JP2002349178A - Rock crack measurement method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crack measuring method and device for base rock for obtaining precise data for shape and opening pressure of a crack in a base rock and the like. SOLUTION: A boring hole 21 is bored in the base rock 20, and a hole internal pressurizer 1 to act on the inner wall of the boring hole 21 close thereto is inserted to the hole 21. The hole internal pressurizer 1 is pressurized to open the crack in the hole inner wall, the change of distance between two or more electrodes 15 mounted on the pressurizer 1 is taken as the change of impedance, the relation of the pressure changed according to pressurization with the impedance or the relation of the pressure changed according to decompression with the impedance is determined, and the crack of the rock base 20 is measured on the basis of this relation between pressure and impedance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring cracks in a rock, which is carried out when building a structure underground or above the ground, when building a dam or the like, when measuring rock stress, or in the case of geothermal development. A borehole is excavated at the location where the hole is to be drilled, and a pressurizer in the hole that works in close contact with the inner wall of the borehole is inserted into the borehole, and the pressurizer in the hole is pressed to open a crack in the rock inside the hole. And a method and device for measuring

[0002]

2. Description of the Related Art Of the methods for observing cracks in the inner wall of a rock, when a borehole television is used, it is often impossible to detect a close crack. When using a molding packer to open a crack by applying internal pressure and copy its shape to the surface, even if the crack does not open due to the applied internal pressure, it is not known at that time whether the crack opened or not. You have to pull it out of and start over. Further, even when the crack is opened, the pressure when the crack is actually opened is not known. Furthermore, even when there are a plurality of opened cracks, each of which is opened with a different internal pressure, it is impossible to know the pressure at which each crack is actually opened. As described above, according to the conventional technology, it is impossible to simultaneously measure the shape of the crack and the mechanical characteristics of what internal pressure the crack is opened. Further, when there are a plurality of cracks that open at different internal pressures, it is not possible to know the opening pressure of each crack.

[0003]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned problems of the prior art, and has been developed to accurately determine the strength of a rock mass, the shape of a crack, its opening pressure, closing pressure, and the like. It is an object of the present invention to provide a method and an apparatus for measuring cracks in a rock mass to obtain data.

[0004]

According to the method of the present invention, a boring hole is excavated at a position where a crack in a rock is measured, and an in-hole pressurizer which works in close contact with the inner wall of the boring hole is inserted into the boring hole. In a method for measuring cracks in rock, which presses the pressurizer in the hole to open a crack in the inner wall of the hole, preparing a pressurizer in the hole provided with a plurality of electrodes at intervals on the surface of the elastic cylindrical body, Electrodes are pressed against the rock wall by pressurizing the in-hole pressurizer, the change in impedance between the electrodes due to the opening of the crack is detected, and the crack is measured by the change in the impedance.

Further, in the method of the present invention, after the pressurizing operation is completed, the pressure is reduced and the change in impedance between the electrodes due to the closing of the crack is measured.

According to the present invention, a boring hole is excavated at a position where a crack in a rock is measured, and an in-hole pressurizer acting in close contact with the inner wall of the boring hole is inserted into the boring hole. In a crack measuring apparatus for a rock mass which presses a pressurizer to open a crack in an inner wall of a hole, a plurality of electrodes are arranged at intervals on a surface of an elastic cylindrical body of the pressurizer in the hole, and the electrodes are arranged in a matrix. It is connected to an impedance measuring instrument via a switch.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIGS. 1 to 3, an in-hole pressurizer 1 used in the present invention is called an electrode packer, and fixing brackets 3 and 4 are attached to both ends of a rubber cylinder 2 which is an inflatable elastic cylinder. A mandrel 5 is inserted into the rubber cylinder 2. And one fixing bracket 3
Is fixed to the mandrel 5 with bolts 7,
A plate 8 in contact with the step 5a of the mandrel 5 is fixed to the fixing member 4 with bolts 9, and an O-ring 10 for sealing is interposed on the contact surface between the fixing members 3, 4 and the mandrel 5. . In this way, the rubber cylinder 2 is airtightly and firmly attached to the mandrel 5. The mandrel 5 is formed with a flow path 5b for feeding the pressurized fluid to the rubber cylinder 2, and the flow path 5b is formed by a pipe 11
And a switching valve 12 connected to a pressurizer 13.

A large number of electrodes 15 are provided on the surface of the rubber cylinder 2 at predetermined intervals. As shown in the figure, in this embodiment, eight electrodes 15 are provided in three rows in the circumferential direction in the circumferential direction, and each electrode 15 is connected to a measuring instrument 17 via a signal line 16. . A pressure converter 18 is provided in the flow path 5b, and a pressure signal of the pressure converter is also input to the measuring device 17 via the signal line 16.

The in-hole pressurizer 1 has, for example, a length of 500 mm, an outer diameter of the rubber cylinder 2 of 58 mm, and a length of 250 mm.
mm, and the outer diameter of the fixtures 3 and 4 is 64 mm. And, on the surface of the rubber cylinder 2, the center and the upper and lower 60m from the center
Eight electrodes 15 are provided on the circumference at the position of m.

The measuring device 17 is a matrix switch 17a.
And a resistance / pressure measuring device 17b. By switching the matrix switch 17a, two adjacent electrodes 15 are connected to the resistance / pressure measuring device 17b,
The impedance between the electrodes 15 is calculated by the resistance / pressure measuring device 17b, and the impedance is recorded together with the pressure signal of the pressure converter 18.

Next, the operation of the present invention will be described. As shown in FIG. 4, a boring hole 21 is drilled in the rock 20 to be measured, and the in-hole pressurizer 1 is inserted into the boring hole 21 using the insertion rod 22. When the switching valve 12 is opened toward the pressurizer in the hole, the high-pressure water of the pressurizer 13 is supplied to the pipe 11 and the flow path 5 of the mandrel 5.
b, the rubber cylinder 2 bulges and closely adheres to the boring hole 21, and further bulges to form the boring hole 2.
1. Open existing cracks in the inner wall or generate new cracks.

In the process of sending the high-pressure water from the pressurizer 13 to the in-hole pressurizer 1, the matrix switch 17a of the measuring device 17 is sequentially switched, the impedance between the electrodes 15 is calculated, and the pressure converter 18 The impedance is recorded sequentially with the pressure signal. Then, the presence or absence and shape of the crack in the rock 20 are measured based on the relationship between the pressure and the impedance. Further, by switching the switching valve 12, the high-pressure water in the bore pressurizer is gradually reduced in pressure, and the cracks opened by pressurization can be closed. Thereafter, the switching valve 12 is opened and closed, and pressurization and depressurization are repeatedly measured several times, so that the relationship between pressure and impedance can be accurately measured.

As shown in FIG. 5, when the in-hole pressurizer 1 inserted into the boring hole 21 is pressurized and a crack 20a in the hole wall is opened, the rubber cylinder 2 applies the resistance between the electrodes 15b and 15c. The impedance calculated by the pressure measuring device 17b increases. Then, the impedance is recorded by the resistance / pressure measuring device 17b together with the pressure signal of the pressure transducer 18, and data is obtained as shown in FIG. That is, as shown in FIG. 6, the electrodes 15b-15
Between c, the resistance between the electrodes greatly increases from the point a where the crack is opened. In addition, the pressure calculated by the resistance / pressure measuring device 17b between the electrodes 15b and 15c is greatly reduced by reducing the pressure of the high-pressure water in the pressurizer in the hole and gradually closing the cracks opened by pressurization. That is, as shown in FIG. 6, the change in resistance between the electrodes 15 b and 15 c is reduced from the point a ′ where the crack is closed, as compared with the area between the electrodes 15 a and 15 b where there is no crack.

As shown in FIG. 7, when the crack 20x is oblique to the boring hole 21, each of the electrodes (1 to 8) provided in the in-hole pressurizer 1 in three rows A to C is provided. 8), the crack opening position is sequentially moved and detected as indicated by the symbol x in FIG. 8, and the inclination and direction thereof can be known.

When the measurement of this position is completed, the switching valve 12 is opened to the atmosphere to contract the in-hole pressurizer 1, the in-hole pressurizer 1 is moved deep into the boring hole 21, and
Switch to measure. In this way, the presence / absence and shape of the crack in the rock 20 and the pressure when the crack is opened or closed are measured.

Further, by narrowing the interval between the electrodes 15 provided in the in-hole pressurizer 1, the direction and inclination of the crack can be measured more accurately.
By determining the impedance between every other or every other electrode 15, it is also possible to detect the presence or absence and shape of a large crack straddling between the electrodes 15. Further, the impedance between the electrodes 15 is obtained, and the presence / absence and shape of the crack are comprehensively determined therefrom, whereby finer detection can be performed. In this embodiment,
The in-hole pressurizer 1 is pressurized with high-pressure water, but may be pressurized with high-pressure air, high-pressure oil, or the like.

[0017]

The effects of the present invention will be described below. The crack measuring method and the crack measuring device of the rock of the present invention insert a pressurizer in a hole provided with a plurality of electrodes in a boring hole drilled in the rock, and pressurize or depressurize the pressurizer in the hole to open the crack. Since the rock is closed and the crack in the rock is measured based on the relationship between the pressure and the change in impedance between the electrodes, accurate data such as the shape of the crack, its opening, the closing pressure, and the rock strength can be obtained.

By accurately knowing the shape of the crack and the pressure at which it opens / closes, the following advantages are obtained in the technical field to which the present invention belongs.

A. Measurement of crack characteristics during grouting and geothermal development There is usually a discontinuity in rock. For example, in grouting, where cement mortar is injected from a borehole to reinforce rock or block water, it is important to determine in which direction the mortar is to be filled through which discontinuous surface. May be. Also,
Press water at normal temperature into the hot rock through the borehole.
In geothermal technology that recovers high-temperature steam or hot water from another borehole, the direction in which the injected water flows is an important concern. Several existing cracks are observed on the inner wall of the borehole according to the discontinuity in the rock. Since the injected cement mortar or water flows into the existing cracks opened according to the injection pressure, the flowing direction may change depending on the pressure applied. Therefore, it is important to know how much pressure each crack in the inner wall of the hole opens and how much pressure it closes. The present invention makes that possible.

B. Accurate measurement of rock stress When measuring rock stress by the hydraulic fracturing method, for simplicity, the case where a vertical fracture crack is generated is described. The internal pressure Pb when the crack occurs, and the crack is closed and then reopened By using the internal pressure Pr, the shut-in pressure Ps, and the tensile strength T of the rock mass, the maximum stress SH and the minimum stress Sh in a plane perpendicular to the hole axis are expressed as follows. SH = 3Sh-Pb + T (1) SH = 3Sh-Pr (2) Sh = Ps (3) This is a basic concept of rock stress measurement by a hydraulic crushing method and is widely used. However, it has been pointed out that although the measured value of Ps is generally reliable, the measured value of Pb, particularly Pr, includes a large error.
That is, Pb may need to use an equation different from equation (1) depending on the condition of water penetration. Also, it is very difficult to read Pr from the water pressure time change curve, and even if it is read, the equation (2) does not hold. For this reason, SH is not considered to have good accuracy among rock stresses obtained by the hydraulic fracturing method. Some research reports conclude that SH is not required by conventional hydraulic fracturing.

In the crack measuring method of the present invention, since the water pressure is not applied to the inner wall of the hole, the above-described problem of measuring Pb and Pr does not occur. (2) can be applied. Therefore, S
H can be determined accurately. At the same time, the tensile strength T of the rock can be determined.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of an in-hole pressurizer of a rock crack measuring apparatus of the present invention.

FIG. 2 is a longitudinal sectional view of the in-hole pressurizer.

FIG. 3 is a cross-sectional view of an in-hole pressurizer.

FIG. 4 is a schematic diagram illustrating a method for measuring cracks in rock mass according to the present invention.

FIG. 5 is a sectional view showing a crack opening portion of a hole wall.

FIG. 6 is a graph showing a change in resistance between electrodes due to crack opening and closing.

FIG. 7 is a view for explaining detection when a crack is inclined with respect to a boring hole.

FIG. 8 is a view showing crack detection at each of the positions A to C in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... In-hole pressurizer 2 ... Rubber cylinder 3, 4 ... Fixture 5 ... Mandrel 5a ... Step part 5b ... Flow path 6, 8 ... Plate 7, 9 Bolt 10 O-ring 11 Pipe 12 Switching valve 13 Pressurizer 15 Electrode 16 Signal line 17 Measuring instrument 17a Matrix switch 17b ··· Resistance and pressure measuring device 18 ··· Pressure transducer 20 · · · Rock bed 21 · · · Boring hole 22 · · · Insertion rod

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Tanaka 1-312 Higashimonmae, Kawasaki-ku, Kawasaki-shi, Kanagawa F-term (reference) 2G060 AA14 AE04 AF06 AG11 EA06 2G061 AA02 AB01 AB03 BA03 CA06 DA01 EA01 EA10 EB03

Claims (3)

[Claims] 1. A boring hole is excavated at a position where a crack in a bedrock is to be measured, and an in-hole pressurizer acting in close contact with an inner wall of the boring hole is inserted into the boring hole, and the in-hole pressurizer is pressurized. In the method for measuring cracks in a rock mass opening a crack in an inner wall of a hole, a pressurizer in a hole in which a plurality of electrodes are provided at intervals on a surface of an elastic cylinder is prepared, and the pressurizer in the hole is pressurized to press the hole pressurizer. A method for measuring cracks in a rock, comprising crimping an electrode on the rock, detecting a change in impedance between the electrodes due to the opening of the crack, and measuring the crack based on the change in the impedance. 2. The method for measuring cracks in a rock mass according to claim 1, wherein after the pressurizing operation is completed, the pressure is reduced to measure a change in impedance between the electrodes when the cracks are closed. 3. A boring hole is excavated at a position where a crack in a bedrock is to be measured, and an in-hole pressurizer acting in close contact with an inner wall of the boring hole is inserted into the boring hole, and the in-hole pressurizer is pressurized. In a crack measuring device for a rock mass that opens a crack in an inner wall of a hole, a plurality of electrodes are arranged at an interval in an elastic cylinder of the pressurizer in the hole, and the electrodes are measured with an impedance measuring device via a matrix switch. A crack measuring device for rock mass, characterized in that it is connected to a rock.