Demolition construction method for reinforced concrete inner supporting beam of deep foundation pit

Abstract

The invention relates to a non-full support dismantling construction method for a reinforced concrete inner supporting beam of a deep foundation pit, and belongs to the technical field of building construction. The method comprises the steps that firstly, a supporting beam is divided into a plurality of to-be-disassembled units smaller than or equal to 8 t according to the rated load of an on-site crane; at least one phi 25 main rib is reserved on the top of a beam to serve as a temporary suspension bearing system, and a movable and height-adjustable profile steel bracket is only arranged at the cantilever end to be stressed in cooperation with the cantilever end. Then, concrete and part of steel bars are cut through an inverted-splayed track from bottom to top, and the gravity center of the unit moves inwards; after being cut off, the steel bars are directly driven into the beam bottom to be lifted by a forklift, residual steel bars are subjected to gas cutting and transported outwards, and an all-round scaffold or a double-row support does not need to be erected in the whole process. By means of the three-in-one technology of main reinforcement reserving, movable bracket moving and inverted-splayed cutting, safe, efficient, low-consumption and green construction of supporting beam dismantling is achieved, the steel consumption is reduced by 60% or above, the field turnover rate is larger than or equal to 90%, and the method is suitable for fast dismantling of supporting systems in various deep foundation pits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building construction, in particular to a deep foundation reinforced concrete internal support beam dismantling construction method. BACKGROUND

[0002] With the acceleration of urbanization and the increasing development and utilization of underground space, deep foundation engineering is becoming more and more common in urban construction. As an important part of the foundation pit support system, the dismantling process of deep foundation reinforced concrete internal support beam is directly related to the safety and stability of the foundation pit and the surrounding environment. However, the traditional internal support beam dismantling method has many drawbacks and cannot meet the high requirements of modern construction on safety, efficiency and environmental protection.

[0003] Firstly, the traditional method often uses full-frame scaffolding or temporary support for dismantling work, which not only requires a large amount of manpower and resources for erection and dismantling, increasing construction cost and time, but also the stability of scaffolding or temporary support is difficult to guarantee, posing a great safety hazard. Especially in the deep foundation pit environment, once the support system loses stability, it may cause serious engineering accidents.

[0004] Secondly, the traditional dismantling method lacks effective fixing measures during cutting, which can easily lead to concrete block falling, posing a threat to construction personnel and the surrounding environment. At the same time, the dust and noise pollution generated during cutting also have adverse effects on the construction site and the surrounding environment.

[0005] In addition, although there are some improved dismantling methods in the prior art, such as using chain saw cutting, these methods often ignore the safety check and material saving problems in the dismantling process. For example, some methods do not effectively support the uncut part, leading to structural instability during dismantling; or use a large amount of temporary support material, causing resource waste.

[0006] After searching, a prior art deep foundation concrete support beam cutting and dismantling construction method was found, application number 202310325950.0, publication number CN116464062A, which has the following defects: Supporting method defects: Using "double-row scaffolding" or "stirrup" as the only force system, the entire load of the cut beam section is instantaneously transferred to the scaffolding, which needs to be designed according to the full-span load, resulting in steel consumption ≥ 150 kg / m 2 ; The scaffolding vertical rods are densely arranged, and the forklift cannot directly enter the beam bottom, requiring secondary transportation, increasing the risk of one-time lifting.

[0007] Cutting sequence defects: Using horizontal segmented cutting, the cut is in the shape of a "one", and after cutting, the main reinforcement is completely disabled without any "second insurance". The weight of the cutting section is not strictly controlled, and large blocks of more than 10 t often occur, which exceeds the rated load of the automobile crane on the trestle board, resulting in the risk of overload.

[0008] Defects in temporary process hole setting: Only round holes are opened on the side of the beam for the saw blade to pass through, without considering the chain saw rotation radius and cooling water return, and the chain is often stuck or broken due to hole position deviation on site.

[0009] Defects in water stop and drainage: The cooling water is directly discharged into the foundation pit, carrying a large amount of cement slurry, blocking the dewatering well point, causing the water level outside the pit to rise, and inducing sudden gushing. SUMMARY

[0010] The present application aims to overcome the defects of the prior art and provide a deep foundation pit reinforced concrete internal support beam demolition construction method, which solves the problems of low safety, low efficiency, and large material consumption in the traditional deep foundation pit reinforced concrete internal support beam demolition method.

[0011] To solve the above technical problems, the present application is implemented as follows: A deep foundation pit reinforced concrete internal support beam demolition construction method, characterized in that it comprises: a) presetting a cutting partition line on the beam body to be demolished, so that each partition forms a to-be-demolished unit not greater than the rated load of the on-site hoisting equipment; b) retaining at least one original structure main reinforcement on the top of each to-be-demolished unit without cutting, to form a temporary suspended load-bearing system of the unit during cutting; c) setting a movable and height-adjustable steel bracket under the overhanging end of the to-be-demolished unit or the end of the adjacent undemolished section, and wedging with the beam bottom to form a local stress support point that works cooperatively with the temporary suspended load-bearing system; d) cutting the concrete and part of the reinforcement in an inverted V-shaped trajectory from bottom to top, so that the center of gravity of the cut unit shifts to the inside of the foundation pit, and remains instantaneously stable under the combined action of the temporary suspended load-bearing system and the steel bracket; e) using a forklift to directly lift the cut unit, cutting the remaining reinforcement, and then transporting it to the hoisting point and outside, and then removing the steel bracket for the next unit cycle; Wherein, the whole process does not need to set up full support or double-row scaffolding, and the temporary suspended load-bearing system, steel bracket, and inverted V-shaped cutting trajectory jointly constitute a complete safety-economy integrated construction method for deep foundation pit reinforced concrete internal support beam demolition.

[0012] The weight of the unit to be demolished is determined by the following steps: taking the lattice column spacing, the beam cross-sectional size, the concrete weight and the rated load of the on-site automobile crane on the trestle board as variables, establishing a load-length inversion model, and multiplying the obtained theoretical length by a safety reduction factor of 0.85-0.90 to obtain the final cutting length.

[0013] The deep foundation pit reinforced concrete internal support beam demolition construction method, characterized in that: the temporary suspension bearing system is composed of one Φ25 main reinforcement on each side of the upper end of the beam body, which continues to bear the weight of the unit to be demolished until the forklift completely supports the bottom after cutting is completed, and the tensile bearing capacity is checked by the following formula: F R = 2 × (πd 2 / 4) × f yk / γ s ≥ 1.5 × G unit Wherein: d is the diameter of the main reinforcement, f yk is the standard value of the yield strength of the main reinforcement, γ s is the safety factor of the steel material, and G unit is the weight of the unit to be demolished.

[0014] The deep foundation pit reinforced concrete internal support beam demolition construction method, characterized in that: the movable steel bracket is composed of standard channel steel and angle steel connected by high-strength bolts or quick locking pins, the top beam is provided with replaceable wooden wedge pads, and the bottom is provided with universal rollers or sliding shoes to realize overall translation under the traction of manual or forklift.

[0015] The deep foundation pit reinforced concrete internal support beam demolition construction method, characterized in that: the inverted V-shaped cutting track forms an inwardly converging inclination angle of 5°-20° in vertical projection, and the cutting starting point is located within 1 / 8-1 / 6 of the cross-sectional height of the beam body, so that the horizontal displacement of the cut unit is controlled within 10 mm.

[0016] The deep foundation pit reinforced concrete internal support beam demolition construction method, characterized in that: a φ40 mm process hole is drilled on the side of the beam body continuous wall once before cutting, and the concrete is removed from the upper main reinforcement on the inside of the surrounding purlin with a pneumatic pick, so that the chainsaw rope penetrates from below the retained main reinforcement, ensuring that the sawing track and the retained main reinforcement do not interfere with each other.

[0017] The deep foundation pit reinforced concrete internal support beam demolition construction method, characterized in that the forklift bottom supporting process comprises: a) The front end of the forklift fork is provided with an adjustable height rubber pad to avoid point contact damage to the concrete; b) The fork insertion depth is not less than 2 / 3 of the section height of the unit to be disassembled, and a detachable counterweight is added to the rear axle of the forklift to ensure the stability of the whole machine under an 8t load.

[0018] The deep foundation pit reinforced concrete internal support beam dismantling construction method is characterized in that: an independent water supply and drainage system is arranged in the dismantling operation area, wherein each chain saw is supplied with water through a 10mm-diameter hose for cooling, and cutting sewage is treated by a site sedimentation tank and then reused or discharged in compliance with regulations to prevent the dewatering well of the foundation pit from being blocked.

[0019] The deep foundation pit reinforced concrete internal support beam dismantling construction method is characterized in that: a temporary steel wire rope lifeline is arranged at both ends of a unit that has been cut but not lifted yet, the steel wire rope has a diameter of not less than 12mm, and is fixed on a pre-buried lifting ring on the top of the beam or an adjacent undismantled beam section through a reusable clamp to provide personnel access and operation anti-falling protection.

[0020] The deep foundation pit reinforced concrete internal support beam dismantling construction method is characterized in that: the steel bracket, the steel wire rope lifeline and the sedimentation tank assembly are all standard modules that can be recycled, can be integrally hoisted to the next dismantling operation surface, have a recycling rate of not less than 90%, and no full scaffolding is left on site after the dismantling is completed, meeting the requirements of green construction.

[0021] The deep foundation pit reinforced concrete internal support beam dismantling construction method provided by the application can ensure the safety and stability of the dismantling process through precise measurement and laying of a line, opening of a process hole, arrangement of a steel bracket, use of a steel wire rope railing and other measures.

[0022] The original upper main reinforcement of the reinforced concrete internal support is used as a fixing measure after cutting, and inverted V-shaped cutting is adopted, further reducing the risk of overturning, saving labor and materials, avoiding the consumption of excessive stirrups and steel materials, and having good economic value and practical application value. BRIEF DESCRIPTION OF DRAWINGS

[0023] The application will be further described in detail below in combination with the drawings and embodiments: Figure 1 Cutting diagram Figure One .

[0024] Figure 2 Cutting diagram Figure Two . DETAILED DESCRIPTION

[0025] The technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the scope of the present application. Embodiment 1 As shown in Figure 1 、 2 : A deep foundation reinforced concrete inner support beam demolition construction method, the steps are as follows: Step one: When measuring and laying the cutting line, the support cutting line should be accurately marked according to the cutting block line planned in the construction organization design, so as to ensure the safety of cutting and hoisting construction.

[0026] Step two: Cutting process hole is opened to expose the upper main reinforcement of the beam. In order to ensure the cutting construction of the ring beam, a cutting process hole of φ40 is opened outside the ring (on one side of the continuous wall) before cutting, which is used for the installation of cutting chain.

[0027] Step three: Lower type steel drag frame of concrete support, gap between concrete supports is firmly padded with square wood.

[0028] Step four: Steel wire rope handrail setting. Considering the safety of walking and construction operation of construction personnel, steel wire rope lifeline is set on both sides of the support beam.

[0029] Step five: Water and electricity connection for cutting. The chain saw is used to cut from bottom to top, and the upper main reinforcement of the beam is not broken.

[0030] Step six: Forklift inserts into the beam bottom, holds the concrete block tightly upwards, and then forks the concrete block to the hoisting position after cutting the steel bar with gas cutting, and then hoists and transports the concrete block to the outside of the vehicle for external transportation.

[0031] Step seven: Fork out the cut concrete block and transport it to the designated hoisting position for external transportation.

[0032] Step eight: Clean up and transport the construction waste on site.

[0033] 1) Measurement and setting out Mark the cutting line according to the calculation. The cutting weight is controlled within 8 tons for each section. Use red paint to mark the line. The cutting weight should be divided into several sections according to the support length between the lattice columns, and be flexibly controlled.

[0034] 2) Provide the power connection position of the total power supply box for construction. In order to facilitate construction, multiple power supply total distribution boxes can be arranged according to the actual situation on site.

[0035] Power supply for diamond chain saw: 380V~50 / 60 Hz 3P+N+PE or 3P+PE (AC).

[0036] 3)Construction water a. Cutting reinforced concrete requires water cooling. A device requires only a 10mm water pipe. The total water supply depends on the number of construction devices and the use time. Each device is connected to a water pipe.

[0037] b. The drainage system should be arranged according to the actual situation on site. Do not discharge cooling sewage at will.

[0038] 4)Steel drag bracket: steel drag bracket is made of channel steel and angle steel. The height of the steel drag bracket is determined according to the distance between the support lower surface and the operating distance. In order to facilitate movement, the connection method is a combination of welding and screw connection. The gap between the steel drag bracket and the support is filled with wood.

[0039] 5)Cutting construction process and step: mark the cutting line and open the process hole.

[0040] First, determine the length between the two lattice structures and the support section. The support cutting weight is less than 8 tons. Determine the number of support sections between the lattice structures and mark the cutting line. In order to ensure that the support does not fall during cutting construction, a process hole should be opened. One main reinforcement is reserved on each side of the upper end of the support. The process hole is opened using a pneumatic pick to remove the concrete on both sides. The upper end of the inside of the surrounding purlin is removed using a pneumatic pick to expose the upper main reinforcement. A 4cm diameter air drill is used to drill through the support beam near the continuous wall. The sawing rope passes through the reserved main reinforcement from below. The other side has a vertical hole. In order to ensure safety, the hanging reinforcement of the surrounding purlin should not be cut off before removing the surrounding purlin.

[0041] The support between the lattice columns is cut into two sections. The knife cut is inverted V-shaped. The first section is removed first. The second section is supported by a steel drag bracket, which is used to support the cantilever beam.

[0042] After the forklift forks the first section, the steel drag bracket supports one end of the second section. The main reinforcement on the upper surface of the two ends of this section is burned off using a gas cutting gun. The beam is short-hauled to the hoist position on the skid, and the section is placed on the skid. Wait for the crane to hoist the section to the ground and load it onto the truck for disposal. After the forklift returns, the second section is short-hauled to the hoisting point.

[0043] The support between the lattice columns is cut into three sections (the first section is in the middle, and the second and third sections are on both sides of the first section).

[0044] The inverted V-shaped cutting edge is first taken ① section, ② section and ③ section are supported by the steel drag support, the steel drag support is used for supporting the cantilever beam. After the forklift forks ① section, the steel drag support supports one end of ② section and ③ section, the gas cutting gun is used to burn off the main reinforcement reserved on the support of the two ends of ① section, the short barge is taken to the lifting position by the forklift, and is placed on the cushion wood, and then the section is lifted to the ground by the crane and is transported out for disposal. After the forklift returns, ② section is taken to the lifting point, and finally ③ section is taken to the lifting point and is lifted to the ground. The steel drag support is mainly used for supporting the cantilever end. Through the following safety check, ① section does not need to be supported. The safety calculation of the cutting section reserves two main reinforcements at each end, and the bearing capacity is calculated according to the main reinforcement diameter of 25, as follows: The truck is parked on the trestle board or the edge of the foundation pit, the concrete blocks cut in the foundation pit are lifted to the ground, and are transported out for disposal. This process is relatively dangerous, and a special person is required to command the lifting work during the lifting operation. The crane operator must strictly follow the crane operation rules to carry out the lifting operation, and is prohibited from violating the command and operation.

[0045] Specifically, the present application changes the "full-span full-frame scaffold" to a "movable steel drag support + reserved main reinforcement" combined force system: Only the steel drag support (channel steel + angle iron welding / bolt connection) is arranged under the cantilever end or the remaining section after the segmented cutting, and the height is adjusted according to the actual gap, which can be tightly plugged with square wood.

[0046] The cutting weight of each section is less than or equal to 8 t, the design load of the drag support is significantly reduced, and the amount of steel is reduced to less than 1 / 3 of the full-frame support.

[0047] There is no vertical pole obstacle at the bottom of the drag support, the forklift can directly drive into the beam bottom, saving the secondary transportation, and solving the problems of large amount of steel and large space occupation of the full-frame support.

[0048] Secondly, one main reinforcement is reserved on each side of the upper end of the support beam before cutting, forming a "steel lifting rod" effect: The calculation shows that the tensile bearing capacity of 2xΦ25 main reinforcement is greater than the weight of 8 t concrete block x safety factor, meeting the requirements of temporary suspension.

[0049] The inverted V-shaped cutting edge (first inside and then outside) moves the center of gravity of the concrete block inward, reduces the overturning moment, and forms a "double insurance" together with the reserved main reinforcement, solving the problem of complete failure of the main reinforcement after cutting and no secondary insurance.

[0050] Further, the principle of "segmented weight ≤8 t" is clarified: First, the section length is calculated according to the lattice column spacing and beam section, and the cutting line is marked with red paint; If the lattice column spacing is larger, the whole span is divided into three sections, ensuring that the weight and size of each section are within the rated load range of the truck crane trestle board, solving the problem of uncontrollable cutting section weight and overloading during hoisting.

[0051] Then, set up the combination process of "φ40 cutting process hole + pickaxe chiseling": The φ40 air drill is used to form a hole on the side of the continuous wall to ensure the accuracy of the chain saw rope trajectory; The upper concrete inside the surrounding purlin is removed by pickaxe to expose the main reinforcement, providing a sawing rope channel and serving as an inspection port for retaining the main reinforcement, avoiding blind threading, and solving the problems of inaccurate process hole positioning, chain jamming, and chain breaking.

[0052] Finally, a "point-to-point water supply + centralized drainage" system is established: Each chain saw is independently connected to a 10mm water pipe, and the water consumption is controllable; A sewage collection trench and sedimentation tank are set up on site, and the cooling water is reused after sedimentation or discharged in accordance with regulations to prevent mud from entering the dewatering system and solve the problem of random cooling sewage discharge and clogging of dewatering wells.

[0053] The application also sets up "steel wire rope lifeline" on both sides of the support beam to replace the traditional steel pipe railing: Installation / removal only requires buckle fixation, and the material can be recycled; it does not invade the forklift walking area, reducing additional scaffolding, and solving the problems of personnel passage and the lack of operation platform.

[0054] Example 2 A subway station deep foundation pit has a plan size of 180m×22m and an excavation depth of 17.8m; the internal support system uses three steel reinforced concrete ring beams + counter beams, among which the second counter beam has a cross section of 800mm×1000mm, C35 concrete, and 10Φ25 main reinforcement on the upper and lower parts. The beam span is 9.0m and is located between the two lattice columns. The truck crane (50t) walks on the trestle board, which has a rated lifting capacity of 10t at this location, considering a 1.25 dynamic load factor, allowing a maximum lifting weight of 8t.

[0055] Step 1: Cutting partition and calculation (1) Take the concrete unit weight as 25 kN / m 3 , the beam self-weight as 0.8×1.0×25=20 kN / m; (2) Allowable length L=8t / 20 kN / m=4.0 m; (3) The 9m span is divided into three sections: ①2.8m, ②3.2m, and ③3.0m, all of which are less than 4.0m, meeting the requirements.

[0056] Step 2: Setting out and process hole Cutting line is set out at the top of the beam with total station instrument and marked with red paint. A φ40 mm hole is drilled with air drill at 50 mm inside the cutting line on the side of the continuous wall, with the center of the hole being 150 mm above the top of the beam. Then, the hole is chiseled with air pick inside the surrounding purlin to expose the upper row of main reinforcement and confirm that 2Φ25 is reserved.

[0057] Step 3: Fabrication and positioning of movable steel bracket (1) The main limb of the bracket is composed of double-spliced [16a channel steel column, 1.5 m high; double-spliced 12 channel steel, 1.2 m long; the column and the beam are connected by 10.9S M20 high-strength bolts, and 10 mm steel plates are welded at the bottom and 4 φ80 mm universal wheels are provided; (2) A 50 mm x 100 mm square wood is laid on the top and wedged tightly to ensure no gap with the beam bottom; (3) The self-weight of the bracket is 0.25 t, the bearing capacity is calculated to be >12 t, and the safety factor is ≥3.

[0058] Step 4: Inverted V-shaped cutting A 380V hydraulic chain saw is used to cut from bottom to top; the saw rope is inserted from the φ40 hole and forms an inverted V-shaped cutting edge from bottom to top, with an internal convergence angle of 12°. The chain saw uses 6 L / min of water during cutting, which is connected to the on-site three-stage sedimentation tank through a φ10 hose.

[0059] Step 5: Forklift lifting and transfer After cutting is completed, the remaining 2Φ25 main reinforcement is still suspended in the unit. The forks of the 50-type forklift are lengthened to 2.4 m, with a 20 mm rubber pad at the front end, and the insertion depth is 0.75 m; a 2 t counterweight is installed on the rear axle of the forklift, and the whole machine is stable. After the remaining main reinforcement is cut off by gas cutting, the forklift transfers the concrete block to the edge of the trestle board, and a 50 t crane directly loads it onto the truck for external transportation.

[0060] Step 6: Circulation and turnover The bracket is slid to the next unit as a whole by the forklift; the steel wire lifeline is fixed again using the original lifting ring; the sedimentation tank sludge is cleaned once per shift, and the reuse rate of supernatant is 85%.

[0061] Implementation effect A 9 m single-span beam is completed by a three-person team in 6 hours; compared with the traditional full-frame scaffold scheme, about 2.1 t of steel is saved, 4 workdays of labor are reduced, there is no scaffold left on site, and the requirements of the "Green Construction Guidelines" are met.

[0062] Example 3 If the lattice column spacing is 12 m, it needs to be divided into four sections according to the calculation, the cutting sequence and bracket setting are the same as in Example 2, only the bracket height is adjusted to 2.0 m, and the rest of the parameters remain unchanged, achieving the same goal of safety, efficiency, and low consumption.

[0063] By adopting the above technical solution, the full-floor scaffolding is replaced by "retaining the main reinforcement + movable steel bracket". After cutting, the instantaneous load of the beam section is jointly borne by the main reinforcement suspension and the bracket, and the risk of instability is reduced by more than 90%; the inverted eight-shaped blade moves the center of gravity of the concrete block inward, and the measured maximum horizontal displacement is ≤5mm, avoiding the sudden outward tilt caused by traditional horizontal cutting; there are no densely packed vertical poles on site, and the forklift can drive directly to the bottom of the beam, and the risk of secondary transportation and falling from height is simultaneously eliminated.

[0064] Steel usage: Only 12 kg of steel is consumed for each linear meter of support beam removed, which is about 92% less than the full-floor scaffolding solution (about 150 kg / m). A single 180 m foundation pit saves about 25 t of steel. • Labor: A three-person team can complete the project, shortening the construction period from 2 days / span to 0.5 days / span, and reducing labor costs by 70%. • Turnover: Steel brackets, wire rope lifelines, and sedimentation tanks are all standard modules with a turnover rate of ≥90% and no one-time consumption.

[0065] The cooling water reuse rate after three-stage sedimentation is ≥85%, there is no direct sewage discharge on site, and the sediment residue is regularly transported out for brick making; there is no scaffolding erection or dismantling, no welding sparks, and the noise is less than 75 dB, which meets the environmental protection requirements of urban night construction; after the demolition is completed, there is no residue on site, reducing construction waste by about 15 m 3 / across.

[0066] The cutting-lifting-hoisting process is a continuous flow operation, with an average time of 20 minutes per section. The bracket height is adjustable (1.2–2.2 m), suitable for different beam heights and spans. Lattice column spacing of 6–15 m can be quickly adapted by adjusting the segment length, without the need to redesign the support system.

[0067] The "load-length inversion model" is used to precisely control the cutting weight and avoid overloaded lifting. The process holes, inverted eight angles, and bracket structures have been standardized to form an enterprise-level construction method that can be directly copied and promoted to deep foundation pit projects such as subway stations and high-rise building basements.

[0068] In summary, the embodiments have verified the comprehensive advantages of the present invention of "safety, economy, greenness and efficiency" in a real engineering environment, and have significant promotion value.

[0069] The above are only embodiments provided for this application and are not intended to limit this application. Although this application has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application should be included in the scope of protection of this application.

Claims

1. A method for dismantling reinforced concrete inner support beams in a deep foundation pit, characterized in that It includes: a) Preset cutting partition lines on the beam to be demolished so that each partition forms a unit to be demolished that is no larger than the rated load of the on-site lifting equipment; b) At least one main reinforcement of the original structure shall be retained at the top of each unit to be dismantled, so as to form a temporary suspension bearing system for the unit during the cutting process; c) A movable and height-adjustable steel bracket is provided only below the cantilevered end of the unit to be dismantled or the end of the adjacent undismantled segment, and is wedged tightly against the bottom of the beam to form a local load-bearing fulcrum that cooperates with the temporary suspension bearing system; d) cutting the concrete and part of the steel bars in an inverted figure-eight trajectory from bottom to top, so that the center of gravity of the cut unit is shifted toward the inside of the foundation pit, and the temporary suspension bearing system and the steel bracket jointly maintain instantaneous stability; e) Use a forklift to drive directly to the bottom of the beam to lift the cut unit, gas cut the remaining reinforcement and transport it to the lifting point for transportation, then remove the steel bracket to be recycled for the next unit; There is no need to set up full-floor supports or double-row scaffolding during the entire process, and the temporary suspension bearing system, steel bracket and inverted figure-eight cutting track together constitute a complete safety-economic integrated construction method for dismantling the reinforced concrete inner support beams of deep foundation pits.

2. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 1, characterized in that The weight of the unit to be disassembled is determined by the following steps: using the lattice column spacing, beam cross-sectional dimensions, concrete weight, and the rated load of the on-site truck crane on the trestle deck as variables, a load-length inversion model is established, and the resulting theoretical length is multiplied by a safety reduction factor of 0.85 to 0.90 to obtain the final cutting length.

3. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 1, characterized in that: The temporary suspension bearing system consists of a Φ25 main reinforcement retained on both sides of the upper end of the beam. After the cutting is completed, the main reinforcement continues to bear the weight of the unit to be disassembled until the forklift is fully supported. Its tensile bearing capacity is verified by the following formula: F R = 2 × (πd 2 / 4) × f yk / c s ≥ 1.5 × G unit Where: d is the main reinforcement diameter, f yk is the standard value of the main reinforcement yield strength, γ s is the safety factor of steel material, G unit The weight of the unit to be dismantled.

4. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 1, characterized in that: The movable steel bracket is made of standard channel steel and angle steel connected by high-strength bolts or quick locking pins. Its top beam is provided with a replaceable wooden wedge pad, and the bottom is equipped with universal rollers or sliding shoes to achieve overall translation under manual or forklift traction.

5. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 1, characterized in that: The inverted eight-shaped cutting trajectory forms an inward inclination angle of 5° to 20° in the vertical projection, and the cutting starting point is located at 1 / 8 to 1 / 6 of the cross-section height within the center of gravity of the beam section, so as to control the horizontal displacement of the unit after cutting within 10 mm.

6. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 1, characterized in that: Before cutting, a φ40 mm process hole is drilled on the side of the continuous wall of the beam body, and the concrete on the inner side of the purlin is removed with a jackhammer to expose the upper main reinforcement, so that the chain saw rope passes through from under the retained main reinforcement to ensure that the sawing trajectory and the retained main reinforcement do not interfere with each other.

7. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 3, characterized in that The forklift bottoming process includes: a) A rubber pad with adjustable height is installed at the front end of the forklift fork to prevent point contact and damage to the concrete; b) The insertion depth of the forklift shall not be less than 2 / 3 of the cross-section height of the unit to be dismantled, and a removable counterweight shall be installed on the rear axle of the forklift to ensure the stability of the entire machine under an 8t load.

8. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 1, characterized in that: An independent water supply and drainage system is set up in the demolition work area, in which each chain saw is cooled by water supplied through a hose with a diameter of 10 mm. The cutting wastewater is treated in an on-site sedimentation tank and then reused or discharged in compliance with regulations to prevent clogging of the foundation pit drainage well.

9. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 1, characterized in that: Temporary wire rope lifelines are set at both ends of the units that have been cut but not yet lifted. The diameter of the wire rope is not less than 12 mm and it is fixed to the pre-buried lifting rings on the top of the beam or the adjacent undismantled beam section through reusable clamps to provide personnel passage and anti-fall protection for operations.

10. The method for dismantling reinforced concrete inner support beams in a deep foundation pit according to claim 9, characterized in that: The steel bracket, wire rope lifeline and sedimentation tank components are all turnaround standard modules that can be hoisted as a whole to the next demolition work surface, achieving a turnover rate of ≥90%. After the demolition is completed, there will be no scaffolding left on the site, meeting the requirements of green construction.

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