Foundation pit slope pile foundation site construction method based on livelihood engineering

Abstract

The invention relates to the technical field of foundation pit engineering, and particularly discloses a foundation pit slope pile foundation site construction method based on livelihood engineering. A foundation pit slope pile foundation site construction method based on livelihood engineering comprises the following steps that S1, site investigation and cleaning are conducted, specifically, geological investigation is conducted on a foundation pit slope, and soil layer distribution parameters and mechanical parameters are obtained; cleaning the surface of the site, and removing weeds and broken stone obstacles to obtain a flat construction working surface; s2, side slope trimming; s3, pile position lofting is carried out; s4, drilling and forming a hole; s5, hole cleaning; s6, manufacturing a reinforcement cage; s7, mounting a reinforcement cage; s8, preparing concrete; s9, concrete pouring; and S10, pile body maintenance and slope supporting are carried out. The foundation pit slope pile foundation site construction method based on the livelihood engineering can be used for livelihood engineering foundation pit slope supporting with complex hydrogeological conditions or high long-term safety requirements, and has the advantage that the pile foundation engineering quality is improved through process control.

Description

Technical Field

[0001] This application relates to the field of foundation pit engineering technology, and more specifically, it relates to an on-site construction method for foundation pit slope pile foundation based on a public welfare project. Background Technology

[0002] The on-site construction of existing foundation pit slope pile foundations requires flexible selection based on the depth of the foundation pit, geological conditions, and surrounding environment. Commonly used pile types include reinforced concrete cast-in-place piles, precast piles, SMW method piles, and steel pipe piles. Through core processes such as pile location layout, hole drilling, hole cleaning, reinforcement cage fabrication and installation, and concrete pouring, combined with water-stop curtains, internal supports, or anchor bolts, structures such as pile support and composite support are formed. These structures are widely used for soil retention and water stoppage in shallow and medium-depth foundation pits, deformation control in deep foundation pits, and slope stability protection in sensitive environments to resist soil and water pressure, prevent foundation pit collapse and slope slippage, and create safe conditions for underground structure construction.

[0003] The on-site construction of foundation pit slope pile foundations involves selecting suitable pile types and following the conventional process of drilling, cleaning, installing steel cages, and pouring concrete. Slope protection is achieved with the help of water-stopping or support measures. However, there is a lack of quantitative control from geological exploration to slope protection. The mud slurry ratio for the drilling stage is mostly adjusted based on experience. The concrete mix is ​​not fully coordinated with the compatibility of workability and strength development. The control of the tremie pipe burial depth during the pouring stage lacks precise management. Furthermore, the collaborative stress design between the pile foundation and the slope is not emphasized. As a result, the borehole wall is prone to collapse or diameter reduction, and the pile body may experience segregation, pile breakage, and other integrity defects. The long-term stability of the slope is insufficient, making it difficult to fully meet the safety requirements of foundation pit engineering in complex geological or sensitive environments. Summary of the Invention

[0004] To address the issues of structural defects in pile bodies and low slope stability caused by the lack of quantitative control in the on-site construction of foundation pit slope pile foundations, this application provides an on-site construction method for foundation pit slope pile foundations based on public welfare projects.

[0005] A method for on-site construction of foundation pit slope pile foundations for public welfare projects includes the following steps: S1. Site Investigation and Cleaning: Conduct a geological investigation of the foundation pit slope to obtain soil layer distribution parameters and mechanical parameters, including soil type and groundwater level; then clean the site surface, remove weeds, gravel obstacles, and obtain a flat construction working surface; S2. Slope trimming: The slope is trimmed mechanically or manually, and the slope ratio is controlled between 1:1.5 and 1:2. After trimming, a stable slope surface is obtained. S3. Pile location layout: Use surveying instruments to layout the center of the pile location, mark the pile location points, and obtain the layout pile location points; S4. Drilling: Drilling is carried out at the marked pile location, with the borehole diameter controlled between 800mm and 1200mm and the borehole depth equal to the designed pile length. During the drilling process, wall-protecting mud is injected. The mud consists of water, bentonite, and additives, and the mud specific gravity is controlled between 1.1 and 1.3g / cm³. After drilling, the borehole is obtained. S5. Hole Cleaning: After drilling is completed, hole cleaning is performed to remove sediment from the bottom of the hole. The thickness of the sediment should be controlled to be no more than 50mm to obtain a clean borehole. S6. Reinforcing cage fabrication: HRB400 grade steel bars with a diameter of 20mm to 32mm are used to fabricate the reinforcing cage by welding or binding to obtain the finished reinforcing cage. S7. Reinforcing cage installation: Hoist the finished reinforcing cage into the clean drill hole, and control the verticality deviation of the installation to be no more than 1% to obtain the in-place reinforcing cage. S8. Concrete mix design: Concrete is prepared using P.O42.5 cement, medium and coarse sand, crushed stone and water. The concrete strength grade is controlled at C30 to C40, the water-cement ratio is 0.4 to 0.5, and the slump is 180 mm to 220 mm to obtain fresh concrete. S9. Concrete pouring: Fresh concrete is continuously poured into the borehole using the tremie method, with the tremie pipe buried at a depth of 2m to 6m, and poured to the design elevation to obtain the pile body; S10. Pile curing and slope protection: Moisturize the pile body for no less than 7 days, and control the curing temperature between 5℃ and 30℃ to obtain a pile body with the required strength. Then, after the pile foundation construction is completed, slope protection is carried out by using shotcrete with wire mesh. The shotcrete strength grade is not lower than C20 and the thickness is 50mm to 100mm to obtain a stable slope.

[0006] By adopting the above technical solution, this method integrates the entire process of quality control from geological exploration to slope support. In particular, during the drilling stage, precise proportions of wall-protecting mud are used to maintain the stability of the borehole wall, providing a foundation for the subsequent installation of the reinforcing cage. In the concrete preparation stage, an improved mix ratio is used to ensure that the workability and strength development of the concrete match. In the pouring stage, the concrete density is ensured by controlling the tremie pipe burial depth. Ultimately, the pile foundation and the slope form a synergistic force-bearing system, thus achieving the effect of good pile integrity and high long-term slope stability.

[0007] Preferably, in step S2, the flatness deviation of the slope surface after trimming is no more than 50mm.

[0008] By adopting the above technical solution, the surface flatness deviation of the slope is controlled within 50mm, which aims to provide an accurate reference surface for subsequent pile location layout. At the same time, it avoids the drilling machine from being unstable or deviating due to uneven surface, thus improving the accuracy of pile location layout and the verticality of hole formation.

[0009] Preferably, in step S4, the drilling speed is controlled at 1 m / min to 2 m / min, and the mud viscosity is controlled at 18 s to 22 s during the drilling process.

[0010] By adopting the above technical solution, the drilling speed and mud viscosity are linked and controlled to avoid drilling too fast and causing stuck drill or hole wall collapse. At the same time, the mud viscosity of 18s to 22s ensures that the mud has sufficient cuttings carrying capacity and wall protection effect, thus achieving a balance between hole formation efficiency and hole wall quality.

[0011] Preferably, in step S4, the additive is sodium carbonate, and the amount added is 0.5% to 2.0% of the total mass of the mud.

[0012] By adopting the above technical solution, sodium carbonate is added as a dispersant. Sodium carbonate replaces calcium ions with sodium ions to fully disperse bentonite particles, thereby improving the colloidal content and stability of the mud. This provides a basis for reducing the sand content of the mud in subsequent hole cleaning operations, thus achieving the effect of enhancing the mud wall protection performance and reducing sediment at the bottom of the hole.

[0013] Preferably, in step S4, a thickener, namely carboxymethyl cellulose, is added to the wall-protecting mud at an amount of 0.1% to 0.5% of the total mass of the mud, and is added during the mud preparation process.

[0014] By adopting the above technical solution, carboxymethyl cellulose is added as a thickener during the mud preparation stage. Carboxymethyl cellulose increases the viscosity of the mud liquid phase through its long-chain molecular structure, thereby improving its suspension and slag-carrying capacity in sand or gravel layers, indirectly reducing the load of subsequent hole cleaning operations. Therefore, it achieves the effect of enhancing the safety of drilling in complex formations.

[0015] Preferably, in step S5, the hole cleaning adopts a positive circulation cleaning method, the cleaning time is not less than 30 minutes, and the sand content of the mud in the hole is controlled to be no more than 8% after cleaning.

[0016] By adopting the above technical solution, the positive circulation cleaning method is used and the minimum cleaning time is guaranteed. This time ensures that the number of mud circulations is sufficient to carry the sediment at the bottom of the hole to the surface, while the sand content of the mud is controlled below 8%. The purpose is to provide a clean interface for the installation of the reinforcing cage and the pouring of concrete, thus achieving the effect of avoiding weak interlayers at the bottom of the pile and ensuring the resistance at the pile end.

[0017] Preferably, in step S6, when fabricating the reinforcing cage, the spacing between the reinforcing bars is controlled to be between 100mm and 150mm, and the thickness of the protective layer is not less than 50mm; after the reinforcing cage is formed, its diameter deviation is checked to be no greater than ±10mm.

[0018] By adopting the above technical solution, the spacing of the reinforcing bars and the thickness of the protective layer are controlled. These dimensional requirements are based on the structural specifications for the bonding, anchorage, and durability protection of the reinforcing bars by concrete. The 50mm protective layer can meet the minimum thickness requirements of concrete structures for Class II environments, while the diameter deviation control ensures that the reinforcing cage is successfully hoisted into the hole. Therefore, the effect of ensuring the stress performance of the pile structure and the operability of construction is achieved.

[0019] Preferably, in step S8, a water-reducing agent is added during concrete preparation. The water-reducing agent is a polycarboxylate-based water-reducing agent, and the addition amount is 0.5% to 1.0% of the cement mass, added by mixing into the water; the initial setting time of the concrete is controlled to be no less than 4 hours.

[0020] By adopting the above technical solution, the addition of polycarboxylate superplasticizer and control of initial setting time allow the superplasticizer to disperse cement particles through steric hindrance, thereby reducing the water-cement ratio while ensuring workability. The 4-hour initial setting time is set according to the construction interruption risk that may be encountered during pile foundation grouting, reserving sufficient safety margin for continuous grouting using the tremie method. Therefore, the effect of high concrete strength and construction efficiency is achieved.

[0021] Preferably, in step S9, during concrete pouring, the diameter of the conduit is controlled between 250mm and 300mm, and the concrete rising speed is controlled to be no more than 2m / h during the pouring process.

[0022] By adopting the above technical solution, the diameter of the guide pipe and the concrete rising speed are limited. The selection of the guide pipe diameter is based on the matching relationship between the pile diameter and the maximum particle size of the coarse aggregate in the concrete, while the rising speed of 2m / h is based on the limit of the building pile foundation to avoid the floating of the steel cage or the segregation of the concrete. The two work together to ensure that the concrete is evenly spread in the hole, thus achieving the effect of the pile body being dense as a whole and without the defects of mud inclusion and broken pile.

[0023] Preferably, in step S10, the pile body is maintained by covering it with geotextile and sprinkling water to keep it moist, with a maintenance humidity of not less than 90% and watering not less than 4 times a day; when supporting the slope, the spraying pressure is controlled at 0.4 to 0.6 MPa.

[0024] By adopting the above technical solution, the use of covering and moisturizing curing and control of spraying pressure, 90% humidity and a watering frequency of 4 times a day based on the sensitivity of silicate cement hydration to environmental humidity can prevent plastic cracks on the pile surface; while the spraying pressure of 0.4 to 0.6 MPa ensures that the concrete and the slope surface are tightly bonded without excessive rebound, thus achieving the effect of full development of pile strength and reliable bonding of slope support layer.

[0025] In summary, this application has the following beneficial effects: 0. This application adopts an integrated quality control system covering the entire process from geological exploration to slope support. This system maintains the stability of the borehole wall by using precisely proportioned wall-protecting mud during the drilling stage, ensures the coordination of workability and strength development by improving the water-cement ratio and additives during the concrete preparation stage, and ensures continuous and dense concrete pouring by controlling the burial depth of the guide pipe during the grouting stage. As a result, the pile foundation and the slope form a synergistic force-bearing mechanism, thereby improving the structural integrity of the pile body and the long-term stability of the slope.

[0026] 1. In this application, the positive circulation process is preferred in the hole cleaning operation, and the operation time and mud index are controlled. Since this process carries the sediment at the bottom of the hole through the continuous circulation of mud flow and ensures that the sand content of the mud is reduced, it provides a clean interface condition for the installation of the reinforcing cage and the pouring of concrete. Therefore, it achieves the effect of preventing the weak interlayer at the bottom of the pile and ensuring the performance of the pile end resistance.

[0027] 2. The method of this application controls the diameter of the guide pipe and the concrete rising speed. Because the size of the guide pipe matches the pile diameter, the grouting blockage is avoided. The limit of the rising speed prevents the steel cage from floating or the concrete from segregating, thereby ensuring that the concrete is evenly spread in the hole. Therefore, the effect of the pile body being dense as a whole and free from defects such as mud inclusion and broken pile is achieved. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating a method for on-site construction of foundation pit slope pile foundations for a public welfare project, as proposed in this application. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Technical concept: The on-site construction of foundation pit slope pile foundations involves selecting suitable pile types and following the conventional process of drilling, cleaning, installing steel cages, and pouring concrete. Slope protection is achieved with the help of water-stopping or support measures. However, there is a lack of quantitative control from geological exploration to slope protection. The mud slurry ratio for the drilling stage is mostly adjusted based on experience. The concrete mix is ​​not fully coordinated with the compatibility of workability and strength development. The control of the tremie pipe burial depth during the pouring stage lacks precise management. Furthermore, the collaborative stress design between the pile foundation and the slope is not emphasized. As a result, the borehole wall is prone to collapse or diameter reduction, and the pile body may experience segregation, pile breakage, and other integrity defects. The long-term stability of the slope is insufficient, making it difficult to fully meet the safety requirements of foundation pit engineering in complex geological or sensitive environments.

[0031] This application discloses a method for on-site construction of foundation pit slope pile foundations for public welfare projects, including the following steps: S1, on-site investigation and clearing: geological investigation of the foundation pit slope is carried out to obtain soil layer distribution parameters and mechanical parameters; then the site surface is cleared, weeds and gravel obstacles are removed to obtain a flat construction working surface; S2, slope trimming; S3, pile location layout; S4, drilling; S5, hole cleaning; S6, reinforcement cage fabrication; S7, reinforcement cage installation; S8, concrete preparation; S9, concrete pouring; S10, pile curing and slope support.

[0032] This application adopts an integrated quality control system covering the entire process from geological exploration to slope support. This system maintains the stability of the borehole wall by using precisely proportioned wall-protecting mud during the drilling stage, ensures the coordination of workability and strength development by improving the water-cement ratio and additives during the concrete preparation stage, and ensures continuous and dense concrete pouring by controlling the tremie pipe depth during the grouting stage. As a result, the pile foundation and the slope form a synergistic force-bearing mechanism, thereby improving the structural integrity of the pile body and the long-term stability of the slope.

[0033] Example 1 This embodiment provides a method for on-site construction of foundation pit slope pile foundations for public welfare projects, including the following steps: S1. Site Investigation and Cleaning: Conduct a geological investigation of the foundation pit slope to obtain soil layer distribution parameters and mechanical parameters, including soil type and groundwater level; then clean the site surface, remove weeds, gravel obstacles, and obtain a flat construction working surface; S2. Slope trimming: The slope is trimmed mechanically or manually, and the slope ratio is controlled at 1:1.5. After trimming, a stable slope surface is obtained. The flatness deviation of the slope surface after repair should not exceed 50mm.

[0034] S3. Pile location layout: Use surveying instruments to layout the center of the pile location, mark the pile location points, and obtain the layout pile location points; S4. Drilling: Drilling is carried out at the marked pile location, with the borehole diameter controlled at 800mm and the borehole depth at the designed pile length. During the drilling process, wall protection mud is injected. The mud consists of water, bentonite and additives, and the mud specific gravity is controlled at 1.1g / cm³. After drilling, the borehole is obtained. Among them, the drilling speed is controlled at 1m / min, and the mud viscosity is controlled at 18s during the drilling process; The additive is sodium carbonate, and the amount added is 0.5% of the total mass of the mud. The wall-protecting mud also contains a thickener, which is carboxymethyl cellulose, added at a rate of 0.1% of the total mud mass during the mud preparation process.

[0035] S5. Hole Cleaning: After drilling is completed, hole cleaning is performed to remove sediment from the bottom of the hole. The thickness of the sediment should be controlled to be no more than 50mm to obtain a clean borehole. The hole cleaning process adopts the positive circulation cleaning method, and the cleaning time is not less than 30 minutes. After cleaning, the sand content of the mud in the hole is controlled to be no more than 8%.

[0036] S6. Reinforcing cage fabrication: HRB400 grade steel bars with a diameter of 20mm are used to fabricate the reinforcing cage by welding or binding to obtain the finished reinforcing cage. During the fabrication of the reinforcing cage, the spacing between reinforcing bars is controlled at 100mm, and the thickness of the protective layer is not less than 50mm; after the reinforcing cage is formed, its diameter deviation is checked and is not greater than ±10mm.

[0037] S7. Reinforcing cage installation: Hoist the finished reinforcing cage into the clean drill hole, and control the verticality deviation of the installation to be no more than 1% to obtain the in-place reinforcing cage. S8. Concrete mix design: P.O42.5 cement, medium and coarse sand, crushed stone and water are used to mix concrete. The concrete strength grade is controlled at C30, the water-cement ratio is 0.4 and the slump is 180mm to obtain fresh concrete. In addition, a water-reducing agent is added during concrete preparation. The water-reducing agent is a polycarboxylate-based water-reducing agent, and the addition amount is 0.5% of the cement mass, which is added to the water. The initial setting time of the concrete is controlled to be no less than 4 hours.

[0038] S9. Concrete pouring: Fresh concrete is continuously poured into the borehole using the tremie method, with the tremie pipe buried at a depth of 2m, and poured to the design elevation to obtain the pile body. During concrete pouring, the diameter of the duct is controlled at 250mm, and the concrete pouring speed is controlled to be no more than 2m / h.

[0039] S10. Pile body curing and slope protection: The pile body is moisturized and cured for no less than 7 days, and the curing temperature is controlled at 5℃ to obtain a pile body with the required strength. Then, after the pile foundation construction is completed, slope protection is carried out by using wire mesh shotcrete. The shotcrete strength grade is not lower than C20 and the thickness is 50mm to obtain a stable slope. Among them, the pile body maintenance adopts covering geotextile and sprinkling water to keep it moist, with a maintenance humidity of not less than 90%, and watering at least 4 times a day; when supporting the slope, the spraying pressure is controlled at 0.4MPa.

[0040] Example 2 This embodiment provides a method for on-site construction of foundation pit slope pile foundations for public welfare projects, including the following steps: S1. Site Investigation and Cleaning: Conduct a geological investigation of the foundation pit slope to obtain soil layer distribution parameters and mechanical parameters, including soil type and groundwater level; then clean the site surface, remove weeds, gravel obstacles, and obtain a flat construction working surface; S2. Slope trimming: The slope is trimmed mechanically or manually to control the slope ratio at 1:1.75, resulting in a stable slope surface. The flatness deviation of the slope surface after repair should not exceed 50mm.

[0041] S3. Pile location layout: Use surveying instruments to layout the center of the pile location, mark the pile location points, and obtain the layout pile location points; S4. Drilling: Drilling is carried out at the marked pile location, with the borehole diameter controlled at 1000mm and the borehole depth at the designed pile length. During the drilling process, wall protection mud is injected. The mud is composed of water, bentonite and additives, and the mud specific gravity is controlled at 1.2g / cm³. After the borehole is formed, the borehole is obtained. The drilling speed was controlled at 1.5 m / min, and the mud viscosity was controlled at 20 s during the drilling process. The additive is sodium carbonate, and the amount added is 1.25% of the total mass of the mud. The wall-protecting mud also contains a thickener, which is carboxymethyl cellulose, added at a rate of 0.3% of the total mud mass during the mud preparation process.

[0042] S5. Hole Cleaning: After drilling is completed, hole cleaning is performed to remove sediment from the bottom of the hole. The thickness of the sediment should be controlled to be no more than 50mm to obtain a clean borehole. The hole cleaning process adopts the positive circulation cleaning method, and the cleaning time is not less than 30 minutes. After cleaning, the sand content of the mud in the hole is controlled to be no more than 8%.

[0043] S6. Reinforcing cage fabrication: HRB400 grade steel bars with a diameter of 26mm are used to fabricate the reinforcing cage by welding or binding to obtain the finished reinforcing cage. During the fabrication of the reinforcing cage, the spacing between reinforcing bars is controlled at 125mm, and the thickness of the protective layer is not less than 50mm; after the reinforcing cage is formed, its diameter deviation is checked and is not greater than ±10mm.

[0044] S7. Reinforcing cage installation: Hoist the finished reinforcing cage into the clean drill hole, and control the verticality deviation of the installation to be no more than 1% to obtain the in-place reinforcing cage. S8. Concrete mix design: Concrete is prepared using P.O42.5 cement, medium and coarse sand, crushed stone and water. The concrete strength grade is controlled at C35, the water-cement ratio is 0.45 and the slump is 200mm to obtain fresh concrete. During concrete preparation, a water-reducing agent is added. The water-reducing agent is a polycarboxylate-based water-reducing agent, and the addition amount is 0.75% of the cement mass, which is added to the water. The initial setting time of the concrete is controlled to be no less than 4 hours.

[0045] S9. Concrete pouring: Fresh concrete is continuously poured into the borehole using the tremie method, with the tremie pipe buried at a depth of 4m, and poured to the design elevation to obtain the pile body. During concrete pouring, the diameter of the duct is controlled at 275mm, and the concrete pouring speed is controlled to be no more than 2m / h.

[0046] S10. Pile curing and slope protection: Moisturize the pile body for no less than 7 days, and control the curing temperature at 17.5℃ to obtain a pile body with the required strength. Then, after the pile foundation construction is completed, slope protection is carried out by using shotcrete with wire mesh. The shotcrete strength grade is not lower than C20 and the thickness is 75mm to obtain a stable slope. Among them, the pile body maintenance adopts covering geotextile and watering to keep it moist, with a maintenance humidity of not less than 90%, and watering not less than 4 times a day; when supporting the slope, the spraying pressure is controlled at 0.5MPa.

[0047] Example 3 This embodiment provides a method for on-site construction of foundation pit slope pile foundations for public welfare projects, including the following steps: S1. Site Investigation and Cleaning: Conduct a geological investigation of the foundation pit slope to obtain soil layer distribution parameters and mechanical parameters, including soil type and groundwater level; then clean the site surface, remove weeds, gravel obstacles, and obtain a flat construction working surface; S2. Slope trimming: The slope is trimmed by mechanical or manual means, and the slope ratio is controlled at 1:2. After trimming, a stable slope surface is obtained. The flatness deviation of the slope surface after repair should not exceed 50mm.

[0048] S3. Pile location layout: Use surveying instruments to layout the center of the pile location, mark the pile location points, and obtain the layout pile location points; S4. Drilling: Drilling is carried out at the marked pile location, with the borehole diameter controlled at 1200mm and the borehole depth at the designed pile length. During the drilling process, wall protection mud is injected. The mud consists of water, bentonite and additives, and the mud specific gravity is controlled at 1.3g / cm³. After drilling, the borehole is obtained. Among them, the drilling speed is controlled at 2m / min, and the mud viscosity is controlled at 22s during the drilling process; The additive is sodium carbonate, and the amount added is 2.0% of the total mass of the mud. The wall-protecting mud also contains a thickener, which is carboxymethyl cellulose, added at a rate of 0.5% of the total mud mass during the mud preparation process.

[0049] S5. Hole Cleaning: After drilling is completed, hole cleaning is performed to remove sediment from the bottom of the hole. The thickness of the sediment should be controlled to be no more than 50mm to obtain a clean borehole. The hole cleaning process adopts the positive circulation cleaning method, and the cleaning time is not less than 30 minutes. After cleaning, the sand content of the mud in the hole is controlled to be no more than 8%.

[0050] S6. Reinforcing cage fabrication: HRB400 grade steel bars with a diameter of 32mm are used to fabricate the reinforcing cage by welding or binding to obtain the finished reinforcing cage. During the fabrication of the reinforcing cage, the spacing between reinforcing bars should be controlled at 150mm, and the thickness of the protective layer should be no less than 50mm. After the reinforcing cage is formed, its diameter deviation should be checked and found to be no greater than ±10mm.

[0051] S7. Reinforcing cage installation: Hoist the finished reinforcing cage into the clean drill hole, and control the verticality deviation of the installation to be no more than 1% to obtain the in-place reinforcing cage. S8. Concrete mix design: Concrete is prepared using P.O42.5 cement, medium and coarse sand, crushed stone and water. The concrete strength grade is controlled at C40, the water-cement ratio is 0.5 and the slump is 220mm to obtain fresh concrete. In addition, a water-reducing agent is added during concrete preparation. The water-reducing agent is a polycarboxylate-based water-reducing agent, and the addition amount is 1.0% of the cement mass, which is added to the water. The initial setting time of the concrete is controlled to be no less than 4 hours.

[0052] S9. Concrete pouring: Fresh concrete is continuously poured into the borehole using the tremie method, with the tremie pipe buried at a depth of 6m, and poured to the design elevation to obtain the pile body. During concrete pouring, the diameter of the duct is controlled at 300mm, and the concrete pouring speed is controlled to be no more than 2m / h.

[0053] S10. Pile body curing and slope support: Moisturize the pile body for no less than 7 days and control the curing temperature at 30℃ to obtain a pile body with the required strength. Then, after the pile foundation construction is completed, slope support is carried out by using wire mesh shotcrete. The shotcrete strength grade is not lower than C20 and the thickness is 100mm to obtain a stable slope. Among them, the pile body maintenance adopts covering geotextile and watering to keep it moist, with a maintenance humidity of not less than 90%, and watering at least 4 times a day; when supporting the slope, the spraying pressure is controlled at 0.6MPa.

[0054] Comparative Example 1 The comparative example refers to the content of Example 1, except that the slope ratio is controlled at 1:1.0 in the S2 slope trimming, and the rest is the same as Example 1.

[0055] Comparative Example 2 The comparative example refers to the content of Example 1, except that the drilling diameter is controlled at 560mm in S4 drilling, and the rest is the same as in Example 1.

[0056] Comparative Example 3 The comparative example refers to the content of Example 1, except that the drilling speed is controlled at 0.7m / min during the S4 drilling process, and the rest is the same as Example 1.

[0057] Comparative Example 4 The comparative example refers to the content of Example 1, except that the mud specific gravity is controlled at 1.43 g / cm³ during S4 drilling. The rest of the content is the same as Example 1.

[0058] Comparative Example 5 The comparative example refers to the content of Example 1, except that HRB400 grade steel bars with a diameter of 14mm are used in the fabrication of the S6 steel cage. The rest of the content is the same as that in Example 1.

[0059] Comparative Example 6 The comparative example refers to the content of Example 1, except that the water-cement ratio is controlled at 0.52 in the preparation of S8 concrete, and the rest is the same as in Example 1.

[0060] Performance testing Sample preparation: To evaluate the impact of different construction parameters on pile foundation performance, full-scale test piles were cast on simulated foundation pit slopes under the same geological conditions according to the construction methods described in Examples 1-3 and Comparative Examples 1-6. Three parallel test pile samples were prepared for each example and comparative example for subsequent performance testing. All samples were tested after reaching 28 days of age under standard curing conditions.

[0061] Pile integrity testing: The low-strain reflected wave method is used to test the integrity of the test piles. During the test, an acceleration sensor is installed at the pile head, and a momentary hammering excitation is applied to generate a stress wave. The stress wave propagates along the pile body and is reflected at the pile bottom or at the interface where there are defects in the pile body. By analyzing the morphology, wave velocity, and time history curve characteristics of the reflected wave signal received by the sensor, it is determined whether there are defects such as necking, necking, segregation, or pile breakage in the pile body. This test is conducted in accordance with the Technical Specification for Testing of Building Foundation Piles JGJ106-2014.

[0062] Vertical compressive bearing capacity testing of single piles: A slow-maintained load method is used to conduct a static load test on the vertical compressive bearing capacity of single piles. The test applies vertical loads to the test pile in stages through a surcharge platform or anchor pile reaction system. After each load reaches a relatively stable standard, it is maintained for a certain period of time, and the settlement at the top of the pile is accurately recorded until the predetermined maximum test load is reached or the pile body fails. The ultimate bearing capacity or bearing capacity characteristic value of the single pile is determined by plotting the load-settlement curve. This test is performed in accordance with the "Technical Specification for Testing of Building Foundation Piles" JGJ106-2014.

[0063] Concrete strength testing of pile body: The concrete strength of test piles that have reached the curing period is verified by core drilling. Concrete core samples of specified diameter are drilled at different locations in the pile body using a hydraulic drilling rig. The obtained core samples are processed into standard specimens with a height-to-diameter ratio of 1:1 in the laboratory, and then their compressive strength is determined by a pressure testing machine. The core sample strength is converted into standard cubic compressive strength and compared with the design strength grade. This test is carried out in accordance with the Technical Specification for Testing Concrete Strength by Core Drilling Method CECS03:2007.

[0064] Slope stability testing: To assess the overall stability of the slope after pile foundation construction, a physical model of the slope including test piles was constructed. By simulating actual working conditions, additional loads were applied in stages at the top of the slope, and displacement sensors were used to monitor the horizontal and vertical displacement changes of the slope surface and the top of the piles. When a significant sliding surface appeared on the slope or the displacement increased sharply, the critical load at this time was recorded. This test refers to the relevant principles of the "Technical Specification for Building Slope Engineering" GB50330-2013.

[0065] The performance of the drilling mud is correlated with the stability of the borehole wall: Although the condition of the borehole wall cannot be directly detected after pile formation, the wall protection effect of the mud can be indirectly evaluated by monitoring the performance indicators and circulation of the mud during drilling, and recording the collapse of the borehole wall from the time of drilling to the time of grouting. The smoothness of drilling operations and the borehole wall integrity rate of the comparative example and the embodiment under the same geological conditions are recorded. This evaluation is based on the requirements for mud wall protection in the "Code for Design of Building Pile Foundations" JGJ94-2008.

[0066] Table 1:

[0067] Example Conclusion: As can be seen from Examples 1-3 and Comparative Example 1, and Table 1, adopting a reasonable slope gradient can ensure that the pile foundation and the slope work together to form a stable support system; an excessively steep slope will weaken the overall stability of the pile foundation and the surrounding soil. Even if the pile itself is of good quality, the slope is prone to instability, thus failing to exert the bearing capacity of the pile foundation; this method ensures the overall safety of the pile foundation-slope composite structure by optimizing the slope gradient.

[0068] As can be seen from Examples 1-3 and Comparative Example 2, and Table 1, an appropriate borehole diameter is fundamental to ensuring that the pile foundation has a sufficient bearing area; an excessively small borehole diameter will reduce the pile cross-section, resulting in a decrease in the bearing capacity of a single pile; this method ensures that the pile foundation can provide the required support force by matching the borehole diameter to the engineering requirements.

[0069] As can be seen from Examples 1-3 and Comparative Example 3, and Table 1, controlling an appropriate drilling speed can ensure high-quality hole formation. Too slow a drilling speed will prolong the hole wall exposure time, increase the risk of hole wall instability caused by mud soaking and formation disturbance, and easily lead to defects such as necking. This method improves hole formation quality by improving drilling efficiency while ensuring hole wall stability.

[0070] As can be seen from Examples 1-3 and Comparative Example 4, and Table 1, controlling the specific gravity of the wall-protecting mud within a reasonable range has a synergistic effect on maintaining borehole stability and ensuring the quality of concrete pouring. Excessive mud specific gravity will increase its consistency, affect mud circulation, and may form an excessively thick mud cake in the strata, which will lead to difficulty in cleaning the borehole, excessive sediment, and segregation of the pile body concrete. This method provides a foundation for forming a complete and dense pile body by controlling the mud properties.

[0071] As can be seen from Examples 1-3 and Comparative Example 5, and Table 1, configuring a steel cage that meets the design requirements can ensure the bearing capacity of the pile foundation; reducing the diameter of the main reinforcement will weaken the bending and compressive strength of the pile body, resulting in insufficient bearing capacity of the pile foundation; this method ensures the specifications and quality of the steel cage, enabling the pile foundation to effectively transfer and bear the load.

[0072] As can be seen from Examples 1-3 and Comparative Example 6, and Table 1, controlling the water-cement ratio within a low range can ensure the acquisition of high-strength, high-performance pile concrete; an excessively high water-cement ratio will reduce the density and strength of the concrete and increase the tendency of segregation, affecting the structural integrity and bearing durability of the pile body; this method ensures the mechanical properties of the pile concrete by improving the concrete mix proportion.

[0073] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for on-site construction of foundation pit slope pile foundations for public welfare projects, characterized in that, Includes the following steps: S1. Site Investigation and Cleaning: Conduct a geological investigation of the foundation pit slope to obtain soil layer distribution parameters and mechanical parameters, including soil type and groundwater level; then clean the site surface, remove weeds, gravel obstacles, and obtain a flat construction working surface; S2. Slope trimming: The slope is trimmed mechanically or manually, and the slope ratio is controlled between 1:1.5 and 1:

2. After trimming, a stable slope surface is obtained. S3. Pile location layout: Use surveying instruments to layout the center of the pile location, mark the pile location points, and obtain the layout pile location points; S4. Drilling: Drilling is carried out at the marked pile location, with the borehole diameter controlled between 800mm and 1200mm and the borehole depth equal to the designed pile length. During the drilling process, wall-protecting mud is injected. The mud consists of water, bentonite, and additives, and the mud specific gravity is controlled between 1.1 and 1.3g / cm³. After drilling, the borehole is obtained. S5. Hole Cleaning: After drilling is completed, hole cleaning is performed to remove sediment from the bottom of the hole. The thickness of the sediment should be controlled to be no more than 50mm to obtain a clean borehole. S6. Reinforcing cage fabrication: HRB400 grade steel bars with a diameter of 20mm to 32mm are used to fabricate the reinforcing cage by welding or binding to obtain the finished reinforcing cage. S7. Reinforcing cage installation: Hoist the finished reinforcing cage into the clean drill hole, and control the verticality deviation of the installation to be no more than 1% to obtain the in-place reinforcing cage. S8. Concrete mix design: Concrete is prepared using P.O42.5 cement, medium and coarse sand, crushed stone and water. The concrete strength grade is controlled at C30 to C40, the water-cement ratio is 0.4 to 0.5, and the slump is 180 mm to 220 mm to obtain fresh concrete. S9. Concrete pouring: Fresh concrete is continuously poured into the borehole using the tremie method, with the tremie pipe buried at a depth of 2m to 6m, and poured to the design elevation to obtain the pile body; S10. Pile curing and slope protection: Moisturize the pile body for no less than 7 days, and control the curing temperature between 5℃ and 30℃ to obtain a pile body with the required strength. Then, after the pile foundation construction is completed, slope protection is carried out by using shotcrete with wire mesh. The shotcrete strength grade is not lower than C20 and the thickness is 50mm to 100mm to obtain a stable slope.

2. The on-site construction method for foundation pit slope pile foundation based on a public welfare project, as described in claim 1, is characterized in that... In step S2, the flatness deviation of the slope surface after trimming should not exceed 50mm.

3. The on-site construction method for foundation pit slope pile foundation based on a public welfare project, as described in claim 1, is characterized in that... In step S4, the drilling speed is controlled at 1 m / min to 2 m / min, and the mud viscosity is controlled at 18 to 22 s during the drilling process.

4. The on-site construction method for foundation pit slope pile foundation based on a public welfare project, as described in claim 1, is characterized in that... In step S4, the additive is sodium carbonate, and the amount added is 0.5% to 2.0% of the total mass of the mud.

5. The on-site construction method for foundation pit slope pile foundation based on a public welfare project, as described in claim 1, is characterized in that... In step S4, a thickener, carboxymethyl cellulose, is added to the wall-protecting mud at a rate of 0.1% to 0.5% of the total mud mass. This thickener is added during the mud preparation process.

6. The on-site construction method for foundation pit slope pile foundation based on a public welfare project, as described in claim 1, is characterized in that... In step S5, the hole cleaning adopts the positive circulation cleaning method, the cleaning time is not less than 30 minutes, and the sand content of the mud in the hole is controlled not to exceed 8% after cleaning.

7. The on-site construction method for foundation pit slope pile foundation based on a public welfare project, as described in claim 1, is characterized in that... In step S6, when fabricating the reinforcing cage, the spacing between the reinforcing bars is controlled to be between 100mm and 150mm, and the thickness of the protective layer is not less than 50mm; after the reinforcing cage is formed, its diameter deviation is checked to be no greater than ±10mm.

8. The on-site construction method for foundation pit slope pile foundation based on a public welfare project, as described in claim 1, is characterized in that... In step S8, a water-reducing agent is added during concrete preparation. The water-reducing agent is a polycarboxylate-based water-reducing agent, and the addition amount is 0.5% to 1.0% of the cement mass, which is added to the water. The initial setting time of the concrete is controlled to be no less than 4 hours.

9. A method for on-site construction of foundation pit slope pile foundations for public welfare projects, as described in claim 1, is characterized in that... In step S9, during concrete pouring, the diameter of the tremie pipe is controlled between 250mm and 300mm, and the concrete pouring speed is controlled to be no more than 2m / h.

10. A method for on-site construction of foundation pit slope pile foundations for public welfare projects according to claim 1, characterized in that, In step S10, the pile body is maintained by covering it with geotextile and sprinkling water to keep it moist, with a maintenance humidity of not less than 90%, and watering is carried out no less than 4 times a day; when supporting the slope, the spraying pressure is controlled at 0.4 to 0.6 MPa.

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