An anti-floating anchor rod with adjustable initial vertical rigidity and a construction method thereof

Abstract

This invention discloses an anti-buoyancy anchor with adjustable initial vertical stiffness and its construction method. The anti-buoyancy anchor includes an anchor bar, an anchor body, and a top retarder section. The anchor bar is vertically arranged, with the anchor body and the top retarder section arranged sequentially from bottom to top along the vertical direction on its outer periphery. The lower end of the top retarder section is inserted downward into the anchor body, and the upper end of the anchor bar is embedded in the basement floor slab. A layer of space is reserved between the anchor body and the basement floor slab as a cushion layer for arranging the top retarder section. The remaining part of the cushion layer is used for pouring concrete. The top retarder section contains a retardering adhesive for changing stiffness, and the retardering adhesive is arranged on the outer periphery of the anchor bar. The construction method is to change the vertical stiffness by the curing time difference of the retardering adhesive. In the initial stage of construction, the vertical force is supported by the foundation soil, and the anchor does not bear pressure. This invention has a simple structure, is convenient to construct, and economically and efficiently solves the problem of improper pressure on anchors.

Description

Technical Field

[0001] This invention belongs to the field of foundation technology for building engineering, and in particular relates to an anti-buoyancy anchor with adjustable initial vertical stiffness and its construction method. Background Technology

[0002] For underground structures with high groundwater levels, measures are typically required to meet anti-buoyancy requirements. One common anti-buoyancy method is to install anti-buoyancy anchors under the foundation or basement slab. Anti-buoyancy anchors are designed to resist the buoyancy force generated by groundwater under high water levels. They are usually designed and calculated as tension members, without fully considering the vertical compressive stress requirements under low water levels. When the groundwater level drops or is at a low level, the buoyancy force decreases significantly. The structure's self-weight and the upper vertical load are shared by the foundation soil and the anti-buoyancy anchors. However, because the vertical stiffness of the anti-buoyancy anchors is much greater than the subgrade coefficient of the natural foundation soil, a significant force distribution deflection occurs under vertical loads. This alters the original force transmission path of the upper structure's vertical load, causing most of the vertical load to no longer be borne by the foundation soil but to be directly transferred and concentrated on the anti-buoyancy anchors. This forces the anchors to change from their designed tension state to a long-term compressive state. Anti-buoyancy anchors are mostly slender rods with low compressive bearing capacity, making them prone to bending, buckling, yielding, or even fracture under pressure. Furthermore, the pressure on the anchors can push the basement floor slab upwards, ultimately causing structural damage such as cracking, bulging, and leakage, severely impacting the overall safety and normal use of the foundation and underground structure.

[0003] Therefore, it is necessary to invent an anti-buoyancy anchor with adjustable initial vertical stiffness to avoid stress on the anchor under low water conditions and ensure the anchor's pull-out resistance. Summary of the Invention

[0004] Existing anti-buoyancy anchors cannot adjust their vertical stiffness. The vertical stiffness of the anchor is mainly determined by the anchor diameter and soil parameters. Typically, the vertical stiffness of the anchor is greater than that of the natural foundation soil, causing the foundation stress to deviate from the preset force transmission pattern, resulting in anchor damage, cracking and leakage of the basement floor slab, etc. Therefore, this invention provides an anti-buoyancy anchor with adjustable initial vertical stiffness and its construction method. During the construction phase (when the anti-buoyancy anchor is not needed), the vertical stiffness of the anti-buoyancy anchor is reduced so that the anchor does not bear the vertical load of the superstructure. When the building is completed and the anti-buoyancy anchor is needed, the connection between the anchor and the basement floor slab is reliable, ensuring its pull-out resistance.

[0005] The technical solution adopted in this invention is: I. An anti-buoyancy anchor with adjustable initial vertical stiffness The device includes an anchor bar, an anchor body, and a top retarder section. The anchor bar is vertically arranged, with the anchor body and the top retarder section arranged sequentially from bottom to top along its outer periphery in a vertical direction. The lower end of the top retarder section is inserted into the interior of the anchor body, and the upper end of the anchor bar is embedded into the interior of the basement floor slab. A layer of space is reserved between the anchor body and the basement floor slab as a cushion layer for arranging the top retarder section. The remaining part of the cushion layer is used for pouring concrete. The top retarder section contains a retarder adhesive for changing stiffness, and the retarder adhesive is arranged on the outer periphery of the anchor bar.

[0006] The rod top slow-setting section includes an outer waterproof rubber sleeve and a steel sheath. The steel sheath is built into the outer waterproof rubber sleeve, and the anchor rod reinforcement is placed inside the steel sheath. The anchor rod reinforcement, the outer waterproof rubber sleeve, and the steel sheath are all arranged coaxially. Asphalt waterproof sealant is placed between the outer waterproof rubber sleeve and the steel sheath, and slow-setting adhesive is placed between the steel sheath and the anchor rod reinforcement. The steel sheath is inserted downward into the anchor body.

[0007] The steel sheath is divided into upper and lower parts. The upper part is a corrugated section of the steel sheath, which is a wave-shaped structure extending vertically. The lower part is a straight section of the steel sheath. The corrugated section of the steel sheath is compressed by vertical pressure to reduce its vertical dimension. The retarding adhesive is arranged between the corrugated section of the steel sheath and the anchor rod. The straight section of the steel sheath is used to insert into the anchor body.

[0008] The stiffness of the retarded adhesive changes as it cures over time: Before curing, the retarded adhesive is in the form of a paste with a first strength; After curing, the retarded adhesive cures to form an adhesive layer with a second strength that wraps around the periphery of the anchor bar. The second strength is greater than the first strength, thereby enhancing the vertical stiffness of the retarded adhesive.

[0009] The upper end of the steel sheath is provided with a top metal cover plate, and a through hole is provided in the middle of the top metal cover plate along the vertical direction. The through hole is used for the anchor rod to pass through.

[0010] The material of the anchor body includes either cement mortar or concrete.

[0011] The retarded adhesive is a moisture-curing retarded adhesive as specified in the group standard TCECS 10116-2021.

[0012] II. A construction method for an anti-buoyancy anchor with adjustable initial vertical stiffness. The construction method is as follows: Step 1: Complete the construction of the anchor rod reinforcement and anchor body, and reserve a cushion layer between the top of the anchor body and the basement floor slab for the construction of the slow-setting section at the top of the rod; Step 2: Before the anchor body initially sets, the steel sleeve is put on the outside of the anchor rod reinforcement, and the lower part of the steel sleeve is inserted into the unset anchor body. Step 3: After the anchor body has initially set, inject a retarding adhesive between the steel sheath and the anchor rod reinforcement. Step 4: Slide the outer waterproof rubber sleeve onto the outside of the steel sheath, and inject asphalt waterproof sealant between the steel sheath and the outer waterproof rubber sleeve; Step 5: Cover the top of the steel sheath with a top metal cover plate, and anchor the anchor rod through the pre-drilled through hole in the top metal cover plate and anchor it into the basement floor slab; Step 6: Continue pouring concrete under the basement floor slab to form a concrete cushion layer, which is then bonded to the outer waterproof rubber sleeve. After the concrete cushion layer is poured in step 6, the groundwater level is lower than the predetermined height. The basement floor slab transmits pressure to the steel sheath through the top metal cover plate. The retarding adhesive inside the steel sheath is in a paste state with the first strength. The vertical stiffness of both the steel sheath and the retarding adhesive is lower than that of the foundation soil. The retarding adhesive is compressed and deformed along with the steel sheath and the corrugated section of the steel sheath, thereby allowing the pressure of the basement floor slab to be directly transmitted to the foundation soil below the concrete cushion layer. Step 7: Continue construction of the basement floor slab and its superstructure, whereby the slow-setting adhesive cures over time to form a bonding layer with a second strength.

[0013] In step 7, the slow-setting adhesive cures over time to form an adhesive layer with a second strength, which wraps around the anchor bar to enhance vertical stiffness. The vertical stiffness of the adhesive layer with the second strength is greater than that of the foundation soil. When the groundwater level rises to a predetermined height, the pressure of the basement floor slab is converted into tension, and the tension of the basement floor slab is transmitted to the anchor body through the adhesive layer with the second strength.

[0014] The present invention has the following beneficial effects: This invention cleverly utilizes the characteristics of retarded adhesives and the unique timeframe for the effectiveness of anti-buoyancy anchors to disclose an anti-buoyancy anchor with adjustable initial vertical stiffness. The invention connects the basement floor slab and the anti-buoyancy anchor through a retarded section at the top of the anchor. Before reaching its curing period, the retarded adhesive in this section is in a paste-like, low-viscosity state and lacks vertical stiffness. When the retarded section is subjected to pressure from the basement floor slab, it can deform freely without transmitting force to the lower anti-buoyancy anchor. The pressure from the raft foundation is effectively transferred to the foundation soil beneath the basement floor slab. As the superstructure is constructed layer by layer, the entire structural weight is transferred to the foundation soil until the retarded adhesive reaches its curing period, forming a high-strength bonding layer that tightly bonds with the anchor reinforcement, sharing the load and creating vertical stiffness to meet the pull-out resistance requirements of the anti-buoyancy anchor. Furthermore, the dense bonding layer formed by the retarded adhesive effectively protects the reinforcement at the anchor end, improving the anchor's durability; the outer asphalt waterproof sealant effectively achieves the waterproofing requirements at the connection between the anchor top and the basement floor slab. This invention has a simple structure, is easy to construct, and solves the problem of improper pressure on anchor bolts in an economical and efficient manner. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the connection between the underground foundation slab and the anti-buoyancy anchor provided by the present invention; Figure 2 This is a three-dimensional isometric view of the rod-top retarding section provided by the present invention; Figure 3 This is a structural breakdown diagram of the rod-top retarding section provided by the present invention; Figure 4 This is an enlarged schematic diagram of the connection between the underground foundation slab and the anti-buoyancy anchor provided by the present invention.

[0016] In the diagram, 1-basement floor slab; 2-subbase layer; 3-anti-buoyancy anchor rod body; 301-anchor rod reinforcement; 302-anchor body; 4-retarding section at the top of the rod; 401-outer waterproof rubber sleeve; 402-top metal cover plate; 403-steel sheath; 4031-corrugated section of steel sheath; 4032-straight section of steel sheath; 404-asphalt waterproof sealant; 405-retarding adhesive. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] like Figure 1 and Figure 4As shown, an anti-buoyancy anchor bolt with adjustable initial vertical stiffness includes anchor bolt reinforcement 301, anchor body 302, and a rod top retarding section 4. The anchor bolt reinforcement 301 and anchor body 302 form the anti-buoyancy anchor bolt body 3. The anchor body 302 is used to wrap the anchor bolt reinforcement 301, and there are three anchor bolt reinforcements 301. All anchor bolt reinforcements 301 are arranged vertically, and the anchor body 302 and the rod top retarding section 4 are arranged sequentially from bottom to top along the vertical direction on the outer periphery of the entire bolt. The lower part of the rod top retarding section 4... The anchor rod is inserted downward into the interior of the anchor body 302. The upper ends of all the anchor rods 301 are used to pass through the top retarding section 4 and then be embedded into the interior of the basement floor slab 1. A layer of space is reserved between the anchor body 302 and the basement floor slab 1 as a cushion layer 1 for arranging the top retarding section 4. The remaining part of the cushion layer 1 is used for pouring concrete. The top retarding section 4 contains a retarding adhesive 405 for changing the stiffness. The retarding adhesive 405 is arranged on the outer periphery of the entire anchor rod 301.

[0019] like Figure 2 As shown, the slow-setting section 4 at the top of the rod includes an outer waterproof rubber collar 401 and a steel sheath 403. The steel sheath 403 is built into the outer waterproof rubber collar 401. All anchor rod reinforcements 301 are built into the steel sheath 403. The anchor rod reinforcements 301 as a whole, the outer waterproof rubber collar 401 and the steel sheath 403 are all arranged coaxially. Asphalt waterproof sealant 404 is arranged between the outer waterproof rubber collar 401 and the steel sheath 403. Slow-setting adhesive 405 is arranged between the steel sheath 403 and the anchor rod reinforcements 301 as a whole. The steel sheath 403 is inserted downward into the anchor body 302.

[0020] The outer waterproof rubber collar 401 has the same diameter as the anti-buoyancy anchor rod 3, and its height is the same as the thickness of the pad layer 2 under the basement floor slab 1.

[0021] like Figure 3 As shown, the steel sheath 403 is divided into upper and lower parts. The upper part is the corrugated section 4031 of the steel sheath, which is a wave-shaped structure extending vertically. The lower part is the straight section 4032 of the steel sheath, which is without corrugations. The corrugated section 4031 of the steel sheath is compressed by vertical pressure, thereby reducing its vertical dimension. Specifically, the amount of compression should be able to reach 30% to 60% of the free length. Furthermore, a retarding adhesive 405 is arranged between the corrugated section 4031 of the steel sheath and the anchor rod rib 301. The straight section 4032 of the steel sheath has a certain vertical stiffness to meet the requirements for its insertion into the anchor body 302. Specifically, the steel sheath 403 is made of metal and its diameter is 40 to 50 mm smaller than that of the anchor body 302.

[0022] The length of the corrugated steel sleeve section 4031 is the same as the thickness of the pad 2 under the basement floor slab 1, generally 100mm~150mm, and is used for assembly in the pad 2.

[0023] The stiffness of the retarded adhesive 405 changes as it cures over time: Before curing, the retarded adhesive 405 is a paste with first strength and low vertical stiffness. After curing, the retarding adhesive 405 gradually cures to form an adhesive layer with a second strength, which wraps tightly around the outer periphery of the anchor rod 301 and shares the stress. The second strength is greater than the first strength, thereby enhancing the vertical stiffness of the retarding adhesive 405.

[0024] The curing period is generally 180 days, 270 days, or 360 days, which can be selected according to the construction schedule.

[0025] A top metal cover plate 402 is arranged at the top of the upper end of the steel sheath 403. A through hole is opened vertically in the middle of the top metal cover plate 402, which is used for all the anchor rods 301 to pass through.

[0026] The material of anchor 302 typically includes either cement mortar or fine aggregate concrete.

[0027] Retarded adhesive 405 adopts the moisture-curing slow-setting adhesive as defined in the group standard TCECS 10116-2021. It consists of epoxy resin, moisture-curing hardener, additives, and aggregates, and cures slowly by relying on ambient moisture, with a curing period adjustable from 3 to 24 months.

[0028] A construction method for an anti-buoyancy anchor with adjustable initial vertical stiffness is as follows: Step 1: Complete the construction of anchor rod reinforcement 301 and anchor body 302, and reserve a cushion layer 2 between the top of anchor body 302 and basement floor slab 1 for the construction of the slow-setting section 4 at the top of the rod. The construction of anchor rod reinforcement 301 and anchor body 302 in step 1 includes surveying and setting out, drilling, hole cleaning, fabrication and installation of anti-buoyancy anchor rod 3 and grouting; Step 2: Before the anchor body 302 initially sets, a steel sleeve 403 is fitted over the entire outer side of the anchor rod reinforcement 301, and the lower straight section of the steel sleeve 403 is inserted into the unset anchor body 302. Step 3: After the anchor body 302 has initially set, inject a retarding adhesive 405 between the steel sheath 403 and the anchor rod reinforcement 301. Step 4: Put an outer waterproof rubber sleeve 401 on the outside of the steel sheath 403, and inject asphalt waterproof sealant 404 between the steel sheath 403 and the outer waterproof rubber sleeve 401. Step 5: Cover the top of the steel sheath 403 with a top metal cover plate 402 to prevent concrete from mixing into the retarding adhesive 405 during the pouring of the basement floor slab 1. All anchor bars 301 pass through the pre-reserved through holes on the top metal cover plate 402 and are anchored into the basement floor slab 1. Step 6: Continue to pour concrete and apply waterproof membrane to the cushion layer 2 under the basement floor slab 1 to form a concrete cushion layer. The concrete cushion layer and the outer waterproof rubber sleeve 401 should fit tightly together. After the concrete cushion layer is poured in step 6, the groundwater is in the first working condition of low water level. The groundwater has a low first buoyancy, which is insufficient to support the self-weight of the structure and the vertical load. At this time, the basement floor slab 1 generates pressure. The basement floor slab 1 transmits the pressure to the steel sleeve 403 through the top metal cover plate 402. The retarding adhesive 405 in the steel sleeve 403 is in the first strength paste state. The vertical stiffness of the steel sleeve 403 and the retarding adhesive 405 is lower than that of the foundation soil. The retarding adhesive 405 is compressed and deformed together with the steel sleeve 403 and the corrugated section 4031 of the steel sleeve under pressure. This allows the pressure of the basement floor slab 1 to be directly transmitted to the foundation soil below the concrete cushion layer, avoiding the pressure effect of the anti-buoyancy anchor rod 3. Step 7: Continue construction of the basement floor slab 1 and its upper structure. The slow-setting adhesive 405 cures over time to form a bonding layer with a second strength, which is tightly bonded to the anchor rod reinforcement 301 to share the load and form vertical stiffness, thus meeting the pull-out requirements of the anti-buoyancy anchor rod.

[0029] In step 7, the slow-setting adhesive 405 gradually solidifies over time to form an adhesive layer with a second strength, which wraps tightly around the outer periphery of the anchor rod 301 and works together to enhance the vertical stiffness, thus meeting the pull-out requirements of the anti-buoyancy anchor rod. The vertical stiffness of the adhesive layer with the second strength is much greater than that of the foundation soil. When the groundwater level rises to the predetermined height, the pressure of the basement floor slab (1) is converted into tension. Specifically, at this time, under the second working condition of high water level, the groundwater is under a higher second buoyancy, which is greater than the first buoyancy. The water level in the second working condition is higher than that in the first working condition. The second buoyancy still generates an upward tension after supporting the self-weight of the structure and the vertical load. The tension of the basement floor slab 1 is transmitted to the anchor body 302 through the adhesive layer with the second strength, so that the anti-buoyancy anchor rod 3 can play the role of bearing the tension.

Claims

1. An anti-buoyancy anchor with adjustable initial vertical stiffness, characterized in that: The device includes an anchor bar (301), an anchor body (302), and a rod top retarder section (4). The anchor bar (301) is arranged vertically, and the anchor body (302) and the rod top retarder section (4) are arranged sequentially from bottom to top along the vertical direction on its outer periphery. The lower end of the rod top retarder section (4) is inserted downward into the interior of the anchor body (302). The upper end of the anchor bar (301) is used to embed into the interior of the basement floor slab (1). A layer of space is reserved between the anchor body (302) and the basement floor slab (1) as a cushion layer (1) for arranging the rod top retarder section (4). The remaining part of the cushion layer (1) is used for pouring concrete. The rod top retarder section (4) contains a retarder adhesive (405) for changing stiffness. The retarder adhesive (405) is arranged on the outer periphery of the anchor bar (301).

2. The anti-buoyancy anchor bolt with adjustable initial vertical stiffness according to claim 1, characterized in that: The rod top slow-setting section (4) includes an outer waterproof rubber sleeve (401) and a steel sleeve (403). The steel sleeve (403) is built into the outer waterproof rubber sleeve (401). The anchor rod reinforcement (301) is built into the steel sleeve (403). The anchor rod reinforcement (301), the outer waterproof rubber sleeve (401), and the steel sleeve (403) are all coaxially arranged. Asphalt waterproof sealant (404) is arranged between the outer waterproof rubber sleeve (401) and the steel sleeve (403). Slow-setting adhesive (405) is arranged between the steel sleeve (403) and the anchor rod reinforcement (301). The steel sleeve (403) is inserted downward into the anchor body (302).

3. The anti-buoyancy anchor bolt with adjustable initial vertical stiffness according to claim 2, characterized in that: The steel sheath (403) is divided into upper and lower parts. The upper part is a corrugated section (4031) of the steel sheath, which is a wave-shaped structure extending vertically. The lower part is a straight section (4032) of the steel sheath. The corrugated section (4031) of the steel sheath is compressed by vertical pressure to reduce the vertical dimension. The retarding adhesive (405) is arranged between the corrugated section (4031) of the steel sheath and the anchor rod (301). The straight section (4032) of the steel sheath is used to insert into the anchor body (302).

4. The anti-buoyancy anchor bolt with adjustable initial vertical stiffness according to claim 3, characterized in that: The stiffness of the retarded adhesive (405) changes as it cures over time: Before curing, the retarded adhesive (405) is in the form of a paste with a first strength; After curing, the retarding adhesive (405) cures to form an adhesive layer with a second strength that wraps around the outer periphery of the anchor bar (301). The second strength is greater than the first strength, thereby enhancing the vertical stiffness of the retarding adhesive (405).

5. The anti-buoyancy anchor bolt with adjustable initial vertical stiffness according to claim 2, characterized in that: The upper end of the steel sheath (403) is provided with a top metal cover plate (402), and a through hole is provided in the middle of the top metal cover plate (402) along the vertical direction. The through hole is used for the anchor rod (301) to pass through.

6. The anti-buoyancy anchor bolt with adjustable initial vertical stiffness according to claim 2, characterized in that: The material of the anchor (302) includes either cement mortar or concrete.

7. The anti-buoyancy anchor bolt with adjustable initial vertical stiffness according to claim 4, characterized in that: The retarded adhesive (405) is a moisture-curing retarded adhesive as specified in the group standard TCECS 10116-2021.

8. A construction method for an anti-buoyancy anchor with adjustable initial vertical stiffness as described in any one of claims 5-7, characterized in that, The construction method is as follows: Step 1: Complete the construction of the anchor rod reinforcement (301) and the anchor body (302), and reserve a cushion layer (2) between the top of the anchor body (302) and the basement floor slab (1) for the construction of the rod top slowing section (4). Step 2: Before the anchor body (302) initially sets, the steel sleeve (403) is put on the outside of the anchor rod reinforcement (301), and the lower part of the steel sleeve (403) is inserted into the unset anchor body (302); Step 3: After the anchor body (302) has initially set, a slow-setting adhesive (405) is injected between the steel sheath (403) and the anchor rod reinforcement (301). Step 4: Put the outer waterproof rubber sleeve (401) on the outside of the steel sleeve (403), and inject asphalt waterproof sealant (404) between the steel sleeve (403) and the outer waterproof rubber sleeve (401). Step 5: Cover the top of the steel sheath (403) with a top metal cover plate (402), and the anchor rod (301) passes through the pre-reserved through hole on the top metal cover plate (402) and is anchored into the basement floor slab (1); Step 6: Continue to pour concrete for the cushion layer (2) under the basement floor slab (1) to form a concrete cushion layer. The concrete cushion layer and the outer waterproof rubber sleeve (401) are attached together. Step 7: Continue construction of the basement floor slab (1) and its superstructure, wherein the retarded adhesive (405) cures over time to form an adhesive layer with a second strength.

9. A construction method for an anti-buoyancy anchor with adjustable initial vertical stiffness according to claim 8, characterized in that: After the concrete cushion layer is poured in step 6, the basement floor slab (1) transmits pressure to the steel sheath (403) through the top metal cover plate (402). The retarding adhesive (405) inside the steel sheath (403) is in a paste state with the first strength. The vertical stiffness of the steel sheath (403) and the retarding adhesive (405) is lower than that of the foundation soil. The retarding adhesive (405) is compressed and deformed together with the steel sheath (403) and the corrugated section (4031) of the steel sheath, so that the pressure of the basement floor slab (1) is directly transmitted to the foundation soil below the concrete cushion layer through the concrete cushion layer.

10. A construction method for an anti-buoyancy anchor with adjustable initial vertical stiffness according to claim 8, characterized in that: In step 7, the retarded adhesive (405) cures over time to form an adhesive layer with a second strength, which wraps around the anchor bar (301) to enhance the vertical stiffness. The vertical stiffness of the adhesive layer with the second strength is greater than that of the foundation soil. When the groundwater level rises to a predetermined height, the pressure of the basement floor slab (1) is converted into tension. The tension of the basement floor slab (1) is transmitted to the anchor body (302) through the adhesive layer with the second strength.

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