HU construction method pile and pre-stressed anchor cable combined foundation pit supporting structure

Abstract

The utility model belongs to the technical field of building construction, and discloses an HU construction method pile combined pre-stressed anchor cable foundation pit combined supporting structure which comprises a foundation pit and further comprises a plurality of H-shaped steel arranged on the periphery of the foundation pit, and Larsen steel sheet piles are arranged on the sides, away from the foundation pit, of the H-shaped steel. H-shaped steel and Larsen steel sheet piles are combined to form the steel sheet pile continuous wall with the water stopping and soil retaining functions, steel enclosing purlins are installed on the sides, close to a foundation pit, of the H-shaped steel, the steel enclosing purlins are of a double-splicing H-shaped structure, steel strands penetrate through the middles of the H-shaped steel and the Larsen steel sheet piles, the first ends of the steel strands are connected with the steel enclosing purlins through steel base plates and anchorage devices, and the second ends of the steel strands are connected with the steel enclosing purlins. The second end of the steel strand is provided with an expanded end, and a jet grouting mixing pile is arranged on the steel strand close to the expanded end. According to the foundation pit combined supporting structure combining the HU construction method piles with the pre-stressed anchor cables, the advantages of the Larsen steel sheet piles, the H-shaped steel and the pre-stressed anchor cables are organically combined, the Larsen steel sheet piles and the H-shaped steel are combined to be high in stability, the pile forming speed is high, and the foundation pit combined supporting structure has the water stopping function and the soil retaining function.

Description

Technical Field

[0001] This utility model belongs to the field of building construction technology, and in particular relates to a combined support structure for foundation pits using the HU method of pile construction and prestressed anchor cable construction. Background Technology

[0002] Foundation pit engineering is characterized by complex construction environments, high technical difficulty, and numerous unpredictable factors. Soft soil foundation pits are prone to displacement and settlement during construction, impacting the surrounding environment. Therefore, the foundation pit support scheme must be selected in conjunction with the surrounding environmental conditions. On the other hand, although foundation pit support is a temporary structure, its cost is relatively high, and its impact on the total project cost cannot be ignored. Therefore, choosing a foundation pit support method that is both economical and environmentally friendly is of great practical significance.

[0003] For single-story underground structure construction with large, irregularly shaped pits and complex surrounding environments, there are many options for pit support. Support structures include bored pile support, SMW (soil-mixed concrete) support, composite soil nailing support, and cement-mixed pile gravity retaining walls; support methods include concrete horizontal supports and internal steel supports (steel pipes or structural steel). The optimal selection of the pit support scheme has a significant impact on the safety of the surrounding environment, construction technology, and economic investment.

[0004] In order to find the best balance between environmental protection and economic benefits, and to differentiate the specific requirements of the environment on the support system, the forms of foundation pit support were optimized and compared, resulting in a combined support structure for foundation pits using the HU method of piles and prestressed anchor cables. Utility Model Content

[0005] The purpose of this utility model is to provide a combined support structure for foundation pits using the HU method of pile construction and prestressed anchor cables, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, this utility model provides the following technical solution:

[0007] A combined support structure for a foundation pit using the HU method of pile construction and prestressed anchor cables includes a foundation pit and several H-beams arranged around the perimeter of the foundation pit. Larssen sheet piles are installed on the side of the H-beams away from the foundation pit. The H-beams and Larssen sheet piles are combined to form a continuous sheet pile wall serving both as a water-stopping and retaining wall. A steel waler is installed on the side of the H-beams closest to the foundation pit. The steel waler adopts a double-H-shaped structure. A steel strand passes through the middle of the H-beams and the Larssen sheet piles. The first end of the steel strand is connected to the steel waler via a steel pad and an anchor. The second end of the steel strand has an enlarged end, and a jet grouting pile is installed near the enlarged end of the steel strand.

[0008] Furthermore, the inclination of each H-beam and Larssen sheet pile shall not exceed 2% to ensure stability and flatness.

[0009] Furthermore: the enlarged end is 2m long, the aperture is not less than 800mm, and the enlarged end is sprayed with a pressure of 20-30Mpa to ensure the stability of the force.

[0010] Furthermore, the jet grouting and mixing pile adopts an anchor cable drilling rig grouting molding structure to ensure that the steel strand is locked after being pre-tensioned, and is firmly connected to the steel waler and anchor.

[0011] Compared with existing technologies, the beneficial effects are:

[0012] 1. The combined support structure organically combines the advantages of Larssen sheet piles, H-beams and prestressed anchors. The combination of Larssen sheet piles and H-beams has high stability, fast pile formation speed and has both water-stopping and soil-retaining functions. The prestressed anchors are flexible in setting, easy to install and disassemble and can be recycled and reused.

[0013] 2. The basin-shaped excavation in the middle area of ​​the foundation pit is unobstructed, with a large operating space and high earthwork excavation efficiency.

[0014] 3. It can simultaneously organize the excavation of the earthwork around the foundation pit and the construction of the basement slab, which can speed up the construction progress of the basement. Attached Figure Description

[0015] Figure 1 This is a plan view of the combined support structure for a HU method pile and prestressed anchor cable foundation pit described in this utility model.

[0016] Figure 2 This is a partially enlarged schematic diagram of area A of the HU method pile combined with prestressed anchor cable foundation pit composite support structure described in this utility model;

[0017] Figure 3 This is an AA sectional view of a combined support structure for a foundation pit using the HU method pile and prestressed anchor cable, as described in this utility model.

[0018] Figure 4 This is a detailed drawing of the connection between the steel waler and steel strand in a combined support structure for a prestressed anchor cable foundation pit using the HU method, as described in this utility model.

[0019] In the attached diagram, the following are the reference numerals: 1. H-beam; 2. Larssen sheet pile; 3. Steel waler; 4. Steel strand; 5. Jet grouting pile; 6. Enlarged end; 7. Steel pad; 8. Anchorage; 9. Excavation pit; 10. Bottom plate. Detailed Implementation

[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0021] Please see Figures 1-4 A combined support structure for a foundation pit 9 using the HU method of pile construction includes a foundation pit 9 and several H-beams 1 arranged around the periphery of the foundation pit 9. Larssen sheet piles 2 are installed on the side of the H-beams 1 away from the foundation pit 9. The H-beams 1 and Larssen sheet piles 2 are combined to form a continuous sheet pile wall for both water stopping and soil retaining. A steel waler 3 is installed on the side of the H-beams 1 close to the foundation pit 9. The steel waler 3 adopts a double H-shaped structure. A steel strand 4 passes through the middle of the H-beams 1 and the Larssen sheet piles 2. The first end of the steel strand 4 is connected to the steel waler 3 through a steel pad 7 and an anchor 8. The second end of the steel strand 4 is provided with an enlarged end 6. A jet grouting and mixing pile 5 is provided near the enlarged end 6 of the steel strand 4.

[0022] Furthermore: the inclination of each H-beam 1 and Larssen sheet pile 2 shall not exceed 2% to ensure stability and flatness; the enlarged end 6 shall be 2m long with a hole diameter of not less than 800mm, and the enlarged end 6 shall be grouted at a pressure of 20-30Mpa to ensure the stability of the load; the jet grouting and mixing pile 5 shall be formed by anchor cable drilling rig grouting to ensure that the steel strand 4 is locked after pretensioning and is firmly connected to the steel waler 3 and anchor 8.

[0023] Working principle: H-beam 1 and Larssen sheet pile 2 are combined to form a continuous sheet pile wall that serves as both a water stop and a retaining wall. The high bending resistance of H-beam 1 is fully utilized to withstand the lateral water and soil pressure. The Larssen sheet pile 2 is formed in one piece and has low permeability to prevent the seepage of groundwater. Steel strand 4, steel pad 7 and anchor 8 form a prestressed anchor cable structure. The prestressed anchor cable structure can effectively reduce the stress level of the soil around the anchor cable, reduce the displacement and internal force of the support structure, and control the deformation of the support structure.

[0024] The construction process specifically includes the following steps:

[0025] (1) Driving of H-beam 1 and Larssen sheet piles 2

[0026] In this embodiment, the H-beam 1 support uses H500×300×11×18 steel, and specifically includes the following steps: material inspection → material hoisting → pile driver positioning → driving of H-beam 1 and Larssen sheet piles 2.

[0027] ① Material inspection

[0028] Visual inspection includes items such as surface defects, length, width, thickness, height, end rectangle ratio, straightness, and lock shape.

[0029] ② Material hoisting

[0030] Two-point lifting is recommended for loading and unloading H-beams 1 and Larssen sheet piles 2. During lifting, the number of sheet piles lifted at one time should not be too large, and care should be taken to protect the interlocking joints from damage.

[0031] ③ Piling machine in place

[0032] Set up a total station on one side of the construction site and adjust the position of the piling machine. Under unified command, ensure the piling machine is in place, carefully checking the top, bottom, left, and right sides before moving it. Remove any obstacles promptly. After moving, check the positioning and correct any errors. The piling machine should be stable and level.

[0033] ④ Driving of H-beams 1 and Larssen sheet piles 2

[0034] Both H-beams 1 and Larssen sheet piles 2 are driven using a driving and pulling machine with a vibratory hammer. Before driving, it is essential to be familiar with the underground pipelines and structures, and to carefully mark out the accurate centerline of the support piles.

[0035] Before piling, each H-beam 1 and Larssen sheet pile 2 is inspected. Ordinary sheet piles with severe corrosion and deformation of the connecting interlocks are rejected. Those that fail to meet the standards can only be used after repair.

[0036] Before driving the piles, apply grease to the interlocks of the Larssen sheet piles to facilitate driving and pulling them out.

[0037] After the H-beam 1 and Larssen sheet pile 2 are lifted by the driving and pulling machine, they are manually aligned and positioned. During the driving process, the inclination of each pile is constantly measured and monitored to ensure it does not exceed 2%. If the inclination is too large to be corrected by pulling, the pile is pulled out and re-driven. The depth of each drive is generally 0.5 meters to 3 meters. The Larssen sheet pile 2 should be driven one after another continuously, and care should be taken to ensure that the elevation of the pile tops does not differ too much.

[0038] (2) Prestressed anchor cable construction

[0039] This embodiment uses 2S15.2 prestressed recyclable anchor cables with a hole diameter of 500mm, a total length of 25.0m or 28.0m, an inclination angle of 15° or 25°, a horizontal spacing of 3.2m, and a prestressing lock of 150KN. The specific steps include: layout → hole drilling → cable fabrication → anchor cable installation → first grouting → second high-pressure grouting → anchor cable tensioning and locking.

[0040] ① Laying out the lines

[0041] The on-site surveying and layout personnel laid out the lines according to the design requirements, and after inspection by a designated person, construction records were made.

[0042] ②Hole formation

[0043] The diameter of the anchoring section is 500mm, and the design depth is 25.0m or 28.0m. The anchor hole depth should not be less than the design depth of 500mm. The drilling angle is 15° or 25°. A full-casing anchor drilling rig is used for full-casing drilling. The anchor drilling rig is equipped with an angle measuring device to strictly control the angle. After drilling, the cable is placed into the hole, and then the casing is removed for the first grouting.

[0044] If borehole collapse occurs during drilling, mud should be used to protect the borehole wall during drilling. The mud density should be 1.25–1.3. After drilling, the borehole should be washed promptly until the specific gravity of the mud flowing out of the borehole is less than 1.10 g / cm³. 3 Until then; during the drilling process, pay attention to controlling the verticality of the anchor hole and the inclination angle of the anchor cable. After the hole is formed, check and accept the hole depth, hole diameter, and inclination angle, and make good construction records and hidden works inspection records.

[0045] ③ Cable construction

[0046] The cable body must be processed on a flat, mud-free surface, with an error of less than 50mm for each strand. A positioning bracket should be installed every 1.6 meters along the cable's axis and securely tied with wire. The protective layer of the cable body should be no less than 20mm thick. Free sections of the cable body should be coated with lubricating oil and wrapped with plastic sheeting or a plastic tube. Both ends should be tightly wrapped to prevent cement grout from seeping in.

[0047] The cable body can only be lowered after it has passed the processing and inspection. It should be stacked neatly and clearly labeled. During the transportation of the cable body, appropriate manpower should be allocated to prevent it from getting contaminated with mud and water. After the cable body is placed into the hole, the exposed tension length should be 0.5-1m (based on the outer skin of the crown beam / waist beam).

[0048] ④ Anchor cable installation

[0049] Anchor cables should be lowered immediately after drilling, and the steel strands should be kept from twisting during the placement of anchor cables.

[0050] ⑤ First grouting

[0051] The first grouting should be carried out within 2 hours after the anchor cable is installed in the hole, and immediately after the hole is cleaned. The first grouting material is cement slurry, using 42.5R ordinary Portland cement, with 0.03% ethanolamine added as an early strength agent, a water-cement ratio of 0.5, and a mixing tank with a diameter of 1m and a height of 0.9m. Calculations show that 0.31m of water is placed in the mixing tank, and 10 bags of cement are added to prepare a 0.5 cement slurry. The first grouting is stopped once the water and impurities in the borehole are displaced and cement slurry flows out of the borehole.

[0052] ⑥ Second high-pressure grouting

[0053] The second grouting uses pure cement grout with a water-cement ratio of 0.5, with 0.3% triethanolamine added as an early strength agent. The grouting pressure should not be less than 2.0 MPa, and can be adjusted appropriately according to specific conditions and experience. The second grouting should be carried out before the initial setting of the first grouting, with an interval of 3 hours.

[0054] ⑦ Anchor cable tensioning and locking

[0055] Tensioning equipment must be calibrated by a metrology department, and the calibration parameters shall be used as the basis for on-site tensioning. Tensioning can only be carried out when the strength of both the anchor body and the pedestal concrete is greater than 70% of the design strength. When tensioning anchor cables, attention should be paid to the impact on adjacent anchor cables, and measures such as alternating anchor tensioning can be adopted.

[0056] Anchorages that meet the technical requirements should be used; anchor cables should be tensioned to the design locking value and locked; if significant prestress loss is found after the anchor cables are locked, compensatory tensioning should be carried out.

[0057] (3) Earthwork excavation

[0058] ① Before excavation, wellpoint dewatering was carried out outside the foundation pit 9 to keep the foundation pit 9 dry and facilitate excavation. The machinery inlet and outlet passages and the surrounding area were replaced with steel plates to diffuse the pressure and reduce lateral pressure.

[0059] ② Earthwork excavation should be carried out in strict zoning, segmentation, and symmetrical excavation in conjunction with the post-cast strip. The length of each segment along the edge of the pit should not exceed 20 meters. Over-excavation is strictly prohibited. Effective measures should be taken to reduce the long-side effect and the adverse impact of large-area construction on the foundation pit 9. The excavation method should be adjusted according to the monitoring data.

[0060] ③ The excavation of foundation pit 9 should be carried out in the following ways: excavation, repair, paving, pouring and masonry should be carried out simultaneously. The time without a cushion layer at the bottom of the pit should not exceed 24 hours to ensure that the soil of foundation pit 9 is not exposed for a long time and to improve the stability of foundation pit 9. The cushion layer should be poured up to the lower sill line of foundation pit 9 so that the cushion layer forms a rigid support point for the retaining structure. The foundation slab 10 and force transmission belt should be constructed as soon as possible.

[0061] ④ Based on the actual water flow rate at the bottom of foundation pit 9, if necessary, dig a 300×300 cross-section drainage ditch around foundation pit 9 on the inner side of foundation pit 9, more than 7m away from the slope toe. Set up a water collection pit every 30 meters to drain the water in the pit in time, keep the working surface and bottom of the pit dry, and do a good job of organized drainage inside and outside foundation pit 9.

[0062] (4) Backfilling of foundation pit 9

[0063] Based on the location and structural characteristics of the buildings in this project, after the basement exterior wall structure is completed and the concrete strength meets the design requirements, waterproof coating can be applied to the exterior wall panels. After inspection and acceptance, protective boards can be installed before backfilling. Backfilling should be carried out evenly and symmetrically, and compacted in layers. When compacting manually, the thickness of each layer should not exceed 250mm, and when compacting mechanically, the thickness of each layer should not exceed 300mm. Backfilling will be carried out using a combination of mechanical and manual filling, in layers, with each layer being 200-350mm thick and compacted by a combination of manual and mechanical (frog-type) compaction, layer by layer until the outdoor ground level is reached.

[0064] (5) Prestressed anchor cable recycling

[0065] Construction preparation → Dismantling and cutting → Anchor cable recovery → Cleaning and tidying.

[0066] ① Construction preparation

[0067] Construction preparation is the preliminary work for the entire recycling operation, including personnel organization, material preparation, and equipment debugging. This involves preparing the necessary materials and equipment, including cutting tools, recycling devices, and cleaning tools. The construction equipment must be inspected and tested to ensure its normal operation. A detailed work plan and safety measures must be developed to ensure a safe and controllable construction process.

[0068] ② Disassembly and cutting

[0069] Determine the cutting location and length, and measure and mark them according to project requirements. Use appropriate cutting tools, such as electric saws or cable cutters, to cut the prestressed anchor cables. Safety should be prioritized during the process to avoid damaging the anchor cable material, and the cuts should be smooth and accurate. After cutting, the anchoring equipment needs to be dismantled. Handle dismantling carefully to avoid damaging the equipment. After dismantling, clean the anchoring area to ensure smooth progress of subsequent work.

[0070] ③ Anchor cable recovery

[0071] Using specialized recovery equipment, such as jacks and hydraulic lifts, the cut anchor cables are extracted section by section vertically and removed from the structure. The integrity and condition of the recovered anchor cables are inspected, and damaged or deteriorated cables are classified and treated. The recovered anchor cables are cleaned to remove dirt and corrosion, and surface inspection and measurement are performed.

[0072] ④ Cleaning and tidying up

[0073] The recovered anchor cables are sorted and classified, and archived and labeled according to material, performance, and usage condition. The anchor cables are then sorted and packaged to ensure easy storage and transportation. The construction site is cleaned up, removing garbage and debris, and the work area is restored to a tidy state.

[0074] (6) Removal of H-beam 1 and Larssen sheet pile 2

[0075] Pile extraction starting point and sequence → Vibration and extraction → Backfilling of pile hole.

[0076] ① Piling start point and sequence

[0077] For closed sheet pile walls, the starting point for pile extraction should be at least 5 corner piles away. The starting point for extraction can be determined based on the conditions during pile driving, and a skip extraction method can be used if necessary. The sequence of pile extraction is preferably the reverse of the pile driving sequence.

[0078] ② Vibration and pulling

[0079] When extracting the pile, first use a pile driver to clamp the head of the H-beam 1 and Larssen sheet pile 2 and vibrate for 1 to 2 minutes. Use a vibratory hammer to loosen the interlocking joint of the sheet pile to reduce soil adhesion, loosen the soil around the H-beam 1 and Larssen sheet pile 2, and generate "liquefaction" to reduce the frictional resistance of the soil on the pile. Then slowly vibrate and pull upwards while vibrating.

[0080] For H-beams 1 and Larssen sheet piles 2, which have high extraction resistance, an intermittent vibration method can be used. First, use a vibratory hammer to vibrate the pile down 100-300mm, and then alternate between vibrating and pulling with the vibratory hammer. During extraction, pay attention to the load of the pile driver. If it is difficult to pull the pile up or it cannot be pulled up, stop the extraction. Vibrate for 1-2 minutes, then lower the hammer down 0.5m-1.0m and then pull it up again. Repeat this process to pull the pile out.

[0081] ③ Backfilling pile holes

[0082] After the H-beam 1 and Larssen sheet pile 2 are removed, the pile hole should be backfilled in a timely manner, and measures should be taken to compact it.

[0083] (7) Engineering monitoring

[0084] To ensure the proper and effective functioning of the combined support structure of the HU method pile and prestressed anchor cable foundation pit 9 and to prevent abnormal situations, comprehensive monitoring of foundation pit 9 is essential. Engineering monitoring includes: surface settlement monitoring, soil horizontal deformation monitoring, pit bottom heave deformation monitoring, support structure internal force monitoring, support axial force monitoring, and groundwater level monitoring. Based on the feedback results of engineering monitoring, the deformation amount and deformation pattern of the strata are understood to guide construction.

[0085] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A combined support structure for a foundation pit using the HU method of pile construction and prestressed anchor cable, comprising a foundation pit (9), characterized in that: It also includes several H-beams (1) set around the periphery of the foundation pit (9). A Larssen sheet pile (2) is set on the side of the H-beam (1) away from the foundation pit (9). The H-beam (1) and the Larssen sheet pile (2) are combined to form a continuous sheet pile wall for both water stopping and soil retaining. A steel waler (3) is installed on the side of the H-beam (1) close to the foundation pit (9). The steel waler (3) adopts a double H-shaped structure. A steel strand (4) passes through the middle of the H-beam (1) and the Larssen sheet pile (2). The first end of the steel strand (4) is connected to the steel waler (3) through a steel pad (7) and an anchor (8). The second end of the steel strand (4) is provided with an enlarged end (6). A jet grouting pile (5) is set near the enlarged end (6) of the steel strand (4).

2. The combined support structure for foundation pits using the HU method pile and prestressed anchor cable as described in claim 1, characterized in that: The inclination of each of the H-beams (1) and the Larssen sheet piles (2) shall not exceed 2%.

3. The combined support structure for foundation pits using the HU method pile and prestressed anchor cable as described in claim 1, characterized in that: The enlarged end (6) is 2m long and has a hole diameter of not less than 800mm. The enlarged end (6) is sprayed with a pressure of 20-30Mpa.

4. The combined support structure for foundation pits using the HU method pile and prestressed anchor cable as described in claim 1, characterized in that: The jet grouting pile (5) adopts an anchor cable drilling rig grouting molding structure.

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