A method for construction of a underpinning pile and a detection anchor pile

Abstract

The application relates to the technical field of building municipal foundation pit support and foundation piles, in particular to a construction method of underpinning piles and anchor piles for detection. The construction method comprises the following steps: S1. early construction; S2. determining a pile position; S3. small geological drilling machine construction; S4. small rotary jet drilling machine construction; S5. small spiral anchor rod drilling machine construction; S6. underpinning pile construction; S7. anchor pile construction; S8. cyclic construction; S9. static load test; and S10. slope protection pile construction. In the construction method, four to five small-diameter steel pipes are used to replace a large-diameter steel pipe as the underpinning piles and the anchor piles, the problem of insufficient power of the remanufactured small long spiral drilling machine is solved, and the problem that the reaction force of the large-diameter steel pipe is difficult to provide after rotary jetting and static pressure implantation is solved, so that the application has the effect of adapting to the narrow construction site of old house reconstruction, and large-scale mechanical equipment cannot enter the site.

Description

Technical Field

[0001] The present application relates to the technical field of building municipal foundation pit support and foundation piles, and in particular to a construction method for underpinning piles and anchor piles for testing. Background Art

[0002] Urban development is a dynamic process of continuous updating and change. The renovation of old houses has become one of the important engineering projects that are currently being vigorously promoted. The reason for promoting the renovation of old houses is mainly to increase the existing utilization rate of houses, improve the living environment, house functions and housing conditions.

[0003] The renovation project for an environmentally sensitive, narrow building site involved demolishing all but the exterior facade of the building and constructing a new structure. Furthermore, new basement structures were constructed indoors and outdoors. The project's north, south, and west sides border a lake, with the west exterior wall approximately 4 meters from the water. This left a working surface of only 3.2 meters for 800mm piles, making it impossible for large machinery to enter the construction site. Summary of the Invention

[0004] In order to address the problem that the construction site of old house renovation is narrow and large machinery and equipment cannot enter the site, the present application provides a construction method for replacement piles and anchor piles for testing.

[0005] The present application provides a construction method for underpinning piles and anchor piles for testing, which adopts the following technical solutions:

[0006] A construction method for underpinning piles and anchor piles for testing comprises the following steps:

[0007] S1. Preliminary construction: dock cofferdam construction and site leveling;

[0008] S2. Determine pile positions: Measure, lay out, locate, and verify the positions of underpinning and interlocking piles.

[0009] S3. Construction with a small geological drilling rig: Using the pile position determined in step S2, drill the hole with casing using a small geological drilling rig. Once the drill reaches the designed depth, remove the drill rig and fill the casing with soil in layers and compact it. After each section is filled, the casing is withdrawn a section until it reaches the hole opening. As the casing is withdrawn, it is reversed and removed section by section, ultimately forming a soil column.

[0010] S4. Construction of a small jet-jet drill: A small jet-jet drill is positioned. Following the soil column formed in step S3, the drill is aligned with the center of the column and jet-jet cement-soil piles are formed. The outer jet-jet cement-soil piles interlock to form a water-stop curtain. Underpinning piles are selected for static load testing. The underpinning piles on either side of the underpinning pile serve as anchor piles.

[0011] S5. Construction of a Small Spiral Anchor Drilling Rig: The small spiral anchor drilling rig is positioned. Following the cement-soil jet grouting piles formed in step S4, the rig is used to drill small pile holes in the cement-soil jet grouting piles that serve as underpinning and anchor piles. Once the drill reaches the designed depth, the drill is raised and the hole opening is moved away.

[0012] S6. Underpinning pile construction: Insert a small-diameter steel pipe into the small pile hole, connect the hole ends in sections, then insert a grouting pipe into the bottom of the hole and fill it with cement slurry; perform secondary grouting.

[0013] S7. Anchor pile construction: Following the small pile holes formed in step S5, partially bonded prestressed pullout-resistant steel pipe piles are placed into the small pile holes. A grouting pipe is then inserted into the bottom of the hole and filled with cement slurry. A secondary grouting process is then performed.

[0014] S8. Loop construction: Steps S5 to S7 are repeated. During the grouting process of the underpinning pile or anchor pile, a small steel pipe pile is constructed on another pile. Then, another small steel pipe pile is constructed on the same pile. The cycle is completed for all small steel pipe piles. A total of 4 to 5 small pile holes are drilled on each underpinning pile or anchor pile. The number of small pile holes corresponds to the number of small-diameter steel pipes or partially bonded prestressed pull-out steel pipe piles implanted.

[0015] S9. Static load test: When testing the bearing capacity of underpinning piles, the steel strands in the partially bonded prestressed pullout-resistant steel pipe piles on both sides of the anchor piles are prestressed and locked to the operating tool iron, and then a static load test is performed.

[0016] S10. Slope protection pile construction: After the static load test, prestress the steel strands to lock the top of the anchor piles, converting the anchor piles into partially bonded prestressed slope protection piles.

[0017] By adopting the above technical solution, in view of the fact that the construction site for the renovation of old houses is relatively narrow and large equipment cannot enter the site, and conventional drilling equipment cannot be used, 4 to 5 small-diameter steel pipes are used to replace one large-diameter steel pipe as an underpinning pile, which solves the problem of insufficient power of the modified small and long spiral drilling machine, and at the same time solves the problem of difficulty in providing reaction force for the static pressure implantation of large-diameter steel pipes after rotary grouting. During the grouting construction of the underpinning pile or anchor pile, the drilling rig can be moved away to construct a small steel pipe pile of another pile, and then come back to construct another small steel pipe pile on the pile, completing all the small steel pipe piles in a cycle. The construction process of the anchor pile and the underpinning pile adopts the same construction method. The cyclic construction can save a lot of construction time and shorten the construction period without interfering with each other. All small-diameter steel pipe piles used as anchor piles are made into partially bonded prestressed pull-out steel pipe piles, which alleviates the disadvantages of welding steel bars on large-diameter steel pipes and also reduces the problem of cracking concrete or cement slurry.

[0018] Optionally, in the S3 step, first, a large-diameter alloy drill bit and drill are used for drilling, and drilling is performed until the upper end of the drill is flush with the ground surface, then a small-diameter drill bit and drill are used for drilling in the casing, and drilling is performed at a depth greater than the casing depth each time until the designed hole depth is reached, then the inner drill bit and drill are removed, and dry soil is filled into the hole, and each filled section is tamped.

[0019] By using the above technical solution, first, a large-diameter drill bit is used for drilling, then a small-diameter drill bit is used for drilling, the casing is conveniently followed for drilling, the drill bit is drilled until the designed hole depth is reached, then the inner drill bit and drill are removed, and dry soil is filled into the hole, and each filled section is tamped, which can reinforce the pile hole and avoid mud pollution caused by mud wall protection.

[0020] Optionally, in the S4 step, the cement-soil rotary jet grouting pile is hit according to the design requirements, and finally, the cement-soil rotary jet grouting piles are mutually engaged by 15-20 cm to form a continuous rotary jet grouting cement-soil waterproof curtain.

[0021] By using the above technical solution, the cement-soil rotary jet grouting pile is hit according to the design requirements, which can reduce the influence on the quality of the adjacent formed pile during construction, and the continuous cement-soil rotary jet grouting pile waterproof curtain can block the surrounding lake water or underground water.

[0022] Optionally, after the S4 step is completed, 1-2 days are waited, and then the S5 step is performed.

[0023] By using the above technical solution, 1-2 days are waited after the cement-soil rotary jet grouting pile is formed by rotary jet grouting, at this time, the strength of the cement grout reaches about 80% of the final strength, and then the small spiral anchor drill is constructed, which can reduce the probability of hole collapse caused by insufficient strength of the cement-soil rotary jet grouting pile and can also alleviate the problem that the small spiral anchor drill is difficult to drill due to the excessive strength of the cement-soil rotary jet grouting pile.

[0024] Optionally, in the S5 step, there is slight hole collapse during lifting of the drill, and cement grout is injected while the drill is lifted, and then the S6 step is performed.

[0025] By using the above technical solution, there may be slight hole collapse during lifting of the drill, and at this time, the cement grout can be injected while the drill is lifted to reinforce the inner wall of the pile hole and reduce the problem of large-area hole collapse of the pile hole.

[0026] Optionally, in the S7 step, the partial bonded prestressed uplift-resistant steel pipe pile includes the small-diameter steel pipe and a plurality of steel strands, the bottom of the small-diameter steel pipe is symmetrically provided with a plurality of through holes, and the partially stripped and degreased steel strands pass through the corresponding two through holes from the radial direction of the small-diameter steel pipe, and the two ends of each steel strand extend beyond the top of the small-diameter steel pipe along the axial direction of the small-diameter steel pipe.

[0027] By adopting the technical scheme, the problem that large mechanical equipment cannot enter the site can be solved by forming an anchor pile by using multiple small-diameter steel pipe piles, and the multiple small-diameter steel pipe piles are all made into partially bonded prestressed uplift steel pipe piles, a section of the steel strand is bonded with the cement slurry by being stripped of grease, and the other section is separated from the cement slurry by the skin sleeve, the problem of welding steel bars on a large-diameter steel pipe is solved, and the problem of cracking of the cement slurry is alleviated.

[0028] Optionally, the length of the section of the steel strand stripped of grease is only 1-2 m.

[0029] By adopting the technical scheme, because the section of the steel strand stripped of grease is both threaded through the through hole formed in the bottom of the small-diameter steel pipe and bonded with the cement slurry in the bottom, the anchoring length can meet the tensile requirement, and the length of the section of the steel strand stripped of grease only needs to be 1-2 m, which can reduce labor costs and improve construction efficiency.

[0030] Optionally, in the S10 step, the prestress locking value only needs to be 20-30 kN.

[0031] By adopting the technical scheme, because the steel strand only needs to provide a certain stable tension after completing the static load test to maintain the function of the partially bonded prestressed uplift steel pipe pile as a slope protection pile for a long time, and the bending resistance of the slope protection pile can be improved at this time.

[0032] Optionally, the underpinning pile that cannot be formed at one time is supplemented in subsequent steps.

[0033] By adopting the technical scheme, when the underpinning pile is formed for the first time, the indoor underpinning pile cannot be completed due to the blockage of part of the structure, and after the indoor structure members are removed in subsequent steps, the indoor underpinning pile that has not been completed is supplemented until all the designed indoor underpinning piles are completed.

[0034] Optionally, in the S10 step, the steel strand is cut off after the static load test is completed.

[0035] By adopting the technical scheme, the anchor pile does not need to be used as a detection pile after the static load test is completed, and the steel strand can be directly used as a slope protection pile after being cut off.

[0036] In summary, the present application includes at least one of the following beneficial technical effects:

[0037] 1. Four to five small-diameter steel pipes are used to replace a large-diameter steel pipe as an underpinning pile, which solves the problem of insufficient power of the modified small long spiral drill, and solves the problem that the reaction force of the large-diameter steel pipe is difficult to provide after rotary jetting and static pressure implantation.

[0038] 2. In the process of grouting construction of the underpinning pile or anchor pile, the drilling machine can be removed to construct another small steel pipe pile, and then come back to construct another small steel pipe pile on the pile, and the construction process of anchor pile and underpinning pile is the same as the construction method, and the circulating construction can save a lot of construction time and shorten the construction period, and at the same time, it will not interfere with each other.

[0039] 3. All small-diameter steel pipe piles for anchor piles are made into partially bonded prestressed uplift steel pipe piles, which can alleviate the problems of welding steel bars on large-diameter steel pipes, and can also alleviate the problem of cracking of concrete or cement slurry.

[0040] 4. After the formation of the cement-soil jet grouting pile by the rotary jet cement slurry, wait for 1 to 2 days, at which time the strength of the cement slurry reaches about 80% of the final strength, then carry out the small spiral anchor drill construction, which can reduce the probability of hole collapse due to insufficient strength of the cement-soil jet grouting pile, and can also alleviate the problem of difficulty in drilling by the small spiral anchor drill due to the excessive strength of the cement-soil jet grouting pile.

[0041] 5. There may be slight hole collapse during the lifting of the drilling tool, at which time the cement slurry can be pressed and grouted while lifting the drilling tool to reinforce the inner wall of the pile hole and reduce the problem of large-area hole collapse of the pile hole.

[0042] 6. Because the stripped and degreased section of the steel strand passes through the through hole opened at the bottom of the small-diameter steel pipe and is bonded with the cement slurry at the bottom, the anchoring length can meet the tensile requirement, and the stripped and degreased length of the steel strand only needs 1-2m, which can reduce labor cost and improve construction efficiency.

[0043] 7. After the static load test of the steel strand, only a certain stable tension is needed to maintain the partially bonded prestressed uplift steel pipe pile as a slope protection pile, and the bending resistance of the slope protection pile can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a schematic view of the facade of the old house that needs to be renovated in the present application.

[0045] Figure 2 is a schematic view of the process of the old house renovation construction technology in the present application.

[0046] Figure 3 is a schematic view of the surrounding environment of the old house that needs to be renovated in the present application.

[0047] Figure 4 is a schematic view of the position of each pile in the present application.

[0048] Figure 5 is a schematic view of the structure of the underpinning pile in the present application.

[0049] Figure 6It is a structural diagram of the anchor pile in this application.

[0050] Figure 7 It is a flow chart of the construction process of partially bonded prestressed pull-out resistant steel pipe piles in this application.

[0051] Figure 8 It is a structural diagram of the static load test in this application.

[0052] Figure 9 It is a schematic diagram of the anchoring of the steel strand after the static load test in this application.

[0053] Figure 10 It is a structural diagram of the exterior wall steel support construction in this application.

[0054] Figure 11 It is a structural diagram of the horizontal support construction in this application.

[0055] Figure numerals: 1. underpinning pile; 11. Outdoor underpinning pile; 12. Indoor underpinning pile; 2. Interlocking pile; 3. Foundation pit retaining axis; 4. Water-stop curtain; 5. Small diameter steel pipe; 6. Anchor pile; 7. Steel strand; 8. Steel plate; 9. Anchor; 110. Steel frame; 120. Cantilever beam; 130. Horizontal support; 140. Wall beam; 150. Underpinning beam. DETAILED DESCRIPTION

[0056] The following is combined with Figure 1 To the attached Figure 11 , further details of this application are given.

[0057] like Figure 1 As shown, the project was built in the 1950s. The structure is a brick-concrete structure system, the foundation is concrete and rubble stone strip foundation, the burial depth is about 1.5m to 3.65m, the building height H is about 10m, the roof is gabled, and the eaves extension length L is about 2m.

[0058] like Figure 2 As shown, the general construction process for renovating an old house and adding a basement is as follows: 1. Demolition of outdoor attached buildings, manual excavation of pipelines, construction of dock cofferdams, and construction guide trenches; 2. Construction of external interlocking piles, underpinning piles, and supporting piles; 3. Construction of indoor underpinning piles, pedestals, and supports; 4. Construction of outdoor sandwich wall beams, pin keys, and underpinnings; 5. Construction of external wall steel supports; 6. Demolition of the original roof and indoor structural components; 7. Construction of indoor underpinning piles, pedestals, and supports, and completion of any step that could not be done in step 3; 8. Excavation and removal of the original foundation; 9. Construction of a new raft slab and new basement exterior walls; 10. Completion of the conversion of the force transmission system between the external original wall and the new basement exterior wall structure; 11. Demolition of the indoor underpinning structure; 12. Construction of a new above-ground structure; 13. Restoration of the roof and outdoor attached buildings; 14. Demolition of the external wall steel supports.

[0059] like Figure 3 As shown, the project's north, south, and west sides are adjacent to a lake, approximately 1.5 meters above the site surface and 2 meters deep. The west exterior wall is approximately 4 meters from the water, leaving an 800mm pile construction surface. The available working surface for mechanical equipment is only 3.2 meters wide. Similarly, the 9.5m eaves height limit also dictates that the drilling rig selection should consider the 9.5m height limit. Furthermore, the geological conditions are complex, and the underpinning and interlocking piles are designed with a 700mm diameter and 13m length. This also necessitates consideration of adequate power when selecting a drilling rig.

[0060] Due to the sensitive nature of the project site, noise, vibration, and mud contamination were unacceptable. Manual drilling was not an option, and rotary drilling rigs were not suitable due to excessive noise. Vibratory hammers were also not an option due to noise and vibration, and reverse circulation of the mud wall was also not an option. The outdoor steel pipe piles, measuring φ600×20, were designed to be drilled using a small auger, pressure-casted with concrete or cement slurry, and then embedded in the steel pipes. The indoor steel pipe piles, measuring φ426×16, were constructed using a cement-soil jet grouting and static pressure steel pipe pile construction process. The characteristic bearing capacity of a single pile was 600kN. The smallest chassis currently available for long auger rigs is 10m×4m, which is not suitable for this site. A modified small auger anchor drill rig was used, but its power was insufficient to meet the requirements for a 700mm diameter, 7m penetration into the sand and gravel formation, and a total length of 13m. Insufficient power was a critical weakness. Furthermore, the static pressure steel pipe pile resistance after cement-soil jet grouting should be at least 1200kN, a significant reaction force that was difficult to achieve under current indoor conditions. If pile loads are used for pile bearing capacity testing, the site conditions will obviously not be met. Furthermore, if steel bars are welded to existing steel pipes, hot work (i.e., electric welding) is generally not permitted in these locations. Even if electric welding were possible, the steel pipes would be subjected to large upward pull forces, which could also crack the concrete or cement paste.

[0061] This embodiment discloses a construction method for underpinning piles and anchor piles for testing to comprehensively solve the above problems, including the following steps:

[0062] S1. Construction preparation and early construction:

[0063] 1. Construction preparation: 1. Collect information, conduct on-site surveys, and carefully prepare the construction organization design; 2. Preparation of raw materials: Cement must have a factory quality certificate. When purchasing, its variety, grade, packaging, and factory date should be inspected and accepted, and it should be stored in accordance with relevant regulations. For every 200 tons of cement supplied, samples need to be taken for inspection, and a small amount of samples should be taken from each of the 10 bags; 3. Mechanical equipment and auxiliary equipment: Carry out inspections before entering the site to ensure the intact rate; 4. Provide necessary training to operators, and do a good job of briefing on safety, technology, environmental protection, etc.

[0064] 2. Demolition of outdoor ancillary buildings: Demolish the ancillary buildings outside the main structure to facilitate the subsequent construction of the main structure and the entry of mechanical equipment.

[0065] 3. Manual exploration and excavation of pipelines: There are many underground pipelines in the city around this project, including gas, heat, communications, sewage, etc. Manual exploration and excavation of pipelines are used to mark the underground pipelines to avoid blind excavation and reduce construction accidents.

[0066] 4. Dock cofferdam construction: The project is adjacent to the lake on the north, south and west sides. The lake surface is about 1.5m from the site ground and the water depth is about 2m. The bottom is treated with traditional reinforced soil layered rolling and anti-seepage treatment. Targeted plans must be taken in advance for the dock cofferdam to prevent lake water from backflowing or seeping into the foundation pit. At the same time, foundation pit excavation and drainage construction need to ensure the safety of the lake water.

[0067] 5. Leveling of the site: to facilitate subsequent measurement, layout and entry of mechanical equipment.

[0068] S2. Determine the pile position: refer to Figure 4 Measure, lay out, and verify the positions of underpinning piles 1 and interlocking piles 2. Underpinning pile 1 includes outdoor underpinning piles 11 and indoor underpinning piles 12. Outdoor underpinning piles 11 also serve as support piles. Measure and lay out the lines on the leveled site. Use measuring instruments to position stakes at both ends of the laid lines to prevent deviations in the pile positions and review them at any time. Use a steel chisel or punch to drill a deep hole in the ground, fill it with white lime powder, and insert a clear marker such as a wooden stick or steel bar at the pile position. Mark each side of the bends on the wall for verification, especially at the corners.

[0069] S3. Small geological drilling rig construction: The selected small geological drilling rig has dimensions that meet the requirements of a narrow site, including length, width, and height, and is noise-free and free of mud contamination. Following the pile position determined in step S2, the operator strictly controls the movement of the small geological drilling rig, ensuring the pile hole axis is in place and not deviated. The operator uses the rig's built-in leveling device to adjust the verticality of the column. The maximum height of the vertical column should be lower than the eaves height, and the verticality deviation of the drill tool should be within the designed range.

[0070] When drilling, first use a larger diameter alloy drill bit and drill string to drill until the top of the drill string is flush with the ground surface. Then, switch to a smaller diameter drill bit and drill string and drill into the casing. Each drilling depth should be greater than the casing depth to facilitate the next drilling. When the designed hole depth is reached, remove the drill bit and drill string, fill the hole with dry soil, and tamp it. After each section is filled, pull out the casing a section until it reaches the hole mouth. The casing is reversed and removed section by section to form a soil column. Its position is marked promptly. Excavate the guide trench and organize the inspection.

[0071] Better yet, using hydrolyzed polyacrylamide and water glass drilling fluid wall protection can save the casing wall protection procedure, wherein the amount of 1% hydrolyzed polyacrylamide added is 0.5% of the drilling fluid volume ratio, and the amount of water glass added is 10% of the drilling fluid volume ratio.

[0072] S4. Construction of a small jet grouting drill: The small jet grouting drill is in place. The selected small jet grouting drill has dimensions that meet the requirements of a narrow site, and is free of vibration, noise, and mud pollution. According to the soil column formed in step S3, the drill bit is aligned with the center of the soil column, and jet grouting is started using a small pump pressure or a small wind pressure. After reaching the designed depth, the jet grouting is lifted using a large pump pressure or a large wind pressure. The lifting speed is generally controlled at 10 to 25 cm / min until the hole is located, forming a cement soil jet grouting pile. The small pump pressure is 5 to 15 MPa, the large pump pressure is 25 to 40 MPa, the small wind pressure is 0.3 to 0.9 MPa, and the large wind pressure is 1.5 to 2.1 MPa.

[0073] Reference Figure 4 , the outdoor cement soil rotary jet piles are driven in a jump-driving manner according to the design requirements, and the small rotary jet drilling rig moves along the foundation pit retaining axis 3. A part of the cement soil rotary jet piles are used as interlocking piles 2. The outdoor support piles 11 and the interlocking piles 2 are arranged at intervals and interlock with each other by 15 to 20 cm to form a continuous rotary jet cement soil water-stop curtain 4. The water-stop curtain 4 can block the surrounding lake water or groundwater. The indoor cement soil rotary jet piles are rotary jetted in sequence according to the pile positions determined in step S2. The cement soil rotary jet piles adopt a jump-driving construction sequence to reduce the impact on the quality of adjacent piles during the construction process. After each cement soil rotary jet pile is completed, it is necessary to wait for 1 to 2 days before proceeding to step S5.

[0074] Reference Figure 4 , an underpinning pile (1) that needs to be subjected to a static load test is selected, and the underpinning piles (1) on both sides of the underpinning pile (1) are constructed as anchor piles (6).

[0075] S5. Construction of small spiral anchor drilling rig: The small spiral anchor drilling rig is in place. The selected small spiral anchor drilling rig has dimensions that can meet the requirements of a narrow site, and has no vibration, noise, or mud pollution. According to the cement soil rotary jet pile formed in step S4, the small spiral anchor drilling rig is used to level and adjust the verticality of the drill bit. The drilling rig is used to drill a small pile hole on the cement soil rotary jet pile that serves as the support pile (1) and anchor pile (6). After reaching the designed depth, the hole position is moved away. If there is a slight hole collapse during the process of lifting the drill bit, cement slurry is injected while the drill bit is lifted.

[0076] S6. Underpinning pile 1 construction: refer to Figure 5 According to the small pile hole formed in step S5, the small diameter steel pipe 5 is implanted into the small pile hole, and the hole mouth is connected in sections when necessary. Each underpinning pile 1 is composed of 4 to 5 small diameter steel pipes 5. The small diameter steel pipe 5 is welded with a central bracket at an axial interval of 1 to 2m. After the small diameter steel pipe 5 enters the pile hole, the stability of the small diameter steel pipe 5 can be improved, making it less likely to tilt, thereby improving the strength of the pile after formation. The grouting pipe is inserted into the bottom of the hole and filled with cement slurry. After the grouting pipe is pulled out, when the cement slurry is lower than the design elevation, secondary grouting is performed.

[0077] S7. Anchor pile 6 construction: refer to Figure 4 and Figure 6 According to the determined position of the underpinning pile 1 to be subjected to the static load test, the underpinning piles 1 on both sides of the underpinning pile 1 are constructed as anchor piles 6. The anchor piles 6 are partially bonded prestressed pull-out steel pipe piles formed by utilizing the existing small-diameter steel pipe 5. The partially bonded prestressed pull-out steel pipe piles include a small-diameter steel pipe 5 and two steel strands 7. Four through holes are symmetrically provided at the bottom of the small-diameter steel pipe 5. Two partially peeled and degreased steel strands 7 pass through the corresponding two through holes in the radial direction of the small-diameter steel pipe 5. Both ends of each steel strand 7 extend beyond the top of the small-diameter steel pipe 5 along the axial direction of the small-diameter steel pipe 5. The steel strands 7 are fixed to the small-diameter steel pipe 5 by binding with fire wire. The peeled and degreased length of the steel strands 7 only needs to be 1 to 2 meters.

[0078] Reference Figure 6 , the same construction as the replacement pile 1 is carried out. According to the small pile hole formed in step S5, a small-diameter steel pipe 5 with a central bracket and tied with two steel strands 7 is hoisted in, and then cement slurry is poured in. Each anchor pile 6 is also composed of 4 to 5 small-diameter steel pipes 5. If there is a slight collapse of the hole, cement slurry can be pressure-filled while the drilling tool is lifted, and then the small-diameter steel pipe 5 with a central bracket and tied with two steel strands 7 is hoisted in. By using partially bonded prestressed pull-out steel pipe piles as anchor piles 6 for static load tests, the disadvantages of welding steel bars on large-diameter steel pipes are overcome, and the disadvantage of cracking the cement slurry is also avoided.

[0079] Reference Figure 7 , which is the construction process flow of partially bonded prestressed pull-out steel pipe piles in this application.

[0080] S8. Cyclic construction: refer to Figure 5 and Figure 6 , looping through steps S5 to S7, during the grouting construction of the underpinning pile 1 or anchor pile 6, the small spiral anchor drill can be moved away to construct a small steel pipe pile on another pile, and then come back to construct another small steel pipe pile on the pile, and the loop is completed to form all the small steel pipe piles to form the underpinning pile 1 or anchor pile 6, and all the small steel pipe piles used as anchor piles 6 are made into partially bonded prestressed pull-out steel pipe piles. A total of 4 to 5 small pile holes are drilled on each underpinning pile (1) or anchor pile (6), and the number of small pile holes corresponds to the number of implanted small-diameter steel pipes (5) or partially bonded prestressed pull-out steel pipe piles.

[0081] By optimizing the design, 4 to 5 small-diameter steel pipes 5 are used to replace one large-diameter steel pipe, which solves the problem of insufficient power of the modified small-length spiral drilling machine. At the same time, it also solves the problem of difficulty in providing reaction force for static pressure implantation of large-diameter steel pipes after rotary grouting.

[0082] S9. Static load test: refer to Figure 8When testing the bearing capacity of the underpinning pile 1, the steel strands 7 in the partially bonded prestressed pullout-resistant steel pipe piles of the anchor piles 6 on both sides are prestressed and locked to the operating tool iron before a static load test is performed. In this embodiment, a jack can be used to perform the bearing test on the underpinning pile 1 during the static load test. The anchor piles 6 on both sides of the underpinning pile 1 provide the tensile force. If the tensile force provided by the anchor piles 6 on the left and right sides of the underpinning pile 1 does not meet the test requirements, additional anchor piles 6 can be added to each side until the underpinning pile 1 meets the static load test requirements.

[0083] S10. Slope protection pile construction: refer to Figure 9 A steel plate 8 is placed at the top of the anchor pile 6. After the static load test, prestress is applied. The steel strand 7 is locked to the steel plate 8 at the top of the anchor pile 6 using an anchor 9, converting the anchor pile 6 into a partially bonded prestressed slope protection pile. This improves the bending resistance of the slope protection pile, and the prestress locking value only needs 20 to 30 kN. In addition, the steel strand 7 can be removed after the static load test to provide a simple slope protection function.

[0084] S11. External wall steel support construction: refer to Figure 10 In the design of this old house renovation project, except for the exterior facade of the building, all other structures are demolished and rebuilt. At the same time, new basement structures are built indoors and outdoors. The exterior walls of the building need to be supported and reinforced, especially at the relatively weak parts such as windows and door openings, to improve safety during the construction process. In this embodiment, a steel frame 110 is erected on the outside of the building wall to support the exterior wall of the building, and a cantilever beam 120 is set at the window opening position to further improve the stability of the building structure. After the support construction is completed, the interior structure can be demolished, and then the unfinished interior underpinning piles 12 can be supplemented until all the designed interior underpinning piles 12 are completed to meet the design requirements and improve safety during the old house renovation process.

[0085] S12. Indoor horizontal support 130 construction: refer to Figure 11 , set up indoor horizontal support 130, indoor horizontal support 130 is combined with the beams of the positive and negative zero floors of the new structure, and serves as permanent beams to improve construction efficiency.

[0086] S13. The force transmission system of the original outer wall and the newly built basement outer wall structure has been converted: Figure 11 , wall beams 140 and underpinning beams 150 are set at the outer walls of the building, which cooperate with the indoor underpinning piles 12 and the outdoor underpinning piles 11 to support the original outer walls of the building, thereby completing the conversion of the force transmission system between the original outer wall and the newly built basement outer wall structure.

[0087] The implementation principle of the embodiment of the present application is: when drilling a hole, a small spiral anchor drilling rig first uses a larger diameter alloy drill bit and drilling tools to drill until the upper end of the drill tool is flush with the ground surface, and then replaces the drill bit and drilling tools with a smaller diameter to drill in the casing. The drilling depth each time is greater than the casing depth until the designed hole depth is reached, the drill bit and drilling tools are pulled out, dry soil is filled into the hole and compacted, and the casing is pulled out a section until the hole mouth is formed after each filling section, and the soil column is formed by cutting the cement soil rotary jet pile according to the designed position and drilling the soil to form a hole.

[0088] During the construction of the underpinning pile 1, the small-diameter steel pipe 5 is implanted in the hole and connected in sections if necessary. Each underpinning pile 1 is composed of 4 to 5 small-diameter steel pipes 5. A central bracket is welded at intervals of 1 to 2 m in the axial direction of the small-diameter steel pipe 5 to improve the stability of the small-diameter steel pipe 5 and prevent it from tilting easily. The anchor pile 6 utilizes the existing small-diameter steel pipe 5 to form a partially bonded prestressed pull-out steel pipe pile. Four through holes are symmetrically provided at the bottom of the small-diameter steel pipe 5. Two partially peeled and degreased steel strands 7 pass through the corresponding two through holes in the radial direction of the small-diameter steel pipe 5. The two ends of each steel strand 7 extend beyond the top of the small-diameter steel pipe 5 along the axial direction of the small-diameter steel pipe 5.

[0089] During the grouting process of underpinning pile 1 or anchor pile 6, the small spiral anchor drill can be moved to work on a small steel pipe pile on another pile, then return to work on another small steel pipe pile on that pile, completing the cycle through all the small steel pipe piles to form underpinning pile 1. Through optimized design, four to five small-diameter steel pipes 5 replace one large-diameter steel pipe, solving the problem of insufficient power for the modified small long spiral drill and also addressing the difficulty in providing reaction force when first jetting and then statically injecting the large-diameter steel pipe.

[0090] The examples of this specific embodiment are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, any equivalent changes made based on the structure, shape, and principle of this application should be included in the scope of protection of this application.

Claims

1. A construction method for underpinning piles and anchor piles for testing, characterized in that: The following steps are involved: S1. Preliminary construction: dock cofferdam construction and site leveling; S2. Determine the pile position: measure, lay out and locate the pile position of the underpinning pile (1) and the occlusal pile (2) and review; S3. Construction with a small geological drilling rig: Using the pile position determined in step S2, drill the hole with casing using a small geological drilling rig. Once the drill reaches the designed depth, remove the drill rig and fill the casing with soil in layers and compact it. After each section is filled, the casing is withdrawn a section until it reaches the hole opening. As the casing is withdrawn, it is reversed and removed section by section, ultimately forming a soil column. S4. Construction of a small rotary jet drilling rig: A small rotary jet drilling rig is in place, and the soil column formed in step S3 is aligned with the drill bit to form a cement soil rotary jet pile at the center of the soil column. The cement soil rotary jet piles on the periphery engage with each other to form a water-stop curtain (4). The underpinning pile (1) that needs to be subjected to a static load test is selected. The underpinning piles (1) on both sides of the underpinning pile (1) are constructed as anchor piles (6); S5. Construction of a small spiral anchor drilling rig: A small spiral anchor drilling rig is in place, and the cement soil jet grouting pile formed in step S4 is formed, and the cement soil jet grouting pile as the underpinning pile (1) and the anchor pile (6) is guided on the drilling rig to drill a small pile hole, and after reaching the designed depth, the drilling tool is lifted and the hole position is removed; S6. Underpinning pile (1) construction: a small diameter steel pipe (5) is implanted into the small pile hole, the segmented hole mouth is connected, and then the grouting pipe is inserted into the bottom of the hole and filled with cement slurry; secondary grouting; S7 anchor pile (6) construction: According to the S5 step forming the small pile hole, the part of the bonded prestressed pull-out steel pile is implanted into the small pile hole, and then the grouting pipe is inserted into the bottom of the hole and filled with cement slurry; secondary grouting; In the step S7, the partially bonded prestressed pull-out resistant steel pipe pile comprises the small-diameter steel pipe (5) and a plurality of steel strands (7), the bottom of the small-diameter steel pipe (5) is symmetrically provided with a plurality of through holes, the partially peeled and degreased steel strands (7) pass through two corresponding through holes in the radial direction of the small-diameter steel pipe (5), and both ends of each steel strand (7) extend in the axial direction of the small-diameter steel pipe (5) and exceed the top of the small-diameter steel pipe (5); S8. Cyclic construction: Cycle steps S5 to S7. During the grouting construction of the underpinning pile (1) or anchor pile (6), construct a small steel pipe pile on another pile, and then come back to construct another small steel pipe pile on the pile, completing the cycle of all small steel pipe piles. A total of 4 to 5 small pile holes are drilled on each underpinning pile (1) or anchor pile (6). The number of small pile holes corresponds to the number of implanted small-diameter steel pipes (5) or partially bonded prestressed pull-out steel pipe piles. S9 static load test: underpinning pile (1) bearing capacity test, the anchor piles (6) on both sides of the partial bonded prestressed pull-out steel pipe piles in the steel strand (7) prestressed lock on the operating tool iron, and then conduct a static load test; S10. Slope protection pile construction: After the static load test is completed, prestressing is applied to lock the steel strand (7) at the top of the anchor pile (6), converting the anchor pile (6) into a partially bonded prestressed slope protection pile.

2. A construction method for underpinning piles and testing anchor piles according to claim 1, characterized in that: In the step S3, first drill with a larger diameter drill bit until the upper end of the drill bit is flush with the ground surface, then replace with a smaller diameter drill bit and drill in the casing. The drilling depth each time is greater than the casing depth until the designed hole depth is reached. Then, remove the drill bit from the casing and fill the hole with dry soil, compacting it after each filling.

3. The construction method of underpinning piles and testing anchor piles according to claim 1, characterized in that: In the step S4, the cement soil jet grouting piles are driven in a staggered manner according to the design requirements, and finally interlock with each other by 15 to 20 cm to form a continuous interlocking jet grouting cement soil water-stop curtain (4).

4. The construction method of underpinning piles and testing anchor piles according to claim 1, characterized in that: After the S4 step is completed, it is necessary to wait for 1 to 2 days before proceeding to the S5 step.

5. The construction method of underpinning piles and testing anchor piles according to claim 1, characterized in that: In the step S5, there is a slight hole collapse during the process of lifting the drill tool. Cement slurry is pressure-filled while the drill tool is lifted, and then the step S6 is performed.

6. The construction method of underpinning piles and testing anchor piles according to claim 1, characterized in that: The length of the peeled and degreased section of the steel strand (7) only needs to be 1 to 2 m.

7. The construction method of underpinning piles and testing anchor piles according to claim 1, characterized in that: In the step S10, the prestress locking value only needs to be 20 to 30 kN.

8. The construction method of underpinning piles and testing anchor piles according to claim 1, characterized in that: If the underpinning pile (1) cannot be formed in one step, it will be made in a subsequent step.

9. The construction method of underpinning piles and testing anchor piles according to claim 1, characterized in that: In the step S10, the steel strands are cut off after the static load test is completed.

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