Steel casing and cast-in-place pile drag reduction composite structure
By using the hook connection of the bend and the design of the sealing and reinforcing plate, the problems of inconvenient operation and insufficient connection strength of steel casing in cast-in-place pile construction are solved, realizing convenient and safe construction and high-strength concrete structure.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA NUCLEAR POWER ENGINEERING CO LTD
- Filing Date
- 2026-02-26
- Publication Date
- 2026-05-15
AI Technical Summary
Existing steel casings are inconvenient to operate in cast-in-place pile construction and have insufficient connection strength, making them easy to be pulled through, which affects construction safety and effectiveness.
The connection adopts a hook-shaped bend at the bend, eliminating the need for axial full-length reinforcing ribs. Adjacent semi-circular plates are anchored by fasteners to form a multi-layer steel plate connection, which enhances the connection strength. Sealing and reinforcing plates are added at the splicing corners to seal the gaps.
It improves the convenience and safety of construction, enhances connection strength, avoids bulging, and improves the overall strength and structural stability of concrete.
Smart Images
Figure CN122039632A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of pile foundation engineering technology, and in particular to a steel casing and a drag-reducing composite structure for cast-in-place piles. Background Technology
[0002] Currently, the main technology used in cast-in-place pile construction to reduce negative skin friction is the combined use of reinforcing cages, steel casings, and drag-reducing layers. Specifically, the steel casing is fitted over the reinforcing cage and tied to it, while the drag-reducing layer is applied to the outside of the steel casing to achieve drag reduction. However, the current main form of the steel casing consists of two semi-circular steel plates connected together. Each semi-circular steel plate includes a semi-circular plate, a semi-circular rib, and an axially continuous rib. Multiple semi-circular ribs are provided and fixedly installed inside the semi-circular plate. The axially continuous rib is fixedly installed at the edge of the semi-circular plate and extends inward. The ends of the semi-circular ribs contact the axially continuous ribs, and bolt holes are provided on both the semi-circular ribs and the axially continuous ribs. When connecting multiple semi-circular plates, adjacent semi-circular plates are spliced together first, and then the two semi-circular ribs are connected and locked together with bolts. This is relatively easy to achieve. However, after splicing one semi-circular plate, a reinforcing cage needs to be placed in. After the reinforcing cage is placed in, the installation of the next semi-circular plate is done piece by piece, with adjacent pieces connected by semi-circular ribs. After the connection is completed, the axial longitudinal ribs of the lower semi-circular plate are connected to the axial longitudinal ribs of the upper semi-circular plate with bolts. This requires the operator to drill into a closed annular space to operate, which is very inconvenient. Furthermore, due to the deep hole of the cast-in-place pile, the lateral pressure exerted by the concrete on the steel casing is extremely high. Currently, the steel casing is generally only 2mm thick at most, and the thickness of the axial longitudinal ribs is also similar. Using simple bolt connections, the axial longitudinal ribs are easily pulled through, leading to bulging of the formwork and affecting the subsequent construction effect. Therefore, there is an urgent need for a composite structure for reducing the drag of the cast-in-place pile and the steel casing to solve the above-mentioned technical problems. Summary of the Invention
[0003] The purpose of this invention is to provide a steel casing and a drag-reducing composite structure for cast-in-place piles to solve the problems existing in the prior art. The structure has higher strength and is more convenient and safer to construct.
[0004] To achieve the above objectives, the present invention provides the following solution: This invention provides a steel casing, comprising a first semi-annular segment and a second semi-annular segment. The first semi-annular segment includes multiple first semi-annular units, and the second semi-annular segment includes multiple second semi-annular units. Each first semi-annular unit includes a first arc-shaped reinforcing rib, a first semi-annular plate, and a connecting piece. The first arc-shaped reinforcing rib is fixedly disposed within the first semi-annular plate, and the length of the first arc-shaped reinforcing rib is less than the length of the first semi-annular plate. Two adjacent first semi-annular plates are connected by the connecting piece, and the connecting piece is fitted to the outer side of two adjacent first semi-annular plates. The second semi-annular unit includes a second arc-shaped reinforcing rib and a second semi-annular plate. Two arc-shaped reinforcing ribs are fixedly disposed inside the second semi-annular plate, and the length of the second arc-shaped reinforcing ribs is less than the length of the second semi-annular plate. Two adjacent second semi-annular plates are connected by the second arc-shaped reinforcing ribs. The first semi-annular plate includes a first main body and an inwardly bent first bending portion. The second semi-annular plate includes a second main body and an outwardly bent second bending portion. The first main body, the second bending portion, the first bending portion, and the second main body can fit together in sequence. The fixing member can pass through the first main body, the second bending portion, the first bending portion, and the second main body in sequence to fix the first bending portion and the second bending portion.
[0005] In some embodiments, a sealing reinforcement plate is also included, which covers the splicing corner positions of two adjacent first semi-annular plates and two adjacent second semi-annular plates, and the sealing reinforcement plate is anchored to the two adjacent first semi-annular plates and the two adjacent second semi-annular plates by second rivets.
[0006] In some embodiments, the length of the sealing reinforcement plate is greater than the distance between the first ends of two adjacent first arc-shaped reinforcing ribs and the first ends of the second arc-shaped reinforcing ribs.
[0007] In some embodiments, the first bend and the second bend have the same dimensions.
[0008] In some implementations, the width is 50mm-80mm, the bending angle is 180°, and the bending curvature diameter is not less than the thickness of the semi-circular plate.
[0009] In some embodiments, the fastener is a first rivet, the first main body has a plurality of first rivet holes at the end near the first bend, the first bend has a plurality of second rivet holes, the second main body has a plurality of third rivet holes at the end near the second bend, and the second bend has a plurality of fourth rivet holes, and the first rivet can pass through the first rivet holes, the fourth rivet holes, the second rivet holes and the third rivet holes in sequence.
[0010] In some embodiments, the second arc-shaped reinforcing rib has multiple bolt holes, and two adjacent second arc-shaped reinforcing ribs are connected by high-strength bolts.
[0011] In some embodiments, the distance between the first end of the arc-shaped reinforcing rib and the first end of the semi-annular plate is greater than twice the length of the bend.
[0012] The present invention achieves the following technical effects compared to the prior art: First, compared to existing structures, the steel casing of this invention eliminates the need for a continuous reinforcing rib in the axial direction, instead employing a hook-shaped bend in the bending section. During connection, adjacent semi-annular plates are first spliced and fixed to form a second semi-annular segment. Then, the first bend of the first semi-annular plate is hooked with the second bend of the second semi-annular segment, and anchored using fasteners. Adjacent first semi-annular plates are then connected by connecting pieces. Throughout the process, operators no longer need to crawl inside the steel casing, significantly improving ease of operation and safety. Furthermore, the first main body, second bend, first bend, and second main body can sequentially fit the equivalent of four layers of steel plates. After the fasteners pass through, the multiple layers of steel plates are not easily pulled through, and the connection strength depends almost entirely on the strength of the fasteners. Using high-strength fasteners can greatly improve the connection strength between the first and second semi-annular segments. Compared to the previous direct connection using only thin steel plates and bolts, this method changes point contact to line contact or even surface contact, significantly improving connection strength and preventing bulging during concrete pouring. This connection method can improve both the convenience and safety of construction, as well as the strength of the structure.
[0013] Moreover, it should be emphasized that the connection structure of the present invention can also simultaneously achieve other better and more unpredictable effects. For existing structural configurations, there are long semi-circular ribs and axial reinforcing ribs that run the entire length. This configuration has the following problems: First, axial separation. After the two semi-circular steel plates are spliced together, the two axial reinforcing ribs are fitted together, and the semi-circular ribs abut against the axial reinforcing ribs. When pouring concrete, the two semi-circular ribs completely enclose each other, which separates the concrete in the axial direction, creating gaps and affecting the strength. Second, circumferential separation. The two axial reinforcing ribs separate the concrete in the circumferential direction, creating gaps and affecting the strength. The connection structure provided by this invention eliminates the need for axial reinforcing ribs, allowing the concrete to be completely connected in the circumferential direction without any separation joints. This results in higher concrete strength. Furthermore, the length of the arc-shaped reinforcing ribs in this invention is less than the length of the semi-circular plate, creating a gap between the first and second arc-shaped reinforcing ribs. Although the arc-shaped reinforcing ribs still separate the concrete in the axial direction, the gaps prevent the first and second arc-shaped reinforcing ribs from forming a complete circle when joined. The axial concrete is not completely separated, maintaining a continuous connection. Compared to existing connection methods, this also improves the concrete strength to some extent. Therefore, the concrete in this invention forms a complete circle in the circumferential direction without any breaks, and also has a certain range of continuous connection in the axial direction, which greatly enhances the concrete strength. Attached Figure Description
[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0015] Figure 1 This is a schematic diagram of the composite structure for reducing drag in cast-in-place piles in some embodiments of the present invention; Figure 2 This is a schematic diagram of the unspliced state of the steel casing in some embodiments of the present invention; Figure 3 This is a schematic diagram of the splicing of the top protective sleeve in some embodiments of the present invention; Figure 4 This is a schematic diagram of the sealing and reinforcing plate in some embodiments of the present invention; Figure 5 This is a schematic diagram showing the connection between the first bent portion and the second bent portion in some embodiments of the present invention.
[0016] In the figure: 1-First semi-annular segment; 11-First semi-annular plate; 12-First arc-shaped reinforcing rib; 13-First bend; 14-First main body; 2-Second semi-annular segment; 21-Second semi-annular plate; 22-Second arc-shaped reinforcing rib; 23-Second bend; 24-Second main body; 3-Drag-reducing layer; 4-Bolt hole; 5-Connecting piece; 6-First rivet; 7-Third rivet; 8-Sealing and reinforcing plate. Detailed Implementation
[0017] 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.
[0018] The purpose of this invention is to provide a steel casing and cast-in-place pile drag-reducing composite structure to solve the problems existing in the prior art. The structure has higher strength and is more convenient and safer to construct.
[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1
[0020] like Figures 1-5As shown, the present invention provides a steel casing, including a first semi-annular segment 1 and a second semi-annular segment 2. The first semi-annular segment 1 includes multiple first semi-annular units, and the second semi-annular segment 2 includes multiple second semi-annular units. Each first semi-annular unit includes a first arc-shaped reinforcing rib 12, a first semi-annular plate 11, and a connecting piece 5. The first arc-shaped reinforcing rib 12 is fixedly disposed within the first semi-annular plate 11, and the length of the first arc-shaped reinforcing rib 12 is less than the length of the first semi-annular plate 11. Two adjacent first semi-annular plates 11 are connected by the connecting piece 5, and the connecting piece 5 is fitted onto the outer side of two adjacent first semi-annular plates 11. Specifically, after the connecting piece 5 is fitted onto the outer side of two adjacent first semi-annular plates 11, it is anchored by a third rivet 7. The second semi-annular unit includes a second arc-shaped reinforcing rib 22 and a second semi-annular plate 21. The second arc-shaped reinforcing rib 22 is fixedly disposed inside the second semi-annular plate 21, and the length of the second arc-shaped reinforcing rib 22 is less than the length of the second semi-annular plate 21. Two adjacent second semi-annular plates 21 are connected by the second arc-shaped reinforcing rib 22. Specifically, the two second arc-shaped reinforcing ribs 22 can be connected by bolts passing through them and locked by nuts. The first semi-annular plate 11 includes a first main body 14 and an inwardly bent first bent portion 13. The second semi-annular plate 21 includes a second main body 24 and an outwardly bent second bent portion 23. The first main body 14, the second bent portion 23, the first bent portion 13, and the second main body 24 can fit together in sequence. The fastener can pass through the first main body 14, the second bent portion 23, the first bent portion 13, and the second main body 24 in sequence to fix the first bent portion 13 and the second bent portion 23.
[0021] First, compared to existing structures, the steel casing in this embodiment eliminates the axially continuous reinforcing ribs and adopts a hook-shaped bend in the bending section. During connection, it is only necessary to first splice and fix adjacent semi-annular plates to form the second semi-annular segment 2, then hook the first bend 13 of the first semi-annular plate 11 with the second bend 23 of the second semi-annular segment 2, and then anchor it using fasteners. Adjacent first semi-annular plates 11 are then connected by connecting pieces 5. Throughout the process, operators no longer need to crawl into the steel casing, greatly improving ease of operation and safety. Furthermore, the first main body 14, the second bend 23, the first bend 13, and the second main body 24 can sequentially fit the equivalent of four layers of steel plates. After the fasteners pass through, the multiple layers of steel plates are not easily pulled through. The connection strength depends almost entirely on the strength of the fasteners; using high-strength fasteners can significantly improve the connection strength between the first semi-annular segment 1 and the second semi-annular segment 2. Compared to the previous direct connection between thin steel plates and bolts, this new method changes point contact to line contact or even surface contact, significantly improving connection strength and preventing bulging during concrete pouring. This connection method enhances both construction convenience and safety while also increasing structural strength.
[0022] Moreover, it should be emphasized that the connection structure of this embodiment can also achieve other better and more unpredictable effects simultaneously. For existing structural configurations, there are long semi-circular ribs and axial reinforcing ribs that run the entire length. This configuration has the following problems: First, axial separation. After the two semi-circular steel plates are spliced together, the two axial reinforcing ribs are fitted together, and the semi-circular ribs abut against the axial reinforcing ribs. When pouring concrete, the two semi-circular ribs completely enclose each other, which separates the concrete in the axial direction, creating gaps and affecting the strength. Second, circumferential separation. The two axial reinforcing ribs separate the concrete in the circumferential direction, creating gaps and affecting the strength. The connection structure provided in this embodiment eliminates the need for axial reinforcing ribs, allowing the concrete to be completely connected in the circumferential direction without any separation joints. This results in higher concrete strength. Furthermore, the length of the arc-shaped reinforcing ribs in this embodiment is less than the length of the semi-circular plate, creating a gap between the first arc-shaped reinforcing rib 12 and the second arc-shaped reinforcing rib 22. Although the arc-shaped reinforcing ribs still separate the concrete in the axial direction, the gaps prevent the first arc-shaped reinforcing rib 12 and the second arc-shaped reinforcing rib 22 from forming an incomplete circle. The axial concrete is not completely separated, maintaining a continuous connection. Compared to existing connection methods, this also improves the concrete strength to some extent. Therefore, the concrete in this embodiment forms a complete circle in the circumferential direction without any breaks, and also has a certain range of continuous connection in the axial direction, which greatly improves the concrete strength.
[0023] It should be noted that the connecting piece 5 is a rectangle or rhombus shape, 70mm wide and 140mm long. It is anchored to the outside of the adjacent first semi-annular plate 11 by the third rivet 7, and multiple connecting pieces 5 are evenly arranged in the circumferential direction. The 70mm×140mm connecting piece provides sufficient stress-bearing area, which can effectively disperse the stress at the splice and avoid stress concentration and tearing. The size is not too large, the amount of steel used is reasonable, and the processing, transportation and installation costs are low, resulting in high cost performance. All third rivets 7 are driven on the outside of the casing, so the operator does not need to crawl into the casing, which greatly reduces the risk of working in confined spaces. The installation process is simple and can be completed quickly, significantly improving construction efficiency.
[0024] In some embodiments, the steel casing further includes a sealing and reinforcing plate 9, which covers the splicing corner of two adjacent first semi-annular plates 11 and two adjacent second semi-annular plates 21, and the sealing and reinforcing plate 9 is anchored to the two adjacent first semi-annular plates 11 and the two adjacent second semi-annular plates 21 by second rivets. The steel casing is spliced from multiple segments of first semi-annular plates 11 and second semi-annular plates 21, and the splicing corner (the intersection of circumferential and axial splicing) is the weakest point most prone to gaps and misalignment. The sealing and reinforcing plate 9 covers this corner, forming a closed corner sealing structure, which can effectively seal the grout overflow channel during concrete pouring, avoiding grout leakage, grout runoff, and honeycomb surface defects. When pouring concrete, the corner is no longer a weak area, which can effectively resist the lateral pressure of concrete, significantly reduce the risk of bulging, deformation, and misalignment, and ensure the roundness and dimensional accuracy of the casing. It should be noted that the material of the sealing and reinforcing plate 9 is preferably galvanized steel plate or polymer.
[0025] In some embodiments, the length of the sealing and reinforcing plate 9 is greater than the distance between the first ends of two adjacent first arc-shaped reinforcing ribs 12 and the first ends of second arc-shaped reinforcing ribs 22. It should be noted that the first ends of the first arc-shaped reinforcing ribs 12 and 22 are located on the same side. The lengths of the first arc-shaped reinforcing ribs 12 and 22 are less than that of the semi-circular plate, and there is an axial gap between their ends. This is the weakest channel most prone to grout leakage during concrete pouring. The length of the sealing and reinforcing plate 9 is greater than this gap, which can completely cover and seal it, preventing grout from overflowing from the gap at the end of the reinforcing rib from the source, ensuring that the concrete is dense and free of honeycomb pitting. Furthermore, the length of the sealing and reinforcing plate 9 covering this end gap allows the end of the reinforcing rib to be directly pressed and anchored under the sealing plate, forming a rigid constraint at the end, effectively limiting its deformation and displacement, and avoiding problems such as unevenness of the inner wall of the casing, localized loosening of the concrete, and decreased bonding strength caused by deformation of the end of the reinforcing rib. The gap at the end of the arc-shaped reinforcing rib is a key channel for axial concrete connection. The sealing and reinforcing plate 9 only covers the outside of the gap and does not block the internal concrete connection path. The concrete can form a continuous whole through the gap in the axial direction, avoiding axial separation joints caused by the complete enclosure of the reinforcing rib, improving the overall strength of the concrete and the integrity of the structure, and improving the ease of operation.
[0026] In some embodiments, the first bend 13 and the second bend 23 have the same dimensions, with a width of 50mm-80mm, a bending angle of 180°, and a bending curvature diameter not less than the thickness of the semi-annular plate. The consistent width, thickness, and bending form on both sides ensure symmetrical stress distribution, preventing excessive stress, warping, and tearing on one side. This results in uniform overall rigidity after splicing, and better roundness and stability of the casing. The 50-80mm width creates a sufficiently large surface and line contact area, increasing the stress area when rivets penetrate multiple layers of steel plates, making them less prone to tearing or puncture. The 180° bend creates interlocking hooks on both sides, forming a mechanical interlock after splicing. This interlocking structure alone can resist significant tensile and opening forces. Even if the rivet fails, the interlocking structure can still maintain a basic connection, providing higher safety and redundancy. The 180° bend allows the four layers—the first main body 14, the second bend 23, the first bend 13, and the second main body 24—to be sequentially bonded together, forming a laminated steel plate effect. This significantly increases local rigidity, effectively resisting bulging, deformation, and misalignment, and ensuring the roundness and dimensional accuracy of the casing. With a curvature diameter greater than or equal to the plate thickness and a sufficiently large bending radius, the material deformation at the bend is uniform, preventing significant work hardening and microcracks. This improves the fatigue life and structural durability of the bend, making it particularly suitable for vibration, impact, and cyclic loading conditions.
[0027] In some embodiments, the fastener is a first rivet 6. The first main body 14 has a plurality of first rivet holes near the end of the first bent portion 13, the first bent portion 13 has a plurality of second rivet holes, the second main body 24 has a plurality of third rivet holes near the end of the second bent portion 23, and the second bent portion 23 has a plurality of fourth rivet holes. The first rivet 6 can pass through the first rivet holes, the fourth rivet holes, the second rivet holes, and the third rivet holes in sequence. The length of the first bent portion 13 is the same as that of the second bent portion 23, so the lengths are the same. This ensures that the end of the first bent portion 13 abuts against the bending point of the second bent portion 23 and the second main body 24, and the end of the second bent portion 23 abuts against the bending point of the first bent portion 13 and the first main body 14, thus ensuring linear contact of the bent portions and improving overall strength.
[0028] In a preferred embodiment, the first rivets 6 are arranged in at least two staggered rows, forming a double-row multi-point anchorage. The increased number of first rivets 6 improves the overall shear and tensile bearing capacity. The two rows of staggered first rivets 6 constrain the joint from two different directions, resisting both normal tensile forces (preventing opening) and tangential shear forces (preventing slippage). Furthermore, the staggered arrangement of the two rows disperses stress paths, resulting in more uniform stress distribution on the plate between holes and a significant reduction in stress peak values.
[0029] It should also be noted that self-tapping screws can be used for fasteners, as long as they allow for external installation and provide a good connection and locking effect.
[0030] In some embodiments, the second arc-shaped reinforcing rib 22 has multiple bolt holes 4, and adjacent second arc-shaped reinforcing ribs 22 are connected by high-strength bolts. The direct connection of adjacent second arc-shaped reinforcing ribs 22 with high-strength bolts connects the axially segmented reinforcing ribs into a continuous circumferential reinforcing band. Under the action of concrete lateral pressure and soil lateral pressure, the circumferential stiffness of the casing is significantly improved, and the overall effect is closer to that of a whole ring reinforcement, significantly enhancing its resistance to ellipticization and deformation. High-strength bolts with a performance grade of 8.8 are preferably used. The first arc-shaped reinforcing rib 12 only serves to help form the first semi-annular plate 11, and the first arc-shaped reinforcing ribs 12 are not connected by bolts.
[0031] In some embodiments, the distance between the first end of the arc-shaped reinforcing rib and the first end of the semi-annular plate is greater than twice the length of the bent portion, ensuring that the bent portion can be smoothly inserted without obstruction.
[0032] Preferably, the arc length of the semi-circular plate is 200-240 mm longer than the arc length of the arc-shaped reinforcing rib, preferably 220 mm, and the distance between the first end of the arc-shaped reinforcing rib and the first end of the semi-circular plate is the same as the distance between the second end of the arc-shaped reinforcing rib and the second end of the semi-circular plate. A 100-120 mm allowance, preferably 110 mm, is left at each end of the semi-circular plate to form an axial overlap zone, where a second rivet or sealing reinforcement plate 9 can be arranged. The sufficient length of the overlap zone allows for multiple rows of rivets, significantly improving connection strength, shear resistance, and pull-out resistance. The reinforcing rib is shorter than the plate body, and after assembly, there is an axial gap of not less than 110 mm between the ends of adjacent reinforcing ribs. This gap ensures that the concrete is not completely interrupted in the axial direction, maintaining a continuous channel and avoiding strength reduction caused by axial separation joints. The reinforcing ribs are symmetrically arranged in the center of the semi-circular plate, with the same margin at both ends, resulting in uniform stress and eliminating problems such as excessive stress on one side or uneven deformation. This makes the steel casing symmetrical in circumferential and axial stiffness, easier to ensure roundness and straightness, and stronger resistance to ellipticization and deformation. Example 2
[0033] like Figure 1 As shown, this embodiment also provides a composite structure for reducing the drag of cast-in-place piles, including a reinforcing cage, a drag-reducing layer 3, and a steel casing as described in Embodiment 1. The reinforcing cage is fixedly installed inside the steel casing, and the drag-reducing layer 3 is applied to the outer circumference of the steel casing. The steel casing provides rigid support and stable space, preventing the pile from directly contacting the soil and physically cutting off most of the path for the transmission of side friction. The drag-reducing layer 3 on the outer side further effectively reduces the friction coefficient. The dual mechanisms work synergistically to achieve a significant reduction in negative skin friction.
[0034] It should be noted that each semi-circular plate is 1m-2m long and 0.75-2mm thick, while the drag-reducing layer 3 is 3mm-6mm thick. The reinforcing cage uses double-strand No. 16 galvanized iron wire as binding material, with the arc-shaped reinforcing ribs tied to the main reinforcing bars at approximately 2m intervals to form a stable whole. The 1m-2m length ensures sufficient rigidity for each section, preventing bending or twisting during hoisting, splicing, and sinking. The 2m binding interval matches the length of the semi-circular plate (1m-2m), and each section of the casing has at least one binding point, with the main reinforcing bars and reinforcing ribs fixed in relative positions.
[0035] In some embodiments, the drag-reducing layer 3 is a polymer-modified bitumen roll, with at least one layer laid outside the steel casing, and the overlap length is not less than 100mm. Specifically, two layers of polymer-modified bitumen roll with a self-adhesive layer and a thickness of 3mm can be selected.
[0036] The following structures are suitable for common soft soil and fill soil strata: First, the components are prefabricated. The semi-circular plate is made of 1.0mm thick galvanized steel sheet, cold-pressed into an arc shape matching the designed pile diameter using a special mold. Arc-shaped reinforcing ribs are welded along the entire arc of the upper and lower edges of each semi-circular plate. The arc length of these reinforcing ribs is approximately 220mm shorter than the main arc length of the semi-circular plate, leaving approximately 110mm free end areas at each end of the semi-circular plate. Bolt holes 4 are pre-punched at certain intervals on the arc-shaped reinforcing ribs.
[0037] Secondly, for the vertical side of the semi-circular plate, a 50mm wide, 180° bent section is formed by roll forming. The bending directions of the first bent section 13 and the second bent section 23 are set to be opposite, one inward and the other outward. In the overlapping area of the bent section, two rows of staggered rivet holes are prefabricated.
[0038] During on-site construction, follow these procedures: 1. Assembly of the second semi-circular segment 2: Hoist adjacent second semi-circular plates 21 to a level site. The second bends 23 are all outward-facing. Adjacent semi-circular plates are connected at the second arc-shaped reinforcing ribs 22 with high-strength bolts. Align all bolt holes 4, insert high-strength bolts of grade 8.8 and tighten the nuts. Repeat this step until the designed pile length is reached, forming a continuous second semi-circular segment 2.
[0039] 2. Rebar cage hoisting into the formwork: Hoist the prefabricated rebar cage into the assembled second semi-circular section 2. Use double-strand No. 16 galvanized iron wire as binding material to tie and fix the second arc-shaped reinforcing rib 22 of the steel casing to the main reinforcement of the rebar cage at intervals of about 2m to form a stable whole.
[0040] 3. Assembly of the first semi-annular segment 1: Install the first semi-annular plates 11 one by one, and interlock the first bent part 13 and the second bent part 23 to form an interlocking structure. After aligning the rivet holes, use blind rivets as fasteners to secure them, thereby forming a complete annular segment. Adjacent first semi-annular plates 11 are connected by connecting pieces 5. The connecting pieces 5 are rectangular or rhomboid in shape with a width of 70mm and a length of 140mm, and are anchored to the outside of adjacent first semi-annular plates 11 by rivets.
[0041] 4. Install sealing and reinforcing plates 9: Take two arc-shaped thin steel plates as sealing and reinforcing plates 9, cover the outside of the connected free end area, and use the second rivet to fasten them to the semi-circular plates on both sides to achieve sealing and reinforcement of the free end gap.
[0042] 5. Laying drag-reducing layer 3: In this embodiment, two layers of 3mm thick polymer-modified bitumen rolls with self-adhesive layers are selected as drag-reducing layer 3. Remove the release film on the back of the roll, tightly wrap it around the outside of the assembled steel casing, and ensure that the adhesion is flat and free of air bubbles. The overlap width at the joints should not be less than 100mm, thus forming a complete drag-reducing layer 3.
[0043] 6. Overall Lowering: Using pile foundation lifting equipment, the entire drag-reducing composite structure of the cast-in-place pile is lifted and lowered vertically and slowly into the pre-drilled pile hole, allowing for subsequent concrete pouring. During concrete pouring, the steel casing effectively resists lateral pressure and prevents formwork bulging; the outer drag-reducing layer 3 permanently isolates the pile body from the soil.
[0044] Furthermore, for environments with higher groundwater levels and projects with higher requirements for drag reduction and durability, the following structures can be selected: Structural strength enhancement: The thickness of the semi-circular plate is increased to 1.8 mm to improve its own stiffness.
[0045] Enhanced Connection Method: In addition to the existing arc-shaped reinforcing rib connection, six steel reinforcing plates are added to the outside of the steel casing to connect adjacent semi-circular plates. These reinforcing plates span the joint between the two semi-circular plates and are riveted to the semi-circular plates on both sides using multiple rivets, providing extra safety redundancy for the connection.
[0046] Upgraded drag-reducing materials: Drag-reducing layer 3 uses a liquid two-component polyurethane coating. During construction, an airless spraying device is used to evenly spray the coating onto the outer surface of the steel casing. After curing at room temperature, it forms a continuous, dense, and elastic polymer coating with a thickness of approximately 5mm. This coating has extremely strong adhesion to the steel casing and exhibits excellent water resistance, chemical corrosion resistance, and aging resistance.
[0047] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.
Claims
1. A steel casing, characterized in that: The system includes a first semi-annular segment and a second semi-annular segment. The first semi-annular segment includes multiple first semi-annular units, and the second semi-annular segment includes multiple second semi-annular units. Each first semi-annular unit includes a first arc-shaped reinforcing rib, a first semi-annular plate, and a connecting piece. The first arc-shaped reinforcing rib is fixedly disposed within the first semi-annular plate, and its length is less than the length of the first semi-annular plate. Two adjacent first semi-annular plates are connected by the connecting piece, which is fitted to the outer sides of the two adjacent first semi-annular plates. Each second semi-annular unit includes a second arc-shaped reinforcing rib and a second semi-annular plate. The second semi-annular plate is fixedly disposed within the second semi-annular plate, and the length of the second arc-shaped reinforcing rib is less than the length of the second semi-annular plate. Two adjacent second semi-annular plates are connected by the second arc-shaped reinforcing rib. The first semi-annular plate includes a first main body and an inwardly bent first bending portion. The second semi-annular plate includes a second main body and an outwardly bent second bending portion. The first main body, the second bending portion, the first bending portion, and the second main body can be fitted together in sequence. The fixing member can pass through the first main body, the second bending portion, the first bending portion, and the second main body in sequence to fix the first bending portion and the second bending portion.
2. The steel casing according to claim 1, characterized in that: It also includes a sealing and reinforcing plate, which covers the splicing corner of two adjacent first semi-annular plates and two adjacent second semi-annular plates, and the sealing and reinforcing plate is anchored to the two adjacent first semi-annular plates and the two adjacent second semi-annular plates by second rivets.
3. The steel casing according to claim 2, characterized in that: The length of the sealing and reinforcing plate is greater than the distance between the first ends of the first arc-shaped reinforcing ribs and the first ends of the second arc-shaped reinforcing ribs, which are adjacent to each other.
4. The steel casing according to claim 1, characterized in that: The first bend and the second bend have the same dimensions.
5. The steel casing according to claim 4, characterized in that: The width of the bent section is 50mm-80mm, the bending angle is 180°, and the bending curvature diameter is not less than the thickness of the semi-circular plate.
6. The steel casing according to claim 1, characterized in that: The fastener is a first rivet. The first main body has a plurality of first rivet holes at the end near the first bend. The first bend has a plurality of second rivet holes. The second main body has a plurality of third rivet holes at the end near the second bend. The second bend has a plurality of fourth rivet holes. The first rivet can pass through the first rivet holes, the fourth rivet holes, the second rivet holes, and the third rivet holes in sequence.
7. The steel casing according to claim 1, characterized in that: The second arc-shaped reinforcing rib has multiple bolt holes, and two adjacent second arc-shaped reinforcing ribs are connected by high-strength bolts.
8. The steel casing according to claim 1, characterized in that: The distance between the first end of the arc-shaped reinforcing rib and the first end of the semi-circular plate is greater than twice the length of the bent portion.
9. A composite structure for reducing drag in cast-in-place piles, characterized in that: It includes a reinforcing cage, a drag-reducing layer, and a steel casing as described in any one of claims 1-8, wherein the reinforcing cage is fixedly disposed inside the steel casing, and the drag-reducing layer is applied to the outer circumferential surface of the steel casing.
10. The composite structure for reducing drag in cast-in-place piles according to claim 9, characterized in that: The drag-reducing layer is a polymer-modified bitumen roll, and at least one layer is laid outside the steel casing, with an overlap length of not less than 100mm.