A method for supporting bottom plate mass concrete pouring of an embedded limited space and a distribution system

Abstract

This application relates to the technical field of building construction, and in particular to a method and system for pouring large-volume concrete for a foundation slab embedded in a confined space. It is applicable to complex conditions such as permanent concrete supports embedded within a foundation pit without removal, dense steel lattice columns, and confined upper space. The method includes: dividing the pouring area into zones based on obstacle distribution and the shape of the varying thickness of the foundation slab; pre-embedding independently stressed steel supports in the subbase; connecting the concrete placing machine to the pre-embedded supports via a quick-release structure; employing a sloped layered pushing process and utilizing flexible hoses to deliver concrete into the concealed area; quickly relocating the placing machine to an adjacent zone within 15 minutes of completing each zone; and completing the pouring of the thinner zone before the thicker zone initially sets to eliminate cold joints. The concrete placing system includes a placing machine equipped with a quick-release base, a multi-stage folding telescopic boom, and flexible hoses, and can also be equipped with a track-guided trolley for automatic relocation. This invention solves the technical problem of cold joints caused by excessively long equipment relocation time within confined spaces.

Description

Technical Field

[0001] This application relates to the technical field of building construction, and in particular to a method for pouring large-volume concrete for a base plate that supports an embedded confined space, as well as a concrete placement system. Background Technology

[0002] The foundation slab of super high-rise buildings is usually formed by integral casting of large volume concrete, which requires extremely high continuity of casting. If the joint time of concrete in adjacent areas exceeds the initial setting time, cold joints will be formed, which will seriously affect the structural integrity and waterproof performance of the foundation slab.

[0003] In some super high-rise building projects, the foundation pit support system uses reinforced concrete internal bracing, which is designed as a permanent structure, directly embedded inside the foundation slab and not removed during construction. Simultaneously, the foundation pit is densely packed with steel lattice columns, with the upper support structure retained, resulting in severe division and compression of the working space inside the pit by the permanent bracing, steel lattice columns, and upper structure. Under these conditions, the foundation slab often exhibits a variable thickness shape, thicker in the middle and thinner at the perimeter, with a large volume of concrete poured and a wide coverage area.

[0004] The core technical challenge caused by the above working conditions is that conventional concrete placing booms cannot quickly move to different work positions and continuously cover the entire pouring area in confined spaces. When the placing boom needs to be moved from one work area to another, due to the obstruction of permanent supports and dense steel lattice columns, the disassembly, assembly, and relocation of traditional equipment requires the cooperation of large hoisting machinery, which takes too long. This results in the joint interval between adjacent pouring sections exceeding the initial setting time of the concrete, inevitably forming construction cold joints, which cannot meet the quality requirements for continuous pouring and forming of large-volume concrete slabs.

[0005] Therefore, there is an urgent need for a construction method and supporting equipment that can enable rapid relocation and continuous pouring in a confined space with embedded supports and dense steel lattice columns, so as to ensure continuous forming of the entire area of ​​the variable thickness large volume base plate without cold joints. Summary of the Invention

[0006] The purpose of this invention is to provide a method for pouring large-volume concrete for a base plate with a support embedded confined space, as well as a concrete placing system, to solve the technical problem that the concrete placing machine cannot move quickly within the confined space, resulting in cold joints formed at the joints of adjacent sections exceeding the initial setting time.

[0007] Firstly, this application provides a method for pouring large-volume concrete for a base slab supporting an embedded confined space, employing the following technical solution: A method for pouring large-volume concrete for a base slab supporting an embedded confined space includes the following steps: S1. Delineation of pouring zones: Based on the location of permanent concrete supports in the foundation pit, the distribution of steel lattice columns, and the boundary between the thick and thin sections of the base slab, the base slab pouring area is divided into several pouring zones, with the working radius of the concrete placing boom as the benchmark, and the pouring sequence of each zone is determined. S2. Pre-embedded support positioning and installation: At the predetermined machine position of each pouring section on the base plate, avoiding the positions of permanent supports and steel lattice columns, pre-embedded steel supports are installed. The pre-embedded steel supports are directly fixed to the base plate and do not rely on the permanent support structure for stress. S3. Concrete placing boom installation: Fix the base of the concrete placing boom to the pre-embedded steel bracket and connect it to the concrete conveying pump pipe; S4. Thick section layered pouring: First, pour the thick section in the middle of the base plate using a sloping layered pouring process, with each layer not exceeding 500mm in thickness. During the pouring process, the concrete placing machine uses a flexible material feeding hose to reach the bottom of the permanent support and the shaded area at the base of the steel lattice column to feed the concrete, and works in conjunction with vibration to make the concrete dense. S5. Quick-release relocation and continuation: After the pouring of a single section is completed, the entire concrete placing boom is moved to the adjacent section, and the relocation time shall not exceed 15 minutes. S6. Thin Zone Connection Pouring: Before the thick zone concrete sets, the adjacent thin zone is poured to achieve continuous coverage of the thick and thin zones at the sloping joint before initial setting. S7. Repeat steps S4 to S6 to complete the continuous pouring of all pouring zones in sequence.

[0008] By adopting the above technical solution, and by pre-embedding steel supports in the subbase and using a quick-release structure to connect the concrete placing boom base, the concrete placing boom can complete the dismantling, relocation, and re-fixing of cross-zone sections within 15 minutes without the need for large hoisting equipment. This relocation time is much shorter than the initial setting time of the concrete, thus ensuring that the concrete of adjacent pouring zones completes the overlap and coverage before initial setting, eliminating construction cold joints. At the same time, flexible material delivery hoses are used to deliver material to shielded areas that conventional equipment cannot reach, such as the bottom of permanent supports and the base of steel lattice columns, ensuring the compactness of the concrete filling at the joints. The pre-embedded supports are independently fixed to the subbase, avoiding additional loads and damage to the permanent support structure.

[0009] Preferably, in step S1, the pouring zones are defined based on the working radius of a single concrete placing boom of 1m, and the working coverage of adjacent zones overlaps, with the width of the overlapping area not less than 2m.

[0010] By adopting the above technical solution, an overlapping area of ​​no less than 2m is set between adjacent zones, so that the pouring surfaces of adjacent zones can cross-cover each other in the overlapping area, avoiding blind spots due to geometric errors at the zone boundaries or deviations in the actual operating radius of the concrete placing boom, and ensuring the continuity of concrete at the zone boundaries.

[0011] Preferably, in step S2, the pre-embedded steel support includes an anchoring section embedded in the pad layer and a connecting section extending out of the pad layer surface. The top of the connecting section is provided with a flange connecting plate and a leveling structure for docking with the base of the fabric placing machine.

[0012] By adopting the above technical solutions, the anchoring section embedded in the pad layer provides stable anti-overturning capacity and horizontal shear capacity, enabling the concrete placing boom to remain stable under the action of pumping reaction force and boom rotational inertia; the flange connection plate at the top of the connecting section provides a standardized docking interface, which, together with the leveling structure, can ensure the levelness of the concrete placing boom base when the pad layer surface is uneven, thereby ensuring the accuracy and safety of boom rotation and extension.

[0013] Preferably, in step S4, for the shaded area directly below the permanent support, the following pouring process is adopted: first, the flexible hose is inserted directly below the bottom surface of the support for filling material, and the vibrator is inserted obliquely from the gap of the steel bars on the side of the support for vibration, so that the concrete is squeezed out from the bottom of the support to both sides to release air, until the concrete at the bottom of the support is dense and without voids.

[0014] By adopting the above technical solution, the area directly below the permanent support is the most difficult to fill using conventional pouring methods. When concrete is poured from above, it is easily blocked by the support section, forming cavities and accumulating air bubbles on its bottom surface. By using a flexible hose to penetrate from the side directly below the support bottom surface for targeted filling, and using an obliquely inserted vibrator to squeeze the concrete outwards to release air, a filling path of "from bottom to top and from center to outwards" is formed, effectively eliminating voids in the support bottom surface and preventing the formation of leakage channels later.

[0015] Preferably, in step S5, during the relocation of the concrete placing machine, the concrete surface of the already poured area is subjected to secondary vibration or immersion re-vibration treatment to eliminate the bleeding layer and laitance generated on the concrete surface during the relocation interval.

[0016] By adopting the above technical solution, during the 15-minute interval of the concrete placing boom relocation, the surface of the poured concrete will bleed water and laitance due to its own settlement. If not treated, a weak interlayer will be formed between the subsequent cover layer and the poured layer. By arranging secondary vibration or re-vibration during the relocation interval, the bleed water and laitance will be re-mixed into the concrete or removed to the surface for cleaning, thus ensuring the interlayer bonding strength.

[0017] Preferably, in step S6, a variable cross-section transition zone is provided between the thick and thin areas. During pouring, a stepped layer is used to find the slope in the transition zone. The horizontal extension length of each step is not less than 3 times the thickness of the layer, so that the slope is not greater than 1:3.

[0018] By adopting the above technical solution, there is a thickness difference of up to 3.2m between the thick and thin areas. If a steep slope transition is used, the concrete will slide and flow on the slope due to its own weight, resulting in aggregate separation and slope instability. By controlling the slope to no more than 1:3 and ensuring that the horizontal extension length of each step layer is no less than 3 times the layer thickness, the concrete can be self-stabilized on the slope, avoiding collapse and segregation. At the same time, the stepped layering method makes the area of ​​each layer controllable, which is convenient for vibration compaction.

[0019] Preferably, after step S7 is completed, step S8 is also included: cutting the pre-embedded steel brackets of each pouring section to a depth of not less than 500mm below the design elevation of the bottom plate, and performing rust prevention and waterproof sealing treatment on the cut surface.

[0020] By adopting the above technical solution, the pre-embedded steel bracket serves as a temporary load-bearing component during the construction phase. After the bottom slab concrete is poured, there is no need for it to remain above the bottom slab surface. Cutting it to 500mm below the design elevation of the bottom slab ensures that the flatness of the bottom slab surface meets the requirements of subsequent processes and prevents the exposed steel from rusting and expanding, which could damage the concrete surface layer of the bottom slab. The anti-rust coating and waterproof mortar sealing treatment further block the channels for water to penetrate along the steel interface, ensuring the overall waterproof performance of the bottom slab.

[0021] On the other hand, this application provides a concrete placement system for supporting the casting of an embedded confined space base plate, including a concrete placement machine; the concrete placement machine includes: The base is detachable and has a flange connection structure at the bottom, which is used to connect or disconnect the base to the steel bracket embedded in the pad layer by bolts. The base is equipped with a slewing bearing. A multi-stage folding telescopic boom is hinged above a slewing bearing and includes at least two folding boom sections that are hinged in sequence and a telescopic boom section located within the end folding boom section. The folding boom sections are folded and unfolded by hydraulic cylinders, and the telescopic boom section is extended and retracted by hydraulic cylinders. A flexible discharge hose, connected to the end of the telescopic boom, is used to guide concrete to an area shielded by obstacles. The concrete delivery interface is located at the base or the root of the boom and is used to connect to an external concrete delivery pump pipe.

[0022] By adopting the above technical solutions, the detachable base, through flange bolts and pre-embedded steel brackets, enables the rapid erection and dismantling of the concrete placing boom, meeting the time requirement of cross-zone relocation within 15 minutes; the multi-stage folding telescopic boom has both folding and telescopic movement modes. The folding mode is used to adjust the vertical posture of the boom to adapt to limited clearance, while the telescopic mode is used to pass through the narrow gap between permanent supports and steel lattice columns in the horizontal direction. The combination of the two allows the boom to flexibly avoid and cover all material unloading points in spaces divided by multiple obstacles; the flexible unloading hose at the end provides flexible extension in shielded areas that the rigid boom cannot access, precisely guiding concrete to the bottom surface of the support and the base of the steel lattice column.

[0023] Preferably, it also includes a detachable track, which is laid on top of the cushion layer along the gap between the permanent support and the steel lattice column in the foundation pit; the path of the detachable track passes above the pre-embedded steel support, and the detachable track is fixedly connected to the pre-embedded steel support. The electric-driven traveling trolley, set on the track, includes a drive motor, traveling wheel set and braking mechanism, to achieve reciprocating travel along the track and stop at a fixed point directly above the pre-embedded steel bracket; the concrete placing machine is fixedly installed on the traveling trolley.

[0024] By adopting the above technical solution, the concrete placing machine automatically moves to the next work point along the preset track path, replacing manual handling and relocation with a track and electric-driven trolley. During the relocation process, there is no need to disassemble the base or lift equipment, and the relocation time is further shortened to the trolley travel time (usually 1 to 3 minutes), which greatly improves the connection efficiency between zones and is more conducive to ensuring the timeliness of continuous pouring. The modular design of the detachable track allows it to adapt to the spatial layout of different supports and steel lattice column gaps, and it can be disassembled, recycled and reused after construction.

[0025] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention solves the problem of rapid relocation of the concrete placing boom within confined spaces, eliminating cold joints in construction. By pre-embedding steel supports in the subbase and connecting them to the boom base, the boom can quickly complete the disassembly, transport, and re-fixing across zones. This relocation time is much shorter than the initial setting time of large-volume concrete, ensuring that the concrete in adjacent pouring zones overlaps and covers each other before initial setting. This eliminates cold joints caused by excessively long equipment relocation times, enabling continuous, cold-joint-free casting of large-volume, variable-thickness base slabs throughout the entire area. 2. This invention solves the problem of concrete compaction in the concealed areas of the permanent support base and the base of the steel lattice column. The invention utilizes a flexible discharge hose at the end of the concrete placing boom to deliver concrete directly beneath the permanent support base and into the densely reinforced area at the base of the steel lattice column for targeted filling. This is combined with a vibrator inserted obliquely into the gaps between the reinforcing bars on the support side for air removal and compaction, forming a filling path of "squeezing and venting from the center outwards." This effectively eliminates voids and air pockets in the concealed areas caused by conventional pouring methods, ensuring the structural density and waterproofing performance of the concrete at the joints. 3. This invention achieves an orderly connection between the thick and thin sections of the variable-thickness base plate, avoiding quality defects at the variable cross-section. The invention employs a "thick first, thin later" pouring sequence, controlling the slope gradient to no more than 1:3 in the transition section between the thick and thin sections using a stepped, layered slope-finding method. This ensures the self-stability of the concrete on the slope and avoids landslides and aggregate segregation under steep slope conditions. Simultaneously, strict timing control ensures that the thin section is poured before the thick section concrete initially sets, guaranteeing the integrity of the variable cross-section. 4. The pre-embedded support bears the load independently without damaging the existing permanent structure. In this invention, the pre-embedded steel support is directly anchored in the concrete foundation. The self-weight of the concrete placing boom and the pumping reaction force are transferred to the foundation by the support. It does not rely on permanent supports or steel lattice columns for load bearing, thus avoiding the application of additional loads to the permanent structure or causing surface damage, and ensuring the design safety of the permanent structure. 5. When using a track-based concrete placing system, the concrete placing machine is fixed on an electrically driven trolley and automatically moves along the track, further reducing the moving time. No manual disassembly or reassembly of the base is required, resulting in a high degree of automation, making it particularly suitable for efficient continuous pouring of large-area foundation slabs. Both moving methods can be flexibly selected or combined according to the space conditions within the foundation pit, offering wide adaptability. Attached Figure Description

[0026] Figure 1 This is a flowchart of the process for pouring large-volume concrete for the base slab. Detailed Implementation Example 1

[0027] This embodiment uses a large-volume concrete foundation slab project for a super high-rise building as its application background. The foundation pit is approximately 26m deep, with a core raft slab thickness of 5.0m in the middle and a perimeter podium slab thickness of 1.8m. The total pouring area of ​​the foundation slab is approximately 6000m², and the total concrete volume is approximately 18000m³. The foundation pit adopts a support system of diaphragm walls with internal bracing. The fourth layer of support is a reinforced concrete support with an 800mm×800mm cross-section. This support is designed as a permanent structure, located within the thickness range of the foundation slab, and is not removed during construction; it is directly encased by the foundation slab concrete to form a whole. The third layer of support is a temporary steel support, located approximately 2.4m above the permanent support, and must be retained during the foundation slab pouring stage. Therefore, the clear height from the foundation slab surface to the bottom of the temporary steel support is only approximately 3.2m. A 600mm×600mm steel lattice column is installed approximately every 6m along the longitudinal and transverse directions within the foundation pit as a temporary vertical support.

[0028] The aforementioned working conditions create a three-dimensional confined working environment characterized by horizontal cutting under permanent support, vertical compression under temporary support, and dense interweaving of steel lattice columns within the space. Under these conditions, the foundation slab concrete must be poured continuously in one go, without any construction joints.

[0029] The method for pouring large-volume concrete for supporting a confined space in this embodiment employs a construction method using a mobile concrete placing boom in conjunction with a pre-embedded steel support frame. The specific steps are as follows: I. Delineation of Pouring Zones Based on the planar location of the permanent supports (the supports are spaced approximately 9m apart along the long axis of the foundation pit), the distribution of the steel lattice columns (the longitudinal and transverse spacing is approximately 6m), and the boundary line between the 5.0m thick and 1.8m thin sections of the base plate, the area is divided with the 10m effective working radius of a single concrete placing boom as the benchmark.

[0030] The zoning principles are as follows: each zone is covered by one concrete placing boom position, which is set at the geometric center of the zone or at the front end of the pouring direction; the location of the boom position must meet the safety distance requirements of not less than 1.0m from the side of the nearest permanent support and not less than 0.8m from the outer edge of the nearest steel lattice column; the working coverage of two adjacent zones shall have an overlap area of ​​not less than 2m at the boundary.

[0031] In this embodiment, the total area of ​​the base plate is approximately 6000 m². Based on the theoretical value of approximately 314 m² (with a radius of 10 m) covered by a single concrete placing boom, and considering that the actual effective coverage rate after obstruction is approximately 60%~70%, the plate is divided into approximately 32 pouring zones. The pouring sequence starts from one end of the 5.0 m thick zone in the middle of the base plate, proceeds sequentially along the long axis of the thick zone, and then expands to the thinner zones on both sides after completing the thick zone.

[0032] When determining the pouring sequence, based on the initial setting time determined by the concrete mix proportion test (the concrete in this project adopts a slow-setting mix proportion with an initial setting time of 8 to 10 hours), the maximum allowable pouring time and total relocation time budget for each zone are calculated backwards to ensure that the total time from the start of pouring in the first zone to the completion of the joint coverage of the adjacent zone does not exceed the initial setting time.

[0033] II. Positioning and Installation of Pre-embedded Brackets During the concrete pouring stage of the foundation layer, pre-embedded steel supports are installed at the designated machine locations in each zone. The structure of the steel supports in this embodiment is as follows: Anchorage Section: The pre-embedded steel support consists of four short steel columns, vertically embedded in the concrete foundation. The four short columns are arranged in a rectangle, with the center of the rectangle being the center point of the machine position. Anchoring steel bars are welded to the flanges of each short column to enhance the anchorage force with the concrete foundation. The bottom of the four short columns is welded to a steel base plate, which is placed flat on top of the foundation formwork and poured in together with the foundation.

[0034] Connection Section: Four short steel columns extend 300mm above the pad surface to serve as connection sections. Flange connection plates are installed between the four short columns and welded to them. Bolts are pre-installed on the flange connection plates.

[0035] All 32 pre-embedded steel supports were installed in one go during the foundation stage. After installation, the surface of the short columns was coated with anti-rust paint for protection.

[0036] The pre-embedded steel support is directly anchored to the cushion layer and independently bears the self-weight of the concrete placing boom and the pumping reaction force, without relying on permanent supports or steel lattice columns for load bearing.

[0037] III. Installation of the Concrete Feeding Machine The fabric laying machine used in this embodiment is a specially designed low-profile, multi-stage folding and telescopic fabric laying machine, and its main technical parameters are as follows: The folded height of the entire machine is 2.8m (meeting the 3.2m clearance requirement, with a 0.4m safety clearance at the top). The maximum working radius when the boom is fully extended is 12m (the effective coverage radius after obstruction is approximately 10m). Boom structure: three folding boom sections plus one telescopic boom section. The first boom section is 3.5m long, the second boom section is 3.5m long, and the third boom section is 3.0m long. The third boom section has a telescopic mechanism with a telescopic stroke of 3.0m. Each boom section has a rectangular cross-section, with an outer width of 500mm and a height of 400mm, allowing passage through the side gaps of adjacent permanent supports (with a net width of not less than 800mm, allowing a single boom section to pass through with a safety clearance of not less than 150mm on each side).

[0038] The base flange and flange connecting plate of the fabric placing boom are connected by a quick-release structure. The quick-release structure includes a first adapter plate bolted to the base flange and a second adapter plate bolted to the flange connecting plate. The second adapter plate has bolt holes corresponding to the bolts on the flange connecting plate. A leveling nut is provided on the underside of the second adapter plate for quick leveling, and a fixing nut is provided on the upper side of the second adapter plate for a fixed connection with the flange connecting plate.

[0039] The second adapter plate has a groove at its center, the size of which corresponds to the size of the first adapter plate, allowing the first adapter plate to be completely placed within the groove for quick positioning. The first and second adapter plates are connected by four to six high-strength bolts.

[0040] Installation process: First, install the second adapter plate onto the flange connection plate, level and fix the second adapter plate.

[0041] Use a manual hydraulic pallet trolley (gantry height within 2.0m) to transport the folded concrete placing boom from the pit passage to the vicinity of the machine position. Use a hand chain hoist to lift the concrete placing boom, move it horizontally until it is directly above the flange connection plate, and then slowly lower it. After manually aligning the bolt holes, insert the high-strength bolts one by one and apply the designed pre-tightening torque.

[0042] After installation, connect the concrete delivery pump pipe to the delivery interface on the side of the base, turn on the hydraulic pump station, and test the folding, unfolding, and telescopic movements of each boom section one by one to confirm that the stroke is in place and that there is no interference with the surrounding permanent supports and steel lattice columns during movement in all directions. Perform a 360° test rotation of the slewing bearing and record the clearance at each angle position.

[0043] IV. Thick-layered casting The 5.0m thick section in the middle of the base slab is poured in layers. The key points of the pouring process are as follows: Layering method: A sloping layering process is adopted, in which the concrete is poured forward at an incline from the starting point, with each layer's thickness controlled within 500mm and the slope not exceeding 1:6. The leading edge of each layer extends continuously along the direction of advancement, and the subsequent layer is covered by the next layer of concrete. This method keeps the pouring surface in a flowing state, avoiding planar joints.

[0044] Boom Movement Control: During the pouring process, the boom needs to rotate 360° to cover all areas within the designated zone. When encountering permanent supports on the boom's rotation path, the following avoidance methods are adopted depending on the height and location of the supports: If the support is located within the horizontal rotation plane of the boom, the first boom section remains stationary, the second boom section is folded to raise it over the top surface of the support, or the telescopic boom section is used to pass horizontally through the support gap; if the support is located below the boom and does not affect the rotation, it can be rotated normally. When encountering steel lattice columns on the rotation path, since the column cross-section is only 600mm and the spacing is 6m, and the boom cross-section is 500mm wide, it can pass through the clearance on the side of the column. When passing, the rotation speed should be reduced and the spacing should be observed and confirmed by a designated person.

[0045] Cutting materials in concealed areas: The area directly below the permanent support base and the area with denser stirrups at the base of the steel lattice columns are concealed areas that are difficult to reach using conventional cutting methods. For these areas, the following specialized casting process is adopted: For the area directly beneath the permanent support: The operator uses a remote control to extend the telescopic boom to the side of the support. A 3.0m long flexible discharge hose, made of high-strength steel wire reinforced rubber and covered with a wear-resistant nylon sheath, is manually connected to the hose. The hose end is inserted through the bottom space of the support side directly beneath the support surface. The height of the hose end from the poured concrete surface is controlled within 0.5~1.0m to reduce the impact of falling concrete and prevent aggregate segregation. After pumping is started, concrete is poured directly into the cavity below the support surface through the hose. Simultaneously, the vibrator operator inserts a vibrator at a 30°~45° angle into the area below the support surface through the gaps between the horizontal reinforcing bars on the side of the support (gap not less than 100mm) for thorough vibration. Under the action of vibration, the concrete spreads and flows from the center of the support surface outwards, squeezing out any air bubbles accumulated on the support surface. Continue feeding and vibrating until concrete can be observed overflowing from the bottom of the support and level with the surrounding concrete surface from both sides and ends. At this point, it is confirmed that the bottom of the support has been completely filled and compacted.

[0046] For the base area of ​​steel lattice columns: The column base is typically equipped with denser stirrups spaced 100-150mm apart. A flexible hose can be inserted through the gaps in the stirrups to allow material to be poured into the column base. The pouring speed should be appropriately reduced (controlling the pumping rate to 60%-70% of normal flow rate) to avoid high-speed impact causing misalignment of the reinforcement at the column base. A vibrator should be inserted through the gaps in the stirrups for compaction, with each point vibrating for at least 20 seconds, until the concrete surface no longer shows significant settling and no more large air bubbles escape.

[0047] The flexible hose extends from below the permanent support side into the bottom surface of the support for filling, and is inserted obliquely through the gaps in the steel bars on the side of the support to form a filling path for air release from the center outward.

[0048] V. Quick-release relocation and connection Once the pouring of a section meets the design requirements, the concrete placing boom is quickly relocated. The relocation procedure is as follows: Stop pumping and close the pump outlet valve. The operator disconnects the connector between the end flexible hose and the boom end. Retract the boom to its fully folded position. Pull out the quick-release pin of the quick-release mechanism; at this point, the concrete placing boom base detaches from the pre-embedded bracket.

[0049] Use a hydraulic pallet truck to lift the entire placing boom off the flange and move it horizontally to the pre-embedded bracket position in the adjacent section (the moving distance is usually 6~12m, and the moving time is about 3 minutes). At the same time, remove the second connecting plate from the original position and install it in the new position. Lower the placing boom into the new position, align it, and secure it. Reconnect the pump pipe and the end hose.

[0050] In actual construction operations, the entire process takes approximately 13 to 14 minutes, which meets the relocation time requirement of less than 15 minutes.

[0051] During the relocation, the concrete surface of the already poured area will develop a layer of bleed water and laitance due to cement particle settling and water rising. During construction, two workers will perform a secondary re-vibration treatment on the poured surface during the relocation: using an immersion vibrator, insert it into the surface of the poured layer in a quincunx pattern, with an insertion depth of 50-100mm, vibrating for 5-10 seconds at each point to break up the surface bleed layer and reintegrate the laitance into the concrete. After re-vibration, any remaining surface water will be removed with a sponge or absorbent material.

[0052] VI. Thin-zone connection pouring When the thick section pouring progresses to the variable cross-section transition zone adjacent to the 1.8m thin section, the connection pouring shall be carried out according to the following process: The elevation difference between the 5.0m thick section and the 1.8m thin section in this project is 3.2m, with a variable cross-section transition zone between them. The horizontal length of the transition zone is approximately 10m (determined according to the structural design drawings). A stepped, layered slope-finding method is used in the transition zone: each layer maintains a thickness of 500mm, but the horizontal extension endpoint of each layer is recessed by at least 1500mm towards the thinner section compared to the previous layer (i.e., the horizontal extension length is not less than 500mm × 3 = 1500mm), thus forming a stepped slope with a gradient not exceeding 1:3.

[0053] After the last layer of the thick section is poured, the concrete placing boom is moved to the corresponding position in the thin section (or the boom's operating radius is used to directly cover the adjacent thin section area), and then the thin section is poured. The thickness of each layer in the thin section also does not exceed 500mm. Since the total thickness of the thin section is 1.8m, only 4 layers are needed to reach the design elevation.

[0054] Key timing control: The time interval from the completion of the last layer of the thick transition zone to the first layer of thin concrete covering the toe of the transition zone slope must be strictly controlled within the initial setting time of the concrete. The initial setting time of the concrete in this project is 8-10 hours, and the above time interval is usually 1-2 hours (including the displacement time), which meets the requirements.

[0055] VII. Continue pouring until completion. Following the predetermined zoning order and pouring sequence, repeat steps four through six to complete the continuous pouring of all 32 pouring zones. Throughout the process, a designated person records the start and end times of pouring for each zone, the relocation time, and the time interval between adjacent zones to ensure that all joints are covered within the initial setting time.

[0056] After all the pouring is completed, the base slab achieves a seamless, integral shape with no construction cold joints throughout the entire area.

[0057] 8. Post-treatment of embedded supports After the base slab concrete is poured and cured to the design strength, the embedded steel supports extending from the base slab at each machine location are treated: the connecting steel sections are cut using an oxy-acetylene torch to 50mm below the design elevation of the base slab. The cut surfaces are then ground smooth with an angle grinder to remove burrs and oxide layers, and two coats of epoxy zinc-rich anti-rust primer are applied. After the anti-rust paint dries, polyurethane waterproof sealant is filled into the cut recesses, and then high-strength waterproof mortar is applied to seal the surface until it is flush with the base slab. Example 2

[0058] The engineering conditions in this embodiment are the same as in Embodiment 1. The difference from Embodiment 1 is that the concrete placing machine does not adopt a quick-release movement method for each machine position, but is fixedly installed on an electrically driven traveling trolley. The trolley is set on a detachable track and travels along a preset path. The rapid transfer of the concrete placing machine between different zones is achieved by the movement of the trolley.

[0059] The fabric system in this embodiment is configured as follows: Detachable track: Steel rails with a gauge of 1.0m are used. The track is composed of multiple segments spliced ​​together, with adjacent segments quickly connected using fishplates and high-strength bolts. A set of sleepers is installed at the bottom of the track every 1.0m, and the sleepers are fixed to the foundation surface using expansion bolts. The track is laid along the passageway between permanent supports within the excavation pit. The route selection principle is: the centerline of the track should be at least 0.8m from the side of the nearest permanent support and at least 0.6m from the outer edge of the nearest steel lattice column to ensure that the trolley does not collide with obstacles during passage.

[0060] In this embodiment, based on the layout of the foundation pit, two main tracks are laid along the long axis of the base slab, each track being approximately 80m long, covering all sections along the length of the base slab. In areas requiring coverage in the width direction, a concrete placing boom with a 10m operating radius is used to cover both sides.

[0061] Electric-driven trolley: The trolley is a four-wheeled steel structure. It is driven by a variable frequency speed-regulating motor that drives two drive wheels. The travel speed is 0~10m / min, infinitely adjustable. The trolley is equipped with an electromagnetic brake that locks the drive wheels when stopped at a designated point. A connecting flange is located on top of the trolley to mate with the concrete placing boom base. The concrete placing boom is bolted to the top of the trolley and remains attached throughout the construction process.

[0062] Fabric feeding machine main unit: The structural parameters are the same as in Example 1, including a multi-stage folding telescopic boom and a flexible end feed hose. The base and the trolley are fixedly connected, eliminating the need for a quick-release function.

[0063] Concrete pump pipe connection: The pump pipe is led out from the fixed pump station at the edge of the foundation pit and laid along one side of the track. A swivel joint is provided at the trolley connection point, allowing the pump pipe to turn with the trolley without twisting. A quick-connect branch port is provided every 10m on the main pipe, and the trolley is connected to the branch port through a flexible hose when it reaches the corresponding position.

[0064] The construction steps are as follows: Step 1: Track Laying: After the subgrade is completed and before the bottom slab reinforcement is tied, measure and mark the track route on the subgrade according to the design. Install sleepers and expansion bolts, and lay the track section by section, connecting them with fishplates. After laying, check the track flatness and gauge. The track surface elevation deviation should not exceed ±3mm, and the gauge deviation should not exceed ±2mm. The path of the detachable track passes above the pre-embedded steel support, and the detachable track is fixedly connected to the pre-embedded steel support with track bolts.

[0065] Step 2: System Installation and Debugging: Place the electric-driven trolley onto the track, and install and secure the concrete placing boom above the trolley. Connect the electrical and hydraulic lines, and connect the pump pipes. Perform a no-load test run of the trolley along the track to check the smoothness of movement and the reliability of braking. Conduct a boom deployment test at each preset stopping point to confirm there are no obstructions.

[0066] Step 3, Pouring Operation: Drive the trolley to the first stopping point (the center of the first section of the thick area), and lock the electromagnetic brake. Extend the boom to perform layered pouring, using the same pouring process as the inclined layered pushing process and the special pouring process for the shielded area in Step 4 of Example 1.

[0067] Step 4, Moving and Relocating: After the area covered by the current stopping point is poured, the boom is retracted to the folded state, the brake is released, and the trolley moves along the track to the next stopping point (the walking distance is usually 8~12m, and the relocation time is about 1.5~2.5 minutes at a walking speed of 5m / min). After re-braking, the boom is extended to continue pouring.

[0068] Since the trolley relocation time is only 1.5 to 2.5 minutes, which is much shorter than the 13 to 14 minutes manual quick-release relocation time in Example 1, the guarantee of continuous pouring sequence is more sufficient.

[0069] Step 5, Thin Zone Connection Casting: The process is the same as Step 6 in Example 1. When the trolley reaches the stopping point at the junction of the thick and thin zones, the working radius of the concrete placing boom is used to simultaneously cover the edge of the thick zone and the starting section of the thin zone, achieving a seamless connection.

[0070] Step Six: Cyclic Pouring: The trolley stops at the corresponding points of each zone along the track in sequence, repeating the pouring and moving actions until all zones are poured.

[0071] Step 7: System Dismantling: After all pouring is completed, lift the concrete placing boom and trolley off the track. Dismantle the fishplate section by section, removing the track and pulling out the sleeper expansion bolts. Seal the sleeper bolt holes with waterproof mortar. After cleaning and maintenance, all equipment and tracks are recycled and stored for reuse in similar projects.

[0072] Compared to Example 1, Example 2 features extremely fast relocation speed (1.5~2.5 minutes), requires no manual handling, has a high degree of automation, and significantly improves the efficiency of continuous pouring of large-area base slabs. The disadvantage is that it requires pre-laying of tracks, has certain requirements for the continuity and straightness of the channel, and may not be possible to lay tracks in local areas where the supports and steel lattice columns are densely or irregularly arranged.

[0073] However, since Implementation Example 1 does not require the laying of tracks, it has lower requirements for the width of the passage in the foundation pit, making it highly adaptable and suitable for working conditions where the arrangement of supports and steel lattice columns is extremely irregular and continuous tracks cannot be laid.

[0074] In actual engineering projects, two schemes can be flexibly selected or combined according to the space conditions in the foundation pit: the track-walking type is used in the main passage area where the laying conditions are available, and the detachable and movable type is used in the locally restricted area.

[0075] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for pouring large-volume concrete for a base slab supporting an embedded confined space, characterized in that, Includes the following steps: S1. Delineation of pouring zones: Based on the location of permanent concrete supports in the foundation pit, the distribution of steel lattice columns, and the boundary between the thick and thin sections of the base slab, the base slab pouring area is divided into several pouring zones, with the working radius of the concrete placing boom as the benchmark, and the pouring sequence of each zone is determined. S2. Pre-embedded support positioning and installation: At the predetermined machine position of each pouring section on the base plate, avoiding the positions of permanent supports and steel lattice columns, pre-embedded steel supports are installed. The pre-embedded steel supports are directly fixed to the base plate and do not rely on the permanent support structure for stress. S3. Concrete placing boom installation: Fix the base of the concrete placing boom to the pre-embedded steel bracket and connect it to the concrete conveying pump pipe; S4. Thick section layered pouring: First, pour the thick section in the middle of the base plate using a sloping layered pouring process, with each layer not exceeding 500mm in thickness. During the pouring process, the concrete placing machine uses a flexible material feeding hose to reach the bottom of the permanent support and the shaded area at the base of the steel lattice column to feed the concrete, and works in conjunction with vibration to make the concrete dense. S5. Quick-release relocation and continuation: After the pouring of a single section is completed, the entire concrete placing boom is moved to the adjacent section, and the relocation time shall not exceed 15 minutes. S6. Thin Zone Connection Pouring: Before the initial setting of the thick zone concrete, the adjacent thin zone is poured to achieve continuous coverage of the thick and thin zones at the sloping overlap before initial setting. S7. Repeat steps S4 to S6 to complete the continuous pouring of all pouring zones in sequence.

2. The method for pouring large-volume concrete for a base slab with an embedded confined space according to claim 1, characterized in that: In step S1, the pouring zones are defined based on the working radius of a single concrete placing boom of 1m. The working coverage of adjacent zones overlaps, and the width of the overlapping area is not less than 2m.

3. The method for pouring large-volume concrete for a base slab with an embedded confined space according to claim 1, characterized in that: In step S2, the pre-embedded steel support includes an anchoring section embedded in the pad layer and a connecting section extending out of the pad layer surface. The top of the connecting section is equipped with a flange connecting plate and a leveling structure for docking with the base of the fabric placing machine.

4. The method for pouring large-volume concrete for a base slab with an embedded confined space according to claim 1, characterized in that: In step S4, for the shaded area directly below the permanent support, the following pouring process is adopted: First, the flexible hose is inserted directly below the bottom surface of the support for filling and pouring. The vibrator is inserted obliquely from the gap of the steel bars on the side of the support for vibration, so that the concrete is squeezed out from the bottom of the support to both sides to release air, until the concrete at the bottom of the support is dense and without voids.

5. The method for pouring large-volume concrete for a base slab with an embedded confined space according to claim 1, characterized in that: In step S5, during the relocation of the concrete placing boom, the concrete surface of the already poured area is subjected to secondary vibration or immersion re-vibration treatment to eliminate the bleeding layer and laitance generated on the concrete surface during the relocation interval.

6. The method for pouring large-volume concrete for a base slab with an embedded confined space according to claim 1, characterized in that: In step S6, a variable cross-section transition zone is provided between the thick and thin zones. During pouring, a stepped layering slope is used in the transition zone. The horizontal extension length of each step layer is not less than 3 times the thickness of the layer, so that the slope is not greater than 1:

3.

7. The method for pouring large-volume concrete for a base slab with an embedded confined space according to claim 1, characterized in that: After step S7 is completed, step S8 is also included: cut the pre-embedded steel brackets of each pouring section to a depth of not less than 500mm below the design elevation of the bottom plate, and perform rust prevention and waterproof sealing treatment on the cut surface.

8. A fabric placement system for supporting the casting of a base plate embedded in a confined space, characterized in that, Includes a placing boom; the placing boom includes: The base is detachable and has a flange connection structure at the bottom, which is used to connect or disconnect the base to the steel bracket embedded in the pad layer by bolts. The base is equipped with a slewing bearing. A multi-stage folding telescopic boom is hinged above a slewing bearing and includes at least two folding boom sections that are hinged in sequence and a telescopic boom section located within the end folding boom section. The folding boom sections are folded and unfolded by hydraulic cylinders, and the telescopic boom section is extended and retracted by hydraulic cylinders. A flexible discharge hose, connected to the end of the telescopic boom, is used to guide concrete to an area shielded by obstacles. The concrete delivery interface is located at the base or the root of the boom and is used to connect to an external concrete delivery pump pipe.

9. The fabric placement system for supporting the casting of an embedded confined space base plate according to claim 8, characterized in that, It also includes a detachable track, which is laid on top of the cushion layer along the gap between the permanent support and the steel lattice column in the foundation pit; the path of the detachable track passes above the pre-embedded steel support, and the detachable track is fixedly connected to the pre-embedded steel support. The electric-driven trolley, set on the track, includes a drive motor, a set of wheels and a braking mechanism, to achieve reciprocating movement along the track and stop at a fixed point directly above the pre-embedded steel support. The fabric laying machine is fixedly installed on the traveling trolley.

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