Anti-floating anchor rod construction method for existing building in high-water-level and strong-permeable-layer foundation

Abstract

The invention relates to an anti-floating anchor rod construction method for an existing building in a high-water-level and strong-permeable-layer foundation. The anti-floating anchor rod construction method comprises the following steps that S1, an anti-floating anchor rod and a dewatering well are positioned on the bottom face of a basement; s2, a dewatering well is constructed firstly; s3, constructing an anti-floating anchor rod, and synchronously dewatering when the anti-floating anchor rod is constructed; s4, hole cleaning is conducted after all-casing follow-up construction is conducted to the preset elevation; s5, an anti-floating anchor rod body, a primary grouting pipe, a secondary grouting short pipe and a secondary grouting long pipe are placed; s6, synchronous dewatering is conducted through the dewatering wells on the periphery; s7, primary grouting is conducted through a primary grouting pipe; s8, after primary grouting is conducted till overflow of the hole opening, the steel sleeve is slowly pulled out, and then supplementary grouting is conducted; and S9, after primary grouting is initially set, secondary grouting is conducted. The invention aims to provide an anti-floating anchor rod construction method aiming at the technical bottleneck of construction of an existing building anti-floating anchor rod in a high-water-level and strong-permeable-layer foundation, and the effects of stable anchor rod hole forming, dense grouting and reliable long-term anchoring force can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of building engineering foundation reinforcement, and in particular to an anti-floating anchor rod construction method for existing buildings in a high water level and highly permeable layer foundation. Background Art

[0002] Due to the continuous occurrence of ground subsidence during urban construction, Beijing has taken a series of other measures in recent years, and the groundwater level has continued to rise. Urban renewal continues to improve the ecological environment and strictly control ground subsidence. The rise in groundwater levels is a major trend in the development of urban renewal. According to data from the Beijing Water Authority, the depth of groundwater levels in the plain areas of Beijing has risen from 25.75m in 2015 to 13.39m in August 2024, an increase of about 12m in 10 years, especially in the past four years, it has risen by about 8m, exceeding the original design of the anti-floating water level, causing many buildings to crack in the basement floor, leakage and other diseases, how to solve these existing building anti-floating problems is imminent.

[0003] There are usually three ways to deal with the high anti-floating water level. The first is to add floors to the existing building to increase the load, but whether the existing columns and foundations can meet the requirements of the new load, and adding floors also changes the original plan, so this method is generally not used; the second is to use active precipitation, that is, to set up a large number of precipitation wells around and inside the basement, and continuously precipitate water to keep the groundwater level below the anti-floating water level requirements, but this method is costly and difficult to use for anti-floating management, and cannot completely solve the anti-floating problem; the third is to add anti-floating anchors inside the basement. Traditional anti-floating anchor construction methods include drilling and grouting methods, prestressed anchor methods, etc. The core is to resist the buoyancy of groundwater through the friction between the anchor and the formation. In conventional formations, these methods can effectively provide pull-out resistance. However, in high water levels and highly permeable strata, conventional technologies face the following challenges: 1. Limited construction conditions: When the groundwater level is higher than the bottom plate, it is impossible to drill holes directly; 2. The grouting anchor body cannot solidify: The flow of groundwater in the highly permeable layer causes the slurry to be lost, and the anchor body is difficult to form.

[0004] At present, the anti-floating anchor construction technology mainly focuses on the following directions: improving grouting materials, dewatering auxiliary construction, grouting technology and improving the anti-floating anchor structure. The invention patent with publication number CN115434377A (patent name: Anti-floating anchor construction method under high water level and large permeability coefficient conditions) is to improve the grouting material, specifically by on-site drilling, adjusting the mix ratio of the grouting liquid, and reducing the loss of slurry by adding quick-setting agent or high-viscosity material; the invention patent with publication number CN116752524A (patent name: Anti-floating anchor construction method under high water level and sand and gravel geological conditions) is to improve the grouting process, specifically by using the grouting nozzle of a high-pressure rotary jet machine to send it into the preset depth in the target hole, dividing the target hole into several construction sections along the height direction, and performing high-pressure spraying operations by lifting and rotating the grouting nozzle synchronously in each construction section from bottom to top; the above two existing patents are acceptable for strata where the water flow is relatively static, but in strata with high water levels and strong permeability, since the water is in a flowing state, the quality of the grouting anchor body is seriously affected. Some experts and scholars have also studied the use of dewatering to assist construction. The dewatering wells use single-point wells or are arranged asymmetrically. Due to the lack of synchronous control of the groundwater level, the water level fluctuates during the drilling process, which also affects the quality of the grouting anchor.

[0005] In summary, the existing technology generally has the problem of grouting failure in high dynamic groundwater flow. Therefore, it is urgent to solve the technical bottleneck of the application of anti-floating anchor rods in improving the anti-floating capacity of existing buildings. Summary of the invention

[0006] The purpose of the present invention is to address the technical bottleneck of anti-floating anchor construction of existing buildings in high water level and highly permeable layer foundations, and to provide an anti-floating anchor construction method for existing buildings in high water level and highly permeable layer foundations, which can achieve the effects of stable anchor hole forming, dense grouting and reliable long-term anchoring force.

[0007] The purpose of the present invention is achieved through the following technical solution: A method for constructing an anti-floating anchor rod for an existing building in a high water level and a highly permeable layer foundation, comprising the following steps:

[0008] S1. Position the anti-floating anchor rods and drainage wells on the bottom of the basement. Set up a number of drainage wells that are evenly spaced and symmetrically arranged around the anti-floating anchor rods;

[0009] S2. First construct a dewatering well to lower the groundwater to a certain position below the basement floor to ensure that the anti-floating anchor drilling is a dry operation and that groundwater does not emerge from the hole during the anti-floating anchor drilling process;

[0010] S3. Construction of anti-floating anchor rods. The anti-floating anchor rods adopt the full casing follow-up construction process. When constructing the anti-floating anchor rods, the water level should be lowered simultaneously to keep the water level elevation relatively constant;

[0011] S4. After the full casing is constructed to the predetermined elevation, the hole is cleaned;

[0012] S5. After the hole is cleaned, the anti-floating anchor rod body, the primary grouting pipe, the secondary grouting short pipe and the secondary grouting long pipe are placed, and a number of grouting holes are vertically spaced on the side walls of the secondary grouting short pipe and the secondary grouting long pipe;

[0013] S6. Clean the hole again, dewater the surrounding dewatering wells synchronously, strictly control the dewatering rate of each dewatering well, keep the dewatering amount the same, make the water in the borehole in a relatively static state, and measure the groundwater level elevation in the borehole. The PLC controller is used to control the dewatering well synchronously to link the water pumps of each dewatering well.

[0014] S7. After the groundwater level is stabilized, grouting is performed once through a grouting pipe, and the grouting liquid uses an improved grouting liquid;

[0015] S8. After the primary grouting is completed until the grout overflows from the orifice, slowly pull out the steel casing used in the full casing follow-up construction, and then perform additional grouting through the primary grouting pipe until the grout overflows from the orifice again;

[0016] S9. After the initial setting of the primary grouting, the secondary grouting is carried out, and the secondary grouting short tube and the secondary grouting long tube are grouted simultaneously in the secondary grouting.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] The present invention can improve the anti-floating ability of existing buildings, reduce building safety hazards caused by basement diseases, extend the service life, and help the sustainable development of urban underground space; at the same time, it has the advantages of short construction period and controllable cost.

[0019] The present invention can solve the difficult problems of anti-floating anchor construction and grouting solidification in high water level and highly permeable foundation, fill the technical gap in this field and promote technological progress in the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the groundwater level in the basement of an existing building exceeding the anti-floating water level;

[0021] Figure 2 This is a schematic diagram of the construction of anti-floating anchor rods in the basement of an existing building according to the present invention;

[0022] Figure 3 It is a plan view of the anti-floating anchor rod and the dewatering well of the present invention;

[0023] Figure 4 This is a large-scale drawing of the anti-floating anchor rod of the present invention;

[0024] Figure 5 for Figure 4 AA section of medium anti-floating anchor;

[0025] Figure 6 for Figure 4 Sectional view of medium-resistant floating anchor BB.

[0026] Explanation of numbers: 1 basement, 2 anti-floating anchor, 2-1 anti-floating anchor rod body, 2-2 primary grouting pipe, 2-3 secondary grouting short pipe, 2-4 secondary grouting long pipe, 2-5 grouting hole, 3 dewatering well. DETAILED DESCRIPTION

[0027] The present invention is described in detail below with reference to the accompanying drawings and embodiments:

[0028] like Figure 1-6 The figure shows a schematic diagram of an embodiment of an anti-floating anchor rod construction method for an existing building in a high water level and a highly permeable layer foundation provided by the present invention, comprising the following steps:

[0029] Step S1.

[0030] The anti-floating anchor rod 2 and the precipitation well 3 are positioned on the bottom surface of the basement 1. A number of precipitation wells 3 are arranged with equal spacing and symmetrical arrangement around the anti-floating anchor rod 2 to ensure the synchronization of subsequent precipitation. No flow field is generated in the area of ​​the anti-floating anchor rod 2. In this embodiment, the spacing between the precipitation wells is 2.5-3 times the spacing between the anchor rods, and the aperture of the precipitation well is ≥300mm. Figure 2 and Figure 3 Schematic diagram of the layout in .

[0031] Step S2.

[0032] First, a dewatering well 3 is constructed to lower the groundwater to a certain position below the bottom plate of the basement 1, ensuring that the drilling of the anti-floating anchor 2 is in a dry operation. During the drilling of the anti-floating anchor 2, groundwater will not emerge from the hole, providing construction conditions for the anti-floating anchor;

[0033] The depth, aperture, water output and other parameters of the precipitation well are determined according to the design requirements.

[0034] Step S3.

[0035] Construct the anti-floating anchor 2. The anti-floating anchor 2 adopts the full casing follow-up construction process. When constructing the anti-floating anchor 2, the water level should be lowered synchronously to keep the water level elevation relatively constant;

[0036] Step S4.

[0037] After the whole casing is constructed to the predetermined elevation, the hole is cleaned;

[0038] Step S5.

[0039] After the hole is cleaned, the anti-floating anchor rod body 2-1, the primary grouting pipe 2-2, the secondary grouting short pipe 2-3 and the secondary grouting long pipe 2-4 are placed, and a plurality of grouting holes 2-5 distributed vertically at intervals are opened on the side walls of the secondary grouting short pipe 2-3 and the secondary grouting long pipe 2-4;

[0040] The anti-floating anchor rod body 2-1 can be made of steel bars or steel strands. There are many types of existing anti-floating anchor rods, all of which can be used.

[0041] The primary grouting pipe 2-2, the secondary grouting short pipe 2-3 and the secondary grouting long pipe 2-4 are all made of ∅21PVC plastic pipe.

[0042] The secondary grouting pipe is not limited to using only two long pipes and short pipes. If the length of a single anti-floating anchor is very long, secondary grouting pipes can be added in sections at the anchoring section of the anti-floating anchor according to design requirements.

[0043] In step S5, the ends of the primary grouting pipe 2-2 and the secondary grouting long pipe 2-4 are arranged near the end of the anchoring section of the anti-floating anchor 2; the end of the secondary grouting short pipe 2-3 is arranged in the middle of the anchoring section of the anti-floating anchor 2; the secondary grouting long pipe 2-4 has a grouting hole 2-5 in the lower anchoring section area, and the secondary grouting short pipe 2-3 has a grouting hole 2-5 in the upper anchoring section area.

[0044] The vertical spacing between the slurry outlet holes 2-5 is 2000 mm, and two slurry outlet holes 2-5 are provided at the same height.

[0045] The primary grouting pipe 2-2, the secondary grouting short pipe 2-3 and the secondary grouting long pipe 2-4 are all synchronously positioned and tied to the anti-floating anchor rod body 2-1.

[0046] Step S6.

[0047] The hole is cleaned again, and the surrounding precipitation wells 3 are condensed synchronously. The precipitation rate of each precipitation well 3 is strictly controlled to keep the precipitation amount the same, so that the water in the borehole is in a relatively static state, and the groundwater level elevation in the borehole is measured. The precipitation well 3 is synchronously regulated using a PLC controller to link the water pumps of each precipitation well;

[0048] In order to prevent the subsequent grouting fluid from being lost, the groundwater level in the hole should be measured continuously to confirm that the water in the borehole is in a relatively static state and the groundwater level fluctuation is ≤±10mm.

[0049] Step S7.

[0050] After the groundwater level is stabilized, a grouting is performed through the primary grouting pipe 2-2, and the grouting liquid adopts the improved grouting liquid;

[0051] Under normal conditions, the grouting liquid used for anti-floating anchors is cement slurry with a water-cement ratio of 0.5~0.6:1; in high water levels and highly permeable layers, the borehole is filled with water to prevent the grouting liquid from flowing easily and without reducing the quality of the grouting anchor body.

[0052] The grouting liquid for the primary grouting in step S7 is a quick-setting cement-based slurry with a water-cement ratio of 0.4-0.45:1, and nano-silicon dioxide is added in an amount of 1-3% of the cement mass.

[0053] The amount of nano-silicon dioxide added can be determined based on the water quality analysis and requirements of the specific project; the water-cement ratio can be appropriately adjusted to a higher concentration based on project requirements, as long as the pipe is not blocked during the grouting process.

[0054] Step S8.

[0055] After the first grouting is completed until the orifice overflows, the steel casing used in the full casing follow-up construction is slowly pulled out, and then the grouting is supplemented through the first grouting pipe 2-2 until the slurry overflows from the orifice again;

[0056] Step S9.

[0057] After the initial setting of the first grouting (generally within 6 to 8 hours), the secondary grouting is carried out, and in the secondary grouting, the secondary grouting short pipe 2-3 and the secondary grouting long pipe 2-4 are grouted simultaneously.

[0058] In step S9, after the initial setting of the primary grouting (generally within 6 to 8 hours), a second pressure grouting is performed on the pre-buried secondary grouting short pipe 2-3 and the secondary grouting long pipe 2-4. The second grouting uses pure cement slurry with a water-cement ratio of 0.5:1, and grouting is performed along the entire length of the anti-floating anchor rod 2; the secondary grouting is controlled by both cement consumption and grouting pressure.

[0059] The cement dosage for secondary grouting shall be no less than 75kg / m, and the grouting pressure shall be 2~3MPa.

Claims

1. A method for constructing anti-floating anchor rods for existing buildings in high water level and highly permeable layer foundations, characterized in that: The following steps are involved: S1. Positioning the anti-floating anchor rod (2) and the precipitation well (3) on the bottom surface of the basement (1), wherein a plurality of precipitation wells (3) are arranged at equal intervals and symmetrically around the anti-floating anchor rod (2); S2. First, construct a dewatering well (3) to lower the groundwater to a certain position below the basement (1) floor to ensure that the anti-floating anchor (2) drilling is in a dry operation and that groundwater does not emerge from the hole during the anti-floating anchor (2) drilling process; S3. Construct the anti-floating anchor rod (2). The anti-floating anchor rod (2) adopts the full casing follow-up construction process. When constructing the anti-floating anchor rod (2), the water level should be lowered synchronously to keep the water level elevation relatively constant; S4. After the full casing is constructed to the predetermined elevation, the hole is cleaned; S5. After the hole is cleaned, the anti-floating anchor rod body (2-1), the primary grouting pipe (2-2), the secondary grouting short pipe (2-3) and the secondary grouting long pipe (2-4) are placed, and a plurality of grouting holes (2-5) are vertically spaced apart on the side walls of the secondary grouting short pipe (2-3) and the secondary grouting long pipe (2-4); S6. The hole is cleaned again, and the surrounding precipitation wells (3) are synchronously irrigated, and the precipitation rate of each precipitation well (3) is strictly controlled to keep the precipitation amount the same, so that the water in the borehole is in a relatively static state, and the groundwater level elevation in the borehole is measured. The precipitation well (3) is synchronously controlled by a PLC controller to link the water pumps of each precipitation well; S7. After the groundwater level is stabilized, a grouting is performed through the primary grouting pipe (2-2), and the grouting liquid adopts an improved grouting liquid; S8. After the primary grouting is completed until the slurry overflows from the orifice, the steel casing used in the full casing follow-up construction is slowly pulled out, and the grouting is then supplemented through the primary grouting pipe (2-2) until the slurry overflows from the orifice again; S9. After the primary grouting has initially set, the secondary grouting is carried out, and in the secondary grouting, the secondary grouting short tube (2-3) and the secondary grouting long tube (2-4) are grouted simultaneously.

2. The anti-floating anchor construction method for existing buildings in high water level and strong permeable layer foundation according to claim 1 is characterized by: In step S5, the ends of the primary grouting pipe (2-2) and the secondary grouting long pipe (2-4) are arranged near the end of the anchoring section of the anti-floating anchor rod (2); the end of the secondary grouting short pipe (2-3) is arranged in the middle of the anchoring section of the anti-floating anchor rod (2); the secondary grouting long pipe (2-4) is provided with a grouting hole (2-5) in the lower anchoring section area, and the secondary grouting short pipe (2-3) is provided with a grouting hole (2-5) in the upper anchoring section area.

3. The anti-floating anchor construction method for existing buildings in high water level and highly permeable layer foundation according to claim 2 is characterized by: The vertical spacing between the slurry outlet holes (2-5) is 2000 mm, and two slurry outlet holes (2-5) are provided at the same height.

4. The anti-floating anchor construction method for existing buildings in high water level and highly permeable layer foundation according to claim 3 is characterized by: In step S5, the primary grouting pipe (2-2), the secondary grouting short pipe (2-3) and the secondary grouting long pipe (2-4) are all synchronously positioned and tied to the anti-floating anchor rod body (2-1).

5. The anti-floating anchor construction method for existing buildings in high water level and strong permeable layer foundation according to claim 1 is characterized by: The grouting liquid for the primary grouting in step S7 is a quick-setting cement-based slurry with a water-cement ratio of 0.4-0.45:1, and nano-silicon dioxide is added in an amount of 1-3% of the cement mass.

6. The anti-floating anchor construction method for existing buildings in high water level and strong permeable layer foundation according to claim 1 is characterized by: In step S9, after the primary grouting has initially set, a second pressure grouting is performed on the pre-buried secondary grouting short pipe (2-3) and the secondary grouting long pipe (2-4). The second grouting uses pure cement slurry with a water-cement ratio of 0.5:1 and is grouted along the entire length of the anti-floating anchor rod (2). The secondary grouting is controlled by both cement dosage and grouting pressure.

7. The anti-floating anchor construction method for existing buildings in high water level and highly permeable layer foundation according to claim 6 is characterized by: The cement dosage for secondary grouting shall be no less than 75kg / m, and the grouting pressure shall be 2~3MPa.

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