Construction method of HC combined construction method pile for foundation pit support reinforcement

Abstract

The invention discloses a construction method of a foundation pit support reinforcement HC combined construction method pile. The invention provides a construction method of the HC construction method pile for foundation pit support reinforcement. According to the method, through the composite structure design of the H-shaped steel and the Larsen steel sheet pile, the bearing capacity is remarkably improved. The H-shaped steel becomes a core component for bearing lateral pressure of a soil body by virtue of high strength and rigidity of the H-shaped steel, and horizontal load generated in the excavation process of the foundation pit can be effectively resisted; the Larsen steel sheet piles are connected through locking openings to form a continuous waterproof curtain, and meanwhile the overall rigidity of the pile bodies is enhanced. Under the synergistic effect of the two pile bodies, the pile bodies not only can bear higher lateral soil pressure, but also can reduce stress concentration of a single structure through complementation of material performance, so that stable and reliable bearing capacity support is provided for a foundation pit support structure under the complex geological conditions of a deep soft soil layer, a high water level and the like, and structural safety in the foundation pit excavation process is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of foundation pit engineering construction technology, specifically a construction method for foundation pit retaining and reinforcement HC combined pile method. Background Technology

[0002] With the rapid development of urban construction, foundation pit projects are becoming increasingly numerous and complex. Under adverse geological conditions such as soft soil and sand layers, traditional foundation pit retaining structures (such as pile walls) often experience deformation, soil collapse, and leakage due to factors such as soil lateral pressure and groundwater seepage, seriously threatening the safety of the surrounding environment and the progress of the project. Therefore, reinforcing foundation pit retaining structures has become one of the key technologies to ensure the safety of foundation pit projects. Addressing the problems of leakage, displacement, and insufficient bearing capacity that existing foundation pit retaining structures are prone to under complex geological conditions, this paper proposes a highly reliable, efficient, and widely applicable HC method for reinforcing foundation pit retaining structures to improve the safety and stability of foundation pit projects.

[0003] Currently, the commonly used methods for reinforcing foundation pit retaining walls include grouting reinforcement, adding anchor bolts (cables), and micro steel pipe pile reinforcement. Taking micro steel pipe pile reinforcement as an example, its main steps are: first, drilling holes around the retaining structure, then inserting steel pipes into the holes, and finally using pressure grouting to make the steel pipes and the surrounding soil form an integral whole, thereby improving the bearing capacity and deformation resistance of the retaining structure.

[0004] However, existing technologies have the following drawbacks:

[0005] 1) Grouting reinforcement method: The grouting effect is greatly affected by geological conditions. Grouting in permeable layers is prone to grout loss, and the reinforcement effect is unstable.

[0006] 2) Adding anchor bolts (cables): This method requires a large construction space and is difficult to implement in situations with complex surrounding environments and limited site conditions. Furthermore, the anchoring force of anchor bolts (cables) is significantly affected by the properties of the soil.

[0007] 3) Micro steel pipe pile reinforcement method: Steel pipe piles have relatively low bearing capacity, and their reinforcement effect on deep soft soil layers or high lateral pressure foundation pits is limited. Moreover, the construction process is relatively complicated and the construction period is long. Summary of the Invention

[0008] The purpose of this invention is to provide a construction method for HC combined pile foundation for foundation pit support reinforcement in order to solve the problems mentioned above.

[0009] The technical solution adopted in this invention is as follows: a construction method for HC combined pile reinforcement for foundation pit retaining walls, the method comprising the following steps:

[0010] S1: Construction Preparation: Clear the construction site, level the ground, and measure and set out the positions of the HC method piles, alternating H-beams and Larssen sheet piles. Check the performance of the construction equipment to ensure its normal operation.

[0011] S2: Pretreatment of H-beams and Larssen sheet piles:

[0012] Surface treatment: Remove rust and oil stains from the surface of H-beams and Larssen sheet piles, and apply a friction reducer with a thickness of ≥2mm to facilitate later extraction and recycling.

[0013] Positioning marks: Mark the insertion depth on the H-beams and Larssen sheet piles, and weld positioning steel plates to control the verticality of the insertion.

[0014] S3: Lifting and Insertion:

[0015] Lifting equipment: A long-arm hydraulic pile driver is used to clamp H-beams and Larssen sheet piles and lift them vertically.

[0016] Insertion control: Slowly lower the H-beam and Larssen sheet pile to the tongue and groove joint of the already inserted Larssen sheet pile and H-beam, adjust the verticality, and then apply pressure through the hydraulic clamp to ensure insertion to the designed depth. The insertion speed is controlled at 1.0-1.5 m / min, and the elevation of the top surface of the steel section is monitored throughout the process.

[0017] S4: Pile top fixing: After insertion, immediately set up I-beam clamps or steel reinforcement supports on the pile top to temporarily connect the H-beams to the adjacent piles to prevent the steel from shifting or floating.

[0018] S5: Real-time monitoring: Displacement monitoring points will be set up within 12 hours after construction is completed, with a monitoring frequency of once per day, focusing on the horizontal displacement and settlement of the pile top. Inclinometers will be used to detect deep displacement of the pile body, with a monitoring section set up every 5m to ensure that the overall deformation is ≤10mm.

[0019] In a preferred embodiment, in step S1, the site clearing process requires removing surface debris to a depth of no less than 30cm to ensure no hard objects such as stones or tree roots remain. Site leveling is performed using a combination of bulldozers and road rollers, with surface flatness error controlled within ±5cm to ensure the stability of subsequent equipment movement and pile construction. For soft soil layers, the surface layer needs to be replaced with graded sand and gravel, compacted in 20cm layers.

[0020] In a preferred embodiment, in step S1, control points need to be checked before measurement and layout, and the plane position error should not exceed 15mm. When laying out the pile positions, the design axis is used as the reference, and the polar coordinate method is used to measure point by point. The distance error between adjacent pile positions is controlled within ±10mm, and the pile center is marked with a wooden stake. A 20cm long steel bar is inserted at the pile center as a positioning mark.

[0021] In a preferred embodiment, in step S2, the surface treatment employs sandblasting to remove rust, achieving a rust removal grade of Sa2.5. The friction-reducing agent is applied within 4 hours after rust removal. The friction-reducing agent is epoxy coal tar pitch coating. Before application, the coating must be thoroughly stirred. A high-pressure airless sprayer is used, with the spraying speed controlled between 0.5 and 1 m / s. The dry film thickness is monitored in real-time using a wet film thickness gauge, with at least 3 points measured for every 10 m of steel section. The average thickness is not less than 2 mm, and the coating drying time is no less than 4 hours.

[0022] In a preferred embodiment, in step S2, the positioning marks need to be completed before the steel section and sheet pile leave the factory. The insertion depth scale line is processed by mechanical scoring, with a scoring depth of 0.5mm and a width of 2mm. One mark is made every 1m along the length of the pile, and the scale value is clearly identifiable. The positioning steel plate is made of Q235b steel plate of the same material as the H-section steel, with dimensions of 100mm×50mm×10mm. It is welded to the side of the steel section steel at a distance of 50cm from the top of the pile. The welding is done by manual arc welding, with a welding length of not less than 40mm and a weld leg height of 6mm. After welding, a penetration test is required to ensure that there are no cracks or porosity defects, and the welding deformation is controlled within 0.5mm / m.

[0023] In a preferred embodiment, in step S3, the H-beam lifting points are set at 1 / 3 of the pile length from both ends, and the Larssen sheet pile lifting points are set at 1 / 4 and 3 / 4 of the pile length. Special lifting tools are used to connect the lifting points to the pile body, and the rated load of the lifting tools is not less than twice the weight of the pile. During lifting, the angle between the pile body and the ground is maintained at 85°–90°, and the lifting speed is controlled within 0.5 m / s.

[0024] In a preferred embodiment, during step S3, the descent speed of the hydraulic pile driver / extractor is kept consistent with the pile insertion speed. The initial insertion speed is controlled at 0.8 m / min, and adjusted to 1.0–1.5 m / min after the pile stabilizes. Verticality control employs a dual theodolite orthogonal monitoring method. Two theodolites are set up at 90° angles on either side of the pile. Verticality deviation is observed every 1 m of insertion. Insertion is stopped immediately when the deviation exceeds 0.3%, and correction is performed by adjusting the pile hammer's tilt angle, with each correction not exceeding 0.2°. Pile top elevation is monitored using a level. The top elevation is measured every 2 m of insertion, with the final insertion depth error controlled within ±50 mm and the elevation error not exceeding ±3 cm.

[0025] In a preferred embodiment, in step S4, the I-beam clamp is made of No. 10 hot-rolled ordinary I-beam. The contact part between the clamp and the flange of the H-beam is processed into an arc shape. When installing the clamp, the I-beam is first cut into segments that match the length of the pile top and connected to the pile body with M20 high-strength bolts. The bolt spacing is 20cm, and each clamp is equipped with no less than 4 bolts. The bolt preload reaches 400N·m. The steel bar support is made of HRB400E steel bars with a diameter of 25mm and is welded. The support is arranged in a "well" shape, and the intersection of the horizontal and vertical bars is connected by double-sided welding.

[0026] In a preferred embodiment, during step S4, a level is used to measure the flatness of the pile top during the overall stability check. The height difference between adjacent pile tops should not exceed 5mm, and the deviation of the pile top axis should be controlled within 10mm. At the same time, a visual inspection is performed on the connection parts to ensure that the welds are free of undercut and slag inclusions, the bolts are free of stripping and breakage, and there is no gap between the clamps and the pile body.

[0027] In a preferred embodiment, in step S5, the monitoring point layout must be completed within 12 hours after the pile construction is completed. A monitoring point is set every 5m along the perimeter of the foundation pit. The monitoring point uses a stainless steel measuring nail with a diameter of 12mm, which is inserted into the concrete at the top of the pile to a depth of not less than 50mm. The horizontal displacement and settlement monitoring of the pile top is carried out using a Leica TS60 total station, according to the accuracy requirements of second-order leveling. Each monitoring needs to be observed independently twice. When the difference between the two measurements does not exceed 2mm, the average value is taken as the result.

[0028] Deep displacement monitoring utilizes a CX-03 inclinometer. The inclinometer tube is a 70mm diameter PVC pipe with a cross-shaped guide groove in the wall, the groove's accuracy error not exceeding 0.5mm / m. The inclinometer tube must be embedded simultaneously during pile construction, with the embedment depth matching the pile length. The bottom of the tube is sealed, and the top extends 30cm above the pile top and is covered for protection. During measurement, the inclinometer probe is slowly raised from the bottom of the inclinometer tube at a controlled speed of 0.5m / s. A reading is recorded every 0.5m. Each monitoring section requires two measurements, one forward and one reverse, with the slope difference between the two measurements not exceeding 0.1mm / m. Monitoring data is compiled into a daily report, and any instance of horizontal displacement at the pile top exceeding 5mm or daily deformation rate exceeding 2mm / d is immediately reported.

[0029] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0030] 1. In this invention, a significant improvement in bearing capacity is achieved through the composite structural design of H-beams and Larssen sheet piles. The H-beams, with their high strength and stiffness, become the core component bearing the lateral pressure of the soil, effectively resisting the horizontal loads generated during excavation. The Larssen sheet piles, connected by interlocking joints, form a continuous water-stop curtain, while simultaneously enhancing the overall stiffness of the pile body. Through their synergistic effect, the pile body can not only withstand higher lateral earth pressure but also reduce stress concentration in a single structure through the complementary properties of the materials. This provides stable and reliable bearing capacity support for the foundation pit retaining structure under complex geological conditions such as deep soft soil layers and high water levels, ensuring structural safety during the excavation process.

[0031] 2. This invention utilizes a dedicated hydraulic pile driver / extractor to achieve integrated construction, significantly simplifying the multi-equipment collaborative process in traditional reinforcement methods. From the pretreatment and hoisting of H-beams and Larssen sheet piles to their insertion, each process can be completed consecutively on the same equipment, reducing time losses due to equipment changes and process connections. Simultaneously, the process design emphasizes practicality, such as the alternate-pile arrangement and standardized verticality control procedures, all of which reduce the complexity of construction operations. This efficient construction mode significantly shortens the construction time for a single pile, resulting in a substantial reduction in the overall construction period compared to traditional grouting reinforcement or micro-steel pipe pile methods, making it particularly suitable for urban foundation pit projects with stringent time requirements.

[0032] 3. In this invention, the adaptability of the HC combined pile method to the construction site is reflected in its low requirements for space and geological conditions. Its construction equipment is relatively compact with a small operating radius. Even in densely built-up urban centers with narrow roads, pile construction can be completed by adjusting equipment positioning and construction sequence, solving the problem of traditional anchor (cable) methods requiring large operating spaces. Simultaneously, the material properties and construction technology of the piles are highly adaptable to geological conditions. Whether it is soft soil, sand, or silt, the pile insertion depth and connection method can be optimized to adapt to changes in strata, eliminating the need for large-scale site leveling or complex pretreatment projects, effectively overcoming the constraints of site limitations on foundation pit reinforcement construction.

[0033] 4. In this invention, the construction method fully demonstrates its environmental friendliness during construction. The specialized hydraulic equipment operates with low noise levels, avoiding the high-decibel noise pollution generated by traditional impact construction machinery and reducing interference to surrounding residential areas, schools, and other sensitive areas. The construction process does not require large amounts of cement, sand, or other building materials, avoiding groundwater pollution that may be caused by grout loss in grouting reinforcement methods; at the same time, H-beams and Larssen sheet piles are recyclable and reusable, reducing the generation of construction waste. These low-noise and low-pollution construction characteristics give this method a significant advantage in foundation pit engineering in environmentally sensitive areas, meeting the requirements of green construction in modern urban development. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the process principle of the present invention;

[0035] Figure 2 This is a front view of the HC method pile construction of the present invention;

[0036] Figure 3 This is a side view of the HC method pile construction of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] Example:

[0039] Reference Figure 1-3 A construction method for HC combined pile reinforcement for foundation pit retaining walls, comprising the following steps:

[0040] S1: Construction Preparation: Clear the construction site, level the ground, and measure and set out the positions of the HC method piles, alternating H-beams and Larssen sheet piles. Check the performance of the construction equipment to ensure its normal operation.

[0041] S2: Pretreatment of H-beams and Larssen sheet piles:

[0042] Surface treatment: Remove rust and oil stains from the surface of H-beams and Larssen sheet piles, and apply a friction reducer with a thickness of ≥2mm to facilitate later extraction and recycling.

[0043] Positioning marks: Mark the insertion depth on the H-beams and Larssen sheet piles, and weld positioning steel plates to control the verticality of the insertion.

[0044] S3: Lifting and Insertion:

[0045] Lifting equipment: A long-arm hydraulic pile driver is used to clamp H-beams and Larssen sheet piles and lift them vertically.

[0046] Insertion control: Slowly lower the H-beam and Larssen sheet pile to the tongue and groove joint of the already inserted Larssen sheet pile and H-beam, adjust the verticality, and then apply pressure through the hydraulic clamp to ensure insertion to the designed depth. The insertion speed is controlled at 1.0-1.5 m / min, and the elevation of the top surface of the steel section is monitored throughout the process.

[0047] S4: Pile top fixing: After insertion, immediately set up I-beam clamps or steel reinforcement supports on the pile top to temporarily connect the H-beams to the adjacent piles to prevent the steel from shifting or floating.

[0048] S5: Real-time monitoring: Displacement monitoring points will be set up within 12 hours after construction is completed, with a monitoring frequency of once per day, focusing on the horizontal displacement and settlement of the pile top. Inclinometers will be used to detect deep displacement of the pile body, with a monitoring section set up every 5m to ensure that the overall deformation is ≤10mm.

[0049] In step S1, the site clearing process requires removing surface debris to a depth of no less than 30cm to ensure no hard objects such as stones or tree roots remain. Site leveling is performed using a combination of bulldozers and road rollers, with surface flatness error controlled within ±5cm to ensure the stability of subsequent equipment movement and pile construction. For soft soil layers, the surface layer needs to be replaced with graded sand and gravel, compacted in 20cm layers.

[0050] In step S1, control points need to be checked before measurement and layout, and the plane position error should not exceed 15mm. When laying out the pile positions, the design axis is used as the reference, and the polar coordinate method is used to measure point by point. The distance error between adjacent pile positions is controlled within ±10mm, and the pile center is marked with a wooden stake. A 20cm long steel bar is inserted at the pile center as a positioning mark.

[0051] In step S2, the surface treatment employs sandblasting to remove rust, achieving a rust removal grade of Sa2.5. The friction-reducing agent is applied within 4 hours after rust removal. Epoxy coal tar coating is used as the friction-reducing agent. Before application, the coating must be thoroughly stirred. A high-pressure airless sprayer is used, with the spraying speed controlled between 0.5 and 1 m / s. The dry film thickness is monitored in real-time using a wet film thickness gauge, with at least 3 points measured for every 10 m of steel section. The average thickness is not less than 2 mm, and the coating drying time is no less than 4 hours.

[0052] In step S2, the positioning marks must be completed before the steel section and sheet piles leave the factory. The insertion depth scale line is machined by mechanical scoring, with a scoring depth of 0.5mm and a width of 2mm. One mark is made every 1m along the length of the pile, and the scale value is clearly identifiable. The positioning steel plate is made of Q235b steel plate of the same material as the H-section steel, with dimensions of 100mm×50mm×10mm. It is welded to the side of the steel section steel 50cm from the top of the pile. The welding is done by manual arc welding, with a welding length of not less than 40mm and a weld leg height of 6mm. After welding, a penetrant test is required to ensure that there are no cracks or porosity defects, and the welding deformation is controlled within 0.5mm / m.

[0053] In step S3, the lifting points for the H-beams are set at 1 / 3 of the pile length from both ends, and the lifting points for the Larssen sheet piles are set at 1 / 4 and 3 / 4 of the pile length. Special lifting equipment is used to connect the lifting points to the pile, and the rated load of the lifting equipment is not less than twice the weight of the pile. During lifting, the angle between the pile and the ground is maintained at 85°–90°, and the lifting speed is controlled within 0.5 m / s.

[0054] In step S3, during the insertion process, the descent speed of the hydraulic pile driver / extractor is kept consistent with the pile insertion speed. The initial insertion speed is controlled at 0.8 m / min, and adjusted to 1.0–1.5 m / min after the pile stabilizes. Verticality control employs a dual theodolite orthogonal monitoring method. Two theodolites are set up at 90° angles on either side of the pile. Verticality deviation is observed every 1 m of insertion. Insertion is stopped immediately when the deviation exceeds 0.3%, and correction is performed by adjusting the pile hammer's tilt angle, with each correction not exceeding 0.2°. Pile top elevation is monitored using a level. The top elevation is measured every 2 m of insertion, with the final insertion depth error controlled within ±50 mm and the elevation error not exceeding ±3 cm.

[0055] In step S4, the I-beam clamp is made of No. 10 hot-rolled ordinary I-beam. The contact part between the clamp and the flange of the H-beam is processed into an arc shape. When installing the clamp, the I-beam is first cut into sections that match the length of the pile top and connected to the pile body with M20 high-strength bolts. The bolt spacing is 20cm. Each clamp is equipped with no less than 4 bolts. The bolt preload reaches 400N·m. The steel bar support is made of 25mm diameter HRB400E steel bars welded together. The support is arranged in a "well" shape, and the intersection of the horizontal and vertical bars is connected by double-sided welding.

[0056] In step S4, during the overall stability check, a level is used to measure the flatness of the pile top. The height difference between adjacent pile tops should not exceed 5mm, and the deviation of the pile top axis should be controlled within 10mm. At the same time, a visual inspection is performed on the connection parts to ensure that the welds are free of undercut and slag inclusions, the bolts are free of stripping and breakage, and there is no gap between the clamps and the pile body.

[0057] In step S5, the monitoring point setup must be completed within 12 hours after the pile construction is completed. A monitoring point on the top of the pile should be set up every 5m along the perimeter of the foundation pit. The monitoring point uses a stainless steel measuring nail with a diameter of 12mm, which is inserted into the concrete at the top of the pile to a depth of not less than 50mm. The horizontal displacement and settlement monitoring of the pile top is carried out using a Leica TS60 total station, according to the accuracy requirements of second-order leveling. Each monitoring needs to be observed twice independently. When the difference between the two measurements does not exceed 2mm, the average value is taken as the result.

[0058] Deep displacement monitoring utilizes a CX-03 inclinometer. The inclinometer tube is a 70mm diameter PVC pipe with a cross-shaped guide groove in the wall, the groove's accuracy error not exceeding 0.5mm / m. The inclinometer tube must be embedded simultaneously during pile construction, with the embedment depth matching the pile length. The bottom of the tube is sealed, and the top extends 30cm above the pile top and is covered for protection. During measurement, the inclinometer probe is slowly raised from the bottom of the inclinometer tube at a controlled speed of 0.5m / s. A reading is recorded every 0.5m. Each monitoring section requires two measurements, one forward and one reverse, with the slope difference between the two measurements not exceeding 0.1mm / m. Monitoring data is compiled into a daily report, and any instance of horizontal displacement at the pile top exceeding 5mm or daily deformation rate exceeding 2mm / d is immediately reported.

[0059] Comparative Example 1: Grouting Reinforcement Method Experiment:

[0060] The grouting fluid was prepared using 42.5 grade ordinary Portland cement with a water-cement ratio of 1:1.2, and 3% water glass was added as a quick-setting agent. The grouting pressure was controlled between 1.5 and 2.0 MPa. The experiment was conducted in silty clay strata, with a borehole diameter of 100 mm, a depth of 12 m, and a pile spacing of 1.2 m in a staggered pattern. A retreating segmented grouting process was adopted, with each segment 1.5 m long and a grouting flow rate of 30 L / min. Curing was carried out for 7 days after grouting. The experimental site was the edge area of ​​a 4 m wide foundation pit. Monitoring equipment included a hydraulic support to measure the bearing capacity of the reinforced area, a noise meter to monitor the operating noise of the grouting pump, and records of grout loss and the extent of soil contamination in the surrounding area.

[0061] Comparative Example 2: Experiment using the method of adding anchor bolts (cables):

[0062] The experiment used 20mm diameter HRB400E steel anchor rods, 15m in length (8m anchorage section and 7m free section), with a drilled hole diameter of 130mm and an inclination angle of 15°. Construction was carried out in sandy soil using a geological drilling rig. Cement grout (water-cement ratio 0.5) was injected into the hole at a pressure of 0.8MPa. Anchor rods were spaced 2.0m apart, with 5 rods per row. The tension load was controlled at 150kN, applied in three stages (50%, 75%, and 100% of the design load), with a holding time of 30 minutes. The experimental site was 6m wide and equipped with a 200t hydraulic tensioning device. Anchor rod pull-out force, retaining structure displacement, and drilling noise were monitored (measured 5m away from the device).

[0063] Comparative Example 3: Experiment on the reinforcement method of micro-steel pipe piles:

[0064] The experiment used Φ159×8mm seamless steel pipes (Q235B material), with a pile length of 18m and a pile spacing of 1.5m, arranged in a rectangular pattern. Construction was carried out in silty clay strata, using a spiral drilling rig (200mm diameter) at a drilling speed of 0.5m / min. After cleaning the hole, the steel pipe was inserted, and cement grout (water-cement ratio 0.6) was injected into the pipe at a grouting pressure of 1.2MPa. The grouting pipe was buried 50cm into the bottom of the hole. The construction equipment was a small crawler-mounted drilling rig, and the site width was 5m. Monitoring included the single pile bearing capacity (load test), construction period (total time for 100 piles recorded), and steel pipe recovery rate (pull-out test after construction).

[0065] The experimental data comparison is shown in the table below:

[0066]

[0067]

[0068] From the above, we can conclude that:

[0069] In this invention, a significant improvement in bearing capacity is achieved through a composite structural design of H-beams and Larssen sheet piles. The H-beams, with their high strength and stiffness, become the core component bearing the lateral pressure of the soil, effectively resisting the horizontal loads generated during excavation. The Larssen sheet piles, connected by interlocking joints, form a continuous water-stop curtain, while simultaneously enhancing the overall stiffness of the pile body. Through their synergistic effect, the pile body can not only withstand higher lateral earth pressure but also reduce stress concentration in a single structure through the complementary properties of the materials. This provides stable and reliable bearing capacity support for the foundation pit retaining structure under complex geological conditions such as deep soft soil layers and high water levels, ensuring structural safety during the excavation process.

[0070] This invention employs a dedicated hydraulic pile driver and extractor to achieve integrated construction, significantly simplifying the multi-equipment collaborative process in traditional reinforcement methods. From the pretreatment and hoisting of H-beams and Larssen sheet piles to their insertion, each step can be completed consecutively on the same equipment, reducing time losses due to equipment changes and process connections. Simultaneously, the process design emphasizes practicality, such as the alternate-pile arrangement and standardized verticality control procedures, all of which reduce the complexity of construction operations. This efficient construction mode significantly shortens the construction time for a single pile, resulting in a substantial reduction in the overall construction period compared to traditional grouting reinforcement or micro-steel pipe pile methods, making it particularly suitable for urban foundation pit projects with stringent time requirements.

[0071] In this invention, the adaptability of the HC combined pile method to the construction site is reflected in its low requirements for space and geological conditions. Its construction equipment is relatively compact with a small operating radius. Even in densely built-up urban centers with narrow roads, pile construction can be completed by adjusting equipment positioning and construction sequence, solving the problem of traditional anchor (cable) methods requiring large operating spaces. Simultaneously, the material properties and construction technology of the piles are highly adaptable to geological conditions. Whether in soft soil, sand, or silt, the pile insertion depth and connection method can be optimized to adapt to changes in strata, eliminating the need for large-scale site leveling or complex pretreatment projects, effectively overcoming the constraints of site limitations on foundation pit reinforcement construction.

[0072] This invention demonstrates environmental friendliness during construction. The specialized hydraulic equipment operates with low noise levels, avoiding the high-decibel noise pollution generated by traditional impact construction machinery and minimizing disturbance to nearby residential areas, schools, and other sensitive locations. The construction process requires minimal cement, sand, and other building materials, avoiding groundwater pollution that may result from grout loss in grouting reinforcement methods. Furthermore, the H-beams and Larssen sheet piles are recyclable and reusable, reducing construction waste. These low-noise and low-pollution characteristics give this method a significant advantage in foundation pit engineering in environmentally sensitive areas, meeting the requirements of green construction in modern urban development.

[0073] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the term "comprising" or any other variations thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A construction method for HC combined pile reinforcement of foundation pit retaining wall, characterized in that: The method includes the following steps: S1: Construction preparation: Clean the construction site, level the ground, measure and set out the location of HC method piles, and place H-beams and Larssen steel sheet piles alternately; check the performance of construction equipment to ensure its normal operation. S2: Pretreatment of H-beams and Larssen sheet piles: Surface treatment: Remove rust and oil stains from the surface of H-beams and Larssen sheet piles, and apply a friction reducer with a thickness of ≥2mm to facilitate later extraction and recycling; Positioning marks: Mark the insertion depth on the H-beams and Larssen sheet piles, and weld positioning steel plates to control the verticality of the insertion; S3: Lifting and Insertion: Lifting equipment: A long-arm hydraulic pile driver is used to clamp H-beams and Larssen sheet piles and lift them vertically; Insertion control: Slowly lower the H-beam and Larssen sheet pile to the tongue and groove joint of the already inserted Larssen sheet pile and H-beam, adjust the verticality, and then apply pressure through the hydraulic clamp to ensure that it is inserted to the design depth; the insertion speed is controlled at 1.0 to 1.5 m / min, and the elevation of the top surface of the steel section is monitored throughout the process; S4: Pile top fixing: After insertion, immediately set up I-beam clamps or steel reinforcement supports on the pile top to temporarily connect the H-beam to the adjacent pile body to prevent the steel from shifting or floating. S5: Real-time monitoring: Displacement monitoring points will be set up within 12 hours after construction is completed, with a monitoring frequency of once a day, focusing on the horizontal displacement and settlement of the pile top; an inclinometer will be used to detect the deep displacement of the pile body, with a monitoring section set up every 5m to ensure that the overall deformation is ≤10mm.

2. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S1, the surface debris must be removed to a depth of no less than 30cm during the site clearing process to ensure that no hard objects remain. The site leveling is carried out by bulldozing and road roller operation, and the surface flatness error is controlled within ±5cm to ensure the stability of subsequent equipment movement and pile construction. For soft soil layers, the surface layer of the site needs to be replaced with graded sand and gravel as the replacement material, and the layer is compacted in layers with a thickness of 20cm.

3. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S1, before measurement and layout, control points need to be checked and the plane position error should not exceed 15mm. When laying out the pile positions, the design axis is used as the reference, and the polar coordinate method is used to measure and set each point. The distance error between adjacent pile positions is controlled within ±10mm. The pile center is marked with a wooden stake, and a 20cm long steel bar is inserted at the pile center as a positioning mark.

4. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S2, the surface treatment adopts sandblasting rust removal process to achieve a rust removal grade of Sa2.

5. The friction reducing agent is applied within 4 hours after rust removal. The friction reducing agent is epoxy coal tar pitch coating. Before application, the coating needs to be stirred evenly. High-pressure airless sprayer is used for construction. The spraying speed is controlled at 0.5-1m / s. The dry film thickness is monitored in real time by wet film thickness gauge. At least 3 points are tested for every 10m of steel section. The average thickness is not less than 2mm. The coating drying time is not less than 4 hours.

5. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S2, the positioning marks need to be completed before the steel section and sheet pile leave the factory. The insertion depth scale line is processed by mechanical scoring, with a scoring depth of 0.5mm and a width of 2mm. One mark is made every 1m along the length of the pile body, and the scale value is clearly identifiable. The positioning steel plate is made of Q235b steel plate of the same material as the H-section steel, with a size of 100mm×50mm×10mm. It is welded to the side of the steel section steel at a distance of 50cm from the top of the pile. The welding is done by manual electric arc welding, with a welding length of not less than 40mm and a weld leg height of 6mm. After welding, a penetration test is required to ensure that there are no cracks or porosity defects, and the welding deformation is controlled within 0.5mm / m.

6. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S3, the H-beam lifting point is set at 1 / 3 of the pile length from both ends, and the Larssen sheet pile lifting point is set at 1 / 4 and 3 / 4 of the pile length. Special lifting tools are used to connect the lifting points to the pile body, and the rated load of the lifting tools is not less than twice the weight of the pile body. During lifting, the angle between the pile body and the ground is maintained at 85° to 90°, and the lifting speed is controlled within 0.5m / s.

7. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S3, during the insertion process, the descent speed of the pile hammer of the hydraulic pile driver is kept consistent with the insertion speed of the pile body. The initial insertion speed is controlled at 0.8 m / min, and after the pile body stabilizes, it is adjusted to 1.0-1.5 m / min. Verticality control adopts the orthogonal monitoring method of dual theodolites. Two theodolites are set up on both sides of the pile body at 90°. The verticality deviation is observed every 1 m of insertion. When the deviation exceeds 0.3%, the insertion is stopped immediately, and the deviation is corrected by adjusting the tilt angle of the pile hammer. The correction range does not exceed 0.2° each time. The pile top elevation is monitored using a level. The top elevation is measured every 2 m of insertion. The final insertion depth error is controlled within ±50 mm, and the elevation error does not exceed ±3 cm.

8. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S4, the I-beam clamp is made of No. 10 hot-rolled ordinary I-beam. The contact part between the clamp and the flange of the H-beam is processed into an arc shape. When installing the clamp, the I-beam is first cut into segments that match the length of the pile top and connected to the pile body with M20 high-strength bolts. The bolt spacing is 20cm. Each clamp is equipped with no less than 4 bolts. The bolt preload reaches 400N·m. The steel bar support is made of HRB400E steel bars with a diameter of 25mm. The support is arranged in a "well" shape. The intersection of the horizontal and vertical bars is connected by double-sided welding.

9. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S4, during the overall stability check, a level is used to measure the flatness of the pile top. The height difference between adjacent pile tops should not exceed 5mm, and the deviation of the pile top axis should be controlled within 10mm. At the same time, the connection parts are visually inspected to ensure that the welding is free of undercut and slag inclusion, the bolts are free of stripping and breakage, and there is no gap between the clamp and the pile body.

10. The construction method of HC combined pile for foundation pit retaining and reinforcement as described in claim 1, characterized in that: In step S5, the monitoring point layout must be completed within 12 hours after the pile construction is completed. A monitoring point on the top of the pile is set every 5m along the perimeter of the foundation pit. The monitoring point uses a stainless steel measuring nail with a diameter of 12mm, which is inserted into the concrete at the top of the pile to a depth of not less than 50mm. The horizontal displacement and settlement monitoring of the pile top is carried out using a Leica TS60 total station, according to the accuracy requirements of second-order leveling. Each monitoring needs to be observed twice independently. When the difference between the two measurements does not exceed 2mm, the average value is taken as the result. Deep displacement monitoring uses a CX-03 inclinometer. The inclinometer tube is a 70mm diameter PVC pipe with a cross-shaped guide groove in the wall. The accuracy error of the guide groove should not exceed 0.5mm / m. The inclinometer tube needs to be buried simultaneously during pile construction, with the burial depth consistent with the pile length. The bottom of the tube is sealed, and the top of the tube is 30cm above the pile top and covered for protection. During measurement, the inclinometer probe is slowly raised from the bottom of the inclinometer tube at a speed controlled at 0.5m / s. A reading is recorded every 0.5m. Each monitoring section needs to be measured twice, forward and reverse, and the slope difference between the two measurements should not exceed 0.1mm / m. The monitoring data is compiled into a report daily, and it is reported immediately when the horizontal displacement of the pile top exceeds 5mm or the daily deformation rate exceeds 2mm / d.

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