JP7802279B2 - Stress measurement device - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applied. Presented at the 31st Tunnel Engineering Research Conference on November 26, 2021.

One embodiment of the present invention relates to the structure of a stress measurement device using the stress release method.

Numerical analysis techniques are used when designing mountain tunnels. When performing numerical analysis, the initial stress state of the ground has a significant impact on the analysis results. Therefore, it is important to accurately grasp the initial stress state of the ground. The overcoring method is known as one method for measuring stress in the ground. With the overcoring method, a stress measurement device is inserted into a measurement hole (also called a "borehole") formed in the ground, and the initial stress state is evaluated by measuring the deformation of the measurement hole caused by drilling the outer periphery of the measurement hole.

A known example of a device for measuring the deformation of a measurement hole is a stress measuring device that includes a long main body, a first support member in the hole provided at the tip end of the main body, a second support member in the hole provided at the base end of the main body, and a measuring unit provided between the support members in the hole of the main body (see Patent Document 1).

Japanese Patent Application Laid-Open No. 2020-066843

The overcoring method measures the deformation in the diameter direction of the measurement hole and the deformation in the length direction of the hole. The stress measurement device uses a contact-type strain gauge to measure the hole length and deformation in the diameter direction of the measurement hole. Conventional stress measurement devices have the problem that the measurement results include displacement in the length direction of the hole that occurs when the gauge is inserted into the measurement hole, making it difficult to accurately measure deformation in the diameter direction in particular.

In light of these problems, one embodiment of the present invention aims to provide a stress measuring device that can accurately measure stress.

A stress measuring device according to one embodiment of the present invention includes a first housing containing a rod, a first sensor arranged on the first end side of the first housing, a second sensor arranged on the second end side of the first housing opposite the first end, and a second housing connected to the first end side of the first housing. The first sensor includes a first elastic plate extending in the axial direction of the rod and having one end fixed to the first housing and the other end as a free end, a first strain gauge attached to the first elastic plate, and a contact roller attached to the free end of the first elastic plate. The second sensor includes a second elastic plate extending in the axial direction of the rod and one end fixed to the first housing, a second strain gauge attached to the second elastic plate, and a contact pin attached to the other end side of the second elastic plate. The contact roller of the first sensor and the contact pin of the second sensor are arranged on the second end side of the first elastic plate and the second elastic plate relative to the first end side.

In one embodiment of the present invention, the first housing includes a first support member provided on the side of the first end of the rod and having an outer diameter larger than the outer diameter of the rod, and a second support member provided on the side of the second end of the rod and having an outer diameter larger than the outer diameter of the rod, and the first elastic plate may be cantilevered on the first support member, and the second elastic plate may be attached to the second support member.

In one embodiment of the present invention, the first housing and the second housing may be connected via a universal joint, and in this configuration, a gap may be provided between the first housing and the second housing.

In one embodiment of the present invention, the first elastic plate may be configured to elastically deform in the axial radial direction of the rod, and the second elastic plate may be configured to elastically deform in the axial length direction of the rod. The second elastic plate may have a curved portion, and a second strain gauge may be provided in the curved portion.

In one embodiment of the present invention, it is preferable that the contact roller and contact pin protrude outward from the outer surface of the first housing.

In one embodiment of the present invention, it is preferable that multiple first sensors and multiple second sensors are arranged along the outer periphery of the first housing.

In one embodiment of the present invention, it is preferable that the first strain gauge is configured to measure displacement in the diameter direction of the measurement hole, and the second strain gauge is configured to measure displacement in the length direction of the measurement hole.

In one embodiment of the present invention, a data logger may be provided within the second housing to record the measurements of the first strain gauge and the second strain gauge.

In a stress measuring device according to one embodiment of the present invention, the tip of the sensor that measures the amount of deformation in the diameter direction of the measurement hole has a roller structure, which makes it possible to eliminate the influence of displacement in the length direction of the measurement hole that occurs when the sensor is inserted into the measurement hole, and to accurately measure the distortion in the diameter direction of the measurement hole.

1 shows the configuration of a stress measuring device according to one embodiment of the present invention. 1A and 1B show partial structures of a stress measuring device according to an embodiment of the present invention, in which FIG. 1A shows a cross-sectional structure of a first sensor portion, and FIG. 1B shows a cross-sectional structure corresponding to the section A1-A2. 1A and 1B show partial structures of a stress measuring device according to an embodiment of the present invention, in which (A) shows a cross-sectional structure of a second sensor portion, (B) shows a planar structure of the second sensor, (C) shows a cross-sectional structure corresponding to the section B1-B2, and (D) shows a cross-sectional structure corresponding to the section C1-C2. 1 shows a state in which a stress measuring device according to an embodiment of the present invention is inserted into a measurement hole.

Embodiments of the present invention will be described below with reference to the drawings. However, the present invention can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. For clarity of explanation, the drawings may show the length, width, height, thickness, shape, etc. of each part schematically compared to the actual form. However, these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each figure, elements similar to those previously described with reference to the previous figures may be designated by the same reference numerals (or reference numerals with A, B, a, b, etc. suffixed thereto), and detailed descriptions may be omitted as appropriate. Furthermore, the letters "first" and "second" attached to each element are convenient labels used to distinguish between elements, and have no further meaning unless otherwise specified.

Figure 1 shows the configuration of a stress measurement device 100 according to one embodiment of the present invention. The stress measurement device 100 according to this embodiment can be used to evaluate initial stress using the overcoring method and can measure the amount of displacement in the diameter and length directions of the measurement hole formed by boring due to stress release. The stress measurement device 100 includes a first sensor unit 1001 that measures the amount of displacement in the diameter direction of the measurement hole and a second sensor unit 1002 that measures the amount of displacement in the length direction of the measurement hole. The stress measurement device 100 has a cylindrical external shape, and the diameter and length directions of the measurement hole approximately coincide with the axial diameter and length directions of the stress measurement device 100, respectively. Therefore, the amount of displacement in the diameter direction of the stress measurement device 100 corresponds to the amount of displacement in the diameter direction of the measurement hole, and the amount of displacement in the axial length direction of the stress measurement device 100 corresponds to the amount of displacement in the length direction of the measurement hole. The stress measurement device 100 also includes a data logger 124 that collects data measured by the first sensor unit 1001 and the second sensor unit 1002.

As shown in FIG. 1, the stress measuring device 100 is composed of a first housing 102 and a second housing 104. The first housing 102 and the second housing 104 are elongated so that they can be inserted into the measurement hole, and are arranged in series in the longitudinal direction. The first housing 102 and the second housing 104 preferably have a cylindrical shape to stabilize their position within the measurement hole. The first housing 102 and the second housing 104 are separate housings and are connected by a universal joint 122. The first housing 102 is provided with a first sensor unit 1001 and a second sensor unit 1002, and the second housing 104 houses a data logger 124 and a battery 126. The first sensor unit 1001 is provided with a first sensor 106, and the second sensor unit 1002 is provided with a second sensor 108.

The stress measuring device 100 is inserted into the measurement hole in the X1 direction shown in Figure 1 and removed in the X2 direction. That is, the stress measuring device 100 is inserted into the measurement hole with the second housing 104 first, followed by the first housing 102.

The first housing 102 includes a rod 1023, a first support member 1021 provided on the first end L1 side of the rod 1023, and a second support member 1022 provided on the second end R1 side. An example of the rod 1023 is a cylindrical or rod-shaped member that extends linearly in the material axis direction. In this specification, the material axis direction of the rod 1023 is also referred to as the "axial length direction," and the direction perpendicular to the material axis direction is also referred to as the "axial diameter direction."

A first sensor 106 is attached to the first support member 1021, and a second sensor 108 is attached to the second support member 1022. The first sensor 106 has a structure in which a first strain gauge 110 and a contact roller 118 are attached to a first elastic plate 114. The second sensor 108 has a structure in which a second strain gauge 112 is attached to a second elastic plate 116, and a contact pin 120 is connected to one end. The contact roller 118 and contact pin 120 protrude outside the first housing 102 and are arranged to come into contact with the inner wall surface of the measurement hole when the stress measuring device 100 is inserted into the measurement hole and displacement is measured.

The second housing 104 houses a data logger 124, a battery 126, and the like. The data logger 124 is connected to the first strain gauge 110 and the second strain gauge 112 by wiring (not shown). The data logger 124 may also be connected to the first strain gauge 110 and the second strain gauge 112 wirelessly. The data logger 124 is supplied with power from the battery 126, allowing it to collect data without the need for wired or wireless remote control. In other words, the stress measuring device 100 can operate independently and independently within the measurement hole.

The second housing 104 is provided with contact pins 130. The contact pins 130 may include a first contact pin 1301 provided on the second end R2 side of the second housing 104 (the side connected to the first housing 102) and a second contact pin 1302 provided on the first end L2 opposite the second end R2. The first contact pins 1301 and second contact pins 1302 are preferably provided at multiple locations along the outer periphery of the second housing 104. The first contact pins 1301 and second contact pins 1302 are provided so as to protrude from the second housing 104. The first contact pins 1301 and second contact pins 1302 are elastic, and the height at which they protrude from the second housing 104 can be adjusted as appropriate. The second housing 104 is provided with elastic contact pins 130 (first contact pin 1301, second contact pin 1302), which prevents the body portion from directly contacting the inner wall surface of the measurement hole. When the second housing 104 is installed inside the measurement hole, the contact pins 130 (first contact pin 1301, second contact pin 1302) can be brought into contact with the inner wall surface at two points, allowing the stress measuring device 100 to be securely fixed in place.

The stress measuring device 100 is inserted into the measurement hole using a pushing tool from the side of the first housing 102. The first housing 102 and the second housing 104 are connected by a universal joint 122, and the second housing 104 is provided with elastic contact pins 130 (first contact pin 1301, second contact pin 1302). This absorbs any wobble that occurs in the diameter direction of the measurement hole when the stress measuring device 100 is inserted into the measurement hole, improving the linearity of the stress measuring device 100.

Figure 2(A) shows a side view of the first sensor unit 1001, and Figure 2(B) shows a cross-sectional structure corresponding to the A1-A2 line shown in Figure 2(A). Figure 2(A) shows the configuration of the first housing 102, including the rod 1023, first support member 1021, and part of the second support member 1022. A universal joint 122 is attached to the first end L1 of the first housing 102 (one end of the rod 1023). The universal joint 122 is connected to the second housing 104.

As shown in FIG. 2(A), a gap G1 is provided between the first end L1 of the first housing 102 and the adjacent end (second end R2 side) of the second housing 104. The first housing 102 and the second housing 104 are connected by a universal joint 122, allowing for bending at this connection; however, the range of bending is restricted by arranging the first housing 102 and the second housing 104 in close proximity to each other with the gap G1. The range of the gap G1 can be set as appropriate, but is typically set to a distance of 0.5 mm to 2 mm, for example, 1 mm. As described above, by arranging the first housing 102 and the second housing 104 with the gap G1, it is possible to absorb any wobble that occurs in the diameter direction of the measurement hole when the stress measurement device 100 is inserted into and removed from the measurement hole.

The first support member 1021 is provided on the first end L1 side of the first housing 102 (in other words, on the first end L1 side of the rod 1023). The second support member 1022 is provided on the second end R1 side of the first housing 102 (in other words, on the second end R1 side of the rod 1023). As shown in FIG. 2(A), the first housing 102 may have a structure in which the first support member 1021, second support member 1022, and rod 1023 are formed as separate parts and assembled together. Although not shown, the first housing 102 may also have a structure in which the portions corresponding to the first support member 1021, second support member 1022, and rod 1023 are integrally molded.

The first housing 102 is not limited to the structure shown in FIGS. 1 and 2(A), and may have a shape different from that shown as long as it allows the first sensor unit 1001 and the second sensor unit 1002 to be arranged along the insertion direction X1 of the stress measuring device 100. For example, a member corresponding to the rod 1023 may have a shape that also serves the functions of the first support member 1021 and the second support member 1022.

The first elastic plate 114 is attached to the first support member 1021. The first elastic plate 114 is attached to the outer periphery of the first support member 1021. There are no limitations on the method of attaching the first elastic plate 114, and it may be fastened with a fastener such as a screw, for example. The first elastic plate 114 is a plate-shaped member extending in a direction parallel to the axial length of the rod 1023. The first elastic plate 114 is attached such that one end is fixed to the first support member 1021 and the other end does not contact the first housing 102. In other words, the first elastic plate 114 is attached to the first support member 1021 in a cantilevered manner, with one end being a fixed end and the other end being a free end. The first elastic plate 114 is attached to the first support member 1021 in a cantilevered manner, and the free end is movable in the axial radial direction of the rod 1023.

A first strain gauge 110 is attached to the first support member 1021. The first strain gauge 110 is attached between the fixed end and free end of the first elastic plate 114. The first strain gauge 110 is attached to at least one surface of the first elastic plate 114, and preferably to both surfaces. The first strain gauge 110 deforms and its resistance value changes as the free end of the first elastic plate 114 is displaced in the axial radial direction. The data logger 124 electrically detects changes in the electrical resistance of the first strain gauge 110 and has the function of recording changes in strain over time.

A contact roller 118 is attached to the other end (free end) of the first elastic plate 114. The contact roller 118 is attached so that the rolling direction of the roller is parallel to the axial length direction of the stress measuring device 100. As shown in Figures 2(A) and 2(B), the contact roller 118 attached to the first elastic plate 114 is provided so as to protrude from the first support member 1021. Because the contact roller 118 protrudes from the first support member 1021, the contact roller 118 comes into contact with the inner wall surface of the measurement hole when the stress measuring device 100 is inserted into the measurement hole. Even when the contact roller 118 comes into contact with the inner wall surface of the measurement hole, the rotation of the roller generates almost no friction when the measurement hole is displaced in the hole length direction, so the first elastic plate 114 does not deform in the hole length direction. Meanwhile, the contact roller 118 is pressed against the inner wall surface of the measurement hole by the elastic force of the first elastic plate 114, and can therefore deform the first elastic plate 114 in response to deformation of the measurement hole in the diameter direction.

As shown in Figure 2(B), multiple first sensors 106, each comprising a first elastic plate 114 to which a first strain gauge 110 and a contact roller 118 are attached, are attached around the periphery of the first support member 1021. There is no limit to the number of first sensors 106, but for example, as shown in Figure 2(B), eight first sensors 106 may be provided around the rod 1023 at 45-degree angular intervals. The contact rollers 118 attached facing each direction are all arranged so as to contact the inner wall surface of the measurement hole. By providing first sensors 106 facing each direction in this way, it is possible to accurately measure the displacement of the measurement hole in the diameter direction.

Figure 3(A) shows a side view of the second sensor unit 1002. The second sensor unit 1002 is provided with a second sensor 108. Figure 3(A) shows a portion of the rod 1023 that constitutes the first housing 102, the second support member 1022, and the structure of the second sensor 108. Figure 3(B) shows a plan view of the second sensor 108. Furthermore, Figure 3(C) shows the cross-sectional structure corresponding to the B1-B2 structure shown in Figure 3(A), and Figure 3(D) shows the cross-sectional structure corresponding to the C1-C2 structure.

As shown in FIG. 3(A), the second support member 1022 is attached to the end of the rod 1023 on the second end R1 side. The second support member 1022 has an outer diameter larger than the outer diameter of the rod 1023, and has the second sensor 108 attached to it. The second sensor 108 includes a second strain gauge 112, a second elastic plate 116, and a contact pin 120. The second elastic plate 116 is formed from the same material as the first elastic plate 114, but differs in shape from the first elastic plate 114 in that it has a curved portion 1161.

The second sensor 108 is not attached directly to the second support member 1022, but is attached to the second support member 1022 via a sensor support member 132. The second elastic plate 116 is positioned so that its curved portion 1161 protrudes from the sensor support member 132, and one end is fixed to the sensor support member 132. The other end of the second elastic plate 116 is attached to a fixture 1322. The fixture 1322 is a member that is slidably attached to the sensor support member 132, and also functions as a spacer that ensures that the heights of one end and the other end of the second elastic plate 116 are horizontal. A contact pin 120 is attached to the fixture 1322. In this way, the contact pin 120 is attached to the second elastic plate 116 via the fixture 1322. The fixture 1322 connects the second elastic plate 116 and the contact pin 120, and has the function of transmitting the displacement of the contact pin 120 to the second elastic plate 116.

As shown in Figure 3 (B), a slit 1321 is formed in the sensor support member 132. The contact pin 120 is inserted into the slit 1321, and a fixing device 1322 is attached from below. At the point where the contact pin 120 is inserted into the slit 1321, the sensor support member 132 and fixing device 1322 are sandwiched between fasteners (bolts) from above and below. The movement of the contact pin 120 is restricted by the slit 1321 and the fasteners (bolts). The contact pin 120 can be displaced in the longitudinal direction of the slit 1321, but cannot be displaced in the width direction of the slit 1321 or the thickness direction of the sensor support member 132.

When the stress measuring device 100 is inserted into the measurement hole, the contact pin 120 abuts against the inner wall surface of the measurement hole. It is preferable that the tip of the contact pin 120 has a tapered shape. By having the second sensor 108 have a contact pin 120 with this shape, it becomes possible to accurately measure the displacement of the measurement hole in the hole length direction.

The second sensor 108 has a rectangular shape in a plan view, and is arranged with its longitudinal direction parallel to the axial direction of the rod 1023. The contact pin 120 is arranged so that it can be displaced in a direction parallel to the axial direction, allowing the second sensor 108 to measure displacement of the measurement hole in the hole length direction. The contact pin 120 may be attached directly to the second elastic plate 116, or may be attached via a fixing device 1322.

The sensor support member 132 is attached to the second support member 1022 via a joint 134 (a hinge or universal joint). The tip of the sensor support member 132 (the end opposite to the side where the joint 134 is attached) is positioned so that its inner surface forms a gap with the second support member 1022, and a stopper 138 is inserted through it. The stopper 138 is screwed to the second support member 1022. An elastic body 136 is provided in the gap between the sensor support member 132 and the second support member. The elastic body 136 is, for example, a spring. With this structure, the tip of the sensor support member 132 can be displaced up and down (or left and right, depending on the attachment position of the sensor support member 132) with the joint 134 as the fulcrum. Furthermore, when the stopper 138 is removed, the sensor support member 132 can be displaced so that it opens widely outward with the joint 134 as the fulcrum.

The second sensor 108 measures the displacement of the measurement hole in the length direction by the second elastic plate 116 deforming in the length direction as the contact pin 120 displaces in the length direction of the measurement hole, causing the resistance value of the second strain gauge 112 to change. The data logger 124 electrically detects changes in the electrical resistance of the second strain gauge 112 and records changes in strain over time.

As shown in FIG. 3(C), multiple second sensors 108, each having a second elastic plate 116 to which a second strain gauge 112 and a contact pin 120 are attached, are attached around the second support member 1022. There is no limit to the number of second sensors 108; for example, as shown in FIG. 3(C), four second sensors may be provided around the second support member 1022, spaced 90 degrees apart. FIG. 3(D) also shows the cross-sectional shape of the tip of the sensor support member 132. At the tip, a stopper 138 is inserted into the sensor support member 132, restricting the range of movement of the tip of the sensor support member 132 to the space between the stopper 138 and the floor formed by the second support member 1022. The sensor support member 132 is prevented from easily swinging due to vibration by the pressure exerted by the stopper 138 and the repulsive force of the elastic body 136.

In the second sensor unit 1002, contact pins 120 are attached facing in each direction so as to contact the inner wall surface of the measurement hole. By providing second sensors 108 facing in each direction in this way, deformation of the measurement hole in the hole length direction can be accurately measured.

The first sensor 106 and the second sensor 108 have different shapes but use the same materials. The first elastic plate 114 and the second elastic plate are, for example, leaf springs. The leaf springs may be made of metals such as carbon steel, stainless steel, nickel steel, or titanium alloys, or non-metals such as rubber, plastic, or ceramics. It is preferable to use a plate-shaped member for the first elastic plate 114 in order to attach a strain gauge, but if a wire-shaped strain gauge (wire strain gauge) is used, an elastic wire material such as piano wire may be used.

The first strain gauge 110 and the second strain gauge 112 are, for example, metal strain gauges in which metal resistors are laid out in a zigzag pattern on a thin insulator.

As described with reference to Figures 1, 2, and 3, the first sensor 106 has its contact roller 118 positioned closer to the second end R1 of the first housing 102 than the fixed end of the first elastic plate 114, and the second sensor 108 has its contact pin 120 positioned closer to the second end R1 of the first housing 102 than the fixed end of the second elastic plate 116. By arranging the contact roller 118 and contact pin 120 in this manner, the stress measuring device 100 can be smoothly inserted into the measurement hole, and stress (strain) in the axial direction of the stress measuring device 100 is not applied to the first sensor 106 and second sensor 108 during insertion. This allows the initial stress of the natural ground to be measured accurately.

Figure 4 shows the stress measuring device 100 inserted into the measurement hole 200. The stress measuring device 100 shown in this embodiment can measure the initial stress of the natural ground using the overcoring method. The stress measuring device of this embodiment can measure the initial stress of the natural ground using the hole diameter change method. The stress measuring device 100 is inserted into the measurement hole 200 drilled into the natural ground, and then the outer periphery of the measurement hole is drilled to release the stress, and the displacement of the measurement hole 200 is measured. After measurement, the stress measuring device 100 is removed from the measurement hole 200, and the measured data is read from the data logger 124 to calculate the initial stress of the natural ground.

Figure 4 shows a state in which the measurement holes 200 are formed in directions parallel to the X1 and X2 directions. The stress measuring device 100 is inserted into the measurement hole 200 along the X1 direction. Specifically, the stress measuring device 100 is inserted into the measurement hole 200 with the second housing 104 at the front, followed by the first housing 102.

When the second housing 104 is inserted into the measurement hole 200, the elastic contact pins 130 (first contact pin 1301, second contact pin 13602) come into contact with the inner wall surface of the measurement hole 200. Due to the action of the contact pins 130 (first contact pin 1301, second contact pin 1302), the second housing 104 does not come into contact with the inner wall surface of the measurement hole 200, and its central axis is maintained aligned with the center of the measurement hole 200. In other words, the second housing 104, which is located at the front of the stress measurement device 100, is centered within the measurement hole 200. This allows the stress measurement device 100 to be inserted smoothly and stably into the measurement hole 200. With this configuration, the central axis of the measurement hole 200 and the central axis of the stress measurement device 100 can be aligned when inserting and removing the stress measurement device 100 from the measurement hole 200, improving measurement accuracy.

The first housing 102 is inserted into the measurement hole 200 after the second housing 104. In practice, the stress measuring device 100 is inserted into the measurement hole 200 by pushing it in from the second end R1 side of the first housing 102 using an instrument (not shown). The second housing 104 has a built-in data logger 124 and battery 126 and a stable center of gravity, so the stress measuring device 100 can be inserted without shaking when inserted into the measurement hole 200. Figure 4 shows the state in which the stress measuring device 100 has been inserted to a predetermined position in the measurement hole 200 and the instrument has been removed.

The first housing 102 has a first sensor unit 1001 and a second sensor unit 1002. The first sensor unit 1001 has a first sensor 106 that measures displacement of the measurement hole in the diameter direction, and the second sensor unit 1002 has a second sensor 108 that measures displacement of the measurement hole in the length direction. The first sensor 106 has a contact roller 118. Before the stress measuring device 100 is inserted into the measurement hole 200, the contact roller 118 and contact pin 120 protrude outward from the first housing 102. When the stress measuring device 100 is inserted into the measurement hole 200, the contact roller 118 and contact pin 120 are inserted while in contact with the inner wall surface of the measurement hole 200. Even when the stress measuring device 100 reaches the measurement position, the contact roller 118 and contact pin 120 remain in contact with the inner wall surface.

When the first housing 102 is inserted into the measurement hole 200, the contact roller 118 is pushed inward and displaced from the standby position to the measurement position. Because the first elastic plate 114 is elastic, it becomes bent as the contact roller 118 displaces. At this time, it is preferable that a gap be left between the contact roller 118 and the rod 1023 so that the contact roller 118 can displace further inward.

The first sensor 106 contacts the inner wall surface of the measurement hole 200 via the contact roller 118. This allows the rotation of the contact roller 118 to dissipate any displacement in the axial direction of the stress measuring device 100 when the first housing 102 is inserted and when it is placed in the measurement position, preventing this displacement in the axial direction from acting on the first elastic plate 114. Therefore, the first sensor 106 can accurately measure positive and negative displacement in the diameter direction of the measurement hole 200 without being affected by displacement in the axial direction of the stress measuring device 100 that occurs during insertion.

In addition, when the first housing 102 is placed in the measurement position, the position of the contact pin 120 of the second sensor 108 is displaced inward. In reality, the tip of the sensor support member 132 is displaced inward and tilted, with the position of the joint 134 as the center of rotation. The contact pin 120 sinks inward together with the sensor support member 132 and is pressed against the inner wall surface by the reaction force of the elastic body 136. As explained with reference to Figures 3(A) and 3(B), the contact pin 120 is attached to the sensor support member 132 and can only be displaced in the direction of the slit 1321, so that displacement in the hole length direction can be measured without being affected by displacement in the hole diameter direction of the measurement hole 200.

Although not shown in Figure 4, in the overcoring method, the stress measuring device 100 is inserted into the measurement hole 200, and then the outer periphery of the measurement hole 200 is bored. The stress measuring device 100 detects deformation in the diameter direction of the measurement hole 200 caused by boring using the first sensor 106, and detects deformation in the length direction of the hole using the second sensor 108. As mentioned above, the first sensor 106 has the contact roller 118 in contact with the inner wall surface, so it can deflect deformation in the length direction of the measurement hole 200 and accurately measure deformation in the diameter direction. Furthermore, the second sensor 108 can measure deformation in the length direction of the measurement hole 200 because the second elastic plate 116 has a curved portion and the contact pin 120 is pressed against the inner wall surface by the action of the elastic body 136. By providing multiple first sensors 106 and second sensors 108 along the outer periphery of the first housing 102, it is possible to measure displacement in any direction, including the diameter and length directions, of the measurement hole 200.

The data logger 124 has the function of recording the displacement of the measurement hole 200 measured by the first strain gauge 110 and the second strain gauge 112 in chronological order at predetermined intervals. The displacement of the measurement hole 200 recorded in the data logger 124 is read out by a computer or the like after the stress measuring device 100 is removed from the measurement hole 200, and the stress of the ground is calculated from the displacement of the measurement hole 200. Because the second housing 104 has a built-in battery 126, there is no need to supply power via a wire to operate the data logger 124, and the data logger 124 can collect data autonomously within the measurement hole 200.

Although not shown, the second housing 104 may be equipped with a camera and lighting, allowing the operator to insert and remove the stress measuring device 100 from the measurement hole while viewing the image captured by the camera. This allows the operator to smoothly perform insertion and removal operations while checking the position and condition of the stress measuring device 100, without relying solely on visual inspection.

As described above, with the stress measuring device 100 according to one embodiment of the present invention, the first sensor 106, which detects displacement in the diameter direction of the measurement hole, is provided with a contact roller 118 that contacts the inner wall surface of the measurement hole. This allows displacement in the hole length direction that occurs during insertion into the insertion hole and during measurement (overcoring) to be deflected, enabling accurate measurement of displacement in the hole diameter direction.

Note that while this embodiment has been described based on measuring the initial stress of the ground, the stress measuring device 100 can also be applied to measuring stress in existing tunnels, the back ground of underground cavities, and existing concrete structures.

100: Stress measuring device, 1001: First sensor unit, 1002: Second sensor unit, 102: First housing, 1021: First support member, 1022: Second support member, 1023: Rod, 104: Second housing, 106: First sensor, 108: Second sensor, 110: First strain gauge, 112: Second strain gauge, 114: First elastic plate, 116: Second elastic plate, 1 161: Curved portion, 118: Contact roller, 120: Contact pin, 122: Universal joint, 124: Data logger, 126: Battery, 130: Contact pin, 1301: First contact pin, 1302: Second contact pin, 132: Sensor support member, 1321: Slit, 1322: Fixture, 134: Joint, 136: Elastic body, 138: Stopper, 200: Measurement hole

Claims (9)

a first housing including a rod;
a first sensor disposed on a first end side of the first housing;
a second sensor disposed on a second end side of the first housing opposite to the first end side;
a second housing coupled to a side of the first end of the first housing,
The first sensor is
a first elastic plate extending in the axial direction of the rod, one end of which is fixed to the first housing and the other end of which is a free end;
a first strain gauge attached to the first elastic plate;
a contact roller attached to a free end of the first elastic plate;
The second sensor is
a second elastic plate extending in the axial direction of the rod and having one end fixed to the first housing;
a second strain gauge attached to the second elastic plate;
a contact pin attached to the other end of the second elastic plate,
the contact roller and the contact pin are disposed on the second end side of the first elastic plate and the second elastic plate relative to the first end side ,
A stress measuring device, characterized in that the first elastic plate elastically deforms in the axial radial direction of the rod, and the second elastic plate elastically deforms in the axial length direction of the rod . a first housing including a rod;
a first sensor disposed on a first end side of the first housing;
a second sensor disposed on a second end side of the first housing opposite to the first end side;
a second housing coupled to a side of the first end of the first housing,
The first sensor is
a first elastic plate extending in the axial direction of the rod, one end of which is fixed to the first housing and the other end of which is a free end;
a first strain gauge attached to the first elastic plate;
a contact roller attached to a free end of the first elastic plate;
The second sensor is
a second elastic plate extending in the axial direction of the rod and having one end fixed to the first housing;
a second strain gauge attached to the second elastic plate;
a contact pin attached to the other end of the second elastic plate,
the contact roller and the contact pin are disposed on the second end side of the first elastic plate and the second elastic plate relative to the first end side,
A stress measuring device characterized in that the first strain gauge measures displacement in the diameter direction of the measurement hole, and the second strain gauge measures displacement in the length direction of the measurement hole . The first housing includes:
a first support member provided on the first end of the rod and having an outer diameter larger than an outer diameter of the rod;
a second support member provided on the second end of the rod and having an outer diameter larger than an outer diameter of the rod;
Including,
3. The stress measuring device according to claim 1, wherein the first elastic plate is cantilevered by the first support member, and the second elastic plate is attached to the second support member. The stress measuring device according to claim 1 or 2, wherein the first housing and the second housing are connected via a universal joint. The stress measuring device according to claim 4 , wherein a gap is provided between the first housing and the second housing. A stress measuring device according to any one of claims 1 to 5, wherein the second elastic plate has a curved portion, and the second strain gauge is provided in the curved portion. A stress measuring device according to any one of claims 1 to 6, wherein the contact roller and the contact pin protrude outward from the outer surface of the first housing. The stress measuring device described in any one of claims 1 to 7, wherein a plurality of the first sensors and the second sensors are arranged along the outer periphery of the first housing. The strain gauge according to any one of claims 1 to 8 , further comprising a data logger that records measured values of the first strain gauge and the second strain gauge, the data logger being provided in the second housing.
The stress measuring device described herein.