Overlapped pile foundation construction technology and construction method for recycling old piles

Abstract

The invention relates to a construction technology and a construction method for a composite pile foundation by recycling old piles. The method comprises the steps that firstly, a soil body is excavated to a certain depth on an old pile foundation, the integrity and durability of old piles are detected, and the old piles which do not meet the recycling requirement are cut off and abandoned; in order to improve the bearing capacity of the foundation, new cast-in-situ bored piles are complementarily driven below the elevation of the cut-off old piles, and a new and old pile combined bearing structure is formed; leveling the pile heads of the cut old piles and new piles, binding steel bars, and pouring to form a reinforced concrete laminated slab; and a second layer of new piles are constructed above the laminated slab, pile heads of the new piles and the reserved complete old pile heads are connected through a bearing platform to jointly bear, and finally the laminated pile foundation with the high bearing performance is formed. The use amount of new piles in old building and bridge reconstruction can be remarkably reduced, and carbon emission of a newly-built pile foundation project is reduced. Moreover, the second-layer structure of the laminated pile foundation can be backfilled with soil and can also be combined with underground parking lots, underground markets and the like, and a new building underground space utilization scheme is provided.

Description

Technical Field

[0001] The invention belongs to the technical field of pile foundation engineering, and relates to a composite pile foundation construction technology and a construction method for reusing old piles. Background Art

[0002] The demolition and renovation of old buildings and bridges is inevitable during urban renewal and infrastructure construction. The presence of old piles not only creates significant underground structural space but can also interfere with the design and construction of new pile foundations, potentially posing a safety threat to surrounding buildings. Furthermore, the direct removal of old piles presents numerous hazards. For example, removing existing piles can disturb the surrounding subsoil, leading to a loss of surface friction on the new piles and a reduction in their bearing capacity below design requirements. Existing high-bearing-capacity piles are difficult to remove en bloc, and the process often results in broken piles, residual piles, and collapsed holes. Furthermore, blindly removing old piles whose integrity and bearing capacity meet operational requirements wastes resources and financial resources and significantly impacts the construction schedule of new construction projects. Research and statistics from the Japan Construction Industry Federation (2018) show that the rational reuse of old piles can reduce CO2 emissions from new pile foundation projects by up to 70% (saving on new piles and reducing carbon emissions during the removal process). Therefore, the rational and efficient use of old piles has become an essential option for urban renewal and building renovation.

[0003] Against the backdrop of accelerating urbanization and the advancement of sustainable development strategies, the reuse of existing pile foundations has become a key approach to improving resource utilization efficiency and reducing environmental burdens. However, the actual reuse of existing pile foundations faces many challenges, including damaged pile integrity, severe corrosion, and insufficient bearing capacity. These issues not only limit the direct application of old piles, but also make it difficult to meet the design and safety requirements of new construction projects. Therefore, there is an urgent need to propose a new construction method that aims to effectively evaluate the integrity and durability of old piles during construction and adopt a reasonable method of adding new piles to fully reuse existing pile foundations to meet the design requirements of new construction projects. Summary of the Invention

[0004] The purpose of the present invention is to propose a composite pile foundation construction technology and construction method for reusing old piles, so as to realize the reuse of existing old piles generated during the renovation of old buildings, improve the bearing capacity of the pile foundation, and reduce the carbon emissions generated by new pile foundation projects.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention proposes a composite pile foundation construction technology and construction method for reusing old piles, including the following construction method steps:

[0007] (1) Excavate the soil to the target depth on the old pile foundation left over from the demolition and reconstruction of the original building, check the integrity of the pile head and pile body and the durability of the old pile material. If it meets the reuse requirements, it will be retained. If not, it should be cut off and abandoned at the target depth, and the base elevation should be cleaned;

[0008] (2) Determine the number, configuration, and spacing of new piles below the base based on bearing requirements, and add the first layer of new piles near the cut-off old piles;

[0009] (3) Overlap and cast the composite slab at the pile heads of the cut-off old piles and the first layer of new piles to connect the new and old piles. The intact old piles should penetrate the composite slab layer;

[0010] (4) Determine the configuration, quantity and location of the second layer of new piles on the composite slab, install the pile end sleeves and steel casings of the new piles, and pour the concrete protective layer at the pile ends of the new piles;

[0011] (5) Backfill the excavated site and compact it to the required density;

[0012] (6) Place precast piles in the steel casing, or place steel cages and pour concrete to form the second layer of new piles;

[0013] (7) The pedestal is cast together at the pile heads of the second layer of new piles and the old piles that are retained as a whole, forming a composite pile foundation based on the reuse of old piles.

[0014] Furthermore, the target depth of the excavated soil needs to comprehensively consider the on-site soil conditions, the integrity of the old piles and the durability of the materials, and implement layered excavation and testing (each layer is 0.1 times the length of the old piles). For soils with high salt content, high water content or strongly corroded piles, the excavation depth should be increased appropriately, but the total depth should not exceed 0.5 times the length of the old piles to reduce the excavation workload.

[0015] Furthermore, the first layer of new piles are bored cast-in-place piles to reduce the disturbance of the new piles to the soil around the existing pile foundations. They are located near the cut-off old piles, and the pile spacing should not be less than 1.5 times the pile diameter. The heads of the bored piles and the heads of the cut-off old piles are at the same elevation.

[0016] Furthermore, the composite slab is composed of a precast concrete base plate (including a precast concrete layer, truss reinforcement, etc.) and a cast-in-situ concrete composite layer. The diagonal connecting rods of the truss reinforcement ensure the final bonding between the precast components and the cast-in-situ concrete.

[0017] Furthermore, the pile heads of the first layer of new piles and the cut-off old piles should be embedded together in the composite slab to a certain depth, which should be greater than the thickness of the precast concrete base plate, and the pile heads should have exposed steel bars after pretreatment and be anchored together in the composite slab layer.

[0018] Furthermore, the intact old piles should penetrate the composite slab layer and be fixed by pouring high-strength concrete at the connection parts.

[0019] Furthermore, a second layer of new piles can be added above the composite slab where the old piles are cut off. Cast-in-place piles can be used. High-strength concrete is poured on-site to create a sleeve at the end of the pile at a preset location on the composite slab. A new pile steel casing and reinforcement cage are then placed inside. A concrete pile end protection layer is then cast on top of the composite slab. Finally, the pouring is completed after backfilling. Alternatively, precast piles can be used based on site conditions, ensuring a secure connection between the new piles, the sleeve, and the composite slab. The new piles can be placed in the same location as the old piles or between adjacent new and old piles in the first layer, with an appropriately increased pile diameter.

[0020] Furthermore, after all pile foundations are in place, the pedestal is poured with reinforced concrete on site, and the pile head constraint of the new and old piles is adjusted by adjusting the depth of the pile head embedded in the pedestal or the length of the anchoring steel bar, thereby further improving the overall horizontal bearing capacity and seismic resistance of the mixed pile group.

[0021] Compared with existing technologies, this invention tests the integrity and durability of existing pile foundations while excavating, truncates old piles that don't meet the requirements at the target excavation depth, and uses a composite plate, pile end sleeve, and pile end protective layer structure to effectively achieve an integrated connection between the upper and lower layers of new and old pile foundations. This changes the limitation of existing pile foundation construction methods that requires old piles that don't meet bearing requirements to be removed, reduces the length of new piles used in new construction, minimizes the disturbance of surrounding soil during pile foundation construction, and fully utilizes existing piles in old buildings. Furthermore, this technology can also reduce the number of new piles used to a certain extent, lowering economic costs, improving construction efficiency and pile foundation bearing capacity, and achieving energy conservation, emission reduction, and reduced resource waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a front view of a composite pile foundation that reuses old piles in an embodiment of the present invention;

[0023] Figure 2 is a top view of a composite pile foundation that reuses old piles in an embodiment of the present invention;

[0024] Figure 3 is a schematic structural diagram of a composite plate according to an embodiment of the present invention;

[0025] Figure 4 1. It is a top view of the prefabricated plate structure of the composite plate and the connection position between the prefabricated plate and the pile foundation in an embodiment of the present invention;

[0026] Figure 5 is a schematic diagram of the connection between the composite plate and the pile foundation in an embodiment of the present invention;

[0027] Figure 6It is a construction flow chart of the present invention.

[0028] In the figure: 1-the first layer of bored and cast-in-place new piles, 2-the truncated old piles, 3-the composite slab; 4-the cast-in-place concrete pile end protective layer; 5-the sleeves at the ends of the second layer of new piles; 6-the intact old piles; 7-the second layer of new piles; 8-the cap; 301-the precast concrete layer of the composite slab; 302-the composite slab truss reinforcement; 303-the cast-in-place concrete layer of the composite slab. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operating process. Obviously, the embodiments described herein are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0030] In order to fully reuse old piles in the renovation process of old buildings and improve the bearing capacity of existing pile foundations, the present invention proposes a composite pile foundation construction technology and construction method that reuses old piles. The construction flow chart is as follows: Figure 6 As shown. It includes the following steps:

[0031] (1) Excavate the soil to the target depth on the old pile foundation left over from the demolition and reconstruction of the original building, check the integrity of the pile head and pile body and the durability of the old pile material. If it meets the reuse requirements, it will be retained. If not, it will be cut off and abandoned at the target excavation depth, and the base elevation will be cleaned;

[0032] (2) Determine the number, configuration, and spacing of new piles below the excavation base based on the bearing requirements, and add the first layer of new piles near the cut-off old piles;

[0033] (3) Overlap and cast the composite slab at the pile heads of the cut-off old piles and the first layer of new piles to connect the new and old piles. The intact old piles should pass through the composite slab layer;

[0034] (4) Determine the configuration, quantity and location of the second layer of new piles on the composite slab, install the pile end sleeves and steel casings of the new piles, and pour the concrete protective layer at the pile ends of the new piles;

[0035] (5) Backfill the excavated site and compact it to the required density;

[0036] (6) Place precast piles in the steel casing, or place steel cages and pour concrete to form the second layer of new piles;

[0037] (7) The pedestal is cast together at the pile heads of the second layer of new piles and the old piles that are retained as a whole, forming a composite pile foundation based on the reuse of old piles.

[0038] In some specific implementations, the target depth of the excavated soil needs to comprehensively consider the on-site soil conditions, the integrity of the old piles and the durability of the materials, and implement layered excavation and testing (each layer is 0.1 times the length of the old piles). For soils with high salt content, high water content or strongly corroded piles, the excavation depth should be increased appropriately, but the total depth should not exceed 0.5 times the length of the old piles to reduce the excavation workload.

[0039] In some specific implementations, the integrity of the pile head and the pile body of the old pile is determined by appearance inspection and time-domain and frequency-domain signal characteristics (LECM related regulations).

[0040] In some specific embodiments, the durability testing of the old piles includes both strength and corrosion testing. For strength testing, the core drilling method is used to test the compressive strength of the old pile concrete, and several stressed steel bars are removed from the old piles and cut and processed for testing the tensile strength of the steel bars. For corrosion testing, the carbonation depth of the old pile concrete is tested using a phenolphthalein ethanol indicator, the chloride ion concentration of the old pile concrete is tested using a rapid chloride ion analyzer, and the degree of steel corrosion is tested using the natural potential method.

[0041] In some specific embodiments, the new piles added in the first layer are bored concrete cast-in-place piles to reduce the disturbance of the new piles to the soil around the existing pile foundations. The new piles are located near the cut-off old piles, and the pile spacing is not less than 1.5 times the pile diameter. The pile heads of the cast-in-place piles are at the same elevation as the pile heads of the cut-off old piles.

[0042] In some specific embodiments, the composite slab is composed of a precast concrete base plate (including a precast concrete layer, truss reinforcement, etc.) and a cast-in-place concrete composite layer. The diagonal connecting rods of the truss reinforcement ensure a tight bond between the precast components and the cast-in-place concrete layer.

[0043] In some specific embodiments, the first layer of new piles and the pile heads of truncated old piles should be embedded in the composite slab layer, with the pile heads having exposed rebar after pretreatment and anchored together in the composite slab. Intact old piles should fully penetrate the composite slab. A cutting device should be used to cut the precast concrete base slab at the corresponding designed locations, with the cut area slightly larger than the pile cross-sectional area. The new and old piles should be inserted through the precast concrete base slab and secured with high-strength concrete at the corresponding interface locations. Finally, in-situ concrete is cast atop the precast concrete base slab to form the composite slab structure.

[0044] In some specific implementations, a second layer of new piles is added above the composite slab where the old piles are cut off. Cast-in-place piles can be used. High-strength concrete is poured on-site to create a sleeve at the end of the pile at a pre-set location on the composite slab. A steel casing and a steel cage are then placed inside. A concrete sleeve is then cast above the composite slab to protect the pile ends. The concrete is then backfilled and poured. Alternatively, precast piles can be used based on site conditions, ensuring a secure connection between the new piles, the sleeve, and the composite slab. The new piles can be placed in the same location as the old piles or between adjacent new and old piles in the first layer, with an appropriately increased diameter to increase bearing capacity.

[0045] In some specific embodiments, after all the pile foundations are in place, the pedestal is poured on site with reinforced concrete, and the pile head constraint of the new and old piles is adjusted by changing the depth of the pile head embedded in the pedestal or the depth of the anchoring steel bars to prevent lateral overload of the new and old pile foundations, thereby further improving the overall horizontal bearing capacity and seismic performance of the mixed pile group.

[0046] The above implementation is described in more detail below with reference to specific examples.

[0047] Example:

[0048] For example, a bridge reconstruction and renovation project site originally housed a 3×2 pile group foundation. The old piles were cast-in-place concrete piles, 30 meters long and 1 meter in diameter. Due to the long-term overloading of the road bridge, the bridge had undergone severe deformation. Excavation and inspection below the pier cap revealed varying degrees of cracking in all six foundation piles, impacting the normal operation of the bridge. Therefore, the present invention proposes a composite pile foundation construction technology and method that reuses old piles. After a thorough assessment of the existing pile foundation, a suitable method for adding new piles was adopted to reinforce the pile foundation.

[0049] The specific implementation steps are as follows: Figure 1-Figure 5 ,

[0050] a: Determine and excavate the target depth of the old pile foundation soil layer, which is 15m in this embodiment, with each layer excavated 3m deep, for a total of 5 layers.

[0051] b: Durability tests are conducted on each layer of old piles excavated, mainly including: using a core drill to cut a core sample at a random measuring point on the pile body and processing it into a standard compressive test piece (diameter 0.1m, height 0.1m) for testing the compressive strength of the old pile concrete; then, the pile body concrete is crushed and ground to prepare a solution, and the chloride ion concentration of the pile body concrete is tested using a rapid chloride ion analyzer; a main load-bearing reinforcement is cut out at the same position as mentioned above, and the tensile strength of the reinforcement is tested after cutting; one measuring area is taken from each layer of old piles excavated, and three measuring points are taken from each measuring area, and the carbonation depth of the concrete at the measuring points is tested using phenolphthalein ethanol indicator; representative parts of the concrete that may be corroded (such as exposed reinforcement parts) in each layer of pile body excavated are used as measuring areas, and the degree of reinforcement corrosion is tested using the natural potential method.

[0052] c: Determine the integrity of the pile head and pile body of the old pile through appearance inspection and time domain and frequency domain signal characteristics (LECM relevant regulations).

[0053] d: Based on the integrity and durability of the pile heads and pile bodies of the old piles, the four old piles 2 that do not meet the reuse requirements are cut off and abandoned at 0.1m above the excavation bottom, and the pile heads are ensured to have exposed pile head anchor steel bars.

[0054] e: Four new piles 1 are added below the excavation bottom by drilling and grouting method in the middle of the existing piles. The pile diameter is 1m, the pile length is 20m, the pile spacing is 2m, the concrete strength grade is C30, and the pile top position is slightly higher than the excavation bottom (to ensure that the pile head is embedded in the composite slab layer to a depth of 0.1m).

[0055] f: Use a cutting device to cut the precast concrete base plate 301. The cutting area is slightly larger than the cross-sectional area of ​​the piles. The new pile 1 and the old piles 2 and 6 are then passed through the precast concrete base plate 301 (the thickness of the precast concrete layer is 0.06m). C40 concrete is poured and fixed at the interface between piles 1, 2, and 6 and the base plate 301. A concrete layer 303 (thickness 0.24m) is cast on top of the precast concrete base plate 301 to form a composite slab structure 3. The longitudinal main reinforcement at the top of the pile is anchored into the composite slab at a depth of 20 times the longitudinal main reinforcement diameter and bent 90 degrees toward the pile axis. Figure 3 、 Figure 4 ;

[0056] g: According to the bearing capacity design requirements of the new construction project, four pile end casings 5 ​​are cast with C40 concrete above the composite slab structure 3 between the cut-off old pile 2 and the added new pile 1, and four new pile steel casings with a diameter of 1.2m are placed.

[0057] h: Use C30 concrete to cast a 0.2m thick pile end protection layer 4 on top of the composite slab;

[0058] i: Use C30 concrete to re-pour the concrete sampling points and cracked and damaged areas of the retained old piles, and backfill the excavated site in layers. After the excavated soil layer is compacted to the required density, place a steel cage in the steel casing and pour C30 concrete to form the second layer of new piles 7.

[0059] j: After all pile foundations are in place, cap 8 is cast on site at the pile heads of old pile 6 and new pile 7. The pile heads are embedded in the cap to a depth of 0.1m. The longitudinal main reinforcement of the pile top of the new pile 7 is anchored in the cap 8 at 35 times the diameter of the longitudinal main reinforcement, and the longitudinal main reinforcement of the pile top of the old pile 6 is anchored in the cap 8 at 20 times the diameter of the longitudinal main reinforcement, thus forming the foundation of the new pier.

[0060] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A composite pile foundation construction technology and construction method for reusing old piles, characterized in that: The following steps are involved: (1) Excavate the soil to the target depth based on the old piles left over from the demolition and reconstruction of the original building, check the integrity of the pile heads and pile bodies and the durability of the old pile materials, cut off and discard the old piles that do not meet the reuse requirements at the target depth, and clean the base elevation; (2) Determine the number, configuration, and spacing of new piles below the base based on bearing requirements, and add the first layer of new piles near the cutoff of the old piles; (3) Overlap and cast the composite slab at the pile heads of the cut-off old piles and the first layer of new piles to connect the new and old piles. The intact old piles should pass through the composite slab layer; (4) Determine the configuration, quantity and location of the second layer of new piles on the composite slab, install the pile end sleeves and steel casings of the new piles, and pour the concrete protective layer at the pile ends of the new piles; (5) Backfill the excavated site and compact it to the required density; (6) Place precast piles in the steel casing, or place steel cages and pour concrete through formwork support to form a second layer of new piles; (7) The pedestal is cast together at the pile heads of the second layer of new piles and the old piles that are retained as a whole, forming a composite pile foundation based on the reuse of old piles.

2. The composite pile foundation construction technology and construction method for reusing old piles according to claim 1 is characterized in that: The target depth of soil excavation needs to comprehensively consider the on-site soil conditions, the integrity of the old piles and the durability of the materials, and implement layered excavation and testing (each layer is 0.1 times the length of the old piles). For soils with high salt content, high water content or severely corroded piles, the excavation depth should be increased appropriately. The total depth should not exceed 0.5 times the length of the old piles to reduce the excavation workload.

3. The composite pile foundation construction technology and construction method for reusing old piles according to claim 1 is characterized in that: The first layer of new piles are bored cast-in-place piles to reduce the disturbance to the soil around the existing pile foundations. They are located near the cut-off old piles, with a pile spacing of no less than 1.5 times the pile diameter. The cast-in-place pile heads are at the same elevation as the cut-off old pile heads.

4. The composite pile foundation construction technology and construction method for reusing old piles according to claim 1 is characterized in that: The composite slab is composed of a precast concrete base plate (including a precast concrete layer and truss reinforcement) and a cast-in-place concrete composite layer. The final bonding between the precast components and the cast-in-place concrete is ensured by the diagonal connecting rods of the truss reinforcement.

5. The composite pile foundation construction technology and construction method for reusing old piles according to claim 1 is characterized in that: The first layer of new piles and the pile heads of the cut-off old piles are embedded in the composite slab to a certain depth, which is greater than the thickness of the precast concrete base plate. The pile heads all have exposed steel bars after pretreatment and are anchored into the composite slab layer.

6. The composite pile foundation construction technology and construction method for reusing old piles according to claim 1 is characterized in that: The intact old piles should penetrate the composite slab and be fixed with high-strength concrete at the connection parts.

7. The composite pile foundation construction technology and construction method for reusing old piles according to claim 1 is characterized in that: A second layer of new piles is added above the composite slab where the old piles are cut off. Cast-in-place piles are used, and the pile end sleeves are cast on-site with high-strength concrete at the preset position on the composite slab. New pile steel casings and steel cages are built in, and a concrete pile end protection layer is cast on-site above the composite slab. Finally, the pouring is completed after backfilling. Alternatively, prefabricated piles can be used according to site conditions, and a firm connection between the new piles, pile end sleeves and composite slabs must be ensured. The new piles can be placed in the original location of the old piles, or between adjacent new and old piles in the first layer, and the pile diameter can be appropriately increased.

8. The composite pile foundation construction technology and construction method for reusing old piles according to claim 1 is characterized in that: After all pile foundations are in place, the pedestal is poured with reinforced concrete on site, and the pile head constraint of the new and old piles is adjusted by adjusting the depth of the pile head embedded in the pedestal or the length of the anchoring steel bars, thereby further improving the horizontal bearing capacity and seismic resistance of the mixed pile group.

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