Small-tonnage foundation pile uplift load test device and bearing capacity calculation method thereof

Abstract

The invention discloses a small-tonnage foundation pile uplift load test device and a bearing capacity calculation method thereof, and relates to the field of civil engineering detection.The small-tonnage foundation pile uplift load test device comprises a foundation pile exposed pile head and a high-strength anchoring top plate of a force transmission frame, the anchoring top plate is arranged on the upper surface of a pressure sensor, and a through hole matched with a high-strength force transmission bolt rod is formed in the anchoring top plate; the anchoring top plate is connected to a high-strength threaded bolt rod of the force transmission frame in a sleeving mode, the anchoring top plate and the force transmission bolt rod are fixed through a connecting assembly, the force transmission bolt rod is welded to the upper surface of the U-shaped fastener, the reusable force transmission frame is formed, and the force transmission frame is connected with a hoop on the surface of an exposed pile head of a foundation pile through a high-strength bolt. The device is simple in structure, convenient to install and capable of being repeatedly used, the bearing capacity calculation method is verified through field tests, and good generalization performance is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering detection, and particularly relates to a small-tonnage pile foundation uplift load test device and a bearing capacity calculation method thereof. Background Art

[0002] The pile foundation uplift load test is the most intuitive and effective method for testing the uplift bearing capacity of pile foundations, and is also often used to verify whether the uplift bearing capacity of pile foundations meets the design requirements. At present, the piles set under structures such as wind power, solar thermal energy storage power generation, petroleum, communication, and transportation facilities often bear large uplift forces due to wind force, buoyancy, etc. Whether the uplift bearing capacity of the pile foundation meets the requirements is the key to ensuring the stability of the upper structure. The pile foundations of such structures often have a small diameter, a shallow depth, and a small tonnage.

[0003] Existing small-tonnage pile foundation uplift load test methods often use welding, fabricating pile caps and embedding large bolt rods, etc. to connect with the reaction beam. The connection method is cumbersome, the test period is long, and the existing embedded parts are severely damaged, affecting the long-term safe use of the pile foundation in the later stage. Moreover, the calculation of its uplift bearing capacity has always been the focus of discussion.

[0004] In order to solve the above disadvantages of the vertical uplift bearing capacity test of pile foundations, the present invention patent proposes a reusable small-tonnage pile foundation uplift load test device and a bearing capacity calculation method thereof, with low equipment cost, reusable, and a reliable bearing capacity calculation method. Summary of the Invention

[0005] The purpose of the present invention is to provide a small-tonnage pile foundation uplift load test device and a bearing capacity calculation method thereof in order to solve the above problems.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, there is provided a small-tonnage pile foundation uplift load test device and a bearing capacity calculation method thereof, including a high-strength embedded bolt rod with threads on the top exposed at the top of the exposed pile head (15) of the pile foundation and the exposed pile head (15) of the pile foundation. Four reference frames (10) for supporting two reference beams (11) are arranged on both sides of the exposed pile head (15) of the pile foundation. The reference beams (11) are symmetrically arranged on both sides of the exposed pile head (15) of the pile foundation. The reference frames (10) are symmetrically embedded at the bottom sides of both ends of the reference beams (11). The two ends of the reference beams (11) are in the square card slots on the reference frames (10). It is characterized in that:

[0008] The connecting component includes a hoop (1) and a force transfer frame. The hoop (1) is sleeved on the surface of the pile body of the exposed pile head (15) of the foundation pile, and the hoop (1) is located below the upper surface of the exposed pile head (15) of the foundation pile. The U-shaped buckle (3) is located above the connection of the hoop (1) and is connected by high-strength bolts. The high-strength bolt rod (4) is screwed into the high-strength bolt on the upper surface of the anchor plate (9);

[0009] The force transfer frame (14) is composed of high-strength bolt rods (4) welded to the upper surface of the U-shaped buckle (3). The U-shaped buckle (4) is arranged on the upper surface of the connection of the hoop (1). A through hole matching the connection hole of the hoop (1) is opened on the U-shaped buckle (4). The U-shaped buckle (4) is sleeved on the connection of the hoop (1), and the U-shaped buckle (4) and the hoop (1) are connected by high-strength bolts; the high-strength bolt rod (3) passes through the anchor plate (9) arranged on the upper surface of the pressure sensor and is fixedly connected on the upper surface of the anchor plate (9) with high-strength bolts.

[0010] Furthermore, it also includes rubber gaskets (2) arranged at the upper and lower ends inside the hoop (1), and the rubber gaskets (2) are attached to the upper and lower ends inside the hoop (1).

[0011] Furthermore, there is a square card slot on the reference frame (10) that matches the outer contour of the cross-section of the reference beam to fix the reference beam (11). A magnetic base (12) is adsorbed above the reference beam (11), and a dial indicator (13) is arranged at the tail end of the magnetic base (12).

[0012] Furthermore, the pressure measurement component includes a pressure sensor (8) and a hydraulic jack (7). The pressure sensor (8) is installed on the lower side of the anchor plate (9), and the hydraulic jack (7) is arranged below the pressure sensor (8).

[0013] Furthermore, a reaction beam (6) is installed at one end of the hydraulic jack (7) away from the pressure sensor (8). Support legs (5) for supporting the reaction beam (6) are arranged at the bottom sides of both ends of the reaction beam (6). The support legs (5) and the reaction beam (6) are made of H-shaped steel, and their webs are reinforced with steel plates.

[0014] Furthermore, a bearing capacity calculation method for a small-tonnage foundation pile uplift load test device is as follows:

[0015] S1. Sleeve the hoop on the exposed pile body of the foundation pile;

[0016] S2. Sleeve the force transfer frame on the connection of the hoop and connect the hoop and the force transfer frame with high-strength bolts;

[0017] S3. Place the reference frames symmetrically on both sides of the pile, install the reference beam on the reference frames, place the dial indicator with a magnetic base on the reference beam, and place the tip of the dial indicator on the surface of the pile top of the foundation pile;

[0018] S4. Symmetrically place the outriggers on the steel plate and place the reaction beam passing through the force transfer frame on the outriggers;

[0019] S5. Place the hydraulic jack in the force transfer frame above the force transfer beam;

[0020] S6. Place the pressure sensor above the hydraulic jack;

[0021] S7. Place the high-strength bolt rod of the anchoring roof plate passing through the force transfer frame above the pressure sensor and fix it with the anchoring screw;

[0022] S8. Start the jack, test and record the vertical displacement of the foundation pile under each level of load;

[0023] S9. After completing all the test work, disassemble the anchoring roof plate, pressure sensor, jack, electronic dial gauge, force transfer beam, outriggers and force transfer frame in sequence;

[0024] S10. Substitute the recorded data into the formula to obtain the uplift load of the container. The specific calculation process is as follows:

[0025] The static equilibrium relationship formula of the micro-pile section is as follows:

[0026] (1)

[0027] That is:

[0028] (2)

[0029] Among them, is the axial force of the micro-section; is the perimeter of the pile; is the skin friction of the pile side soil;

[0030] The relationship between the tensile deformation dW and the axial force Q:

[0031] (3)

[0032] Among them, is the elastic modulus of the pile; A is the cross-sectional area of the pile;

[0033] After differentiating equation (3) with respect to Z and substituting equation (2) and sorting out, we can get:

[0034] (4)

[0035] The expression of the pile side soil load transfer:

[0036] (5)

[0037] Among them, , is the shear stiffness coefficient of the soil on the pile side; W is the displacement of the pile top; is the displacement when the pile reaches the elastic limit

[0038] Substituting equation (5) into equation (4) gives:

[0039] (6)

[0040] where is the displacement of the pile body in the elastic stage; is the displacement of the pile body in the plastic stage

[0041] Substitute (7); (8) into equation (6) to finally obtain:

[0042] (9)

[0043] (10)

[0044] Substitute the load of the previous level where both the curve slope and the upward deformation development rate of the pile top in the S-lgt curve of the test pile change significantly into Substitute the displacement into , , and through equations (7), (8), (9), and (10), we can obtain , ; Substitute the required into equation (5) to obtain the skin friction of the soil on the pile side;

[0045] Ultimate bearing capacity:

[0046] (11)

[0047] where, is the uplift load, is the effective gravity of the pile.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention adopts a reusable force transfer frame, avoiding the cumbersome process of repeated welding. It not only protects the integrity of the high-strength embedded bolt rod of the pile body, improves the reliability of the test device, but also makes it more convenient to adjust the height of the test device due to the thread at the top of the force transfer bar. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic diagram of the uplift pile analysis model of the present invention;

[0051] Figure 2The pile - side soil load transfer function curve of the double - broken - line hardening model of the present invention;

[0052] Figure 3 The perspective view of the present invention;

[0053] Figure 4 The schematic diagram of the connection structure between the hydraulic jack and the reaction beam of the present invention;

[0055] Figure 5 The schematic diagram of the hoop structure of the present invention;

[0056] Figure 6 The schematic diagram of the force - transfer frame structure of the present invention;

[0057] Figure 7 The schematic diagram of the force - transfer frame sleeved with the hoop.

[0058] In the figure: 1. Hoop; 2. Rubber gasket; 3. U - shaped buckle; 4. High - strength threaded rod; 5. Leg; 6. Reaction beam; 7. Hydraulic jack; 8. Pressure sensor; 9. Anchoring roof plate; 10. Reference frame; 11. Reference beam; 12. Magnetic base; 13. Dial indicator; 14. Force - transfer frame; 15. Exposed pile head of the basic pile. Detailed implementation manners

[0059] To make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with the detailed implementation manners.

[0060] The present invention provides a small - tonnage basic pile uplift load test device and its bearing capacity calculation method. Refer to Figures 1-2 , the calculation method of the uplift bearing capacity of a small - scale uplift pile is as follows:

[0061] S1. Sleeve the hoop on the exposed pile body of the basic pile;

[0062] S2. Sleeve the force - transfer frame at the connection of the hoop and connect the hoop and the force - transfer frame with high - strength bolts;

[0063] S3. Place the reference frame symmetrically on both sides of the pile, install the reference beam on the reference frame, place the dial indicator with a magnetic base on the reference beam, and place the tip of the dial indicator on the surface of the basic pile top;

[0064] S4. Place the legs symmetrically on the steel plate and place the reaction beam passing through the force - transfer frame on the legs;

[0065] S5. Place the hydraulic jack in the force - transfer frame above the force - transfer beam;

[0066] S6. Place the pressure sensor above the hydraulic jack;

[0067] S7. Place the high-strength bolt rod of the anchoring roof slab passing through the force transfer frame above the pressure sensor and fix it with the anchoring screw;

[0068] S8. Start the jack, test and record the vertical displacement of the foundation pile under each level of load;

[0069] S9. After completing all the test work, disassemble the anchoring roof slab, pressure sensor, jack, electronic dial gauge, force transfer beam, support legs and force transfer frame in sequence;

[0070] S10. Substitute the recorded data into the formula to calculate the uplift load of the container. The specific calculation process is as follows:

[0071] According to Figure 1 the static equilibrium relationship of the micro pile segment can be obtained:

[0072] (1)

[0073] That is:

[0074] (2)

[0075] Among them, is the axial force of the micro segment; is the perimeter of the pile; is the skin friction of the pile side soil;

[0076] The relationship between the tensile deformation dW and the axial force Q:

[0077] (3)

[0078] Among them, is the elastic modulus of the pile; A is the cross-sectional area of the pile;

[0079] After differentiating equation (3) with respect to Z and substituting equation (2) and arranging, we can get:

[0080] (4)

[0081] As Figure 2 it can be seen that the expression of the soil load transfer on the pile side is:

[0082] (5)

[0083] Among them, 、 are the soil shear stiffness coefficients on the pile side; W is the pile top displacement; is the displacement when the pile reaches the elastic limit

[0084] Substituting equation (5) into equation (4) gives:

[0085] (6)

[0086] wherein is the pile body displacement in the elastic stage; is the pile body displacement in the plastic stage

[0087] Substitute (7); Substitute (8) into equation (6), and finally we can get:

[0088] (9)

[0089] (10)

[0090] Substitute the previous level of load at which both the curve slope and the upward pull deformation development rate of the test pile S-lgt curve change significantly into Substitute the displacement into and , and through equations (7), (8), (9), and (10), we can obtain and ; Substitute the required into equation (5) to obtain the skin friction of the pile side soil.

[0091] Ultimate bearing capacity:

[0092] (11)

[0093] wherein, is the uplift load, is the effective gravity of the pile

[0094] Referring to Figures 3-7 as shown, the present invention provides a reusable small-tonnage pile uplift load test device, including the exposed pile head 15 of the pile foundation. A high-strength embedded bolt rod with its top exposed is arranged inside the exposed pile head 15 of the pile foundation. Reference frames 10 and reference beams 11 are arranged on both sides of the exposed pile head 15 of the pile foundation. The reference beams 11 are symmetrically arranged on both sides of the exposed pile head 15 of the pile foundation. The reference frames 10 are symmetrically buried at the bottom sides of both ends of the reference beams 11. The reference frames 10 are used to support the reference beams 11. A magnetic base 12 is adsorbed above the reference beam 11. A dial gauge 13 is sleeved on the deflecting rod end of the magnetic base 12. A force transfer frame 14 is composed of a high-strength bolt rod 4 and a U-shaped buckle 3. The high-strength bolt rod 4 is welded on the upper surface of the U-shaped buckle 3. The U-shaped buckle 4 is arranged on the upper surface of the connection part of the hoop 1. A through hole matching the connection hole of the hoop 1 is opened on the U-shaped buckle 4. The U-shaped buckle 4 is sleeved on the connection part of the hoop 1. The U-shaped buckle 4 and the hoop 1 are connected by high-strength bolts; the high-strength bolt rod 3 passes through the anchor top plate 9 arranged on the upper surface of the pressure sensor and is fixedly connected on the upper surface of the anchor top plate 9 with high-strength bolts

[0095] Specifically, a reference frame 10 is buried at a certain distance on both sides of the pile body. The two ends of the reference beam 11 are placed in the card slots on the reference frame 10. A dial indicator 13 is sleeved on the magnetic base 12, and the sleeved dial indicator 13 is placed on the top edge of the exposed pile head 15 of the foundation pile. The position of the magnetic base 12 is adjusted to adsorb it on the reference beam 11. During the detection, the length of the output end of the hydraulic jack 7 is increased to drive the anchoring roof plate 9 to pull the high-strength bolt rod 4, and the force transmission frame 14 is pulled upward. The pressure sensor 8 records the pulling force generated by the hydraulic jack 7;

[0096] In this embodiment, the magnetic base 12 has magnetism and can be adsorbed on the reference beam 11 made of metal material. The reference beams 11 are symmetrically arranged. A hooping 1 with a suitable diameter is prefabricated according to the pile diameter of the exposed pile head 15 of the foundation pile, and rubber gaskets 2 are pasted on the upper and lower ends of the inner side of the hooping 1;

[0097] As a further implementation manner of this embodiment, as Figures 3-7 shown, a force transmission frame 14 is provided at the connection of the hooping 1. The force transmission frame 14 is composed of a high-strength bolt rod 4 and a U-shaped buckle 3. The top of the high-strength threaded rod 4 is provided with an anchoring nut screwed on the thread at its top. The high-strength threaded rod 4 penetrates through the anchoring roof plate 9, and the anchoring nut is sleeved on the threaded steel bar of the force transmission steel bar above the anchoring roof plate 9. The bottom U-shaped buckle 3 of the force transmission frame 14 is sleeved at the connection of the hooping 1. A through hole matching the high-strength threaded rod 4 of the force transmission frame 14 is opened on the anchoring roof plate 9. A pressure measuring assembly is arranged below the anchoring roof plate 9. The pressure measuring assembly includes a pressure sensor 8 and a hydraulic jack 7. The pressure sensor 8 is installed on the lower side of the anchoring roof plate 9, and the hydraulic jack 7 is arranged below the pressure sensor 8. The bottom of the hydraulic jack is placed at the mid-span position of the reaction beam 6. The web of the reaction beam is reinforced with steel plates. Legs 5 for supporting the reaction beam 6 are arranged at the bottom sides of both ends of the reaction beam 6. The legs 5 are made of H-shaped steel, and their webs are reinforced with steel plates;

[0098] Specifically, the high-strength threaded rod 4 is welded to the upper surface of the top plate of the U-shaped buckle 3. The reaction beam 6 is erected directly above the high-strength embedded bolt rod on the exposed pile head 15 of the foundation pile. Both ends of the reaction beam 6 are placed on the legs 5 on both sides of the exposed pile head 15 of the foundation pile. A hydraulic jack 7 is erected at the mid-span position of the reaction beam 6. A pressure sensor 8 is placed above the hydraulic jack 7. An anchoring roof plate 9 is installed on the top surface of the pressure sensor 8. The anchoring roof plate 9 is sleeved outside the force transmission steel bar in the force transmission frame 14, and an anchoring nut is screwed on the top of the force transmission steel bar;

[0099] In this embodiment, the central points of the anchoring roof 9, the pressure sensor 8, the hydraulic jack 7 and the reaction beam 6 are on the same vertical line as the center position of the exposed pile head 15 of the foundation pile. The high-strength threaded rod in the force transfer frame 14 is welded to the upper surface of the roof plate of the U-shaped buckle 3. The welding length of the high-strength threaded rod 4 and the roof plate of the U-shaped buckle 4 is not less than 5 cm, the diameter of the high-strength threaded rod is not less than 12 mm of the magnetic base, and the anchoring roof 9 is made of a thick steel plate with a thickness of not less than 5 cm.

[0100] Substitute the previous-level load and displacement at which both the curve slope and the development rate of the uplift deformation of the pile top in the S-lgt curve of the test pile change significantly into 、 The shear stiffness can be obtained 、 , and its calculation formula is as follows:

[0101]

[0102]

[0103] Substitute the required shear stiffness into equation (5) to obtain the side friction resistance of the pile, and its calculation formula:

[0104]

[0105] Then substitute the obtained side friction resistance into equation (9) to obtain the uplift load of the pile, and its calculation formula:

[0106]

[0107] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, in any aspect, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0108] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A small tonnage pile pull-out load test device, characterized in that: The invention comprises an exposed pile head (15) of a foundation pile and a high-strength embedded bolt rod with a threaded top exposed at the top of the exposed pile head (15), four reference frames (10) for supporting two reference beams (11) are arranged on both sides of the exposed pile head (15), the reference beams (11) are symmetrically arranged on both sides of the exposed pile head (15), the reference frames (10) are symmetrically embedded at the bottom sides of both ends of the reference beams (11), and both ends of the reference beams (11) are in square slots on the reference frames (10), and the invention is characterized in that: The connection assembly comprises a clamp (1) and a force transmission frame, wherein the clamp (1) is sleeved on the pile body surface of the exposed pile head (15) of the foundation pile, and the clamp (1) is located below the upper surface of the exposed pile head (15) of the foundation pile, and the U-shaped buckle (3) is located above the connection of the clamp (1) and is connected with a high-strength bolt, and the high-strength bolt rod (4) is screwed into the high-strength bolt on the upper surface of the anchoring top plate (9); The force transmission frame (14) is composed of a high-strength bolt rod (4) welded to the upper surface of a U-shaped buckle (3); the U-shaped buckle (4) is arranged on the upper surface of the connection of the clamp (1); a through hole that matches the connection hole of the clamp (1) is opened on the U-shaped buckle (4); the U-shaped buckle (4) is sleeved on the connection of the clamp (1); the U-shaped buckle (4) and the clamp (1) are connected by high-strength bolts; the high-strength bolt rod (3) passes through an anchoring top plate (9) arranged on the upper surface of the pressure sensor, and is connected and fixed on the upper surface of the anchoring top plate (9) by high-strength bolts.

2. A small tonnage pile pull-out load test device according to claim 1, characterized in that: It also includes rubber gaskets (2) arranged at the upper and lower ends of the inner side of the clamp (1), and the rubber gasket (2) is in contact with the upper and lower ends of the inner side of the clamp (1).

3. A small-tonnage pile pull-out load test device according to claim 1, characterized in that: The reference frame (10) has a square slot that matches the outer contour of the reference beam cross section to fix the reference beam (11), a magnetic meter base (12) is adsorbed above the reference beam (11), and a dial indicator (13) is arranged at the tail end of the magnetic meter base (12).

4. A small-tonnage pile pull-out load test device according to claim 1, characterized in that: The pressure measuring assembly comprises a pressure sensor (8) and a hydraulic jack (7); the pressure sensor (8) is mounted on the lower side of the anchoring top plate (9), and the hydraulic jack (7) is arranged below the pressure sensor (8).

5. A small-tonnage pile pull-out load test device according to claim 4, characterized in that: A reaction beam (6) is installed at one end of the hydraulic jack (7) away from the pressure sensor (8), and legs (5) for supporting the reaction beam (6) are arranged at the bottom sides of both ends of the reaction beam (6). The legs (5) and the reaction beam (6) are made of H-shaped steel, and the webs thereof are reinforced with steel plates.

6. The method for calculating the bearing capacity of a small-tonnage pile pullout load test device according to claim 1, characterized in that: The specific contents are as follows: S1. Put the clamp on the exposed pile body of the foundation pile; S2. Sleeve the force transmission frame onto the connection of the clamp and connect the clamp and the force transmission frame with high-strength bolts; S3. Place the reference frame symmetrically on both sides of the pile, install the reference beam on the reference frame, place the dial indicator with a magnetic base on the reference beam, and place the dial indicator needle on the top surface of the foundation pile; S4. Place the outriggers symmetrically on the steel plate, and place the reaction beams passing through the force transmission frame on the outriggers; S5. Place the hydraulic jack in the force transmission frame above the force transmission beam; S6. Place the pressure sensor above the hydraulic jack; S7. Place the anchor top plate through the high-strength bolt rod of the force transmission frame above the pressure sensor and fix it with anchor screws; S8. Start the jack to test and record the vertical displacement of the piles under various loads; S9. After completing all the testing work, disassemble the anchoring top plate, pressure sensor, jack, electronic dial indicator, force transmission beam, outrigger and force transmission frame in sequence; S10. Substituting the recorded data into the formula, the pull-out load of the container can be obtained. The specific calculation process is as follows: The static equilibrium relationship formula of the micro pile segment is as follows: (1) Right now: (2) in, is the axial force of the micro segment; is the circumference of the pile; is the soil friction resistance on the pile side; Relationship between tensile deformation dW and axial force Q: (3) in, is the elastic modulus of the pile; A is the cross-sectional area of ​​the pile; After taking the derivative of (3) with respect to Z, substitute (2) into it and we get: (4) The expression of soil load transfer on pile side is: (5) in, , is the shear stiffness coefficient of the soil on the pile side; W is the displacement of the pile top; is the displacement when the pile reaches the elastic limit Substituting (5) into (4) we can obtain: (6) in is the pile displacement in the elastic stage; is the pile displacement in the plastic stage Will (7); Substituting (8) into (6), we can finally obtain: (9) (10) Substitute the previous load where the slope of the S-lgt curve of the test pile and the rate of development of the uplift deformation at the top of the pile change significantly into Displacement Substitution , , through (7), (8), (9), (10) we can get , ; The required Substituting into (5) we can get the soil friction resistance on the pile side; Ultimate bearing capacity: (11) in, To resist pull-out load, is the effective weight of the pile.

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