Pile vertical compressive static load test method

Abstract

The present application relates to the field of pile foundation load test method, and specifically discloses a kind of pile vertical compressive static load test method, comprising: reinforcing pressure end, installing jack, installing measuring device, building pressure platform, loading test and unloading test and other steps, wherein in the step of installing test device, by embedding the casing in the top layer soil of experimental site and driving the reference pile into the bottom layer soil from the center position of the casing, an isolation zone is formed between the reference pile and the casing, so that during the loading test and unloading test, the influence of the deformation of the top layer soil caused by extrusion and rebound on the position of the reference pile can be reduced, and the offset and measurement error can be greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of pile foundation load testing methods, and specifically relates to a method for testing the vertical compressive static load of piles. Background Technology

[0002] The static load test for vertical compressive strength of piles is a testing method used to evaluate the vertical compressive bearing capacity of piles. Its basic principle is to uniformly transfer the vertical load to the foundation piles of the building, and obtain the Q-s curve and auxiliary curves such as s-lg t of the static load test by measuring the settlement of the pile top under different loads. Then, the characteristic value of the vertical compressive bearing capacity of the single pile and other parameters are derived from the curves.

[0003] The experiment mainly used hydraulic jacks, reaction devices, and measuring devices. Among them, the counterweight platform is a commonly used reaction device structure, which includes supports, counterweights, main beams, and secondary beams. The measuring device includes a reference pile, a reference beam, a magnetic base, and a displacement gauge (or dial gauge). In use, the hydraulic jacks apply a load to the main beam, and the displacement gauge is used to accurately measure the settlement displacement of the pile. However, during use, because the shallow soil is close to the support and the soil itself has a resilient modulus, when the hydraulic jack applies a load, the soil in the upper pile hole of the reference pile can rebound and move. When the hydraulic jack unloads the load, the supporting pressure of the support increases, causing the surface soil at its bottom to move outward. This, in turn, causes the soil in the upper pile hole of the reference pile to be subjected to lateral compressive force and thus move horizontally. As a result, the upper end of the reference pile will tilt, causing the reference beam to jump vertically, affecting the error value of the settlement of the pile measured by the displacement gauge. At the same time, when large construction equipment is operating around the construction site, it will also cause some disturbance to the positioning of the reference pile.

[0004] Patent document with application number "CN201910876551.7" discloses a pile foundation static load test structure and its testing method, including a counterweight, a platform set at the bottom of the counterweight, a main beam set at the bottom of the platform directly above the pile foundation, a jack set between the main beam and the pile foundation, and a dial gauge set on the pile foundation for detecting pile foundation settlement. It also includes supports set at the bottom of the platform on both sides of the pile foundation and load-bearing platforms set at the bottom of the supports and wider than the supports. A connecting device is provided between the load-bearing platforms and the platform to connect the load-bearing platforms and the supports to the platform. In the prior art, when the jack is loaded and unloaded, the shallow soil around the load-bearing platform at the bottom of the supports is still squeezed or rebounded, which causes the reference pile on which the dial gauge is installed to be displaced and produce errors. Therefore, the method in the prior art still has the problems mentioned above.

[0005] The above background information is provided only to aid in understanding the inventive concept and technical solution of this invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above information was disclosed on the filing date of this patent application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0006] The purpose of this invention is to provide a method for testing the vertical compressive static load of piles, thereby overcoming the shortcomings of existing pile compressive static load tests, where the upper soil of the reference pile shifts due to compression and rebound during jack loading and unloading, leading to increased measurement errors of the displacement gauge.

[0007] To achieve the above objectives, the present invention provides a method for testing the vertical compressive static load of a pile, comprising the following steps: S1. Reinforce the bearing end: Cast or install a pile cap on the pile head of the pile being tested, and install a measuring plate; S2. Install jacks: Install jacks on the top of the pile cap, connect the oil pump and pressure sensor, and install the support and main beam; S3. Install measuring device: Install the casing, install the reference pile at the center of the casing, build a support beam and reference beam on the reference pile, and install the magnetic base and displacement gauge on the reference beam so that the measuring end of the displacement gauge abuts against the measuring plate. S4. Construct a counterweight platform: Construct secondary beams on the supports and place counterweight blocks; S5. Loading test: The pile under test is loaded in a graded loading manner. After each load is applied, the load is maintained for a specified time and the settlement at the top of the pile is measured at different time intervals. S6. Unloading test: The pile under test is unloaded in stages. During unloading, the load of each stage is maintained for a certain period of time and the settlement at the top of the pile is measured in different time periods. After unloading to zero, the maintenance time is not less than 3 hours and the residual settlement at the top of the pile is measured in different time periods.

[0008] Preferably, in the above technical solution, in step S1, the measuring plate is fixedly installed on the side of the pile cap, and the installation position is 200mm below the top of the pile cap.

[0009] Preferably, in the above technical solution, in step S1, when the diameter or side width of the pile being tested is greater than 500mm, four measuring plates should be symmetrically placed around it; when the diameter or side width of the pile being tested is not greater than 500mm, two measuring plates should be symmetrically placed around it.

[0010] Preferably, in the above technical solution, in step S3, both ends of the support beam are fixedly connected to the ends of the two reference piles and kept horizontally, one end of the reference beam is fixedly connected to the support beam by a buckle, and the other end of the reference beam is simply supported on another support beam.

[0011] Preferably, in the above technical solution, in step S3, the inner diameter of the casing is larger than the diameter of the reference pile, and an isolation zone is formed between the inner wall of the casing and the outer side of the reference pile.

[0012] Preferably, in the above technical solution, in step S3, a core rod is detachably fitted inside the casing. The outer diameter of the core rod matches the inner diameter of the casing and can fit against the inner wall of the casing. A centering cone is provided at the bottom end of the core rod, and the diameter of the centering cone is consistent with the diameter of the reference pile. A stop block is provided at the top end of the core rod, and the bottom of the stop block can abut against the top end of the casing. The centering cone can drill a centering hole in the soil layer below the casing, and the lower end of the reference pile can be inserted into the centering hole.

[0013] Preferably, the above technical solution further includes a positioning bracket, wherein a positioning ring is provided in the middle of the positioning bracket, and a plurality of outwardly extending legs are provided on the outer periphery of the positioning ring. The inner diameter of the positioning ring is consistent with the outer diameter of the protective sleeve, and the protective sleeve can pass through the positioning ring. The end of the supporting leg is provided with a first through-pin hole.

[0014] Preferably, the above technical solution further includes a positioning support cylinder, the bottom of which is provided with a sleeve hole that can fit around the outer periphery of the positioning ring, the top of which is provided with a support hole that matches the outer diameter of the reference pile, the pile body of the reference pile can pass through the support hole and be supported and limited, and the side of the positioning support cylinder is provided with an elastic opening groove, one end of which extends outward from the top of the positioning support cylinder.

[0015] Preferably, in the above technical solution, the bottom of the positioning support cylinder is provided with a flange, the flange is provided with a second through-pin hole, and the support leg is provided with a threaded hole, the position of the threaded hole being consistent with the position of the second through-pin hole.

[0016] Preferably, in the above technical solution, steps S1 and S2 further include a waterproof component, which includes a fixing ring and a waterproof film bag. The bottom of the fixing ring is provided with a magnetic ring. The fixing ring is fitted around the outer periphery of the displacement gauge and is magnetically fixed to the measuring plate through the magnetic ring. The bottom of the waterproof film bag is provided with a bottom opening. The edge of the bottom opening is clamped between the magnetic ring and the measuring plate. The side of the waterproof film bag is provided with a top opening. The magnetic base is fixedly connected to the displacement gauge through a rod. The rod can pass through the top opening and its side is sealed to the top opening.

[0017] Compared with existing technologies, the present invention has the following advantages: 1. The pile vertical compressive static load test method of the present invention involves inserting a casing into the top layer of soil in the test site and driving the reference pile into the bottom layer of soil from the center of the casing, so that an isolation zone is formed between the reference pile and the casing. This reduces the influence of the deformation of the top layer of soil caused by compression and rebound on the position of the reference pile during loading and unloading tests, and can significantly reduce the offset and measurement error.

[0018] 2. In this invention, one end of the reference beam is fixedly connected to a support beam, and the other end of the reference beam is simply supported on another support beam. This open structure can, to a certain extent, avoid the influence of temperature changes and displacement of the reference pile on the deflection of the reference beam, thereby further reducing measurement errors.

[0019] 3. The core rod in this invention can be fitted inside the casing, and a stop block is provided at the top of the core rod. This stop block not only abuts against the top of the casing but also serves as a counterweight and force exertion. By applying pulse hammering to the top of the stop block, the casing can be implanted below the soil surface with the help of the counterweight and limiting effect of the stop block. Furthermore, a centering cone is provided at the lower end of the core rod, which can form a centering hole while the casing is being implanted downwards. The centering hole can position the reference pile, thereby ensuring the uniform thickness of the isolation zone.

[0020] 4. The positioning bracket in this invention is provided with a positioning ring in the middle, which can support the outer side of the protective cylinder. At the same time, the positioning ring can also center the sleeve hole at the bottom of the positioning support cylinder. When the benchmark pile is driven in, the support hole at the top of the positioning support cylinder can not only straighten and support the benchmark pile, thus facilitating one person to work alone, but also center the benchmark pile to prevent deviation during driving. The opening groove on the side of the positioning support cylinder can play a circumferential elastic buffering role when the benchmark pile is driven in, so as to prevent the lateral force from being transmitted to the positioning bracket and causing the positioning bracket to deviate, thus making the positioning inaccurate and causing the pile axis of the benchmark pile to be skewed.

[0021] 5. The waterproof component of this invention includes a fixing ring and a waterproof film bag. The bottom of the fixing ring is provided with a magnetic ring, which is fixedly installed on the measuring plate by attraction. At the same time, it can also press the edge of the bottom opening of the waterproof film bag and seal the bottom opening. The waterproof film bag is made of lightweight material and will not interfere with the displacement gauge and the rod of the magnetic base. The top opening of the bag can make way for the rod and can be sealed with tape, making it convenient and quick to use. Attached Figure Description

[0022] Figure 1 This is a schematic flowchart of the static load test method for vertical compressive strength of piles according to the present invention.

[0023] Figure 2 This is a schematic diagram of the installation of the counterweight platform and the testing device.

[0024] Figure 3 This is a schematic diagram of the installation of the pile under test and the measuring device.

[0025] Figure 4 It is an assembly drawing of the positioning bracket, the protective sleeve, and the core rod.

[0026] Figure 5 It is an assembly structure diagram of the positioning bracket, casing, positioning support and reference pile.

[0027] Figure 6 This is a partial cross-sectional view of the positioning support.

[0028] Figure 7 This is a structural diagram of the waterproof component. Explanation of key figure labels: 100 - Pile cap, 110 - Measuring plate; 200-jack; 300-Casing, 310-Benchmark pile, 320-Support beam, 330-Benchmark beam, 340-Magnetic base, 350-Displacement gauge, 360-Branch pipe; 400 - Support pier, 410 - Main beam, 420 - Secondary beam, 430 - Counterweight block; 500-Core rod, 510-Centering cone, 520-Stop block; 600-Positioning bracket, 610-Positioning ring sleeve, 620-Support leg, 621-Threaded hole, 630-First through nail hole, 640-Positioning support cylinder, 650-Sleeve hole, 660-Support hole, 670-Elastic opening groove, 680-Flange, 690-Second through nail hole; 700 - Waterproof component, 710 - Fixing ring, 720 - Waterproof film bag, 721 - Bottom bag opening, 722 - Top bag opening, 730 - Magnetic ring. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "top surface," "bottom surface," "inner," "outer," "inner side," and "outer side," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0031] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. Where the terms "first," "second," and "third" are used for descriptive purposes and to distinguish technical features, they should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the sequential relationship of the indicated technical features.

[0032] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.

[0033] like Figures 1 to 5 As shown, the method for testing the vertical compressive static load of the pile in this embodiment includes the following steps: S1. Reinforce the bearing end: Cast or install a pile cap 100 at the pile head of the pile being tested, and install a measuring plate 110 on the side of the pile cap 100. The installation position is 200mm below the top of the pile cap 100. When the diameter or side width of the pile being tested is greater than 500mm, four measuring plates 110 should be symmetrically placed around it. When the diameter or side width of the pile being tested is not greater than 500mm, two measuring plates 110 should be symmetrically placed around it. S2. Install jack 200: Install jack 200 on the top of pile cap 100, connect oil pump and pressure sensor. When the load capacity is large, steel plate can be placed between the top surface of pile cap 100 and jack 200 to protect the bearing surface of pile cap 100. Place support pier 400 around the pile under test, and install main beam 410 so that the bottom of main beam 410 is aligned with the top of jack 200. S3. Install the measuring device: Set up the positioning support 600, insert the casing 300 into the bottom hole through the positioning ring 610, insert the core rod 500 into the casing 300, and drive the core rod 500 and casing 300 together into the soil layer. Drill a centering hole at the bottom of the casing 300, then pull out the core rod 500. Fit the positioning support 640 onto the positioning ring 610, insert the benchmark pile 310 into the casing 300 through the support hole 660, with the lower end inserted into the centering hole, and continue driving the benchmark pile 310 into the lower soil layer. The inner diameter of the casing 300 is larger than the diameter of the reference pile 310, forming an isolation zone between the inner wall of the casing 300 and the outer side of the reference pile 310. Then, a support beam 320 is built between two adjacent reference piles 310, and the support beam 320 is kept horizontal. A reference beam 330 is installed between the two support beams 320. One end of the reference beam 330 is fixedly connected to the support beam 320 by a buckle, and the other end of the reference beam 330 is simply supported on another support beam 320. An outwardly extending branch pipe 360 ​​is installed on the reference beam 330. The length and angle of the branch pipe 360 ​​are adjustable. A magnetic base 340 is attracted to the branch pipe 360, and a displacement meter 350 is installed on the rod of the magnetic base 340, so that the measuring end of the displacement meter 350 abuts against the measuring plate 110. The rod extends outward from the side of the displacement meter 350. A waterproof component 700 is installed between the detection plate and the displacement meter 350. S4. Construct a counterweight platform: Construct a secondary beam 420 on the support 400, and place counterweight blocks 430 layer by layer on the secondary beam 420. S5. Loading Test: The tested piles are loaded using a graded loading method. The maximum load value is 2.0 times the characteristic value of the design single pile vertical bearing capacity. The graded load is 1 / 10 of the maximum load or the estimated ultimate bearing capacity. The first grade is twice the graded load. After each graded load reaches relative stability, the next graded load is added. After each graded load is applied, the pile top settlement should be measured at 5 min, 15 min, 30 min, 45 min, and 60 min, and thereafter every 30 min. S6. Unloading Test: The pile under test is unloaded in stages. The amount of unloading at each stage is twice the amount of the stage load during loading. Each stage of unloading should be maintained for 1 hour. The settlement at the top of the pile is measured at 15 minutes, 30 minutes and 60 minutes. Then the first stage of load can be unloaded. After unloading to zero, the maintenance time should not be less than 3 hours. The measurement time is 15 minutes and 30 minutes. After that, the residual settlement at the top of the pile is measured every 30 minutes.

[0034] It should be noted that in step S1 above, if the pile being tested is a cast-in-place concrete pile, the loose and broken layer and low-strength concrete at the top of the pile should be broken first to expose the main reinforcement, and the pile head should be cleaned before the pile cap 100 is poured; if the pile being tested is a pipe pile, a clamp can be directly installed on the side of the pile head to form a detachable pile cap 100 structure, and the measuring plate 110 can be installed on the outside of the clamp.

[0035] In addition, the driving depth of the casing 300 depends on the soil type of the foundation soil. If the foundation soil is soft soil, sand, or other loose soil, the driving depth of the casing 300 shall not be less than 600 mm. If the foundation soil is dense clay or rock, the driving depth shall not be less than 300 mm.

[0036] More in detail, such as Figure 4 As shown, the bottom end of the core rod 500 is provided with a centering cone 510, the diameter of which is the same as the diameter of the reference pile 310. The top end of the core rod 500 is provided with a stop block 520, the diameter of which is larger than the diameter of the casing 300 and the bottom of which can abut against the top end of the casing 300. The diameter of the centering cone is smaller than the diameter of the core rod 500 and is the same as the diameter of the reference pile 310. An inverted conical surface is provided between the centering cone and the lower end of the core rod 500. The centering cone can chisel a centering hole in the soil layer below the casing 300 so that the lower end of the reference pile 310 can be inserted into the centering hole.

[0037] More in detail, such as Figure 5 and Figure 6As shown, the positioning bracket 600 consists of a positioning ring 610 and support legs 620. Four outwardly extending support legs 620 are provided on the outer periphery of the positioning ring 610. The inner diameter of the positioning ring 610 matches the outer diameter of the protective sleeve 300, allowing the protective sleeve 300 to pass through the positioning ring 610. A first through-hole 630 is provided at the end of each support leg 620, which can be used to install ground nails to fix the positioning bracket 600. A sleeve hole 650 is provided at the bottom of the positioning sleeve 640, which can fit around the outer periphery of the positioning ring 610. A support hole 660 is provided at the top of the positioning sleeve 640, the diameter of which is the same as that of the reference pile 3. The outer diameter of the 10 matches and the axis of the support hole 660 coincides with the axis of the sleeve hole 650. The pile body of the reference pile 310 can pass through the support hole 660 and be supported and limited. The side of the positioning support cylinder 640 is provided with an elastic opening groove 670. One end of the elastic opening groove 670 extends outward from the top of the positioning support cylinder 640. The bottom of the positioning support cylinder 640 is provided with a flange 680. The flange 680 is provided with a second through nail hole 690. The support leg 620 is provided with a threaded hole 621. The position of the threaded hole 621 is consistent with the position of the second through nail hole 690. By installing bolts in the threaded hole 621, the flange 680 and the positioning can be locked and fixed together.

[0038] More in detail, such as Figure 7 As shown, the waterproof assembly 700 includes a fixing ring 710 and a waterproof film bag 720. A magnetic ring 730 is fixedly connected to the bottom of the fixing ring 710. The magnetic ring 730 can be used to fix the fixing ring 710 around the displacement meter 350 and magnetically attached to the measuring plate 110. The bottom of the waterproof film bag 720 is provided with a bottom bag opening 721. The edge of the bottom bag opening 721 is clamped between the magnetic ring 730 and the measuring plate 110. A top bag opening 722 is opened on the side of the waterproof film bag. The magnetic base 340 is fixedly connected to the displacement meter 350 through the meter rod. The meter rod can pass through the top bag opening 722, and its side can be sealed with waterproof tape.

[0039] In summary, the pile vertical compressive static load test method in this embodiment involves embedding a casing 300 in the top layer of soil at the test site and driving the reference pile 310 from the center of the casing 300 into the bottom layer of soil, thus forming an isolation zone between the reference pile 310 and the casing 300. This reduces the impact of deformation caused by compression and rebound of the top layer of soil on the position of the reference pile 310 during loading and unloading tests, significantly reducing offset and measurement errors. Furthermore, the waterproof component 700 also serves to waterproof the electronic displacement gauge 350, preventing seepage from the foundation pit or rainwater from affecting the function of the displacement gauge 350.

[0040] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is obvious that many changes and variations can be made based on the above teachings. Although embodiments of the invention have been shown and described, these specific embodiments are merely explanations of the invention and are not intended to limit it. The specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. The purpose of selecting and describing exemplary embodiments is to explain the specific principles of the invention and its practical application, so that those skilled in the art, after reading this specification, can make modifications, substitutions, variations, and various choices and changes to the embodiments as needed without departing from the principles and spirit of the invention, provided that such modifications, substitutions, variations, and choices and changes are within the scope of the claims of the invention and are protected by patent law.

Claims

1. A method for testing the vertical compressive static load of a pile, characterized in that, Includes the following steps: S1. Reinforce the bearing end: Cast or install a pile cap on the pile head of the pile being tested, and install a measuring plate; S2. Install jacks: Install jacks on the top of the pile cap, connect the oil pump and pressure sensor, and install the support and main beam; S3. Install measuring device: Install the casing, install the reference pile at the center of the casing, build a support beam and reference beam on the reference pile, and install the magnetic base and displacement gauge on the reference beam so that the measuring end of the displacement gauge abuts against the measuring plate. S4. Construct a counterweight platform: Construct secondary beams on the supports and place counterweight blocks; S5. Loading test: The pile under test is loaded in a graded loading manner. After each load is applied, the load is maintained for a specified time and the settlement at the top of the pile is measured at different time intervals. S6. Unloading test: The pile under test is unloaded in stages. During unloading, the load of each stage is maintained for a certain period of time and the settlement at the top of the pile is measured in different time periods. After unloading to zero, the maintenance time is not less than 3 hours and the residual settlement at the top of the pile is measured in different time periods.

2. The method for testing the vertical compressive static load of a pile according to claim 1, characterized in that, In step S1, the measuring plate is fixedly installed on the side of the pile cap, with the installation position 200mm below the top of the pile cap.

3. The method for testing the vertical compressive static load of a pile according to claim 2, characterized in that, In step S1, when the diameter or side width of the pile being tested is greater than 500mm, four measuring plates should be symmetrically placed around its circumference; when the diameter or side width of the pile being tested is not greater than 500mm, two measuring plates should be symmetrically placed around its circumference.

4. The method for testing the vertical compressive static load of a pile according to claim 1, characterized in that, In step S3, both ends of the support beam are fixedly connected to the ends of the two reference piles and kept horizontal. One end of the reference beam is fixedly connected to the support beam by a buckle, and the other end of the reference beam is simply supported on another support beam.

5. The method for testing the vertical compressive static load of a pile according to claim 1, characterized in that, In step S3, the inner diameter of the casing is larger than the diameter of the reference pile, and an isolation zone is formed between the inner wall of the casing and the outer side of the reference pile.

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