Construction method and joint of pre-tensioning and post-anchoring type prestressed anti-floating anchor rod

Abstract

The invention relates to a construction method of a pre-tensioning and post-anchoring type prestressed anti-floating anchor rod and a node. The method comprises the following steps: measuring, placing and positioning an anchor hole; surface sundries in the construction range are cleaned; tapping and anchoring test and process test inspection are carried out; anti-floating anchor rods are firstly constructed, surface soil between the anti-floating anchor rods and surface soil and sundries of anchor heads are removed, and then a cushion layer is constructed and waterproof is achieved; or, the cushion layer and the waterproof layer are constructed firstly, then the anti-floating anchor rods are constructed, and the surface soil between the anti-floating anchor rods and the surface soil and sundries of the anchor heads are removed; installing a pre-stress part and applying pre-stress; bending the reinforcing steel bars and connecting; and pouring bottom plate concrete. Prestress is applied to the anchor rod firstly, and finally, a bottom plate concrete structure is poured, so that the construction waiting time for tensioning the anchor rod is shortened, the anchor rod is prevented from rusting and being damaged, a waterproof layer is not prone to being damaged, and damage to the bottom plate caused by the finally applied prestress is reduced. Prestressed anchor rod construction and tensioning and underground structure construction do not interfere with each other, tensioning locking is facilitated, and construction steps are simplified.

Description

Technical Field

[0001] The invention relates to the technical field of anti-floating anchor rod construction, and more particularly to a construction method and a node of a prestressed anti-floating anchor rod that is tensioned first and then anchored. Background Art

[0002] In the design of basement structures, groundwater buoyancy is an issue that needs to be taken seriously. When the deadweight of the basement structure or the upper covering soil cannot offset the groundwater buoyancy, the stability and safety of the basement may be affected. In order to solve this problem, structural anti-floating design is usually carried out, and measures such as anti-pullout piles and anti-floating anchors are set up to offset the adverse effects of groundwater.

[0003] Conventional prestressed anti-floating anchor rods are prestressed after the base plate structure is completed. There is a long waiting time for prestressing, which makes the anchor rods prone to rust and damage. At the same time, there is a risk of easily damaging the waterproof layer and causing stress concentration to cause cracks and leakage in the base plate.

[0004] Therefore, how to provide a construction method and node for prestressed anti-floating anchor rods that are tensioned first and then anchored, so that the construction and tensioning of the prestressed anchor rods do not interfere with the construction of underground structures, facilitate construction management, and facilitate tensioning and locking, and simplify construction steps, is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] The present invention aims to solve one of the above-mentioned technical problems in the prior art at least to a certain extent.

[0006] To this end, an object of the present invention is to provide a construction method to solve the problems existing in the construction of conventional prestressed anti-floating anchor rods.

[0007] Another object is to provide a prestressed anti-floating anchor construction node that is tensioned first and then anchored.

[0008] The technical solution of the present invention is a construction method of a prestressed anti-floating anchor rod that is tensioned first and then anchored, comprising the following steps:

[0009] S1. Anchor hole measurement and positioning;

[0010] S2. Clean up the surface debris within the construction area;

[0011] S3. Drilling test anchoring and process test inspection;

[0012] S4. First construct the anti-floating anchor rods, clean the loose soil between the anti-floating anchor rods and the anchor heads, and then construct the cushion layer and waterproofing;

[0013] Or, construct the cushion layer and waterproofing first, then construct the anti-floating anchor rods, clean up the loose soil between the anti-floating anchor rods and remove loose soil and debris from the anchor heads;

[0014] S5. Install prestressed parts and apply prestress;

[0015] S6, bending and connecting steel bars;

[0016] S7. Pouring of base slab concrete.

[0017] According to the method of the present invention, in S1, it is ensured that the anchor hole positioning deviation is no more than 20 mm and should not be greater than 100 mm.

[0018] According to the method of the present invention, before the main reinforcement of the anchor rod in S3 is placed into the hole, a bracket for centering and positioning should be installed first to ensure that the anchor rod is in the center of the drilled hole, and the deviation of the anchor rod in the hole should not be greater than 5%; the drilling depth should exceed the design length of the anchor rod by no less than 0.5m, and the test anchor rod also serves as the engineering anchor rod.

[0019] According to the method of the present invention, in S3, while trial anchoring, a construction process test is carried out to obtain a suitable construction process and parameters, and the parameters at least include the mix ratio of the grouting material, the grouting pressure, and the grouting amount.

[0020] According to the method of the present invention, the connection node between the anti-floating anchor rod and the foundation bottom plate in S4 is treated with a permeable crystalline waterproof material, and no less than two layers of water-swellable rubber should be provided on the anchor rod body before pouring the foundation concrete.

[0021] According to the method of the present invention, the bottom grouting of the hole in S4 adopts the underwater bottom grouting method, the grouting amount is based on filling the hole, and the filling coefficient is above 1.1; the cement-sand ratio of the grouting slurry is 0.8-1.5, the water-cement ratio is 0.38-0.5, and the grouting pressure is 0.3-3.0MPa; the slurry should be stirred evenly and sieved, used as soon as it is mixed, and the slurry should be used up before initial setting; the grouting can be stopped when the hole mouth overflows, and when the slurry cannot fill the anchor body after hardening, additional grouting should be carried out.

[0022] According to the method of the present invention, the grouting pipe is tied together with the anchor bar and put into the drill hole, the distance from the end of the grouting pipe to the bottom of the hole is 190-210mm, the drilling depth exceeds the design length of the anchor rod and is not less than 0.5m; after the anchor rod body is placed to the design elevation and slurry returns from the hole mouth, the grouting pipe is pulled out, and the grouting pipe should be pulled out while grouting, and the pulling height does not exceed the slurry surface in the hole. After the grouting pipe is pulled out, it is filled with cement slurry.

[0023] According to the method of the present invention, S5 installs the prestressed member and applies the prestress, and the application of the prestress is carried out in stages.

[0024] The present invention provides a prestressed anti-floating anchor construction node that is tensioned first and then anchored, comprising:

[0025] The bottom plate has the bottom plate main reinforcement and the structural reinforcement arranged in a bent manner;

[0026] A concrete cushion layer and a waterproof layer are located at the bottom of the base plate;

[0027] The anchor rod comprises an anchoring section and a free section. The free end is anti-corrosive with a heat shrink tubing, and its bottom enters the bottom of the borehole and is connected to the conical bearing body. The anchoring section is located in the base plate and is anchored by an anchor piece. Prestress is first applied, and a concrete cushion layer and a waterproof layer are poured, or the concrete cushion layer and the waterproof layer are first poured, prestress is applied, and then the base plate is poured.

[0028] According to the construction node of the present invention, the concrete cushion layer and the waterproof layer have a plain concrete cushion layer and a waterproof layer located on the plain concrete cushion layer; the anchor rod is provided with a pad relative to the upper part of the waterproof layer, and the anchoring section of the anchor rod has two steel bar spirals arranged in both directions in the area between the pad and the anchor plate, and the anchor rod has two water-swellable rubber rings arranged at intervals in the area, and the plain concrete cushion layer is thickened within a range of L near the anchor rod.

[0029] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. Improve construction efficiency: By using the method of tensioning first and then anchoring, the construction and tensioning of prestressed anchor rods do not interfere with the construction of underground structures, which simplifies the construction steps and facilitates construction management.

[0031] 2. Enhanced waterproof performance: The anchor nodes are treated with penetrating crystalline waterproof materials, and water-swelling rubber is set on the anchor rod body, which effectively improves the waterproof effect and reduces the risk of cracking and leakage of the base plate.

[0032] 3. Ensure construction quality: Through trial anchoring and process test inspection, obtain appropriate construction technology and parameters to ensure that the mix ratio of grouting materials, grouting pressure and grouting volume meet the design requirements, thus ensuring construction quality.

[0033] 4. Reduce construction hazards: Use underwater bottom hole grouting method, the grouting amount is based on filling the hole, and the filling coefficient is above 1.1, which ensures the fullness and uniformity of the grouting and reduces construction hazards caused by insufficient grouting.

[0034] 5. Extend service life: By treating the anchor rod with anti-corrosion treatment and using heat shrink tubing for anti-corrosion, the service life of the anchor rod is extended and the maintenance cost is reduced.

[0035] 6. Strong adaptability: The present invention is applicable to various complex geological conditions, especially areas with high groundwater levels or poor geological conditions, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0037] Figure 1 A structural schematic diagram of a prestressed anti-floating anchor construction node provided by the present invention that is tensioned first and then anchored;

[0038] Figure 2 for Figure 1 A magnified schematic diagram of part A in FIG.

[0039] Figure 3 The schematic diagram of the structure of the conical carrier is shown;

[0040] Figure 4 This is a schematic diagram of cleaning the slurry and leveling after excavation to the base, and placing anchor rods after pouring the foundation cushion layer;

[0041] Figure 5 It is a schematic diagram of applying prestress to the rod body after the prestressing component is installed on the anchor rod;

[0042] Figure 6 Schematic diagram of bending steel bars for installing the base plate and pouring concrete as a whole;

[0043] Figure 7 The present invention is a flow chart of a construction method of a prestressed anti-floating anchor rod that is tensioned first and then anchored. DETAILED DESCRIPTION

[0044] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0045] In the description of the present invention, it is necessary to understand that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0046] Because the traditional prestressed anti-floating anchor rods are prestressed after the base plate structure is completed, there is a long waiting time for prestressing, which makes the anchor rods prone to rust and damage. At the same time, there is a risk of easily damaging the waterproof layer and causing stress concentration to cause cracks and leakage in the base plate.

[0047] In view of this, the present invention provides a construction method of a prestressed anti-floating anchor rod that is tensioned first and then anchored. Figure 7 , including the following steps:

[0048] S1. Anchor hole measurement and positioning;

[0049] S2. Clean up the surface debris within the construction area;

[0050] S3. Drilling test anchoring and process test inspection;

[0051] S4. First construct the anti-floating anchor rods, clean the loose soil between the anti-floating anchor rods and the anchor heads, and then construct the cushion layer and waterproofing;

[0052] Or, construct the cushion layer and waterproofing first, then construct the anti-floating anchor rods, clean up the loose soil between the anti-floating anchor rods and remove loose soil and debris from the anchor heads;

[0053] S5. Install prestressed parts and apply prestress;

[0054] S6, bending and connecting steel bars;

[0055] S7. Pouring of base slab concrete.

[0056] The above-mentioned embodiment of the present invention reduces the waiting time for anchor tensioning by first applying prestress to the anchor rods and finally pouring the bottom plate concrete structure, prevents the anchor rods from rusting and being damaged, is not easy to damage the waterproof layer, and reduces the damage to the bottom plate caused by the final application of prestress. The prestressed anti-floating anchor rods used in the present invention are tensioned first and then anchored. The construction of the prestressed anchor rods and the tensioning and underground structure construction do not interfere with each other, which is convenient for construction management, and is easy to tension and lock, simplifying the construction steps.

[0057] There are two methods for the construction process of the anti-floating anchor rod in the present invention: construct the anchor rod first and then pour the cushion concrete, or first pour the cushion concrete and then construct the anchor rod. The following embodiments of the invention adopt the method of constructing the anchor rod first and then pouring the cushion concrete.

[0058] The anchor bolt method is to pour the cushion concrete first and then construct the anchor bolt. The foundation form is pile + cap + raft foundation. The foundation form is complex, and the anti-floating anchor bolts are distributed between the pile and the cap. Because the cap cross-section height is greater than the raft cross-section, the pile top elevation is lower than the raft bottom elevation, making it difficult to excavate the earthwork simultaneously. At the same time, there are many pile foundations, and the amount of work required to cut the pile head and clean the soil between the piles is large. Before the cushion construction, the pile foundation needs to be inspected and accepted in sections, and the overall construction period is relatively long.

[0059] The method of constructing anchor rods first and then pouring cushion concrete is to construct anchor rods first, then excavate the remaining soil, cut the pile heads, clean the soil between piles, and accept the pile foundation, and then pour cushion concrete. At that time, the strength growth of the anchor rod anchor body basically reaches the conditions for the pull-out test, avoiding the technical interval of waiting for the anchor rod anchor body strength growth after pouring cushion concrete. The disadvantage is that earthwork needs to be reserved, and the small spacing between anchor rods makes earthwork cleaning more difficult. During the process, the protection of the anchor rods needs to be strengthened to avoid disturbance of the anchor rods during earthwork cleaning.

[0060] In the embodiment of the present invention, S1 ensures that the anchor hole positioning deviation is no greater than 20 mm and should not be greater than 100 mm.

[0061] In the embodiment of the present invention, before the main reinforcement of the anchor rod in S3 is placed into the hole, a bracket for centering and positioning should be installed first to ensure that the anchor rod is in the center of the drilled hole, and the deviation of the anchor rod in the hole should not be greater than 5%; the drilling depth should exceed the design length of the anchor rod by no less than 0.5m, and the test anchor rod also serves as the engineering anchor rod.

[0062] Advantageously, in S3, while conducting the anchoring test, a construction process test is performed to obtain appropriate construction technology and parameters, and the parameters include at least the mix ratio of the grouting material, the grouting pressure, and the grouting amount.

[0063] In one embodiment of the present invention, the connection node between the anti-floating anchor rod and the foundation slab in S4 is treated with a permeable crystalline waterproof material, and at least two layers of water-swellable rubber should be provided on the anchor rod body before pouring the foundation concrete.

[0064] Among them, the S4 bottom hole grouting adopts underwater bottom hole grouting method, the grouting volume is based on filling the hole, and the filling coefficient is above 1.1; the grouting slurry is prepared with a cement-sand ratio of 0.8-1.5, a water-cement ratio of 0.38-0.5, and a grouting pressure of 0.3-3.0MPa; the slurry should be stirred evenly and sieved, and used as it is mixed, and the slurry should be used up before the initial setting; the grouting can be stopped when the hole mouth overflows, and the grouting should be supplemented when the slurry cannot fill the anchor body after hardening. The grouting pipe is tied together with the anchor bar and put into the borehole. The distance from the end of the grouting pipe to the bottom of the hole is 190-210mm, and the drilling depth exceeds the design length of the anchor rod and is not less than 0.5m; when the anchor rod body is placed to the design elevation, the grouting pipe is pulled out after the slurry returns from the hole mouth. The grouting pipe should be pulled out while grouting, and the pulling height should not exceed the slurry surface in the hole. The grouting pipe is filled with cement slurry after being pulled out.

[0065] In the present invention, S5 installs the prestressed member and applies the prestress, and the application of the prestress is carried out in stages.

[0066] See attached Figure 1-6 The present invention also provides a prestressed anti-floating anchor construction node that is tensioned first and then anchored, comprising:

[0067] The bottom plate 1 has a bottom plate main reinforcement 11 and a bent structural reinforcement 12;

[0068] A concrete cushion layer and a waterproof layer 5 are located at the bottom of the base plate 1;

[0069] The anchor rod 2 includes an anchoring section and a free section. The free end is anti-corrosive with a heat shrink tubing, and its bottom enters the bottom of the borehole and is connected to the conical bearing body 6. The anchoring section is located in the base plate 1 and is anchored by an anchor. Prestress is first applied, and a concrete cushion layer and a waterproof layer 5 are poured, or the concrete cushion layer and the waterproof layer 5 are first poured, prestress is applied, and then the base plate 1 is poured.

[0070] The present invention adopts a heat shrinkable sleeve for corrosion protection in the free section of the anchor rod, which does not need to be directly bonded with concrete, thereby increasing the service life.

[0071] The concrete cushion layer and waterproof layer 5 described in the present invention include a plain concrete cushion layer 51 and a waterproof layer 52 located on the plain concrete cushion layer 51; the anchor rod 2 is provided with a pad 41 on the upper part of the waterproof layer 52, and two steel bars 3 in each bidirectional direction of the anchoring section of the anchor rod 2 are spirally arranged in the area between the pad 41 and the anchor plate 4, and two water-swellable rubber rings 21 are arranged at intervals on the anchor rod 2 in this area, and the plain concrete cushion layer 51 is thickened and arranged within a range L near the anchor rod 2.

[0072] The range of L is determined according to the specifications of the anchor plate.

[0073] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0074] Among them, regarding the anchor rod, considering the corrosiveness of groundwater, the anchor rod body can be composed of a whole 32mm diameter fine-rolled threaded steel bar. It is strictly forbidden to cut the rod body during construction. The rod body connection should ensure that it is operated in accordance with the construction regulations. The extension and screwing in of the special connector should be marked one by one to ensure a firm connection. Welding is strictly prohibited. The prestressing of the anchor body can be applied with a torque wrench. The anchor sealing construction can begin after the anchor cement slurry has initially set. Before construction, the anchor head slurry at the top of the anchor rod should be cleaned and painted, and then the cement-based grouting material should be poured in. After the cushion layer and waterproofing construction are completed, the raft slab embedded components are installed, and the torque wrench is used to tighten and apply prestress, and then it is delivered to the next process after tightening.

[0075] Before the anchor grouting operation begins, trial drilling and grouting should be carried out to optimize and finally determine the grouting parameters.

[0076] The grouting pressure value is 0.3MPa~3.0MPa (determined comprehensively based on the on-site pile test), and the grouting should be made dense. The positioning deviation of the anchor hole should not be greater than 20mm and should not be greater than 100mm. The deviation of the anchor in the hole should not be greater than 5%; the drilling depth should not be less than 0.5m beyond the design length of the anchor.

[0077] Before the anchor rod main reinforcement cage is placed in the hole, a bracket for centering and positioning should be installed to ensure that the reinforcement is in the center of the drilled hole. The spacing between the bracket rock nails is 1 to 2 meters, and the structure of the bracket should not hinder the free flow of slurry. Grouting can only be carried out after the anchor rod hole is cleaned.

[0078] The connection node between the anti-floating anchor and the foundation slab should meet the overall waterproof grade and structural requirements of the foundation slab. The anchor node can be treated with permeable crystalline waterproof materials, and at least two water-expandable rubber rings should be installed on the anchor rod body before pouring the foundation concrete. Under precipitation conditions, the adverse effects of pumping on anchor grouting should be avoided.

[0079] After the anchor is installed, it shall not be knocked, collided or pulled before the grouting strength reaches 70% of the design strength. The grouting of the anchor can be repeated but shall comply with the following provisions:

[0080] a. The secondary grouting material should be pure cement slurry with a water-cement ratio of 0.45 to 0.50;

[0081] b. Grouting of the grout-stopping sealing device should be carried out after the grout overflows from the hole, and the grouting pressure should not be less than 2.0MPa;

[0082] c After the first normal pressure grouting is completed, the grouting pipe, grouting gun and grouting sleeve should be cleaned. The second high pressure grouting of the anchor body should be carried out after the strength of the cement stone body formed by the first grouting reaches 5.0MPa. The grouting pressure and grouting time can be determined according to the volume of the anchoring section and carried out in sections from bottom to top.

[0083] The lime-sand ratio of the slurry preparation should be 0.8-1.5, and the water-cement ratio should be 0.38-0.5; the mud content of the sand should not be greater than 3% by weight, and the content of harmful substances such as mica, organic matter, sulfide and sulfate in the sand should not be greater than 1% by weight.

[0084] The water used for grouting materials should meet the following requirements: Mixing water should be drinking water, and sewage should not be used. When other water sources are used, they must be tested to confirm that they are harmless to cement paste and rod materials.

[0085] Cement slurry is required to have low viscosity, good fluidity, good injectability, good stability, and be non-toxic, odorless, and environmentally friendly. Finer materials should be selected for grouting. The slurry should shrink less when solidifying and can firmly bond with the soil.

[0086] Regarding anchors, anchor plates and matching prestressed nuts are made of 40Cr grade alloy steel.

[0087] In order to further illustrate the present invention, the following examples are described:

[0088] Engineering geological conditions

[0089] The overall terrain of the proposed project site is relatively flat, with large undulations in some areas, mainly due to the soil slopes accumulated in the early stage. The maximum ground elevation is 85.93m, the minimum is 80.21m, and the relative height difference of the surface is 5.72m. The original landform of the site is an alluvial plain.

[0090] According to the survey report, the site exposed within the survey depth range is covered by Quaternary alluvial clay and sand layers, and underlying by Ordovician limestone strata. It is divided into 6 layers from top to bottom. The rock and soil stratification and characteristics are described as follows:

[0091] The first layer is miscellaneous fill soil, the second layer is silty clay, and the third layer is sandy silty clay;

[0092] The first layer of the fourth layer: clay, the fourth layer: medium-coarse sand; the fifth layer: silty clay; the first layer of the sixth layer: medium-weathered and broken limestone; the sixth layer: medium-weathered limestone;

[0093] Groundwater conditions

[0094] The groundwater types are mainly pore water and karst fissure water in the Quaternary soil layer. The average depth of the stable groundwater level is about 6.17 meters, corresponding to an elevation of 75.42 meters. The site is mainly Quaternary pore water in the 4th layer of coarse sand. According to regional hydrogeological data, the annual variation of groundwater is about 2.0-4.0 meters. The highest water level in the past 3-5 years is about 2.50 meters deep (corresponding to an elevation of about 79.00 meters). The highest water level in history is about 1.80 meters deep (corresponding to an elevation of about 79.80 meters).

[0095] In the above scenario, the detailed construction process is as follows:

[0096] (1) Measurement and positioning

[0097] Using a total station, according to the determined coordinates, the main axis is measured and laid out at the bottom of the trench, and the anchor points are measured and laid out according to the anti-floating anchor plan. The point line is determined by wooden stakes and white lime points (30cm deep) to ensure that it is not deviated or lost. The anchor hole positioning deviation should not be greater than 20mm.

[0098] (2) Clearing the surface of loose soil

[0099] Determine the boundary of the surface clearing according to the construction scope and design requirements. The boundary should be clear and well-defined, and set obvious signs to avoid exceeding or missing the surface clearing area during surface clearing. Use appropriate tools, such as shovels, brooms, etc., to clean up surface debris within the construction scope, such as branches, leaves, stones, etc. Be careful when cleaning to avoid unnecessary damage to the soil. Use appropriate tools to remove the loose soil to make the surface of the soil layer clean and tidy. The removed loose soil should be piled up for subsequent treatment.

[0100] (3) Drilling test anchoring and process testing

[0101] During the anchoring test, the construction process test is carried out. The feasibility and reliability of the construction process are tested through the test, including the mix ratio of the grouting material, the grouting pressure, the grouting volume and other parameters. At the same time, the bonding between the anchor rod and the grouting material is observed to evaluate its reliability. According to the results of the anchoring test and process test, a detailed analysis and evaluation is carried out. If the anchoring force and construction process do not meet the design requirements, the relevant parameters should be adjusted, and the anchoring test and process test should be carried out again. Until the appropriate construction process and parameters are found to ensure the stability and reliability of the anchor rod.

[0102] (4) Anti-floating anchor construction

[0103] 1) Pile driver in place

[0104] When the anchor drill is in place, it must remain stable without tilting or shifting. To accurately control the drilling depth, a control scale should be made on the drill frame for observation and recording during construction. Drilling inclination control: The vertical deviation of the drilling hole should not exceed 5%.

[0105] 2) Drilling

[0106] Adjust the drill rod and use a water drill to drill the hole. The diameter of the hole is 180mm, and the drilling depth should be no less than 0.5m beyond the designed length of the anchor rod.

[0107] 3) Grouting at the bottom of the hole

[0108] The underwater bottom hole grouting method is adopted. The first grouting volume is based on filling the hole, and the filling coefficient is above 1.1. The cement-sand ratio of the grouting slurry should be 0.8-1.5, the water-cement ratio should be 0.38-0.5, and the grouting pressure should be 0.3-3.0MPa. The slurry should be stirred evenly and sieved, and used as soon as it is mixed. The slurry should be used up before the initial setting. When the grouting overflows from the hole, the grouting can be stopped. When the slurry cannot fill the anchor body after hardening, grouting should be carried out. The number of test blocks for slurry strength test should not be less than one group for every 30 anchor rods, and each group of test blocks should not be less than 6.

[0109] 4) Place the rod

[0110] The anchor rod should be derusted, and the thickness of the mortar protective layer should not be less than 25mm. Install the anchor rod body that has passed the hidden inspection, strictly control the rod body elevation, and control the length of the anchoring section. When inserting the steel bars, the anchor bars should be prevented from twisting, compression, and bending, and the rod body should be placed at the same angle as the drilling angle. The grouting pipe and the anchor bar are tied together and placed in the drill hole. The distance from the end of the grouting pipe to the bottom of the hole should be 200mm. The drilling depth should not be less than 0.5m beyond the design length of the anchor rod, and it should not be too deep. The anchor rod should be cut as long as possible. If it must be connected, mechanical connection should be used, and it should be staggered by 40d, and the joint rate in the same connection area should be 25%.

[0111] 5) Pull out the casing

[0112] After the rod is secured to the designed elevation and slurry flows out of the hole, pull out the casing.

[0113] 6) Filling

[0114] The grouting pipe should be pulled out while grouting, and the pulling height should not exceed the grouting surface in the hole. The grouting pipe should be filled with cement grout after being pulled out. The cement grout in the anchor hole should have enough curing time, and the anchor rod should not be moved during the curing period.

[0115] (5) Cleaning of loose soil between anchor rods and anchor heads

[0116] Remove loose soil, debris, etc. between the anchor rods to facilitate subsequent construction.

[0117] (6) Pad and waterproofing construction

[0118] After the anchor construction is completed, the cushion layer and waterproof layer are constructed. The cushion layer material should have sufficient strength and durability, and the waterproof layer should have good waterproof performance.

[0119] The connection node between the anti-floating anchor rod and the foundation slab should meet the overall waterproof grade and structural requirements of the foundation slab. The anchor rod node should be treated with penetrating crystalline waterproof material, and at least two layers of water-swelling rubber should be installed on the anchor rod body before pouring the foundation concrete.

[0120] (7) Prestressing

[0121] According to the design requirements, install the prestressed parts and apply prestress. The application of prestress should be carried out in stages and appropriate equipment should be used for loading. The value of prestress should meet the design requirements to ensure the stability of the anchor.

[0122] (8) Delivery of poured concrete.

[0123] In the above embodiments, the design of the anti-floating anchor rod takes into account many factors, including the nature of the stratum, the change of the groundwater level, and the interaction between the anchor rod and the surrounding soil. The type, length, rock penetration depth, and pull-out resistance of the anchor rod are carefully calculated and designed based on detailed geological survey reports and engineering requirements. In addition, the technical requirements during the construction process are also very strict, including the material selection of the anchor rod body, the joint connection method, the prestressing method, the anchor sealing process, the locking and anchor sealing process, etc., all to ensure that the anchor rod can play its role effectively and provide sufficient pull-out resistance to resist the buoyancy of groundwater.

[0124] By using high-strength precision-rolled threaded steel bars as anchor rod materials and using special connectors for extension and screwing, the overall strength and stability of the anchor rod can be ensured. At the same time, the application and control of prestress is also an important part of ensuring the performance of the anchor rod. It is necessary to operate in accordance with strict construction regulations and apply prestress through a torque wrench to ensure that each anchor rod can meet the pull-out resistance characteristic value and acceptance value required by the design.

[0125] In summary, the design and construction of the anti-floating anchor in the present invention is a comprehensive technical challenge, involving knowledge in multiple fields such as geology, civil engineering, and material science. Through scientific design and meticulous construction management, the impact of groundwater on the stability of buildings can be effectively resolved to ensure the safety and reliability of the project.

[0126] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0127] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A construction method of prestressed anti-floating anchor rod with tensioning first and then anchoring, characterized in that: The following steps are involved: S1. Anchor hole measurement and positioning; S2. Clean up the surface debris within the construction area; S3. Drilling test anchoring and process test inspection; S4. First construct the anti-floating anchor rods, clean the loose soil between the anti-floating anchor rods and the anchor heads, and then construct the cushion layer and waterproofing; Or, construct the cushion layer and waterproofing first, then construct the anti-floating anchor rods, clean up the loose soil between the anti-floating anchor rods and remove loose soil and debris from the anchor heads; S5. Install prestressed parts and apply prestress; S6, bending and connecting steel bars; S7. Pouring of base slab concrete.

2. The construction method of a prestressed anti-floating anchor rod of the tensioning-first-anchoring-later type according to claim 1 is characterized in that: In S1, ensure that the anchor hole positioning deviation is no more than 20mm and should not be greater than 100mm.

3. The construction method of the prestressed anti-floating anchor rod of the tensioning-first-anchoring-later type according to claim 1 is characterized in that: Before the main reinforcement of S3 anchor rod is placed into the hole, a bracket for centering and positioning should be installed first to ensure that the anchor rod is in the center of the drilled hole. The deviation of the anchor rod in the hole should not be greater than 5%. The drilling depth should exceed the design length of the anchor rod by no less than 0.5m. The test anchor rod also serves as the engineering anchor rod.

4. The construction method of the prestressed anti-floating anchor rod of the tensioning-first-anchoring-later type according to claim 1 is characterized in that: In S3, while testing the anchoring, a construction process test is carried out to obtain appropriate construction technology and parameters, and the parameters at least include the mix ratio of the grouting material, the grouting pressure, and the grouting amount.

5. The construction method of the prestressed anti-floating anchor rod of the tensioning-first-anchoring-later type according to claim 1 is characterized in that: In S4, the connection nodes between the anti-floating anchor rod and the foundation slab are treated with permeable crystalline waterproof materials, and no less than two layers of water-swelling rubber should be installed on the anchor rod body before pouring the foundation concrete.

6. The construction method of the prestressed anti-floating anchor rod of the tensioning-first-anchoring-later type according to claim 1 is characterized in that: For S4 hole bottom grouting, underwater hole bottom grouting method is adopted. The grouting volume is based on filling the hole, and the filling coefficient is above 1.

1. The cement-sand ratio of the grouting slurry is 0.8-1.5, the water-cement ratio is 0.38-0.5, and the grouting pressure is 0.3-3.0MPa. The slurry should be stirred evenly and sieved, and used as soon as it is mixed. The slurry should be used up before initial setting. Grouting can be stopped when the hole mouth overflows. When the slurry cannot fill the anchor body after hardening, additional grouting should be carried out.

7. The construction method of the prestressed anti-floating anchor rod of the tensioning-first-anchoring-later type according to claim 6 is characterized in that: The grouting pipe is tied together with the anchor bar and put into the drill hole. The distance from the end of the grouting pipe to the bottom of the hole is 190-210mm. The drilling depth exceeds the design length of the anchor rod and is not less than 0.5m. After the anchor rod body is placed to the design elevation and slurry returns from the hole mouth, the grouting pipe is pulled out. The grouting pipe should be pulled out while grouting. The pulling height should not exceed the slurry surface in the hole. After the grouting pipe is pulled out, it is filled with cement slurry.

8. The construction method of the prestressed anti-floating anchor rod of the tensioning-first-anchoring-later type according to claim 6 is characterized in that: S5 installs prestressed parts and applies prestress. The application of prestress is carried out in stages.

9. A prestressed anti-floating anchor construction node that is tensioned first and then anchored, characterized in that: include: A bottom plate (1) having bottom plate main reinforcement (11) and bent structural reinforcement (12); A concrete cushion layer and a waterproof layer (5) are located at the bottom of the base plate (1); The anchor rod (2) comprises an anchoring section and a free section, wherein the free end is protected against corrosion by a heat shrink tubing, and the bottom of the free end enters the bottom of the borehole and is connected to a conical bearing body (6); the anchoring section is located in the base plate (1) and is anchored by an anchor piece, and prestress is first applied, and a concrete cushion layer and a waterproof layer (5) are poured, or the concrete cushion layer and the waterproof layer (5) are first poured, prestress is applied, and then the base plate (1) is poured.

10. The prestressed anti-floating anchor construction node of the tensioning-first-anchoring-later type according to claim 9, characterized in that: The concrete cushion layer and waterproof layer (5) comprises a plain concrete cushion layer (51) and a waterproof layer (52) located on the plain concrete cushion layer (51); the anchor rod (2) is provided with a pad (41) on the upper part of the waterproof layer (52); two steel bars (3) are spirally arranged in both directions in the anchoring section of the anchor rod (2) in the area between the pad (41) and the anchoring plate (4); two water-expandable rubber rings (21) are arranged at intervals on the anchor rod (2) in the area; and the plain concrete cushion layer (51) is thickened within a range L near the anchor rod (2).

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