Underground structure anti-floating system using pressure type prestressed anchor rod

Abstract

The application relates to the technical field of building structures, in particular to an underground structure anti-floating system applying pressure type prestressed anchor rods, which comprises pressure type prestressed anchor rods embedded in the bottom plate of an underground structure, the pressure type prestressed anchor rods comprise prestressed reinforcement, a sleeve and a metal carrier and are divided into anchoring sections, free sections and tension sections from bottom to top along the height direction, the sleeve is sleeved on the periphery of the prestressed reinforcement, and a certain gap is formed between the sleeve and the prestressed reinforcement; the metal carrier is arranged at the bottom of the prestressed reinforcement and the sleeve and is connected with the prestressed reinforcement and the sleeve respectively and blocks the gap between the prestressed reinforcement and the sleeve; the tension end of the prestressed reinforcement is provided with a steel backing plate, a secondary grouting pipe is reserved on the steel backing plate, grouting is carried out through the secondary grouting pipe to block the gap between the prestressed reinforcement and the bottom plate of the underground structure, and a waterproof structure is arranged between the prestressed reinforcement and the bottom plate of the underground structure. The application has the advantages of reasonable structure, clear function, strong operability, novel design and the like.

Description

Technical Field

[0001] This invention relates to the field of building structure technology, and in particular to an anti-buoyancy system for underground structures using pressure-type prestressed anchors. Background Technology

[0002] The building structure industry is developing rapidly, but land and social resources are limited, and the focus of urban development is shifting from above-ground to the utilization of underground space. In areas with abundant groundwater, groundwater often appears at a depth of 0.5m below the outdoor ground level. Under the action of water reaction force, underground structures are prone to insufficient buoyancy resistance. Without anti-buoyancy measures, the entire basement will float like a boat.

[0003] Currently, anti-buoyancy measures mainly include increasing counterweights, anti-uplift piles, and anti-uplift anchors.

[0004] The addition of counterweight mainly balances the buoyancy of groundwater by increasing the weight of the base plate (base plate thickness and surface layer) or top plate (cover soil). The construction is relatively simple. However, the addition of counterweight also becomes a load on the structure, which increases the cost of the structure itself.

[0005] Tension piles are generally placed under columns, similar to bearing piles. However, because the column spacing in basements is generally large, the buoyancy is transferred through the deformation of the base slab at mid-span. Therefore, the base slab generally needs to have sufficient rigidity, resulting in a larger slab thickness and reinforcement. This requires higher investment, longer construction period, and lower economic benefits.

[0006] Compared to using anti-uplift piles, as long as the soil distribution is suitable and the rock layer is shallow, anti-uplift anchors can effectively shorten the construction period (due to ease of construction) and reduce costs. Furthermore, their construction machinery is small, flexible, and convenient, allowing operation in confined spaces, which is one of their widely recognized advantages. As an important approach and method for anti-uplift design of basements, anchor anti-uplift is increasingly being applied in engineering sites with rock foundations.

[0007] The drafting group of the "Technical Standard for Anti-buoyancy in Building Engineering" (JGJ) The "Explanation of Major Issues in JGJ476-2019" states: "Recent investigations into accidents involving anti-buoyancy anchor bolts show that, besides the excessively low anti-buoyancy design water level, the main reason for anti-buoyancy failure is the commonly used fully bonded tension-type anti-buoyancy anchor bolts (i.e., ordinary anchor bolts). During operation, the grout is under tension, making it prone to cracking. Grouting / grouting also suffers from construction quality defects, making it difficult to guarantee that current construction techniques will meet all anti-buoyancy requirements." The new "Technical Standard for Anti-Buoyancy in Building Engineering" (JGJ476-2019), implemented on March 1, 2020, clearly outlines requirements for crack control in anti-buoyancy anchor bolts. Article 7.5.8 states: "For projects with an anti-buoyancy design grade of A, design should be based on the absence of cracks, and under the standard combination of load effects, no tensile force should be generated in the anchor grout. For projects with an anti-buoyancy design grade of B, design should be based on crack control, and under the standard combination of load effects, the tensile stress in the anchor grout should not exceed the axial tensile strength of the anchor grout." The GB standard, implemented on January 1, 2022... The 55001-2021 General Specification for Engineering Structures stipulates that the durability of a structure is a necessary condition to ensure that the structure can be used normally within its design service life.

[0008] The above content consistently indicates that fully bonded tension-type anti-buoyancy anchors (i.e., ordinary anchors) can no longer meet the requirements of current standards and practical applications. Prestressing can effectively solve these problems. The atlas "Anti-buoyancy Anchors for Building Structures" (22G815), which came into effect on October 1, 2022, provides design guidelines, selection instructions, and joint construction details for anchors, offering further technical guidelines for anchor design. However, in engineering practice, it has been found that the joint construction methods in the atlas are significantly affected by construction experience, and the reliability of its waterproofing structure, in particular, needs improvement. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of the prior art by providing an anti-buoyancy system for underground structures using pressure-type prestressed anchors. This system achieves anti-buoyancy by embedding pressure-type prestressed anchors at the bottom slab of the underground structure, which can satisfy pull-out resistance, control cracks to ensure full-length compression, and effectively waterproof the construction nodes.

[0010] The objective of this invention is achieved through the following technical solutions:

[0011] An anti-buoyancy system for underground structures using pressure-type prestressed anchors is characterized by comprising pressure-type prestressed anchors embedded in the foundation slab of the underground structure. Each pressure-type prestressed anchor includes prestressed steel bars, sleeves, and a metal load-bearing body, and is divided into an anchoring section, a free section, and a tensioning section along the height direction from bottom to top.

[0012] The sleeve is fitted around the prestressed steel bar, with a certain gap between them. The metal support body is set at the bottom of the prestressed steel bar and the sleeve, and is connected to both of them and seals the gap between them.

[0013] A steel pad is provided at the tensioning end of the prestressed steel bar, and a secondary grouting pipe is reserved on the steel pad. Grouting is performed through the secondary grouting pipe to seal the gap between the prestressed steel bar and the underground structure base plate. A waterproof structure is provided between the prestressed steel bar and the underground structure base plate.

[0014] The portion of the prestressed steel bars located within the base slab of the underground structure is fitted with a corrugated pipe, which is welded to the steel pad.

[0015] The corrugated pipe is surrounded by spiral hoops.

[0016] The anchorage section of the pressure-type prestressed anchor rod is surrounded by a steel cage, which is connected and fixed to the sleeve and the metal bearing body. A grouting body is formed around the steel cage by grouting.

[0017] The waterproof structure includes a water-swellable sealing ring sleeved on the prestressed steel bars and a water-swellable sealing ring located at the connection position between the prestressed steel bars and the underground structure bottom plate.

[0018] After tensioning, the prestressed steel bars are anchored to the steel pad by nuts, and the ends of the prestressed steel bars are sealed by pouring micro-expansion fine stone concrete.

[0019] A positioning frame is provided around the free section of the pressure-type prestressed anchor rod.

[0020] The advantages of this invention are:

[0021] 1) The anchorage section adopts an integrated metal bearing body, which can not only connect prestressed steel bars, but also connect matching sleeves. After tightening, it prevents groundwater from flowing along the inside of the sleeve and the prestressed steel bars to the bottom slab.

[0022] 2) The purpose of setting up a steel cage in the anchorage section is to solve the problem of a small amount of loose soil accumulating at the bottom of the hole in the anchorage section, which causes the prestressing tendons to be stretched loosely and cannot be tensioned by controlling the elongation of the prestressing tendons; after the steel cage is set up, even if there is loose soil in the grout, the grouting body of the anchorage section with the steel cage can effectively transfer the prestress and will not be loose.

[0023] 3) A corrugated pipe transition section is set in the tensioning section. After tensioning, a secondary protection is carried out using micro-expansion cement grout. In addition, a water-swellable water-stop ring between the anchor rod and the base plate blocks the path of groundwater upward along the corrugated pipe.

[0024] 4) The tensioning platform is located inside the base slab. After the prestressed tendons are tensioned, a higher grade of micro-expansion fine stone concrete is poured to once again block the path of groundwater upward along the prestressed steel bars or metal corrugated pipes.

[0025] 5) After the anchor rod body is constructed, the basement floor slab can be constructed without delaying the construction period.

[0026] 6) It can meet the structural bearing capacity requirements, solve the pain points of construction and use, improve construction efficiency, shorten the project period, and reduce investment costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention;

[0028] Figure 2 This is a schematic diagram of the anchoring section in this invention;

[0029] Figure 3 This is a schematic diagram of the steel cage structure in this invention;

[0030] Figure 4 This is a schematic diagram of the structure of the metal support in this invention;

[0031] Figure 5 for Figure 1 AA section view in the middle;

[0032] Figure 6 for Figure 1 The aa cross-section diagram. Detailed Implementation

[0033] The features and other related features of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, so as to facilitate understanding by those skilled in the art:

[0034] like Figure 1-6 As shown in the figure, markings 1-25 represent: 1. Prestressed steel bar, 2. Sleeve, 3. Steel cage, 4. Metal bearing body, 5. Positioning frame, 6. Steel pad, 7. Nut, 8. External thread, 9. Internal thread, 10. Ring bracket, 11. Weld point, 12. Welding surface, 13. Grouting pipe, 14. Grouting body, 15. Spiral stirrup, 16. Metal corrugated pipe, 17. Water-swellable sealing ring, 18. Secondary grouting vent hole, 19. Secondary grouting pipe, 20. Micro-expansion fine stone concrete, 21. Micro-expansion cement slurry, 22. Waterproof membrane, 23. Plain concrete cushion layer, 24. Bottom slab reinforcement.

[0035] Example: Figures 1 to 6 As shown, in this embodiment, pressure-type prestressed anchors are mainly used for anti-buoyancy in underground structures, such as basements, so that the underground structure can resist the buoyancy of groundwater and ensure the structural stability of the underground structure.

[0036] Specifically, such as Figure 1 As shown, the pressure-type prestressed anchor bolt body in this embodiment includes a prestressed steel bar 1, a sleeve 2, and a metal support body 4. The prestressed steel bar 1 passes through the inside of the sleeve 2, and is used to provide prestress. The sleeve 2 separates the prestressed steel bar 1 from the subsequent grouting material and provides some protection for the prestressed steel bar 1. The metal support body 4 is located at the bottom end of the prestressed steel bar 1 and the sleeve 2. (Combined with...) Figure 2 and Figure 4 As shown, the metal support 4 has a groove that matches the size of the prestressed steel bar 1. An internal thread 9 is provided on the inner wall of the groove. An external thread matching the internal thread 9 is provided at the corresponding position at the bottom end of the prestressed steel bar 1 (or the prestressed steel bar 1 may be a threaded steel bar), allowing the metal support 4 and the prestressed steel bar 1 to form a tightened connection through the engagement of the internal and external threads. A connecting ring is provided on the top surface of the metal support 4. The thickness of the connecting ring matches the gap between the prestressed steel bar 1 and the sleeve 2, allowing the connecting ring to be inserted between the prestressed steel bar 1 and the sleeve 2. An external thread 8 is provided on the outer wall of the connecting ring, and an internal thread matching the external thread 8 is partially provided on the inner wall of the bottom end of the sleeve 2, allowing the metal support 4 and the sleeve 2 to form a tightened connection through the engagement of the internal and external threads.

[0037] At this point, the metal support 4 can play multiple roles. First, since it is connected to the prestressed steel bar 1 and the sleeve 2 respectively and inserted into the gap between them, the metal support 4 can effectively block the upward hydraulic path of groundwater along the gap between the prestressed steel bar 1 and the sleeve 2, thus avoiding corrosion caused by groundwater. Second, by tightening the internal thread with the prestressed steel bar 1, it provides the anchoring effect for prestressing tension, ensuring the prestress of the prestressed steel bar 1. Third, it improves the integrity of the prestressed steel bar 1 and the sleeve 2, thereby improving the tensile bearing capacity of the anchorage end and the mechanical stability of the end anchorage area, and avoiding stress concentration.

[0038] like Figure 1 As shown, the pressure-type prestressed anchor rod in this embodiment is divided into three sections along its height direction from bottom to top: the anchoring section, the free section, and the tensioning section.

[0039] The anchorage section, located at the bottom of the capillary tube, mainly comprises a metal load-bearing body 4 and a reinforcing cage 3. (Combined) Figure 2 and Figure 3As shown, the reinforcing cage consists of three longitudinal bars and annular supports 10 arranged at certain intervals. The sleeve 2 is set at the center of the annular supports 10. The annular supports 10 are fixed by welding the longitudinal bars to form an integral structure. Weld points 11 are formed between the longitudinal bars and the annular supports 10. The bottom of the longitudinal bars is bent horizontally to form a welding surface 12. The welding surface 12 is welded and fixed to the metal bearing body 4 to form an integral structure. After grouting through the grouting pipe 13, an end anchor body is formed, which effectively provides end anchoring force. Even if there is loose soil in the grout, the prestress can be effectively transmitted through the grouting body 14 of the anchoring section with the reinforcing cage 3, avoiding voids and ensuring effective end anchoring force.

[0040] The free section is located above the anchorage section. Its main function is to provide a telescopic beam for tensioning. It mainly consists of grouting 14, sleeve 2, positioning frame 5, and prestressed steel reinforcement 1. Lubricating grease can be injected into the sleeve 2. The positioning frame 5 is installed around the sleeve 2 for positioning during construction, ensuring accuracy, especially the overall verticality of the anchor rod.

[0041] The tensioning section is located above the free section, and its main function is to tension and anchor the prestressed steel bars 1. For example... Figure 1 As shown, a steel pad 6 is provided at the top of the prestressed steel bar 1. After the prestressed steel bar 1 is tensioned, it can be anchored to the steel pad 6 by a nut 7.

[0042] like Figure 1 As shown, in this embodiment, the tensioning section of the prestressed steel bar 1 is embedded in the underground structure base slab, and a metal corrugated pipe 16 is partially sleeved on it. The metal corrugated pipe 16 is used to protect the prestressed steel bar 1. Spiral stirrups 15 are sleeved around the metal corrugated pipe 16 to increase the connection performance between it and the underground structure base slab, thereby ensuring that the prestress of the prestressed steel bar 1 can be effectively applied to the underground structure base slab.

[0043] A secondary grouting vent hole 19 and a secondary grouting pipe 20 are provided on the steel pad 6. After the prestressed steel bar 1 is tensioned, micro-expansion cement grout 22 is injected into the metal corrugated pipe 16 through the secondary grouting pipe 20 for secondary protection. The secondary grouting vent hole 19 is used to release air during grouting to ensure grouting quality. At the same time, a water-swellable water-stop ring 17 is set on the prestressed steel bar 1, and a water-swellable water-stop ring 18 is set at the connection position between the prestressed steel bar 1 and the underground structure bottom slab to further block the upward path of groundwater along the metal corrugated pipe 16 and improve waterproof performance. After tensioning, the top of the prestressed steel bar 1 is cut off, so that its top end is lower than the underground structure bottom slab and sealed with micro-expansion fine stone concrete 21.

[0044] In this embodiment, the underground structure base slab is composed of a plain concrete cushion layer 24 and a waterproof membrane 23 laid on top of it, which can further prevent the upward path of groundwater.

[0045] This embodiment includes the following steps during construction:

[0046] 1) Drill holes at the designed locations of the pressure-type stress anchor bolts.

[0047] 2) Select the length of the prestressed steel bar 1 according to the hole depth, and set threaded ends (external threads) at both ends of the prestressed steel bar 1 to match the metal support body 4 and the nut 7 of the tensioning section. Tighten the prestressed steel bar 1 to the metal support body 4.

[0048] 3) Insert a sleeve 2 of the same size into the outside of the prestressed steel bar 1. The sleeve 2 is connected to the metal support body 4 by threaded connection and the space between the sleeve 2 and the prestressed steel bar 1 is filled with grease.

[0049] 4) A steel cage 3 is installed in the anchorage section and welded to the metal load-bearing body 4.

[0050] 5) Set up a positioning frame 5 at the free section of the sleeve 2 and insert the rod into the anchor hole.

[0051] 6) Grouting and secondary grouting are performed into the anchor bolt holes to form a grouting body 14 in the anchoring section.

[0052] 7) Waterproofing of the building under the foundation slab and reinforced waterproofing of the top of the anchor rod (water-swellable sealing ring).

[0053] 8) A water-swellable sealing ring 17 is installed on the prestressed steel bar. The steel pad 6 and the metal corrugated pipe 16 are welded together, and a spiral stirrup 15 is fitted on it, which passes through the prestressed steel bar 1 and is placed on the pole.

[0054] 9) Tie the bottom slab reinforcement of the underground structure to 25mm, reserve the position of the tensioning platform, and pour the bottom slab of the underground structure.

[0055] 10) After the base plate has reached a certain strength, tension the prestressed steel bar 1 and lock it with the nut 7, and cut off the excess part at the top of the prestressed steel bar 1.

[0056] 11) Grouting is performed from the secondary grouting pipe 20 reserved in the steel pad 6, and the metal corrugated pipe 16 is filled with micro-expansion cement grout 22.

[0057] 12) Pour a higher-grade micro-expansion fine stone concrete 21 to fill the tensioning platform.

[0058] 13) Construction surface layer of the underground structure base slab.

[0059] Although the above embodiments have described the concept and embodiments of the present invention in detail with reference to the accompanying drawings, those skilled in the art will recognize that various improvements and modifications can still be made to the present invention without departing from the scope of the claims, and therefore will not be elaborated here.

Claims

1. An anti-buoyancy system for underground structures using pressure-type prestressed anchors, characterized in that: This includes pressure-type prestressed anchors embedded in the foundation slab of underground structures. The pressure-type prestressed anchors consist of prestressed steel bars, sleeves, and a metal load-bearing body, and are divided into an anchoring section, a free section, and a tensioning section along the height direction from bottom to top. The sleeve is fitted around the prestressed steel bar, with a certain gap between them. The metal support body is set at the bottom of the prestressed steel bar and the sleeve, and is connected to both of them and seals the gap between them. A steel pad is provided at the tensioning end of the prestressed steel bar, and a secondary grouting pipe is reserved on the steel pad. Grouting is performed through the secondary grouting pipe to seal the gap between the prestressed steel bar and the underground structure slab. A waterproof structure is provided between the prestressed steel bar and the underground structure slab. The anchorage section of the pressure-type prestressed anchor rod is surrounded by a steel cage, which is connected and fixed to the sleeve and the metal bearing body. A grouting body is formed around the steel cage by grouting. The metal support has a groove that matches the size of the prestressed steel bar, and an internal thread is provided on the inner wall of the groove. An external thread matching the internal thread is provided at a corresponding position at the bottom end of the prestressed steel bar, allowing the metal support and the prestressed steel bar to form a tightened connection through the engagement of the internal and external threads. A connecting ring is provided on the top surface of the metal support, the thickness of which matches the gap between the prestressed steel bar and the sleeve, allowing the connecting ring to be inserted between the prestressed steel bar and the sleeve. An external thread is provided on the outer wall of the connecting ring, and a matching internal thread is provided on a partial portion of the inner wall at the bottom end of the sleeve, allowing the metal support and the sleeve to form a tightened connection through the engagement of the internal and external threads.

2. The anti-buoyancy system for underground structures using pressure-type prestressed anchors according to claim 1, characterized in that: The portion of the prestressed steel bars located within the base slab of the underground structure is fitted with a corrugated pipe, which is welded to the steel pad.

3. The anti-buoyancy system for underground structures using pressure-type prestressed anchors according to claim 2, characterized in that: The corrugated pipe is surrounded by spiral hoops.

4. The anti-buoyancy system for underground structures using pressure-type prestressed anchors according to claim 1, characterized in that: The waterproof structure includes a water-swellable sealing ring sleeved on the prestressed steel bars and a water-swellable sealing ring located at the connection position between the prestressed steel bars and the underground structure bottom plate.

5. The anti-buoyancy system for underground structures using pressure-type prestressed anchors according to claim 1, characterized in that: After tensioning, the prestressed steel bars are anchored to the steel pad by nuts, and the ends of the prestressed steel bars are sealed by pouring micro-expansion fine stone concrete.

6. The anti-buoyancy system for underground structures using pressure-type prestressed anchors according to claim 1, characterized in that: A positioning frame is provided around the free section of the pressure-type prestressed anchor rod.

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