Deep foundation pit enclosure structure reverse construction method under influence of large-diameter pipeline

Abstract

The application discloses a deep foundation pit enclosure structure reverse construction method under the influence of large-diameter pipelines, and belongs to the underground engineering construction field. The method comprises the following steps: proving pipeline data; pre-reinforcing soil bodies outside the reverse enclosure structure before foundation pit excavation; excavating earthwork layer by layer, and performing jet anchor support every 1m of excavation; after the jet anchor strength reaches the standard, small advance guide pipes are arranged towards the soil side to perform secondary grouting reinforcement on the blind area soil bodies under the pipelines; reinforcing steel bars are bound and connected with the existing enclosure structures on both sides through anchoring, and mold concrete is constructed to complete one excavation cycle; the excavation, jet anchor, grouting and reverse construction steps are repeated until the base. The application can realize the closure of the enclosure structure without pipeline relocation, effectively solves the problem that the deep foundation pit enclosure structure cannot be constructed under the condition that the large-diameter pipelines cannot be relocated, ensures the safety of the foundation pit excavation, and the structure is reliable, and is suitable for underground diaphragm walls or pile enclosure structures.

Description

Technical Field

[0001] This invention relates to the field of engineering construction technology, specifically to a method for reverse construction of deep foundation pit retaining structures under the influence of large-diameter pipelines. Background Technology

[0002] This invention relates to the field of underground engineering construction technology, specifically to a construction method for a deep foundation pit retaining structure affected by large-diameter pipelines.

[0003] In the development of urban underground space, deep foundation pit projects often face complex pipeline relocation issues. Especially for large-diameter pipelines (such as water supply, gas, and electricity lines), relocation is often not feasible due to site conditions, the importance of the pipeline's function, relocation costs, and the surrounding environment. In such cases, the retaining structure at the pipeline location (such as diaphragm walls or pile retaining structures) cannot be constructed using conventional methods, resulting in the deep foundation pit retaining structure failing to close properly, severely impacting the overall stability of the pit and construction safety.

[0004] Currently, the industry standard for constructing retaining structures under the influence of pipelines generally adopts the conventional approach of first relocating the pipeline and then constructing the retaining structure. While this method can achieve a closed retaining structure, it is difficult to apply when the pipeline cannot be relocated. There is currently a lack of a method in the technology to safely and effectively complete the construction of retaining structures at pipeline locations without relocating large-diameter pipelines.

[0005] Therefore, there is an urgent need to develop a reverse construction method for the retaining structure of deep foundation pits affected by large-diameter pipelines, in order to solve the technical problem of the inability to close the retaining structure and ensure the safety and smooth implementation of deep foundation pit projects. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects in the existing technology and provide a reverse construction method for the retaining structure of deep foundation pits under the influence of large-diameter pipelines. This invention can achieve the closure of the retaining structure without relocating the pipeline, effectively solving the problem that the retaining structure of deep foundation pits cannot be constructed under the condition that large-diameter pipelines cannot be relocated, ensuring the safety of foundation pit excavation, and ensuring structural reliability. It is applicable to underground continuous wall or pile-type retaining structures.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for reverse construction of deep foundation pit retaining structures under the influence of large-diameter pipelines, comprising the following steps:

[0008] (1) Locate pipeline information: Determine the location, burial depth, type and material of the pipeline to provide a basis for subsequent construction;

[0009] (2) Before the excavation of the foundation pit, the soil outside the reverse retaining structure shall be pre-reinforced to prevent soil deformation, collapse or water inrush during the excavation process;

[0010] (3) Excavate the earthwork layer by layer, and carry out shotcrete support every 1 meter of excavation to ensure the stability of the excavation surface;

[0011] (4) After the shotcrete strength reaches the required level, drive the advanced small guide pipes to the soil-facing side to perform secondary grouting reinforcement on the soil in the blind area below the pipeline to make up for the pre-reinforced blind area;

[0012] (5) Tie the reinforcing bars and connect them with the existing retaining structures on both sides, and construct the formwork concrete to complete one excavation cycle;

[0013] (6) Repeat steps (3) to (5) and construct downwards layer by layer until the foundation is excavated and the entire retaining structure is completed.

[0014] To further optimize this invention, the following technical solutions may be preferred:

[0015] Preferably, in step (2), Φ600@450mm double-pipe jet grouting piles are used for pre-reinforcement, with a pressure of not less than 20MPa, a cement content of not less than 220kg / m, a lifting speed of not more than 20cm / min, a 20cm safety space between the center point of the jet grouting pile and the edge of the pipeline, and grouting is stopped at the pipeline position. The verticality is checked every 3 meters of drilling.

[0016] Preferably, in step (3), a Φ8 steel mesh is installed at 150mm×150mm for every 1 meter of excavation, and 50mm thick C25 concrete is sprayed.

[0017] Preferably, the advanced small guide pipe mentioned in step (4) is a Φ42 steel pipe with L=3.5m, t=3.5mm, hole spacing of 0.6m×1m, staggered arrangement, and driven 10 degrees downward towards the soil-facing side; the grout is a single-component cement grout with cement strength grade of 42.5MPa, water-cement ratio of 0.6:1~1.5:1, grouting pressure of 0.5~1.0MPa, and grout diffusion radius R=1.0m.

[0018] Preferably, the thickness of the cast concrete in step (5) is 400mm, the strength grade is C30, the vertical steel bars are pre-inserted into the soil below, and the upper and lower layers of steel bars are welded on one side with a welding length of 10d.

[0019] Preferably, the retaining structure is a diaphragm wall or a pile-type retaining structure, and the pipeline is a large-diameter existing pipeline that has no conditions for relocation.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) No need to relocate pipelines: The retaining structure is constructed directly below and around the large-diameter pipelines that cannot be relocated, avoiding the high costs, long cycles and social impacts caused by pipeline relocation.

[0022] (2) Construction safety and reliability: Through the three-level protection system of "pre-reinforcement + shotcrete + secondary grouting", soil deformation, collapse and water inrush are effectively controlled, ensuring the safety of the entire process of foundation pit excavation and retaining structure construction.

[0023] (3) Effective closure of the enclosure structure: The reverse method is adopted to construct the formwork concrete layer by layer and connect it with the existing enclosure structure on both sides by anchoring the rebar. The vertical rebars are welded to the upper and lower layers to form a complete stress system and meet the structural service life requirements.

[0024] (4) Strong adaptability: It is suitable for underground continuous walls or pile-type retaining structures and has good adaptability to various large-diameter pipelines (such as water supply, gas supply, electricity, etc.). Attached Figure Description

[0025] Figure 1 This is a plan view of the reverse construction method for the retaining structure of a deep foundation pit under the influence of a large-diameter pipeline, provided by the present invention.

[0026] Figure 2 Elevation and cross-sectional views of the reverse construction method for deep foundation pit retaining structure under the influence of large-diameter pipelines provided by the present invention.

[0027] Figure 3 The construction flowchart of the reverse construction method for deep foundation pit retaining structure under the influence of large-diameter pipelines provided by the present invention;

[0028] Figure 4 This is a schematic diagram of the pipeline data discovery stage provided by the present invention;

[0029] Figure 5 This is a schematic diagram of the pre-reinforcement stage of the jet grouting pile provided by the present invention;

[0030] Figure 6 This is a schematic diagram of the earthwork excavation and shotcrete stage provided by the present invention.

[0031] Figure 7 This is a large-scale image of an advanced small catheter;

[0032] Figure 8 This is a schematic diagram of the reverse construction stage (every 1 meter of excavation) of the retaining structure provided by the present invention.

[0033] The annotations in the figure are explained as follows: ② Double-tube jet grouting pile ③ Advanced small catheter ④ Reverse construction of enclosure structure ⑤ Pipelines that cannot be relocated within the foundation pit Detailed Implementation

[0034] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1 (Basic Implementation)

[0036] A deep foundation pit project, designed with diaphragm walls as the retaining structure, has a depth of 12m. A DN1000 water supply pipeline exists within the pit area (e.g., ...). Figure 2 As shown in mark ⑤, the pipeline is buried at a depth of 3.5m. Since it is a main urban water supply pipe, relocation is not feasible. The construction method of this invention is used, as detailed below:

[0037] Step 1: Determine pipeline information (e.g.) Figure 3 , Figure 4 (As shown)

[0038] Through on-site detection, ground-penetrating radar scanning, pipeline instrumentation, and retrieval of existing data, the pipeline's location, burial depth, diameter, and material were confirmed. Specifically, such as... Figure 4 As shown, the pipeline is located in the south-central part of the foundation pit, at a depth of 3.5m, with a diameter of 1000mm, made of ductile iron, and is a main urban water supply pipe with an operating pressure of 0.4MPa. Furthermore, no other important pipelines are found within 3m on either side of the pipeline.

[0039] Alternative solutions: For different types of pipelines (such as gas, electricity, communication, and heating), corresponding safety requirements should be added during the exploration phase. For example, gas pipelines need to be inspected for leaks, and electricity pipelines need to be checked for energization and voltage levels. Exploration methods may include: ground-penetrating radar, pipeline locators, manual pit exploration, and robotic pipeline inspection.

[0040] Step 2: Soil pre-reinforcement (e.g.) Figure 1 , Figure 2 , Figure 5 (As shown)

[0041] Before excavation of the foundation pit, jet grouting piles were used to pre-reinforce the soil outside the pipeline location. For example... Figure 1 and Figure 2 As shown, retaining structures have been constructed on both sides of the pipeline (marked ①). Double-pipe jet grouting piles (marked ②) are being constructed below and around the pipeline (marked ⑤). The reinforcement range is 3m × 2.5m (horizontal length × width), and the reinforcement depth extends 2m below the foundation (i.e., 14m deep).

[0042] like Figure 5As shown, a Φ600@450mm double-pipe jet grouting pile (marked ②) was used, with a pressure of 20MPa, a cement content of 220kg / m³, and a lifting speed of 18cm / min. A 20cm safety space was maintained between the center point of the jet grouting pile and the edge of the pipeline. The verticality was checked every 3 meters of drilling (the deviation should not exceed 1%), and grouting was stopped at the pipeline location.

[0043] Alternative solutions:

[0044] Alternatives to jet grouting piles: Triple-tube jet grouting piles (suitable for sandy soil and gravel layers) or single-tube jet grouting piles (suitable for soft clay and silt) can be used.

[0045] Pre-reinforcement alternatives: Deep mixing piles (cement-soil mixing piles) can be used in soft soil areas, while grouting reinforcement (sleeve valve grouting, splitting grouting) can be used in hard soil or rock areas.

[0046] Reinforcement range adjustment: Depending on the pipeline diameter, soil conditions and foundation pit depth, the reinforcement range can be adjusted from 2m×2m to 4m×3m, and the reinforcement depth can be 1m to 3m deeper than the foundation.

[0047] Safety distance adjustment: For flexible pipelines (such as PE pipes), the safety distance can be increased to 30cm to 40cm; for rigid pipelines (such as steel pipes and cast iron pipes), the safety distance can be appropriately reduced to 15cm, provided that the pipeline is not under pressure.

[0048] Verticality control: Total station or inclinometer can be used for detection. Detection should be performed every 2m to 4m of drilling, with an allowable deviation of 0.5% to 1.5%.

[0049] Step 3: Layer-by-layer excavation and shotcrete support (e.g.) Figure 3 , Figure 6 (As shown)

[0050] Excavate layer by layer from top to bottom, in 1-meter increments. Clean the excavated surface immediately after each meter of excavation. Figure 6 As shown, a Φ8 steel mesh is installed at 150mm×150mm (bidirectional), and 50mm thick C25 concrete is sprayed. The shotcrete strength must reach 5MPa or higher (tested on a test block cured under the same conditions on site) before proceeding to the next step.

[0051] Alternative solutions:

[0052] Cycle thickness adjustment: Depending on the stability of the strata, the excavation cycle thickness can be 0.5m, 0.8m, 1.0m, or 1.2m. When the stability is poor, the smaller value should be used.

[0053] Alternatives to steel mesh: Φ6@100×100, Φ10@200×200, etc., or welded steel mesh or precast steel mesh sheets can be used.

[0054] Alternative materials for shotcrete: C20 to C30 shotcrete can be used, or an accelerator (3% to 8%) can be added to improve early strength. Fiber shotcrete (steel fiber or polypropylene fiber) can also be used to enhance crack resistance.

[0055] Shotcrete thickness adjustment: Depending on the soil pressure and excavation depth, the shotcrete thickness can be 30mm to 80mm.

[0056] Step 4: Secondary grouting reinforcement using advanced small guide pipes (e.g.) Figure 2 , Figure 7 (As shown)

[0057] After the shotcrete anchor strength meets the standard, install a Φ42 pre-installed small guide pipe (marked ③) at a 10-degree angle downwards and towards the soil-facing side. For example... Figure 7 As shown, the advanced small guide pipes (marked ③) are arranged in the soil within the blind zone below the pipeline (marked ⑤), with a length of L=3.5m, a diameter of t=3.5mm, and a hole spacing of 0.6m×1m (horizontal×vertical), arranged in a staggered pattern. Grouting uses single-component cement grout (42.5MPa ordinary Portland cement, water-cement ratio 1:1), with a grouting pressure of 0.8MPa and a grout diffusion radius of 1.0m. Grouting is completed when the pressure stabilizes or the grouting volume in a single hole reaches the design value.

[0058] Alternative solutions:

[0059] Small guide tube specifications can be adjusted: different specifications such as Φ32, Φ38, Φ45, and Φ48 can be used, with length L=2.5m~5.0m and wall thickness t=3.0mm~4.5mm.

[0060] Installation angle adjustment: The angle can be 5° to 15°, depending on the pipeline burial depth and the location of the retaining structure, to avoid damaging the pipeline.

[0061] Grouting material alternatives:

[0062] Two-component grout (cement-water glass): suitable for rapid water sealing and sand layer reinforcement, with a volume ratio of 1:0.3 to 1:1.

[0063] Chemical grouts (polyurethane, acrylate): suitable for treating micro-cracks and water inrush.

[0064] Ultrafine cement slurry: suitable for fine sand layers.

[0065] Grouting parameter adjustments: water-cement ratio 0.6:1~1.5:1, grouting pressure 0.3MPa~1.5MPa, diffusion radius 0.8m~1.5m. For loose soil layers, use low pressure and large diffusion radius; for dense soil layers, use high pressure and small diffusion radius.

[0066] Hole spacing adjustment: can be 0.4m×0.8m~0.8m×1.2m, depending on the formation permeability and grout diffusion radius.

[0067] Step 5: Construct the reverse enclosure structure (e.g.) Figure 1 , Figure 2 , Figure 8 (As shown)

[0068] like Figure 1 and Figure 2 As shown, a reverse-construction retaining structure (marked ④) is constructed layer by layer below the pipeline (marked ⑤), forming a closure with the existing retaining structures (marked ①) on both sides of the pipeline. Specifically, as... Figure 8 As shown, reinforcing bars are tied after every 1 meter of excavation. Vertical reinforcing bars are pre-inserted into the soil below (insertion depth not less than 30cm or 10 times the diameter of the reinforcing bar). Horizontal reinforcing bars are connected to the existing diaphragm walls on both sides by anchoring (anchoring depth not less than 15d). The upper and lower layers of reinforcing bars are welded on one side, with a welding length of 10d (d is the diameter of the reinforcing bar). After the formwork is erected, a 400mm thick layer of C30 cast-in-place concrete (marked ④) is poured, vibrated to compact, and cured to 70% of the design strength before the next cycle can begin.

[0069] Alternative solutions:

[0070] Retaining structure types: In addition to diaphragm walls, it is also applicable to pile retaining structures (drilled piles, manually excavated piles, sheet piles, SMW method piles, etc.).

[0071] Adjustment of cast-in-place concrete thickness: Depending on the depth of the foundation pit and the stress requirements, the thickness can be 300mm to 600mm, and the strength grade can be C25 to C40.

[0072] Alternative solutions for rebar connection:

[0073] Chemical anchoring: uses epoxy resin or anchoring adhesive, suitable for smaller spacing.

[0074] Mechanical connections: sleeve connections and cold extrusion connections, suitable for large-diameter steel bars.

[0075] Embedded connectors: suitable for prefabricated enclosure structures.

[0076] Reinforcing bar connection methods: In addition to single-sided welding (10d), double-sided welding (5d), lap splicing (35d), mechanical sleeve connection, etc. can be used.

[0077] Vertical reinforcement bar length: The length inserted into the soil below can be 20cm to 50cm, or determined according to the excavation depth of the next cycle.

[0078] Maintenance conditions: Covering, water spraying, or applying a curing agent can be used for curing. The curing time should not be less than 7 days (at room temperature).

[0079] Step 6: Repeat the loop (e.g.) Figure 3 (As shown)

[0080] Repeat steps 3 to 5, constructing layer by layer downwards. After each cycle, check the verticality, flatness, and rebar connection quality of the retaining structure until the excavation reaches the foundation (depth 12m). The retaining structure (marked ④) is then completely constructed in reverse. Figure 1 and Figure 2 The diagram shows a closed structure.

[0081] Quality inspection and acceptance:

[0082] A small strain test is performed every three cycles to check the integrity of the enclosure structure.

[0083] Core sampling is performed every 5 cycles to test the strength of the cast concrete and its bonding with the soil.

[0084] After the foundation pit excavation is completed, the overall verticality is tested, and the allowable deviation is 1 / 300.

[0085] Example 2 (Applicable to silty sand formations)

[0086] A foundation pit is located in a silty sand layer with a high groundwater level, and the pipeline is a DN800 gas pipeline. Based on Example 1, the following adjustments are made:

[0087] Pre-reinforcement (e.g.) Figure 5 As shown): Triple-tube jet grouting piles (marked ②) are used, with a pressure of 25MPa, a cement content of 250kg / m, a lifting speed of 15cm / min, and the reinforcement range is expanded to 3.5m×3m.

[0088] Shotcrete anchor support (such as) Figure 6 As shown): 8% quick-setting agent was added to the shotcrete, and the steel mesh was changed to Φ10@100×100.

[0089] Grouting reinforcement (such as...) Figure 7 As shown): Cement-water glass two-component grout (volume ratio 1:0.5) is used, the grouting pressure is 1.0MPa, the grout diffusion radius is 0.8m, and the gelation time is shortened to prevent grout loss.

[0090] Cast concrete (such as) Figure 8 As shown): The thickness is adjusted to 500mm, the strength is C35, and the steel bars are double-sided welded (5d).

[0091] Example 3 (Applicable to stiff plastic clay soil layers)

[0092] A foundation pit is located in a stiff plastic clay layer, and the pipeline is a DN1200 rainwater pipe. Adjustments are as follows:

[0093] Pre-reinforcement: Deep mixing piles (replacing jet grouting piles) are used, with a pile diameter of Φ600, a cement content of 200kg / m, and a lifting speed of 25cm / min.

[0094] Excavation cycle (e.g.) Figure 3 As shown): It can be increased to 1.2m / cycle.

[0095] Advanced small catheters (such as) Figure 7 As shown): the drilling angle is 5°, the length is 3.0m, and the hole spacing is 0.8m × 1.2m.

[0096] Grouting: Single-component cement grout with a water-cement ratio of 1.2:1 and a grouting pressure of 0.5 MPa is used.

[0097] Reinforcing bar connection: Vertical reinforcing bars are reserved at 40cm and lapped (35d).

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for reverse construction of the retaining structure of a deep foundation pit under the influence of a large-diameter pipeline, characterized in that, Includes the following steps: (1) Explore pipeline information and determine the location, burial depth, type and material of the pipeline; (2) Before the excavation of the foundation pit, the soil outside the reverse retaining structure shall be pre-reinforced; (3) Excavate the earthwork layer by layer, and provide shotcrete support for every 1 meter of excavation; (4) After the shotcrete strength reaches the required level, drive the advanced small guide pipe towards the soil-facing side to carry out secondary grouting reinforcement of the soil in the blind area below the pipeline; (5) Tie the reinforcing bars and connect them with the existing retaining structures on both sides, and construct the formwork concrete to complete one excavation cycle; (6) Repeat steps (3) to (5) until the foundation is excavated and the entire retaining structure is completed.

2. The method for reverse construction of deep foundation pit retaining structure under the influence of large-diameter pipelines according to claim 1, characterized in that, The pre-reinforcement described in step (2) uses Φ600@450mm double-pipe jet grouting piles with a pressure of not less than 20MPa, a cement content of not less than 220kg / m, a lifting speed of not more than 20cm / min, and a 20cm safety space between the center point of the jet grouting pile and the edge of the pipeline.

3. The method for reverse construction of deep foundation pit retaining structure under the influence of large-diameter pipelines according to claim 2, characterized in that, The jet grouting reinforcement range is 3m×2.5m, and the reinforcement depth is 2m deeper than the excavated foundation. Grouting is stopped at the pipeline location, and the verticality is checked every 3 meters of drilling.

4. The method for reverse construction of deep foundation pit retaining structure under the influence of large-diameter pipelines according to claim 1, characterized in that, In step (3), Φ8 steel mesh is installed at 150mm×150mm for every 1 meter of excavation, and 50mm thick C25 concrete is sprayed.

5. The method for reverse construction of deep foundation pit retaining structure under the influence of large-diameter pipelines according to claim 1, characterized in that, The advanced small guide pipe mentioned in step (4) is a Φ42 steel pipe with L=3.5m, t=3.5mm, and a hole spacing of 0.6m×1m, which is staggered and driven 10 degrees downward towards the soil-facing side.

6. The method for reverse construction of deep foundation pit retaining structure under the influence of large-diameter pipelines according to claim 5, characterized in that, The grouting slurry is a single-component cement slurry, the cement strength grade is 42.5MPa ordinary Portland cement, the water-cement ratio is 0.6:1 to 1.5:1, the grouting pressure is 0.5 to 1.0MPa, and the slurry diffusion radius R = 1.0m.

7. The method for reverse construction of deep foundation pit retaining structure under the influence of large-diameter pipelines according to claim 1, characterized in that, The thickness of the cast-in-place concrete in step (5) is 400mm, the strength grade is C30, the vertical steel bars are pre-inserted into the soil below, and the upper and lower layers of steel bars are welded on one side with a welding length of 10d.

8. The method for reverse construction of deep foundation pit retaining structure under the influence of large-diameter pipelines according to claim 1, characterized in that, The retaining structure is a diaphragm wall or a pile-type retaining structure, and the pipeline is a large-diameter existing pipeline with no relocation conditions.

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