Miniature steel pipe uplift pile structure and construction method

Abstract

The present application relates to a kind of micro steel pipe uplift pile structure and construction method, including the pile body implanted in foundation, the pile body includes steel pipe concrete combination core and the cast-in-situ concrete pile body wrapped in the outer side of steel pipe concrete combination core, the cast-in-situ concrete pile body includes straight pole section and expansion section, multiple expansion sections are vertically spaced distribution and form bearing disc along pile body, the steel pipe concrete combination core includes steel pipe and the inner core concrete filled in steel pipe inside, the bottom of steel pipe is equipped with cone head, steel pipe outer wall is welded with triangular reinforcing wing plate along circumference direction, multiple balance ring is fixedly sleeved in steel pipe outer wall interval, steel pipe is through length structure or multi-section flange splicing structure, steel pipe top is welded with anchor plate, and the anchor plate is used to bury in pile foundation upper structure.The present application provides anti-floating force with the combination of composite pile formed by steel pipe and concrete, improves the overall structural stability and anti-deformation capacity of pile body.

Description

Technical Field

[0001] This invention relates to the field of anti-uplift pile construction technology, specifically to a micro steel pipe anti-uplift pile structure and construction method. Background Technology

[0002] In recent years, the development and utilization of urban underground space has continued to expand, and the burial depth of underground structures has been increasing. The problem of buoyancy stability of underground structures has become increasingly prominent, and has become a key control factor in the design and construction of underground engineering projects. Currently, the mainstream technologies for solving structural buoyancy issues in engineering include anti-buoyancy anchors, increasing the structure's self-weight counterweight, and setting up tension pile foundations. Among these, tension piles are the most widely used in building and municipal engineering due to their reliable force bearing, good deformation control, and stable buoyancy resistance. Tension piles, also known as anti-buoyancy piles, have the core function of providing upward resistance to pull-out forces through the frictional resistance between the pile and the soil and the pile's own weight when the underground structure is below the groundwater level and its self-weight is insufficient to counteract the buoyancy of the groundwater, thus ensuring the overall stability of the structure.

[0003] At present, tension piles have gradually evolved from the traditional uniform cross-section form to various types of piles such as enlarged base non-uniform cross-section and prestressed piles. However, the mainstream tension piles are still mainly reinforced concrete cast-in-place piles. That is, traditional uniform cross-section bored cast-in-place piles rely on the pile side friction and the pile body weight to resist the upward pull force. On this basis, bored enlarged base cast-in-place piles have been developed to increase the pull force by enlarging the pile end, but the material properties of reinforced concrete have not been changed.

[0004] Furthermore, concrete has extremely low tensile strength, making the pile body prone to premature through-cracks under continuous uplift loads. Once cracks develop, the concrete quickly withdraws from the load, leaving the longitudinal reinforcement to bear the entire tensile force. Since uplift piles are constantly exposed to a damp, corrosive underground environment, concrete cracking directly exposes the reinforcement to groundwater, acids, alkalis, salts, and harmful ions, leading to corrosion expansion, cross-sectional weakening, and further exacerbating crack propagation. This significantly reduces the durability and service life of the pile and the entire underground structure. Additionally, traditional cast-in-place piles require large borehole sizes, complex construction procedures, and high material consumption. They also present challenges in drilling in confined spaces and complex geological environments, making it difficult to meet engineering construction requirements.

[0005] Therefore, it is necessary to study a micro-steel pipe anti-uplift pile structure and construction method. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a micro steel pipe anti-tension pile structure and construction method, which effectively solves the problems of low tensile strength, easy cracking, and poor durability of existing anti-tension piles.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a method for constructing micro-steel pipe anti-tension piles, comprising the following steps: Step 1: Based on the geological survey results, determine the geological parameters of the construction area, the location of construction piles, and the design depth and position of the bearing plate. Locate and lay out the construction area and level the site. Step 2: Prepare a continuous or segmented steel pipe, weld a tapered guide head to the bottom of the steel pipe, weld reinforcing wing plates and connecting plates to the steel pipe body, and fix a balance ring on the connecting plate; Step 3: Based on the marked pile position, vertical drilling is carried out. During the drilling process, hole enlargement is carried out at each hard soil layer elevation position preset by the drill rod to form an enlarged section. After drilling to the designed elevation of the bottom of the hole, hole enlargement is carried out to form the pile end enlarged head, and the pile end enlarged head is embedded in the hard bearing layer. Step 4: Pressurize concrete into the pile hole through the internal channel of the drill rod, continuously pouring while raising the drill rod, and stabilize the pressure at each enlarged section until the pressurization of the entire pile hole is completed, and the final elevation of the concrete pouring exceeds the design pile top elevation. Step 5: Before the concrete has initially set, calibrate the verticality of the steel pipe and press it vertically into the middle of the pile hole. During the pressing process, continuously add concrete into the pile hole to ensure that the pressing speed matches the grouting speed, and monitor and adjust the verticality of the steel pipe in real time. Step 6: After the steel pipe is pressed into place, pour concrete into the steel pipe to the design elevation and vibrate to remove air. After the pile foundation has been cured and formed, remove the over-poured part of the pile head and cut off the excess steel pipe at the top. Weld an anchor plate to the top of the steel pipe and connect it to the upper structure.

[0008] Furthermore, in step 3, when a quicksand layer exists in the construction area, a steel casing is hammered into the ground to protect the wall before drilling. The construction steps include: first, making a steel casing with a length greater than the thickness of the quicksand layer and a lower end that can be embedded in the stable soil layer for more than 1.0m; then, vertically driving the steel casing into the soil until the bottom end passes through the quicksand layer and enters the stable hard soil layer, forming a protective wall for the quicksand layer; and completing the drilling, hole enlargement, and concrete pouring under the protection of the steel casing, pouring the concrete until the liquid level exceeds the top elevation of the steel casing; after pressing the steel pipe in before the concrete initially sets, slowly pulling out the steel casing, replenishing concrete in time during the extraction process to ensure that the liquid level is always not lower than the bottom of the steel casing.

[0009] Furthermore, in step 4, before pouring concrete, 0.5m of cement slurry is pumped into the drill pipe channel to lubricate the pipe; the drill pipe lifting speed is controlled at 0.5-0.8m / min, and the concrete pumping volume is not less than 0.3m. 3 / min, the concrete surface inside the hole is always more than 1.0m higher than the bottom of the drill pipe during the grouting process; the pressure stabilization treatment time at each enlargement section is 3min, and the concrete over-pouring height is at least 500mm.

[0010] Furthermore, in step 4, the concrete injected into the pile hole is a slow-setting, super-fluid self-compacting concrete with a slump of 220-240 mm, a spread of not less than 650 mm, and an initial setting time of not less than 10 h.

[0011] Furthermore, in step 3, the enlarged sections are all located in hard soil layers with a spacing of 5-6m, and the enlarged head at the bottom of the pile is embedded in the hard bearing layer for no less than 1.2m.

[0012] The present invention also provides a micro steel pipe anti-uplift pile structure, including a pile body implanted in the foundation. The pile body includes a steel pipe concrete composite core and a cast-in-place concrete pile body wrapped around the outside of the steel pipe concrete composite core. The cast-in-place concrete pile body includes a straight section and an enlarged section. The diameter of the enlarged section is larger than that of the straight section. Multiple enlarged sections are distributed vertically along the pile body at intervals to form a bearing plate. An enlarged pile end head is provided at the bottom of the pile body.

[0013] Furthermore, the steel-concrete composite core includes a steel pipe and an inner core concrete poured inside the steel pipe. The bottom of the steel pipe is provided with a cone head, and triangular reinforcing wing plates are welded to the outer wall of the steel pipe along the circumferential direction. Multiple sets of wing plates are arranged in segments along the length of the steel pipe.

[0014] Furthermore, a connecting plate is welded to the outer wall of the steel pipe, and multiple balance rings are fixedly sleeved on the connecting plate at intervals to assist in the straightness control of the steel pipe during the pressing process.

[0015] Furthermore, the steel pipe is a continuous structure or a multi-section flange splicing structure, and an anchor plate is welded to the top of the steel pipe. The anchor plate is used to be embedded in the upper structure of the pile foundation.

[0016] The beneficial effects of the above technical solution are as follows: The micro steel pipe anti-uplift pile structure and construction method provided by the present invention provide anti-buoyancy force with a composite pile formed by steel pipe and concrete; the main vertical load is borne by the steel pipe concrete pile core, and the load is progressively transferred to the concrete core and then to the surrounding soil through the lateral resistance of the steel pipe and concrete. The load transfer path is clear and the transfer efficiency is high, which significantly improves the uplift bearing capacity of the pile body; at the same time, the hole is enlarged at a preset position in the hard soil layer of the pile body to form an enlarged section, which greatly increases the contact area between the pile body and the soil, further improving the anchorage force and uplift bearing capacity of the pile body, realizing the advantages of small pile diameter and high bearing capacity, and effectively meeting the anti-buoyancy stability requirements of underground structures.

[0017] In the composite structure formed by steel pipe and concrete in this invention, the steel pipe, as the main tension member, avoids the concrete directly bearing tensile stress. The concrete filling and wrapping of the steel pipe not only prevents the inner wall of the steel pipe from being eroded by the underground corrosive environment, but also provides support for the steel pipe to prevent it from being unstable due to tensile deformation. At the same time, there is no risk of cracking after the pile body is formed, eliminating the erosion of the internal stress members by groundwater and corrosive ions, and greatly improving the long-term durability and service life of the pile body in the underground humid and corrosive ion-containing environment.

[0018] In addition, for complex geological conditions such as soft soil layers and quicksand layers, steel casing wall protection technology can be used to solve the problems of borehole wall collapse and inability to form holes, effectively reducing quality defects such as pipe blockage, segregation, and pile breakage during construction, and ensuring controllable pile quality. Moreover, the steel pipe can be spliced ​​in the form of segmented flanges, which makes the processing and construction operation flexible and adaptable to narrow construction spaces and complex construction conditions in urban underground engineering, greatly improving geological adaptability and site adaptability.

[0019] The reinforcing wing plates and anti-slip keys on the steel pipe body in this invention enhance the anchoring and interlocking effect between the steel pipe and the concrete. The balance ring ensures the verticality and coaxiality of the steel pipe during the implantation process, making the steel pipe concrete composite core and the outer concrete pile body more tightly bonded. This allows the pile body to form a complete force-bearing system, and the pile body is subjected to uniform stress under pull-out loads, effectively avoiding structural damage caused by local stress concentration, and further improving the overall structural stability and deformation resistance of the pile body. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the cross-sectional structure of the anti-uplift pile of the present invention; Figure 2 This is a schematic diagram of the steel pipe embodiment of the present invention; Figure 3 This is a schematic diagram of an embodiment of the steel casing of the present invention; Figure 4 This is a schematic diagram of the construction method of the present invention.

[0021] Attached reference numerals: 1-Pile hole, 11-Straight rod section, 12-Enlarged section, 2-Steel pipe, 3-Balance ring, 4-Wing plate, 5-Cone head, 6-Connecting plate, 7-Steel casing. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Example 1: This example aims to provide a construction method for micro steel pipe anti-uplift piles, which is mainly used to construct high-bearing capacity and high-durability anti-buoyancy pile foundations for underground structures under complex geological conditions. This achieves uniform and effective transfer of anti-uplift load from the inner core of the steel pipe concrete to the outer core of the concrete and the surrounding soil, fundamentally solving the problems of easy cracking and poor durability of traditional cast-in-place piles, and significantly improving construction efficiency, pile quality and geological adaptability.

[0023] like Figure 4 As shown in the embodiment, the construction method for micro-steel pipe anti-tension piles specifically includes the following construction steps: Step 1: Construction Preparation Based on the results of the preliminary geological survey, the geological parameters such as the water content of the soft soil in the construction area are clarified, and the distribution and burial depth of the soft soil layer, quicksand layer, and hard soil layer are determined. Then, the construction area is located and laid out, and the pile positions to be constructed are determined and marked. At the same time, the design depth and position of the bearing plate are determined and marked on the drill rod. For example, the bearing plate spacing can be set at the underground hard soil layer position of 5-6m. Such a plate spacing can match the rigidity requirements of the long spiral drill rod, avoid deformation of the drill rod during construction, and ensure the construction accuracy of the bearing plate.

[0024] Furthermore, the work site needs to be leveled before construction. In this embodiment, a combination of a single-layer steel plate and a 300mm crushed stone cushion layer is used to lay a long spiral drilling rig on the ground to form a working plane, ensuring smooth movement and stable operation of the drilling rig. At the same time, concrete for grouting is prepared in the construction area. Retarded super-fluid self-compacting concrete is selected, with a slump of 220-240mm, a spread of not less than 650mm, and an initial setting time of not less than 10h. These parameters are suitable for the implantation window period of soft soil geology, which can effectively avoid premature concrete setting and ensure full bonding between concrete, steel pipe 2, and soil during the implantation of steel pipe 2, while reducing pipe blockage and segregation problems during construction.

[0025] Step 2: Steel Pipe Processing In this embodiment, the steel pipe is made of Q355B with a wall thickness ≥12mm. The steel pipe 2 is a continuous cylindrical structure. A conical guide head is welded to the bottom of the steel pipe, which facilitates the smooth insertion of the steel pipe into the pile hole and reduces resistance. Triangular reinforcing wing plates 4 are welded to the steel pipe body. The wing plates 4 are uniformly welded to the outer wall of the steel pipe along the circumference, and multiple sets are welded from top to bottom along the length of the steel pipe to form a reliable anchoring connection with the concrete, further improving the bearing capacity and overall stability of the pile. Connecting plates 6 are uniformly welded to the steel pipe body along the circumference. Multiple balance rings 3 are fixedly welded to the connecting plates 6 at intervals to assist in the straightness control of the steel pipe 2 during the pressing process into the pile hole 1, ensuring that the steel pipe 2 is always in the center position of the pile hole 1, avoiding deviation, and ensuring uniform stress on the pile. In addition, anti-slip keys can be uniformly welded to the outer wall of the steel pipe 2 to further enhance the bond between the pile and the concrete and soil, and improve the pull-out bearing capacity.

[0026] The length of steel pipe 2 is greater than the design depth of pile hole 1. This ensures that after the steel pipe is properly inserted into the pile hole, its top can extend above the ground pile hole marking line, providing operating space for subsequent steel pipe centering operations. In practical applications, if the pile hole is deep, multiple steel pipe sections can be combined and spliced. That is, adjacent steel pipes are quickly connected by flanges and fixed by bolts, replacing the traditional welding process, improving splicing efficiency and connection reliability. The flange thickness is not less than 16mm, and the bolts are 8.8 grade high-strength bolts to ensure the tensile and shear resistance of the spliced ​​parts.

[0027] Step 3: Hole Formation The existing high-torque long spiral drilling rig is selected for hole drilling. In the specific implementation process, the drilling rig is first moved to the predetermined pile position and the rig body is leveled to ensure that the center of the rig's overhead crane, the center of the drill rod, and the center of the pile position are aligned to ensure vertical drilling of the drill rod and avoid tilting of the pile hole. Before drilling, the elevation line corresponding to the preset position of the bearing plate is marked on the drill rod and the elevation parameter is input into the drilling rig control system. When the drill rod reaches the elevation line, the hole diameter is enlarged at the key bearing layer position to form an enlarged section space, thereby realizing automatic positioning of the bearing plate position and improving construction efficiency and accuracy.

[0028] Then, after the drilling rig position is determined, it is started and a low-speed uniform drilling mode is used for hole formation to reduce disturbance to the soft soil hole wall and prevent hole wall collapse. When the drill rod drills to the pre-marked design elevation of the first bearing plate, the foldable hole enlarging device at the bottom of the drill rod is activated to enlarge the diameter on the side wall of the pile hole, forming the enlarged section 12. After the enlargement is completed, the device is retracted and the initial drill bit is used to continue drilling to the next elevation or the bottom of the hole. That is, after the hole enlargement is completed, the original drill bit is switched back and drilling continues downward until the design position of the next bearing plate is reached. The above hole enlargement operation is repeated until all bearing plate enlarged sections 12 are constructed. Finally, drilling continues to the design elevation of the bottom of the pile hole and hole enlargement is carried out to form the pile end enlarged head, ensuring that the bottom of the pile hole is embedded in the hard bearing layer for not less than 1.2m, ensuring the stability of the pile's pull-out bearing capacity. In this embodiment, an enlarged section 12 is formed in the pile body and pile bottom, and the enlarged section 12 is set in the hard soil layer to increase the contact area between the pile body and the soil, thereby providing stronger pull-out anchoring force.

[0029] It should be noted that in practical applications, when it is necessary to switch to the bearing plate design position for hole enlargement, the drilling operation can be paused, and the drill bit can be disassembled and replaced with a hole enlarger that is compatible with the inner diameter of the hole. Alternatively, the drill bit at the end of the drill rod can be set as a foldable hole enlargement device, such as the enlarged drill rod structure disclosed in patent CN112832232A or other existing hole enlargement drill bit equipment, to achieve the switching of drill bits corresponding to different drilling positions. This allows different types of drill bits to be used for construction operations in the straight section of the pile and the enlarged section of the pile.

[0030] Step 4: Concrete pouring Once the drill rod reaches the bottom of the designed hole, without pulling it out, immediately start the concrete pump to begin pouring concrete through the internal channel of the drill rod. Specifically, first pump 0.5m of concrete into the internal channel of the drill rod. 3 Cement slurry is used to lubricate the delivery pipeline to prevent concrete from sticking and clogging inside. Then, pre-prepared super-fluid concrete is injected into the pile hole. The drill rod pauses at the bottom of the hole for 3-5 minutes, allowing the concrete's own weight to flow and fill the enlarged space at the bottom of the hole, expelling air and ensuring the concrete's density. After the bottom of the hole is filled, the drill rod is slowly and uniformly raised while concrete is continuously poured, with strict control over the matching of the drill rod raising speed and the concrete pumping rate. The drill rod raising speed is controlled at 0.5-0.8 m / min, and the concrete pumping rate is not less than 0.3 m³ / min. 3 / min, ensuring that the concrete surface inside the hole is always more than 1.0m higher than the bottom of the drill rod during the grouting process, so as to ensure the self-stability of the soft soil hole wall and prevent the hole wall from collapsing.

[0031] When the concrete is poured to the level of the first bearing plate +0.5m, the drilling rod is lifted and pressure is stabilized for 3 minutes to ensure that the concrete in the enlarged section is fully filled and that the inner cavity of the enlarged section 12 of the bearing plate is completely filled with concrete, avoiding quality defects such as voids and lack of compaction. After the pressure stabilization is completed and the enlarged section is filled with concrete, the drilling rod is lifted again, and the above steps are repeated to complete the pressure pouring of each enlarged section from bottom to top, until the drilling rod is completely lifted outside the pile hole, completing the concrete pressure pouring operation for the entire pile hole.

[0032] In addition, the final elevation of the concrete pouring must exceed the design pile top elevation by at least 500mm. After the concrete has cured to the design strength, the over-poured portion at the pile top is removed. This is mainly because the concrete at the pile top is prone to forming low-strength, poor-quality laitance during the pouring process due to contact with mud and sediment. Therefore, by over-pouring, the over-poured section is removed after the pile body has hardened, thereby ensuring that the remaining pile head portion connected to the structure is concrete with qualified strength and reliable quality.

[0033] Step 5: Insert the steel pipe After the concrete is poured into the pile hole through the drill rod, reaching an elevation close to the top of the pile but not full, such as 1.0m below the hole opening, the drill rod is withdrawn from the pile hole. At this time, the concrete has not yet initially set. Immediately, a double-point balancing hoisting device is used to pre-calibrate the verticality of the steel pipe with the pile hole. Then, the steel pipe 2 is immediately pressed into the pile hole along the guide ring set at the pile hole opening. As the steel pipe 2 is pressed in, its bottom will displace the concrete below, requiring continuous replenishment of new concrete from above to fill the gap occupied by the steel pipe 2. That is, concrete is continuously poured into the annular space between the steel pipe and the hole wall, and it is necessary to ensure the pressure of the steel pipe 2. The insertion speed must match the concrete pouring speed, and ensure that the concrete level is always higher than the bottom of the steel pipe 2. This prevents voids, air gaps, or broken piles from forming on the bottom or side of the steel pipe 2 during the pressing process due to untimely concrete supply. It also ensures a tight and continuous bond between the steel pipe 2 and the concrete, and between the concrete and the soil in the borehole. Through synchronous control, the fluidity and pressure of the continuously poured concrete can be used to wrap and lubricate the steel pipe as it is inserted into the pile hole, thereby expelling air and forming a dense and firmly bonded steel-concrete composite pile to ensure the pile's bearing capacity and anti-buoyancy performance.

[0034] Furthermore, during the steel pipe implantation process, a dual theodolite is used for real-time verticality monitoring. The verticality of the steel pipe 2 is checked every 1m of implantation. If the deviation exceeds 0.8%, the implantation operation is stopped immediately and correction is carried out. Construction can continue only after the correction is qualified. In practical applications, the top of the steel pipe 2 can be connected to the guide frame on the drilling rig crane to further ensure the coaxiality of the steel pipe during implantation and avoid the steel pipe deviation from affecting the pile's stress.

[0035] After the steel pipe is inserted into place, it is subjected to secondary pressure, which can be achieved by slight rotation, vibration or static pressure, to ensure a tight bond between the steel pipe and the concrete, and between the concrete and the soil of the borehole wall, eliminating gaps and making the pipe the main tension member. The concrete fills and wraps the steel pipe, tightly bonding it with the soil, and transferring the anti-buoyancy force to the enlarged section 12.

[0036] Step 6: Concrete Filling Concrete was poured into the steel pipe up to the design elevation of the pile top. A vibrator was used to gently vent the air (avoiding contact with the flanges) to ensure the steel pipe 2 was densely packed, guaranteeing close contact between the inner wall of the steel pipe 2 and the concrete, preventing contact with the atmosphere and thus corrosion. Simultaneously, the dense packing ensured that the internal concrete provided support during the pile's pull-out stress, preventing pipe diameter deformation and local instability due to tension. Additionally, based on the design elevation, the excess concrete at the top of the pile head was removed, and the excess steel pipe was cut off. A 500*500*30mm thick anchor plate was then bevel-welded to the steel pipe. After forming, reinforcing steel was laid on top of the pile hole 1 to construct a raft foundation, which was then cast together with the pile top.

[0037] In addition, in practical applications, after drilling and before inserting the steel pipe, a grouting pipe, such as a PVC grouting pipe, can be laid along the inner wall of the pile hole. The bottom end of the grouting pipe is lowered to near the bottom of the hole, and then cement grout is injected into the gap between the pile hole wall and the soil through the grouting pipe. The grouting pipe needs to be raised synchronously with the rise of the concrete liquid level, and the grouting pipe should always be kept below the top surface of the concrete grout. When the grouting pipe is raised to the bearing plate (enlarged section 12) area, grouting should be carried out under stable pressure for about 5 minutes to ensure that the cement grout fully penetrates into the surrounding soft soil and the weak interlayer in the middle of this key part, thereby significantly improving the side friction resistance of these areas. In this way, the pressure of the injected cement grout forms a penetrating, compacting and solidifying transitional reinforcement layer between the concrete and the hole wall soil. At the same time, it can effectively fill the irregular, concave or locally collapsed areas of the hole wall caused by drilling, ensuring that the final pile body has a regular shape and a tight pile-soil contact.

[0038] Step 7: Quality Inspection After the concrete has cured and formed, the bearing plate is tested using ultrasonic imaging (test holes can be pre-drilled in the sidewall of the steel pipe) to check the compactness of the concrete filling and the integrity of the pile body. The sonic logging method (the steel pipe serves as the channel for the sonic logging tube) is used instead of the traditional low-strain method. Bearing capacity testing is also conducted, such as sampling 5% of the piles for static load testing, loading them to 1.5 times the design value, and controlling the settlement to ≤40mm. This verifies whether the pull-out bearing capacity of the pile body meets the design requirements.

[0039] The micro-steel pipe anti-uplift pile construction method provided in this embodiment has higher construction efficiency. It uses small-diameter steel pipes and concrete cores as the main anti-uplift components of the pile, and combines multiple load transfer methods of steel pipe concrete inner core, concrete outer core and surrounding soil to make the uplift force transfer more uniform and deeper, thereby reducing the cross-sectional size while increasing the bearing capacity. Moreover, during construction, the borehole is expanded in hard soil layer to form a bearing plate, and combined with the triangular reinforcing wing plate welded on the steel pipe, the anchoring effect is better. It can not only achieve the goals of small pile diameter, high bearing capacity and low cost, but also ensure that high-quality piles can still be formed under complex and weak geological conditions, significantly improving the uplift resistance of steel pipe piles and solving the problem of anti-buoyancy of building foundation slabs.

[0040] Example 2 is based on Example 1. The similarities between this example and Example 1 will not be repeated. The difference is that when the geological conditions after exploration include strata with extremely poor self-stability such as quicksand layers and deep soft soil, which makes it easy for the borehole wall to collapse and impossible to form a hole when drilling directly, this example provides a pile construction method based on steel casing 7. By using steel casing 7 to penetrate and isolate unstable strata, all core pile construction procedures can be completed under the protection of the casing, and then the casing can be pulled out to ensure normal hole construction.

[0041] like Figure 3 and 4 As shown, the pile construction method based on steel casing wall provided in this embodiment specifically includes the following steps: Step 1: Based on the results of the preliminary geological survey, accurately determine the depth and thickness of unstable strata such as quicksand layers. Based on this depth, construct a steel casing with a length greater than the thickness of the quicksand layer and an embedded end in a stable soil layer of not less than 1.0m to ensure the formation of a stable temporary borehole wall. The diameter of the casing can be slightly larger than the designed pile diameter, thereby providing operating space for subsequent drilling, hole enlargement and steel pipe 2 insertion.

[0042] Step 2: Use a 150T crawler crane to lift the steel casing 7 to the pile position, and use a vibratory hammer to drive the steel casing 7 vertically into the soil until its bottom end penetrates the quicksand layer and enters the lower stable hard soil layer or bearing layer, thereby establishing a rigid hole wall protection that completely covers the depth of the soil layer with poor self-stability.

[0043] Step 3: Under the protection of the steel casing 7, subsequent operations are carried out. At this time, the steel casing 7 is always located in the soil. Specifically, after the steel casing 7 is driven into the preset position of the stratum, the drill rod of the drilling rig is drilled downward from the center of the steel casing 7. Under the protection of the casing, the drill is drilled to the designed bottom elevation of the hole. Then, according to the construction method of Example 1 above, at the preset hard soil layer position, the foldable hole expansion device at the bottom of the drill rod is activated to form the bearing plate enlargement section 12. Immediately, concrete is poured into the pile hole 1 through the drill rod. The concrete needs to be poured until the liquid level exceeds the top elevation of the steel casing 7 to ensure that the bottom of the steel casing 7 is sealed by concrete.

[0044] Step 4: After the concrete is poured and before it sets, immediately press the prefabricated steel pipe 2 vertically into the concrete inside the casing. After the steel pipe 2 is inserted and fixed to the design elevation, slight disturbance can be made to ensure that it is tightly bonded to the concrete.

[0045] Step 5: Once the steel pipe 2 is in place and the concrete at the borehole opening still has good fluidity, slowly, evenly, and continuously pull out the steel casing 7. During the pulling process, monitor the concrete level inside the borehole and replenish concrete as needed to ensure the level is never lower than the bottom of the steel casing 7. Use the gravity pressure of the concrete to prevent quicksand from flowing in. After the casing is completely pulled out, the pile body concrete will fill the space originally occupied by the casing, forming a complete pile body. Then, proceed with the subsequent construction according to the steps described in Example 1 above until the pile body is fully formed.

[0046] The pile construction method based on steel casing wall provided in this embodiment effectively solves the problems of difficult pile construction and uncontrollable quality in extremely soft strata. It also solves the problems of pile foundations in complex strata being unable to be drilled and the collapse of holes in thick sand and gravel backfill layers. Especially in quicksand layers and construction sites where water pressure cannot rise, the long casing can ensure normal drilling construction. It can reduce the impact of groundwater and pore water pressure on pile quality, making the pile less prone to quality defects such as necking, segregation, mud inclusion, and honeycombing, thereby ensuring the load-bearing reliability and durability of the pile as an uplift member.

[0047] Example 3: Based on the above examples, this example provides a micro-steel pipe tension pile structure, applying the micro-steel pipe tension pile construction method described in Example 1, such as... Figure 1 and 2 As shown, the anti-tension pile structure in this embodiment includes a pile body implanted in the foundation. The pile body is composed of a steel pipe concrete composite core and an outer cast-in-place concrete pile body. The pile body includes an enlarged section 12 located in the hard soil bearing layer and a straight section 11 located in the ordinary soil layer. The diameter of the enlarged section 12 is larger than that of the straight section 11, forming multiple bearing plates distributed along the pile body. The steel pipe concrete composite core and the outer cast-in-place concrete pile body are integrally cast.

[0048] The steel-concrete composite core serves as the primary tensile component. It comprises a small-diameter steel pipe made of high-strength steel, either continuous or connected by segmented flanges. Expanded-diameter flanges 4 are welded to the outer wall of the steel pipe. After the pile is formed, the flanges are embedded in the concrete. Anti-slip keys are also spaced along the steel pipe 2 to enhance its interlocking with the concrete, forming reliable pull-out anchor points. Connecting plates 6 are welded vertically at intervals along the outer wall of the steel pipe 2. Balance rings 3 are welded to the outside of the connecting plates 6 to guide and maintain the verticality of the steel pipe 2 during installation and to enhance its overall stability. The interior of the steel pipe is filled with dense inner core concrete, forming a steel-concrete composite load-bearing body together with the steel pipe and preventing corrosion of the inner wall of the steel pipe.

[0049] In actual construction, a foldable borehole drill bit is used to form an enlarged section of the pile hole at a predetermined position; super-fluid concrete is poured to form concrete slurry inside the pile hole; before the concrete initially sets, a steel pipe equipped with the aforementioned foldable diameter-enlarging flange is pressed into the pile hole, and the flange is opened in the concrete; finally, concrete is poured into the steel pipe and necessary secondary grouting is performed around the pile.

[0050] The micro-steel tube anti-uplift pile structure provided in this embodiment uses a steel-concrete composite as the main load-bearing component of the pile body. The bearing capacity of the steel-concrete core far exceeds the uplift bearing capacity of traditional uniform cross-section piles. It has a small pile diameter and flexible construction, making it particularly suitable for anti-buoyancy engineering in confined spaces or complex strata. Furthermore, the steel-concrete core bears the main load, which is then transferred to the outer concrete core through the lateral resistance of the steel tube and concrete, and then transferred to the surrounding soil from the outer concrete core. This forms a progressive transfer mode with a clearer and more reliable path, greatly improving the ultimate uplift bearing capacity of a single pile, fundamentally inhibiting the generation of harmful through cracks, and significantly improving the long-term durability and service life of the pile in humid and corrosive environments.

[0051] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for constructing micro-steel pipe anti-tension piles, characterized in that: Includes the following steps: Step 1: Based on the geological survey results, determine the geological parameters of the construction area, the location of construction piles, and the design depth and position of the bearing plate. Locate and lay out the construction area and level the site. Step 2: Prepare a continuous or segmented steel pipe (2), weld a conical guide head to the bottom of the steel pipe (2), weld a reinforcing wing plate (4) and a connecting plate (6) to the steel pipe (2), and fix a balance ring (3) on the connecting plate (6); Step 3: Based on the calibrated pile position, vertical drilling is carried out. During the drilling process, hole enlargement operation is carried out at each hard soil layer elevation position preset by the drill rod to form an enlarged section (12). After drilling to the bottom design elevation, hole enlargement is carried out to form the pile end enlarged head, and the pile end enlarged head is embedded in the hard bearing layer. Step 4: Press concrete into the pile hole (1) through the internal channel of the drill rod, continuously pour concrete while lifting the drill rod, and perform pressure stabilization treatment at each enlarged section (12) until the entire pile hole (1) is pressurized and the final concrete pouring elevation exceeds the designed pile top elevation. Step 5: Before the concrete has set, the steel pipe (2) is vertically pressed into the middle of the pile hole (1) after the verticality is calibrated. During the pressing process, concrete is continuously added into the pile hole (1) to ensure that the pressing speed matches the grouting speed, and the verticality of the steel pipe (2) is monitored and adjusted in real time. Step 6: After the steel pipe (2) is pressed into place, concrete is poured into the steel pipe (2) to the design elevation and vibrated to remove air. After the pile foundation is cured and formed, the excess steel pipe (2) at the top is cut off after removing the over-poured part of the pile head. Anchor plates are welded to the top of the steel pipe (2) and connected to the upper structure.

2. The construction method for micro-steel pipe anti-tension piles according to claim 1, characterized in that: In step 3, when there is a quicksand layer in the construction area, a steel casing (7) is hammered into the ground to protect the wall before drilling. The construction steps include: first, making a steel casing (7) with a length greater than the thickness of the quicksand layer and a lower end that can be embedded in the stable soil layer for more than 1.0m; then, vertically driving the steel casing (7) into the soil until the bottom end passes through the quicksand layer and enters the stable hard soil layer to form a protective wall for the quicksand layer; and completing the drilling, hole enlargement and concrete pouring under the protection of the steel casing (7). The concrete is poured until the liquid level exceeds the top elevation of the steel casing (7); after pressing the steel pipe (2) in before the concrete sets, the steel casing (7) is slowly pulled out. During the pulling process, concrete is replenished in time to ensure that the liquid level is always not lower than the bottom of the steel casing (7).

3. The construction method for micro-steel pipe anti-tension piles according to claim 2, characterized in that: In step 4, before pouring concrete, pump 0.5m of cement slurry into the drill pipe channel to lubricate the pipe; control the drill pipe lifting speed to 0.5-0.8m / min, and the concrete pumping volume to be no less than 0.3m. 3 / min, the concrete surface inside the hole is always more than 1.0m higher than the bottom of the drill rod during the grouting process; the pressure stabilization treatment time at each enlarged section (12) is 3min, and the concrete over-grouting height is at least 500mm.

4. The construction method for micro-steel pipe anti-tension piles according to claim 3, characterized in that: In step 4, the concrete injected into the pile hole (1) is a slow-setting super-fluid self-compacting concrete with a slump of 220-240mm, an expansion of not less than 650mm, and an initial setting time of not less than 10h.

5. The construction method for micro-steel pipe anti-tension piles according to claim 2, characterized in that: In step 3, the enlarged sections (12) are all set in the hard soil layer and the spacing is 5-6m. The enlarged head at the bottom of the pile is embedded in the hard bearing layer for no less than 1.2m.

6. The construction method for micro-steel pipe anti-uplift piles according to claim 2, characterized in that: In step 5, the verticality of the steel pipe (2) is monitored in real time during the pressing process. It is checked every 1m of insertion. When the verticality deviation exceeds 0.8%, it is corrected. After the steel pipe (2) is inserted into place, a second pressurization process is carried out.

7. A micro-steel pipe anti-tension pile structure, using the micro-steel pipe anti-tension pile construction method according to any one of claims 1-6, characterized in that: The pile body includes a pile body embedded in the foundation. The pile body includes a steel pipe concrete composite core and a cast-in-place concrete pile body wrapped around the outside of the steel pipe concrete composite core. The cast-in-place concrete pile body includes a straight rod section (11) and an enlarged section (12). The diameter of the enlarged section (12) is larger than that of the straight rod section (11). Multiple enlarged sections (12) are distributed vertically along the pile body to form a bearing plate. An enlarged pile end head is provided at the bottom of the pile body.

8. The method for constructing micro-steel pipe anti-tension piles according to claim 7, characterized in that: The steel-concrete composite core includes a steel pipe (2) and an inner core concrete poured inside the steel pipe. The bottom of the steel pipe (2) is provided with a cone head (5). The outer wall of the steel pipe (2) is welded with a triangular reinforcing wing plate (4) along the circumferential direction. The wing plate (4) is arranged in multiple groups in sections along the length of the steel pipe (2).

9. The construction method for micro-steel pipe anti-tension piles according to claim 7, characterized in that: The steel pipe (2) has a connecting plate (6) welded to its outer wall. Multiple balance rings (3) are fixedly sleeved on the connecting plate (6) at intervals to assist in the straightness control of the steel pipe (2) during the pressing process.

10. The construction method for micro-steel pipe anti-tension piles according to claim 7, characterized in that: The steel pipe (2) is a continuous structure or a multi-section flange splicing structure. An anchor plate is welded to the top of the steel pipe (2), and the anchor plate is used to be embedded in the upper structure of the pile foundation.

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