Construction method of prestressed tension cast-in-place integral open caisson

Abstract

The invention relates to a prestress tension cast-in-place integral open caisson construction method which comprises the steps that a foundation pit is excavated in a preset area, a bottom layer well body is arranged in the foundation pit, a steel strand penetrates into a threading pipe of a lower open caisson body, and the prestress tension procedure is executed; the open caisson structure is controlled to gradually sink by a corresponding depth size; and the steps of lower open caisson body manufacturing and open caisson structure sinking are repeatedly executed till the open caisson structure reaches the preset design depth, the reinforcement cage of the lower open caisson body of the upper layer is connected to the lower open caisson body of the lower layer through the connection mechanism, and at least one machinable area is reserved in the preset area of the open caisson structure. The open caisson structure is cast in place, and the requirement for the construction site area is lowered. The open caisson structure forms tensioning prestress through the steel strands, and the supporting force of the open caisson structure on surrounding soil is improved. The preset area of the open caisson structure forms a machinable area, so that tunneling equipment can conveniently tunnel into a soil body from the machinable area in the later period.

Description

Technical Field

[0001] This invention relates to the field of construction technology, and in particular to a method for constructing a prestressed tensioned cast-in-place integral caisson. Background Technology

[0002] During the construction of subway tunnels, urban railways, and municipal integrated utility tunnels, construction shafts are typically required as working shafts for shield tunneling launches or other construction operations. These working shafts are generally constructed using processes such as trenching with a trenching machine and on-site binding of steel reinforcement cages. During the excavation of the foundation pit, temporary support structures must be used to support the diaphragm wall to ensure the stability and safety of the excavation process.

[0003] This construction method has the following limitations: First, it requires a large construction site and relies on large equipment such as trenching machines, cranes, and excavators; second, trenching operations are easily affected by complex and variable geological conditions and poor mud wall protection, which can lead to substandard construction quality of the diaphragm wall; third, the on-site fabrication and hoisting of the reinforcing cage requires high technical expertise, as its large size and significant weight necessitate large processing areas and heavy-duty lifting equipment, making it difficult to implement in urban core areas or space-constrained sites, thus limiting the applicability of this method; furthermore, the treatment of diaphragm wall joints is challenging, and traditional methods... Joint types (such as interlocking pipe joints and corrugated pipe joints) are prone to leakage channels due to construction deviations or concrete shrinkage, resulting in large investment in later leak sealing and maintenance, and affecting the overall waterproofing reliability of the project. On the other hand, the process has poor coordination, and multiple large pieces of equipment are required to work together in the trenching, rebar cage hoisting and concrete pouring stages. Delays in any stage will cause delays in the construction period, making it difficult to meet the requirements of rapid construction in urban projects. Finally, ultra-deep trench excavation can easily disturb the stress state of the surrounding soil, which may cause settlement of nearby buildings or deformation of underground pipelines, increasing construction safety risks and environmental control pressures.

[0004] Furthermore, urban construction projects generally have tight schedules, and existing construction techniques are not yet able to meet the requirements of tight schedules in terms of efficiency, so technological improvements are urgently needed. Summary of the Invention

[0005] To overcome the problems existing in related technologies, this invention provides a prestressed tensioning cast-in-place integral caisson construction method to solve problems such as large construction site requirements, uncontrollable construction quality, long construction period, significant impact on the surrounding environment, and high construction costs.

[0006] According to a first aspect of the present invention, a method for constructing a prestressed tensioned cast-in-place integral caisson is provided, the method comprising: Excavate a foundation pit in the pre-designed area and install a bottom well body inside the foundation pit; The lower well body is constructed in layers above the bottom well body. The reinforcing steel cage of each lower well body is pre-embedded with a fixed conduit, and concrete is poured and cured. Then, the steel strand is threaded into the conduit and a prestressing tensioning process is performed on the steel strand to form a prestress that resists the lateral pressure of the surrounding soil in the lower well body. The foundation pit soil below the bottom well body is excavated to a predetermined depth, and the caisson structure is gradually sunk to the corresponding depth. Repeat the steps of constructing and sinking the caisson body until the caisson structure reaches the preset design depth. The sinking steel cage of the upper layer of the caisson body is connected to the lower layer of the caisson body through a connecting mechanism. The caisson body and the bottom layer of the caisson body are connected to form the caisson structure. At least one cuttable area is reserved in the preset area of ​​the caisson structure.

[0007] In one embodiment, reserving at least one machinable area in a predetermined area of ​​the caisson structure includes: A reinforcing edge is formed at the edge of the machinable area of ​​the sunken reinforcing cage; Multiple cutting ribs are provided in the machinable area, and the multiple cutting ribs are fixed to the sinking steel cage respectively. The cutting ribs are made of machinable material. Pour concrete into the cuttable area.

[0008] In one embodiment, the sunken reinforcing cage forms a reinforcing edge at the edge of the machinable area, including: A ring-shaped reinforcing rib is provided at the edge of the machinable area, and the reinforcing bars of the sunken steel cage and the reinforcing rib are connected to form a reinforced edge; or, A reinforcing plate is provided at the edge of the cuttable area, and the reinforcing bars of the sunken steel cage are connected to the reinforcing plate to form a reinforced edge.

[0009] In one embodiment, the prestressing tensioning process for the steel strand includes: Install working anchor plates, clamps, and limiting plates at both ends of the steel strand; Align the jack with the axis of the steel strand to avoid eccentric force during tensioning; The jacks at both ends of the control steel strand are used to apply tension prestress synchronously and uniformly, with the same tensioning parameters; When the tension prestress on the steel strand reaches the preset value and is in a stable state, the clamps and steel strand are locked, and the jacks are unloaded.

[0010] In one embodiment, the jacks at both ends of the control steel strand synchronously and uniformly apply load force, including: The preset tension prestress is divided into multiple levels of loading force, and the jacks are controlled to apply the load step by step according to the loading force. After each loading force is applied, maintain the preset loading time to keep the tension prestress of the steel strands acting on the caisson structure stable. The elongation of the steel strand and the pressure value of the jack are detected under each level of loading force. When the elongation is within the allowable deviation range, the jack is controlled to apply the next level of loading force.

[0011] In one embodiment, the controlled caisson structure is gradually lowered to the designed height, including: Detection sensors were installed around the perimeter of the caisson structure; Real-time monitoring of the sinking attitude parameters of the caisson structure; The excavation parameters of the soil are controlled based on the attitude parameters.

[0012] In one embodiment, controlling the excavation parameters of the soil according to the attitude parameters includes: Detect the subsidence of each sidewall of the caisson structure; Determine the deviation of the caisson structure from its opposite side; When the deviation exceeds the preset value, the excavation volume of the soil on the side with smaller subsidence will be increased.

[0013] In one embodiment, the caisson structure is polygonal, circular, elliptical, irregularly circular, or a combination of multiple shapes; The pre-embedded fixing conduit in the sinking steel cage of each sinking well body includes: The transverse conduit is installed by running horizontally and bending along the sunken steel cage; The longitudinal conduit is threaded and bent along the longitudinal direction of the sunken steel cage; The transverse and longitudinal conduits are arranged alternately in space along the height direction of the sunken reinforcing cage.

[0014] In one embodiment, the step of setting up a bottom well within the foundation pit includes: Install templates in the foundation pit excavated in the preset area, place the bottom reinforcement cage in the space enclosed by the templates, and embed at least one arc-shaped conduit in the bottom reinforcement cage. The bending direction of the arc-shaped conduit is set according to the tensioning direction of the prestressed steel strand. After the concrete is poured and vibrated to compact it, a preset curing time is set, and the connecting mechanism of the bottom steel cage extends beyond the top surface of the poured concrete. The steel strands are threaded through the conduit and the prestressing tensioning process is performed.

[0015] In one embodiment, the bottom well body includes a peripheral wall, multiple reinforcing beams intersecting the inner side of the peripheral wall, and a connecting mechanism extending beyond the top of the peripheral wall. The bottom of the peripheral wall and the bottom of the reinforcing beams are provided with cutting edges. When the caisson structure reaches the preset design depth, concrete is poured to seal the bottom of the caisson.

[0016] The technical solutions provided by the embodiments of the present invention can include the following beneficial effects: The reinforcing cage can be factory-fabricated; both the bottom layer and multiple layers of the caisson are cast on-site at the foundation pit, eliminating the need for large equipment and reducing the requirements for construction site area and interference with the surrounding environment. The caisson structure can always provide rigid support to the soil surrounding the foundation pit, thus eliminating the need to build a continuous wall around the foundation pit, greatly shortening the construction period and maintaining construction safety. The caisson structure forms tension prestress through steel strands; the direction of the prestress formed after tensioning the steel strands is opposite to the direction of the soil force, improving the supporting force of the caisson structure on the surrounding soil. A cutable area is formed in the preset area of ​​the caisson structure, facilitating the subsequent excavation equipment to excavate into the soil from this cutable area, improving the convenience of excavation construction. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0018] Figure 1 This is a flowchart illustrating a construction method according to one embodiment.

[0019] Figure 2 This is a schematic diagram illustrating a caisson structure according to one embodiment.

[0020] Figure 3 This is a schematic diagram illustrating the bending of a steel strand within a well structure according to one embodiment.

[0021] Figure 4 This is a schematic diagram illustrating the sinking of a caisson structure in a foundation pit, according to one embodiment.

[0022] In the figure, the caisson structure is 10; the bottom well body is 11; the reinforcing beam is 111; the peripheral wall is 112; the cutting edge is 113; the lower caisson body is 12; the machinable area is 13; the reinforcing edge is 131; the steel strand is 14; the transverse conduit is 141; and the longitudinal conduit is 142. Detailed Implementation

[0023] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images, and should not be construed as limiting the invention. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art.

[0024] like Figures 1 to 4As shown, this invention provides a method for constructing a prestressed tensioned cast-in-place integral caisson, wherein the caisson structure 10 is cast in place on the construction site to form an integral structure. Preferably, the caisson structure 10 is a rectangular structure or a non-circular caisson structure 10 with at least one plane. The caisson structure 10 serves as the working shaft at the starting or receiving position of tunnel excavation; or, the caisson structure 10 serves as one of the intersection points of tunnel construction. To facilitate the excavation work of the tunneling equipment, during the on-site casting process of the caisson structure 10, at least one cuttable area 13 is reserved in a predetermined area of ​​the caisson structure 10. The structural strength of the cuttable area 13 is less than the structural strength of the surrounding main body of the caisson structure 10, thereby reducing the difficulty of tunneling equipment breaking through the caisson. Preferably, the caisson structure 10 is a rectangular structure, and the cuttable area 13 is located on one of the rectangular walls; or, multiple rectangular walls are provided with cuttable areas 13 to achieve multi-point cutting excavation.

[0025] The construction method includes the following steps: Step S101: Excavate a foundation pit in a predetermined area and install a bottom well body 11 within the pit. The bottom well body 11 includes a peripheral wall 112, multiple reinforcing beams 111 intersecting to the inner side of the peripheral wall 112, and a connecting mechanism extending beyond the top of the peripheral wall 112. Cutting edges 113 are provided at the bottom of the peripheral wall 112 and the bottom of the reinforcing beams 111. The ground formwork is excavated according to the design drawings and is used for casting the cutting edge structure. The reinforcing beams 111 are in a cross or grid structure to support the peripheral wall 112 and improve the structural strength and stability of the bottom well body 11. Preferably, the cutting edges 113 of the reinforcing beams 111 are cast using the ground formwork; optionally, wooden formwork is used to facilitate later removal.

[0026] In one embodiment, a ring beam structure or retaining structure is constructed around the pre-defined area to prevent the wellhead from collapsing during the excavation of the foundation pit.

[0027] In one embodiment, the bottom well body 11 is a precast concrete structure with an internal steel reinforcement cage to adjust the structural strength and stability. The use of precast components for the bottom well body 11 results in shorter construction efficiency.

[0028] In another embodiment, the bottom well body 11 is constructed using cast-in-place concrete. A foundation pit is excavated in a predetermined area, and a formwork is installed. The space enclosed by the formwork forms the shape of the caisson structure 10. The bottom reinforcement cage is placed within the space enclosed by the formwork. The bottom reinforcement cage can be constructed by placing multiple reinforcing bars inside the formwork and binding them on-site; alternatively, multiple long reinforcement cages can be prefabricated in a factory and assembled and bound on-site to form the bottom reinforcement cage. Furthermore, the upward-facing reinforcing bars of the bottom reinforcement cage are equipped with a splicing mechanism. This splicing mechanism can employ straight thread sleeves, tapered thread sleeves, extrusion sleeves, self-locking connecting sleeves, or other splicing components. The splicing mechanism enables efficient transmission of axial force in the reinforcing bars, ensuring that the tensile strength of the spliced ​​portion is not less than 1.1 times the standard value of the parent material.

[0029] After the bottom reinforcement cage is fixed, at least one arc-shaped conduit is pre-embedded in the bottom reinforcement cage. The bending direction of the arc-shaped conduit is set according to the tensioning direction of the prestressed steel strand 14. The conduit is used to insert the steel strand 14. The conduit is bent into an arc shape and symmetrically connected to the bottom reinforcement cage to ensure that the stress is balanced.

[0030] After pouring and compacting the concrete, allow it to cure for the preset time. Fill the space enclosed by the formwork with concrete, ensuring the connection mechanism of the bottom reinforcing cage extends beyond the top surface of the poured concrete. Use a vibrating device to thoroughly compact the concrete, improving its density. Then, cure the concrete according to the curing standards, for example, a curing period of 13-15 days, to ensure a stable curing effect.

[0031] The conduit is connected to the bottom reinforcement cage and encased in concrete. Steel strands 14 are threaded through the conduit so that both ends of the steel strands 14 exit the conduit and can be easily connected to the loading mechanism. In this step, both ends of the steel strands 14 are connected to the loading mechanism, which performs prestressing tensioning on the bottom well body 11 through the steel strands 14. The load applied by the loading mechanism to the steel strands 14 can tighten the steel strands 14 and form tension prestress within the bottom well body 11. The tension prestress is directed outwards from the bottom well body 11, effectively counteracting the forces exerted on the bottom well body 11 by the soil, significantly improving the overall crack resistance and load-bearing stability of the structure.

[0032] Step S102: The lower well body is constructed in layers above the bottom well body 11, increasing the height of the well structure layer by layer. A fixed conduit is embedded in the lower reinforcing cage of each layer; concrete is poured and cured; then steel strands are threaded through the conduit, and prestressing is applied to the steel strands. The lower reinforcing cage in the bottom lower well body is connected to the connection mechanism of the bottom well body 11, and the upper and lower lower well bodies are interconnected to form a unified structure with the bottom reinforcing cage of the bottom well body 11. The lower reinforcing cage can be tied on-site, or multiple long reinforcing cages can be prefabricated in a factory and assembled and tied on-site. At least one curved conduit is embedded in the lower reinforcing cage, with the bending direction of the conduit in the lower reinforcing cage being the same as that in the bottom reinforcing cage, so that the prestressing direction of the steel strands 14 within the conduit is the same.

[0033] After the sinking formwork is fixed, concrete is poured, vibrated to compact it, and then cured for a preset time. The sinking formwork extends beyond the preset height above the ground, and the sinking reinforcement cage is equipped with a connecting mechanism that extends beyond the top surface of the poured concrete. Unlike the construction of the bottom well body 11, the cast-in-place portion of the sinking well body 12 is located above the ground, allowing for convenient operation.

[0034] The steel strand 14 is threaded through the conduit, and a prestressing tensioning process is performed on the lower caisson body 12 through the steel strand 14 to form prestressing stress within the lower caisson body to resist the lateral pressure of the surrounding soil. The concrete curing of the bottom caisson body 11 is basically the same as that of the lower caisson body 12, and the prestressing tensioning process of the steel strand 14 of the bottom caisson body 11 is basically the same as that of the lower caisson body 12, which can be understood by reference and will not be repeated here.

[0035] In a preferred embodiment, the caisson structure 10 is a polygonal, circular, elliptical, irregular circular, or irregularly shaped ring structure. The pre-embedded fixing conduit within the sinking steel cage of each lower caisson body includes the following steps: The transverse conduit 141 is installed by running horizontally and bending along the sunken steel cage; The longitudinal conduit 142 is installed by running along the longitudinal direction of the sunken steel cage and bending it. The transverse conduit 141 and the longitudinal conduit 142 are arranged alternately in space along the height direction of the sunken steel cage.

[0036] Taking a rectangular caisson body 12 as an example, the longer side of the caisson body 12 is transverse, and the shorter side is longitudinal. The two ends of the transverse conduit 141 extend from the two ends of the longer side of the caisson body 12, and the middle of the transverse conduit 141 bends and protrudes towards the opposite side of the longer side of the caisson body 12. The two ends of the longitudinal conduit 142 extend from the two ends of the shorter side of the caisson body 12, and the middle of the transverse conduit 141 bends and protrudes towards the opposite side of the shorter side of the caisson body 12. Along the height of the caisson body 12, multiple transverse conduits 141 and multiple longitudinal conduits 142 are staggered to avoid interference in the same layer of space. Furthermore, along the height of the caisson body 12, the prestressing sequence of the multiple steel strands 14 follows a loading sequence of first the two ends, then the middle, symmetrical and uniform, and graded loading. The direction of the prestressing force exerted by the steel strands on the caisson body is opposite to the direction of the soil pressure on the caisson body.

[0037] Step S103, sinking of the caisson structure 10: The foundation pit soil below the bottom well body 11 is excavated to a predetermined depth, and the caisson structure 10 is gradually sunk to the corresponding depth. After the bottom well body 12 is completed, one or more bottom well bodies 12 and the bottom well body 11 constitute the caisson structure 10. The excavation equipment excavates the foundation pit soil to reduce the soil below the bottom well body 11, and the caisson structure 10 gradually sinks under its own weight or the push of pressure equipment. The caisson structure 10 can sink to a gradually decreasing depth as the excavation equipment excavates; the caisson structure 10 can also sink to a decreasing depth using pressure equipment after the excavation equipment has completed its excavation.

[0038] Step S104 involves the fabrication of the upper-level caisson body 12. The sinking steel cage of the upper-level caisson body 12 is connected to the lower-level caisson body 12 via a connecting mechanism. The caisson bodies 12 are fabricated layer by layer. Other steps are essentially the same as the fabrication steps for connecting the lower-level caisson body 12 to the lower-level caisson body 11, and will not be repeated here. The difference lies in that at least one cutable area 13 is reserved in the pre-designed area of ​​some caisson bodies 12 during the fabrication process. Step S104 (fabrication of the caisson body 12) and step S103 (sinking of the caisson structure 10) are repeated until the pre-designed depth of the caisson structure 1 is reached in step S105.

[0039] Both the bottom-level well body 11 and the multi-layered caisson body 12 are cast on-site at the foundation pit, eliminating the need for large equipment and reducing the required construction site area. The caisson structure 10 provides rigid support to the surrounding soil of the foundation pit at all times, thus eliminating the need to build a continuous wall around the foundation pit, greatly shortening the construction period and maintaining construction safety. The caisson structure 10 is prestressed by steel strands 14. After tensioning, the direction of the prestress is opposite to the direction of the soil force, improving the support force of the caisson structure 10 on the surrounding soil. A cutable area 13 is formed in the pre-designed area of ​​the caisson structure 10, which facilitates the subsequent tunneling equipment to break through the soil from the cutable area 13, improving the convenience of tunneling construction. It is worth mentioning that the prestressing of the caisson structure 10 not only improves the structural strength of the caisson structure 10, but also counteracts the additional stress generated on the well wall when the tunneling machine starts.

[0040] like Figures 1 to 4 As shown, at least one machinable region 13 is reserved in a predetermined area of ​​the caisson structure 10. The machinable region 13 can be formed at the same level of the lower caisson body 12, and can be formed by casting two or three consecutive lower caisson bodies 12. The preparation of the machinable region 13 includes the following steps: A reinforcing edge 131 is formed at the edge of the cuttable area 13 of the sinking steel cage. The cuttable area 13 is a weak area of ​​the caisson structure 10 and also a breach area for the tunneling equipment. Optionally, the cuttable area 13 is a circular or rectangular spatial area, and the cuttable area 13 penetrates the sidewall of the caisson structure 10.

[0041] Strengthening the edge 131 can improve the edge strength of the machinable region 13 to maintain the shape stability of the machinable region 13. Strengthening the edge 131 creates local reinforcement of the machinable region 13, providing stable support for subsequent construction.

[0042] The machinable region 13 includes integral reinforcement and mesh reinforcement.

[0043] In the integral reinforcement, a reinforcing plate is installed at the edge of the cuttable area 13. The reinforcing plate is a ring-shaped tubular structure that can form a ring-shaped reinforcement structure around the cuttable area 13. The reinforcing bars of the sunken steel cage and the reinforcing plate are connected as a whole, for example, the reinforcing bars and the reinforcing plate are welded and fixed, so that the reinforcing plate constitutes the integral reinforced edge 131 of the cuttable area 13. Preferably, the reinforcing plate can be used as a pre-embedded part for connecting the tunneling equipment, so as to improve the connection tightness between the tunneling equipment and the caisson structure 10, and at the same time facilitate the transfer of the force of the tunneling equipment to the caisson structure 10, thereby improving the convenience and accuracy of the tunneling equipment construction.

[0044] In the mesh reinforcement, annular reinforcing ribs are provided at the edge of the cutable area 13. These ribs can be a ring structure formed by the merging of two semicircular arcs, or a full ring structure. The reinforcing bars of the sunken steel cage are connected to the reinforcing ribs to form the reinforced edge 131. The axial diameter of the reinforcing ribs is greater than or equal to the diameter of the reinforcing bars to improve the structural strength at the edge. The reinforcing ribs and reinforcing bars are welded together to form a mesh reinforcement structure. Further, one or more reinforcing ribs are added to the internal area of ​​the wall to further improve the structural strength. Even further, the oppositely arranged reinforcing ribs are connected and fixed by transverse reinforcing bars to form an annular mesh structure, and welded to other reinforcing bars in the steel cage to improve the overall structural strength.

[0045] After reinforcing the edge 131, multiple cutting ribs are installed within the machinable area 13. These cutting ribs are fixed to the sinking steel reinforcement cage and are made of machinable materials. The cutting ribs are arranged in a staggered pattern, both horizontally and vertically, to reinforce the concrete. The cutting ribs are made of machinable materials such as fiberglass, bamboo strips, and fiber optic strips, providing machinable conditions for the tunneling equipment to break through the tunnel while maintaining the structural strength and shape stability of the machinable area 13.

[0046] Concrete is poured into the cuttable area 13 to ensure the integrity of the overall wall surface of the caisson structure 10. The cuttable area 13 is poured simultaneously with the other areas of the reinforcing cage to maintain overall consistency. The concrete in the cuttable area 13 can be poured simultaneously with the concrete in the area of ​​the sinking reinforcing cage; alternatively, the concrete in the cuttable area 13 can be poured independently. The concrete in the cuttable area 13 can be the same as or different from the concrete in other areas of the caisson body 12, and can be flexibly adjusted according to design requirements.

[0047] After the concrete curing of the bottom well body 11 or the sinking well body 12 is completed, the steel strand 14 is threaded out along the conduit, and a prestressing tensioning process is performed on the steel strand 14. The prestressing tensioning process includes the following steps: Working anchor plates, clamps, and limiting plates are installed at both ends of the steel strand 14. The working anchor plates, clamps, and limiting plates are existing prestressing tensioning structural components, which are the same as existing product structures and working principles, and will not be described in detail here.

[0048] Align the jack with the axis of steel strand 14 to avoid eccentric force during tensioning; after the pre-installation of the working anchor plate, clamps and limiting plate is completed, install the jack mechanism to complete the preparation work for prestressing tensioning.

[0049] The jacks at both ends of the steel strand 14 are used to apply tension prestress synchronously and uniformly, with identical tensioning parameters. Unlike the existing unidirectional tensioning construction of the steel strand 14, in this step, both ends of the steel strand 14 are uniformly and synchronously pressurized by jacks. This ensures that the steel strand 14 is stretched synchronously towards both ends, thereby maintaining a balanced tension prestress applied to the concrete by the steel strand 14. This reduces the risk of eccentric load and also avoids structural displacement or localized stress concentration caused by excessive unilateral load.

[0050] As the jacks at both ends gradually apply pressure, when the tension prestress on the steel strand 14 reaches the preset value and is in a stable state, the clamps and the steel strand 14 are locked, and the jacks are unloaded.

[0051] The process of controlling the jacks at both ends of the steel strand 14 to synchronously and uniformly apply the load includes the following loading steps: The preset tensioning prestress is divided into multiple loading forces, and the jacks are controlled to apply the load step by step according to the loading force. The total tensioning prestress needs to be increased gradually so that both the lower caisson body 12 and the bottom caisson body 11 can adapt to the pressure of the steel strands 14, while also avoiding the risk of the concrete cracking due to excessively rapid increase in internal pressure.

[0052] In a preferred embodiment, the tensioning prestress is controlled in four stages of loading. These four stages of loading can maintain both appropriate loading efficiency and loading stability, thereby reducing the risk of concrete cracking.

[0053] Furthermore, the first-stage loading force is 15%-25% of the tensioned prestress, for example, the first-stage loading force is 15%, 18%, 20%, or 25% of the tensioned prestress. The second-stage loading force is 40%-55% of the tensioned prestress, for example, the second-stage loading force is 40%, 45%, 50%, or 55% of the tensioned prestress; the third-stage loading force is 70%-80% of the tensioned prestress, for example, the third-stage loading force is 70%, 75%, or 80% of the tensioned prestress; and the fourth-stage loading force is 100% of the tensioned prestress.

[0054] After each loading force is applied, a preset loading time is maintained to ensure the stability of the tension prestress exerted by the steel strand 14 on the caisson structure 10. Specifically, the load is held for 4-6 minutes after each loading force is applied. For example, the load is held for 4 minutes, 5 minutes, and 6 minutes after each loading force is applied.

[0055] Furthermore, after each level of loading force is applied, it is necessary to check the elongation of the steel strand 14 and the pressure value of the jack under each level of loading force. When the elongation is within the allowable deviation range, the jack is controlled to apply the next level of loading force. When the elongation of the steel strand 14 exceeds the allowable deviation range, the quality of the steel strand 14 does not meet the requirements or it breaks due to tension, causing the loading force to not meet the preset requirements, and it needs to be inspected or replaced.

[0056] The elongation of the steel strand 14 and the pressure value of the jack are within the normal range. After the loading time reaches the required level, the jack is controlled to apply the next level of loading force.

[0057] After the tensioning and prestressing of each layer of the caisson body 12 is completed, the soil below the bottom caisson body 11 needs to be excavated so that the caisson structure 10 can gradually move downwards. The sinking height is less than or equal to the height of the caisson body 12.

[0058] like Figures 1 to 4 As shown, to further improve the downward angle of the caisson structure 10 to meet the preset angle requirements, it is necessary to inspect the caisson structure 10. Controlling the gradual sinking of the caisson structure 10 to the design height includes the following steps: Detection sensors are installed around the caisson structure 10. The detection sensors can be set as displacement sensors or angle sensors, and multiple detection sensors can simultaneously detect the sinking amount of the caisson structure 10.

[0059] The attitude parameters of the caisson structure 10 during sinking are monitored in real time. When there is a difference between the two sides of the caisson structure 10, the caisson structure 10 has a deviation value during sinking and the sinking attitude of the caisson structure 10 needs to be adjusted.

[0060] The excavation parameters of the soil are controlled according to the attitude parameters to adjust the sinking attitude of the caisson structure 10, thereby ensuring that the sinking range of the caisson structure 10 meets the preset requirements.

[0061] Specifically, controlling the excavation parameters of the soil based on attitude parameters includes the following steps: Detect the subsidence of each sidewall of the caisson structure 10; Determine the deviation of the caisson structure 10 from the opposite side; When the deviation exceeds the preset value, the excavation volume of the soil on the side with smaller subsidence will be increased.

[0062] Multiple displacement sensors are installed around the caisson structure 10 to monitor its sinking process in real time. A difference in displacement between two opposite sides indicates that the caisson structure 10 is tilting. The side with the greater displacement is identified as the side that has sunk more, and the other side as the side that has sunk less. The excavation strategy is adjusted based on the tilt: excavation stops on the side with greater sinking, while more excavation continues on the side with less sinking until the caisson reaches equilibrium. This excavation process is repeated alternately.

[0063] More preferably, the caisson structure 10 is rectangular. Optionally, four displacement sensors are set to detect the four sides of the caisson structure 10, thereby realizing the four-way tilt detection of the caisson structure 10 and facilitating real-time monitoring of the downward attitude of the caisson structure 10.

[0064] After the caisson structure 10 is lowered to the designed depth, the bottom of the caisson is sealed. After the sealing is completed and passes inspection, the mud and water inside the caisson are pumped out to create working conditions for subsequent construction.

[0065] It should be understood that this application is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of this application and include common knowledge or customary techniques in the art that are not disclosed in this invention.

Claims

1. A method for constructing a prestressed tensioned cast-in-place integral caisson, characterized in that, The construction method includes: Excavate a foundation pit in the pre-designed area and install a bottom well body inside the foundation pit; The lower well body is constructed in layers above the bottom well body. The reinforcing steel cage of each lower well body is pre-embedded with a fixed conduit, and concrete is poured and cured. Then, the steel strand is threaded into the conduit and a prestressing tensioning process is performed on the steel strand to form a prestress that resists the lateral pressure of the surrounding soil in the lower well body. The foundation pit soil below the bottom well body is excavated to a predetermined depth, and the caisson structure is gradually sunk to the corresponding depth. Repeat the steps of constructing and sinking the caisson body until the caisson structure reaches the preset design depth. The sinking steel cage of the upper layer of the caisson body is connected to the lower layer of the caisson body through a connecting mechanism. The caisson body and the bottom layer of the caisson body are connected to form the caisson structure. At least one cuttable area is reserved in the preset area of ​​the caisson structure.

2. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 1, characterized in that, The provision of at least one machinable area in the predetermined area of ​​the caisson structure includes: A reinforcing edge is formed at the edge of the machinable area of ​​the sunken reinforcing cage; Multiple cutting ribs are provided in the machinable area, and the multiple cutting ribs are fixed to the sinking steel cage respectively. The cutting ribs are made of machinable material. Pour concrete into the cuttable area.

3. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 2, characterized in that, The sunken steel cage forms a reinforced edge at the edge of the machinable area, including: A ring-shaped reinforcing rib is provided at the edge of the machinable area, and the reinforcing bars of the sunken steel cage and the reinforcing rib are connected to form a reinforced edge; or, A reinforcing plate is provided at the edge of the cuttable area, and the reinforcing bars of the sunken steel cage are connected to the reinforcing plate to form a reinforced edge.

4. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 2, characterized in that, The prestressing tensioning process for the steel strand includes: Install working anchor plates, clamps, and limiting plates at both ends of the steel strand; Align the jack with the axis of the steel strand to avoid eccentric force during tensioning; The jacks at both ends of the control steel strand are used to apply tension prestress synchronously and uniformly, with the same tensioning parameters; When the tension prestress on the steel strand reaches the preset value and is in a stable state, the clamps and steel strand are locked, and the jacks are unloaded.

5. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 4, characterized in that, The jacks at both ends of the control steel strand synchronously and uniformly apply load force, including: The preset tension prestress is divided into multiple levels of loading force, and the jacks are controlled to apply the load step by step according to the loading force. After each loading force is applied, maintain the preset loading time to keep the tension prestress of the steel strands acting on the caisson structure stable. The elongation of the steel strand and the pressure value of the jack are detected under each level of loading force. When the elongation is within the allowable deviation range, the jack is controlled to apply the next level of loading force.

6. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 1, characterized in that, The controlled caisson structure gradually sinks to the designed height, including: Detection sensors were installed around the perimeter of the caisson structure; Real-time monitoring of the sinking attitude parameters of the caisson structure; The excavation parameters of the soil are controlled based on the attitude parameters.

7. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 6, characterized in that, The step of controlling the excavation parameters of the soil based on the attitude parameters includes: Detect the subsidence of each sidewall of the caisson structure; Determine the deviation of the caisson structure from its opposite side; When the deviation exceeds the preset value, the excavation volume of the soil on the side with smaller subsidence will be increased.

8. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 1, characterized in that, The caisson structure can be polygonal, circular, elliptical, irregularly circular, or irregularly shaped ring structure; The pre-embedded fixing conduit in the sinking steel cage of each sinking well body includes: The transverse conduit is installed by running horizontally and bending along the sunken steel cage; The longitudinal conduit is threaded and bent along the longitudinal direction of the sunken steel cage; The transverse and longitudinal conduits are arranged alternately in space along the height direction of the sunken reinforcing cage.

9. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 1, characterized in that, The provision of a bottom well within the foundation pit includes: Install templates in the foundation pit excavated in the preset area, place the bottom reinforcement cage in the space enclosed by the templates, and embed at least one arc-shaped conduit in the bottom reinforcement cage. The bending direction of the arc-shaped conduit is set according to the tensioning direction of the prestressed steel strand. After the concrete is poured and vibrated to compact it, a preset curing time is set, and the connecting mechanism of the bottom steel cage extends beyond the top surface of the poured concrete. The steel strands are threaded through the conduit and the prestressing tensioning process is performed.

10. The construction method for prestressed tensioned cast-in-place integral caissons according to claim 9, characterized in that, The bottom well body includes a peripheral wall, multiple reinforcing beams intersecting the inner side of the peripheral wall, and a connecting mechanism extending beyond the top of the peripheral wall. The bottom of the peripheral wall and the bottom of the reinforcing beams are provided with cutting edges. When the caisson structure reaches the preset design depth, concrete is poured to seal the bottom of the caisson.

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