JP2005037313A - Stress measurement probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost stress measurement probe for measuring stresses with high accuracy by creating artificial cracks in a desired direction not depending on a stress field by a simple mechanism. <P>SOLUTION: This stress measurement probe 1 is inserted into an under-ground dug drill hole to generate cracks for stress measurement. This probe comprises a pair of semi-cylindrical pressure shells 2a to 2d for generating cracks by contacting with a hole wall of the drill hole, a pair of semi-elliptic pressure plates 4a to 4d for pressing the pressure shells 2a to 2d by contacting with the inner sides of the pair of pressure shells 2a to 2d, at least one piston for pressing the pressure plates 4a to 4d from the inner sides of the pair of pressure plates 4a to 4d, cylinder boxes 6a and 6b for housing the piston, and a displacement measurement part 11 for measuring the displacement of the cracks. The semi-cylindrical pressure shells 2a to 2d are formed so that their wall thicknesses are thicker in their semi-cylinder middle parts than in their semi-cylinder both end parts. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a borehole jack type one-side crushing stress measurement probe for measuring stress of a rock mass by creating an artificial crack in a borehole drilled underground.

  In general, when excavating underground or open pits, or when constructing large-scale construction works such as tunnels, deep underground cavities, rock slopes, and dams, the bedrock is used for reliable and rational design. The stress measurement is performed. In addition, earthquakes are usually caused by rocks on both sides of a fault that are stationary and suddenly slip and shake. The force acting on the fault surface, that is, the component that presses the rocks on both sides of the fault surface against each other It is possible to know when an earthquake occurs by examining temporal changes in the normal stress and shear stress, which is a component that tries to slide rocks on both sides. Stress measurement is used.

  As methods for measuring the initial rock mass stress of the rock mass, the stress release method and the method of creating an artificial crack in the rock mass by loading in the borehole are widely used. Attaching a strain gauge to the surface near the tip of the borehole drilled to overcoring the borehole, release the surrounding restraint pressure, that is, stress, and measure the strain and shape deformation that occurs at this time It is possible to measure the initial rock stress. However, since the stress release method assumes that the rock mass is a continuum and installs the device in the borehole, it accurately detects the stress that causes the sliding deformation and swelling behavior of discontinuous surfaces such as cracks in the rock mass. I can't. Therefore, in Patent Document 1, a specific structure is provided by providing three planes and three displacement sensors orthogonal to each other in the front structure and the rear structure of an elongated device composed of a front structure and a rear structure. The stress acting on the discontinuous surface and its vicinity can be measured three-dimensionally.

On the other hand, the hydraulic fracturing method, the dry two-side crushing method, the dry one-side crushing method, the plate fracturing method, and the like are known as methods for creating an artificial crack in the rock by loading into the borehole. Here, each stress measuring method is demonstrated using FIG.
FIG. 9A is a conceptual diagram for explaining the principle of the hydraulic fracturing method according to the prior art, and FIG. 9B is a conceptual diagram for explaining the principle of the dry two-side crushing method according to the prior art. is there. FIG. 9 (c) is a conceptual diagram for explaining the principle of the dry one-side crushing method according to the prior art, and FIG. 9 (d) is a concept for explaining the principle of the plate fracturing method according to the prior art. FIG. In these figures, the artificial cracking direction indicated by the broken line in FIG. 9, the direction of the maximum principal stress σ ₁ , the direction of the minimum principal stress σ ₂ , the placement relationship of the loading means, and the loading in the borehole A graph showing the pressure change of the artificial crack is shown.

In the hydraulic crushing method, a probe is inserted into the hole wall 26, high pressure water is allowed to flow inside the probe, and uniform water pressure is applied to the entire surface of the hole wall 26 of the borehole to generate cracks in the hole wall 26 (FIG. 9). again added to water pressure as shown in a) re opened crack, reopening pressure at this time, i.e., closed pressure P _s of the artificial cracks to be detected immediately after stop of applying a loading pressure P _r hydraulically Is used to calculate the maximum principal stress σ ₁ and the minimum principal stress σ ₂ . A stress measurement system using the hydraulic fracturing method will be described later. Code P _s is the closed pressure artificial cracks.

In the dry two-side crushing method, similar to the hydraulic fracturing method, a uniform loading pressure is applied to the entire hole wall 26 to generate an artificial crack in the hole wall 26, and then the loading pressure is again applied to the hole wall 26 to resume. The maximum principal stress σ ₁ and the minimum principal stress σ ₂ are calculated by measuring the mouth pressure P _n and are flexible and elastically deformable formed on the outer peripheral surface of the probe as shown in FIG. 9B. A loading pressure is applied to the hole wall 26 by flowing a high-pressure fluid through the urethane sleeve 27. Therefore, since such a structure, that is, a structure in which the fluid flows through the urethane sleeve 27, a sealed space is formed between the tank storing the fluid and the inside of the hole. Is effective in not flowing down into the hole wall 26. P _n1 and P _n2 are the reopening pressure of the primary crack and the reopening pressure of the secondary crack, respectively.

Furthermore, in the dry one-side crushing method, a uniform loading pressure is applied to the entire surface of the hole wall 26 to generate an artificial crack in the hole wall 26 as in the hydraulic fracturing method and the dry two-side crushing method. The maximum principal stress σ ₁ and the minimum principal stress σ ₂ are calculated by measuring the reopening pressure P _n by applying pressure, and as shown in FIG. 9C, the dry type two stress shown in FIG. The outer peripheral surface of the surface crushing probe is further covered with a friction shell 28 made of a half-pipe steel plate. In the dry one-side crushing method having such a structure, the periphery of the hole wall 26 other than the specific crushing one surface is a friction shell by applying the fluid pressure by the high-pressure fluid fed into the urethane sleeve 27 to the hole wall 26 through the friction shell 28. It is possible to form an artificial crack in a direction in which the maximum principal stress σ ₁ and the minimum principal stress σ ₂ are not generated, that is, a direction not depending on the stress field. Therefore, it is possible to create an artificial crack in an arbitrarily set direction.

In the plate fracturing method, a pair of vertical plates 29a and 29b having outer peripheral surfaces having the same radius of curvature as the radius of curvature of the hole wall 26 are identified by pressurizing with a plurality of borehole jacks instead of the loading force due to the flow pressure of the high-pressure fluid. The maximum principal stress σ ₁ and the minimum principal stress σ ₂ are calculated by generating a crack on one surface and measuring the reopening pressure P _n of the artificial crack. Reference sign G is a loading force.

Here, a stress measurement system using the most commonly used hydraulic fracturing method will be described.
FIG. 10 is a conceptual diagram of a hydraulic crushing stress measurement system using a wireline method according to the prior art.
As shown in FIG. 10, the hydraulic crushing stress measurement system based on the wire line system is a pair of upper and lower packers 30 and 30 that are brought into close contact with the bore wall, and a flow path switching valve that adjusts the amount of high-pressure water flowing into the packers 30 and 30. 31 and a pressure gauge 32, a steel cable 34 for inserting the probe into the borehole, a wire line mechanism including a pulley and a winch 37, and a high-pressure hose 33 for supplying high-pressure water to the probe. The opening displacement of the artificial crack due to hydraulic fracturing is measured and controlled from the relative movement of the pump 36, a high-pressure water supply system (not shown) including a water tank and a flow meter 35, and the two packers 30 and 30. A measurement / control system including an amplifier 38, an A / D converter 39, and a computer 40 is included. With this structure, after inserting the probe into the borehole, high-pressure water is fed from the pump 36 into the probe via the high-pressure hose 33 to expand the packers 30 and 30 in the borehole, thereby crushing the hole wall of the borehole. To do. Then, the upper and lower two packers 30 and 30 are pushed back by the stress caused by the artificial crack generated by the crushing together with the crushing, and these move. Therefore, by measuring the relative movement of the two packers 30, 30, the opening displacement amount of the artificial crack caused by hydraulic fracturing can be calculated, and the stress of the artificial crack can be measured. The measured data is recorded and analyzed by the computer 40, and the behavior of artificial crushing can be observed in real time on the screen of the computer 40. In addition, this hydraulic crushing stress measurement system can measure stress at a depth of about 1000 m.

  However, the stress measurement method using the wire-line-type hydraulic crushing stress measurement system as shown in FIG. 10 indirectly measures the pressure acting on the crushing section, which makes it difficult to perform accurate measurement. There was a problem of being.

In order to cope with such a problem, several inventions and devices have been disclosed.
For example, Patent Literature 2 discloses a hydraulic crushing type stress measurement that can measure stress with high accuracy without using a cable that requires difficult pressure sealing processing under the name of “hydraulic crushing type stress measuring method and apparatus”. Inventions relating to methods and apparatus are disclosed.
In the hydraulic fracturing type stress measuring device disclosed in Patent Document 2, a measuring device is provided between the two packers 30 and 30 shown in FIG. 10, and both ends of the measuring device, that is, the packers 30 and 30 and the measuring device are provided. Further, by providing a sensor riser at the connecting portion, and providing a shock absorbing damper on the measuring device side, the measuring device can be arranged at the center position of the boring hole, so that more accurate measurement can be performed.

Patent Document 3 discloses an invention relating to a hydraulic fracturing packer capable of directly measuring an opening amount of an artificial crack under the name “hydraulic fracturing packer”.
The packer for hydraulic fracturing disclosed in Patent Document 3 is formed by forming the packers 30 and 30 shown in FIG. 10 with layers made of a plurality of rubber seals and metal rings, and a pressure line and a water injection line are provided inside the packers 30 and 30. When a pressure is applied to the packer 30 through the pressure line, the rubber seal constituting the packer 30 is compressed and the packers 30 and 3 expand in the radial direction and are fixed to the hole wall of the borehole. It has a structure. And when the packers 30 and 30 are fixed to the hole wall of a boring hole, it is set as the structure where a water injection space is formed between the two packers 30 and 30. FIG. Therefore, since the opening displacement of the artificial crack is not constrained by providing a plurality of rubber seal layers in the packer 30, the opening displacement amount of the artificial crack can be directly measured at the place where the artificial crack is formed.
JP-A-11-304601 JP-A-10-220160 Japanese Patent Laid-Open No. 9-256772

However, in the conventional technology described above, in the hydraulic crushing method as disclosed in Patent Document 2 and Patent Document 3, an artificial crack is formed in a desired direction in order to apply uniform water pressure to the entire hole wall of the borehole. There is a problem that the re-opening pressure cannot be accurately measured because a water pressure similar to the injection pressure is applied in the artificial crack before the artificial crack is re-opened. Furthermore, in the stress field (rock mass) with the principal stress ratio σ ₁ / σ ₂ > 3, the tangential stress σ _θ = 3σ ₂ −σ ₁ <0 (tensile stress) in the hole wall in the σ ₁ direction becomes reopened by internal pressure loading. Since the reopening has already been performed before the reopening, the reopening pressure cannot be detected.

In the dry two-side crushing method, high-pressure water is not allowed to flow into the borehole, but it is not possible to create an artificial crack in the desired direction as in the hydraulic fracturing method, and the main stress ratio In the stress field of σ ₁ / σ ₂ > 3, the re-opening pressure cannot be detected, and the outer peripheral surface of the probe, that is, the surface in contact with the hole wall is formed of the urethane sleeve, so that an accurate displacement amount is measured. There is a problem that the point corresponding to the reopening pressure P _{n1 of the} primary crack or the reopening pressure P _n2 of the secondary crack is not clear. there were. Further, there is a problem that the reopening pressure P _{n1 of the} primary crack or the reopening pressure P _n2 of the secondary crack is detected from the measured value, and the stress cannot be calculated using these values. In addition, in order to improve the detection accuracy of the reopening pressure P _{n1 of the} primary crack or the reopening pressure P _n2 of the secondary crack, a water pressure larger than the water pressure of the hydraulic fracturing method must be applied. There was a problem that the pressure resistance of the probe had to be higher than that of the hydraulic fracturing method.

In the dry one-side crushing method, a friction shell is further provided outside the sleeve of the probe so that the periphery of the hole wall other than the specific crushing one surface is dynamically consolidated with the friction shell, and the maximum principal stress σ ₁ and the minimum principal stress σ ₂ Although an artificial crack can be created in a direction in which it does not occur, that is, in a direction that does not depend on the stress field, it is difficult to detect the reopening pressure _Pn as in the dry two-side crushing method, and the pressure resistance of the probe must be increased. There was a problem. In addition, the mechanism that generates the friction effect for mechanically uniting the periphery of the hole wall other than the specific crushing surface with the friction shell and the mechanism for preventing the probe sleeve from rupturing are complex mechanisms, and there are many failures of the device. There was a problem that not only the manufacturing cost of the apparatus was improved but also the reliability of the apparatus was lacking.

  In the plate fracturing method, the load pressure mechanism has a structure in which a pair of vertical plates having an outer peripheral surface having the same radius of curvature as the radius of curvature of the hole wall is pressed with multiple borehole jacks, thereby cracking a specific surface. Although it can be generated, there has been a problem that advanced technology is required to produce a pair of vertical plates having an outer peripheral surface having the same radius of curvature as that of the hole wall. For example, when the hole wall is loaded with a saddle plate whose radius of curvature of the outer peripheral surface is smaller than the curvature radius of the hole wall, the direct stress applied to the hole wall in the loading direction is maximized, that is, both ends of the saddle plate, Large direct stress and shear stress do not occur at the contact part of the pair of vertical plates, and the contact range between the vertical plate and the inner peripheral surface of the hole wall is about half that of the inner peripheral surface of the hole wall. Therefore, there is a problem that not only the crack is generated in the portion of the hole wall where the saddle type plate is not in contact, but also the place where the crack occurs cannot be specified. Conversely, when the hole wall is loaded with a saddle plate having a radius of curvature of the outer peripheral surface larger than that of the hole wall, a large direct stress and shear stress are generated at both ends of the saddle plate. Because of its high rigidity, shear failure occurs at the contact portion between the vertical plate and the hole wall, that is, both ends of the vertical plate, and it is possible to create a crack in the hole wall in the hole diameter direction perpendicular to the intended loading direction. There was a problem that it was not possible.

  The present invention has been made in response to such a conventional situation, and is an inexpensive stress measurement capable of measuring stress with high accuracy by creating an artificial crack in a desired direction independent of a stress field with a simple mechanism. An object is to provide a probe.

In order to achieve the above object, a stress measurement probe according to claim 1 is a stress measurement probe which is inserted into a borehole drilled underground to generate a crack and measure the stress. A pair of semi-cylindrical pressure shells that abut against the wall to generate cracks, a pair of semi-elliptical pressure plates that abut against the inside of the pair of pressure shells and press the pressure shell, and A semi-cylindrical pressure shell having at least one piston that presses the pressure plate from the inside of the pair of pressure plates, a cylinder box that accommodates the piston, and a displacement measuring unit that measures the displacement of the crack. The wall thickness of the half cylinder is formed thicker at the center of the half cylinder than at both ends of the half cylinder.
In the stress measurement probe having the above configuration, the thickness of the semi-cylindrical central portion of the semi-cylindrical pressure shell is formed to be thicker than the thickness of both end portions of the semi-cylindrical, so that the pressure is applied with a short piston movement in the loading direction It has the effect of applying loading pressure to the plate and the pressure shell, and by reducing the rigidity by reducing the thickness of both ends of the half cylinder, the pressure shell can be applied to the hole wall with almost no gap when loading pressure is applied. It has the effect | action of contact | abutting.

A stress measurement probe according to a second aspect of the present invention is the stress measurement probe according to the first aspect, wherein irregularities are formed on the outer peripheral surface of the semi-cylindrical pressure shell.
The stress measurement probe having the above-described configuration has an effect that irregularities formed on the outer peripheral surface of the semi-cylindrical pressure shell bite into the hole wall when a loading pressure is applied to the hole wall. Thus, it is possible to easily transmit the loading pressure to the hole wall and to prevent the semi-cylindrical pressure shell from being displaced in the circumferential direction in the hole wall.

A stress measurement probe according to a third aspect of the present invention is the stress measurement probe according to the first or second aspect, wherein the pressure plate and the pressure shell include at least one shear pin inserted through each other. The shear pin is ruptured with a predetermined desired shearing force.
The stress measurement probe having the above configuration has an effect that the pressure plate and the pressure shell can be easily separated by connecting the pressure plate and the pressure shell with a breakable shear pin.

A stress measurement probe according to a fourth aspect of the present invention is the stress measurement probe according to any one of the first to third aspects, wherein a plurality of pistons are provided, and the plurality of pistons are accommodated in a cylinder box. is there.
In the stress measurement probe having the above-described configuration, when a plurality of pistons are accommodated in the cylinder box, when the piston presses one pressure plate, the cylinder box that accommodates the piston is paired with a reaction force. It has the effect of pressing the pressure plate. Moreover, it has the effect | action that it is excellent in intensity | strength rather than accommodating in a cylinder box for every piston and installing a some cylinder box by setting it as the structure which accommodates a some piston in a cylinder box.

  In the stress measurement probe according to claim 1 of the present invention, the pressure shell is fitted over a wide range of the hole wall by moving the piston in the loading direction over a short distance, and a specific place of the hole wall is pressed in this state. Therefore, an artificial crack can be generated at a desired location on the hole wall by rotating the stress measurement probe in the borehole to change the loading direction to an arbitrary direction. This makes it possible to perform highly accurate stress measurement.

  Moreover, in the stress measurement probe according to claim 2 of the present invention, in addition to the effect of claim 1, it is possible to prevent the semi-cylindrical pressure shell from shifting in the circumferential direction. There is an effect that it can be stably fixed to the hole wall.

  In the stress measurement probe according to claim 3 of the present invention, in addition to the effects of claims 1 and 2, the stress measurement probe is preset when the stress measurement probe is stuck in the hole for some reason. The shear pin can be cut by pulling it up with a greater force, and the pressure shell on the outermost periphery of the stress measurement probe can be left behind to recover parts other than the pressure shell, that is, the pressure plate and cylinder box.

  Finally, in the stress measurement probe according to the fourth aspect of the present invention, in addition to the effects of the first to third aspects, a load can be applied in one diameter direction and there is a margin in strength. Therefore, there is an effect that a compact shape can be obtained.

  The objective of measuring the stress with high accuracy by generating an artificial crack at a desired location on the hole wall is realized with a simple structure and without increasing the production cost.

  Hereinafter, an embodiment of a stress measurement probe according to the present invention will be described with reference to FIGS.

FIG. 1 is a conceptual diagram of a stress measurement probe according to an embodiment of the present invention.
The stress measurement probe 1 is used to apply a loading pressure into a borehole drilled in the rock mass to create an artificial crack in the rock mass and measure the displacement of the artificial crack. As shown in FIG. 1, the stress measurement probe 1 measures the opening displacement amount of the artificial cracks formed between the packers 1a and 1b for applying a loading pressure to the hole wall of the borehole and the borehole. The displacement measuring unit 11 and the movement detecting sensor 12 for measuring the positions of the two packers 1a and 1b in the borehole. Reference numeral 7 denotes a coupler into which a suspension means for fixing a wire or the like for suspending the stress measurement probe 1 is inserted. The shape of the coupler 7 may be a screw-in type or a socket type as long as the hanging means can be connected to the stress measurement probe 1.

The packer 1a is provided with a pair of semi-cylindrical pressurizing shells 2a and 2b that directly press the hole wall of the boring hole, and both ends thereof are in contact with both ends of the pressurizing shells 2a and 2b. A pair of semi-elliptical pressure plates 4a and 4b and a cylinder box 6a accommodated in the pressure plates 4a and 4b are provided, and a plurality of pistons (not shown) accommodated in the cylinder box 6a. 1), the pressure plate 4a, 4b can be pressed by hydraulically driving the piston toward the borehole wall side by feeding oil from the oil supply section 8.
Further, the pressure plates 4a and 4b pressed by the pistons press the outer pressure shells 2a and 2b so that they press the hole wall of the boring hole and generate an artificial crack in the boring hole. It has become. Also for the packer 1b, a plurality of pistons in the cylinder box 6b press the pressurizing plates 4c and 4d and the pressurizing shells 2c and 2d on the outside thereof by the same mechanism to press the hole wall of the boring hole, and into the boring hole. Artificial cracks can be generated.

  Further, as shown in FIG. 1, irregularities 3 a to 3 d are formed on the outer peripheral surfaces of the pressure shells 2 a to 2 d. Therefore, when the loading pressure is applied to the pressure plates 4a to 4d and the pressure shells 2a to 2d with a plurality of pistons housed in the cylinder boxes 6a and 6b by hydraulic pressure, the outer circumferential surfaces of the pressure shells 2a to 2d are applied. Since the formed irregularities 3a to 3d bite into the hole wall of the boring hole, it is easier to transmit the loading pressure, and the pressurizing shells 2a to 2d can be prevented from rotating in the circumferential direction. That is, when a loading pressure is applied in the borehole, the stress measurement probe 1 is not displaced from the installation position in the borehole due to a pressurizing impact or the like, and an accurate displacement amount can be measured.

In addition, the pressure shell 2a and the pressure plate 4a, the pressure shell 2b and the pressure plate 4b, the pressure shell 2c and the pressure plate 4c, and the pressure shell 2d and the pressure plate 4d are respectively set to predetermined desired values. Since the shear pins 5a to 5g that can be broken by a shearing force are connected by another shear pin (not shown), the pressure plate and the pressure shell are not broken at the time of loading without being broken. When the stress measurement probe 1 is stuck in the boring hole for some reason, the pressure plates 4a to 4d and the pressure shells 2a to 2d are disconnected by cutting the shear pins 5a to 5g. It is possible to separate.
At that time, it is possible to collect only the pressure shells 2a to 2d in the borehole and collect the pressure plates 4a to 4d and the cylinder boxes 6a and 6b. As a result, the minimum amount of abandonment is sufficient, and the pressure plates 4a to 4d and the cylinder boxes 6a and 6b can be reused, so that the cost can be reduced even in the event of an accident. Reference numerals 13a to 13g are holes for inserting the shear pins 5a to 5g.

  Holes 9a and 9b provided near the center of the pressure plates 4a and 4b connect a device (not shown) for recording and calculating measurement data to a device in the displacement measuring unit 11 or the movement detecting sensor 12. The cables 10a to 10d are provided to be pulled out of the stress measurement probe 1.

  FIG. 2 is a photograph of a prototype of the stress measurement probe according to the present embodiment shown in FIG. 1. The stress measurement probe includes two packers having irregularities formed on the outer peripheral surface and a displacement provided therebetween. The measurement unit and a movement detection sensor attached to the tip of the right packer are configured, and a wire for lifting the stress measurement probe is attached to the end of the left packer. FIG. 1 illustrates a state where the cover is applied to the movement detection sensor, but the cover is removed in the photograph of the prototype of the stress measurement probe illustrated in FIG. 2.

FIG. 3 is an arrow view in the direction indicated by the symbol A in FIG. 3, the same parts as those shown in FIG. 1 are denoted by the same reference numerals, and description of the configuration is omitted.
As described in FIG. 1, the outer peripheral surface of the stress measurement probe 1 that directly contacts the hole wall 14 of the boring hole, that is, the outer peripheral surface of the pressure shells 2a and 2b is a concentric circular shape having a diameter smaller than the diameter of the boring hole. The shape of the pressure shells 2a and 2b is smaller than the diameter of the borehole so that the stress measurement probe 1 does not contact the hole wall 14 when the stress measurement probe 1 is inserted into the borehole. . As a result, the stress measurement probe 1 can be smoothly inserted into the borehole. On the other hand, the inner peripheral surfaces of the pressure shells 2a and 2b are semi-elliptical, and the central portions of the pressure shells 2a and 2b are thicker than both ends. The effect of this shape will be described later.
Further, the outer peripheral surfaces of the pressure plates 4a and 4b provided inside the pressure shells 2a and 2b are semi-elliptical and have both end portions in contact with both end portions of the pressure shells 2a and 2b. However, a small gap is formed between the pressure shells 2a and 2b and the pressure plates 4a and 4b.

  Here, the driving principle of the loading means of the stress measurement probe 1 will be described.

  FIG. 4A is a conceptual diagram before pressing the pressure plate and the pressure shell, and FIG. 4B is a conceptual diagram after pressing the pressure plate and the pressure shell. 4, the same parts as those described in FIGS. 1 and 3 are denoted by the same reference numerals, and description of the configuration is omitted.

As described above, the outer peripheral surfaces of the pressure shells 2a and 2b, which are the outer peripheral surfaces of the packer 1a, are formed in the concentric shape of the bore holes, and the diameter of the circle formed by the pressure shells 2a and 2b, that is, the pressure plate diameter x, the total length of twice the thickness t of the pressure shell central portion and twice the length of the gap a ₂ is twice as long as the gap a ₁ than the hole diameter d of the borehole. Only shortened. This can be expressed by equation (1).

  Therefore, as shown in FIG. 4A, when no loading pressure is applied to the hole wall 14 of the boring hole, the pressurized shells 2a and 2b are not in contact with the hole wall 14 of the boring hole. Further, the inner peripheral surfaces of the pressure shells 2a and 2b are semi-elliptical, and the center portion is thicker than both end portions. Furthermore, the outer peripheral surfaces of the pressure plates 4a and 4b provided inside the pressure shells 2a and 2b have a semi-elliptical shape having a shorter diameter than the inner peripheral surfaces of the pressure shells 2a and 2b. The outer peripheral surfaces of 4a and 4b and the inner peripheral surfaces of the pressure shells 2a and 2b are in contact at both ends, and the inner peripheral surfaces of the pressure shells 2a and 2b and the outer peripheral surfaces of the pressure plates 4a and 4b are in the center. A crescent-shaped gap is formed between them.

When the pressure plates 4a and 4b and the pressure shells 2a and 2b having such a shape are pressed in the directions of the arrow D and the arrow E from the inside of the packer 1a, the pressure plate 4a as shown in FIG. 4b move to arrows D and E, respectively, to press the pressure shells 2a and 2b. As a result, both end portions of the pressure shells 2a and 2b, that is, thin portions are curved outward and opened to the hole wall 14 side of the borehole, so that the outer peripheral surfaces of the pressure shells 2a and 2b The pressure plates 4a and 4b are in close contact with the hole wall 14 and are in close contact with the inside of the pressure shells 2a and 2b, respectively.
Since the outer diameters of the pressure shells 2a and 2b are smaller than the inner diameter of the hole wall 14, both end portions of the pressure shells 2a and 2b are curved outward and are in close contact with the hole wall 14 when they are in close contact with the hole wall 14. There is a need. For this purpose, it is necessary to reduce the wall thickness at both ends to increase flexibility. In addition, since the pressure plates 4a and 4b are formed so as to be in close contact with the inside of the pressure shells 2a and 2b, the shape of the outer peripheral surface of the pressure plates 4a and 4b is such that the pressure shells 2a and 2b are hole walls. 14 is the same as the shape of the inner peripheral surface of the pressure shells 2a and 2b in a state of being in close contact with the pressure shell 14. Because of such a shape, a gap of a ₂ is generated in the normal state, that is, in a state where the pressure plates 4a and 4b are not in close contact with the pressure shells 2a and 2b (the state shown in FIG. 4A). is there.

Thereafter, when the pressure plates 4a and 4b are further pressed, the irregularities 3a and 3b formed on the outer peripheral surfaces of the pressure shells 2a and 2b bite into the hole wall 14, and the pressure shells 2a and 2b are fixed to the hole wall 14. It will be in the state.
Accordingly, the displacement of the pressure shells 2a and 2b in the circumferential direction is suppressed, and the stress measurement probe 1 can be fixed in the boring hole.
The gaps a and a are formed between the pressure plate 4a and the pressure plate 4b by the movement of the pressure plates 4a and 4b in the directions of the arrows D and E. The gaps a and a Cracks 15a and 15b are created. The gap a corresponds to a length obtained by adding the gap a ₁ and the gap a ₂ shown in FIG. 4A, and is expressed as a = a ₁ + a ₂ . In other words, a is the stroke of the pressure plates 4a and 4b. By shortening the stroke, the stroke of the piston that presses the pressure plates 4a and 4b can be shortened, thereby making the probe compact. be able to.
This will be considered in the light of equation (1). In equation (1), a ₁ + a ₂ is obtained, but in order to make the stroke, that is, the gap a as short as possible, the thickness t of the pressure shell is increased in the pressure plates 4a and 4b having a certain size. It will be necessary. That is, in order to shorten the strokes of the pressure plates 4a and 4b, the thickness of the central portion of the pressure shells 2a and 2c is increased to increase the stroke. In addition, since the stroke of the cylinder boxes 6a and 6b that press the pressure plates 4a and 4b can be shortened by shortening the stroke, the cylinder boxes 6a and 6b can be reduced in size.

  Next, a mechanism for loading the pressure plate will be described with reference to FIG.

  5 is a cross-sectional view taken along line BB in FIG. In FIG. 5, the same parts as those described in FIGS. 1, 3, and 4 are denoted by the same reference numerals, and description of the configuration is omitted.

The pressure shells 2a to 2d and the pressure plates 4a to 4d for loading the hole wall 14 of the boring hole are pressed by the cylinder boxes 6a and 6b and a plurality of pistons 17a to 17h accommodated in the cylinder boxes 6a and 6b. The pistons 17a to 17h have bolts 18a to 18h, bolts 19a to 19h connected to the cylinder boxes 6a and 6b, and coils that control the vertical driving of the surrounding bolts 18a to 18h. The springs 20a to 20h are accommodated.
The pistons 17a to 17h that press the pressure plates 4a to 4d are driven by the oil pressure of the oil fed from the oil supply unit 8, and in the cylinder boxes 6a and 6b according to the oil outflow direction F through the flow path 16. When oil is fed into the bolts, the bolts 18a to 18h and the pistons 17a to 17h are pushed out in the direction of arrow D by the hydraulic pressure and the elastic force of the coil springs 20a to 20h. At the same time, the cylinder boxes 6a and 6b are pushed out in the direction of arrow E, which is opposite to the direction of arrow D in which the pistons 17a to 17h are pushed out, by the reaction force of the force pushing out the pistons 17a to 17h. .

As a result, the pistons 17a to 17d and 17e to 17h press the pressure plates 4a and 4c in the direction of the arrow D, and the pressure plates 4a and 4c further press the pressure shells 2a and 2c in the direction of the arrow D. To do. At the same time, the cylinder boxes 6a and 6b connected and integrally formed at the center portion 6c of the cylinder box press the pressure plates 4b and 4d in the direction of arrow E with a uniform force to further pressurize the pressure plates 4b and 4b. 4d presses the pressure shells 2b and 2d in the direction of arrow E.
The pressure shells 2a to 2d, which are the outermost peripheral surfaces of the stress measurement probe 1, are configured to load the hole wall 14 of the boring hole. Reference numeral 5h denotes a shear pin, and reference numeral 21 denotes a hanging bracket for attaching the coupler 7 for fixing a wire or the like for suspending the stress measurement probe 1 to the stress measurement probe 1.

  FIG. 6 is a photograph of a prototype of the cylinder box shown in FIG. 5, showing the pistons 17a to 17d and 17e to 17h being pushed out from the cylinder boxes 6a and 6b.

  Next, an embodiment of the displacement measuring unit 11 for measuring the displacement amount of the cracks 15a and 15b formed in the borehole by the loading pressure of the packers 1a and 1b will be described.

7 is a cross-sectional view taken along the line CC in FIG. In FIG. 7, the same parts as those described in FIGS. 1, 3 to 5 are denoted by the same reference numerals, and description of the configuration is omitted.
FIG. 7 is a diagram showing a displacement measuring unit 11 provided between the packers 1a and 1b, that is, around the cylinder box center 6c. The displacement measuring unit 11 directly measures the opening displacement amount of the cracks 15a and 15b due to loading. The upper claws 22a and 22b and the lower claws 23a and 23b, distance sensors 25a to 25d for sensing the distance between the upper claws and the lower claws, and coil springs 24a to 24d are configured. When the cracks 15a and 15b are opened by loading, the upper claws 22a and 22b are moved upward accordingly, and the distance between the upper claws 22a and the lower claws 23a by the distance sensors 25a and 25b and the distance sensors 25c and 25d. The distance and the distance between the upper claw 22b and the lower claw 23b are measured, and this information is sent to an analysis device such as a computer (not shown) via a cable (not shown). . The coil springs 24a to 24d are for returning the moved upper claws 22a and 22b to their original positions.
In FIG. 7, contact type sensors that directly contact the cracks 15a and 15b and measure the opening displacement of the cracks 15a and 15b, such as the upper claws 22a and 22b and the lower claws 23a and 23b, are used. The opening displacement amount of 15a, 15b, that is, any distance can be used as long as it can measure the distance, convert it into an electrical signal, and output it. For example, the crack 15a, You may make it measure the opening displacement amount of 15b.

FIG. 8 is a diagram conceptually showing data obtained by measurement using the stress measurement probe according to the embodiment of the present invention. 8, parts that are the same as those shown in FIGS. 1, 3 to 5, and 7 are given the same reference numerals, and descriptions thereof are omitted.
As shown in FIG. 8, when the bore 14 of the boring hole is loaded in the directions of the arrow D and the arrow E using the stress measurement probe 1, the opening portion between the pressure plate 4a and the pressure plate 4b, that is, the arrow A crack can be created in a direction perpendicular to the loading pressure direction represented by D and arrow E. That is, a crack can be created at a specific location of the hole wall 14. Therefore, a graph representing the relationship between pressure and hole wall strain as shown in FIG. 8 can be obtained at a desired location of the hole wall 14, and the reopening pressure _Pn and stress can be obtained from this graph.
In general, the stress of a rock mass is measured by loading the artificial crack on the hole wall, unloading it once, then loading it again to reopen the artificial crack, This is done by measuring the pressure, but with the method of detecting from the hole diameter change, such as the conventional dry two-side crushing method, dry one-side crushing method and plate fracturing method, the moment when the artificial crack reopens can be accurately detected. It was difficult. On the other hand, according to the present invention, it is possible to perform highly accurate measurement by measuring the hole wall strain, instead of measuring the displacement in the hole diameter direction. The description of the calculation method of measurement data is omitted. Furthermore, by chamfering the hole wall 14 using a reamer or the like, the affinity between the stress measurement probe 1 and the hole wall 14 can be improved, and the measurement accuracy can be further improved.

In addition, when it is desired to create a crack at a desired location on the hole wall 14 other than the location where the crack is created as shown in FIG. 8, the pressure measuring plate 4a, If a contact part with 4b is arranged, a crack can be generated at a desired location. The rotation angle of the stress measurement probe 1 can be measured by attaching a device that can display the rotation position, such as a gyro sensor.
From the above, in the stress measurement probe according to the embodiment of the present invention, the detection of the restarting high pressure of the crack is not hindered by the inflow of the high pressure fluid into the crack as in the hydraulic fracturing method, and the dry measurement method Since a complicated mechanism like the one-side crushing method is not required, highly accurate stress measurement can be performed with a simple mechanism, and the production cost can be reduced.

  It can create cracks at desired locations in the borehole, and can be applied to equipment that collects more detailed geological data in large-scale civil works such as mining work, tunnels, underground cavities, and dams, and has high sensitivity. It can also be applied to make an earthquake prediction device. Moreover, it can be applied not only to the inspection of boring holes but also to the strength test of concrete after hardening.

It is a conceptual diagram of the stress measurement probe which concerns on the Example of this invention. It is a photograph of the prototype of the stress measurement probe shown in FIG. It is an arrow view to the direction shown by the code | symbol A in FIG. (A) is a conceptual diagram before pressing a pressure plate and a pressure shell, (b) is a conceptual diagram after pressing a pressure plate and a pressure shell. It is a BB sectional view taken on the line in FIG. It is a photograph of the prototype of the cylinder box shown in FIG. It is CC sectional view taken on the line in FIG. It is the figure which showed notionally the data obtained by the measurement using the stress measurement probe which concerns on the Example of this invention. (A) is a conceptual diagram for demonstrating the principle of the hydraulic crushing method based on a prior art, (b) is a conceptual diagram for demonstrating the principle of the dry-type two-side crushing method based on a prior art, (c ) Is a conceptual diagram for explaining the principle of the dry one-side crushing method according to the prior art, and (d) is a conceptual diagram for explaining the principle of the plate fracturing method according to the prior art. It is a conceptual diagram of the hydraulic crushing stress measurement system by the wireline system which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Stress measuring probe 1a, 1b ... Packer 2a-2d ... Pressure shell 3a-3d ... Unevenness 4a-4d ... Pressure plate 5a-5h ... Shear pin 6a, 6b ... Cylinder box 6c ... Cylinder box center part 7 ... Coupler 8 ... Oil supply part 9a, 9b ... Hole 10a to 10d ... Cable 11 ... Displacement measurement part 12 ... Movement detection sensor 13a to 13h ... Hole 14 ... Hole wall 15a, 15b ... Crack 16 ... Flow path 17a to 17h ... Piston 18a to 18h , 19a to 19h ... Bolts 20a to 20h ... Coil springs 21 ... Suspension fittings 22a and 22b ... Upper claws 23a and 23b ... Lower claws 24a to 24d ... Coil springs 25a to 25d ... Distance sensors 26 ... Hole walls 27 ... Urethane sleeves 28 ... Friction shells 29a, 29b ... Vertical plate 30 ... Pack -31 ... Flow path switching valve 32 ... Pressure gauge 33 ... High pressure hose 34 ... Steel cable 35 ... Flow meter 36 ... Pump 37 ... Winch 38 ... Amplifier 39 ... A / D converter 40 ... Computer F ... Oil outflow direction G ... Load Force σ ₁ ... Maximum principal stress σ ₂ ... Minimum principal stress P _r ... Loading pressure P _s ... Artificial crack closing pressure P _n ... Re-opening pressure P _n1 ... Primary crack re-opening pressure P _n2 ... Resumption of secondary crack Mouth pressure a ... Gap a ₁ ... Gap a ₂ ... Gap x ... Pressure plate diameter t ... Pressure shell center thickness d ... Hole diameter

Claims (4)

A stress measurement probe that is inserted into a borehole drilled underground to generate a crack and measure stress, and a pair of semi-cylindrical pressure shells that abut against the hole wall of the borehole to generate a crack; A pair of semi-elliptical pressure plates that abut against the inside of the pair of pressure shells and press the pressure shell, and at least one that presses the pressure plate from the inside of the pair of pressure plates A piston, a cylinder box that accommodates the piston, and a displacement measuring unit that measures the displacement of the crack, and the thickness of the semi-cylindrical pressure shell is more in the center of the semi-cylinder than the ends of the semi-cylinder. A stress measurement probe characterized by being formed thicker. The stress measurement probe according to claim 1, wherein irregularities are formed on an outer peripheral surface of the semi-cylindrical pressure shell. The said pressure plate and the said pressure shell are provided with the at least 1 shear pin penetrated mutually, This shear pin is fractured | ruptured by the predetermined desired shearing force, The Claim 1 or Claim 2 characterized by the above-mentioned. Stress measurement probe. The stress measuring probe according to claim 1, wherein a plurality of the pistons are provided, and the cylinder box accommodates the plurality of pistons.