KR20220072586A - Bidirectional Pile Loading Test - Google Patents

Abstract

The present invention installs a jack on the lower surface of the upper plate disposed on the lower side of the pile, places the lower plate under the jack, and applies hydraulic pressure to the jack to measure the displacement of the upper plate and lower plate, thereby testing the static load bearing capacity of the pile. To a testing apparatus, the bidirectional load test apparatus of the pile according to the present invention, a jack disposed between the top and the bottom of the pile; and at least one strain gauge arranged such that a strain applied to the jack matches a load applied by the jack and a load-strain relationship, wherein the jack includes a piston, and the piston a cylinder for receiving, and a fluid disposed between an upper surface of the piston and a bottom surface of a top of the cylinder, wherein applying pressure to the fluid creates a first force on the piston and a second force on the cylinder a force of 2 is generated, a tendency to separate the piston and cylinder occurs, the at least one strain gauge being included in the piston of the jack, the at least one strain being at least one strain applied by the piston wherein the piston includes a hollow body, a top plate, and a bottom plate, and one of the at least one strain gauge is attached to the top plate and the bottom plate of the piston do it with

Description

Bidirectional Pile Loading Test Apparatus {Bidirectional Pile Loading Test}

The present invention relates to a load testing apparatus for testing the static load bearing capacity of a pile, and more particularly, a jack is installed on the bottom surface of the upper plate disposed on the lower side of the pile, and the lower plate is positioned under the jack, and the jack It relates to a bidirectional load test device that tests the static load bearing capacity of a pile by measuring the displacement of the upper and lower plates by applying hydraulic pressure to the .

In general, a pile loading test (load test of pile) is a test that obtains bearing capacity from the relationship between load and settlement by directly loading a static load on a pile or loading it with a jack, and there are several test methods, representative In addition to the compression load test (actual load test) using the load of a heavy object according to the loading direction, and the pull-out test using the reaction force of the supporting point, there are horizontal load tests and simple pile load test (SPLT).

The pile load test method is the Osterberg Load Cell Test, developed by Osterberg in the early 80's. It is a static load test method that calculates the tip bearing capacity and frictional force of the pile by measuring the downward displacement of the load cell and the upward displacement of the pile by applying pressure to the load cell after installing the attached load cell, pouring and curing the concrete.

In addition, a bidirectional load test method has been developed that improves the disadvantages of the Osterberg load test. For example, in Korean Patent Registration No. 0791306, a plurality of cylinders are configured between the upper plate and the lower plate, and the cylinder is fixed to the upper plate, The upper plate and the lower plate are connected by a connecting member, and a load test device having a telltail that can measure displacement is configured on the upper plate and lower plate, respectively, the load test device is put into the excavated hole, and the concrete is poured and cured Then, while operating the cylinder, the displacement of the upper and lower plates is measured, the bearing force of the tip of the pile and the frictional force on the circumferential surface are calculated, and then the space generated by the operation of the cylinder is grouted to complete the test method. .

Korean Patent Registration No. 10-0791306

When a hydraulic jack is used, the pressure of the hydraulic fluid in the hydraulic jack is measured. Using this pressure measurement and a standard measurement effective in the direction of the force in contact with the hydraulic fluid, calculate the load applied by the hydraulic jack. At this time, the load is calculated by multiplying the pressure of the hydraulic fluid and the direction of the force applied by the pressure effectively by the standard surface area. For example, for a jack that is perpendicular to the direction of the force applied by the jack and has a cross-sectional area A in contact with the hydraulic fluid, the force is calculated as F=P A, where P is the hydraulic fluid pressure.

However, when measuring force in this way, it is sensitive to temperature because the amount and pressure of hydraulic fluid often vary with temperature. In addition, this force measurement method cannot measure specific frictional forces such as friction between the piston and the jack cylinder. Therefore, there can be a significant difference between the actual pressure applied by the hydraulic jack and the load calculated through the hydraulic fluid pressure measurement.

An object of the present invention is to provide a bidirectional load testing apparatus for a pile that can accurately measure the load bearing capacity and stability of the pile using a jack.

According to one embodiment of the present invention, the jack includes one or more strain gauges. One or more strain gauges may be disposed on or within the jack, such as on or within a piston of the jack.

When a jack applies a load or force, one or more materials inside the jack deform or dislodge under the load. One or more strain gages measure strain by measuring this strain or deviation. The measured strain is used to determine the magnitude of the load applied by the jack. According to the present invention, the load applied by the jack can be calculated through the following relational expression.

Here, ε is the strain, A is the area in contact with the hydraulic fluid perpendicular to the direction of the force to be applied by the jack, E is the modulus of elasticity, and L is the length of the material measured by placing the strain on it. According to this embodiment, the load is determined by combining measurement results obtained by measuring a plurality of strain gauges.

According to the present invention, a jack having one or more strain gauges for testing may be placed proximate to or within the pile. A load or force may be applied to the pile, an area of the pile, and/or the ground or other material surrounding the pile. According to one embodiment, a load or force will be applied to the top and/or bottom of the pile, the ground of the pile or other material underneath the pile, an area of the pile under the jack, and/or an area of the pile above the jack. can When a load or force is applied, one or more signals corresponding to one or more strain gages included in the jack are received. According to one embodiment, one or more signals are used to measure the strain of the jack. According to one embodiment, one or more strain gauges are disposed on or within one or more materials of the jack, and the one or more strain gauges are used to measure deformation or deviation of the one or more materials. The measured strain and deviation are again used to measure the strain on the jack.

The measured strain on the jack is then used to determine the magnitude of the applied load or force. monitor the applied load or force using one or more suitably programmed computers; receive and/or process one or more signals; Deformation or disengagement of one or more materials, strain on the jack, and/or another result of the test may be measured, calculated, and/or determined or determined whether the test is complete.

1 is a diagram illustrating the application of a force or pressure P applied to a jack.
2 illustrates pressure (P) versus strain (ε) that may be used to calculate a load applied by a jack based on one or more strains measured inside the jack using one or more strain gauges, in accordance with an embodiment of the present invention; ) shows the curve.
Figure 3 is a view showing a piston of the jack cylinder and the strain gauge is built in, according to an embodiment of the present invention.
4-6 are diagrams illustrating various positions in which a strain gauge may be disposed, according to an embodiment of the present invention.

The configuration shown in the embodiments and drawings described in this specification is only a preferred example of the disclosed invention, and there may be various modifications that can replace the embodiments and drawings of the present specification at the time of filing of the present application.

Hereinafter, with reference to the accompanying drawings, the bidirectional load test apparatus of the pile will be described in detail according to the embodiments described below.

1 is a view showing the load and strain measurement such as the pressure (P) applied to both ends of the jack.

2 is a pressure (P) versus strain (ε) curve that may be used to calculate a load applied by a jack based on one or more strains measured within the jack by one or more strain gauges, in accordance with an embodiment of the present invention; is a diagram showing Figure 2 shows that the relationship between applied pressure and strain does not always form a perfect linear model. A similar curve can be produced for the load versus strain relationship, where the load applied by the jack is equal to the pressure of the pressurized fluid in the jack multiplied by the cross-sectional area of the piston minus the friction force between the cylinder and the piston of the jack. The load applied by the jack can be measured externally, for example by means of conventional weights or other commonly known load measurement methods. According to certain embodiments, a hysteresis can occur in a force versus strain relationship. For example, as the force gradually increases from zero, the measured strain falls short of the value predicted by the linear model, and when the force that was above zero is lowered, the strain falls below the value predicted by the linear model. According to a specific embodiment, after measuring the force versus strain relationship through the average of several repeated movements, the measured relationship can be used to calculate a force, load, or a given measured strain.

Figure 3 shows a jack 1 disposed in an engineering pile 10 (dashed line) in accordance with one embodiment of the present invention.

According to this embodiment, the jack 1 is arranged between the upper part 5 and the lower part 7 of the pile in the middle part 3 . According to one embodiment, the jack 1 is loaded with a load L on the bottom surface 9 of the top 5 of the pile 10 , the top surface 11 of the bottom side of the pile, or both. According to one embodiment shown in FIG. 3 , the load L is applied upwardly to the upper part of the pile, or downwardly to the lower part of the pile. The load L applied to the top is the force applied to the bottom surface 9 of the top of the pile for the top surface of the jack cylinder 13 and to the middle part 3 of the pile by the side of the jack cylinder 13. It may be a combination of applied forces, in which case the intermediate part 3 may then apply a force to the bottom surface 9 of the upper part 5 . According to one embodiment, the jack applies a load to another inner surface of the pile. This may be achieved by displacing the jack at a different location and/or interconnecting the jack with other parts of the pile, for example via rods or other devices for force transmission. According to one embodiment, an extrusion force is applied.

According to an embodiment of the present invention, a tensile force is applied. When a load is applied to the jack and the pile is tested, the top and bottom of the pile may separate. According to FIG. 3 , when the jack is loaded, the upper part 5 and the lower part 7 are separated, so that the intersection of the middle part 3 and the lower part 7 is separated, so that the cylinder 13 of the jack is separated from the middle part and the lower part 7 . Together they move upward and the cylinder 13 and the middle part can lift the upper part 5 .

Hydraulic fluid is supplied to the jack through the hydraulic fluid inlet, and pressure (P) is applied into the cylinder including the piston of the jack. The load L applied to the top of the bottom of the pile and the bottom of the top of the pile may be measured via one or more strain gauges 20 disposed within the top of the piston and/or cylinder. During the pile test, it is possible to provide real-time measurements of strain from a strain gauge 20 disposed on or inside the piston, which is used to measure the load, and the load thus calculated is dependent on the pressure of the hydraulic fluid and the hydraulic fluid. After measuring the direction of the contact force and the effective standard surface area of the jack, it can be confirmed by multiplying the pressure by the surface area. After measuring the pressure of the hydraulic fluid, this pressure is effectively multiplied by the pressure by the standard surface area of the jack, that is, the surface area of the top of the piston in contact with the hydraulic fluid and the surface area of the top of the cylinder, by the direction of the force in contact with the hydraulic fluid. When measuring the load (L) by the jack on the measured pile, it is important that according to L=P _HF × A - F, the friction between the cylinder and the piston of the jack reduces the amount of the load (L) applied to the pile. will be. where L is the load applied to the pile, P _HF is the pressure of the hydraulic fluid, A is the surface area of the jack effectively standard for the direction of the force in contact with the hydraulic fluid, and F is the friction force between the piston and the cylinder of the jack. Accordingly, the load determined by the strain gauge 20 disposed in the piston and/or at the top of the cylinder may be more accurate than the load obtained by multiplying the pressure by the area of the piston after the hydraulic fluid measures the pressure.

4-6 illustrate the location of one or more strain gauges relative to the piston, in accordance with specific embodiments of the present invention. 4 is a plan view of the piston 100, with a strain gauge 101 attached to the surface of the piston, and another strain gauge 102 disposed inside the piston. 5 is a perspective view of a piston with identical strain gauges 101 and 102 . 6 is a plan view of a hollow piston 100 having an annular cross section, a strain gauge 101 attached to the surface of the piston, a strain gauge 102 built into the piston, and a strain disposed close to the piston. a gauge 103 . (Figure 3 shows a piston having a top plate and a bottom plate. A strain gauge is attached to the top plate and bottom plate inside the piston.) According to one specific embodiment, all eccentricities of the piston and/or under load At least three, preferably four, strain gauges can be arranged around the piston so that the bending can be reflected. More specifically, the hollow piston may include a plurality of strain gauges disposed on an inner surface of an inner wall of the piston. Preferably at least three, more preferably at least four strain gauges are arranged symmetrically on the inner circumferential surface of the hollow piston. According to a more specific embodiment, the strain gauge is configured to provide information about the load applied to the upper plate of the piston by measuring the refractive index of the upper plate of the piston to which pressure is applied to the fluid of the jack. and can be connected to the bottom plate. According to a further preferred embodiment, a strain gauge extending from the top plate to the bottom plate is used together with a plurality of strain gauges on the inner surface of the piston wall. Using one or more strain gauges attached to, embedded in, and/or disposed in proximity to the piston, the piston becomes a strain meter that determines the load applied by the jack containing the piston.

One or more strain gauges or other sensors are embedded within one or more materials of the jack. Strain gages include an insulating material that protects the strain gages during casting. In a specific embodiment, the piston is made of iron.

The strain gauge or other sensor may be disposed on one or more surfaces of one or more materials of the jack. Various methods are available for disposing the sensor on a surface. For example, the sensor may be attached to a surface via at least one tightening device, or a portion of the sensor may be attached to a first surface and another portion of the sensor may be attached to a second surface. The sensor is configured to measure the deviation of the first surface relative to the second surface, or vice versa. There are many different tightening devices that can be used in the present invention. For example, mechanical fasteners such as nails, pins, bolts, screws, brackets, or other structures may be used. Alternatively, an adhesive fastener such as an epoxy, glue, or other adhesive may be used.

The clamping device also functions to protect the sensor from electrical and/or temperature changes on the surface. Specifically, a vibrating wire strain gauge may be used. For example, the vibrating wire strain gauge may be included in the piston of FIG. 3 , and as shown in FIG. 6 , the strain gauge may have a cross-sectional shape indicated by 103 . According to still further embodiments, a strain gauge in the form of a wheatstone bridge may be used.

Meanwhile, the load-bearing apparatus of the present invention may include a processor, an input interface, an output interface, an application program, and a program module for controlling the operation of the interface.

In the above, the present invention has been described in detail with reference to the embodiments, but those of ordinary skill in the art to which the present invention pertains may make various substitutions, additions and modifications within the scope without departing from the technical spirit described above. Of course, it should be understood that such modified embodiments also fall within the protection scope of the present invention as defined by the appended claims below.

1: jack 3: middle part
5: upper part of pile 7: lower part of pile
9: lower surface 11: upper surface
13: jack cylinder 20: strain gauge
P : pressure L : load

Claims (1)

a jack placed between the top and bottom of the pile; and,
at least one strain gauge disposed such that the strain applied to the jack corresponds to a load applied by the jack and a load-strain relationship;
the jack comprising a piston, a cylinder for receiving the piston, and a fluid disposed between an upper surface of the piston and a bottom surface of the top of the cylinder;
applying pressure to the fluid creates a first force on the piston and a second force on the cylinder, which tends to separate the piston and cylinder;
the at least one strain gauge is included in the piston of the jack;
wherein the at least one strain is at least one strain applied by the piston, the piston comprising a hollow body, a top plate, and a bottom plate;
One of the at least one strain gauge is a bidirectional load test apparatus of a pile, characterized in that attached to the upper plate and the bottom plate of the piston.

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