Calibration method for measuring equipment for ground investigation

Abstract

To provide a method for calibrating a measurement device for subsurface exploration, which can facilitate calibration by using components used in subsurface exploration or simple jigs.SOLUTION: The present invention is a method for calibrating a measurement device for subsurface exploration mounted to a penetration tester for penetrating a rod into the ground when exploring a target subsurface. The method comprises: installing a first calibration plate on a pedestal part so as to block a route through which the rod passes (step S2); contacting the tip of the rod with the first calibration plate (step S4); loading the rod with a known load based on a weight part and a vibrator and performing measurement by a load measurement unit of the measurement device for subsurface exploration (steps S5, S6); and performing calibration based on the measurement result of the load measurement unit and the known load (step S7).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for calibrating a measuring device for ground investigation that is attached to a penetration testing machine that penetrates a rod into the ground when investigating a target ground. [Background technology]

[0002] In conventional general ground investigations, in the case of small-scale buildings, ground constants related to the strength of the ground are obtained by in-situ tests such as Swedish Weight Sounding (SWS) tests. Then, the study of the ground's bearing capacity against long-term loads is carried out based on these ground constants.

[0003] The SWS test is an investigation method that evaluates the hardness of the ground by measuring the penetration resistance of a rod equipped with a weight. The ground investigation equipment used for this test has been automated in recent years, and automated equipment for loading and unloading the weight, rotation control, and measurement are also becoming widespread.

[0004] On the other hand, the SWS test determines the penetration resistance, and there are many issues with its accuracy. Patent Document 1 proposes a method of obtaining highly accurate information by using a penetration tester and applying vibration to it.

[0005] Here, when trying to confirm the dynamic penetration amount and load by using a vibration exciter to apply vibration using a penetration testing machine for SWS tests as is, as in the method disclosed in Patent Document 1, if a displacement meter or load meter is attached directly to the main body of the device, there is a problem that the vibration will be large and may affect accuracy and durability.

[0006] Therefore, Patent Document 2 proposes a measuring device for ground investigation that is compatible with a wide variety of investigation devices and can perform measurements easily and with high accuracy by attaching a displacement meter or the like as a simple attachment to the middle of the rod. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-17112 A [Patent Document 2] JP 2019-178490 A Summary of the Invention [Problem to be solved by the invention]

[0008] The load measuring section of the ground survey measuring device may be a load meter that measures by attaching a jig with a load cell or strain gauge to the striking part, and the displacement measuring section of the ground survey measuring device may be a precision machine such as a potentiometer or laser displacement meter.

[0009] The measurement devices used in these ground investigation methods are subject to large vibration loads, and therefore require periodic calibration to ensure accuracy when used repeatedly, but this procedure is generally cumbersome.

[0010] Therefore, an object of the present invention is to provide a method for calibrating a measuring device for ground investigation, which can easily perform calibration by utilizing parts and simple jigs used in ground investigation. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the calibration method for a measuring device for ground investigation of the present invention is a calibration method for a measuring device for ground investigation attached to a penetration testing machine that penetrates a rod into the ground when investigating a target ground, the penetration testing machine comprising a base portion having an opening for penetrating the rod into the target ground, and a weight portion and a vibration exciter that apply a load to the upper end of the rod, and is characterized in that the calibration method comprises the steps of: installing a first calibration plate on the base portion so as to block at least the path through which the rod passes in the opening; contacting the tip of the rod with the first calibration plate; loading the rod with a known load based on the weight portion and the vibration exciter and performing measurement using a load measuring unit of the measuring device for ground investigation; and performing calibration based on the measurement result of the load measuring unit and the known load.

[0012] Another invention for a method for calibrating a measuring device for ground investigation is a method for calibrating a measuring device for ground investigation that is attached to a penetration testing machine that penetrates a rod into the ground when investigating the target ground, the penetration testing machine has a base portion having an opening for penetrating the rod into the target ground, and is characterized in that the method includes the steps of: placing a first calibration plate on the base portion so as to block at least the path through which the rod passes in the opening; contacting the tip of the rod with the first calibration plate; performing measurements using the upper surface of the first calibration plate as a reference using a displacement measuring unit of the measuring device for ground investigation; placing a second calibration plate having a known thickness on the first calibration plate; performing measurements using the upper surface of the second calibration plate as a reference using the displacement measuring unit; and performing calibration based on the measurement results of the displacement measuring unit and the thickness of the second calibration plate. Effect of the Invention

[0013] In the method for calibrating the ground investigation measuring device of the present invention configured in this manner, a known load based on the weight part and the vibration exciter of the penetration testing machine is loaded onto the rod, and the load measuring part is calibrated based on the measurement results of the load measuring part at that time.

[0014] In this way, calibration can be easily performed by using parts such as the weight and vibration exciter of the penetration testing machine used for ground surveys, or a simple plate-shaped jig that can be simply placed on the base of the penetration testing machine.

[0015] In another method of calibrating a measuring device for ground investigation according to the present invention, a first calibration plate is placed on the base of a penetration tester, and after a first measurement is performed by the displacement measuring unit, a second calibration plate of known thickness is placed on top of the first calibration plate, and a measurement is performed again by the displacement measuring unit. Then, the displacement measuring unit is calibrated based on the results of the two measurements by the displacement measuring unit.

[0016] In this way, calibration can be easily performed by simply placing the simple, plate-shaped first calibration plate and second calibration plate on the base of the penetration testing machine and performing measurement using the displacement measuring unit. [Brief description of the drawings]

[0017] [Figure 1] 4 is a flowchart illustrating a process flow of a calibration method for a measuring device for ground investigation according to the present embodiment. [Diagram 2] FIG. 13 is a schematic diagram for explaining a method for calibrating a load measuring unit of a measuring device for ground investigation. [Diagram 3] FIG. 2 is a perspective view illustrating an example of the configuration of a measuring device for ground investigation. [Figure 4] 4 is a flowchart illustrating a process flow of a calibration method for a measuring device for ground investigation according to the first embodiment. [Diagram 5] FIG. 13 is an explanatory diagram showing a step of measuring a first calibration plate in the method for calibrating the displacement measuring unit of the measuring device for ground investigation. [Figure 6] FIG. 13 is an explanatory diagram showing a step of measuring a second calibration plate in the method for calibrating the displacement measuring unit of the measuring device for ground investigation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a flow chart for explaining the process flow of the method for calibrating the measuring device for ground investigation according to the present embodiment, and Fig. 2 is a diagram for explaining the method for calibrating the load measuring unit of the measuring device for ground investigation.

[0019] A ground investigation using the ground investigation device 1 described in this embodiment is carried out on a target ground G for which a building such as a house is to be constructed. A ground investigation such as a penetration test is usually carried out directly on the target ground G at one or more points.

[0020] For example, in the case of a small-scale building, a Swedish weight sounding test (SWS test) is generally conducted at one or more points on the target ground G. The Swedish weight sounding test is a type of static penetration test specified in JIS A 1221, and is a ground investigation method that estimates the hardness of the ground from the penetration resistance of a rod when screwing a screw point into the ground.

[0021] 2, the penetration test machine 2 is mainly composed of a base machine 21, a rod 22, a screw point (not shown) attached to the tip (lower end) of the rod 22, a base part 24, and a weight part 25. The base machine 21 is a Swedish sounding test machine that has a proven track record in soil surveys of small buildings.

[0022] On the other hand, the weight unit 25 is used to gradually apply a load to the screw point used in the Swedish Weight Sounding (SWS) test. The weight unit 25 has a total weight of 100 kg according to the standard.

[0023] In the SWS test, the survey results are basically evaluated in 25 cm increments. The rod 22 is composed of unit rods 221 of 1 m or 50 cm connected together. In other words, the measurement is carried out by connecting the unit rods 221 together.

[0024] By attaching a vibration exciter 3 to the penetration testing machine 2 and applying vibrations and impacts, it becomes possible to evaluate the bearing capacity and rigidity of the ground more accurately than with the Swedish sounding test. In order to evaluate the bearing capacity of the ground, accurate measurement data of the applied load and the penetration amount is required.

[0025] That is, it is necessary to accurately measure the dynamic penetration amount and load while striking with the vibration exciter 3. This measurement can be performed by using ground investigation measuring devices such as a displacement meter and a load meter that are originally equipped in the penetration test machine 2.

[0026] Furthermore, as described below, by attaching a strain detector or a displacement meter to a short rod or a jig interposed in the rod 22, it is possible to make a ground survey measuring device equipped with a load measuring section and a displacement measuring section.

[0027] 2, the ground investigation device 1 has a measuring device 4, which serves as a ground investigation measuring device, built between unit rods 221, 221 constituting a rod 22. An example of the measuring device 4 is shown in FIG.

[0028] This measuring device 4 is mainly composed of a short rod 41 interposed between the rod 22, a strain gauge 42 which serves as a strain detector of the load measuring section attached to the short rod 41, and a non-contact displacement meter 43 which serves as a displacement measuring section.

[0029] The short rod 41 is formed of a cylindrical tube with a diameter approximately the same as that of the rod 22, and is provided with an upper connection screw 411 at its upper end and a lower connection screw 412 at its lower end. That is, the short rod 41 interposed between the unit rods 221, 221 is provided with an upper connection screw 411 for connection to the lower end of the upper unit rod 221, and a lower connection screw 412 for connection to the upper end of the lower unit rod 221.

[0030] The strain gauge 42 is attached to the outer circumferential surface 413 of the short rod 41. The direction of expansion and contraction (measurement direction) of this strain gauge 42 coincides with the axial direction of the short rod 41. A plurality of strain gauges 42 are attached to the outer circumferential surface 413 of the short rod 41. For example, a pair of strain gauges 42 can be attached every 180° in the circumferential direction. Also, four strain gauges 42 can be attached every 90° in the circumferential direction.

[0031] The strain gauge 42 is a versatile instrument and can be obtained at a very low cost. In addition, since it can be installed simply by attaching it to the outer circumferential surface 413 of the short rod 41, it can be configured very compactly.

[0032] And, since the material (Young's modulus E) and cross-sectional area A of the short rod 41 are specified, the axial load N acting on the short rod 41 can be easily calculated from the relational expression with the strain ε (ε=σ / E), where σ is the stress intensity in the axial direction (σ=N / A). The strain ε is a value measured by the strain gauge 42, and corresponds to the ratio (ε=ΔL / L) of the displacement ΔL when the load N acts on the total length L.

[0033] On the other hand, the non-contact displacement meter 43 is provided so as to be able to measure the displacement between a predetermined position of the short rod 41 and a corresponding reference point existing in the vertical direction. Specifically, it measures the relative displacement between the protruding part 44 protruding from the outer circumferential surface 413 of the short rod 41 and the upper surface 241 (reference point) of the base part 24 of the penetration tester 2, etc.

[0034] The non-contact displacement meter 43 attached to the underside of the protruding portion 44 protruding perpendicularly to the outer circumferential surface 413 of the short rod 41 is a laser type displacement meter equipped with an irradiation portion and a light receiving portion of the laser S. The laser S irradiated from the irradiation portion of the non-contact displacement meter 43 facing vertically downward is reflected from the upper surface 241 of the base portion 24 of the penetration tester 2 as a reflection point and detected by the light receiving portion.

[0035] The measuring device 4 is equipped with a calculation processing unit that calculates the load N from the strain amount (ε) detected by the strain gauge 42. In addition, the displacement (penetration amount) when the load N acts can be calculated from the detection signal detected by the non-contact displacement meter 43. Then, the allowable bearing capacity and estimated settlement amount can be calculated from the load and penetration amount measured in this way, so that the bearing performance of the ground can be evaluated.

[0036] The measuring device 4 configured in this manner is used under conditions in which it is continuously subjected to vibration by the vibrator 3, and therefore is subjected to a large vibration load. Therefore, if the device is used repeatedly, periodic calibration is required to ensure its accuracy.

[0037] The process flow of the method for calibrating a measuring device for ground investigation according to this embodiment will now be described with reference to the flowchart shown in FIG. First, in step S1, a penetration testing machine 2 is installed as shown in Fig. 2. The installation location does not necessarily have to be on the target ground G.

[0038] Next, in step S2, the first calibration plate 5 is placed on the upper surface 241 of the base 24 of the penetration tester 2. The base 24 of the penetration tester 2 is provided with an opening such as a hole or gap to allow the rod 22 to pass through and penetrate into the target ground G.

[0039] Therefore, when the rod 22 is lowered as during testing, the tip of the rod 22 passes through this open section, so the first calibration plate 5 is placed on the upper surface 241 of the base portion 24 so as to block at least the path through which the rod 22 passes in the open section.

[0040] The first calibration plate 5 is formed of a material and with a thickness capable of withstanding the load of the total weight of the vibration exciter 3 and the weight 25. The penetration tester 2 for performing the SWS test is equipped with weights 25 with a total weight of 100 kg in accordance with the standard. The weight of the vibration exciter 3 is also known. And, since the weights of the weight 25 and the vibration exciter 3 are used as the calibration load, a plate-shaped member capable of withstanding this load is used for the first calibration plate 5.

[0041] In step S3, the rod 22 with the measuring device 4 interposed between the unit rods 221, 221 is set in the penetration tester 2. As a result, the strain gauge 42, which serves as a load measuring unit, is connected to the rod 22.

[0042] Then, in step S4, the tip of the rod 22 is lowered to contact the upper surface 51 of the first calibration plate 5. Figure 2 shows this state. In short, the rod 22 is brought into a state where it can be supported by the first calibration plate 5. Note that while the rod 22 is fixed by the chuck of the penetration tester 2, no load acts on the rod 22, and no load is measured by the load measuring unit.

[0043] In this state, in step S5, the weight of the weight 25 and the vibration exciter 3 is applied as a load to the upper end of the rod 22 by releasing the chuck of the penetration tester 2. Here, the weights of the weight 25 and the vibration exciter 3 are known in advance, and therefore can be said to be known loads.

[0044] The weight of the weight 25 (total 100 kg) and the weight of the vibration exciter 3 can be entirely applied to the rod 22, or only an arbitrary known weight can be applied. In short, among the weights of the parts originally equipped in the penetration tester 2, the parts whose size to be loaded is known are used as the load.

[0045] In step S6, the load value from the no-load state to when a known load set by the weight of weight 25 and vibration exciter 3 is applied is measured by the detection value (strain ε) of strain gauge 42. The amount of strain detected in this manner becomes the measurement result of the load based on weight 25 and vibration exciter 3 by the load measuring unit.

[0046] Therefore, in step S7, the load measuring unit is calibrated so that the load N calculated by the calculation processing unit from the amount of strain detected by the strain gauge 42 is the same magnitude as the known load based on the weight portion 25 and the vibration exciter 3.

[0047] Next, the operation of the method for calibrating a measuring device for ground investigation according to this embodiment will be described. In the method for calibrating the ground investigation measuring device of this embodiment configured as described above, a known load based on the weight 25 of the penetration tester 2 and the vibration exciter 3 is loaded onto the rod 22, and the load measuring section is calibrated based on the measurement results of the strain gauge 42, which serves as a strain detector for the load measuring section at that time.

[0048] In this way, calibration can be easily performed by simply using parts such as the weight 25 and the vibration exciter 3 of the penetration testing machine 2 used for ground investigation, and the simple first calibration plate 5 which is simply placed on the base 24 of the penetration testing machine 2. Therefore, calibration can be performed repeatedly at any time, such as before or during the test, allowing for efficient and highly accurate measurements. EXAMPLES

[0049] Hereinafter, a first embodiment, which is different from the embodiment described above, will be described with reference to Figures 4 to 6. Note that the same terms or the same reference numerals will be used to describe the same or equivalent parts as those described in the embodiment described above.

[0050] In the above embodiment, the method for calibrating the load measuring unit of the measuring device for ground investigation has been described. In this Example 1, the method for calibrating the displacement measuring unit of the measuring device for ground investigation will be described. Specifically, the non-contact displacement meter 43 of the measuring device 4 described in the above embodiment will be used for the description.

[0051] In the calibration method of the non-contact displacement meter 43 of this Example 1, two plate-like members are used. The first plate can be the first calibration plate 5 described in the above embodiment. However, since the calibration method of the non-contact displacement meter 43 does not apply a load to the plate-like members, a different plate-like member can also be used.

[0052] The second plate-like member is the second calibration plate 6. The second calibration plate 6 is a plate-like member with a known thickness. The first calibration plate 5 and the second calibration plate 6 are both installed so as to block at least the path through which the rod 22 passes in the open part of the base part 24.

[0053] Moreover, the first calibration plate 5 and the second calibration plate 6 are formed to have a width that can cover at least an area from the point where the rod 22 passes to the reflection point of the laser S of the non-contact displacement meter 43. Furthermore, the first calibration plate 5 and the second calibration plate 6 are formed to have a constant thickness over the entire area.

[0054] 6, holes 62 are drilled in the second calibration plate 6 at positions corresponding to the path through which the rod 22 passes. The holes 62 are formed, for example, to be slightly larger in diameter than the rod 22 so that the tip of the lowered rod 22 can easily pass through.

[0055] Next, the process flow of the calibration method of the measuring instrument for ground investigation of the first embodiment will be described with reference to the flowchart shown in FIG. First, in step S11, the penetration testing machine 2 is installed as shown in Fig. 5. The installation location does not necessarily have to be on the target ground G.

[0056] Next, in step S12, the first calibration plate 5 is placed on the upper surface 241 of the base 24 of the penetration tester 2. Then, the rod 22 is lowered in the same manner as during testing, and the tip of the rod 22 is brought into contact with the upper surface 51 of the first calibration plate 5 (step S13).

[0057] Next, in step S14, the non-contact displacement meter 43 irradiates the laser S toward the upper surface 51 of the first calibration plate 5. This state is shown in Fig. 5. In short, the distance between the upper surface 51 of the first calibration plate 5 and the non-contact displacement meter 43 is measured based on the detection signal of the non-contact displacement meter 43.

[0058] In this way, after the distance representing the position of the upper surface 51 of the first calibration plate 5 is measured by the non-contact displacement meter 43, the tip of the rod 22 is temporarily lifted to a height equal to or greater than the thickness of the second calibration plate 6.

[0059] Next, in step S15, the second calibration plate 6 is placed on the upper surface 51 of the first calibration plate 5. Then, the tip of the rod 22 is lowered and passed through the hole 62 of the second calibration plate 6 so that the tip of the rod 22 comes into contact with the upper surface 51 of the first calibration plate 5.

[0060] In step S16, the non-contact displacement meter 43 irradiates the laser S toward the upper surface 61 of the second calibration plate 6. This state is shown in Fig. 6. In short, the distance between the upper surface 61 of the second calibration plate 6 and the non-contact displacement meter 43 is measured based on the detection signal of the non-contact displacement meter 43.

[0061] When the distance indicating the position of the upper surface 61 of the second calibration plate 6 is measured by the non-contact displacement meter 43 in this manner, the displacement is calculated from the difference with the position of the upper surface 51 of the first calibration plate 5 measured in step S14. This displacement becomes the measurement result by the displacement measuring unit.

[0062] Therefore, in step S17, the displacement measuring unit is calibrated so that the displacement calculated from the measurement result of the non-contact displacement meter 43 has the same magnitude as the known thickness of the second calibration plate 6.

[0063] In the method for calibrating the ground investigation measuring device of Example 1 configured as described above, the first calibration plate 5 is placed on the base 24 of the penetration tester 2, and an initial measurement is performed using the displacement measuring unit (non-contact displacement meter 43), after which a second calibration plate 6 of known thickness is placed on top of the first calibration plate 5, and measurement is again performed using the non-contact displacement meter 43. Then, based on the results of the two measurements by the non-contact displacement meter 43, the displacement measuring unit is calibrated.

[0064] In this way, calibration can be easily performed by simply placing the simple, plate-shaped first calibration plate 5 and second calibration plate 6 in order on the base 24 of the penetration testing machine 2 and performing measurements using the non-contact displacement meter 43 for each.

[0065] This allows calibration to be performed repeatedly at any time, such as before or during a test, enabling efficient, highly accurate measurements. Other configurations and functions and effects are substantially the same as those of the above-described embodiment, and therefore description thereof will be omitted.

[0066] Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment or example, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0067] For example, in the above-mentioned embodiment and Example 1, the measuring device for ground investigation has been described taking as an example the measuring device 4 equipped with a load measuring unit constituted by a strain gauge 42 and a displacement measuring unit constituted by a non-contact displacement meter 43, but the present invention is not limited to this. The load measuring unit may be constituted by a load cell, and the displacement measuring unit may be constituted by a potentiometer-type displacement meter.

[0068] In addition, in the first embodiment, the second calibration plate 6 having the hole 62 for passing the rod 22 therethrough is described as an example, but the present invention is not limited to this, and the second calibration plate may be large enough to be placed only at the reflection point of the laser S of the non-contact displacement meter 43. In this case, the process of temporarily raising the rod 22 after measuring the upper surface 51 of the first calibration plate 5 can be omitted.

[0069] In addition, in the first embodiment, the method of calibrating the laser-type displacement measuring unit attached to the rod 22 has been described, but the present invention is not limited to this. For example, when a potentiometer-type displacement meter that directly measures the amount of descent of the rod 22 is used as the displacement measuring unit, the tip of the rod 22 is brought into contact with the upper surface 51 of the first calibration plate 5 to perform measurement, and then the tip of the rod 22 is brought into contact with the upper surface 61 of the second calibration plate 6 placed on top of the first calibration plate 5 to perform measurement, thereby measuring a displacement equivalent to the thickness of the second calibration plate 6. [Explanation of symbols]

[0070] 2: Penetration tester 22: Rod 24: Base 25: Weight 3: Vibrator 4: Measuring equipment (measuring equipment for ground investigation) 42: Strain gauge (load measuring part) 43: Non-contact displacement meter (displacement measurement part) 5: First calibration plate 51:Top surface 6: Second calibration plate 61:Top surface G: Target ground

Claims

1. A method for calibrating a measuring device for ground investigation attached to a penetration testing machine that penetrates a rod into the ground when investigating a target ground, comprising: The penetration test machine includes a base having an opening for penetrating the rod into the target ground, a weight for applying a load to an upper end of the rod, and a vibration exciter. a step of placing a first calibration plate on the base portion so as to block at least a path through which the rod passes in the open portion; contacting the tip of the rod with the first calibration plate; A step of loading a known load based on the weight portion and a vibration exciter onto the rod and measuring the load using a load measuring unit of the ground investigation measuring device; A method for calibrating a measuring device for ground investigation, comprising the step of performing calibration based on the measurement results of the load measuring unit and the known load.

2. A method for calibrating a measuring device for ground investigation attached to a penetration testing machine that penetrates a rod into the ground when investigating a target ground, comprising: The penetration tester includes a base having an opening for penetrating the rod into the target ground, a step of placing a first calibration plate on the base portion so as to block at least a path through which the rod passes in the open portion; contacting the tip of the rod with the first calibration plate; performing a measurement based on an upper surface of the first calibration plate by a displacement measuring unit of the ground investigation measuring device; placing a second calibration plate having a known thickness on the first calibration plate; performing a measurement using an upper surface of the second calibration plate as a reference by the displacement measuring unit; A method for calibrating a measuring device for ground investigation, comprising a step of performing calibration based on the measurement results of the displacement measuring unit and the thickness of the second calibration plate.

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