Rigidity-controllable piled raft foundation and construction method thereof

Abstract

The invention relates to the field of construction, and discloses a stiffness-controllable piled raft foundation and a construction method thereof.The stiffness-controllable piled raft foundation comprises a foundation pile, a cavity is formed in the top of the foundation pile, pile body main reinforcements are evenly arranged in the foundation pile, support plates are evenly installed on the top of the foundation pile, and support anchor bars are evenly and fixedly connected to the bottoms of the support plates; a positioning bolt is arranged at the top of the support plate, a rigidity adjusting device is installed at the top of the support plate through the positioning bolt, a reinforcing mesh is evenly arranged in the foundation pile through pile body main ribs, stirrups are evenly arranged on one side of the reinforcing mesh, and a brick moulding bed is arranged on the outer wall of the foundation pile. The rigidity adjusting device is arranged at the top of the foundation pile, and the connecting relation between the rigidity adjusting device and the support plate, the pile body main rib, the reinforcing mesh, the stirrup and other components is reasonably designed, so that the supporting rigidity of the pile foundation is matched with the supporting rigidity of foundation soil, an adjustable connecting structure is formed between the pile top and the raft plate, and deformation between the pile and the soil can be effectively coordinated.

Description

Technical Field

[0001] The invention relates to the technical field of construction, in particular to a controllable rigidity pile raft foundation and a construction method thereof. Background Art

[0002] Construction technology refers to the sum of a series of technical means, methods, processes and measures used in the process of engineering construction to transform design drawings into actual buildings or structures. It covers earthwork, pile foundation engineering, concrete structure construction, steel structure construction, waterproof engineering construction and other aspects. Construction technology runs through the entire process of the project and directly affects the quality, progress, safety and cost of the project. With the continuous development of the construction industry, construction technology is also constantly innovating and improving, such as the application of new building materials, the research and development of intelligent construction equipment, and the promotion of green construction technology, in order to meet the increasingly complex and diverse needs of engineering construction.

[0003] In the construction of pile foundation projects, pile raft foundations are used. When traditional pile raft foundations are used, uncoordinated deformation of piles and soil will occur, resulting in the inability to fully utilize the bearing capacity of the foundation soil. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a controllable stiffness pile-raft foundation and a construction method thereof, which solves the problem that when a traditional pile-raft foundation is used, the pile-soil deformation is not coordinated, resulting in the inability to fully utilize the bearing capacity of the foundation soil.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a controllable stiffness pile raft foundation and a construction method thereof, comprising a foundation pile, a cavity is arranged on the top of the foundation pile, main reinforcement of the pile body is evenly arranged inside the foundation pile, a support plate is evenly installed on the top of the foundation pile, the bottom of the support plate is evenly fixedly connected with support anchor reinforcement, a positioning bolt is arranged on the top of the support plate, a stiffness adjustment device is installed on the top of the support plate through the positioning bolt, a steel mesh is evenly arranged on the inside of the foundation pile through the main reinforcement of the pile body, stirrups are evenly arranged on one side of the steel mesh, a brick mold is arranged on the outer wall of the foundation pile, a sand filling layer is arranged between the foundation pile and the brick mold, a side guard plate is installed on the top outer wall of the foundation pile, a steel cover plate is fixedly connected to the top of the side guard plate, angle steel is evenly arranged on the bottom of the steel cover plate, a grouting pipe joint is evenly arranged on the top of the steel cover plate, and a grouting pipe is installed on the top of the steel cover plate through the grouting pipe joint.

[0006] Preferably, the bottom of the steel cover plate is fixedly connected to the top of the stiffness adjustment device by angle steel, and a special waterproof plug is provided on the top of the grouting pipe. The stiffness adjustment device is used to adjust the displacement or contact stiffness between the support contact points of the object.

[0007] Preferably, a cushion layer is provided on the side of the brick formwork away from the foundation piles, a mortar layer is provided on the top of the sand filling layer, a raft plate is provided on the top of the foundation piles, and the steel cover plate is located below the raft plate.

[0008] Preferably, the angle steel, stiffness adjustment device, support plate, support anchor bar, steel mesh, and stirrups are all located in the cavity, the interior of the grouting pipe is connected to the cavity, and the diameter of the support plate is not less than the diameter of the stiffness adjustment device.

[0009] A controllable stiffness pile raft foundation construction method comprises the following steps: S1. Pile head breaking and reinforcement bending inward: The pile head of the foundation pile is broken and removed to below the bottom surface of the raft slab, and the main reinforcement of the pile body is bent inward at the top of the foundation pile; S2. Brick formwork construction: build brick formwork around the foundation piles; S3. Installation of steel mesh and stirrups on pile top: install steel mesh on the top of the pile and tie it with stirrups; S4. Positioning and installation of the bearing plate: Install the bearing plate to the top of the foundation pile and fix it by spot welding the bearing anchor bars to ensure the horizontality of the bearing plate; S5. Secondary pouring of concrete on the pile top: Secondary pouring of concrete on the bottom of the bearing plate, followed by compaction with an inserted vibrator, and secondary smearing and compaction after the initial setting and before the final setting of the concrete; S6. Installation of the stiffness adjustment device: Install the bottom of the stiffness adjustment device on the top of the support plate through positioning bolts, and fix it with the support plate by spot welding; S7. Installation of steel cover: weld the angle steel fillet around the bottom of the steel cover, and then cover the steel cover on the upper part of the stiffness adjustment device, with its center coinciding with the center of the support plate, and clean up the debris in the cavity; S8, side guard plate installation: weld and fix the side guard plate around the outer circumference of the steel cover plate; S9, side sand filling: use coarse sand to fill the sand filling layer between the side guard plate and the brick formwork tightly, and apply cement mortar on the upper part of the sand filling layer; S10, grouting pipe installation: install the grouting pipe on the top of the steel cover through the grouting pipe joint, and weld it firmly to the steel cover. When grouting is not done, set a special waterproof plug at the mouth of the grouting pipe; S11. Cavity grouting and sealing: The adjustment work is completed through the stiffness adjustment device, and then the cavity is grouted through the grouting pipe. After the grouting is completed, the cavity is sealed Preferably, in step S1, the elevation below is 400 mm, and in step S3, there are no less than two steel meshes.

[0010] Preferably, the inclination of the support plate in step S4 is not greater than 1%, and the height of the secondary pouring in step S5 reaches the bottom of the stiffness adjustment device and does not cover the positioning bolts.

[0011] Preferably, in step S6, the plane position error of the support plate is no more than 10 mm, and the elevation error is no more than 5 mm. In step S7, the diameter of the steel cover plate is 20 mm larger than the diameter of the foundation pile.

[0012] Preferably, the thickness of the cement mortar in step S9 is not less than 20 mm, and the height of the grouting pipe in step S10 is not less than 500 mm higher than the raft slab.

[0013] Preferably, the grouting operation in step S11 is completed continuously at one time, the grouting pressure is not less than 0.5 MPa, and the pressure is maintained for more than 3 minutes after filling, and the cavity is sealed after the internal and external decoration is completed and the building settlement stability is reported to the design unit for review.

[0014] Working principle: Through the synergistic effect of the main reinforcement of the pile body, steel mesh and stirrups, the restraint capacity of concrete is enhanced, and the overall strength and toughness of the foundation pile are improved. The main reinforcement of the pile body, steel mesh and stirrups are evenly arranged inside the foundation pile to form an integral internal structure of the foundation pile. The bottom of the support plate is connected to the foundation pile through the support anchor bar to ensure the horizontality of the support plate. The stiffness adjustment device accurately controls its position through the positioning bolts and is installed on the support plate. By adjusting the stiffness adjustment device, the deformation between the pile and the soil is more coordinated. The brick formwork is used to protect the foundation pile from external factors during construction. The sand filling layer is filled in It plays a certain buffering and filling role between the foundation pile and the brick formwork, which helps to evenly disperse the pressure around the foundation pile. It is installed on the top outer wall of the foundation pile through the side guard plate, and its top is fixedly connected to the steel cover plate, and together with the steel cover plate, it forms a seal and protection for the cavity. At the same time, the bottom of the steel cover plate is connected to the stiffness adjustment device through the angle steel. The angle steel not only increases the stiffness of the steel cover plate, but also plays a horizontal limiting role for the stiffness adjustment device to prevent it from horizontal displacement during the force process. A grouting pipe joint is set on the steel cover plate for installing a grouting pipe, and the grouting pipe is connected to the cavity, providing a channel for the later cavity grouting closure.

[0015] The present invention provides a controllable stiffness pile raft foundation and a construction method thereof, which has the following beneficial effects: 1. The present invention arranges a stiffness adjustment device on the top of the foundation pile and reasonably designs the connection relationship between the device and the support plate, pile main reinforcement, steel mesh, stirrups and other components, so that the supporting stiffness of the pile foundation matches the supporting stiffness of the foundation soil, and forms an adjustable connection structure between the pile top and the raft slab, which can effectively coordinate the deformation between the pile and the soil, ensure that when the upper structure is subjected to load, the pile and soil work together better, and make full use of the natural foundation soil bearing capacity.

[0016] 2. The stiffness adjustment device provided in the present invention can coordinate the deformation difference of pile foundation under different supporting conditions, so that pile foundations with different force performance can coexist and jointly bear the load of the upper structure. In this way, in areas with granite residual soil and karst landform development, where the properties of foundation soil are often quite different, the problem that conventional pile raft foundations cannot meet the needs of high-rise building construction due to excessive differential settlement is solved.

[0017] 3. The present invention arranges a stiffness adjustment device at the pile end to coordinate the deformation of the new and old piles and realize the joint effect of the new and old piles, which is not only convenient for construction, but also can achieve good economic benefits. It also solves the problem that when a building is demolished, due to the consolidation of the soil, the performance of the old piles and the new piles left intact in the foundation is very different, making it difficult to reuse them, which is not only wasteful but also brings great difficulties to the construction of new piles.

[0018] 4. The present invention utilizes a stiffness adjustment device to artificially and precisely regulate the distribution of the overall supporting stiffness of the pile raft foundation, thereby achieving the goal of zero differential settlement or extremely small differential settlement of the building. The integrity and durability of the pile top structure are enhanced by strictly controlling the installation accuracy of each component during the construction process and grouting and sealing the cavity after the building settlement is stable. Grouting and sealing not only protects the components in the cavity from external erosion, but also further improves the connection stability between the pile top and the raft slab, reduces the damage to the foundation structure caused by long-term use and environmental factors, and thus extends the service life of the building. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic cross-sectional view of a pile top structure with a stiffness adjustment device according to the present invention; Figure 2 It is a schematic diagram of the local structure of the support anchor bar of the present invention; Figure 3 It is a schematic diagram of the local structure of the steel cover plate of the present invention; Figure 4 It is a schematic diagram of the partial structure of the foundation pile of the present invention; Figure 5 The present invention is a flowchart of a controllable stiffness pile raft foundation construction method.

[0020] Among them, 1. foundation piles; 2. main reinforcement of the pile body; 3. steel mesh; 4. stirrups; 5. brick formwork; 6. sand filling layer; 7. cushion layer; 8. mortar layer; 9. grouting pipe; 10. special waterproof plug; 11. steel cover plate; 12. angle steel; 13. side guard plate; 14. stiffness adjustment device; 15. support plate; 16. support anchor bar; 17. grouting pipe joint; 18. positioning bolts; 19. raft plate; 20. cavity. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0022] Please refer to the attached Figure 1 -Attached Figure 4 The embodiment of the present invention provides a controllable stiffness pile raft foundation and a construction method thereof, comprising a foundation pile 1, a cavity 20 is arranged on the top of the foundation pile 1, main reinforcement bars 2 of the pile body are evenly arranged inside the foundation pile 1, a support plate 15 is evenly installed on the top of the foundation pile 1, support anchor bars 16 are evenly fixedly connected to the bottom of the support plate 15, a positioning bolt 18 is arranged on the top of the support plate 15, a stiffness adjustment device 14 is installed on the top of the support plate 15 through the positioning bolt 18, a steel mesh 3 is evenly arranged on the inside of the foundation pile 1 through the main reinforcement bars 2 of the pile body, stirrups 4 are evenly arranged on one side of the steel mesh 3, a brick mold 5 is arranged on the outer wall of the foundation pile 1, a sand filling layer 6 is arranged between the foundation pile 1 and the brick mold 5, a side guard plate 13 is installed on the top outer wall of the foundation pile 1, a steel cover plate 11 is fixedly connected to the top of the side guard plate 13, and angle steels 12 are evenly arranged on the bottom of the steel cover plate 11 , grouting pipe joints 17 are evenly arranged on the top of the steel cover plate 11, and a grouting pipe 9 is installed on the top of the steel cover plate 11 through the grouting pipe joints 17; the bottom of the steel cover plate 11 is fixedly connected to the top of the stiffness adjustment device 14 through the angle steel 12, and a special waterproof plug 10 is arranged on the top of the grouting pipe 9. The stiffness adjustment device 14 is used to adjust the displacement or contact stiffness between the support contact points of the object; a cushion layer 7 is arranged on the side of the brick formwork 5 away from the foundation pile 1, a mortar layer 8 is arranged on the top of the sand filling layer 6, a raft 19 is arranged on the top of the foundation pile 1, and the steel cover plate 11 is located below the raft 19; the angle steel 12, the stiffness adjustment device 14, the support plate 15, the support anchor bar 16, the steel mesh 3, and the stirrup 4 are all located in the cavity 20, the interior of the grouting pipe 9 is connected to the cavity 20, and the diameter of the support plate 15 is not less than the diameter of the stiffness adjustment device 14.

[0023] Specifically, the main reinforcement 2, steel mesh 3 and stirrups 4 are evenly arranged inside the pile 1. The main reinforcement 2 of the pile body serves as the main force-bearing component to bear the tensile and compressive loads of the pile. The steel mesh 3 and stirrups 4 work together to enhance the restraint capacity of concrete and improve the overall strength and toughness of the pile. The steel mesh 3 is evenly arranged on the main reinforcement 2 of the pile body so that the internal structure of the pile forms an organic whole, which can more effectively transfer and disperse the load from the superstructure. The stirrups 4 further restrain the concrete to prevent it from lateral deformation during the force-bearing process, thereby improving the bearing capacity and stability of the pile and providing a solid foundation support for the entire pile raft foundation.

[0024] The bottom of the support plate 15 is connected to the foundation pile 1 through the support anchor bar 16, and the support anchor bar 16 is spot-welded and fixed to the steel mesh or the bent vertical force-bearing steel bar of the foundation pile to ensure the horizontality of the support plate 15. A positioning bolt 18 is arranged on the top of the support plate 15, and the stiffness adjustment device 14 is installed in cooperation with the positioning bolt 18 through the bottom bolt hole, and is fixed with auxiliary spot welding. This connection method enables the stiffness adjustment device 14 to be stably installed on the support plate 15, and its position can be accurately controlled by the positioning bolt 18. Its reliable connection with the support plate 15 ensures that it can accurately play the role of adjusting the supporting stiffness at the top of the pile. By adjusting the stiffness, the overall performance of the pile raft foundation can be optimized according to different engineering requirements and geological conditions. In the case of uneven foundation soil properties, by adjusting the stiffness adjustment device 14, the deformation between the pile and the soil can be made more coordinated, avoiding uneven settlement caused by excessive local stiffness differences, thereby solving the problem that the conventional pile raft foundation will have uneven deformation of the pile and the soil when in use, resulting in the inability to give full play to the bearing capacity of the foundation soil.

[0025] A brick formwork 5 is set on the outer wall of the foundation pile 1. On the one hand, the brick formwork 5 protects the foundation pile 1 from being disturbed by external factors during the construction process, and on the other hand, it provides space for the sand filling layer 6. The sand filling layer 6 is filled between the foundation pile 1 and the brick formwork 5, and a mortar layer 8 is applied on the upper part to play a certain buffering and filling role, which helps to evenly disperse the pressure around the foundation pile. The side guard plate 13 is installed on the top outer wall of the foundation pile 1, and its top is fixedly connected to the steel cover plate 11, and together with the steel cover plate 11, it forms a seal and protection for the cavity 20. The bottom of the steel cover plate 11 is connected to the stiffness adjustment device 14 through the angle steel 12. The angle steel 12 not only increases the stiffness of the steel cover plate 11, but also plays a horizontal limiting role for the stiffness adjustment device 14 to prevent it from horizontal displacement during the force-bearing process. A grouting pipe joint 17 is set on the steel cover plate 11 for installing a grouting pipe 9. The grouting pipe 9 is connected to the cavity 20 to provide a channel for later cavity grouting closure.

[0026] The steel cover plate 11, the side guard plate 13, the grouting pipe 9 and other components together with the stiffness adjustment device 14 and the foundation pile 1 form a relatively closed structure. After the settlement of the building is stable, the cavity 20 is grout-sealed through the grouting pipe 9. The grouting material with high strength, self-compacting and micro-expansion effect is selected to fill the gap in the cavity 20 and enhance the integrity of the pile top structure. The cavity 20 after grouting and sealing can prevent the entry of corrosive media such as external moisture and air, and protect the internal components such as the stiffness adjustment device 14 and the support plate 15 from corrosion and damage, thereby improving the durability of the pile top. At the same time, the integrity of the entire structure is enhanced, the connection between the components is tighter, and they can work better together to jointly bear the load transmitted from the upper structure, further improving the long-term stability and reliability of the pile raft foundation. Please refer to the attached Figure 5, a controllable stiffness pile raft foundation construction method, comprising the following steps: S1, breaking and chiseling the pile head and bending the reinforcement inward: the pile head of the foundation pile 1 is chiseled off to below the bottom surface of the raft slab, and the main reinforcement 2 of the pile body is bent inward at the top of the foundation pile 1; S2, brick formwork 5 masonry: masonry brick formwork 5 around the foundation pile 1; S3, installation of the steel mesh 3 and stirrups 4 at the pile top: a steel mesh 3 is installed at the pile top of the foundation pile 1 and is tied with the stirrups 4; S4, positioning and installing the support plate 15: installing the support plate 15 to the top of the foundation pile 1, and fixing it by spot welding the support anchor bar 16 to ensure the horizontality of the support plate 15; S5, secondary pouring of concrete on the pile top: pouring concrete for the bottom of the support plate 15 for the second time, and then vibrating and compacting it with an inserted vibrator, and performing secondary troweling and pressing after the initial setting of the concrete and before the final setting; S6, installation of the stiffness adjustment device 14: the bottom of the stiffness adjustment device 14 is installed on the top of the support plate 15 through the positioning bolts 18, and is fixed to the support plate 15 with the aid of spot welding; S7, installation of the steel cover plate 11: weld the angle steel 12 to the bottom of the steel cover plate 11, and then cover the steel cover plate 11 on the upper part of the stiffness adjustment device 14, with its center coinciding with the center of the support plate 15, and clean up the debris in the cavity; S8, side guard plate 13 installation: the side guard plate 13 is welded and fixed around the outer circumference of the steel cover plate 11; S9, side sand filling: use coarse sand to fill the sand filling layer 6 between the side guard plate 13 and the brick mold 5 tightly, and apply cement mortar on the upper part of the sand filling layer 6; S10, installation of grouting pipe 9: install the grouting pipe 9 on the top of the steel cover plate 11 through the grouting pipe joint 17, and weld it firmly to the steel cover plate 11. When grouting is not performed, a special waterproof plug 10 is provided at the pipe opening of the grouting pipe 9; S11, grouting and sealing of the cavity 20: the adjustment work is completed through the stiffness adjustment device 14, and then the cavity 20 is grouting through the grouting pipe 9. After the grouting is completed, the cavity 20 is sealed.

[0027] In step S1, the elevation below is 400 mm, and in step S3, there are no less than two steel meshes 3.

[0028] In step S4 , the inclination of the support plate 15 is not greater than 1%. In step S5 , the height of the secondary pouring reaches the bottom of the stiffness adjustment device 14 and does not cover the positioning bolts 18 .

[0029] In step S6 , the plane position error of the support plate 15 is not greater than 10 mm, and the elevation error is not greater than 5 mm. In step S7 , the diameter of the steel cover plate 11 is 20 mm larger than the diameter of the foundation pile 1 .

[0030] The thickness of the cement mortar in step S9 is not less than 20 mm, and the height of the grouting pipe 9 in step S10 is not less than 500 mm higher than the raft 19.

[0031] The grouting operation in step S11 is completed continuously at one time, the grouting pressure is not less than 0.5 MPa, and the pressure is maintained for more than 3 minutes after filling. The cavity 20 is closed after the internal and external decoration is completed and the building settlement stability is reported to the design unit for review.

[0032] Specifically, by chiseling the pile head of the foundation pile 1 to 400mm below the bottom surface of the raft slab and bending the main reinforcement 2 of the pile body inward at the pile top, sufficient space is provided for the installation of the subsequent stiffness adjustment device support plate 15, while ensuring the continuity of the main reinforcement 2 of the pile body, so that it can better participate in the force transmission of the pile top structure. The pile head can be chiseled to a certain depth to remove the possible low-strength or damaged parts, ensuring the quality of the foundation pile below the pile top, and providing reliable vertical support for the entire pile raft foundation. After the main reinforcement 2 of the pile body is bent inward, it can be better connected with the steel mesh 3 and stirrups 4 installed later, forming an integral steel skeleton, and enhancing the bearing capacity of the pile top area.

[0033] By building a brick formwork 5 around the foundation pile 1, lateral protection is provided for the foundation pile 1 to prevent the foundation pile 1 from being affected by collision or other external forces during the subsequent construction process. At the same time, the brick formwork 5 forms the boundary of the sand filling layer 6, which is convenient for the sand filling operation and ensures that the shape and size of the sand filling layer 6 meet the design requirements. The brick formwork 5 can also be used as a temporary template during the construction process, and plays a certain restraining role in operations such as pouring concrete to ensure construction quality and accuracy.

[0034] By arranging no less than two steel meshes 3 at the top of the foundation pile 1 and tying them with stirrups 4, the bearing capacity of the concrete at the top of the pile is further enhanced. The steel mesh 3 can evenly disperse the local load transmitted from the upper structure, and the stirrups 4 constrain the steel mesh 3 and the main reinforcement 2 of the pile body to prevent them from displacement or deformation during the force application process. This steel bar arrangement method can improve the crack resistance of the concrete in the pile top area, enable it to better withstand the pressure and deformation generated when the stiffness adjustment device 14 is working, and ensure the stability of the pile top structure.

[0035] The support plate 15 is installed to the top of the foundation pile 1 and fixed by spot welding with the support anchor bar 16 to ensure the horizontality of the support plate 15, and the inclination of the support plate 15 is controlled to be no more than 1%. Accurate positioning and horizontality control of the support plate 15 are the key to ensuring the installation accuracy and normal operation of the stiffness adjustment device 14. The support plate 15 serves as the supporting foundation of the stiffness adjustment device 14, and its horizontality directly affects the stress state and adjustment effect of the stiffness adjustment device 14. If the support plate 15 is tilted or installed unevenly, it may cause uneven stress on the stiffness adjustment device 14, affecting its ability to adjust the support stiffness, and further affecting the performance of the entire pile raft foundation.

[0036] By pouring concrete from the bottom of the support plate 15 to the bottom of the stiffness adjustment device 14 for the second time without covering the positioning bolts 18, the connection strength between the support plate 15 and the foundation pile 1 is ensured, and the positioning bolts 18 can be used normally during the subsequent installation of the stiffness adjustment device 14. Using an inserted vibrator to compact the concrete can make it dense, reduce voids, and improve the strength and durability of the concrete. Performing a second trowel after the initial setting of the concrete and before the final setting can reduce shrinkage cracks on the concrete surface, improve the flatness and density of the concrete surface, and further enhance the quality of the pile top structure.

[0037] By installing the stiffness adjustment device 14 on the top of the support plate 15 through the positioning bolts 18, and spot welding the support plate 15 for auxiliary fixation, while controlling the plane position error of the support plate 15 to be no more than 10 mm, and the elevation error to be no more than 5 mm, the precise installation position and the small error range ensure that the stiffness adjustment device 14 can accurately play its role in adjusting the supporting stiffness. If the installation position is inaccurate or the error is too large, it may cause the stiffness adjustment device 14 to be incoordinated with other components, affecting the stiffness distribution and deformation coordination performance of the entire pile raft foundation.

[0038] The rigidity of the steel cover plate 11 is increased by welding the fillet weld of the angle steel 12 to the bottom of the steel cover plate 11, and then the steel cover plate 11 is covered on the upper part of the rigidity adjustment device 14 so that its center coincides with the center of the support plate 15, and the debris in the cavity is cleaned. The installation of the steel cover plate 11 not only provides top protection for the rigidity adjustment device 14, but also generates a horizontal limit effect through the connection between the angle steel 12 and the rigidity adjustment device 14, preventing the rigidity adjustment device 14 from shifting in the horizontal direction. Cleaning the debris in the cavity can ensure the sealing and grouting effect of the cavity 20, prevent the debris from affecting the filling and solidification of the grouting material, and ensure the integrity of the pile top structure.

[0039] The side guard plates 13 are welded and fixed around the outer circumference of the steel cover plate 11, and together with the steel cover plate 11, they seal and protect the cavity 20. The side guard plates 13 can prevent foreign matter from entering the cavity 20, while enhancing the lateral stability of the pile top structure. When subjected to the load of the upper structure and the external environment, the side guard plates 13 can work in conjunction with other components to jointly resist possible lateral forces and deformations, thereby ensuring the overall stability and safety of the pile raft foundation.

[0040] The sand filling layer 6 between the side guard plate 13 and the brick formwork 5 is filled densely with coarse sand, and cement mortar with a thickness of not less than 20 mm is applied on the top. The filling of the sand filling layer 6 can evenly disperse the pressure around the foundation pile 1 and reduce the uneven settlement of the foundation caused by local pressure concentration. The cement mortar layer can further enhance the stability of the sand filling layer 6 and prevent the loss of sand particles. At the same time, it plays a certain role in waterproofing and leveling, providing good basic conditions for subsequent construction.

[0041] The grouting pipe 9 is installed on the top of the steel cover plate 11 through the grouting pipe joint 17, and is firmly welded to the steel cover plate 11. The height of the grouting pipe 9 is not less than 500mm higher than the raft plate 19. When grouting is not performed, a special waterproof plug 10 is set at the pipe mouth. The installation of the grouting pipe 9 provides a channel for the grouting and sealing of the cavity 20. Its height above the raft plate 19 ensures that the grouting material can smoothly fill the cavity 20 during the grouting process, and facilitates the maintenance and inspection of the grouting pipe 9 during the use of the building. The special waterproof plug 10 can prevent debris from entering the grouting pipe 9 when grouting is not performed, ensuring the smooth flow of the grouting pipe 9 and ensuring the smooth progress of the grouting operation.

[0042] After the stiffness adjusting device 14 completes the adjustment work, the cavity 20 is grouted through the grouting pipe 9, and a suitable grouting material such as high-strength, self-compacting and slightly expanding commercial grouting material is selected. The grouting pressure is not less than 0.5MPa, and it is completed once continuously. After filling, the pressure is maintained for more than 3 minutes, and then the cavity 20 is closed after the internal and external decoration is completed and the building settlement stability is reported to the design unit for review. Grouting sealing can enhance the integrity of the pile top structure, improve the durability of the pile top, and prevent external factors from eroding the components in the cavity 20. At the same time, reasonable grouting parameters and timing selection can ensure the grouting effect, so that the grouting material fully fills the cavity 20 and is closely combined with various components, further improving the long-term stability and reliability of the pile raft foundation.

[0043] The following is further introduced in conjunction with specific embodiments: Example

[0044] 1. Pile head is broken and chiseled, and reinforcement is bent inward: According to the requirements of the design drawings, the pile head is chiseled to 400mm below the bottom elevation of the raft 19. To facilitate the fixed installation of the stiffness adjustment device 14 support plate 15, the vertical force-bearing reinforcement in the foundation pile 1 should not be cut off, but should be bent inward at the pile top.

[0045] 2. Laying of brick formwork 5: Laying of brick formwork 5 around foundation pile 1.

[0046] 3. Installation of steel mesh 3 and stirrups 4 at the pile top: In order to prevent the concrete at the pile top from being cracked or crushed due to insufficient bearing capacity during the load-bearing operation of the stiffness adjustment device 14, no less than two steel meshes 3 and stirrups 4 are arranged at the pile top and tied firmly.

[0047] 4. Positioning and installation of the support plate 15: The support plate 15 is made of steel plate and must have sufficient rigidity. The diameter of the support plate 15 of each stiffness adjustment device 14 should not be smaller than the diameter of the stiffness adjustment device 14. The relative position is ensured to be accurate by welding it to the angle steel 12 at the bottom to form a whole. A positioning bolt is set in the center of each support plate 15 to facilitate the rapid positioning and installation of the stiffness adjustment device 14. Install the support plate 15 of the stiffness adjustment device 14 to the top of the pile. During the installation process, attention should be paid to the elevation control of the support plate 15. The inclination of the support plate 15 should not be greater than 1%. Four anchor bars are set at the bottom of each support plate 15. The anchor bars can be fixed to the steel mesh 3 or the bent vertical force-bearing steel bars of the foundation pile 1 by spot welding to ensure the horizontality of the support plate 15 of the stiffness adjustment device 14 and avoid collision and displacement during the secondary pouring of concrete.

[0048] 5. Secondary pouring of concrete on the top of the pile: The concrete at the bottom of the support plate 15 is poured for the second time, and the bearing capacity of the pile body after pouring should be no less than that of the original pile body. The concrete should be poured to the bottom elevation of the stiffness adjustment device 14 and should not cover the positioning bolts 18. The concrete should be poured continuously and compacted with an inserted vibrator, but excessive vibration should be avoided. After the initial setting of the concrete and before the final setting, the concrete should be pressed for the second time to reduce shrinkage.

[0049] 6. Installation of the stiffness adjustment device 14: When installing the stiffness adjustment device 14, pay attention to distinguishing the top and bottom. The bottom of the device has bolt holes. Insert the positioning bolts 18 aligned with the support plate 15 and tighten them to prevent horizontal displacement after installation. The stiffness adjustment device 14 and the support plate 15 are fixed with the aid of spot welding. During the construction process, practical and reliable protection measures should be taken for the stiffness adjustment device 14 to ensure the horizontal position and flatness of the stiffness adjustment device 14. The plane position error of the stiffness adjustment device 14 should not be greater than 10mm, and the elevation error should not be greater than 5mm.

[0050] 7. Installation of the steel cover plate 11: An angle steel 12 is provided at the bottom of the steel cover plate 11, and the connection between the steel cover plate 11 and the angle steel 12 is made by corner welding. The angle steel 12 can increase the rigidity of the steel cover plate 11. After the installation of the steel cover plate 11 is completed, the bottom angle steel 12 and the rigidity adjustment device 14 are used to fix it to produce a horizontal limit effect. The steel cover plate 11 is provided with a number of reserved holes for installing the grouting pipe 9. Before installing the steel cover plate 11, the debris in the cavity 20 should be checked and cleaned, and the steel cover plate 11 should be covered on the upper part of the rigidity adjustment device 14. The center of the steel cover plate 11 should coincide with the center of the support plate 15. It should be installed accurately to avoid displacement. The diameter of the steel cover plate 11 should be 20 mm larger than the diameter of the pile body.

[0051] 8. Installation of side guard plate 13: The side guard plate 13 is made of thin steel plate and is welded and fixed around the steel cover plate 11. The lower part of the side guard plate 13 and the pile body are ensured to have sufficient overlap length.

[0052] 9. Side sand filling: Use coarse sand to fill the gap between the side guard plate 13 and the brick formwork 5 tightly, and apply a layer of cement mortar with a thickness of not less than 20 mm on the top.

[0053] 10. Installation of grouting pipe 9: galvanized steel pipe should be used for grouting pipe 9. Align grouting pipe 9 through the reserved hole on the steel cover plate and install it firmly with the steel cover plate. Grouting pipe 9 should be higher than the foundation surface of raft slab 19 by no less than 500mm. When grouting operation is not carried out, a special waterproof plug should be set at the pipe mouth to prevent blockage.

[0054] 11. Grouting and sealing of cavity 20: After the stiffness adjustment device 14 completes the adjustment work, the cavity 20 on the pile top should be sealed. The sealing time should be after the internal and external decoration is completed and the building settlement is basically stable and reported to the design unit for review. The grouting material should be commercial grouting material. The grouting material must ensure high fluidity and have high strength, self-compacting and micro-expansion effects. The grouting pressure should not be less than 0.5MPa. The grouting should be completed continuously at one time. After filling, the pressure should be maintained for more than 3 minutes. After the grouting is completed, the grouting port of the grouting pipe 9 should be tightly sealed.

[0055] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A controllable stiffness pile raft foundation, comprising a pile (1), characterized in that: The top of the foundation pile (1) is provided with a cavity (20), the interior of the foundation pile (1) is evenly provided with pile body main reinforcements (2), the top of the foundation pile (1) is evenly installed with a support plate (15), the bottom of the support plate (15) is evenly fixedly connected with a support anchor reinforcement (16), the top of the support plate (15) is provided with a positioning bolt (18), the top of the support plate (15) is installed with a stiffness adjustment device (14) via the positioning bolt (18), the interior of the foundation pile (1) is evenly provided with a steel mesh (3) via the pile body main reinforcements (2), the steel mesh (3) ) is evenly provided with stirrups (4), the outer wall of the foundation pile (1) is provided with a brick formwork (5), a sand filling layer (6) is provided between the foundation pile (1) and the brick formwork (5), a side guard plate (13) is installed on the top outer wall of the foundation pile (1), a steel cover plate (11) is fixedly connected to the top of the side guard plate (13), angle steels (12) are evenly provided on the bottom of the steel cover plate (11), grouting pipe joints (17) are evenly provided on the top of the steel cover plate (11), and a grouting pipe (9) is installed on the top of the steel cover plate (11) through the grouting pipe joint (17).

2. The controllable stiffness pile raft foundation according to claim 1, characterized in that: The bottom of the steel cover plate (11) is fixedly connected to the top of the stiffness adjustment device (14) via an angle steel (12); a special waterproof plug (10) is provided on the top of the grouting pipe (9); and the stiffness adjustment device (14) is used to adjust the displacement or contact stiffness between the support contact points of the object.

3. The controllable stiffness pile raft foundation according to claim 1, characterized in that: A cushion layer (7) is provided on the side of the brick formwork (5) away from the foundation pile (1), a mortar layer (8) is provided on the top of the sand filling layer (6), a raft plate (19) is provided on the top of the foundation pile (1), and the steel cover plate (11) is located below the raft plate (19).

4. The controllable stiffness pile raft foundation according to claim 1, characterized in that: The angle steel (12), the stiffness adjustment device (14), the support plate (15), the support anchor bar (16), the steel mesh (3), and the stirrups (4) are all located in the cavity (20); the interior of the grouting pipe (9) is connected to the cavity (20); and the diameter of the support plate (15) is not less than the diameter of the stiffness adjustment device (14).

5. A controllable stiffness pile raft foundation construction method, characterized in that: The following steps are involved: S1, breaking and chiseling the pile head and bending the reinforcement inward: the pile head of the foundation pile (1) is chiseled off to below the bottom surface of the raft slab, and the main reinforcement (2) of the pile body is bent inward at the top of the foundation pile (1); S2, brick formwork construction: constructing a brick formwork (5) around the foundation pile (1); S3, installation of steel mesh and stirrups at the pile top: a steel mesh (3) is arranged at the pile top of the foundation pile (1) and is tied to the stirrups (4); S4, positioning and installing the support plate: installing the support plate (15) to the top of the foundation pile (1), and fixing it by spot welding the support anchor bar (16) to ensure the horizontality of the support plate (15); S5, secondary pouring of concrete on the pile top: secondary pouring of concrete is performed on the bottom of the support plate (15), and then compaction is performed using an inserted vibrator, and secondary smearing and pressing is performed after the initial setting of the concrete and before the final setting; S6. Installation of the stiffness adjustment device: The bottom of the stiffness adjustment device (14) is installed on the top of the support plate (15) by means of positioning bolts (18), and is fixed to the support plate (15) by means of spot welding; S7, installation of the steel cover: weld the angle steel (12) to the bottom of the steel cover (11), and then cover the steel cover (11) on the upper part of the stiffness adjustment device (14), with its center coinciding with the center of the support plate (15), and clean the debris in the cavity; S8, side guard plate installation: the side guard plate (13) is welded and fixed around the outer circumference of the steel cover plate (11); S9, side sand filling: using coarse sand to fill the sand filling layer (6) between the side guard plate (13) and the brick mold (5) tightly, and applying cement mortar on the upper part of the sand filling layer (6); S10, grouting pipe installation: the grouting pipe (9) is installed on the top of the steel cover plate (11) through the grouting pipe joint (17), and is firmly welded to the steel cover plate (11). When grouting is not performed, a special waterproof plug (10) is provided at the pipe opening of the grouting pipe (9); S11, closing the cavity by grouting: the adjustment work is completed by the stiffness adjustment device (14), and then the cavity (20) is grouted by the grouting pipe (9). After the grouting is completed, the cavity (20) is closed.

6. A controllable stiffness pile raft foundation construction method according to claim 5, characterized in that: In step S1, the elevation below the mark is 400 mm, and in step S3, there are no less than two steel meshes (3).

7. The controllable stiffness pile raft foundation construction method according to claim 5, characterized in that: The inclination of the support plate (15) in step S4 is no more than 1%, and the height of the secondary pouring in step S5 reaches the bottom of the stiffness adjustment device (14) and does not cover the positioning bolts (18).

8. The controllable stiffness pile raft foundation construction method according to claim 5, characterized in that: In step S6, the plane position error of the support plate (15) is not greater than 10 mm, and the elevation error is not greater than 5 mm. In step S7, the diameter of the steel cover plate (11) is 20 mm larger than the diameter of the foundation pile (1).

9. The controllable stiffness pile raft foundation construction method according to claim 5, characterized in that: The thickness of the cement mortar in step S9 is not less than 20 mm, and the height of the grouting pipe (9) in step S10 is not less than 500 mm higher than the raft slab (19).

10. The controllable stiffness pile raft foundation construction method according to claim 5, characterized in that: The grouting operation in step S11 is completed continuously at one time, the grouting pressure is not less than 0.5 MPa, and the pressure is maintained for more than 3 minutes after filling. The cavity (20) is sealed after the internal and external decoration is completed and the building settlement stability is reported to the design unit for review.

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