 300, the alignment accuracy is manually adjusted to ensure that the axis of the reinforcing cage 300 coincides with the axis of the pile hole 100. Two reinforcing bars with a diameter of 12mm-16mm are welded to the main reinforcement of the reinforcing cage 300 as lifting bars. After the reinforcing cage 300 is hoisted into place, the lifting bars are promptly welded and fixed to the casing 200 to prevent the reinforcing cage 300 from floating or sinking during the concrete pouring process.

[0043] Meanwhile, after the 300mm steel cage is hoisted into place, the thickness of the mud at the bottom of the hole is measured again. If the mud thickness is greater than 5cm, the hole needs to be cleaned a second time.

[0044] S5. Lower the grouting pipe 1.

[0045] The grouting pipe 1 is vertically inserted into the reinforcing cage 300, and the lower end of the grouting pipe 1 is inserted into the pebble layer at the bottom of the pile hole 100.

[0046] See Figure 2 and Figure 3 In this embodiment, a plug 11 is welded and fixed to the lower end of the grouting pipe 1, and the upper side of the plug 11 seals the lower end of the grouting pipe 1. The lower side of the plug 11 is conical, and the tip of the plug 11 is set downwards. A grouting hole 12 is provided on the grouting pipe 1 near the plug 11. Multiple sets of grouting holes 12 are provided around the axis of the grouting pipe 1, and each set of grouting holes 12 includes multiple grouting holes 12 evenly spaced in the vertical direction. The outer side of the grouting pipe 1 is covered with a fragile layer 13, which seals the grouting holes 12. The fragile layer 13 includes a rubber strip 131 and an adhesive tape 132. The rubber strip 131 is spirally wound around the grouting pipe 1, and the adhesive tape 132 is wrapped around the outside of the rubber strip 131. In order to reduce the occurrence of the fragile layer 13 falling off, steel wires 14 are tied tightly on both the upper and lower sides of the fragile layer 13.

[0047] In other embodiments, the grouting pipe 1 can be tied to the reinforcing cage 300 by steel wire 14, and the lower side of the grouting pipe 1 extends to the lower end of the reinforcing cage 300 and is inserted into the pebble layer.

[0048] S6. Lower the catheter.

[0049] Lower the guide pipe 300 into the steel cage to keep it vertical.

[0050] S7. Pour concrete.

[0051] Concrete is poured into the pile hole 100 through a guide pipe, with the height of the poured concrete lower than the upper ends of the guide pipe and grouting pipe 1. During the concrete pouring process, the poured concrete is vibrated and compacted promptly.

[0052] S8, Remove and disconnect the catheter and sleeve 200.

[0053] S9. Pile maintenance.

[0054] Waiting for the concrete to harden.

[0055] S10, high-pressure grouting.

[0056] 24 hours after the concrete pouring of the pile body is completed, high-pressure water is injected into the grouting pipe 1. The high-pressure water breaks open the easily broken layer 13, which helps to prevent mud sediment or cement slurry from blocking the grouting pipe.

[0057] After the concrete strength of the cast-in-place pile reaches 50% of the design strength, mortar can be injected into the gravel layer under high pressure through grouting pipe 1. In this embodiment, the mortar is pure cement slurry, with a water-to-cement ratio of approximately 0.45-0.55, preferably 0.5.

[0058] The grouting termination condition is: 1) For piles with a diameter of 800mm, use no less than 2t of mortar; for piles with a diameter of 1000mm, use no less than 2.5t of mortar.

[0059] 2) Grouting pressure is stable at 2.5 MPa.

[0060] 3) When the initial grouting pressure is ≥2MPa and there is no significant decrease, grouting can be completed in one go.

[0061] 4) When the continuous grouting volume of each pile reaches 2t and the grouting pressure is less than 2.5MPa, intermittent grouting shall be adopted, with the shortest interval being 30 minutes and the longest not exceeding 60 minutes.

[0062] 5) When intermittent grouting is used, and the grouting volume is ≥6t, and the grouting pressure is less than 2.5MPa, an early strength agent needs to be added to the cement grout at a dosage of 1% of the cement and mixed evenly.

[0063] S11, Maintenance work.

[0064] If the concrete elevation at the top of the pile is lower than the ground level, backfill with sand and gravel in a timely manner to meet the construction safety requirements and complete the construction of the cast-in-place pile.

[0065] The implementation principle of a drilled pile construction process according to an embodiment of this application is as follows:

[0066] Example 2: Reference Figure 4 and Figure 5 The difference between this embodiment and Embodiment 1 is that: The plug 11 is detachably connected to the lower end of the grouting pipe 1. An embedded part 111 is integrally formed on the upper side of the plug 11. The embedded part 111 is embedded into the lower end of the grouting pipe 1 and is press-fitted with the lower end of the grouting pipe 1. A spiral-infeed plate 15 is fixed to the outer wall of the lower end of the grouting pipe 1. The spiral-infeed plate 15 is spirally wound around the lower end of the grouting pipe 1.

[0067] See Figure 4 and Figure 6 A support frame 2 is provided on the upper side of the grouting pipe 1. The support frame 2 includes a mounting sleeve 21 and an abutment bracket 22 disposed on the mounting sleeve 21. The mounting sleeve 21 is fitted onto the upper side of the grouting pipe 1, and a locking bolt 211 is threaded along its radial direction on the mounting sleeve 21.

[0068] The abutment bracket 22 includes a support tube 221 and an abutment rod 222. One end of the support tube 221 is sealed, and the sealed end of the support tube 221 is hinged to the mounting sleeve 21. The hinge axis between the support tube 221 and the mounting sleeve 21 is perpendicular to the axis of the mounting sleeve 21. A limit block 212 is fixed on the mounting sleeve 21. The limit block 212 is located below the hinge of the support tube 221. When the support tube 221 is horizontal, the lower side of the support tube 221 abuts against the limit block 212. A torsion spring 2211 is sleeved on the hinge axis at the hinge of the support tube 221 and the mounting sleeve 21. The two torsion rods of the torsion spring 2211 abut against the mounting sleeve 21 and the support tube 221 respectively, and the torsion spring 2211 provides torque to the support tube 221 and can press the support tube 221 against the limit block 212. One end of the abutment rod 222 is coaxially inserted into the support tube 221. An elastic element 2212 is provided inside the support tube 221, and the elastic element 2212 abuts against the side of the support tube 221 near the mounting sleeve 21 and the abutment rod 222. In this embodiment, the elastic element 2212 is a compression spring.

[0069] Furthermore, three abutment brackets 22 are evenly spaced around the axis of the mounting sleeve 21 on the mounting sleeve 21, and the limiting block 212, torsion spring 2211 and elastic element 2212 are all corresponding to the abutment brackets 22 one by one.

[0070] In step S5, the grouting pipe 1 is vertically inserted into the reinforcing cage 300, so that the plug 11 contacts the bottom of the pile hole 100; then, the grouting pipe 1 is rotated, and the grouting pipe 1 is screwed into the gravel layer by the screw-in plate 15; then, the grouting pipe 1 is rotated in the opposite direction to make the grouting pipe 1 rise; then, each abutment rod 222 is pushed into the support pipe 221, and the elastic element 2212 is compressed, and the end of the support pipe 221 away from the mounting sleeve 21 and the abutment rod 222 can be tightly wrapped with tape so that the abutment rod 222 is kept in the state of being inside the support pipe 221; subsequently, each support pipe 221 can be rotated to make Each support pipe 221 moves towards the axis of the mounting sleeve 21 and can be secured with ropes. Next, the mounting sleeve 21 is placed on the grouting pipe 1 and the locking bolt 211 is tightened. The locking bolt 211 presses against the grouting pipe 1, locking the mounting sleeve 21 to the upper side of the grouting pipe 1. Finally, the ropes are untied, and the three support pipes 221 will abut against the corresponding limit blocks 212 under the torque of the torsion spring 2211. Then, the tape on the support pipes 221 is removed, and each elastic element 2212 pushes the corresponding abutment rod 222. Each abutment rod 222 will pass through the steel cage 300 and abut against the casing 200.

[0071] It should be noted that the conduit can be inserted into the steel cage 300 between two adjacent support pipes 221.

[0072] In step S8, after the casing 200 is pulled out, the three elastic elements 2212 will continue to push the corresponding abutment rods 222, so that the three abutment rods 222 abut against the side wall of the pile hole 100 respectively.

[0073] In step S10, 24 hours after the pile body concrete is poured, high-pressure water is injected into the grouting pipe 1. The high-pressure water flushes the plug 11 out of the lower end of the grouting pipe 1, which helps to prevent mud sediment or cement slurry from blocking the grouting pipe 1.

[0074] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A construction process for bored cast-in-place piles, characterized in that: Includes the following steps, Install casing (200); Drill pile holes (100); Place the steel cage (300); Lower the grouting pipe (1) and insert the lower end of the grouting pipe (1) into the pebble layer at the bottom of the pile hole (100); Lowering the catheter; Pour concrete; Pile curing, concrete setting; Grout is injected under high pressure into the pebble layer through the grouting pipe (1); The lower end of the grouting pipe (1) is provided with a plug (11), and the upper side of the plug (11) is provided with an embedding part (111). The embedding part (111) is embedded in the lower end of the grouting pipe (1) and is press-fitted with the lower end of the grouting pipe (1). After lowering the grouting pipe (1) and before injecting the mortar, pull up the grouting pipe (1) so that the pebble layer is located below the plug (11) to form an unloading space, and keep the lower end of the grouting pipe (1) in the pebble layer. The lower side of the plug (11) is conical, and the tip of the plug (11) faces downwards: A spiral plate (15) is fixed to the outer wall of the lower end of the grouting pipe (1), and the spiral plate (15) is spirally wound around the lower end of the grouting pipe (1); During the process of lowering the grouting pipe (1), rotate the grouting pipe (1) and make the grouting pipe (1) spin into the pebble layer; After lowering the grouting pipe (1) and before injecting the mortar, rotate the grouting pipe (1) to raise it; The upper end of the grouting pipe (1) is detachably fixed with a support frame (2). When lowering the grouting pipe (1), insert the grouting pipe (1) into the steel cage (300); Install a support frame (2) at the upper end of the grouting pipe (1) and make the periphery of the support frame (2) abut against the side wall of the casing (200); The support frame (2) includes a mounting sleeve (21) and an abutment bracket (22) disposed on the mounting sleeve (21). The mounting sleeve (21) is sleeved on the grouting pipe (1), and a locking bolt (211) is threadedly connected to the mounting sleeve (21). The end of the locking bolt (211) abuts against the grouting pipe (1). The abutment bracket (22) includes a support tube (221) and an abutment rod (222). One end of the support tube (221) is connected to the mounting sleeve (21), and the other end of the support tube (221) extends to the side away from the mounting sleeve (21). One end of the abutment rod (222) is coaxially inserted into the support tube (221). An elastic element (2212) is provided inside the support tube (221). The side of the support tube (221) near the mounting sleeve (21) is sealed. The elastic element (2212) is pressed against the support tube (221) near the mounting sleeve (21) and the abutment rod (222). The side of the abutment rod (222) away from the elastic element (2212) abuts against the inner wall of the protective sleeve (200). The end of the support tube (221) near the mounting sleeve (21) is hinged to the mounting sleeve (21). The hinge axis between the support tube (221) and the mounting sleeve (21) is perpendicular to the axis of the mounting sleeve (21). A limit block (212) is fixed on the mounting sleeve (21). The limit block (212) is located on the side of the hinge of the support tube (221) on the axial direction of the mounting sleeve (21). A torsion spring (2211) is also provided between the mounting sleeve (21) and the support tube (221) to provide torque to the support tube (221) and press the support tube (221) against the limit block (212).

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