Deep foundation pit with limited space and narrow fertilizer trough at high groundwater level and its construction method

Abstract

This invention relates to a deep, confined foundation pit with a narrow space and a method for constructing such pits, including the following specific steps: Step 1, construction preparation; Step 2, construction of the water-retaining system; Step 3, excavation of the pit within the pit; Step 4, anchor bolt support; Step 5, construction of the base slab; Step 6, construction of the sidewalls; Step 7, construction of the trench. This invention improves the construction quality of pits within pits, reduces the impact on the construction environment, and has significant advantages in saving construction costs and accelerating construction speed.

Description

Technical Field

[0001] This invention relates to a deep pit within a pit in a confined space with a high groundwater level and a construction method, which is mainly applicable to the construction of pits within pits in building foundations. Background Technology

[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 high-rise buildings, subway stations, underground parking lots, and other projects being launched. These construction projects often encounter complex geological and construction conditions, such as high groundwater levels, limited space, narrow trenches, and deep pits within pits. On the one hand, available urban land resources are increasingly scarce, and new projects are often located adjacent to existing buildings or municipal facilities, severely compressing the construction space for foundation pits, making narrow trenches the norm. On the other hand, many cities are located in areas with well-developed water systems or high groundwater levels, posing significant challenges to foundation pit engineering. Faced with these challenges, domestic research institutions, universities, and construction companies have collaborated closely, investing substantial resources in technological research and development and practical exploration. This has gradually formed a unique technical system adapted to local engineering needs, covering all aspects from dewatering and support to the refined construction of pits within pits, striving to achieve efficient and economical construction goals while ensuring project safety and quality.

[0003] Through extensive experience in numerous large-scale urban construction projects, a vast amount of engineering case data has been accumulated. Construction teams have become increasingly adept at handling various complex conditions, enabling them to quickly adjust construction parameters based on site conditions. For example, they dynamically optimize the layout of dewatering wells and the details of soil nailing wall support based on different soil types and water levels, significantly improving construction efficiency and success rates. Domestic technology can be adapted to local conditions, addressing geological differences in different regions, such as soft soil layers in the south and sandy soil layers in the north, as well as varying groundwater level patterns. By improving construction techniques, such as adjusting high-pressure jet grouting pile parameters in high-cohesion soil areas to enhance seepage prevention, the stability of foundation pits can be guaranteed under various complex geological conditions. However, some high-end equipment still relies on imports: In key areas such as high-precision monitoring and deep soil reinforcement, some advanced construction equipment, such as high-precision sensors that can provide real-time feedback on diaphragm wall deformation and deep-drilling self-drilling anchor drilling rigs, still lag behind foreign products in terms of stability and accuracy, often requiring imports, which increases project costs and equipment maintenance difficulty.

[0004] In view of this, in response to a series of problems that arise during the construction of deep foundation pits in confined spaces with high groundwater levels, there is an urgent need to invent a simple and effective treatment system for deep foundation pits in confined spaces with high groundwater levels, in order to improve the construction quality of pit-within-pit construction and reduce the impact on the construction environment. Summary of the Invention

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

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution: a construction method for a deep, narrow, and confined foundation pit with a high groundwater level, comprising the following specific steps:

[0007] Step 1: Construction Preparation;

[0008] Step 2: Construction of the water-retaining system; Double rows of high-pressure jet grouting piles are constructed along the perimeter of the foundation pit to form a continuous water-stopping barrier; Then, several I-beams are driven in sequence along the perimeter of the pit-in-pit excavation area, and then the water-retaining plate is hoisted and inserted between two adjacent I-beams.

[0009] Step 3: Excavation of the pit within the pit; The main pit is excavated using the "central island" method, while the pit within the pit is excavated using the "basin" method. A trestle bridge is erected during the excavation process.

[0010] Step 4: Anchor bolt support; hoist the high-strength standardized support to the slope of the foundation pit and anchor the high-strength standardized support with anchor bolts;

[0011] Step 5: Base slab construction;

[0012] Step 6: Sidewall construction; hoist the ribbed GRC wall panels onto the base plate to form the wall. Fill the gap between the bottom of the wall and the base plate with polyurethane sealant; apply a waterproof coating to the outside of the wall.

[0013] Step 7: Construction of the foundation pit; First, install the anti-buoyancy support, and then pump and pour nano-modified foamed concrete in layers between the wall and the slope of the foundation pit.

[0014] As a preferred embodiment, in step two, the diameter of the high-pressure jet grouting pile is 800mm, and the overlap of the high-pressure jet grouting pile is 300mm; clamps are 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 clamp on the I-beam; acrylic grout is pressure-injected at the joint between the water-retaining plate and the I-beam; the spacing between adjacent I-beams is 2.5m.

[0015] As a preferred option, in step three, the trestle is a prefabricated lightweight steel trestle; the trestle includes a main beam, secondary beams, a lower platform plate, and an upper platform plate. Micropiles are installed under the main beams and driven into the soil layer of the foundation pit. A top support is installed on the top of the micropiles and connected to the lower end of the main beam. A groove is provided 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 with soil nails, and the lower platform plate is set at the bottom of the foundation pit. Soil is transported by a remote-controlled dump truck.

[0016] As a preferred option, in step three, the displacement of the pit wall is measured immediately after each layer of excavation using a laser rangefinder, and emergency support is activated when the deformation rate of the pit wall exceeds 2 mm / h.

[0017] As a preferred option, in step four, the high-strength standardized support includes horizontal channel steel and vertical channel steel. The vertical channel steel has reserved holes. The casing follow-up drilling rig drills anchor holes on the slope of the foundation pit. The anchor rod passes through the reserved holes set on the vertical channel steel and is inserted into the anchor hole. Then, grout is injected into the anchor hole, and the anchor rod is tensioned after 7 days of curing.

[0018] As a preferred option, the specific method for 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, and then cover the graded crushed stone cushion layer with an HDPE geomembrane. The joints of the HDPE geomembrane are welded by hot melt welding. The base slab is poured in sections on the graded crushed stone cushion layer using the skip-pour method, and cooling water pipes are pre-embedded during the pouring process.

[0019] As a preferred method, the installation method of the anti-buoyancy support is as follows: set up anchor holes in the wall, install anchor bars in the anchor holes, and connect steel bars to the anchor bars; install a fixing frame on the top of the wall, install cantilever rods on the fixing frame, set up vertical fixing rods on the cantilever rods, and connect the fixing rods to the steel bars.

[0020] As a preferred option, in step seven, an infrared thermal imager is used to detect the compactness of the concrete filling during the pouring process to ensure that the void ratio of the concrete is less than 1%.

[0021] The deep pit within a pit, located in a confined space with a high groundwater level, is constructed using the same method as the deep pit within a pit in a confined space with a high groundwater level.

[0022] This invention has the following characteristics and beneficial effects:

[0023] (1) A prefabricated prefabricated pit edge water-blocking safety protection technology was proposed. The water-blocking system consists of I-beams and water-blocking plates. A clamp is set on the I-beams and the water-blocking plates are embedded in the clamp, which solves the problem of water in pit and reduces the construction difficulty.

[0024] (2) A prefabricated lightweight steel trestle technology for excavation in pits within pits was proposed. The lightweight trestle combined with micropiles was used for excavation in pits within pits, which solved the problems of limited space in pits within pits and the stability of trestle bridges, and improved construction efficiency.

[0025] (3) A standardized support for the construction of prestressed anchor rods in the pit was proposed. The standardized support consists of horizontal channel steel, vertical channel steel, etc., which reduces soil disturbance on the slope of the pit and reduces construction difficulty.

[0026] (4) A foam concrete backfilling technology for fixing anti-buoyancy support with built-in anchor rods in the fertilizer trench was proposed. The side wall is used to reinforce the fertilizer trench for anti-buoyancy. The foam concrete is lightweight and has other characteristics, which improves the fertilizer trench treatment efficiency and reduces the difficulty of fertilizer trench treatment in narrow areas. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the foundation pit of the present invention;

[0028] Figure 2 This is a schematic diagram of the water-blocking structure;

[0029] Figure 3 This is a three-dimensional schematic diagram of the water-blocking structure;

[0030] Figure 4 This is a schematic diagram of a trestle bridge system;

[0031] Figure 5 This is a schematic diagram of a prestressed anchor bolt for a standardized support pit.

[0032] Figure 6 This is a schematic diagram of a prestressed anchor bolt in a pit-within-a-pit system.

[0033] Figure 7 This is a schematic diagram of fertilizer trench backfilling;

[0034] Among them: 1-Foundation pit, 2-Water retaining system, 3-Foundation pit slope, 4-Pit within pit, 5-I-beam, 6-Clamping plate, 7-Water retaining plate, 8-Lower platform plate, 9-Main beam, 10-Secondary beam, 11-Soil nail, 12-Upper platform plate, 13-Top support, 14-Groove, 15-Micropile, 16-High-strength standardized support, 17-Reserved hole, 18-Horizontal channel steel, 19-Vertical channel steel, 20-Anchor rod, 21-Shim, 22-Wall, 23-Foam concrete, 24-Reinforcing bar, 25-Rebar hole, 26-Anchor bar, 27-Fixing rod, 28-Fixing frame, 29-Cantilever rod, 30-Base plate, 31-Trestle bridge. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0036] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0037] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0038] Example 1:

[0039] The pit 1 is excavated into a pit 4. After the pit 1 and pit 4 are excavated, the pit slope 3 is designed. A water-blocking system 2 is set around the pit 4. The water-blocking system 2 is composed of I-beams 5 and water-blocking plates 7. Clamping plates 6 are set on both sides of the I-beams 5. The ends of the water-blocking plates 7 are embedded in the clamping plates 6.

[0040] The trestle bridge 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. Micropiles 15 are set under the main beam 9. A top support 13 is set on the top of the micropiles 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.

[0041] A high-strength standardized support 16 is installed on the foundation pit slope 3. The standardized support 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 in a staggered manner. A reserved hole 17 is set on the vertical channel steel 19. The anchor rod 20 is driven into the foundation pit slope 3 after passing through the reserved hole 17 set on the vertical channel steel 19. A shim 21 is set on the vertical channel steel 19. The shim 21 is set at the connection between the anchor rod 20 and the vertical channel steel 19.

[0042] A wall 22 is poured on the base plate 30. Rebar holes 25 are provided on the wall 22. Anchor bars 26 are installed in the rebar holes 25. Rebars 24 are connected to the anchor bars 26. The rebars 24 are connected to each other by a fixing rod 27. The fixing rod 27 is connected to a fixing frame 28. The fixing frame 28 is installed on the wall 22.

[0043] Example 2:

[0044] The construction method for the deep, narrow, and confined foundation pit with a high groundwater level includes the following steps:

[0045] Step 1: Construction Preparation; 3D ground-penetrating radar scanning is used to clarify the pit-within-a-pit area, trench dimensions, and underground pipeline distribution. BIM modeling is used to optimize the support and water-retaining system for collision detection. Prefabricated components are manufactured in the factory: water-retaining panels, steel trestle modules, and anti-buoyancy supports are prefabricated. The dimensional error of the water-retaining panels, steel trestle modules, and anti-buoyancy supports is less than 2mm. Load tests are conducted on the water-retaining panels, steel trestle modules, and anti-buoyancy supports, with the applied load being 1.2 times the design load.

[0046] Step 2: Construction of the water-retaining system; Double rows of high-pressure jet grouting piles are constructed along the perimeter of the foundation pit. The pile diameter is 800mm, the overlap is 300mm, and the cement content of the high-pressure jet grouting piles is 25%, forming a continuous water-stopping barrier; then, several I-beams 5 are sequentially driven along the perimeter of the excavation area of ​​pit 4 within the pit, with a spacing of 2.5m between adjacent I-beams 5; next, water-retaining plates 7 are hoisted and inserted between two adjacent I-beams 5; the ends of the water-retaining plates 7 are "T"-shaped and embedded in the clamps 6 on the I-beams 5; the water-retaining plates 7 are made of steel-plastic composite material; acrylic grout is pressure-injected into the joint between the water-retaining plates 7 and the I-beams 5.

[0047] Step 3: Pit-within-a-pit excavation; the main pit adopts a "central island" excavation method, with a pre-reserved counterweight platform, the width of which is greater than 5m; the pit-within-a-pit is excavated in three layers using a "basin-style excavation" method, with each layer having an excavation depth of less than 2m, and supports are erected as excavation progresses; during the excavation process, a trestle bridge 31 is erected, with a span of 15m and a load-bearing capacity of 20 tons. The trestle bridge 31 is a prefabricated assembled lightweight steel trestle bridge; the trestle bridge 31 includes a main beam 9, a secondary beam 10, a lower platform slab 8, and an upper platform slab 12, with the main beam... Micropiles 15 are installed below the main beam 9 and driven into the soil layer of the foundation pit. A top support 13 is installed on the top of each 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 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 located at the bottom of the foundation pit. Soil is transported using a remote-controlled dump truck, with a real-time weighing system controlling the single load to be less than 15 m³. Immediately after each layer of excavation, the displacement of the pit wall is measured using a laser rangefinder. Emergency support is activated when the deformation rate of the pit wall exceeds 2 mm / h.

[0048] Step 4: Anchor Bolt Support; The high-strength standardized support 16 is hoisted onto the foundation pit slope 3. The high-strength standardized support 16 includes a horizontal channel steel 18 and a vertical channel steel 19. The vertical channel steel 19 has pre-drilled holes 17. A casing-following drilling rig drills anchor bolt holes on the foundation pit slope 3. The diameter of the anchor bolt holes is 150mm, and the depth is 8m. The high-strength standardized support 16 is anchored using anchor bolts 20. The anchor bolts 20 pass through the pre-drilled holes 17 on the vertical channel steel 19 and are inserted into the anchor bolt holes. The anchor bolts 20 are 25mm diameter precision-rolled threaded steel anchor bolts. Grouting is then performed in the anchor bolt holes at a pressure of 1.2MPa. After 7 days of curing, the anchor bolts are tensioned twice, with a tension force of 200kN (error ±1%).

[0049] Step 5: Base Slab Construction; First, lay a 300mm thick graded crushed stone cushion layer at the bottom of one side of the foundation pit slope 3. The compaction degree of the graded crushed stone cushion layer is greater than 95%. Then, cover the graded crushed stone cushion layer with an HDPE geomembrane. The joints of the HDPE geomembrane are hot-melt welded. Rubber water-stop rings are installed where the anchor rods pass through the base slab. The rubber water-stop rings are made of EPDM material. Micro-expansion concrete is poured around the perimeter, and 8% HEA expansion agent is added to the micro-expansion concrete. The base slab is poured in sections on the graded crushed stone cushion layer using the skip-pour method. The size of each section is less than 30m×30m. Cooling water pipes are pre-embedded during the pouring process. The water temperature difference is less than 25℃. Low-heat cement is used when pouring the base slab 30. The heat of hydration of low-heat cement after 3 days is less than 250kJ / kg.

[0050] Step Six: Side Wall Construction; Hoist the ribbed GRC wall panels onto the base plate 30 to form wall 22. Wall 22 is 200mm thick and has a bending resistance greater than 15kN·m / m. The gap between the bottom of wall 22 and the base plate 30 is filled with polyurethane sealant. A 2mm thick polyurea waterproof coating is applied to the outside of wall 22, with an elongation rate greater than 400%.

[0051] Step 7: Construction of the foundation pit; First, install the anti-buoyancy support, which is installed as follows: Set rebar holes 25 on the wall 22, install anchor bars 26 in the rebar holes 25, and connect steel bars 24 to the anchor bars 26; Install a fixing frame 28 on the top of the wall 22, install cantilever rods 29 on the fixing frame 28, and set vertical fixing rods 27 on the cantilever rods 29, which are connected to the steel bars 24; After the anti-buoyancy support is installed, pump and pour nano-modified foam concrete (nano-modified foam concrete with a density of 600 kg / m³) in layers between the wall 22 and the foundation pit slope 3, with each layer being 0.5 m high. During the pouring process, use an infrared thermal imager to detect the compactness of the concrete filling to ensure that the concrete porosity is less than 1%.

[0052] This invention is not limited to the preferred embodiments described above. Anyone can derive other products in various forms under the guidance of this invention. However, regardless of any changes in shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A construction method for a deep, narrow, and confined foundation pit with a high groundwater level, characterized in that... The specific steps include the following: Step 1: Construction Preparation; Step 2, Water-retaining system construction; Double rows of high-pressure jet grouting piles are constructed along the perimeter of the foundation pit to form a continuous water-stopping barrier; Then, several I-beams (5) are driven sequentially along the perimeter of the excavation area of ​​the pit-in-pit (4), followed by hoisting the water-retaining plate (7) and inserting it between two adjacent I-beams (5); The diameter of the high-pressure jet grouting piles is 800mm, and the overlap of the high-pressure jet grouting piles is 300mm; Clamping plates (6) are set on both sides of the I-beams (5), and the end of the water-retaining plate (7) is "T" shaped, with the end of the water-retaining plate (7) embedded in the clamping plate (6) on the I-beams (5); Acrylic grout is pressure-injected at the joint between the water-retaining plate (7) and the I-beams (5); The spacing between adjacent I-beams (5) is 2.5m; Step 3: Pit-in-pit excavation; The main pit is excavated using a "central island" method, and the pit-in-pit is excavated using a "basin" method. During the excavation process, a trestle bridge (31) is erected. The trestle bridge (31) is a prefabricated lightweight steel trestle bridge. The trestle bridge (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 main beam (9). The micropiles (15) are driven into the soil layer of the pit. A top support (13) is installed on the top of the micropiles (15). The top support (13) is connected to the lower end of the main beam (9). A groove (14) is installed 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 pit slope (3) by soil nails (11). The lower platform plate (8) is set at the bottom of the pit. Soil is transported by a remote-controlled dump truck. Step 4, Anchor Bolt Support; Hoist the high-strength standardized support (16) to the slope (3) of the foundation pit, and anchor the high-strength standardized support (16) with anchor bolts (20); The high-strength standardized support (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 bolt holes on the slope (3) of the foundation pit. The anchor bolt (20) passes through the reserved hole (17) on the vertical channel steel (19) and is inserted into the anchor bolt hole. Then, grout is injected into the anchor bolt hole. After curing for 7 days, the anchor bolt is tensioned. Step 5, base slab construction; 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 HDPE geomembrane, and use hot melt welding at the joints of the HDPE geomembrane; pour the base slab in sections on the graded crushed stone cushion layer by skip-filling method, and pre-embed cooling water pipes during the pouring process; Step 6: Side wall construction; hoist the ribbed GRC wall panel onto the base plate (30), and form the wall (22) through the ribbed GRC wall panel. Fill the gap between the bottom of the wall (22) and the base plate (30) with polyurethane sealant; apply a waterproof coating to the outside of the wall (22). Step 7, construction of the trough; first install the anti-buoyancy support, then pump and pour nano-modified foam concrete in layers between the wall (22) and the foundation pit slope (3); the installation method of the anti-buoyancy support is as follows: set up the anchoring holes (25) on the wall (22), install the anchoring bars (26) in the anchoring holes (25), and connect the reinforcing bars (24) on the anchoring bars (26); install the fixing frame (28) on the top of the wall (22), install the cantilever rod (29) on the fixing frame (28), set the vertical fixing rod (27) on the cantilever rod (29), and connect the fixing rod (27) to the reinforcing bar (24).

2. The construction method for a deep, narrow, and confined foundation pit with a high groundwater level as described in claim 1, characterized in that, In step three, the displacement of the pit wall is measured immediately after each layer of excavation using a laser rangefinder. Emergency support is activated when the deformation rate of the pit wall exceeds 2 mm / h.

3. The construction method for a deep, narrow, and confined foundation pit with a high groundwater level as described in claim 1, characterized in that... In step seven, an infrared thermal imager is used to detect the compactness of the concrete filling during the pouring process to ensure that the void ratio of the concrete is less than 1%.

4. A deep, narrow, and confined foundation pit with a high groundwater level, characterized by: It is constructed using the construction method for deep, narrow, and confined foundation pits with high groundwater levels as described in any one of claims 1-3.

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