Pit-in-pit of deep foundation pit with high underground water level space limited and narrow and fat groove and construction method

Abstract

The invention relates to a pit-in-pit of a deep foundation pit with a high underground water level and a limited space and a narrow and fat groove and a construction method. The construction method comprises the following specific steps that firstly, construction preparation is conducted; secondly, a water retaining system is constructed; 3, digging a pit in the pit; 4, supporting by using an anchor rod; 5, bottom plate construction; sixthly, side walls are constructed; and step 7, constructing a fertilizer groove. The construction quality of the pit-in-pit is improved, the influence on the construction environment is reduced, the construction cost is remarkably saved, and the construction speed is highlighted.

Description

Technical Field

[0001] The present invention relates to a deep foundation pit with a high groundwater level, limited space and narrow trough, and a construction method thereof, and is mainly applicable to the construction of a pit in a foundation of a building project. Background Art

[0002] In recent years, with the accelerated pace of urbanization in my country, the development and utilization of urban underground space has become increasingly frequent, with numerous projects such as high-rise buildings, subway stations, and underground parking garages being launched. These projects often encounter complex geological and construction conditions, such as high groundwater levels, confined space, and narrow, deep excavations. On the one hand, available urban land resources are becoming increasingly scarce, and new projects often abut existing buildings or municipal facilities, severely compressing excavation space and making narrow, deep excavations a common practice. On the other hand, many cities are located in areas with well-developed water systems or high groundwater levels, posing significant challenges for excavation projects. Faced with these challenges, domestic research institutions, universities, and construction companies have collaborated closely, investing significant resources in technological research and development and practical exploration. This has led to the development of a unique technical system tailored to local project needs, encompassing every step from dewatering and support to the refined construction of excavations within excavations. The goal is to achieve efficient and economical construction while ensuring project safety and quality.

[0003] Through numerous large-scale urban construction projects, a vast amount of engineering case data has been accumulated. The construction team has become increasingly adept at handling various complex working conditions, enabling them to quickly adjust construction parameters based on site conditions. For example, they can dynamically optimize the layout of pipe well dewatering and soil nail wall support details based on different soil types and water levels, significantly improving construction efficiency and success rates. Domestic technology can be tailored to regional geological variations, such as soft soil in the south and sandy soil in the north, as well as the varying patterns of groundwater levels across different regions. By improving construction techniques, such as adjusting high-pressure jet grouting parameters in areas with high clay content to enhance anti-seepage effectiveness, foundation pit stability can be ensured under diverse and complex geological conditions. Some high-end equipment relies on imports: In critical areas such as high-precision monitoring and deep soil reinforcement, some advanced construction equipment, such as high-precision sensors that provide real-time feedback on diaphragm wall deformation and deep-drilling anchor drills, still lags behind foreign counterparts in terms of stability and accuracy. Consequently, domestic products often rely on imports, increasing project costs and complicating equipment maintenance.

[0004] In view of this, in order to solve a series of problems arising during the construction of deep foundation pits with limited narrow fertilizer troughs and high groundwater levels, it is urgent to invent a simple and effective pit-in-pit treatment system for deep foundation pits with limited narrow fertilizer troughs and high groundwater levels, so as to improve the construction quality of pits and reduce the impact on the construction environment. Summary of the Invention

[0005] The purpose of the present invention is to improve the construction quality of the pit-in-pit and reduce the impact on the construction environment. It has the advantages of significantly saving construction costs and highlighting the advantages of fast construction speed.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution: a construction method for a deep foundation pit with a high groundwater level, limited space and narrow fertilizer trough, comprising the following specific steps: Step 1: Construction preparation; Step 2: Construction of the water retaining system: Double rows of high-pressure jet grouting piles are installed along the periphery of the foundation pit to form a continuous water barrier. Several I-beams are then placed along the periphery of the pit-in-pit excavation area. The water retaining plates are then hoisted and inserted between two adjacent I-beams. Step 3: Excavation of the pit within the pit: The main pit is excavated in a "center island" manner, and the pit within the pit is excavated in a "basin" manner. During the excavation process, a trestle is erected. Step 4: Anchor support: hoist the high-strength standardized support to the slope of the foundation pit and anchor the high-strength standardized support with anchor rods; Step 5: Base plate construction; Step 6: Side wall construction: hoist the ribbed GRC wall panels onto the bottom plate, form the wall through the ribbed GRC wall panels, and fill the gap between the bottom of the wall and the bottom plate with polyurethane sealant; apply waterproof coating on the outside of the wall; Step 7: Fertilizer trough construction: first install the anti-floating support, and then pump and pour the nano-modified foam concrete in layers between the wall and the foundation pit slope.

[0007] Preferably, in step 2, the pile diameter of the high-pressure rotary jet pile is 800 mm, and the overlap of the high-pressure rotary jet pile is 300 mm; plywood is set on both sides of the I-beam, the end of the water retaining plate is "T"-shaped, and the end of the water retaining plate is embedded in the plywood on the I-beam; acrylic acid salt slurry is pressure-injected at the joint between the water retaining plate and the I-beam; the spacing between adjacent I-beams is 2.5 m.

[0008] Preferably, in step three, the trestle adopts a prefabricated assembled light steel trestle; the trestle includes a main beam, a secondary beam, a lower platform plate, and an upper platform plate, micro piles are arranged under the main beam, the micro piles are driven into the soil layer of the foundation pit, a top support is arranged on the top of the micro pile, the top support is connected to the lower end of the main beam, a groove is arranged on the lower platform plate, and the bottom of the main beam is embedded in the groove on the lower platform plate; the upper platform plate is fixed to the top of the foundation pit slope by soil nails, and the lower platform plate is arranged at the bottom of the foundation pit; soil is transported by a remote-controlled dump truck.

[0009] Preferably, in step three, the pit wall displacement is measured by a laser rangefinder immediately after each layer is excavated, and emergency support is activated when the pit wall deformation rate is greater than 2 mm / h.

[0010] Preferably, in step four, the high-strength standardized bracket includes a transverse channel steel and a vertical channel steel. The vertical channel steel is provided with a reserved hole. The casing follows the drilling rig to drill anchor holes on the slope of the foundation pit. The anchor rods pass through the reserved holes set on the vertical channel steel and are inserted into the anchor rod holes. Then, grouting is injected into the anchor rod holes. After curing for 7 days, the anchor rods are tensioned.

[0011] Preferably, the specific method of step five is as follows: first lay a 300mm thick graded gravel cushion layer at the bottom of one side of the foundation pit slope, then cover the graded gravel cushion layer with a HDPE anti-seepage membrane, and use hot-melt welding at the joints of the HDPE anti-seepage membrane; cast the base plate in blocks on the graded gravel cushion layer by the skipping method, and pre-embed the cooling water pipe during the pouring process.

[0012] Preferably, the installation method of the anti-floating bracket is as follows: setting anchor holes on the wall, installing anchor bars in the anchor holes, and connecting steel bars to the anchor bars; installing a fixing frame on the top of the wall, installing a cantilever rod on the fixing frame, and setting a vertical fixing rod on the cantilever rod, and the fixing rod is connected to the steel bar.

[0013] Preferably, in step seven, an infrared thermal imager is used to detect the concrete filling density during the pouring process to ensure that the concrete void ratio is less than 1%.

[0014] A deep foundation pit with a narrow fertilizer trough and limited space at a high groundwater level is constructed by a construction method of a deep foundation pit with a narrow fertilizer trough and limited space at a high groundwater level.

[0015] The present invention has the following characteristics and beneficial effects: (1) A prefabricated and assembled pit edge water retaining safety protection technology was proposed. The water retaining system consists of I-beams and water retaining plates. A plywood is set on the I-beams, and the water retaining plates are embedded in the plywood. This solves the problem of water-rich pits in pits and reduces the difficulty of construction.

[0016] (2) A prefabricated and assembled light steel trestle excavation technology was proposed. A light trestle combined with micro piles was used for pit-in-pit excavation construction, which solved the problems of limited pit space and trestle stability, and improved construction efficiency.

[0017] (3) A standardized support pit-in-pit prestressed anchor construction technology was proposed. The standardized support consists of horizontal channel steel, vertical channel steel, etc., which reduces the soil disturbance of the pit-in-pit slope and reduces the construction difficulty.

[0018] (4) A foam concrete backfill technology with built-in anchor rods to fix anti-floating supports in fertilizer troughs was proposed. The side walls were used to prevent the steel bars in the fertilizer trough from floating. The poured foam concrete has the characteristics of light weight, which improves the disposal efficiency of fertilizer troughs and reduces the difficulty of handling fertilizer troughs in narrow areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is the foundation pit plan intention of the present invention; Figure 2 It is a schematic diagram of a water retaining structure; Figure 3 It is a three-dimensional schematic diagram of the water retaining structure; Figure 4 It is a schematic diagram of the trestle system; Figure 5 This is a schematic diagram of the prestressed anchor rod in the pit of the standardized support pit; Figure 6 This is a schematic diagram of a prestressed anchor bolt in a pit within a pit; Figure 7 This is a schematic diagram of fertilizer tank backfill; Among them: 1- foundation pit, 2- water retaining system, 3- foundation pit slope, 4- pit in pit, 5- I-beam, 6- plywood, 7- water retaining board, 8- lower platform plate, 9- main beam, 10- secondary beam, 11- soil nails, 12- upper platform plate, 13- top support, 14- groove, 15- micro pile, 16- high-strength standardized bracket, 17- reserved hole, 18- horizontal channel steel, 19- vertical channel steel, 20- anchor rod, 21- gasket, 22- wall, 23- foam concrete, 24- steel bar, 25- embedded rebar hole, 26- anchor bar, 27- fixed rod, 28- fixed frame, 29- cantilever rod, 30- bottom plate, 31- trestle. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0021] It should be understood by those skilled in the art that, in the disclosure of the present invention, the terms "longitudinal", "transverse", "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 accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

[0022] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the elements may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0023] Example 1: A pit within a pit 4 is excavated inside the foundation pit 1. After the excavation of the foundation pit 1 and the pit within a pit 4, a foundation pit slope 3 is designed. A water retaining system 2 is set around the pit within a pit 4. The water retaining system 2 consists of an I-beam 5 and a water retaining plate 7. Clamps 6 are set on both sides of the I-beam 5, and the ends of the water retaining plate 7 are embedded in the clamps 6.

[0024] The trestle 31 includes a main beam 9, a secondary beam 10, a lower platform plate 8, and an upper platform plate 12. The upper platform plate 12 is fixed by soil nails 11. Micro piles 15 are arranged under the main beam 9. A top support 13 is arranged on the top of the micro pile 15. The top support 13 is connected to the lower end of the main beam 9. A groove 14 is provided on the lower platform plate 8. The bottom of the main beam 9 is embedded in the groove 14 on the lower platform plate 8.

[0025] A high-strength standardized bracket 16 is set on the foundation pit slope 3. The standardized bracket includes a horizontal channel steel 18 and a vertical channel steel 19. The horizontal channel steel 18 and the vertical channel steel 19 are arranged horizontally and vertically. A reserved hole 17 is set on the vertical channel steel 19. The anchor rod 20 passes through the reserved hole 17 set on the vertical channel steel 19 and is driven into the foundation pit slope 3. A gasket 21 is set on the vertical channel steel 19. The gasket 21 is set at the connection between the anchor rod 20 and the vertical channel steel 19.

[0026] A wall 22 is cast on the base plate 30 , and anchor holes 25 are provided on the wall 22 . Anchor bars 26 are provided in the anchor holes 25 . Steel bars 24 are connected to the anchor bars 26 . The steel bars 24 are connected to each other through fixing rods 27 . The fixing rods 27 are connected to fixing frames 28 . The fixing frames 28 are provided on the wall 22 .

[0027] Example 2: The construction method of a deep foundation pit with a narrow and limited space at a high groundwater level comprises the following steps: Step 1: Construction Preparation: 3D geological radar scanning was used to determine the extent of the pit within the pit, the dimensions of the fertilizer trough, and the distribution of underground pipelines. BIM models were used to optimize collision detection for the support and water retaining systems. Prefabricated components were factory-produced: water retaining plates, steel trestle modules, and anti-floating supports were prefabricated in advance. The dimensional tolerance of these plates, steel trestle modules, and anti-floating supports was less than 2 mm. Load tests were conducted on these plates, steel trestle modules, and anti-floating supports at 1.2 times the design load.

[0028] Step 2, construction of the water retaining system; construct double rows of high-pressure rotary jet piles along the periphery of the foundation pit, with a pile diameter of 800mm, an overlap of 300mm, and a cement content of 25% of the high-pressure rotary jet piles to form a continuous water-stop barrier; then, a number of I-beams 5 are successively driven along the periphery of the excavation area of the pit-in-pit 4, with a spacing of 2.5m between adjacent I-beams 5; then, the water retaining plate 7 is hoisted and inserted between two adjacent I-beams 5; wherein, the end of the water retaining plate 7 is in a "T" shape, and the end of the water retaining plate 7 is embedded in the plywood 6 on the I-beam 5; the water retaining plate 7 is made of steel-plastic composite material; and acrylate slurry is pressure-injected into the joint between the water retaining plate 7 and the I-beam 5.

[0029] Step 3: Excavation of the pit in the pit; the main pit is excavated in the "center island" style, and a counter-pressure soil platform is reserved, the width of which is greater than 5m; the pit in the pit is excavated in 3 layers in the "basin excavation" mode, and the excavation depth of each layer is less than 2m, and support is provided as the excavation progresses; during the excavation process, a trestle 31 is erected, the trestle 31 has a span of 15m and a bearing capacity of 20 tons, and the trestle 31 adopts a prefabricated light steel trestle; the trestle 31 includes a main beam 9, a secondary beam 10, a lower platform plate 8, and an upper platform plate 12, Micropiles 15 are installed under the foundation pit 9 and driven into the soil. A jacking support 13 is installed on top of the micropiles 15 and connected to the lower end of the main beam 9. A groove 14 is provided on the lower platform plate 8, and the bottom of the main beam 9 is embedded in the groove 14 of the lower platform plate 8. The upper platform plate 12 is fixed to the top of the foundation pit slope 3 with soil nails 11, and the lower platform plate 8 is set at the bottom of the foundation pit. Soil is transported by remote-controlled dump trucks, and a real-time weighing system controls the single load to less than 15m³. After each layer of excavation, the pit wall displacement is immediately measured using a laser rangefinder. Emergency support is activated when the pit wall deformation rate exceeds 2mm / h.

[0030] Step 4: Anchor support; hoist the high-strength standardized bracket 16 to the foundation pit slope 3. The high-strength standardized bracket 16 includes a horizontal channel steel 18 and a vertical channel steel 19. The vertical channel steel 19 is provided with a reserved hole 17. The casing follow-up drilling rig drills anchor holes on the foundation pit slope 3. The diameter of the anchor hole is 150mm and the depth is 8m. The high-strength standardized bracket 16 is anchored by the anchor rod 20. The anchor rod 20 passes through the reserved hole 17 set on the vertical channel steel 19 and is inserted into the anchor hole. The anchor rod 20 adopts a precision-rolled threaded steel anchor rod with a diameter of 25mm. Then, grouting is performed in the anchor hole. The grouting pressure is 1.2MPa. After curing for 7 days, the anchor rod is tensioned twice with a tensioning force of 200kN (error ±1%).

[0031] Step 5, base plate construction; first lay a 300mm thick graded gravel cushion layer at the bottom of one side of the foundation pit slope 3, the compaction degree of the graded gravel cushion layer is greater than 95%, and then cover the graded gravel cushion layer with HDPE anti-seepage membrane, and the joints of the HDPE anti-seepage membrane are hot-melt welded; a rubber water stop ring is set at the anchor rod passing through the base plate, the rubber water stop ring is made of EPDM material, and micro-expansive concrete is poured around it, and 8% HEA expansion agent is added to the micro-expansive concrete; the base plate is cast in blocks on the graded gravel cushion layer by the skipping method, and the size of a single block is less than 30m×30m. Cooling water pipes are pre-buried during the pouring process, and the water temperature difference is less than 25°C. Low-heat cement is used when pouring the base plate 30, and the hydration heat of low-heat cement in 3 days is less than 250kJ / kg.

[0032] Step 6: Side wall construction: hoist the ribbed GRC wall panels onto the bottom plate 30, and form the wall 22 with the ribbed GRC wall panels. The wall 22 is 200 mm thick and has a bending resistance greater than 15 kN·m / m. The gap between the bottom of the wall 22 and the bottom plate 30 is filled with polyurethane sealant. The outer side of the wall 22 is coated with a 2 mm thick polyurea waterproof coating with an elongation greater than 400%. Step seven, fertilizer trough construction; first install the anti-floating support, wherein the anti-floating support is installed as follows: set anchor holes 25 on the wall 22, install anchor bars 26 in the anchor holes 25, and connect the steel bars 24 to the anchor bars 26; install a fixing frame 28 on the top of the wall 22, install a cantilever rod 29 on the fixing frame 28, and set a vertical fixing rod 27 on the cantilever rod 29, and the fixing rod 27 is connected to the steel bars 24; after the anti-floating support is installed, nano-modified foam concrete (nano-modified foam concrete has a density of 600kg / m³) is pumped and poured in layers between the wall 22 and the foundation pit slope 3, with a height of 0.5m for each layer. During the pouring process, an infrared thermal imager is used to detect the concrete filling density to ensure that the concrete void ratio is less than 1%.

[0033] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, any technical solution that is the same or similar to that of the present application falls within the scope of protection of the present invention.

Claims

1. A construction method for a deep foundation pit with a limited and narrow space at a high groundwater level, characterized in that: The specific steps include: Step 1: Construction preparation; Step 2: Construction of the water retaining system; constructing double rows of high-pressure jet grouting piles along the periphery of the foundation pit to form a continuous water barrier; then sequentially driving a number of I-beams (5) along the periphery of the excavation area of the pit-in-pit (4), then hoisting a water retaining plate (7) and inserting the water retaining plate between two adjacent I-beams (5); Step 3: Excavation of the pit within the pit; the main pit is excavated in a "center island" manner, and the pit within the pit is excavated in a "basin" manner, with a trestle (31) being erected during the excavation process; Step 4: Anchor support: hoist the high-strength standardized support (16) onto the foundation pit slope (3), and anchor the high-strength standardized support (16) through the anchor rod (20); Step 5: Base plate construction; Step 6: Side wall construction: hoist the ribbed GRC wall panels onto the bottom plate (30), form the wall body (22) through the ribbed GRC wall panels, and fill the gap between the bottom of the wall body (22) and the bottom plate (30) with polyurethane sealant; apply a waterproof coating on the outside of the wall body (22); Step 7: Fertilizer trough construction: first install the anti-floating support, then pump and pour the nano-modified foam concrete in layers between the wall (22) and the foundation pit slope (3).

2. The construction method of a deep foundation pit with a limited narrow space and a high groundwater level according to claim 1 is characterized in that: In step 2, the pile diameter of the high-pressure rotary jet pile is 800 mm, and the overlap of the high-pressure rotary jet pile is 300 mm; a splint (6) is set on both sides of the I-beam (5), the end of the water retaining plate (7) is "T"-shaped, and the end of the water retaining plate (7) is embedded in the splint (6) on the I-beam (5); the joint between the water retaining plate (7) and the I-beam (5) is pressure-injected with acrylic acid slurry; the spacing between adjacent I-beams (5) is 2.5 m.

3. The construction method of a deep foundation pit with a limited narrow space and a high groundwater level according to claim 1 is characterized in that: In step 3, the trestle (31) adopts a prefabricated assembled light steel trestle; the trestle (31) includes a main beam (9), a secondary beam (10), a lower platform plate (8), and an upper platform plate (12); micro piles (15) are set under the main beam (9); the micro piles (15) are driven into the soil layer of the foundation pit; a top support (13) is set on the top of the micro pile (15); the top support (13) is connected to the lower end of the main beam (9); a groove (14) is set on the lower platform plate (8); the bottom of the main beam (9) is embedded in the groove (14) on the lower platform plate (8); the upper platform plate (12) is fixed to the top of the foundation pit slope (3) by soil nails (11), and the lower platform plate (8) is set at the bottom of the foundation pit; soil is transported by a remote-controlled dump truck.

4. The construction method of a deep foundation pit with a limited narrow space and a high groundwater level according to claim 1 is characterized in that: In step three, the pit wall displacement is measured by a laser rangefinder immediately after each layer is excavated, and emergency support is activated when the pit wall deformation rate is greater than 2 mm / h.

5. The construction method of a deep foundation pit with a limited narrow space and a high groundwater level according to claim 1 is characterized in that: In step 4, the high-strength standardized bracket (16) includes a transverse channel steel (18) and a vertical channel steel (19), and a reserved hole (17) is provided on the vertical channel steel (19). The casing is followed by a drilling rig to drill anchor holes on the foundation pit slope (3). The anchor rod (20) passes through the reserved hole (17) set on the vertical channel steel (19) and is inserted into the anchor rod hole. Then, grouting is injected into the anchor rod hole. After curing for 7 days, the anchor rod is tensioned.

6. The construction method of a deep foundation pit with a limited and narrow fertilizer trough at a high groundwater level according to claim 1 is characterized in that: The specific method of step five is as follows: first lay a 300mm thick graded crushed stone cushion layer at the bottom of one side of the foundation pit slope (3), then cover the graded crushed stone cushion layer with a HDPE anti-seepage membrane, and use hot-melt welding at the joints of the HDPE anti-seepage membrane; cast the bottom plate in blocks on the graded crushed stone cushion layer using the skipping method, and pre-bury the cooling water pipe during the casting process.

7. The construction method of a deep foundation pit with a limited narrow space and a high groundwater level according to claim 1 is characterized in that: The anti-floating bracket is installed as follows: a planting hole (25) is set on the wall (22), an anchor bar (26) is installed in the planting hole (25), and a steel bar (24) is connected to the anchor bar (26); a fixing frame (28) is installed on the top of the wall (22), a cantilever rod (29) is installed on the fixing frame (28), a vertical fixing rod (27) is set on the cantilever rod (29), and the fixing rod (27) is connected to the steel bar (24).

8. The construction method of a deep foundation pit with a limited and narrow fertilizer trough at a high groundwater level according to claim 1 is characterized in that: In step seven, an infrared thermal imager is used to detect the concrete filling density during the pouring process to ensure that the concrete void ratio is less than 1%.

9. Deep foundation pit with limited space and narrow trough at high groundwater level, characterized by: The method is constructed by the construction method of a deep foundation pit in a narrow fertilizer trough with a high groundwater level and limited space as described in any one of claims 1 to 8.

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