A secondary pouring forming construction method of a deep pile raft foundation

Abstract

The application discloses a kind of deep pile raft foundation secondary pouring forming construction methods, in the deep pile raft foundation construction of fill layer or silt layer bad geology area, comprising the following steps: step one, BIM modeling and construction deduction;Step two, foundation and foundation construction: foundation treatment, pile foundation construction, foundation pit earthwork excavation and support;Step three, once pouring construction of pile cap: pouring concrete cushion, laying waterproof layer, binding reinforcement and supporting formwork and once pouring of pile cap concrete;Step four, backfill and secondary pouring finishing.This construction method improves the construction speed, reduces the construction cost, simplifies the operation, is suitable for elevator shaft, pool foundation and deep pile cap construction, is conducive to saving construction period and reducing construction cost.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, specifically to a method for secondary casting and forming of deep pile raft foundations. Background Technology

[0002] In recent years, my country's industrial upgrading process has accelerated, and the rapid growth of high-tech manufacturing has directly driven the continuous expansion of industrial plant construction. Industrial plant construction faces the dual challenges of structural complexity and geological adaptability: on the one hand, influenced by production demands and numerous process-related structures, plant structures are complex, requiring stringent construction techniques; on the other hand, construction sites often involve complex geological conditions such as fill layers and silt layers. Fill layers have low strength, poor compaction, and weak self-stabilizing ability, while silt layers are fluid and plastic, exhibiting weak characteristics such as high water content, low shear strength, high compressibility, and low bearing capacity.

[0003] The combined complexity of the structure and the diversity of the geology significantly increases the difficulty and safety risks of earthwork excavation and concrete pouring, with problems being particularly prominent in areas such as elevator shafts and deep foundations. As a critical load-bearing structure in industrial plants, the construction quality of deep foundation pile raft foundations directly determines the overall safety and service life of the plant. However, the current mainstream brick formwork construction technology is ill-suited to these complex conditions, presenting numerous problems: In terms of cost, brick formwork is a disposable material that cannot be reused, resulting in high material and labor costs; in terms of efficiency, the masonry process is cumbersome and requires a curing period, leading to slow construction progress and failing to meet the demands of rapid plant construction; in terms of adaptability, it is only suitable for regular foundation shapes and geology with good bearing capacity, and is prone to cracking and collapse in complex geological conditions and irregularly shaped foundations; in terms of quality, the accuracy of masonry depends on manual operation, which can easily lead to loose joints and grout leakage, and poor bonding with concrete, affecting the overall bearing capacity of the foundation.

[0004] Given the problems of high cost, low efficiency, poor adaptability and unstable quality in brick formwork construction, there is an urgent need in the field of industrial plant construction for a deep pile raft foundation construction method that is fast, easy to operate, reliable in quality and highly adaptable. Therefore, this application proposes a construction method of secondary casting. Summary of the Invention

[0005] The purpose of this invention is to provide a construction method for secondary casting and molding of deep pile cap raft foundations. This construction method solves the problems of slow construction speed, complicated operation and unreliable quality in the construction of deep pile caps under adverse geological conditions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for secondary casting and forming of deep pile-raft foundations, used in areas with unfavorable geological conditions such as fill or silt layers, includes the following steps: Step 1: BIM Modeling and Construction Simulation: Use Revit software to build a 3D site plan, generate a project BIM model, export the BIM model as an NWC file, and import it into NavisWorks software for construction simulation. Step 2: Foundation and Substructure Construction: S1, Foundation treatment, including earthwork replacement and reinforcement with cement-soil mixing piles; S2, pile foundation construction, adopts the prestressed high-strength concrete pipe pile hammering method, driving the pipe piles into the predetermined position one by one. S3, Excavation and support of the foundation pit: First, excavate in layers, and then deepen the excavation locally according to the foundation depth. The slope of the foundation pit adopts the 1:1 soil nailing wall support form. Step 3: One-time pouring of the foundation: A1. Pouring concrete cushion layer: The concrete cushion layer of the deep foundation is poured after the base is cleaned and the pile inspection is qualified. It is vibrated until it is dense and the top surface is leveled after one-time molding. A2. To lay the waterproof layer, first clean the surface of the base layer of garbage, laitance and debris, apply petroleum series base treatment agent evenly, then place the roll material in the predetermined position, heat the base layer and the bottom surface of the roll material, melt the asphalt into a thin layer, and then roll the roll material while baking and compact it with a pressure roller. A3. Tie the reinforcing bars and set up the formwork. Lay out the four corners of the foundation on the top surface of the concrete pad and mark the lines with ink. Securely tie the foundation reinforcing bars with iron wire and reserve column dowel bars. A4. The foundation concrete is poured in one go, first up to the bottom of the raft slab, using a layered pouring method, advancing from one corner to the opposite corner, with each layer thickness controlled at 500-600cm, and the vibrator depth controlled to penetrate 5-10cm into the lower layer. After the layered pouring is completed, the top surface within the reinforcement range of the pier body is leveled and smoothed, followed by roughening and curing. Step 4: Backfilling and Secondary Pouring Finishing: Plain soil is used for backfilling. For underground structure trenches and ground beam trenches, the backfill soil should be backfilled and compacted in layers with a compaction coefficient ≥0.94. When deep and shallow pits are connected, the deep pit should be filled first, and after leveling, it should be filled and compacted in layers with the shallow pit. When filling in sections, the joint of each layer should be made into a slope greater than 1:1.5, with a compaction overlap of 0.5 to 1.0m. The joints of the upper and lower layers should be staggered by a distance of not less than 500mm. After the backfilling of the deep foundation soil is completed, the raft slab concrete is poured.

[0007] Preferably, in step one, the spacing between the foundations and the overall layout are determined through construction simulation, and visual handover materials are produced.

[0008] Preferably, in S1, the earthwork replacement treatment specifically involves using excavators and bulldozers to work together, first clearing away the silt, and then backfilling with high-quality plain soil in layers.

[0009] Preferably, in step S2, a pile driver is used to drive the pipe piles one by one into the predetermined position. During the operation, the principle of heavy hammering and low impact should be followed.

[0010] Preferably, in step S3, a long-arm backhoe excavator is used for layered excavation, with a single excavation depth not exceeding 1.5 meters. Excavation begins from the natural ground level to the bottom elevation of the raft foundation. For areas with an excavation depth less than 3 meters, the earthwork slope ratio is set at 1:1.3. Local deepening excavation is then carried out based on the foundation depth, i.e., pit-within-pit excavation from the bottom of the raft foundation to the deepest pile cap elevation. During excavation, precise measurements and layout are used to locate the deep pile cap position. The deep pile cap is excavated using a slope excavation method. The excavation of the soil between piles is carried out manually from the inside out, with a 700mm working surface reserved on each side of the pile cap. A 200mm wide drainage ditch is installed, and a sump is set up at one corner of the foundation pit. Water is pumped out in time to ensure the foundation pit is dry. When the mechanical excavation reaches 300mm above the design bottom elevation, manual shovels and wheelbarrows are used to remove loose soil from the foundation to prevent the foundation soil from being disturbed. Before manual cleaning, wooden stakes are set every 4m with a level and the elevation is marked. The cleaning is carried out to 150mm above the design bottom elevation. The cleaning is carried out while the foundation layer is being poured. Due to the high groundwater level and rock surface in the foundation pit area, a 1:1 slope steel pipe soil nailing wall support with single-axis mixing pile water-stop curtain is adopted.

[0011] Preferably, in A1, the concrete cushion layer provides a flat and solid working surface for the construction of the foundation reinforcement and formwork.

[0012] Preferably, in A2, the longitudinal and transverse overlaps of the roll material are both 100mm, and the ends are sealed by baking with a blowtorch.

[0013] Preferably, in A3, the side formwork of the foundation is made of 12mm thick film-coated plywood, the secondary back rib is made of 40×90mm timber, and the main back rib is made of φ48 double steel pipe; when the width of the foundation pit is less than 3000mm, the four wall formwork is supported by steel pipes; when the width of the foundation pit is greater than 3000mm, the horizontal steel pipe is fixed by ground anchors welded on the bottom plate reinforcement, and the four sides are diagonally supported by the horizontal crossbar.

[0014] In this invention, under adverse geological conditions, the construction speed is improved, the construction cost is reduced, and the operation is simplified by using slope protection, wooden formwork support system and secondary pouring of deep foundation concrete. It is applicable to the construction of elevator shafts, water tank foundations and deep foundations, which helps to save construction time and reduce construction costs.

[0015] Compared with traditional brick formwork construction, this invention offers several advantages: In terms of construction cost, the method is significantly lower due to the reusability of wooden formwork; in terms of construction speed, the scientific and efficient process of this invention is much faster than the cumbersome brick formwork construction; in terms of adaptability, brick formwork construction is limited to regular foundations and good geological conditions, while this invention is suitable for complex geological conditions and various types of foundations; in terms of quality control, brick formwork construction is susceptible to problems such as grout leakage due to human error, while this invention, based on BIM, effectively ensures quality, achieving high-efficiency, high-quality, and environmentally friendly construction. Detailed Implementation

[0016] The present invention will be further described below: A method for secondary casting and forming of deep pile-raft foundations, used in areas with unfavorable geological conditions such as fill or silt layers, includes the following steps: Step 1: BIM Modeling and Construction Simulation: Using Revit software, a 3D site plan is constructed, generating a project BIM model. The BIM model from Revit is exported as an NWC file and imported into NavisWorks software for construction simulation. The construction simulation determines the foundation spacing and overall layout, and visual handover materials are created. This allows the construction team to gain a deep understanding of the overall layout and key issues before construction, enabling them to plan solutions in advance, effectively avoiding chaos and errors during construction, and ensuring orderly construction progress.

[0017] Step 2: Foundation and Substructure Construction: S1, Foundation treatment, including earthwork replacement and reinforcement with cement-soil mixing piles; The earthwork replacement treatment specifically involves using six PC220 excavators and six TY220 bulldozers working together to first clear the silt, and then backfilling with high-quality plain soil in layers. The thickness of each backfill layer after compaction is strictly controlled to be about 500mm. In this way, the bearing capacity of the foundation is significantly improved, a stable foundation is built for subsequent construction, and the risks of settlement caused by unstable foundation are effectively reduced.

[0018] S2, pile foundation construction, adopts the prestressed high-strength concrete pipe pile hammering method, driving the pipe piles into the predetermined position one by one. Specifically, the DD103 hammer pile driver is used to drive the pipe piles one by one into the predetermined position. During the operation, the principle of heavy hammer and low blow should be followed to ensure that the pile body enters the soil smoothly and the verticality meets the requirements, so as to ensure the bearing capacity of the pile foundation and enable it to stably bear the load of the superstructure.

[0019] S3, Excavation and support of the foundation pit: First, excavate in layers, and then deepen the excavation locally according to the foundation depth. The slope of the foundation pit adopts the 1:1 soil nailing wall support form. The specific method of layered excavation is to use PC220 and PC60 long-arm backhoe excavators for layered excavation, with a single excavation depth not exceeding 1.5 meters. First, excavate from the natural ground to the bottom elevation of the raft foundation. For areas with an excavation depth of less than 3 meters, the earthwork slope ratio is set to 1:1.3.

[0020] The specific method for deepening the excavation based on the foundation depth is as follows: excavating a pit within a pit from the bottom of the raft foundation to the deepest pile cap elevation. During the excavation process, the location of the deep pile cap is accurately measured and marked. The deep pile cap is excavated using a slope excavation method. The excavation of the soil between the piles is carried out manually from the inside out. A 700mm working surface and a 200mm wide drainage ditch are reserved on each side of the pile cap. A sump is set at one corner of the foundation pit. The MA-75102PP water pump is used to promptly pump out the accumulated water to ensure that the foundation pit is dry. When the mechanical excavation reaches 300mm above the design bottom elevation, manual shovels and wheelbarrows are used to transport and remove the loose soil at the base to prevent the base soil from being disturbed. Before manual cleaning, wooden stakes are set every 4m with a level and the elevation is marked. The cleaning is carried out to 150mm above the design bottom elevation. The cleaning is done as the foundation layer is poured.

[0021] The groundwater level and rock surface in the foundation pit area are relatively high. A φ700@500 single-axis mixing pile water-stop curtain with a 1:1 slope steel pipe soil nailing wall is adopted for support. The water-stop curtain effectively blocks groundwater from seeping into the foundation pit, while the soil nailing wall enhances the stability of the slope and prevents collapse, creating a safe space for foundation pit construction and ensuring that the safety of construction personnel and the construction progress are not affected by slope instability.

[0022] Step 3: One-time pouring of the foundation: A1. Concrete cushion layer pouring: The concrete cushion layer of the deep foundation is poured after the foundation is cleaned and the pile inspection is qualified. 100mm thick C20 concrete is used, supplied by the mixing plant. It is vibrated with a vibrator until it is dense. After one-time molding, the top surface is manually leveled. The concrete cushion layer provides a flat and solid working surface for the construction of foundation reinforcement and formwork, ensuring the accuracy and quality of subsequent construction and avoiding problems such as uneven reinforcement protective layer thickness caused by unevenness of the cushion layer.

[0023] A2. Laying the waterproof layer: Before constructing the waterproof layer, carefully clean the surface of the base layer, removing garbage, laitance, and other debris to ensure that the base layer is firm, flat, clean, and free of sharp objects. After evenly applying a petroleum-based base treatment agent, place the roll material in the predetermined position. Heat the base layer and the bottom surface of the roll material with a liquefied gas or gasoline torch. After the asphalt melts into a thin layer, roll the material while heating it and compact it with a pressure roller. The longitudinal and transverse overlaps of the roll material are both 100mm. Finally, seal the ends with a torch. The waterproof layer effectively prevents groundwater from eroding the foundation and raft concrete, extends the service life of the foundation, and reduces later maintenance costs.

[0024] A3. For rebar tying and formwork erection, mark the four corners of the foundation on the top surface of the concrete pad and mark with ink lines to control the thickness of the concrete cover. Securely tie the foundation rebar with wire and pre-install column dowels. Specifically, use 12mm thick film-coated plywood for the foundation side formwork, 40×90mm timber for secondary back bracing at 300mm intervals, and φ48 double steel pipes for main back bracing at 600mm intervals. When the foundation pit width is less than 3000mm, use steel pipes to firmly support the four wall formwork; when it is greater than 3000mm, weld ground anchors to fix horizontal steel pipes to the bottom slab rebar, and diagonally brace the perimeter to the horizontal crossbars. Precise rebar tying and stable formwork erection ensure the structural strength and dimensional accuracy of the foundation.

[0025] A4. The foundation concrete is poured in one go, first up to the bottom of the raft slab, using a layered pouring method, progressing from one corner to the opposite corner. The thickness of each layer is controlled at 500-600cm to facilitate vibration and heat dissipation. The vibrator is inserted quickly and withdrawn slowly until there are no air bubbles and the concrete surface does not sink, preventing under-vibration or over-vibration. After the layered pouring is completed, the top surface within the reinforcement area of ​​the pier body is manually leveled and smoothed. Subsequent roughening and curing are carried out. After pouring, the concrete is covered and watered for curing according to the weather, keeping the covering moist to ensure stable concrete strength growth, prevent cracking, and guarantee the quality of the foundation concrete.

[0026] Step 4: Backfilling and Secondary Pouring for Finishing: Plain soil is used for backfilling. For underground structure trenches and foundation beam trenches, the backfill soil should be backfilled and compacted in layers, with a compaction coefficient ≥0.94. When deep and shallow pits are connected, the deep pit should be filled first, leveled, and then the shallow pit and the backfill soil should be fully filled and compacted in layers. When backfilling in sections, each layer joint should have a slope greater than 1:1.5, with a compaction overlap of 0.5–1.0m. The joints of upper and lower layers should be staggered by no less than 500mm. Proper backfilling ensures the compaction of the backfill soil, avoids adverse effects of backfill settlement on the foundation, and maintains the stability of the surrounding soil. After the deep foundation soil backfilling is completed, the raft foundation concrete will be poured.

[0027] This completes the secondary pouring and forming of the deep pile raft foundation. The secondary pouring makes the raft slab and the pile cap form an integral structure, which together bears the load of the superstructure, ensuring that the entire foundation structure is stressed in a coordinated manner and improving the stability of the building structure.

[0028] Two construction areas with similar geological conditions and basic design parameters were selected and designated as the experimental group and the control group, respectively. In the experimental group, the secondary casting and molding construction method for deep pile raft foundations proposed in this invention was adopted, and construction was carried out strictly according to the established steps. In the control group, brick formwork was used for construction, and operations were carried out according to traditional process specifications, such as brick masonry and plastering. During the construction process, professional personnel were arranged to record in detail the progress, material usage, and labor input of the two groups. After the construction was completed, professional testing equipment was used to test and evaluate various quality indicators of the foundations of the two groups, such as concrete strength, structural dimensional accuracy, and waterproof performance, and the differences in data on construction cost, construction period, and quality between the two groups were compared and analyzed.

[0029] In comparison, regarding construction costs, the secondary casting method for deep pile raft foundations is significantly lower than brick formwork construction because the wooden formwork can be reused; in terms of construction speed, the former is scientific and efficient, much faster than the cumbersome brick formwork construction; in terms of adaptability, brick formwork construction is limited to regular foundations and good geological conditions, while this invention is applicable to complex geological conditions and various types of pile caps; in terms of quality control, brick formwork construction is susceptible to problems such as grout leakage due to human error, while this invention, based on BIM, can effectively ensure quality.

[0030] The above embodiments are merely illustrative of the concept and implementation of the present invention and are not intended to limit it. Under the concept of the present invention, technical solutions without substantial changes are still within the scope of protection.

Claims

1. A method for secondary casting and forming of a deep pile cap raft foundation, characterized in that: Construction of deep pile-raft foundations in areas with unfavorable geological conditions, such as fill or silt layers, includes the following steps: Step 1: BIM Modeling and Construction Simulation: Use Revit software to build a 3D site plan, generate a project BIM model, export the BIM model as an NWC file, and import it into NavisWorks software for construction simulation. Step 2: Foundation and Substructure Construction: S1, Foundation treatment, including earthwork replacement and reinforcement with cement-soil mixing piles; S2, pile foundation construction, adopts the prestressed high-strength concrete pipe pile hammering method, driving the pipe piles into the predetermined position one by one. S3, Excavation and support of the foundation pit: First, excavate in layers, and then deepen the excavation locally according to the foundation depth. The slope of the foundation pit adopts the 1:1 soil nailing wall support form. Step 3: One-time pouring of the foundation: A1. Pouring concrete cushion layer: The concrete cushion layer of the deep foundation is poured after the base is cleaned and the pile inspection is qualified. It is vibrated until it is dense and the top surface is leveled after one-time molding. A2. To lay the waterproof layer, first clean the surface of the base layer of garbage, laitance and debris, apply petroleum series base treatment agent evenly, then place the roll material in the predetermined position, heat the base layer and the bottom surface of the roll material, melt the asphalt into a thin layer, and then roll the roll material while baking and compact it with a pressure roller. A3. Tie the reinforcing bars and set up the formwork. Lay out the four corners of the foundation on the top surface of the concrete pad and mark the lines with ink. Securely tie the foundation reinforcing bars with iron wire and reserve column dowel bars. A4. The foundation concrete is poured in one go, first up to the bottom of the raft slab, using a layered pouring method, advancing from one corner to the opposite corner, with each layer thickness controlled at 500-600cm, and the vibrator depth controlled to penetrate 5-10cm into the lower layer. After the layered pouring is completed, the top surface within the reinforcement range of the pier body is leveled and smoothed, followed by roughening and curing. Step 4: Backfilling and Secondary Pouring Finishing: Plain soil is used for backfilling. For underground structure trenches and ground beam trenches, the backfill soil should be backfilled and compacted in layers with a compaction coefficient ≥0.

94. When deep and shallow pits are connected, the deep pit should be filled first, and after leveling, it should be filled and compacted in layers with the shallow pit. When filling in sections, the joint of each layer should be made into a slope greater than 1:1.5, with a compaction overlap of 0.5 to 1.0m. The joints of the upper and lower layers should be staggered by a distance of not less than 500mm. After the backfilling of the deep foundation soil is completed, the raft slab concrete is poured.

2. The construction method for secondary casting and molding of deep pile cap raft foundation according to claim 1, characterized in that: In step one, the spacing between the foundations and the overall layout are determined through construction simulation, and visual handover materials are produced.

3. The construction method for secondary casting and molding of deep pile cap raft foundation according to claim 1, characterized in that: In S1, the earthwork replacement treatment specifically involves using excavators and bulldozers to work together, first clearing away the silt, and then backfilling with high-quality plain soil in layers.

4. The method for secondary casting and molding of deep pile cap raft foundation according to claim 1, characterized in that: In S2, a pile driver is used to drive the pipe piles one by one into the predetermined position. During the operation, the principle of heavy hammering and low impact should be followed.

5. The construction method for secondary casting and molding of deep pile cap raft foundation according to claim 1, characterized in that: In S3, a long-arm backhoe excavator is used for layered excavation, with a single excavation depth not exceeding 1.5 meters. Excavation begins from the natural ground level to the bottom elevation of the raft foundation. For areas with an excavation depth less than 3 meters, the earthwork slope ratio is set at 1:1.

3. Local deepening excavation is then carried out based on the foundation depth, i.e., pit-within-pit excavation from the bottom of the raft foundation to the deepest pile cap elevation. During excavation, precise measurements and layout are used to locate the deep pile cap position. The deep pile cap is excavated using a slope excavation method. The excavation of the soil between piles is carried out manually from the inside out. A 700mm working surface and 2... are reserved on each side of the pile cap. A 00mm wide drainage ditch is installed, and a sump is set up at one corner of the foundation pit. Water is pumped out in time to ensure that the foundation pit is dry. When the mechanical excavation reaches 300mm above the design bottom elevation, manual shovels and wheelbarrows are used to remove loose soil from the foundation to prevent the foundation soil from being disturbed. Before manual cleaning, wooden stakes are set every 4m with a level and the elevation is marked. The cleaning is carried out to 150mm above the design bottom elevation. The cleaning is carried out while the foundation layer is being poured. Due to the high groundwater level and rock surface in the foundation pit area, a 1:1 slope steel pipe soil nailing wall support with single-axis mixing pile water-stop curtain is adopted.

6. The construction method for secondary casting and molding of deep pile cap raft foundation according to claim 1, characterized in that: In A1, the concrete cushion layer provides a flat and solid working surface for the construction of the foundation reinforcement and formwork.

7. The method for secondary casting and molding of deep pile cap raft foundation according to claim 1, characterized in that: In A2, the roll material overlaps 100mm in both the longitudinal and transverse directions, and is finally sealed by baking with a blowtorch.

8. The construction method for secondary casting and molding of deep pile cap raft foundation according to claim 1, characterized in that: In the A3, the side formwork of the foundation is made of 12mm thick film-coated plywood, the secondary back rib is made of 40×90mm timber, and the main back rib is made of φ48 double steel pipe. When the width of the foundation pit is less than 3000mm, the four wall formwork is supported by steel pipes. When the width of the foundation pit is greater than 3000mm, the horizontal steel pipe is fixed by welding ground anchors on the bottom plate reinforcement, and the four sides are diagonally supported by the horizontal crossbar.