A combined anchor rod with a prestressed core

Abstract

The present invention discloses a composite anchor rod with a prestressed core. The composite anchor rod consists of an inner prestressed concrete core and an outer cast-in-place anchoring slurry. The concrete core is provided with prestressed tendons and is prefabricated by pre-tensioning. The anchoring slurry wraps around the prestressed concrete core, and the cast-in-place anchoring slurry is formed by placing the prestressed concrete core in a pile hole and solidifying it through one or two grouting injections. The composite anchor rod of the present invention does not require on-site tensioning to lock in prestress, which can not only ensure the quality of the prestressed core, but also greatly shorten the on-site construction period. It can replace existing prestressed and ordinary non-prestressed anchor rods.

Description

Technical Field

[0001] The invention relates to the field of anchor rod construction, in particular to a combined anchor rod with a prestressed rod core. Background Art

[0002] In areas with abundant groundwater, the problem of anti-floating basements is common. Anchor rods are an effective measure to prevent underground structures from floating in construction projects. One end of the rod is connected to the engineering structure, and the other end is deep in the ground to transmit tension to the ground. In addition, anchor rods are also used for main reinforcement of slopes, tunnels, and dams, as well as to resist wind-induced overturning of high-rise buildings. Anchor rods are widely used and have a very mature standardization system and construction process. The relevant national and industry standards include the "Technical Specifications for Geotechnical Anchor Rods and Sprayed Concrete Support Engineering" (GB 50086-2015) and the "Technical Specifications for Geotechnical Anchor Rods (Ropes)". In addition, the "Technical Specifications for Foundation Pit Support" and the "Technical Standards for Anti-Floating Construction Engineering" also have special chapters on anchor rods.

[0003] In terms of type, anchor rods are divided into grouting type and mechanical prestressed anchor rods, tension type and pressure type prestressed anchor rods, load distribution type anchor rods, full-length bonded anchor rods, resin roll and fast-hardening cement roll anchor rods, hollow grouting anchor rods and friction type anchor rods. The common feature of these anchor rods is that they are cast in holes on site.

[0004] For ease of construction, non-prestressed anchors are often used for anti-floating anchors in underground projects. The typical construction process is as follows: anchor fabrication → drilling rig placement → hole drilling → dredging → anchor installation → pressure grouting → completion. These anchors offer significant advantages, including high load-bearing capacity, reliable quality, simple construction, and low overall cost.

[0005] Due to the small diameter of the anchor rod and the relatively large tensile bearing capacity, non-prestressed anchor rods are prone to durability issues due to cracks. Especially in sites where the soil and water are corrosive to the steel bars, cracks in the anchor rods can cause the steel bars to rust and swell, leading to overall anti-floating failure. According to the "Technical Standard for Anti-Floating of Construction Engineering" (JGJ476-2019), projects with a Class A anti-floating design grade should be designed so that the anchor rod anchoring slurry does not generate tensile stress; projects with a Class B anti-floating design grade should be designed so that no cracks appear, and prestressed anchor rods must be used.

[0006] Prestressed technology can effectively control the occurrence of cracks and improve the durability of anchor rods, but prestressed anchor rods must be tensioned after the basement floor is poured. Figure 1 Tensioning on the bottom plate takes a long time to construct, and the holes reserved in the bottom plate are very likely to cause water leakage in the basement. Summary of the Invention

[0007] Unlike existing concrete anchors, which are typically cast on-site, this invention proposes a composite anchor with a prestressed core. This composite anchor comprises a prefabricated prestressed concrete core and a cast-in-place anchoring grout. Grouting pipes are pre-placed in the core, or tied to the outside of the finished core for secondary grouting. This improves the bond between the anchor and the hole wall, thereby enhancing the anchor's pullout resistance. This anchor resolves the problem of existing prestressed anchors requiring a pre-reserved hole in the baseplate, which can lead to basement water leakage.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A combined anchor rod with a prestressed core, the combined anchor rod comprising:

[0010] A prestressed concrete rod core located on the inner side, wherein prestressed tendons are arranged inside the prestressed concrete rod core and are prefabricated by a pre-tensioning method;

[0011] The cast-in-situ anchoring slurry is located on the outside, and the anchoring slurry wraps the prestressed concrete rod core. The cast-in-situ anchoring slurry is formed by placing the prestressed concrete rod core in the pile hole and solidifying it after one or two groutings of the anchoring slurry.

[0012] Furthermore, the outer peripheral surface of the prestressed concrete rod core is provided with a rod core positioning device and a grouting pipe reserved groove.

[0013] Furthermore, there are three prestressed tendons inside the prestressed concrete rod core.

[0014] Furthermore, the radius R1 of the prestressed concrete rod core is 50-75 mm, and the thickness of the anchoring slurry is 30-60 mm.

[0015] Furthermore, the anchoring slurry is cement slurry.

[0016] Furthermore, in order to enhance the bonding performance between the prestressed concrete pile core and the cast-in-situ anchoring slurry, the outer peripheral surface of the prestressed concrete pile core is provided with bamboo-shaped or dot-shaped protrusions or depressions.

[0017] Furthermore, the prestressed concrete rod core may be in the shape of a frustum that is smaller at the top and larger at the bottom.

[0018] A construction method for a combined anchor rod with a prestressed core, the method comprising the following steps:

[0019] S1: The prestressed concrete core is prefabricated in the factory using the pre-tensioning method. The diameter of the prefabricated core is controlled at 100mm to 150mm. The steel bars are first tensioned on the pedestal, and then the concrete core is poured. Grouting pipes are reserved in the core. After the strength reaches the design value, the tensioning end is released to form prestress in the core. At the same time, a section of steel bars is retained on one side of the core for anchoring, and the steel bars on the other side are cut along the end of the core.

[0020] S2: Drilling rig drilling at the construction site;

[0021] S3: Clean the hole, tie the grouting pipe, and then lower the prefabricated rod core to ensure that the prestressed concrete rod core and the drill hole are coaxial;

[0022] S4: performing primary grouting around the prestressed concrete rod core, and performing secondary grouting after the primary grouting solidifies and shrinks to form a cast-in-place anchoring slurry;

[0023] S5: Anchor the reserved steel bars in the rod core into the base plate, cast the base plate, and complete the basement construction.

[0024] Furthermore, when pouring the concrete core in S1, an expansion agent is added to the concrete.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) In corrosive sites, ordinary anchor rods usually develop cracks, reducing their durability; under the long-term effects of fluctuating groundwater levels and alternating dry and wet environments, fine cracks will continue to expand, causing the internal steel bars of the components to rust and reduce their strength, thus leading to serious safety hazards. In this regard, the new industry specifications have proposed mandatory requirements for the use of prestressed anchor rods for projects with design grades A and I; for anchor rods with design grade C, the amount of steel bars can be saved by more than 60-70%. The combined anchor rod of the present invention adopts a pre-tensioning prestressing process to pre-stress the anchor rod body. The rod core of the combined anchor rod can meet the requirements of the specification for no cracks, and can effectively improve the durability and economy of the anti-floating anchor rod.

[0027] (2) At present, conventional prestressed anchor rods must be tensioned after the basement floor is cast. The construction process is cumbersome and has a great impact on the construction period. Different from the current characteristics of all concrete anchor rods being cast on site, through the industrialized prestressing method, the prefabricated rod core is produced in the factory, lowered and installed at the construction site, and the anchor slurry is poured to form a combined anchor rod. The current prefabricated concept and practice of the upper structure are successfully applied to the field of anti-floating anchor rods, making prefabricated components and prefabricated practices appear in the field of anti-floating foundation engineering. Compared with non-prestressed anchor rods and conventional slow-bonding prestressed anchor rods, this innovative approach can not only ensure the quality of the prestressed rod core, but also greatly shorten the on-site construction period and reduce the overall cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a construction drawing of a prestressed anchor rod in the prior art;

[0029] Figure 2 is a schematic diagram of a combined anchor rod of the present invention;

[0030] Figure 3 for Figure 2 Middle AA section;

[0031] Figure 4 It is a schematic diagram of the cross section of a combined anchor rod with a rod core positioning device;

[0032] Figure 5 Schematic diagram of a combined anchor rod when the rod core is a frustum;

[0033] In the figure, there are prestressed concrete rod core 1, cast-in-situ anchoring slurry 2, base plate 3, grouting pipe 4, rod core positioning device 5, prestressed tendons 101, rod core concrete 102, grouting pipe reserved groove 103, and dot-shaped protrusions 104. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments, and the purpose and effects of the present invention will become more apparent. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] The combined anchor rod with prestressed core of the present invention has three innovations:

[0036] (1) Conventional prestressed anti-floating anchor rods are all cast on site, while the composite anchor rod of the present invention is a composite anchor rod that is prefabricated in a factory and cast on site.

[0037] (2) Conventional anchor rods have only two types: non-prestressed and fully prestressed. In the combined anchor rod of the present invention, the prefabricated rod core is a prestressed component, while the anchoring slurry poured on site is a non-prestressed component.

[0038] (3) Traditional prestressed anti-floating anchor rods must be tensioned on the basement floor surface, and they cannot form a complete force-bearing system on their own. This new anchor rod only establishes prestress in the rod body below the floor, forming a self-balancing system in the absence of a floor, which provides better safety during subsequent basement construction conditions.

[0039] like Figure 2 As shown, the combined anchor rod with a prestressed core of the present invention comprises:

[0040] The prestressed concrete rod core 1 located on the inner side is prefabricated by a pre-tensioning method and has prestressed tendons 101 arranged inside;

[0041] The cast-in-place anchoring slurry 2 located on the outside wraps around the prestressed concrete rod core 1. This cast-in-place anchoring slurry 2 is formed by placing the prestressed concrete rod core 1 in the pile hole and then solidifying it through a single grouting process. When the anchoring slurry is cement slurry, the anchoring slurry is formed after a single grouting process. However, when the anchoring slurry is a mixed mortar, the slurry will shrink significantly after the single grouting process, causing cracks in the anchoring slurry. In this case, a secondary grouting process is required. After the secondary grouting process solidifies, the entire anchoring slurry is obtained.

[0042] like Figure 3 As shown, due to the small diameter of the anchor rod, the radius R1 of the prestressed concrete rod core 1 is 50-75mm, and the thickness of the cast-in-place anchor grout 2 is 30-60mm. A single prestressed tendon can be used in the prestressed concrete rod core 1. However, to account for factors such as transportation and construction deviations, three prestressed tendons can be installed in the rod core to enhance the rod's bending resistance. Prestressed steel bars or stranded steel wire can be used in the prestressed concrete rod core 1. The cast-in-place anchor grout 2 is cement grout.

[0043] like Figure 4 As shown, in order to enhance the bonding performance between the prestressed concrete rod core 1 and the cast-in-situ anchoring slurry 2, bamboo-shaped or dot-shaped protrusions 104 may be provided on the outer circumference of the prestressed concrete pile core 1. The rod body is generally circular, but may also be square, elliptical or have other cross-sections. At the same time, in order to avoid the deviation of the prestressed concrete rod core during the placement of the pile hole, the prestressed concrete rod core 1 is preferably provided with a rod core positioning device 5, which may be a 30x30xh protrusion (h is the distance from the rod core to the hole wall - 0.5 cm), 3 of which are provided in the circumferential direction and 2 circles in the longitudinal direction. At the same time, the prestressed concrete rod core 1 is provided with a reserved groove 103 for the grouting pipe, which is used to tie the grouting pipe before the rod core is lowered into the pile hole. There are 2 grouting pipes in total, which are used for primary and secondary grouting respectively.

[0044] like Figure 5 As shown, the prestressed concrete core is preferably a frustum with a smaller top and larger bottom. Under tension, the prestressed concrete core 1 squeezes the cast-in-place anchor grout 2 and the hole wall, resulting in a composite anchor with improved bearing capacity. Furthermore, because it is prefabricated in a factory, this core is easier to manufacture, something that was not possible with conventional cast-in-place anchors.

[0045] To prevent the rod core from misaligning during placement, the rod body is preferably equipped with a three-way positioning device. This device can be a 30x30xh protrusion (h is the distance from the rod core to the hole wall minus 0.5cm), with three circumferentially positioned and two longitudinally positioned. Furthermore, a reserved groove for grouting pipes is provided on the rod core to tie the grouting pipes before the rod core is lowered into the hole. Two grouting pipes are used, one for primary and one for secondary grouting.

[0046] The construction method of the combined anchor rod with a prestressed rod core of the present invention comprises the following steps:

[0047] S1: Prestressed concrete core 1 is prefabricated in the factory using the pre-tensioning method. The diameter of the prefabricated core is controlled at 100mm to 150mm. Rebar is tensioned on a pedestal before the concrete core is poured. Grouting pipes are reserved for the core. Once the strength reaches the design value, the tensioning end is released to form prestress in the core. At the same time, a section of rebar is retained on one side of the core for anchoring, and the rebar on the other side is cut off along the end of the core.

[0048] S2: Drilling rig drilling at the construction site;

[0049] S3: clean the hole, tie the grouting pipe 4, and then lower the prefabricated prestressed concrete rod core 1 to ensure that the prestressed concrete rod core 1 and the pile hole are coaxial;

[0050] S4: Perform primary grouting around the prestressed concrete rod core 1. After the primary grouting solidifies and shrinks, perform secondary grouting to form the cast-in-place anchor slurry 2.

[0051] S5: Anchor the reserved prestressed tendons 101 in the rod core into the bottom plate 3, cast the bottom plate 3, and complete the basement construction.

[0052] Different from conventional prestressed components, since the diameter of the anchor rod is generally 150-240 mm and the length is 4 m-15 m, considering the peripheral anchoring slurry, the prestressed concrete rod core 1 involved in the present invention has a smaller diameter. The application of prestress to it must ensure the positioning accuracy of the prestressed tendons to avoid additional bending moments caused by deviations, and it can also better reflect the advantages of factory prefabrication production.

[0053] Due to the small cross-section of the rod core, its prestressing force will be significantly higher than that of ordinary prestressed members. Elastic compression deformation and subsequent shrinkage creep will further increase prestress loss. Currently, according to the current "Concrete Structure Design Code", the prestress loss of pre-tensioned axially compressed members is shown in the first four items in Table 1. The prestress loss in the table does not include the loss caused by the release of tensioned steel bars, which leads to the compression of the rod body. Given the small cross-section of the rod core, this prestress loss σ is supplemented based on the existing code through analysis. S .

[0054] Table 1 Prestress loss analysis

[0055]

[0056] The following is an example to demonstrate the superiority of the combined anchor rod of the present invention and calculate its prestress loss.

[0057] An 8-meter-long composite pullout pile was analyzed for prestress loss, and the results are shown in Table 2. The concrete strength grade is C40, the pile core diameter is 150 mm, the prestressing tendons are 3 in number, and the prestressing control stress is 994 MPa.

[0058] Table 2 Analysis of prestress loss of a 15m combined pull-out pile

[0059] Prestress loss type <![CDATA[Calculation result / (N / mm 2 )]]> Remark <![CDATA[σ l1 ]]> 75 Take a = 3mm <![CDATA[σ l3 ]]> 40 Take Δt=20℃ <![CDATA[σ l4 ]]> 29.8 — <![CDATA[σ s ]]> 164.0 — <![CDATA[σ l5 ]]> 99.7 —

[0060] Examples show that elastic shrinkage deformation accounts for 24.4% of the total loss. To reduce this prestress loss, an appropriate amount of expansion agent can be added to the rod body. This late-stage expansion of concrete maintains compressive stress within the rod body while also increasing the pressure between the composite pile and the rock and soil, thereby enhancing the pullout bearing capacity of the composite anchor rod. Compared to non-prestressed anchor rods, the steel consumption is reduced by 20-30%.

[0061] Those skilled in the art will understand that the foregoing descriptions are merely preferred embodiments of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art will still be able to modify the technical solutions described in the foregoing examples or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the invention shall be included within the scope of protection of the invention.

Claims

1. A combined anchor rod with a prestressed core, characterized in that: The combined anchor includes: The prestressed concrete core is located on the inner side, and the prestressed concrete core is provided with prestressed tendons and is prefabricated by the pre-tensioning method; the prestressed concrete core contains an expansion agent for enhancing the pull-out bearing capacity of the composite anchor rod; A cast-in-situ anchoring slurry located on the outside, the anchoring slurry wraps the prestressed concrete rod core, and the cast-in-situ anchoring slurry is formed by placing the prestressed concrete rod core in the pile hole and solidifying after grouting the anchoring slurry once or twice; The prestressed concrete rod core is a frustum-shaped rod with a small top and a large bottom. Under the action of tension, the prestressed concrete rod core squeezes the cast-in-place anchoring slurry and the hole wall, and the combined anchor rod has better bearing capacity performance; The radius R1 of the prestressed concrete rod core is 50-75 mm, and the thickness of the anchoring slurry is 30-60 mm; In order to enhance the bonding performance between the prestressed concrete pile core and the cast-in-place anchoring slurry, the outer peripheral surface of the prestressed concrete pile core is provided with bamboo-shaped or dot-shaped protrusions or depressions; The outer peripheral surface of the prestressed concrete rod core is provided with a rod core positioning device and a grouting pipe reserved groove.

2. The combined anchor rod with prestressed core according to claim 1, characterized in that: There are three prestressed tendons inside the prestressed concrete rod core.

3. The combined anchor rod with prestressed core according to claim 1, characterized in that: The anchoring slurry is cement slurry.

4. A construction method for a combined anchor rod with a prestressed core according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: S1: The prestressed concrete core is prefabricated in the factory using the pre-tensioning method. The diameter of the prefabricated core is controlled at 100mm-150mm. The steel bars are first tensioned on the pedestal, and then the concrete core is poured. Grouting pipes are reserved in the core. After the strength reaches the design value, the tensioning end is released to form prestress in the core. At the same time, a section of steel bars is retained on one side of the core for anchoring, and the steel bars on the other side are cut along the end of the core. S2: Drilling rig drilling at the construction site; S3: Clean the hole, tie the grouting pipe, and then lower the prefabricated rod core to ensure that the prestressed concrete rod core and the drill hole are coaxial; S4: performing primary grouting around the prestressed concrete rod core, and performing secondary grouting after the primary grouting solidifies and shrinks to form a cast-in-place anchoring slurry; S5: Anchor the reserved steel bars in the rod core into the base plate, cast the base plate, and complete the basement construction.

5. The construction method of the combined anchor rod with prestressed core according to claim 4, characterized in that: When pouring the concrete core in S1, an expansion agent is added to the concrete.

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