CFG pile reinforcement construction method

Abstract

This invention belongs to the field of CFG pile reinforcement and provides a CFG pile reinforcement construction method, including: drilling or slotting the bottom of the implanted steel pipe to maintain communication between the inner and outer grout surfaces; symmetrically arranging multiple threaded steel bars along the outer wall of the implanted steel pipe from top to bottom to a depth of 1.8-2m on the upper part of the implanted steel pipe; connecting the steel bars and the steel pipe by welding; setting locators at intervals of 1.8-2m on the implanted steel pipe, with multiple symmetrically arranged; positioning and laying out the CFG pile to be reinforced, and then drilling a hole; inserting the implanted steel pipe to the bottom of the hole, while ensuring that the top surface of the implanted steel pipe is flush with the top surface of the original pile; grouting the hole with cement grout, using a water-cement ratio of 0.40-0.50, and ensuring that the 28-day compressive strength of the cement grout is not less than 30 MPa, followed by curing. This invention effectively solves the problem of insufficient bearing capacity of CFG piles. Three sets of single pile static load tests, four sets of single pile composite foundation tests, and pile integrity tests were conducted on the reinforced CFG piles, and all of them met the current national standards and design testing requirements.

Description

Technical Field

[0001] This invention belongs to the field of CFG pile reinforcement, and specifically relates to a CFG pile reinforcement construction method, which improves the bearing capacity of CFG piles and their composite foundations by increasing the bearing capacity of CFG piles and improving their bearing characteristics. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] CFG pile composite foundation technology has been rapidly developed and applied due to its convenient construction process, small foundation deformation, and low cost.

[0004] However, during construction, it is inevitable that some CFG pile composite foundations will fail to meet the design requirements, especially when the bearing capacity of the pile body is insufficient, resulting in the bearing capacity of the single pile composite foundation not meeting the design requirements.

[0005] Patent CN113431035A discloses a CFG pile reverse-insertion steel pipe device and its construction method. Its main purpose is to solve the problem of pile fracture during CFG pile excavation due to the lack of reinforcement in the upper part of the pile. The method provides a construction approach that increases the shear bearing capacity of the pile by adding a steel pipe to the upper part of the pile during construction, thereby reducing pile fracture caused by excavation collisions. Based on construction experience, pile fractures caused by excavation generally occur about 2 meters below the pile top. Therefore, the steel pipe inserted to solve this problem is very short, limited to a shallow depth in the upper part of the pile. The bearing characteristics of the CFG pile do not change. The above design does not aim to improve the bearing capacity of the CFG pile, but mainly aims to improve the integrity of the upper part of the CFG pile, and cannot significantly improve the bearing capacity of the CFG pile.

[0006] Patent CN112832233A discloses an improved CFG pile construction method. Its design purpose is the same as that of patent 202011633164.X. In essence, both involve setting short steel pipes (no more than 4m in length) in the shallower part of the upper part of the CFG pile. Both are carried out before the initial setting of concrete. The above design mainly improves the shear resistance of the upper part of the pile body and prevents pile breakage. However, due to the short steel pipe, the bearing characteristics of the CFG pile are not changed, and the bearing capacity of the pile body cannot be significantly improved. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a CFG pile reinforcement construction method to effectively improve the bearing capacity of CFG piles and their composite foundations.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for constructing CFG pile reinforcement, comprising:

[0010] Based on the concrete strength of the pile body tested by CFG concrete core sampling, the CFG pile body bearing capacity compensation value is determined. The calculation method of the load compensation value is given in "1 Load Compensation Value Design".

[0011] The bearing capacity of CFG piles is improved by drilling holes inside the piles and inserting steel pipes. The length and wall thickness of the inserted steel pipes are determined by calculation (see "2 Steel Pipe Design" for the calculation method). The length of the inserted steel pipes is greater than 2 / 3 of the original CFG pile length. Holes or grooves are made at the bottom of the steel pipes to maintain communication between the inner and outer grout surfaces.

[0012] Multiple threaded steel bars are symmetrically arranged along the outer wall of the steel pipe, from top to bottom, to a depth of 1.8-2m, above the implanted steel pipe to increase the anchorage force between the steel pipe and the grouting material in the CFG pile. This enhances the deformation coordination between the CFG pile concrete and the steel pipe during operation. Anchorage lengths of 35d (d is the diameter of the steel bar) are used between the steel bars and the steel pipe, connected by welding (see details for welding requirements). Figure 2 );

[0013] Positioners are installed at 1.5m intervals along the implanted steel pipe. The positioners are constructed by symmetrically welding multiple short steel bars (18mm-20mm in diameter, 5cm-10cm in length) along the outer circumference of the steel pipe. The steel bars are made of threaded steel, which also increases the anchoring force at the interface between the steel pipe and the grouting material, thus enhancing the deformation coordination between the CFG pile concrete and the steel pipe during operation. (See details of the steel pipe positioner arrangement.) Figure 2 )

[0014] The CFG piles to be reinforced are positioned and laid out, and then holes are drilled. The diameter of the pile hole is about 40mm larger than the designed outer diameter of the steel pipe to be inserted, generally 130~150mm. The designed drilling depth is determined by calculation and should not be less than 2 / 3 of the original CFG pile length.

[0015] Insert the steel pipe to the bottom of the hole, and at the same time, make the top surface of the inserted steel pipe level with the top surface of the original pile.

[0016] The grouting inside the borehole uses cement grout with a water-cement ratio of 0.40~0.50. The cement grout aggregate has a compressive strength of not less than 30 MPa after 28 days. After curing, the grout is ready.

[0017] The purpose of this invention is to address the problem that CFG piles have high soil resistance around them, but the pile bearing capacity is insufficient due to design or construction reasons. By implanting steel pipes, the bearing capacity of the pile body is significantly increased, thereby allowing the soil around the pile to fully exert its bearing capacity on the CFG pile, greatly improving the bearing capacity of the pile body and significantly improving the bearing characteristics of the CFG pile.

[0018] The CFG composite micro steel pipe pile construction technology of this invention is mainly used for the reinforcement of existing CFG foundation piles. When the bearing capacity of the original composite foundation cannot meet the design requirements, if a supplementary pile scheme is adopted, the original pile spacing is less than the minimum spacing requirement for supplementary piles, making supplementary piles unsuitable; or, the on-site construction conditions for large-scale pile foundation construction machinery are not met, and the supplementary pile construction process is prone to crushing or breaking the existing CFG foundation piles, easily disturbing the excavated foundation soil, and reducing the bearing capacity of the foundation soil, making supplementary piles unsuitable. Supplementary piles are also very expensive and have a long construction period.

[0019] Beneficial effects of the present invention

[0020] (1) The “CFG composite micro steel pipe pile construction technology” of the present invention, which adopts the construction process of drilling holes on the top of CFG piles, inserting steel pipes, and injecting high-strength cement grout (or cement mortar), has the following advantages: the construction equipment is very small, and a small geological exploration drilling rig can be used to enter the site for construction, and the construction process causes little disturbance to the surrounding foundation soil layer. The construction speed is fast, and one drilling rig can drill 70m linear meters per day to complete about 10 reinforced piles. Multiple drilling rigs can be used for construction on site at the same time, and the construction period is reduced by more than half compared with the ordinary pile supplementation method. Based on the inventor's existing engineering CFG composite micro steel pipe pile construction technology promotion and construction experience, the CFG pile reinforcement scheme of the present invention can save more than 40% of the project cost of CFG pile foundation reinforcement treatment compared with the traditional pile supplementation scheme.

[0021] (2) The CFG composite micro steel pipe pile is a new type of pile proposed in this invention. Its stress conditions are fundamentally different from those of existing technologies. For example, patents CN113431035A and CN112832233A mainly focus on horizontal shear resistance, and the vertical compressive bearing capacity of the CFG pile body is still completely determined by the strength of the CFG pile concrete. The stress conditions designed in this invention are mainly based on vertical compression. The wall thickness of the steel pipe needs to be determined by the compensation bearing capacity calculation. The length of the steel pipe is greater than or equal to two-thirds of the pile length, or it can be arranged along the entire length. Considering the large vertical shear stress at the contact interface between the steel pipe and the surrounding CFG piles, in order to increase the bonding force under compression and improve the vertical shear bearing capacity of the steel pipe in contact with the grout, this invention adopts the measure of welding threaded steel on the outer wall of the steel pipe.

[0022] (3) For CFG piles constructed using this invention, static load tests on the foundation have demonstrated that inserting a steel pipe two-thirds the length of the CFG pile into the pile reduces the settlement of the pile and composite foundation by more than 50% under the same load, significantly improving the bearing capacity of the foundation while significantly reducing the deformation. The ability of the CFG pile to resist shear loads and horizontal seismic forces is greatly enhanced after the steel pipe is inserted. Using this method, the reinforced CFG piles significantly improve the seismic performance of the building foundation without altering the original foundation and superstructure design.

[0023] After reinforcement with steel pipes, CFG piles are primarily used in composite foundations, but can also be applied as pile foundations. When designing as pile foundations, welded reinforcing bars within the steel pipe can be anchored into the pile cap for integral connection. To avoid incompatibility between the core pile and the CFG concrete at the pile top, threaded reinforcing bars can be arranged at a depth of not less than 2D (D being the CFG pile diameter) and not less than 2m at the pile top to increase the anchoring force at the interface between the steel pipe and the grouting material. By strengthening the anchoring effect between the steel pipe and the grouting material, excessive stress concentration at the top of the core pile can be avoided when the reinforced pile is used as a pile foundation; or when a cushion layer is set above the top of the reinforced pile as a composite foundation reinforcement, the load shared by the core pile at the pile top may be too small, resulting in an excessive load shared by the CFG pile concrete. The reinforcement construction technology of CFG composite micro-steel pipe piles has great design applicability for CFG pile reinforcement, broad application prospects, and will undoubtedly bring significant social benefits.

[0024] (4) The construction method of the present invention is simple, practical and easy to promote. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] Figure 1 This is a schematic diagram of the device structure of the present invention;

[0027] Figure 2 This is a schematic diagram of the reinforcement treatment of the present invention. Detailed Implementation

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] A method for CFG pile reinforcement construction includes:

[0030] The bottom of the implanted steel pipe will be drilled or grooved to keep the inner and outer slurry surfaces connected;

[0031] Multiple threaded steel bars are symmetrically arranged along the outer wall of the steel pipe, from top to bottom, to a depth of 1.8-2m, above the implanted steel pipe to increase the anchorage force at the interface between the steel pipe and the grouting material, and to enhance the coordinated deformation of the CFG pile concrete and the steel pipe. The steel bars and the steel pipe are connected by welding; welding requirements are detailed in [link to welding instructions]. Figure 2 ;

[0032] Positioners are installed at 1.5-2m intervals along the implanted steel pipe. Multiple positioners are constructed by welding short steel bars (5-10cm long, 18-20mm in diameter) along the outer circumference of the steel pipe, arranged symmetrically. The arrangement requirements are detailed below. Figure 2 The locator uses threaded steel, which also serves to increase the anchoring force between the steel pipe and the injection material, so that the deformation of the pile concrete and the steel pipe is coordinated and strengthened when the CFG pile is working.

[0033] The CFG piles to be reinforced are positioned and laid out, then holes are drilled. The hole diameter is 130-150mm, which is about 40mm larger than the outer diameter of the inserted steel pipe. The designed drilling depth is determined by calculation and should not be less than 2 / 3 of the CFG pile length.

[0034] Insert the steel pipe to the bottom of the hole, and at the same time, make the top surface of the steel pipe level with the top surface of the original pile.

[0035] The grouting inside the borehole uses cement grout with a water-cement ratio of 0.40~0.50. The strength of the cement grout is not less than one grade higher than that of the original CFG pile concrete, and the 28-day compressive strength of the aggregate is not less than 30 MPa. After curing, the grout is ready.

[0036] The steel pipes in patents 202110835262.X and 202011633164.X are installed during the pouring of superfluid concrete for CFG piles, before the concrete has solidified. The installed steel pipes are short, generally not exceeding 4m.

[0037] The "CFG composite micro steel pipe pile construction technology" of this invention is carried out after the CFG pile construction is completed and the concrete has solidified. A hole (approximately 130mm in diameter, determined based on bearing capacity compensation strength calculations and steel pipe construction) is drilled in the center of the CFG pile. A steel pipe is inserted and filled with high-strength cement grout or cement mortar. To increase the adhesion between the steel pipe and the grout, a micro-expansion agent can be added to the grout or threaded steel bars can be welded onto the steel pipe. The wall thickness of the steel pipe is determined based on the pile's bearing capacity compensation calculations. The structural requirement for the steel pipe length is not less than two-thirds of the pile length, but it can also be greater than the original CFG pile length based on bearing capacity design requirements. After reinforcement using the above process, a composite pile is formed by the outer cement fly ash crushed stone concrete pile (CFG) and the centrally inserted micro steel pipe, filled with high-strength cement grout.

[0038] The construction equipment for the "CFG composite micro steel pipe pile construction technology" in this application can be a trackless engineering survey drilling rig or a portable cast-in-place pile drilling rig. It requires minimal construction space, causes minimal disturbance to the site's foundation soil, allows multiple drilling rigs to operate simultaneously, and results in fast construction speed and a short construction period. The steel pipe installation construction described in patent numbers 202110835262.X and document 2202011633164.X is combined with the CFG pile construction process and both utilize large drilling rigs.

[0039] In some embodiments, the implanted steel pipe is a Q345 seamless steel pipe with a diameter of 89~92mm, a wall thickness of not less than 7.38mm, and a standard value of axial compressive yield bearing capacity of not less than 650kN; the design length of the steel pipe is 7.5~8m, and the allowable deviation of the steel pipe length is ±100mm.

[0040] In some embodiments, threaded steel bars are welded to the upper part of the implanted steel pipe for reinforcement. The strength grade of the steel bars is not less than HRB335, the diameter is 16~18mm, the length of a single bar is not less than 1.8m, and 4~8 threaded steel bars are welded to each steel pipe.

[0041] In some embodiments, the allowable deviation of the horizontal position of the drilled pile location is 10~12mm.

[0042] In some embodiments, the allowable deviation for borehole verticality is 1% to 1.2%.

[0043] In some embodiments, the height of the top surface of the steel pipe is flush with the height of the original pile top surface, and the allowable height deviation is ±10mm.

[0044] In some embodiments, the connection between the reinforcing bars and the steel pipe is made by welding, with intervals of 45~50cm. Double-sided welding is not less than 8cm, or single-sided welding is not less than 16cm. When single-sided welding is used, the weld points are symmetrically distributed on the left and right.

[0045] In some embodiments, when grouting begins, the grouting pipe should start from the bottom of the hole, and the distance between the guide pipe and the bottom of the hole should not be greater than 20 mm.

[0046] During the grouting process, the drill rod should be kept embedded in the cement grout, and the depth below the grouting surface should be no less than 2.5m.

[0047] In some embodiments, the over-grouting volume is controlled, and grouting can only be stopped when the following conditions are met:

[0048] 1) The slurry overflows from the borehole and its viscosity is consistent with the injected slurry;

[0049] 2) The surface where the grouting stops should be at least 15cm higher than the top of the original pile;

[0050] 3) The grouting volume for over-grouting shall not be less than 2.0m of the borehole length, which is 25% of the theoretical grouting volume of the total borehole length.

[0051] In some embodiments, specific maintenance measures include:

[0052] 1) During grouting, the average daily temperature should not be lower than 5℃. When the average daily temperature is lower than 5℃, the winter construction measures specified in the current standards should be followed.

[0053] 2) After grouting is completed, the exposed parts should be sprayed with curing agent or covered with plastic film in time, and covered with straw bags to keep them moist; when using plastic film to cover, it should be covered tightly to keep water condensing inside the film;

[0054] 3) The grouting material should be kept moist for at least 10 days.

[0055] 4) During winter construction, after grouting is completed, plastic film should be covered and insulation material should be added in time; the initial curing temperature should not be lower than 5℃; water should not be poured when curing under negative temperature conditions.

[0056] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0057] The following embodiments illustrate the reinforcement design calculations:

[0058] 1. Load compensation value design

[0059]

[0060]

[0061] 2. Steel pipe design

[0062] 2.1 The design parameters of the steel pipe section should meet the following formula.

[0063]

[0064]

[0065] 2.2 The design calculation of steel pipe length shall meet the following formulas.

[0066]

[0067]

[0068]

[0069]

[0070] The length of the steel pipe should also meet the structural requirement of not less than 2 / 3 times the length of the CFG pile.

[0071] 2.3 Determination of Drilling Depth

[0072] The drilling depth shall not be less than the length of the steel pipe. When the design length of the steel pipe is less than the length of the CFG pile, the drilling depth shall be determined by Article 2.2.

[0073] 2.4 Strength Requirements for Steel Pipe Grouting Materials

[0074] The strength of the grouting material inside the CFG pile borehole should be higher than the strength of the original CFG pile concrete, and should not be lower than 30 MPa.

[0075] Example 1

[0076] I. Project Overview

[0077] Building #1 of XX Residential Complex is located in XX City. This project utilizes a CFG pile composite foundation, with a total of 188 piles. The design grade of the pile concrete strength is C25, and the effective pile length is 11m. The original design pile diameter was 600mm, but the diameter was increased to 800mm in some areas below the pile top. The design characteristic value of the vertical compressive bearing capacity of a single pile is 1900kN, and the design characteristic value of the composite foundation bearing capacity is 600kPa.

[0078] II. Engineering Geological Overview

[0079] Within the drilling depth range, the strata at this site can be divided into 5 layers, and the strata distribution is as follows:

[0080] 1. Miscellaneous fill; 2. Plain fill; 3. Silty clay; 4. Completely weathered argillaceous conglomerate; 5. Strongly weathered argillaceous conglomerate; 6. Moderately weathered argillaceous conglomerate.

[0081] III. Analysis of Test Results and Reasons for Non-compliance

[0082] (a) Test pile testing

[0083] A total of 3 sets of test piles with a diameter of 600mm were tested, and 3 sets of single-pile composite foundations were tested, all of which met the design requirements.

[0084] (II) Project Acceptance Testing

[0085] Four groups of monopile composite foundations were tested, with eight levels of loading applied. The characteristic value of the composite foundation bearing capacity was 525 kPa for all groups, which is less than the design bearing capacity of 75 kPa for monopile composite foundations, and therefore fails to meet the design requirements. The test loading details are as follows:

[0086] Test points 87#, 88#, 89#, and 93# were loaded in eight stages, with each stage increasing by 150 kPa. Loading was applied in equal increments until reaching 1200 kPa. At this point, the cumulative settlement of the bearing plate was 6% (120 mm) of its width or diameter, at which point loading was terminated and the load was unloaded. Excavation verification confirmed that all piles exhibited concrete cracking, indicating that the load could not be sustained. Low-strain testing of the above-mentioned substandard piles showed no severe defect reflections; core sampling revealed that the core sample strength did not meet design requirements. Analysis indicates that the reason for the substandard bearing capacity of the single-pile composite foundation is insufficient pile bearing capacity, necessitating reinforcement and strengthening of the pile body.

[0087] Test load plate area 4m 2The maximum test load should be 4800kN, the actual maintenance load should be 4200kN, and the reinforcement design value of the single pile bearing capacity should not be less than 600kN.

[0088] Note: For detailed information on foundation testing, please refer to the testing report from Shandong Provincial Construction Engineering Quality Inspection and Testing Center.

[0089] IV. CFG Pile Reinforcement Treatment Scheme

[0090] The CFG pile reinforcement and strengthening method adopts a construction scheme of drilling a core in the middle of the engineering pile, inserting a steel pipe, and then grouting.

[0091] (I) Design Basis

[0092] 1. Current standards: GB 50007 "Code for Design of Foundation", JGJ 79 "Technical Specification for Foundation Treatment of Buildings", GB / T 50448 "Technical Specification for Application of Cement-based Grouting Materials", and DBJ / T 14 "Technical Specification for Safety Appraisal of Building Foundations".

[0093] 2. Technical documents provided by Party A and the construction party

[0094] Engineering geological survey report, design and construction data (including preliminary reinforcement design and construction data), engineering (pile location) plan, relevant test reports (static load test, low strain test, core specimen compressive strength test), etc.

[0095] (II) Scope of Reinforcement

[0096] The remaining 179 piles that did not pass the static load test of single piles and single pile composite foundations.

[0097] (iii) Reinforcing materials

[0098] The specifications and performance parameters of the materials used for reinforcement are as follows:

[0099] 1. The steel pipe is a Q345 seamless steel pipe with a diameter of 89mm, a wall thickness of not less than 7.38mm, and a standard value of axial compressive yield bearing capacity of not less than 650kN. The design length of the steel pipe is 7.5m, and the allowable deviation of the steel pipe length is ±100mm.

[0100] 2. The upper part of the steel pipe is reinforced with threaded steel bars. The strength grade of the steel bars is not less than HRB335, the diameter is 16mm, the length of a single bar is not less than 1.8m, and 4 threaded steel bars are welded to each steel pipe.

[0101] 3. Ordinary Portland cement is used, with a strength grade of not less than 42.5.

[0102] (iv) Reinforcement construction and allowable deviations

[0103] 1. The layout of the drilled pile positions shall be based on the existing layout records of the original pile positions, and the allowable deviation of the horizontal position shall be 10mm.

[0104] 2. The borehole diameter is 130mm, the designed borehole depth is 7.5m, and the allowable deviation of the borehole verticality is 1%.

[0105] 3. The steel pipe should be inserted to the bottom, and the top surface of the steel pipe should be level with the top surface of the original pile. The allowable height deviation is ±10mm.

[0106] 4. The implanted steel pipe should undergo the following processing:

[0107] (1) The bottom of the steel pipe should be perforated or slotted to keep the inner and outer slurry surfaces connected.

[0108] (2) For the implanted steel pipe, the upper part is reinforced. Along the outer wall of the steel pipe from top to bottom to a depth of 1.8m, four 16mm diameter threaded steel bars are symmetrically arranged for reinforcement. The connection between the steel bars and the steel pipe is welded. Every 45cm interval, the double-sided weld is not less than 8cm (or the single-sided weld is not less than 16cm. When using single-sided welding, the weld points should be symmetrical from left to right).

[0109] (3) Positioners are installed at intervals of 1.8m on the steel pipe. The positioners are made of short steel bars with a diameter of 18mm and a length of 5cm to 10cm welded on the outer side of the circumference, and three are arranged symmetrically.

[0110] 5. Cement grout is used for grouting inside the borehole, with a water-cement ratio of 0.40~0.50. The 28-day compressive strength of the cement grout aggregate should not be less than 35MPa (Note: If experienced, an appropriate amount of expansion agent should be added for slight expansion).

[0111] (1) When grouting begins, the grouting pipe should start from the bottom of the hole, and the distance between the guide pipe and the bottom of the hole should not be greater than 20mm. During the grouting process, the drill rod should be kept buried in the cement grout and at a depth of not less than 2.5m below the grouting surface.

[0112] (2) Control the over-grouting volume. Grouting can only be stopped when the following conditions are met:

[0113] 1) The slurry overflows from the borehole and its viscosity is consistent with the injected slurry;

[0114] 2) The surface where the grouting stops should be at least 20cm higher than the top of the original pile (partial enclosure is acceptable).

[0115] 3) The grouting volume for over-grouting shall not be less than 2.0m of the borehole length (25% of the theoretical grouting volume of the total borehole length).

[0116] (3) When the grout shrinkage and the drop in the grouting surface affect the curing of the grout in the borehole, grouting replenishment measures should be taken in time before the cement grout sets.

[0117] (4) Post-grouting curing measures:

[0118] 1) During grouting, the average daily temperature should not be lower than 5℃. When the average daily temperature is lower than 5℃, the winter construction measures specified in the current standards should be followed.

[0119] 2) After grouting is completed, exposed areas should be sprayed with a curing agent or covered with plastic film in a timely manner, and covered with straw bags to keep them moist. When using plastic film, it should be covered tightly to ensure that condensation forms inside the film.

[0120] 3) The grouting material should be kept moist and the curing time should not be less than 10 days.

[0121] 4) During winter construction, after grouting is completed, cover the site with plastic film and then add insulation material. The initial curing temperature should not be lower than 5℃. Do not water the site during curing at sub-zero temperatures.

[0122] 6. Records should be kept for the reinforcement work of each pile:

[0123] (1) Drilling depth; (2) Steel pipe insertion length + reinforcement length; (3) Cement grout water-cement ratio; (4) Theoretical cement grout injection volume; (5) Actual cement grout injection volume.

[0124] 7. Matters not covered herein shall be handled in accordance with the relevant provisions of the current national and provincial standards.

[0125] V. Quality Control Measures

[0126] 1. A construction organization design should be prepared before construction and submitted to the client, supervision unit, and design unit for approval.

[0127] 2. Construction must be carried out strictly in accordance with the reinforcement plan. In case of any special circumstances, relevant parties must be notified in a timely manner and approval must be obtained before proceeding.

[0128] 3. Each process can only proceed to the next process after it has been approved by Party A and the supervisor.

[0129] VI. Quality Inspection

[0130] 1. Material Inspection

[0131] Material inspection shall be carried out in accordance with the relevant requirements of the "Standard for Acceptance of Construction Quality of Building Foundation" GB 50202. Materials may only be used after a qualified inspection report is submitted before construction.

[0132] 2. Cement grout test block strength inspection

[0133] The compressive strength of the cement grout specimens left on site shall not be less than 35 MPa, and the specimens shall be left according to the following requirements:

[0134] (1) Six cubic specimens with a side length of 70.7 mm should be reserved for each group and cured for 28 days according to standard.

[0135] (2) One set is retained for each shift.

[0136] 3. After CFG pile reinforcement, quality inspection should be carried out, including 3 sets of single pile static load tests, 4 sets of single pile composite foundation tests, and low-strain pile integrity testing of 37 piles. The static load tests should be conducted in accordance with the relevant provisions of the current standards "Technical Specification for Building Foundation Treatment" JGJ 79 and "Technical Specification for Testing Building Foundation Piles" JGJ 106.

[0137] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A CFG pile reinforcement construction method, characterized in that, The application relates to a CFG pile reinforcing method. The concrete strength of the CFG pile is detected by coring according to the CFG concrete, and the bearing capacity compensation load of the CFG pile is determined according to the CFG concrete; the compensation load is determined by calculation; The design calculation formula of the load compensation value is as follows: ； wherein, represent the design pile shaft bearing capacity compensation value (N) under the basic combination of action effects; Representative design CFG pile single pile vertical compressive bearing capacity characteristic value (N); Representative CFG pile core concrete axial compressive strength design value (MPa); CFG pile forming process coefficient, should be in accordance with the relevant provisions of the existing national standards value; The net section area of the CFG pile body after deducting the area of the core hole in the pile. The bearing capacity of the CFG pile is improved by drilling a hole in the CFG pile and implanting a steel pipe; the length and wall thickness of the implanted steel pipe are determined by calculation, the length of the implanted steel pipe is greater than 2 / 3 times the length of the original CFG pile, and the bottom of the steel pipe is provided with a hole or a groove to keep the internal and external slurry surfaces connected; The length and thickness of the implanted steel pipe in the hole are determined according to the following formula: The steel pipe section parameter design should satisfy the following formula: ； wherein represents the design value of the axial pressure of the steel pipe under the basic combination of action effects, which takes the design pile shaft bearing capacity compensation value (N); t represents the wall thickness (mm) of the steel pipe; d represents the outer diameter (mm) of the steel pipe; Representative steel compressive strength design value (MPa) shall be taken according to the relevant provisions of the current national standards; The steel pipe length calculation design should satisfy the following formula: ; ; ; wherein, represents the compensation value of the pile shaft bearing capacity (kN) under the basic combination of action effects; D represents the diameter (m) of the CFG pile; represents the thickness (m) of the i-th layer of soil in the range of the arrangement length of the steel pipe; The representative CFG pile side soil friction characteristic value (kPa) shall be valued according to the relevant provisions of the current national industry standard "Building Foundation Treatment Specification" JGJ 79. represents the length of the steel pipe arrangement (m), represents the length of the steel pipe arrangement (m); Lambda represents the bonding coefficient of the steel pipe and the grouting material, and is generally 0.08; The compressive strength of the grouting material test block at the age of 28 days under the indoor standard curing condition is the same as that of the pile body. Represents the outer perimeter of the steel pipe; Note: The length of the steel pipe is calculated in the following , , The symbols have the same meanings as the above formula; A plurality of threaded steel bars are symmetrically arranged on the upper part of the implanted steel pipe from the top to a depth of 1.8-2 m along the outer wall of the steel pipe; the threaded steel bars and the steel pipe are connected through welding; Positioning devices are arranged every 1.8-2 m on the implanted steel pipe, the positioning devices are symmetrically arranged and are made of 5 cm-10 cm short steel bars with a diameter of 18 mm welded on the circumferential outer side; The CFG pile to be reinforced is positioned and laid out, then a hole is drilled, the drilling diameter is 130-150 mm, is greater than the outer diameter 38-42 mm of the implanted steel pipe, the drilling design depth is determined by calculation and is not less than 2 / 3 times the length of the CFG pile; The implanted steel pipe is passed into the hole bottom, and the top surface height of the implanted steel pipe is flush with the original pile top surface height; Cement slurry is used for hole grouting, the water-cement ratio is 0.40-0.50, the cement slurry strength is not less than 1 grade higher than that of the original CFG pile concrete, the 28d compressive strength grade of the cement slurry stone is not less than 30 Mpa, and the cement slurry is cured.

2. The CFG pile reinforcement construction method according to claim 1, wherein The implanted steel pipe is a Q345 seamless steel pipe, the diameter is 89-92 mm, the wall thickness is not less than 7.38 mm, and the axial compression bearing capacity design value is not less than 650 kN; the design length of the steel pipe is 7.5-8 m, and the allowable deviation of the steel pipe length is + / -100 mm.

3. The CFG pile reinforcement construction method according to claim 1, wherein The upper part of the implanted steel pipe is welded with threaded steel bars, the strength grade of the steel bars is not less than HRB335, the diameter is 16-18 mm, the single length is not less than 1.8 m, and 4-8 threaded steel bars are welded on each steel pipe.

4. The CFG pile reinforcement construction method according to claim 1, wherein The horizontal position allowable deviation value of the hole drilling pile position is 10-12 mm.

5. The CFG pile reinforcement construction method according to claim 1, wherein The verticality allowable deviation value of the hole is 1%-1.2%.

6. The CFG pile reinforcement construction method according to claim 1, wherein The top surface height of the steel pipe is flush with the original pile top surface height, and the height allowable deviation is + / -10 mm.

7. The CFG pile reinforcement construction method according to claim 1, wherein The connection between the steel bars and the steel pipe is welding, every 45-50 cm, double-sided welding is not less than 8 cm, or single-sided welding is not less than 16 cm, when single-sided welding is adopted, the welding points are symmetrically distributed on the left and right sides.

8. The CFG pile reinforcement construction method according to claim 1, wherein When the grouting starts, the grouting pipe should start from the hole bottom, and the distance between the pipe and the hole bottom should be not greater than 20 mm; During the grouting process, the drill rod is kept buried in the cement slurry, and the depth below the grouting surface is not less than 2.5 m.

9. The CFG pile reinforcement construction method according to claim 1, wherein When the following conditions are met, the grouting can be stopped: 1) the slurry overflows the hole and has the same consistency as the injected slurry; 2) the slurry injection surface is higher than the original pile top surface by not less than 15 cm. 3) The grouting quantity should be more than 2.0m, which is 25% of the length of the borehole.

10. The CFG pile reinforcement construction method as claimed in claim 1, wherein, The specific measures of maintenance include: 1) The average daily temperature should not be lower than 5℃ when grouting, and the construction should be carried out according to the current standard when the average daily temperature is lower than 5℃; 2) The exposed part should be sprayed with curing agent or covered with plastic film after grouting, and the grass bag should be covered to keep it wet. When using plastic film, it should be covered tightly to keep the film wet; 3) The grouting material should be kept in a wet state, and the maintenance time should not be less than 10d; 4) When constructing in winter, the plastic film should be covered after grouting, and the starting maintenance temperature should not be lower than 5℃. When maintaining under negative temperature conditions, water should not be poured.

Images