Construction technology of foundation pit support

Abstract

The application discloses a construction technology of foundation pit support, relates to the technical field of foundation pit support in building engineering, and has the advantages of improving the integrity of the connecting joint between the lattice column and the reinforcement cage of the cast-in-place pile, and the technical scheme points are as follows: the construction technology comprises the following steps: step one, processing of the lattice column; step two, hoisting and temporary fixing of the reinforcement cage; after the column hole is cleaned, the reinforcement cage is hoisted into the hole and is initially positioned, the reinforcement cage is suspended and fixed at the hole mouth, and a reinforcing hoop plate is additionally arranged below the top of the reinforcement cage; step three, hoisting and perpendicularity checking of the lattice column; step four, triple connection of the lattice column and the reinforcement cage; the lower end of the lattice column is continuously lowered into the reinforcement cage to a predetermined depth, and the welding of the reinforcing steel bars and the reinforcing hoop plate, the connection of the reinforcing steel bars and the reinforcement cage main reinforcement, and the welding of the top of the reinforcement cage main reinforcement and the lattice column angle steel are sequentially adopted; step five, integral lowering after welding; and step six, pouring of the bottom concrete.

Description

Technical Field

[0001] This invention relates to the field of foundation pit support technology in building engineering, specifically to a construction process for foundation pit support. Background Technology

[0002] In deep foundation pit engineering, to meet the vertical bearing requirements of the support system within the pit, it is usually necessary to install piles and steel columns. Due to their good bearing capacity and other advantages, lattice columns are widely used as vertical supports for foundation pits.

[0003] A lattice column is generally welded from four angle steel bars and several connecting plates. Its lower end is anchored within a bored pile, and its upper end connects to the support system within the foundation pit, bearing the vertical load transmitted by the support beam. The main technical problems in the fabrication and installation of existing lattice columns are as follows: The connection node between the lattice column and the cast-in-place pile reinforcement cage: The conventional method is to fix it with only a few connecting bars. The overall integrity of the node is poor. It is easily displaced by impact during the concrete pouring process, which leads to the lattice column being misaligned or tilted, affecting the load-bearing performance and service life of the column. Summary of the Invention

[0004] The purpose of this invention is to provide a construction process for foundation pit support, which has the advantage of improving the integrity of the connection nodes between the lattice column and the cast-in-place pile reinforcement cage.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention provides a construction process for foundation pit support, comprising the following steps: Step 1: Fabrication of lattice columns After the angle steel is cut to the designed length, the lattice column is made by step positioning and welding three lacing plates: the first, middle and the last. Step 2: Lifting and Temporarily Fixing the Reinforcing Cage After cleaning the column pile hole, the steel cage is hoisted into the hole and initially positioned. The steel cage is then suspended and fixed at the hole opening, and a reinforcing stirrup plate is added below the top of the steel cage. Step 3: Installation and Verticality Check of Lattice Columns The processed lattice column is hoisted to the opening and slowly lowered to the top of the steel cage, so that it is in a suspended state. Its verticality is checked by a theodolite. Step 4: Triple connection between lattice column and steel cage After the verticality requirement is met, the lower end of the lattice column is lowered to the predetermined depth inside the steel cage. The grid-shaped steel bars are welded to the reinforcing stirrup plate, tie bars are added to connect with the main reinforcement of the steel cage, and the top of the main reinforcement of the steel cage is welded to the angle steel of the lattice column. Step 5: Lower the whole unit after welding The welded and fixed lattice column and steel cage assembly is lowered as a whole to the design elevation. Step Six: Pour Concrete at Pile Bottom After the pile is lowered into place, concrete is poured at the bottom of the pile, and the pile hole is promptly filled with soil to seal it.

[0006] By adopting the above technical solution, in step two, after cleaning the column pile hole, the reinforcing cage is hoisted into the hole for initial positioning, and then suspended and fixed at the hole opening. A reinforcing hoop plate is added below the top of the reinforcing cage. This operation ensures that the reinforcing cage is in a stable and controllable state in the hole, providing a precise positioning benchmark for the subsequent hoisting and welding connection of the lattice column. After the lower end of the lattice column is lowered to the predetermined depth in the reinforcing cage, a grid-shaped reinforcing bar is welded to the reinforcing hoop plate, tie bars are added to connect with the main reinforcing bars of the reinforcing cage, and the top of the main reinforcing bars of the reinforcing cage is welded to the angle steel of the lattice column to form a triple connection structure. This improves the integrity of the connection node between the lattice column and the cast-in-place pile reinforcing cage. This connection method makes the lattice column and the reinforcing cage form a solid whole, ensuring the stability of the lattice column during the subsequent lowering and concrete pouring process, and reducing displacement or tilting due to impact or disturbance.

[0007] Preferably, in step one, the step-by-step positioning and welding method using three lacing plates ("first, middle, and last") specifically includes: After cutting the angle steel, place wooden blocks at the beginning, end and middle of the angle steel and adjust it to be level. Place the two angle irons on the wooden blocks according to the design dimensions; An arc welding method was used to spot weld a piece of the middle section onto two angle steels; Then, the three connecting plates at the head, middle and tail are fixed by electric welding to ensure the accurate size of the half-lattice column; Two halves of the lattice column are joined and welded together to form a complete lattice column.

[0008] Preferably, in step two, the specific operations for hoisting and temporarily fixing the reinforcing cage are as follows: After cleaning the column pile hole, a steel casing is installed, followed by the lowering of the reinforcing cage. Using an adjustment device, the reinforcing cage is hoisted into the hole and then initially adjusted to ensure that the positional deviation of the reinforcing cage is controlled within ±5cm. A 2m steel cage is exposed at the opening of the column pile hole, and a horizontal bar is used to suspend and support the steel cage on the adjustment device. The reinforcing stirrups are distributed below the top of the steel cage near the opening of the column pile hole, and the reinforcing stirrups are 100% welded to the main reinforcement bars of the steel cage.

[0009] Preferably, in step four, the specific operation of the triple connection is as follows: After the verticality requirement is met, slowly extend the lower end of the lattice column into the steel cage and close to the opening of the column pile hole; The grid-shaped steel reinforcement consists of four short steel bars welded into a grid-shaped frame, which is fitted around the outer perimeter of the lattice column and welded to the reinforcing stirrup plate; The tie bars are short steel bars, with one end welded to the angle steel of the lattice column and the other end welded to the main reinforcement of the steel cage; The top 10cm of the main reinforcement bars of the steel cage are bent inward so that the bent end of the main reinforcement bar is tightly fitted with the outer side of the angle steel of the lattice column. Then, it is welded and fixed to the angle steel of the lattice column. Alternatively, transition connecting bars are welded between the main reinforcement bars of the steel cage and the angle steel of the lattice column for connection.

[0010] Preferably, the adjustment device includes a positioning cylinder coaxially distributed with the steel casing, the positioning cylinder being fixed to the ground, and an annular lifting plate coaxially connected above the positioning cylinder via an elastic element; the crossbar is inserted into the reinforcing cage and placed on the lifting plate, and several horizontally distributed limiting rings are coaxially welded to the inner wall of the reinforcing cage, the crossbar being two in number and supported on the lower end face of the limiting rings respectively; as the reinforcing cage continues to descend, the reinforcing cage presses the lifting plate downward through the crossbar; the positioning cylinder is provided with an adjusting component, and during the descent of the lifting plate until the lower end of the lifting plate abuts against the upper end face of the positioning cylinder, the adjusting component automatically adjusts the reinforcing cage to a coaxial position with the steel casing, at which point the reinforcing cage is suspended inside the steel casing.

[0011] Preferably, after the lower end of the lattice column is slowly inserted into the reinforcing cage for welding, the lattice column is first lifted upwards, and the reinforcing cage is lifted together at the same time to facilitate the removal of the crossbars; at this time, the elastic element pushes the lifting plate upwards, and the adjusting element automatically releases the limit on the reinforcing cage, which facilitates the subsequent lowering of the lattice column and the reinforcing cage.

[0012] Preferably, the elastic element includes several mounting grooves formed on the upper end face of the positioning cylinder, and each mounting groove has a compression spring at the bottom. The end of each compression spring away from the bottom of the mounting groove is fixed to the lower end face of the lifting plate. When the lifting plate abuts against the positioning cylinder, each compression spring is compressed but not pressed together, and each compression spring is located in the mounting groove.

[0013] Preferably, the adjusting component includes several push blocks fixed to the lower end face of the lifting plate. The upper end face of the positioning cylinder has grooves corresponding to the positions of each push block, and a slider is slidably connected within each groove. The lower end of each push block extends into the groove and fits against the slider. Both the slider and the push block have inclined surfaces on their fitting sides. One end of each groove extends out of the inner wall of the positioning cylinder. An adjusting block is fixed to the side of the slider facing the reinforcing cage. As the lifting plate descends until its lower end contacts the upper end face of the positioning cylinder, each push block pushes the corresponding slider through its inclined surface, causing the adjusting block to move out of the groove and then contact the outer wall of the reinforcing cage. When the lifting plate contacts the positioning cylinder, the outer wall of the reinforcing cage is simultaneously contacted by multiple adjusting blocks, completing the coaxial adjustment of the reinforcing cage.

[0014] Preferably, a T-shaped groove is provided on the inclined surface of the push block, and a T-shaped block is provided on the inclined surface of the slider, with the T-shaped block slidably connected in the T-shaped groove.

[0015] Preferably, the adjusting block is coaxially fixed with an adjusting rod on the side away from the reinforcing cage, and one end of each adjusting rod is threaded into the corresponding slider.

[0016] The beneficial effects of this invention are as follows: The steel cage is initially positioned by hoisting it into the hole and then suspended and fixed at the hole opening. A reinforcing stirrup plate is added below the top of the steel cage. This operation ensures the steel cage is in a stable and controllable state within the hole, providing a precise positioning reference for the subsequent hoisting and welding of the lattice column. After the lower end of the lattice column is lowered to a predetermined depth within the steel cage, a triple connection structure is formed by sequentially welding a grid-shaped steel bar to the reinforcing stirrup plate, adding tie bars to connect with the main reinforcement of the steel cage, and welding the top of the main reinforcement of the steel cage to the angle steel of the lattice column. This improves the overall integrity of the connection node between the lattice column and the cast-in-place pile steel cage. This connection method ensures the lattice column and the steel cage form a solid whole, guaranteeing the stability of the lattice column during subsequent lowering and concrete pouring, and reducing displacement or tilting due to impact or disturbance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the construction process in this embodiment; Figure 2 This is a schematic diagram illustrating the structure of the adjustment device in this embodiment; Figure 3 This is a schematic diagram illustrating the structure of the chute in this embodiment; Figure 4 This is a structural schematic diagram illustrating the upper end face of the positioning cylinder in this embodiment; Figure 5 for Figure 4 A magnified structural diagram of part A in the middle.

[0019] Explanation of reference numerals in the attached figures: In the diagram: 1. Steel casing; 11. Positioning cylinder; 12. Lifting plate; 13. Crossbar; 14. Mounting groove; 141. Compression spring; 142. Push block; 15. Slide groove; 151. Sliding block; 152. Inclined surface; 153. Adjusting block; 16. T-slot; 161. T-block; 17. Adjusting rod; 2. Lattice column; 3. Reinforcing cage; 31. Well-shaped reinforcing bars; 32. Reinforcing stirrup plate; 33. Tie bar; 34. Transition connecting reinforcing bars; 35. Limiting ring; 36. Positioning ring. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Furthermore, the terms "installation," "setup," "equipped with," "connection," "linking," and "socketing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0022] A construction process for foundation pit support includes the following steps: Step 1: Fabrication of lattice column 2 After the angle steel is cut to the designed length, the lattice column 2 is made by step positioning and welding of three lacing plates: first, the two angle steels are positioned and their squareness is controlled, then the middle lacing plate, the first lacing plate and the last lacing plate are welded in sequence to form half of the lattice column 2, and then the two half of the lattice column 2 are joined together and welded to form the complete lattice column 2. Step 2: Lifting and Temporarily Fixing Reinforcing Cage 3 After cleaning the column pile hole, the steel cage 3 is hoisted into the hole and initially positioned. The steel cage 3 is then suspended and fixed at the hole opening. A reinforcing hoop plate 32 is added below the top of the steel cage 3. At this time, the reinforcing hoop plate 32 is pre-welded inside the steel cage 3 and is located above the column pile hole. Step 3: Installation and Verticality Check of Lattice Column 2 The processed lattice column 2 is hoisted to the opening and slowly lowered to the top of the steel cage 3, so that it is in a suspended state. The verticality is checked with a theodolite, and the verticality deviation is controlled within 1 / 1000H (H is the length of the lattice column 2). The theodolite is used to accurately check and ensure that the lattice column 2 has the correct vertical posture before being lowered. Step 4: Triple connection between lattice column 2 and steel cage 3 After the verticality requirement is met, the lower end of the lattice column 2 is lowered to the predetermined depth inside the steel cage 3. The grid-shaped steel bars 31 are welded to the reinforcing stirrup plate 32 in sequence, the tie bars 33 are added and connected to the main bars of the steel cage 3, and the top of the main bars of the steel cage 3 are welded to the angle steel of the lattice column 2. Step 5: Lower the whole unit after welding The welded and fixed lattice column 2 and steel cage 3 are assembled and lowered to the design elevation as a whole. Step Six: Pour Concrete at Pile Bottom After the pile is lowered into place, concrete is poured at the bottom of the pile to anchor the lower end of the lattice column 2 into the cast-in-place pile. After the concrete pouring is completed, the pile hole is promptly backfilled to eliminate safety hazards.

[0023] Step Two: After cleaning the column pile hole, the reinforcing cage 3 is hoisted into the hole for initial positioning. The reinforcing cage 3 is then suspended and fixed at the hole opening. A reinforcing stirrup plate 32 is added below the top of the reinforcing cage 3. This operation ensures that the reinforcing cage 3 is in a stable and controllable state within the hole, providing a precise positioning benchmark for the subsequent hoisting and welding connection of the lattice column 2. After the lower end of the lattice column 2 is lowered to the predetermined depth within the reinforcing cage 3, a grid-shaped reinforcing bar 31 is welded to the reinforcing stirrup plate 32, a tie bar 33 is added to connect with the main reinforcement of the reinforcing cage 3, and the top of the main reinforcement of the reinforcing cage 3 is welded to the angle steel of the lattice column 2, forming a triple connection structure. This improves the overall integrity of the connection node between the lattice column 2 and the cast-in-place pile reinforcing cage 3. This connection method makes the lattice column 2 and the reinforcing cage 3 form a solid whole, ensuring the stability of the lattice column 2 during subsequent lowering and concrete pouring, and reducing displacement or tilting due to impact or disturbance.

[0024] Step one, which employs a three-part positioning and welding method involving the "first, middle, and last" lacing plates, specifically includes: The lattice column 2 has a size of 550mm×550mm and is welded from L180×16mm angle steel and 450mm×300mm×12mm gusset plate.

[0025] The specific processing procedure is as follows: After cutting the angle steel to the designed length, wooden blocks are laid at the beginning, end, and middle of the angle steel and adjusted to be level. The horizontal deviation of the wooden blocks should not exceed 2mm. Two angle steels are placed on the wooden blocks according to the designed dimensions. An arc welding is used to spot weld a lacing plate in the middle part to the two angle steels for initial fixation. Then, the three lacing plates at the beginning, middle, and end are fixed by electric welding to ensure the accurate dimensions of the half-lattice column 2. Finally, the two half-lattice columns 2 are joined and welded together to form a complete lattice column 2. This step-by-step positioning welding method effectively controls the thermal deformation and twisting of the angle steel during the welding process, ensuring the cross-sectional dimensional accuracy and squareness of the lattice column 2.

[0026] In step two, the specific operations for hoisting and temporarily fixing the reinforcing cage 3 are as follows: After cleaning the pile hole, steel casing 1 is first installed. The steel casing 1 is buried at the hole opening, with its center coinciding with the center of the pile position, and its top is raised a certain height above the ground. It plays the role of protecting the hole opening, preventing collapse and maintaining the mud level.

[0027] After the steel casing 1 is installed, the adjusting device is used to hoist and temporarily fix the reinforcing cage 3; the specific operation is as follows: The reinforcing cage 3 is hoisted into the hole, and the initial adjustment is made using the adjustment device to control the positional deviation of the reinforcing cage 3 within ±5cm. The reinforcing cage 3 protrudes 2m from the opening of the column pile hole. The reinforcing cage 3 is suspended and supported on the adjustment device using a crossbar 13. At the same time, a reinforcing stirrup plate 32 is added below the top of the reinforcing cage 3 near the opening of the column pile hole. The reinforcing stirrup plate 32 is 100% welded to the main reinforcement of the reinforcing cage 3.

[0028] Through this step, the reinforcing cage 3 is in a stable and controllable state inside the steel casing 1. The steel casing 1 provides precise guidance and positioning benchmarks for the reinforcing cage 3, ensuring that the subsequent hoisting and welding connection of the lattice column 2 can be carried out accurately.

[0029] In step four, the specific operations for triple connections are as follows: After the verticality requirement is met, slowly insert the lower end of the lattice column 2 into the steel cage 3 near the opening of the column pile hole, and then perform triple connection in sequence: First connection: The reinforcing stirrup plate 32 is pre-welded into the reinforcing cage 3. The reinforcing stirrup plate 32 is a ring plate, which can be a ring plate spliced ​​from several arc-shaped plates. A grid-shaped steel bar 31 is used to weld the reinforcing stirrup plate 32 of the reinforcing cage 3 to the lattice column 2. The grid-shaped steel bar 31 is formed by welding four short steel bars into a grid-shaped frame, which fits around the outer perimeter of the lattice column 2 and is welded to the reinforcing stirrup plate 32. The grid-shaped steel bar 31 is also welded to the outer wall of the lattice column 2. There are two grid-shaped steel bars 31, distributed and welded to the upper and lower ends of the reinforcing stirrup plate 32 respectively, forming a double constraint. The grid-shaped steel bar 31 does not extend beyond the outer wall of the reinforcing cage 3. The ring structure of the reinforcing stirrup plate 32 can effectively transfer the concentrated force transmitted by the grid-shaped steel bar 31. The stress is evenly distributed across the entire cross section of the reinforcing cage 3, reducing stress concentration. Simultaneously, the grid-shaped reinforcing bars 31 symmetrically constrain the lattice column 2 from four directions, effectively limiting its horizontal displacement. Compared to directly spot-welding the grid-shaped bars 31 to the main reinforcement of the reinforcing cage 3 (spot welding has a small contact area and limited weld length), the annular reinforcing stirrup plate of this invention forms a surface contact weld with the grid-shaped reinforcing bars, significantly increasing the weld length and greatly improving the connection strength. After the lattice column 2 is lowered to the designed position, the grid-shaped reinforcing bars 31 hug the lattice column 2 from all sides. Subsequently, the grid-shaped reinforcing bars 31 are welded and fixed to the reinforcing stirrup plate 32, forming a rigid positioning frame that provides temporary fixation and stable operating conditions for subsequent tie bar welding and main reinforcement bending welding.

[0030] Second connection: For the part without the reinforcing stirrup plate 32, the lattice column 2 is connected to the main reinforcement of the steel cage 3 by adding tie bars 33 nearby; the tie bars 33 are short steel bars, one end is welded to the angle steel of the lattice column 2, and the other end is welded to the main reinforcement of the steel cage 3.

[0031] The third connection: The top 10cm of the main reinforcement of the steel cage 3 is welded and fixed to the angle steel of the lattice column 2. That is, the top 10cm of the main reinforcement of the steel cage 3 is bent inward so that the end of the bent main reinforcement is closely attached to the outer side of the angle steel of the lattice column 2. Then, double-sided or single-sided lap welding is used for fixing. The welding should be performed symmetrically from all four sides of the lattice column 2. Alternatively, a transition connection steel bar 34 is added. Instead of directly bending the main reinforcement, the transition connection steel bar 34 is welded between the main reinforcement of the steel cage 3 and the angle steel of the lattice column 2 for connection.

[0032] This triple connection enables the lattice column 2 and the steel cage 3 to form a solid whole, ensuring the stability of the lattice column 2 during the subsequent lowering and concrete pouring process.

[0033] The adjustment device includes a positioning cylinder 11 coaxially distributed with the steel casing 1. The positioning cylinder 11 is fixed to the ground. Specifically, several fixing plates are provided around the positioning cylinder 11, and each fixing plate is nailed into the ground by anchor rods, thereby completing the fixation of the positioning cylinder 11. An annular lifting plate 12 is coaxially connected to the top of the positioning cylinder 11 through an elastic element. The crossbar 13 is inserted into the reinforcing cage 3 and placed on the lifting plate 12. Several horizontally distributed limiting rings 35 are coaxially welded to the inner wall of the reinforcing cage 3. Each limiting ring 35 is distributed in contact with each other vertically. There are two crossbars 13, each supporting a different part. The lower end of the limit ring 35 is supported; as the steel cage 3 continues to descend, the steel cage 3 presses the lifting plate 12 downward through the crossbar 13; the positioning cylinder 11 is equipped with an adjusting component. During the descent of the lifting plate 12, after the lower end of the lifting plate 12 contacts the upper end of the positioning cylinder 11, the adjusting component automatically adjusts the steel cage 3 to a coaxial position with the steel casing 1. At this time, the steel cage 3 is suspended inside the steel casing 1; at this time, the crossbar 13 is located below each limit ring 35, and each limit ring 35 is located below the reinforcing stirrup plate 32. The crossbar 13 supports the limit ring 35.

[0034] After the lower end of the lattice column 2 is slowly inserted into the steel cage 3 for welding, the lattice column 2 is lifted upwards first. At this time, the steel cage 3 is lifted together to facilitate the removal of the crossbar 13. At this time, the elastic element pushes the lifting plate 12 upwards, and the adjusting element automatically releases the limit on the steel cage 3, which facilitates the subsequent lowering of the lattice column 2 and the steel cage 3.

[0035] The elastic element includes several mounting grooves 14 formed on the upper end face of the positioning cylinder 11. The mounting grooves 14 are arranged in an array along the center of the positioning cylinder 11. Each mounting groove 14 has a compression spring 141 at its bottom. The end of each compression spring 141 away from the bottom of the mounting groove 14 is fixed to the lower end face of the lifting plate 12. When the lifting plate 12 is in a free state, the compression spring 141 pushes the lifting plate 12 upward. When the lifting plate 12 is subjected to downward pressure, the compression spring 141 is compressed. It should be noted that when the lifting plate 12 descends to the point where its lower end contacts the upper end face of the positioning cylinder 11, each compression spring 141 is compressed but not pressed together, and each compression spring 141 is located within the mounting groove 14, thereby ensuring that the spring is always within the elastic working range and extending its service life.

[0036] The adjusting component includes several push blocks 142 fixed to the lower end face of the lifting plate 12. Each push block 142 is arranged in an array along the center of the positioning cylinder 11. A groove 15 is provided on the upper end face of the positioning cylinder 11 corresponding to each push block 142. The length direction of each groove 15 is distributed along the radial direction of the positioning cylinder 11. A slider 151 is slidably connected within each groove 15. The lower end of each push block 142 extends into the groove 15 and fits against the slider 151. Both the slider 151 and the push block 142 have inclined surfaces 152 on their mating sides. The side of the inclined surface 152 on the push block 142 with a higher height is closer to the reinforcing cage 3, and the side of the inclined surface 152 on the slider 151 with a higher height is also closer to the reinforcing cage 3. One end of each groove 15 extends out of the inner wall of the positioning cylinder 11. An adjusting block 153 is fixedly provided on the side of the slider 151 facing the reinforcing cage 3. The depth of the groove 15 is... The groove wall of the slide 15 extends out of the inner wall of the positioning cylinder 11 only when it is higher than the upper end of the steel casing 1. At this time, the part of the slider 151 that fixes the adjusting block 153 can first extend horizontally, and then fix the adjusting block 153. The height of the adjusting block 153 is higher than that of the steel casing 1, in order to increase the height of the slider 151 and the length of the inclined surface 152. When the lifting plate 12 descends until its lower end contacts the upper end of the positioning cylinder 11, each push block 142 pushes the corresponding slider 151 through the inclined surface 152 to move the adjusting block 153 out of the slide 15 and then contact the outer wall of the reinforcing cage 3. When the lifting plate 12 contacts the positioning cylinder 11, the outer wall of the reinforcing cage 3 is simultaneously contacted by multiple adjusting blocks 153, completing the coaxial adjustment of the reinforcing cage 3. At this time, the distance that each adjusting block 153 extends out of the slide 15 is the same.

[0037] The mounting slots 14, sliding grooves 15, and crossbars 13 are staggered.

[0038] To ensure that the push block 142 and the slider 151 do not separate during relative sliding, a T-shaped groove 16 is provided on the inclined surface 152 of the push block 142. The length of the T-shaped groove 16 is distributed along the inclined direction of the inclined surface 152 of the push block 142 and extends through the bottom of the push block 142. A T-shaped block 161 is provided on the inclined surface 152 of the slider 151. The T-shaped block 161 is slidably connected in the T-shaped groove 16. This T-shaped mating structure allows the two to slide relative to each other along the inclined surface 152 and prevents lateral separation, thus ensuring transmission reliability.

[0039] An adjusting rod 17 is coaxially fixed on the side of the adjusting block 153 away from the reinforcing cage 3, and one end of each adjusting rod 17 is threaded into the corresponding slider 151. By setting the threaded connection between the adjusting rod 17 and the slider 151, the horizontal position of the adjusting block 153 relative to the slider 151 can be adjusted, so that it can be finely adjusted according to the actual diameter deviation of different reinforcing cages 3, ensuring that multiple adjusting blocks 153 can form a uniform radial pressure when they abut against the outer wall of the reinforcing cage 3, further improving the coaxiality accuracy of the reinforcing cage 3 and the steel casing 1. At the same time, the threaded connection is convenient to operate. The adjusting rod 17 can be pre-adjusted according to the actual measured diameter of the reinforcing cage 3 before installation. Precise positioning can be achieved without additional intervention during the descent of the lifting plate 12, which enhances the applicability and adjustment flexibility of the adjustment device.

[0040] The inner wall of the reinforcing cage 3 is coaxially welded with several horizontally distributed positioning rings 36. When each adjusting block 153 abuts against the reinforcing cage 3, it abuts against the outer wall of the corresponding positioning ring 36. The positioning rings 36 are located below the limiting rings 35, and there are gaps between them for the crossbar 13 to pass through. Since the outer ring size of the positioning ring 36 is fixed and is a continuous smooth annular surface, compared with directly abutting against the main reinforcement of the reinforcing cage 3, the contact surface between the adjusting block 153 and the positioning ring 36 is larger and the force is more uniform. At the same time, the positioning ring 36 is coaxially welded to the reinforcing cage 3, and it itself has a high roundness and concentricity. With the positioning ring 36 as the abutment reference, the adjusting block 153 can adjust the reinforcing cage 3 to a position coaxial with the steel casing 1 more accurately, which further improves the accuracy and reliability of coaxial adjustment. By rotating the adjusting rod 17, the extension length of the adjusting block 153 relative to the slider 151 can be changed. Before construction, the operator pre-rotates each adjusting rod 17 according to the designed diameter and actual measured diameter of the positioning ring 36 of the rebar cage 3, so that the front end face of the adjusting block 153 is on the same circumference. When the lifting plate 12 descends and the slider 151 drives the adjusting block 153 to move towards the rebar cage 3, the front end face of the adjusting block 153 can synchronously abut against the outer wall of the positioning ring 36 of the rebar cage 3, achieving coaxial adjustment. Since the adjusting rod 17 and the slider 151 are connected by threads, it can adapt to rebar cages 3 of different diameters or with manufacturing deviations, greatly improving the versatility and adjustment accuracy of the adjusting device.

[0041] Action process: Step 1: Before construction, according to the design diameter and actual measured diameter of the positioning ring 36 of the steel cage 3, rotate each adjusting rod 17 in advance so that the front end face of the adjusting block 153 is on the same circumference. Hoist the steel cage 3 into the hole. When the limiting ring 35 is close to the lifting plate 12, stop the lowering of the steel cage 3. Insert two horizontal rods 13 into the steel cage 3 so that the horizontal rods 13 are placed on the lifting plate 12. At this time, the steel cage 3 continues to be lowered. The horizontal rods 13 support the limiting ring 35. The horizontal rods 13 will press the lifting plate 12 downward, so that the lifting plate 12 begins to move downward against the elastic force of the compression spring 141. Step 2: During the descent of the lifting plate 12, the adjusting mechanism automatically adjusts the reinforcing cage 3 to a coaxial position with the steel casing 1. The specific principle is as follows: When the lifting plate 12 descends, the push block 142 fixed to the lower end face of the lifting plate 12 moves downward accordingly. Since the inclined surface 152 of the push block 142 is in contact with the inclined surface 152 of the slider 151, the push block 142 pushes the slider 151 to move horizontally along the slide groove 15 towards the center of the positioning cylinder 11 during the downward movement. The slider 151 drives the adjusting block 153 to move out of the slide groove 15 simultaneously, so that the front end of the adjusting block 153 abuts against the positioning ring 36 of the reinforcing cage 3. Since multiple adjusting blocks 153 are distributed along the circumference of the reinforcing cage 3, each adjusting block 153 simultaneously The outer wall of the positioning ring 36 is contacted, and radial pressure is applied from different directions. When the lifting plate 12 contacts the positioning cylinder 11, each adjusting block 153 moves out the same distance at the same time, thereby pushing the steel cage 3 to the center position coaxial with the steel casing 1. Due to the thread adjustment function of the adjusting rod 17, the extension length of each adjusting block 153 has been precisely pre-adjusted before construction to ensure that all adjusting blocks 153 contact the positioning ring 36 at the same time, reducing the problem of individual adjusting blocks 153 contacting prematurely or failing to contact due to manufacturing deviation or installation error. When the lifting plate 12 continues to descend until its lower end contacts the upper end of the positioning cylinder 11, the lifting plate 12 stops descending. At this time, each adjusting block 153 contacts the outer wall of the positioning ring 36, and the steel cage 3 is adjusted to the design position coaxial with the steel casing 1, and is suspended on the lifting plate 12 by the crossbar 13 to achieve temporary fixation.

[0042] Step 3: Release the hoisting of the reinforcing cage 3 and begin hoisting the lattice column 2. After its lower end is slowly inserted into the reinforcing cage 3 to complete the triple welding, the crossbar 13 needs to be removed to facilitate the subsequent overall lowering. The specific operation is as follows: First, lift the lattice column 2 upwards. Since the lattice column 2 and the steel cage 3 have been welded and fixed, lift the steel cage 3 upwards at the same time as lifting the lattice column 2. At this time, the pressure of the steel cage 3 on the horizontal bar 13 is released, and the horizontal bar 13 is in a relaxed state, which makes it easy to pull it out from below the limit ring 35. After the crossbar 13 is removed, the steel cage 3 no longer applies downward pressure to the lifting plate 12. At this time, the compression spring 141 of the elastic element releases its elastic force, pushing the lifting plate 12 upward. The lifting plate 12 drives the push block 142 to move upward. During the upward movement of the push block 142, the slider 151 is pulled away from the steel cage 3 by the inclined surface 152. The adjusting block 153 then retracts into the slide groove 15, automatically releasing the limit on the steel cage 3. After that, the lattice column 2 and the steel cage 3 assembly can continue to be lowered to the design elevation.

[0043] The aforementioned adjustment device achieves automatic centering adjustment during the lowering of the rebar cage 3 through the linkage of elastic and adjusting components, eliminating the need for manual intervention and improving construction efficiency and positioning accuracy. Meanwhile, the cooperation between the T-slot 16 and the T-block 161 ensures the stability of the transmission, and the uncompressed design of the compression spring 141 ensures elastic recovery capability. The entire device is compact in structure, easy to operate, and suitable for the construction of rebar cages 3 with different diameters.

[0044] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A construction process for foundation pit support, characterized in that, Includes the following steps: Step 1: Fabrication of lattice columns After cutting the angle steel to the designed length, the lattice column is made by step positioning and welding three lacing plates: the first, middle and the last. Step 2: Lifting and Temporarily Fixing the Reinforcing Cage After cleaning the column pile hole, the steel cage is hoisted into the hole and initially positioned. The steel cage is then suspended and fixed at the hole opening, and a reinforcing stirrup plate is added below the top of the steel cage. Step 3: Installation and Verticality Check of Lattice Columns The processed lattice column is hoisted to the opening and slowly lowered to the top of the steel cage, so that it is in a suspended state. Its verticality is checked by a theodolite. Step 4: Triple connection between lattice column and steel cage After the verticality requirement is met, the lower end of the lattice column is lowered to the predetermined depth inside the steel cage. The grid-shaped steel bars are welded to the reinforcing stirrup plate, tie bars are added to connect with the main reinforcement of the steel cage, and the top of the main reinforcement of the steel cage is welded to the angle steel of the lattice column. Step 5: Lower the whole unit after welding The welded and fixed lattice column and steel cage assembly is lowered as a whole to the design elevation. Step Six: Pour Concrete at Pile Bottom After the pile is lowered into place, concrete is poured at the bottom of the pile, and the pile hole is promptly filled with soil to seal it. In step two, the specific operations for hoisting and temporarily fixing the reinforcing cage are as follows: After cleaning the column pile hole, a steel casing is installed, followed by the lowering of the reinforcing cage. Using an adjustment device, the reinforcing cage is hoisted into the hole and then initially adjusted to ensure that the positional deviation of the reinforcing cage is controlled within ±5cm. A 2m steel cage is exposed at the opening of the column pile hole, and a horizontal bar is used to suspend and support the steel cage on the adjustment device. The reinforcing stirrups are distributed below the top of the steel cage near the opening of the column pile hole, and the reinforcing stirrups are 100% welded to the main reinforcement of the steel cage. The adjustment device includes a positioning cylinder coaxially distributed with the steel casing. The positioning cylinder is fixed to the ground. An annular lifting plate is coaxially connected above the positioning cylinder via an elastic element. The crossbar is inserted into the reinforcing cage and placed on the lifting plate. Several horizontally distributed limiting rings are coaxially welded to the inner wall of the reinforcing cage. There are two crossbars, each supported on the lower end face of the limiting rings. As the reinforcing cage continues to descend, it presses the lifting plate downwards through the crossbars. The positioning cylinder is equipped with an adjusting component. During the descent of the lifting plate, once the lower end of the lifting plate contacts the upper end face of the positioning cylinder, the adjusting component automatically adjusts the reinforcing cage to a coaxial position with the steel casing. At this point, the reinforcing cage is suspended inside the steel casing. The adjusting component includes several push blocks fixed to the lower end face of the lifting plate. The upper end face of the positioning cylinder has grooves corresponding to the positions of each push block, and a slider is slidably connected within each groove. The lower end of each push block extends into the groove and fits against the slider. Both the slider and the push block have inclined surfaces on their fitting sides. One end of each groove extends out of the inner wall of the positioning cylinder. An adjusting block is fixed to the side of the slider facing the reinforcing cage. As the lifting plate descends until its lower end contacts the upper end face of the positioning cylinder, each push block pushes the corresponding slider through its inclined surface, causing the adjusting block to move out of the groove and then contact the outer wall of the reinforcing cage. When the lifting plate contacts the positioning cylinder, the outer wall of the reinforcing cage is simultaneously contacted by multiple adjusting blocks, completing the coaxial adjustment of the reinforcing cage.

2. The construction process for foundation pit support as described in claim 1, characterized in that, Step one, specifically the step-by-step positioning and welding method using three lacing plates ("first, middle, and last"), includes: After cutting the angle steel, place wooden blocks at the beginning, end and middle of the angle steel and adjust it to be level. Place the two angle irons on the wooden blocks according to the design dimensions; An arc welding method was used to spot weld a piece of the middle section onto two angle steels; Then, the three connecting plates at the head, middle and tail are fixed by electric welding to ensure the accurate size of the half-lattice column; Two halves of the lattice column are joined and welded together to form a complete lattice column.

3. The construction process for foundation pit support as described in claim 2, characterized in that, In step four, the specific operation of the triple connection is as follows: After the verticality requirement is met, slowly extend the lower end of the lattice column into the steel cage near the opening of the column pile hole; The grid-shaped steel reinforcement consists of four short steel bars welded into a grid-shaped frame, which is fitted around the outer perimeter of the lattice column and welded to the reinforcing stirrup plate; The tie bars are short steel bars, with one end welded to the angle steel of the lattice column and the other end welded to the main reinforcement of the steel cage; The top 10cm of the main reinforcement bars of the steel cage are bent inward so that the bent end of the main reinforcement bar is tightly fitted with the outer side of the angle steel of the lattice column, and then welded to the angle steel of the lattice column for fixation; or, transition connecting bars are welded between the main reinforcement bars of the steel cage and the angle steel of the lattice column for connection.

4. The construction process for foundation pit support as described in claim 3, characterized in that, After the lower end of the lattice column is slowly inserted into the steel cage for welding, the lattice column is first lifted upwards, and the steel cage is lifted together to facilitate the removal of the crossbars; at this time, the elastic element pushes the lifting plate upwards, and the adjusting element automatically releases the limit on the steel cage, which facilitates the subsequent lowering of the lattice column and steel cage.

5. The construction process for foundation pit support as described in claim 4, characterized in that, The elastic element includes several mounting grooves formed on the upper end face of the positioning cylinder. Each mounting groove has a compression spring at its bottom. The end of each compression spring away from the bottom of the mounting groove is fixed to the lower end face of the lifting plate. When the lifting plate comes into contact with the positioning cylinder, each compression spring is compressed but not pressed together, and each compression spring is located in the mounting groove.

6. The construction process for foundation pit support as described in claim 1, characterized in that, The pusher has a T-shaped groove on its inclined surface, and the slider has a T-shaped block on its inclined surface. The T-shaped block is slidably connected in the T-shaped groove.

7. The construction process for foundation pit support as described in claim 1, characterized in that, The adjusting block is coaxially fixed with an adjusting rod on the side away from the reinforcing cage, and one end of each adjusting rod is threaded into the corresponding slider.

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