Cast-in-situ bored pile casing structure and construction method thereof

Abstract

The invention discloses a cast-in-situ bored pile casing structure and a construction method thereof, and relates to the technical field of cast-in-situ bored piles. The cast-in-situ bored pile casing structure comprises a first drilling area in a soft soil layer and a second drilling area in a hard rock layer, the outer diameter of the first drilling area is larger than that of the second drilling area, and the cast-in-situ bored pile casing structure further comprises an outer casing arranged in the first drilling area; the inner pile casing is coaxially arranged in the outer pile casing, the length of the inner pile casing is larger than that of the outer pile casing, and the lower end of the inner pile casing extends into the second drilling area. Through the staged supporting design of the inner and outer pile casings, the outer pile casing is pulled out in advance after initial setting of concrete, an annular gap is thoroughly cleaned, the problem of negative pressure water absorption caused by the'water sac effect 'between the pile casings and the hole wall is fundamentally eliminated, and after the outer pile casing is moved out, the inner pile casing continuously provides stable supporting for a poured pile body and blocks an underground water permeation path, so that the construction period is shortened, and the construction efficiency is improved. And it is ensured that concrete is not disturbed by dilution of external water in the hardening process, and therefore the traditional process stubborn diseases such as pile top collapse and pile body mud clamping are thoroughly avoided.

Description

Technical Field

[0001] This invention relates to the field of bored pile technology, specifically to a bored pile casing structure and its construction method. Background Technology

[0002] Drilled cast-in-place piles are piles constructed by creating pile holes in the foundation soil on-site through mechanical drilling, steel pipe extrusion, or manual excavation, placing a reinforcing cage inside, and pouring concrete. Due to their mature construction technology, high bearing capacity, and wide applicability, they have been widely used in the foundations of structural engineering projects such as highways and railway bridges. Conventional pile construction methods require the installation of temporary steel casings beforehand. These temporary steel casings do not participate in the structural stress. After the completion of the drilled cast-in-place pile construction, in current conventional pile construction methods, most of the temporary steel casings cannot be recycled and reused, resulting in significant waste.

[0003] Chinese patent CN109811764A discloses a recyclable steel casing for bored pile construction and its construction method. This invention involves drilling and grouting piles inside an inner casing. After the concrete reaches the required strength, the connection between the inner and outer casings is released using a pre-tightening connection removal device. Due to the presence of an annular cavity, the outer casing can be easily pulled out, allowing for recycling and reuse. The inner casing is thinner than existing casings, meaning the material of the recyclable outer casing constitutes a large portion of the overall material of the recyclable steel casing for bored pile construction. Furthermore, the total material of the inner and bottom casings is less than that of existing casings. Therefore, with the outer casing recyclable, the steel consumed by the inner and bottom casings is less than that of existing casings, thus saving resources and reducing costs.

[0004] However, conventional temporary steel casings are only used for borehole wall support during the drilling stage, and are mostly abandoned in the borehole after construction and cannot be recovered. Although the above invention has a high casing recovery rate, there is still waste. In addition, due to the thickness of the casing wall and the mechanical disturbance between the casing and the borehole wall, groundwater accumulates between the casing and the borehole wall. After the casing is pulled out, a water pocket is formed in the gap between the casing and the borehole wall. When the casing is pulled out, a negative pressure water absorption effect is generated, which dilutes the uncured concrete and causes the pile top to sink. Furthermore, groundwater will gradually seep into the space between the bored pile and the borehole wall as the casing is pulled out. The infiltrated groundwater forms a weak interlayer at the interface between the bored pile and the soil layer, which leads to a decrease in the structural stability of the bored pile. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a borehole pile casing structure and its construction method, thus solving the problems raised in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a bored pile casing structure, comprising: a first borehole zone in a soft soil layer and a second borehole zone in a hard rock layer, wherein the outer diameter of the first borehole zone is larger than the outer diameter of the second borehole zone, and further comprising an outer casing disposed within the first borehole zone; an inner casing coaxially disposed within the outer casing, the inner casing having a length greater than the length of the outer casing, and its lower end extending into the interior of the second borehole zone; a bottom liner slidably fitted onto the outside of the inner casing for sealing the bottom of the outer casing; and a connecting assembly. On the upper surface of the bottom liner, a limiting device is used to position the inner casing and to synchronously drive the bottom liner upward when the outer casing moves upward in the first borehole area; a separation component is located on the outer side of the inner casing near the upper end, used to disconnect the outer casing from the bottom liner after the bottom liner is completely separated from the first borehole area, and to fix the bottom liner to the inner casing; wherein, the outer casing and the inner casing are separated by the separation component to expose the first borehole area for concrete pouring, while the inner casing maintains the stability of the concrete pile in the second borehole area.

[0007] Furthermore, the combined assembly includes a T-shaped pile fixed to the upper surface of the bottom liner, with its flange and web forming an overlapping step; a wedge plate located at the lower end of the inner side of the outer casing and slidable along the circumference of the outer casing, distributed on both sides of the T-shaped pile; and a second slot located on the side of the wedge plate near the T-shaped pile. The two opposing wedge plates slide toward the T-shaped pile, causing the overlapping step to engage with the second slot, thus forming a rigid connection between the outer casing, the inner casing, and the bottom liner.

[0008] Furthermore, the separation component includes an upper limit block fixed to the upper end of the outer side of the inner casing. The lower surface of the upper limit block has a first slot adapted to the T-shaped pile at the middle position, and the lower surface of the upper limit block has symmetrical second inclined surfaces on both sides of the first slot. A third inclined surface is provided on the side of the wedge plate facing the T-shaped pile. As the outer casing continues to move upward, the third inclined surface contacts and slides relative to the second inclined surface, driving the two wedge plates to move away from each other, causing the T-shaped pile to disengage from the second slot and insert into the first slot, so that the outer casing automatically separates from the bottom liner.

[0009] Furthermore, the separation assembly also includes a slot, which is opened on the upper side wall of the inner casing; a receiving groove, which is located inside the T-shaped pile and has a sloping bottom surface; and an inclined insert plate, which is located in the receiving groove and can slide along the sloping surface to insert the inclined insert plate into the corresponding slot and fix the bottom liner plate to the upper outer side of the inner casing.

[0010] Furthermore, the lower inner side of the outer casing is uniformly provided with partitions, and a sliding groove is provided between two opposing partitions; the bottom of the wedge plate is provided with a sliding seat, the sliding seat is slidably connected to the sliding groove, and a first spring is installed at one end of the sliding seat, the first spring being stretched to make the sliding seat slide towards the T-shaped pile.

[0011] Furthermore, the outer side of the inner casing is provided with a guide rail along the axial direction, the lower end of the guide rail extends to the bottom of the first drilling area, and is provided with a spherical stop block; the inner side of the bottom liner is provided with a limiting notch adapted to the guide rail, and the outer diameter of the limiting notch is smaller than the outer diameter of the spherical stop block.

[0012] Furthermore, the inclined plate has a slot inside, and a second spring is installed inside the slot. The other end of the second spring is fixed to the inner wall of the receiving groove. The second spring relaxes to push the inclined plate to slide towards the inner protective cylinder.

[0013] Furthermore, the upper surface of the upper limit block is symmetrically provided with a first inclined surface, and the lower surface of the slide block has an arc-shaped structure on the side facing the T-shaped pile.

[0014] Furthermore, the outer protective sleeve has a thickness of 18–30 mm, and the inner protective sleeve has a thickness of 7–10 mm.

[0015] On the other hand, the present invention also provides a method for constructing bored piles, applicable to the aforementioned bored pile casing structure, comprising the following steps: S1. Simultaneously lower the outer casing and inner casing to the design elevation; S2. Concrete is poured into the inner casing to form a concrete cast-in-place pile; S3. After the concrete pile has initially set, pull out the outer casing to expose the annular gap between the first borehole area and the inner casing. S4. Perform water pumping and hole cleaning treatment on the annular gap; S5. Concrete is poured into the annular gap to form the outer layer of cast-in-place piles; S6. After the outer layer of cast-in-place piles has initially set, pull out the inner casing and inject bonding material into the contact surface between the two layers of cast-in-place piles.

[0016] The present invention has the following beneficial effects: (1) The casing structure and construction method of the bored pile, through the phased support design of inner and outer double casings, the outer casing is pulled out first after the concrete has initially set and the annular gap is thoroughly cleaned, which eliminates the problem of negative pressure water absorption caused by the "water bag effect" between the casing and the hole wall from the root. After the outer casing is removed, the inner casing continues to provide stable support for the cast-in-place pile body, blocking the groundwater seepage path and ensuring that the concrete is not affected by external water dilution during the hardening process, thereby completely avoiding the traditional process problems such as pile top collapse and pile body mud inclusion, and significantly improving the integrity and elevation accuracy of the pile.

[0017] (2) The borehole pile casing structure and its construction method realize the dynamic coordinated control of the outer casing, inner casing and bottom liner through the mechanical linkage of the joint component and the separation component. The joint component forms a rigid connection during the drilling stage, which enhances the casing structure's resistance to lateral pressure in soft soil. The separation component automatically triggers unlocking when the outer casing is moved to a safe position, accurately completing the replacement and locking of the bottom liner from the outer casing to the inner casing. This is beneficial for the continued use of external fixed workpieces, ensuring the continuity of the construction process and avoiding the deviation of the inner and outer casings or the retention of the bottom liner due to operational errors.

[0018] (3) The borehole pile casing structure and its construction method optimize the resource utilization rate and stratum adaptability of the inner and outer casings through the inner and outer casings and differentiated hole diameter design. The outer casing matches the large hole diameter requirements of soft soil layer and provides strong support with thick wall structure. The inner casing extends to the small hole diameter area of ​​rock layer. The thin wall design reduces steel consumption. The complete recycling of inner and outer casings reduces material waste. The composite structure of double-layer concrete and cementing layer further reduces the repair cost caused by pile defects.

[0019] (4) The casing structure and construction method of the bored pile can be separated into the bottom liner and the inner and outer casings. During the drilling stage, the bottom liner can be used to seal the bottom of the outer casing to prevent sand from flowing in and to prevent groundwater from seeping into the second drilling area, thereby improving the solidification effect of the inner pile concrete. During the casing extraction stage, it moves out of the soft soil layer along with the outer casing, creating an operating space for cleaning the hole. After separation, it is fixed to the upper end of the inner casing to form a suspension support, which is conducive to the continued use of the external fixed workpiece.

[0020] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the casing structure for bored piles in this invention; Figure 2 This is a schematic diagram of the outer casing of the bored pile casing structure in this invention when it moves upward; Figure 3 In the bored pile casing structure of this invention Figure 2 A partial front view; Figure 4 This is a schematic diagram of the outer casing and bottom liner of the bored pile casing structure in this invention. Figure 5 In the bored pile casing structure of this invention Figure 3 A partial front view; Figure 6 This is a schematic diagram of the outer casing, inner casing, and bottom liner rigidly connected in the casing structure of the bored pile of the present invention; Figure 7 This is a schematic diagram of the installation structure of the wedge plate in the borehole pile casing structure of the present invention; Figure 8 This is a schematic diagram of the installation structure of the inclined plate in the casing structure of the bored pile in this invention; Figure 9 This is a schematic diagram of the connection between the inclined plate and the slot in the casing structure of the bored pile in this invention; Figure 10 This is a schematic diagram of the structure of the bored pile casing in this invention when the second slot separates from the T-shaped pile.

[0022] In the diagram, 1. Outer casing; 2. Inner casing; 3. Bottom liner; 4. Soft soil layer; 5. First drilling zone; 6. Hard rock layer; 7. Second drilling zone; 8. Concrete pile; 9. Guide rail; 10. Upper limit block; 11. First inclined plane; 12. Second inclined plane; 13. First slot; 14. Sliding seat; 15. Wedge plate; 16. Third inclined plane; 17. Second slot; 18. T-shaped pile; 19. Overlapping step; 20. Slide groove; 21. Partition plate; 22. First spring; 23. Receiving groove; 24. Inclined insert plate; 25. Second spring; 26. Slot; 27. Limiting notch. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] In the description of this invention, it should be understood that the terms "opening", "upper", "lower", "thickness", "top", "middle", "length", "inner", "around", etc., which indicate orientation or positional relationship, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0025] The following is based on Figure 1 - Figure 10 This invention describes the borehole pile casing structure and its construction method provided in the embodiments of the present invention.

[0026] Please see Figure 1 - Figure 10This invention provides a technical solution: a bored pile casing structure, including a first borehole area 5 in a soft soil layer 4 and a second borehole area 7 in a hard rock layer 6. The outer diameter of the first borehole area 5 is larger than the outer diameter of the second borehole area 7. The soft soil layer 4 has a high content of silt and fine sand, which is easily disturbed and collapsed, so the borehole diameter needs to be increased to accommodate a thicker outer casing 1 and provide sufficient support space. The hard rock layer 6 has strong self-stability, such as granite and limestone, so the borehole diameter is reduced to reduce drilling costs.

[0027] To support the borehole walls of the first borehole area 5 and the second borehole area 7, the borehole pile casing structure provided in this embodiment also includes an outer casing 1 and an inner casing 2. The outer casing 1 is located in the first borehole area 5 and is mainly used to isolate water and soil pressure and prevent borehole wall instability. The inner casing 2 is coaxially located inside the outer casing 1 and its length is greater than that of the outer casing 1. Its lower end extends into the interior of the second borehole area 7 so that the stress generated during concrete pouring can be accurately transmitted to the hard rock layer 6. In addition, a bottom liner 3 is slidably installed on the outer side of the inner casing 2 along the axial direction. The bottom liner 3 is located at the connection between the first borehole area 5 and the second borehole area 7 and is used to seal the bottom of the outer casing 1 and provide auxiliary support for the outer casing 1. After the outer casing 1 and the upper end of the inner casing 2 are fixed by the external fixing structure, the bottom liner 3 can achieve two-point fixation of the outer casing 1 and the inner casing 2, thereby improving the stability of the outer casing 1 and the inner casing 2 after installation.

[0028] It should be noted that, since conventional casings are prone to negative pressure water absorption after being pulled out, which can cause the initially set concrete grouting column to collapse, requiring subsequent material replenishment to the elevation, this solution adopts the method of pulling out the outer casing 1 in advance and pumping water to clean the gap between the first borehole area 5 and the inner casing 2, eliminating the water pocket effect between the inner casing 2 and the borehole wall, blocking the groundwater seepage path, and maintaining the stability of the concrete grouting pile 8 through the inner casing 2, avoiding groundwater dilution of the concrete, and preventing the concrete grouting pile 8 from collapsing.

[0029] To facilitate the removal of the outer casing 1, the bored pile casing structure provided in this embodiment also includes a connecting assembly. The connecting assembly is located on the upper surface of the bottom liner 3. When the bottom liner 3 is located at the bottom of the first borehole area 5, the connecting assembly can form a rigid connection between the outer casing 1 and the bottom liner 3, thereby providing support for the bottom of the outer casing 1 and limiting the inner casing 2. When the outer casing 1 moves upward in the first borehole area 5, the connecting assembly can simultaneously drive the bottom liner 3 upward to prevent the bottom liner 3 from affecting the concrete pouring effect at the bottom of the first borehole area 5. To facilitate the separation of the outer casing 1 and the inner casing 2, this solution also includes a separation assembly. The separation assembly is located on the outer side of the inner casing 2 near the upper end. It is used to release the connection between the outer casing 1 and the bottom liner 3 after the bottom liner 3 is completely removed from the first borehole area 5, and to fix the bottom liner 3 to the inner casing 2. It should be noted that the bottom liner... The outer diameter of the inner casing 2 is the same as that of the outer casing 1. During the extraction of the outer casing 1, the inner casing 2 is lightweight and the friction between it and the concrete pile 8 and the second borehole area 7 is greater than the friction between the inner casing 2 and the bottom liner 3. This can temporarily maintain the stability of the inner casing 2 and prevent it from moving up or down during the extraction of the outer casing 1. Of course, an external crane can also be used to improve the fixing effect of the inner casing 2 to achieve the same technical effect. After the outer casing 1 is extracted, since the bottom liner 3 has the same outer diameter as the outer casing 1, the external fixing structure can continue to be used to fix the inner casing 2 and the bottom liner 3. In addition, after the outer casing 1 and the inner casing 2 are separated by the separation component, the annular gap between the first borehole area 5 and the inner casing 2 is exposed for concrete pouring. During this process, the inner casing 2 maintains the stability of the concrete pile 8 in the second borehole area 7.

[0030] This solution eliminates the negative pressure water absorption problem caused by the "water pocket effect" between the casing and the borehole wall at its source. After the outer casing 1 is removed, the inner casing 2 continues to provide stable support for the cast-in-place pile, blocking the groundwater seepage path and ensuring that the concrete is not diluted by external water during the hardening process. This completely avoids the stubborn problems of traditional processes such as pile top collapse and mud inclusion in the pile body, and significantly improves the integrity and elevation accuracy of the pile.

[0031] like Figure 2 , Figure 7 and Figure 10As shown, the combined assembly provided in this embodiment includes a T-shaped pile 18 fixed to the upper surface of the bottom liner 3 and a wedge-shaped plate 15 located at the lower inner end of the outer casing 1. The flange and web of the T-shaped pile 18 form an overlapping step 19. The wedge-shaped plate 15 is located at the lower inner end of the outer casing 1, distributed on both sides of the T-shaped pile 18, and can slide circumferentially along the outer casing 1. A second slot 17 is provided on the side of the wedge-shaped plate 15 near the T-shaped pile 18. The two opposing wedge-shaped plates 15 slide toward the T-shaped pile 18, so that the overlapping step 19 is formed. Engages with the second slot 17 to form a rigid connection between the outer casing 1, the inner casing 2, and the bottom liner 3. The bottom liner 3 limits the inner casing 2, which can suppress the horizontal sway caused by drilling vibration and simultaneously seal the upper entrance of the second borehole area 7 to prevent groundwater from seeping in. In addition, after the outer casing 1 is connected to the bottom liner 3, it can ensure that its bottom end is in full contact with the rock surface. When the outer casing 1 moves upward, the bottom liner 3 is pulled synchronously through the rigid connection, which can be used to expose the hole cleaning gap and avoid obstruction of concrete pouring.

[0032] like Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 8 As shown, the separation component provided in this embodiment includes an upper limit block 10, which is fixed to the upper outer side of the inner casing 2. A first slot 13 adapted to the T-shaped pile 18 is provided at the middle position of the lower surface of the upper limit block 10, and a symmetrical second inclined surface 12 is provided on both sides of the first slot 13 on the lower surface of the upper limit block 10. A third inclined surface 16 is provided on the side of the wedge plate 15 facing the T-shaped pile 18. As the outer casing 1 continues to move upward, the third inclined surface 16 contacts and slides relative to the second inclined surface 12, driving the two wedge plates 15 to move away from each other, so that the T-shaped pile 18 disengages from the second slot 17 and inserts into the first slot 13, so that the outer casing 1 automatically separates from the bottom liner 3. It should be noted that the bottom liner 3 is relatively lightweight, and the T-shaped pile 18 and the second slot 17 are subjected to less force during the upward movement, which will not affect its service life.

[0033] like Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 8As shown, the separation assembly provided in this embodiment also includes a slot 26 opened on the upper side wall of the inner casing 2 and a receiving groove 23 provided inside the T-shaped pile 18. The bottom surface of the receiving groove 23 is a sloping structure, and a sloping insert plate 24 is provided in the receiving groove 23. The sloping insert plate 24 can slide along the sloping structure under the action of gravity, so that the sloping insert plate 24 can be inserted into the corresponding slot 26, and the bottom liner 3 is fixed to the upper outer side of the inner casing 2, so as to continue to use the external fixing structure to fix the inner casing 2 and the bottom liner 3. In order to ensure that the sloping insert plate 24 is inserted into the corresponding slot 26, the length and width of the slot 26 are both larger than the length and width of the cross section of the sloping insert plate 24, so as to improve the error tolerance when the sloping insert plate 24 is inserted.

[0034] like Figure 7 As shown, to facilitate the movement of the wedge plate 15, partitions 21 are evenly provided on the lower inner side of the outer casing 1. A sliding groove 20 is provided between two opposing partitions 21. A sliding seat 14 is provided at the bottom of the wedge plate 15. The sliding seat 14 is slidably connected to the sliding groove 20. A first spring 22 is installed at one end of the sliding seat 14. The elastic potential energy of the first spring 22 is released to make the sliding seat 14 slide towards the T-shaped pile 18, so that the second slot 17 on the wedge plate 15 cooperates with the T-shaped pile 18, so that the outer casing 1 is rigidly connected to the bottom liner 3.

[0035] like Figure 1 and Figure 7 As shown, in order to facilitate the sliding of the bottom liner 3, the inner sleeve 2 provided in this embodiment is provided with a guide rail 9 along the axial direction on the outer side. The lower end of the guide rail 9 extends to the bottom of the first drilling area 5 and is provided with a spherical stop. A limiting notch 27 adapted to the guide rail 9 is provided on the inner side of the bottom liner 3. The outer diameter of the limiting notch 27 is smaller than the outer diameter of the spherical stop, thereby limiting the bottom liner 3 when it moves downward.

[0036] like Figure 7 and Figure 8 As shown, since the internal space of the receiving groove 23 is small, and the second spring 25 has a certain length after compression, a slot is provided inside the inclined plate 24. The second spring 25 is installed inside the slot, and the other end of the second spring 25 is fixed to the inner wall of the receiving groove 23. The second spring 25 relaxes to push the inclined plate 24 to slide towards the inner protective cylinder 2. The second spring 25 increases the insertion speed between the inclined plate 24 and the slot 26, ensuring the insertion effect of the inclined plate 24. The slot is designed to accommodate the compressed second spring 25, reducing space waste.

[0037] like Figure 3 As shown, in order to facilitate the assembly between the outer casing 1 and the inner casing 2, a first inclined surface 11 is symmetrically provided on the upper surface of the upper limit block 10, and the lower surface of the slide block 14 facing the T-shaped pile 18 is an arc-shaped structure. Through the sliding between the arc-shaped structure and the first inclined surface 11, the two opposing wedge plates 15 can be driven to move away from each other, so that the outer casing 1 is fitted on the outside of the inner casing 2.

[0038] like Figure 2 As shown, in order to improve the support effect, the outer casing 1 provided in this embodiment has a thickness of 18-30mm, and in order to reduce the gap between the inner and outer cast-in-place piles, the inner casing 2 provided in this embodiment has a thickness of 7-10mm.

[0039] During use (operation), after assembling the outer casing 1 and inner casing 2, they are simultaneously lowered to the design elevation. Then, the drilling and grouting pile construction is carried out inside the second drilling zone 7, specifically including hole cleaning, installation of the reinforcing cage, and concrete pouring, so that the concrete poured inside the inner casing 2 forms the concrete grouting pile 8. At this time, the bottom liner 3 and the inner casing 2 act as an isolation to prevent groundwater seepage. After the concrete grouting pile 8 has initially set, the outer casing 1 is pulled out by a crane. During this process, the outer casing 1 moves upward and the bottom liner 3 moves upward synchronously through the connecting components to prevent the bottom liner 3 from affecting the concrete pouring effect at the bottom of the first drilling zone 5. When the outer casing 1 is completely separated from the first drilling zone 5, the third inclined surface 16 contacts and slides relative to the second inclined surface 12, driving the two opposing wedge plates 15 away from each other, so that the T-shaped pile 18 is disengaged from the second slot 17 and... Insert the first slot 13 to automatically separate the outer casing 1 from the bottom liner 3. At the same time, the inclined plate 24 can slide along the inclined structure under its own gravity and the elastic force of the second spring 25, so that the inclined plate 24 can be inserted into the corresponding slot 26 and the bottom liner 3 is fixed to the upper outer side of the inner casing 2, so that the inner casing 2 and the bottom liner 3 can continue to be fixed by the external fixing structure. At this time, the annular gap between the first drilling area 5 and the inner casing 2 is exposed. The groundwater inside the annular gap is pumped out by the water pump, and the drilling and grouting pile construction is carried out inside the annular gap, so that the concrete is poured in the annular gap to form the outer layer of grouting pile. After the outer layer of grouting pile has initially set, the inner casing 2 is pulled out. At this time, the concrete grouting pile 8 has a better solidification effect. Then, the bonding material is poured into the contact surface between the two layers of grouting piles to ensure a stable connection between the two layers of grouting piles.

[0040] On the other hand, the present invention also provides a method for constructing bored piles, applicable to the above-mentioned bored pile casing structure, comprising the following steps: S1. The outer casing 1 and the inner casing 2 are simultaneously lowered to the design elevation. Specifically, the diameter of the outer casing 1 can match the first borehole area 5 in the soft soil layer 4 to isolate the water and soil pressure in the soft soil layer 4 and prevent the borehole from collapsing. The inner casing 2 extends to the second borehole area 7 in the hard rock layer 6 to provide guidance for the drilling in the hard rock layer 6 and reduce vertical deviation.

[0041] S2. Concrete is poured into the inner casing 2 to form a concrete pile 8, specifically including: S21. Hole cleaning: using air lift reverse circulation method to remove sediment from the bottom of the hole; S22. Reinforcing cage installation: the reinforcing cage is hoisted in sections; S23. Concrete pouring: underwater concrete is continuously poured using the tremie pipe method.

[0042] It should be noted that in this step, the bottom of the outer casing 1 is sealed by the bottom liner 3 to isolate the upper part of the second borehole area 7, block the groundwater seepage path, and thus improve the concrete forming effect.

[0043] S3. After the concrete pile 8 has initially set (approximately 6 to 10 hours after concrete pouring), the outer casing 1 is lifted up by a crane at a speed of 0.5 m / min. The bottom liner 3 is moved up synchronously by the combined components until the outer casing 1 is completely removed from the soft soil layer 4, thereby exposing the annular gap between the first borehole area 5 and the inner casing 2.

[0044] S4. Perform water pumping and hole cleaning treatment on the annular gap.

[0045] S5. Pour concrete into the annular gap to form the outer layer of cast-in-place piles. The specific steps can be repeated from S21 to S23.

[0046] It should be further explained that by filling the annular gap at the soft soil layer 4, a composite pile structure is formed, which enhances the bond with the concrete pile 8, increases the contact area, and improves the support effect at the upper end of the concrete pile 8.

[0047] S6. After the outer layer of cast-in-place piles has initially set, pull out the inner casing 2 and inject adhesive material into the contact surface between the two layers of cast-in-place piles. The adhesive material can be epoxy resin. The adhesive material seals the micro-cracks at the interface, blocks the seepage channels in the later stage, and improves the integrity and durability of the composite pile. The composite structure of the double-layer concrete and the adhesive layer further reduces the repair cost caused by pile defects.

[0048] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0049] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A casing structure for bored piles, characterized in that, include: The first borehole area (5) within the soft soil layer (4) and the second borehole area (7) within the hard rock layer (6), wherein the outer diameter of the first borehole area (5) is larger than the outer diameter of the second borehole area (7), and further includes: The outer casing (1) is located in the first drilling area (5); The inner casing (2) is coaxially disposed inside the outer casing (1), and its length is greater than that of the outer casing (1), and its lower end extends into the interior of the second drilling zone (7); The bottom liner (3) is axially slidably fitted onto the outside of the inner casing (2) to seal the bottom of the outer casing (1); The combined component is located on the upper surface of the bottom liner (3) for limiting the inner casing (2) and for synchronously moving the bottom liner (3) when the outer casing (1) moves upward in the first drilling area (5); The separation component is located on the upper outer side of the inner casing (2) and is used to disconnect the connection between the outer casing (1) and the bottom liner (3) after the bottom liner (3) is completely separated from the first drilling area (5) and fix the bottom liner (3) to the upper end of the inner casing (2). The outer casing (1) and the inner casing (2) are separated by a separation assembly to expose the first borehole area (5) for concrete pouring, while the inner casing (2) maintains the stability of the concrete pile (8) in the second borehole area (7).

2. The casing structure for a bored pile according to claim 1, characterized in that: The joint component includes: T-shaped piles (18) are fixed to the upper surface of the bottom liner (3), and their wing plates and web plates form overlapping steps (19). The wedge plate (15) is located at the lower end of the inner side of the outer casing (1) and can slide around the outer casing (1) in the circumference. It is distributed on both sides of the T-shaped pile (18). The second slot (17) is located on the side of the wedge plate (15) near the T-shaped pile (18); The two opposing wedge plates (15) slide toward the T-shaped pile (18) so that the overlapping step (19) engages with the second slot (17), so that the outer casing (1), inner casing (2), and bottom liner (3) form a rigid connection.

3. The casing structure for a bored pile according to claim 2, characterized in that, The separation component includes: The upper limit block (10) is fixed to the upper end of the outer side of the inner casing (2). The lower surface of the upper limit block (10) is provided with a first slot (13) that is compatible with the T-shaped pile (18) at the middle position. The lower surface of the upper limit block (10) is provided with symmetrical second inclined surfaces (12) on both sides of the first slot (13). The third inclined plane (16) is located on the side of the wedge plate (15) facing the T-shaped pile (18); The outer casing (1) continues to move upward, so that the third inclined surface (16) contacts the second inclined surface (12) and slides relative to each other, driving the two wedge plates (15) to move away from each other, so that the T-shaped pile (18) is disengaged from the second slot (17) and inserted into the first slot (13), so that the outer casing (1) and the bottom liner (3) are automatically separated.

4. The casing structure for a bored pile according to claim 3, characterized in that: The separation component also includes: The slot (26) is located on the upper side wall of the inner sleeve (2); The receiving groove (23) is located inside the T-shaped pile (18), and its bottom surface is a sloping structure; The inclined plate (24) is located in the receiving groove (23) and can slide along the inclined structure so that the inclined plate (24) can be inserted into the corresponding slot (26) and the bottom liner (3) is fixed on the upper side of the inner sleeve (2).

5. The casing structure for a bored pile according to claim 4, characterized in that: The lower inner side of the outer casing (1) is uniformly provided with partitions (21), and a groove (20) is provided between two opposite partitions (21). The bottom of the wedge plate (15) is provided with a slide block (14), which is slidably connected to the slide groove (20), and a first spring (22) is installed at one end of the slide block (14). The first spring (22) is stretched to make the slide block (14) slide towards the T-shaped pile (18).

6. The casing structure for a bored pile according to claim 5, characterized in that: The inner casing (2) is provided with a guide rail (9) along the axial direction on the outer side. The lower end of the guide rail (9) extends to the bottom of the first drilling area (5) and is provided with a spherical stop block. The bottom liner (3) has a limiting notch (27) on its inner side that is adapted to the guide rail (9). The outer diameter of the limiting notch (27) is smaller than the outer diameter of the spherical stop.

7. The casing structure for a bored pile according to claim 6, characterized in that: The inclined plate (24) has a slot inside, and a second spring (25) is installed inside the slot. The other end of the second spring (25) is fixed to the inner wall of the receiving groove (23). The second spring (25) relaxes to push the inclined plate (24) to slide towards the inner tube (2).

8. The casing structure for a bored pile according to claim 7, characterized in that: The upper surface of the upper limit block (10) is symmetrically provided with a first inclined surface (11), and the lower surface of the slide block (14) facing the T-shaped pile (18) is an arc-shaped structure.

9. A casing structure for bored piles according to any one of claims 1-8, characterized in that: The outer casing (1) has a thickness of 18-30 mm, and the inner casing (2) has a thickness of 7-10 mm.

10. A method for constructing bored cast-in-place piles, applicable to the casing structure of a bored cast-in-place pile as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Simultaneously lower the outer casing (1) and the inner casing (2) to the design elevation; S2. Concrete is poured into the inner casing (2) to form a concrete pile (8); S3. After the concrete pile (8) has initially set, pull out the outer casing (1) to expose the annular gap between the first borehole area (5) and the inner casing (2); S4. Perform water pumping and hole cleaning treatment on the annular gap; S5. Concrete is poured into the annular gap to form the outer layer of cast-in-place piles; S6. After the outer layer of cast-in-place piles has initially set, pull out the inner casing (2) and inject bonding material into the contact surface between the two layers of cast-in-place piles.

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