JP4446626B2 - Rock crack measuring method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention excavates a borehole at a position where a crack in a rock mass is to be measured when constructing a structure underground or above the ground, when building a dam, etc., when measuring rock stress, or when developing geothermal energy. In addition, the present invention relates to a method and apparatus for measuring a crack in a rock that opens a crack in an inner wall of the hole by inserting an in-hole pressurizer acting in close contact with the inner wall of the borehole into the borehole and pressurizing the in-hole pressurizer. .
[0002]
[Prior art]
Of the methods for observing cracks in the inner wall of a rock, when using a borehole television, it is often impossible to detect a close crack. When using a mold packer that opens the crack by applying internal pressure and copies its shape to the surface, even if the crack does not open due to the applied internal pressure, it is not known whether the crack has opened at that point. You have to pull it out and start over. Moreover, even when the crack is opened, the pressure when the crack is actually opened is not known. Furthermore, even if there are a plurality of open cracks, each of which is opened at a different internal pressure, the pressure at which each crack actually opened cannot be known. As described above, in the conventional technique, it is impossible to simultaneously measure the shape of the crack and the mechanical characteristic of the internal pressure at which the crack opens. Moreover, when there are a plurality of cracks that open at different internal pressures, the pressure at which each crack opens cannot be known.
[0003]
[Problems to be solved by the invention]
The present invention has been proposed in view of the problems of the prior art as described above, and is used to obtain accurate data such as rock mass strength and crack shape and its opening pressure and closing pressure. It aims at providing the method and apparatus which measure this.
[0004]
[Means for Solving the Problems]
In the method of the present invention, a borehole is excavated at a position where a crack in a rock mass is measured, an in-hole pressurizer acting in close contact with the inner wall of the borehole is inserted into the borehole, and the in-hole pressurizer is pressurized. In the method for measuring cracks in a rock mass that opens a crack on the inner wall of the hole, an in-hole pressurizer having a plurality of electrodes provided at intervals on the surface of the elastic cylinder is prepared, and the in-hole pressurizer is pressurized to provide a hole. An electrode is crimped to the wall bedrock, 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 impedance.
[0005]
Further, in the method of the present invention, after the pressurization operation is completed, the pressure is reduced and the change in impedance between the electrodes due to the closure of the crack is measured.
[0006]
For this purpose, in the present invention, a borehole is excavated at a position to measure a crack in the rock, and an in-hole pressurizer that works in close contact with the inner wall of the borehole is inserted into the borehole. In the rock crack measuring device that pressurizes and opens the crack in the inner wall of the hole, a plurality of electrodes are arranged at intervals on the surface of the elastic cylinder of the in-hole pressurizer, and these electrodes pass through a matrix switch. Connected to an impedance measuring instrument.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described with reference to the accompanying drawings. As shown in FIGS. 1 to 3, the 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. Then, the plate 6 in contact with one of the fixing brackets 3 is fixed to the mandrel 5 with bolts 7, and the plate 8 in contact with the step 5 a of the mandrel 5 is fixed to the fixing brackets 4 with bolts 9, An O-ring 10 for sealing is interposed on the contact surface between 4 and the mandrel 5. In this way, the rubber cylinder 2 is attached to the mandrel 5 in an airtight and firm manner. The mandrel 5 is formed with a flow path 5 b for pumping pressurized fluid to the rubber cylinder 2, and the flow path 5 b is connected to the pressurizer 13 through the pipe 11 and the switching valve 12.
[0008]
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 in the circumferential direction are provided in three rows in the axial direction, and each electrode 15 is connected to a measuring instrument 17 through a signal line 16. . In addition, a pressure transducer 18 is provided in the flow path 5 b, and a pressure signal of the pressure transducer is also input to the measuring instrument 17 through the signal line 16.
[0009]
The in-hole pressurizer 1 has, for example, a length of 500 mm, an outer diameter of the rubber cylinder 2 of 58 mm, a length of 250 mm, and an outer diameter of the fixing brackets 3 and 4 of 64 mm. On the surface of the rubber cylinder 2, eight electrodes 15 are provided around the center at positions 60 mm above and below the center.
[0010]
The measuring instrument 17 includes a matrix switch 17a and a resistance / pressure measuring instrument 17b. By switching the matrix switch 17a, two adjacent electrodes 15 are connected to the resistance / pressure measuring device 17b, and the impedance between the electrodes 15 is calculated by the resistance / pressure measuring device 17b. Is to be recorded.
[0011]
Next, the operation of the present invention will be described. As shown in FIG. 4, a boring hole 21 is made 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 to the in-hole pressurizer side, the high-pressure water in the pressurizer 13 flows into the rubber cylinder 2 through the pipe 11 and the flow path 5b of the mandrel 5, and the rubber cylinder 2 swells and the boring hole 21. The existing crack in the inner wall of the borehole 21 is opened or a new crack is generated.
[0012]
Thus, 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 instrument 17 is sequentially switched, the impedance between the electrodes 15 is calculated, and together with the pressure signal of the pressure transducer 18 Record impedance sequentially. And the presence or absence and shape of the crack of the rock mass 20 are measured based on the relationship between pressure and impedance. Further, by switching the switching valve 12, the high-pressure water inside the in-hole pressurizer can be gradually reduced, and the crack opened by the pressurization can be closed. Thereafter, by opening and closing the switching valve 12 and repeatedly measuring the pressurization and depressurization several times, it is possible to accurately measure the relationship between the pressure and the impedance.
[0013]
As shown in FIG. 5, when the in-hole pressurizer 1 inserted in the boring hole 21 is pressurized and the crack 20a in the hole wall is opened, the rubber tube 2 is a resistance / pressure measuring device between the electrodes 15b and 15c. The impedance calculated in 17b increases. Then, the impedance is recorded by the resistance / pressure measuring instrument 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 resistance between the electrodes is greatly increased from the point a where the cracks are opened between the electrodes 15b and 15c, as compared to between the cracks 15a and 15b. Moreover, the impedance calculated by the resistance / pressure measuring instrument 17b between the electrodes 15b and 15c is greatly reduced by reducing the pressure of the high-pressure water inside the in-hole pressurizer and gradually closing the cracks opened by pressurization. That is, as shown in FIG. 6, the change in resistance between the electrodes decreases from the point a 'where the cracks are closed between the electrodes 15b and 15c, as compared to between the electrodes 15a to 15b where there is no crack.
[0014]
In addition, as shown in FIG. 7, when the crack 20 x is oblique to the boring hole 21, the electrodes (1 to 8) provided in the three rows A to C in the in-hole pressurizer 1. 8, the crack opening position is sequentially moved and detected as indicated by a symbol x, and its inclination and direction can be known.
[0015]
When the measurement of this position is completed, the switching valve 12 is opened to the atmosphere, the in-hole pressurizer 1 is contracted, the in-hole pressurizer 1 is moved to the back of the boring hole 21, and the switching valve 12 is switched again. Measure. In this way, the presence or absence of cracks in the rock mass 20, the shape, and the pressure when the cracks open or close are measured.
[0016]
Further, by increasing the installation interval of the electrodes 15 provided in the in-hole pressurizer 1, the direction and inclination of the crack can be measured with higher accuracy.
Further, by obtaining the impedance between every other electrode or every other electrode 15, it is possible to detect the presence and shape of a large crack across the electrodes 15.
Furthermore, finer detection is possible by obtaining the impedance between the electrodes 15 and comprehensively judging the presence / absence and shape of cracks from them.
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 invention's effect】
The effects of the present invention are described below.
The crack measuring method and crack measuring apparatus of the rock according to the present invention, an in-hole pressurizer provided with a plurality of electrodes is inserted into a borehole drilled in the rock, and the crack is opened by pressurizing or depressurizing the in-hole pressurizer. Since the rock is cracked based on the relationship between the pressure and the change in impedance between the electrodes, accurate data such as the shape of the crack and its opening, the closing pressure and the rock strength can be obtained.
[0018]
Thus, by knowing exactly the shape of the crack and the pressure at which it opens and closes, for example, the following merits occur in the technical field to which the present invention belongs.
[0019]
a. Measurement of crack characteristics in grout construction and geothermal development There are usually discontinuities in the rock. For example, in grout construction where cement mortar or the like is injected from a borehole to reinforce rock mass or stop water, an important issue is which discontinuity of the mortar is filled in which direction. There is a case. Also, in the geothermal technology where hot water or hot water is recovered from another borehole by inserting normal temperature water into the hot rock mass, the direction in which the injected water flows Is an important concern.
Several existing cracks are observed on the inner wall of the borehole depending on the discontinuity in the rock. The pressed cement mortar and water flow into the existing cracks that open according to the press-fitting pressure, so the direction of flow may change depending on what pressure is used. Therefore, it is important to know how much pressure each crack of the inner wall of the hole opens with a higher pressure and how much it closes with a lower pressure. The present invention makes this possible.
[0020]
b. Accurate measurement of rock stress When rock stress is measured by the hydraulic fracturing method, for the sake of simplicity, the case where a longitudinal fracture crack occurs will be described. The internal pressure Pb when the crack occurs, the reopening after the crack is closed once 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 the 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 the hydraulic fracturing method and is widely used. However, although the measured value of Ps is generally reliable, it has been pointed out that the measured value of Pb, particularly Pr, includes a large error. That is, for Pb, there may be a case where an expression different from the expression (1) should be used depending on water permeation conditions. In addition, it is very difficult to read Pr from the time change curve of the water pressure, and even if read, Equation (2) does not hold. For this reason, SH is not considered to have good accuracy among the rock stresses obtained by the hydraulic fracturing method. Some research reports conclude that SH is not required in conventional hydraulic fracturing methods.
[0021]
In the crack measuring method of the present invention, since no water pressure is applied to the inner wall of the hole, the above-mentioned problems in measuring Pb and Pr do not occur, and the measured Pb and Pr are correctly expressed by the formulas (1) and (2). Can be applied. Therefore, it is possible to accurately obtain SH. At the same time, the tensile strength T of the rock can be obtained.
[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 an in-hole pressurizer.
FIG. 3 is a cross-sectional view of the in-hole pressurizer.
FIG. 4 is a schematic diagram for explaining a method for measuring cracks in rock according to the present invention.
FIG. 5 is a cross-sectional view showing a crack opening portion of a hole wall.
FIG. 6 is a graph showing changes in resistance between electrodes due to crack opening and closing.
FIG. 7 is a diagram for explaining detection when a crack is inclined with respect to a boring hole.
8 is a diagram 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 ... Fixing metal fitting 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 / pressure measuring instrument 18 ... Pressure transducer 20 ... Rock 21 ... Boring hole 22 ... Inserting rod

Claims (3)

Drill a boring hole at the position to measure the crack in the bedrock, insert an in-hole pressurizer that works in close contact with the inner wall of the borehole, and pressurize the in-hole pressurizer to crack the inner wall of the hole. In the method for measuring cracks in open rocks, prepare an in-hole pressurizer with a plurality of electrodes provided at intervals on the surface of the elastic cylinder, and pressurize the in-hole pressurizer to crimp the electrodes to the hole wall rock A method for measuring a crack in a rock mass, comprising detecting a change in impedance between the electrodes accompanying the opening of the crack and measuring the crack based on the change in impedance. The method for measuring cracks in a rock mass according to claim 1, wherein after the pressurizing operation is completed, the pressure is reduced and a change in impedance between the electrodes due to the closure of the cracks is measured. Drill a boring hole at the position to measure the crack in the bedrock, insert an in-hole pressurizer that works in close contact with the inner wall of the borehole, and pressurize the in-hole pressurizer to crack the inner wall of the hole. In the crack measuring device for the open rock, a plurality of electrodes are arranged at intervals in the elastic cylinder of the in-hole pressurizer, and these electrodes are connected to an impedance measuring device via a matrix switch. A rock crack measuring device characterized by that.

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