JP2942789B1 - Measurement method of stress inside rock - Google Patents

Abstract

An object of the present invention is to provide a method for three-dimensionally measuring stress acting on the inside of a bedrock, particularly on a specific discontinuous surface and its vicinity. SOLUTION: A displacement measurement device 10 having a structure capable of measuring a three-dimensional displacement between two points is formed by a well 2 formed on a rock mass.
The measured value of the displacement obtained when this is installed in the well 2 while being constrained by the rock 1 and when the inner wall of the well 2 is released from the constrained state with respect to the rock 1 by core piercing. The stress acting on the bedrock 1 is detected using the obtained measured value of the displacement. Therefore, if the displacement measuring device 10 is installed in a portion having the discontinuous surface 3, the stress acting between the rocks 1 and 1 sandwiching the discontinuous surface 3 will be increased. The stress acting on the inside 1 can be measured three-dimensionally by specifying the location of each.

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 a stress acting on a discontinuous surface or the like inside a rock mass, and more particularly to a rock mass related to a stress state which causes a breakage of an existing discontinuous surface or an occurrence mechanism of an earthquake or the like. The present invention relates to a method for three-dimensionally measuring stress in a rock mass necessary for evaluating strain energy, stress state, and the like that cause slip failure of a fault or the like in a rock.

[0002]

2. Description of the Related Art Conventionally, in the field of earthquake engineering or geophysics, seismic wave measurement and strain measurement of rocks and the like have been performed in order to appropriately evaluate the mechanism of earthquake occurrence and damage to rocks caused by earthquakes. Generally, seismometers and accelerometers are used as measurement methods related to such seismic motion in the rock, but these methods use the rock surface caused by the dynamic stress wave of the seismic wave propagating in the rock. By analyzing the vibration of the rock as the amplitude or vibration pressure of the resonating vibrator, the rock phenomena related to the ground motion is analyzed.

[0003] However, such a measurement using a seismometer or an accelerometer is only for grasping the propagation phenomena in the rock after the occurrence of the seismic motion and comprehensively evaluating the vibration direction and the magnitude thereof. It is difficult to specify a discontinuous surface such as a fault and evaluate a stress state acting on the specified discontinuous surface to induce a slip failure.

In the field of rock engineering and civil engineering,
In order to evaluate mechanical deformation in rock, stress (or ground pressure) and displacement are measured in rock where there is no discontinuity. As a measurement method related to the mechanical state in the rock, a pressure manometer or an underground displacement meter based on a stress release method is generally employed. The stress state and deformation state in the rock are evaluated by measuring the strain when the stress is released by drilling the core and the displacement from the hole at the fixed point installed in the well.

[0005] However, these measurements are based on the assumption that the bedrock is a continuum and the apparatus is installed in the wellbore.
It is not possible to properly detect the stress that causes sliding deformation and swelling behavior of discontinuous surfaces such as cracks in rock. In particular, when measuring with a geomanometer, a strain gauge or other sensor is directly attached to the borehole wall in the rock, and the core is pierced around it to measure the strain when the stress is released, or the rock rock due to changes in the stress state is measured. This method evaluates stress by measuring strain, and is difficult to apply as a method of evaluating stress acting on a specific discontinuous surface because it is assumed that the target rock is a continuum. In addition, since the underground displacement meter measures the one-dimensional displacement of the whole rock in the section from the fixed point in the wellbore to the hole mouth, it evaluates three-dimensional stress on a specific discontinuous surface. It is difficult.

[0006]

The present invention focuses on these points, and provides a method for three-dimensionally measuring the stress acting on the inside of a bedrock, particularly on a specific discontinuous surface and its vicinity. Easily evaluate stress conditions that cause the failure of existing discontinuities in rock development, and strain energy and stress conditions that cause slip failures of faults in rocks related to the mechanism of occurrence of earthquakes, etc. The task was to do so.

[0007]

In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for measuring a relative position between at least two points.
Using a displacement measuring device with a structure that can measure dimensional displacement, insert it into a well formed in the rock across the discontinuous surface and restrained against both rocks sandwiching the discontinuous surface Using the measured values of the displacement obtained when the displacement measuring device is installed in the wellbore in the drilled state and the measured values of the displacement obtained when the inner wall of the well is released from the constrained state against the rock by drilling the core The stress acting on a discontinuous surface such as a crack or a fault existing inside is detected.

In the second invention, a displacement measuring device having a structure capable of measuring a relative three-dimensional displacement between at least two points is used similarly to the first invention, and the displacement measuring device is formed on a bedrock. The measured value of the displacement obtained when the displacement measuring device was installed in the borehole while being inserted into the borehole and constrained against the rock, and the inner wall of the well was released from the constrained state by the core drilling By using the measured value of the displacement obtained sometimes, the stress acting on the inside of the rock where there is no discontinuous surface such as a crack or a fault is detected.

According to these methods, a discontinuous surface is specified, and a stress acting on the discontinuous surface or a stress acting on a specific portion in the rock irrespective of the discontinuous surface is three-dimensionally determined. And the stress state inside the rock mass can be properly evaluated from these detection results. Therefore, for example, a risk of the occurrence of a failure such as a fault near the surface of the ground, which is considered to be an occurrence phenomenon such as an earthquake, is evaluated from a comparison with a yield stress at which a crack, a fault, or the like leads to a sliding failure, or a rock collapse phenomenon. It becomes extremely easy to evaluate the risk of fracture such as cracks in the rock. In addition, by analyzing the crustal deformation data and the strain energy accumulated around the fault, etc., the time-dependent rise characteristics of the stress acting on this fault, etc., are analyzed, and the slip fracture yield stress is used as an index to determine the relation to earthquakes, etc. It is also possible to provide a method for predicting the time of occurrence of slip failure.

[0010]

Embodiments of the present invention will be described below. FIG. 1 is an explanatory view of an embodiment of the first invention, FIG. 2 is an explanatory view of an embodiment of the second invention, and FIG. 3 is a schematic sectional view showing an example of a displacement measuring device used in the present invention. In this specification, core drilling means over-coring, that is, cutting the inner wall of a well to increase the inner diameter of the well, and the term “over-coring” is used in the following description.

First, the displacement measuring device shown in FIG. 3 will be described. The illustrated device is a known device disclosed in Japanese Patent Application Laid-Open No. 7-159146, and the device 10 has an elongated shape including a front structure 11 and a rear structure 12.
The front structure 11 has at its rear end three planes 13 orthogonal to each other, and the rear structure 12 has at its front end three displacement sensors 14 facing the planes 13 respectively. The combination of the three sets of planes 13 and the displacement sensors 14 makes the front structure 11 and the rear structure 12
It is configured to detect a relative displacement of. Therefore, if the front structure 11 and the rear structure 12 are respectively fixed to the object to be measured, the portion where the front structure 11 is fixed and the position where the rear structure 12 is fixed, that is, the measurement target 2 The three-dimensional displacement between points can be measured.

A fixing pin 15 is provided on the front structure 11 and a fixing pin 16 is provided on the rear structure 12, respectively. The displacement measuring device 10 is inserted into the well 2 drilled in the rock 1 and fixed. After being moved to a predetermined position by an elongated moving member (not shown) locked on the upper portions of the pins 15 and 16, the lower ends of the fixing pins 15 and 16 are projected to press the inner wall of the well 2. The front structure 11 and the rear structure 12 are in a restrained state fixed to the well 2 respectively. For this reason, for example, if the front structure 11 and the rear structure 12 are constrained on one rock 1 and the other rock 1 sandwiching the discontinuous surface 3, respectively, The three-dimensional displacement between the rocks 1 and 1 can be measured. Reference numeral 17 denotes a waterproof seal provided at a connection portion between the structures 11 and 12 to protect the internal plane 13 and the displacement sensor 14, and 18 denotes a distance between the outer peripheral surfaces of the structures 11 and 12 and the wall surface of the well 2. This is an installation guide for holding and protecting the moving member.

The fixing pins 15 and 16 are provided with, for example, a telescopic device combining a hydraulic cylinder and a spring, and are controlled by hydraulic pressure supplied from a working space at a hole via a pressure line (not shown). Displacement sensor 1
4 is provided with, for example, a differential transformer type detection unit, and its detection output is sent to a control device having a CPU, a memory, a display, and the like via a lead wire (not shown), and displayed and recorded as necessary. It will be used for subsequent data analysis. Note that the displacement measuring device 10 described above is merely an example, and other types of measuring devices can be used as long as the measuring device can detect a relative three-dimensional displacement between at least two points.

Hereinafter, an embodiment of the first invention for detecting a stress acting on a discontinuous surface will be described. In the case of the present invention, the displacement measuring device 10 is inserted into the well 2 formed in the rock 1 and the front structure 11 is inserted into the rock 1 deeper than the discontinuous surface 3 (right side in the figure) as shown in FIG. Is positioned so that the rear structure 12 is located on the rock 1 in front of the discontinuous surface 3 (left side in the figure), and the fixing pins 15 and 16 are protruded and fixed to the well 2. Generally, stress always acts between the rocks 1 and 1 on both sides of the discontinuous surface 3. Therefore, when the displacement measuring device 10 is arranged as described above to be in the restrained state, the well 2 is perforated in a straight line. Even if it is performed, a shift on the order of microns occurs between the front and rear structures 11 and 12,
This shift is detected as a three-dimensional displacement between the rocks 1 and 1.

Next, as shown by a chain line, for example, the inner wall of the well 2 is shaved by a cylindrical cutting tool to increase the inner diameter, that is, core drilling is performed. An overcoring portion 4 reaching the discontinuous surface 3 is formed in the bedrock 1 in the foreground. Incidentally, the inner diameter d of the well 2 is, for example, 66 mm, and the inner diameter D of the overcoring portion 4 is, for example, 96 mm. Due to this over-coring, the rear structure 12 loses the support by the fixing pin 16,
Because the rock 1 is released from the restrained state and receives no stress from the rock 1, the output of the displacement sensor 14 returns to the initial value before receiving the stress. Therefore, by comparing the measured values before and after the release from the restrained state, it is possible to detect the stress acting between the rocks 1 on both sides of the discontinuous surface 3. The difference between the displacement before and after the over-coring obtained in this way is closely related to the deformation characteristic of the discontinuous surface 3, and the stress corresponding to the release by the deformation coefficient as the sliding deformation characteristic of the discontinuous surface 3. Linearly correlated.

Further, the over-coring portion 4 gradually extends from the left side of the drawing and is applied to the portion of the fixing pin 16, and it takes a time on the order of minutes until the over-coring portion 4 is completely released after passing through the portion. During this time, the measured values gradually change from a state where the rock 1 receives the stress to a state where the stress is not received at all. Therefore, by continuously recording and analyzing the change, the effect on the discontinuous surface 3 is obtained. It is possible to detect the state of the applied stress more finely.

The above-described method according to FIG.
Although the measurement is related to the above, it is also possible to detect a stress state in a portion where a discontinuous surface does not exist, such as a crack or a fault inside the rock, or in the vicinity of a specific discontinuous surface by a similar method. The second invention relates to this method.

That is, as shown in FIG. 2, a displacement measuring device 10 is inserted into a well 2 formed in a rock 1
The front structure 11 and the back structure 12
Is fixed to the well 2. Then, the over-coring is performed in the same manner as in the case of FIG. 1 to release the restrained state of the rear structure 12 to the rock 1, whereby the portion where the front structure 11 of the rock 1 is fixed, The stress acting between the parts where the rear structure 12 is fixed is detected. In addition, from the state of change in the measured values until the over-coring portion 4 gradually extends and engages the portion of the fixing pin 16 and passes through this, and is completely released from the restrained state,
It is possible to more finely detect the state of the stress acting on the rock 1 at the portion where the displacement measuring device 10 is disposed.

Further, such measurement is performed by the displacement measuring device 10.
Is repeated while moving forward little by little.
It is possible to measure a stress distribution state in a portion where is formed. In addition, this measurement is performed not only at the portion where the discontinuous surface does not exist at all or near the discontinuous surface, but also by performing the measurement according to the first invention by advancing the displacement measuring device 10 to the discontinuous surface 3. By appropriately selecting the drilling location and the direction of the borehole, for example, by performing measurements even after passing through, the stress state inside the target rock can be detected in more detail.

The data thus obtained is subjected to various analyses. That is, for example, the stress state corresponding to the released portion can be evaluated from the value obtained by evaluating the shear vector displacement and the opening displacement or the closing displacement of the discontinuous surface, and the deformation rigidity characteristics of the discontinuous surface, and the like. The value obtained by evaluating the stress state in the nonexistent part or the rock near the discontinuous surface can be evaluated as being equivalent to the stress state acting on the discontinuous surface. In addition, it is possible to evaluate the stress state that causes the failure of the existing discontinuous surface in rock development, and the strain energy and stress state that cause the slip failure of a fault or the like in the rock related to the occurrence mechanism of earthquakes. it can.

Therefore, by utilizing these results, it is possible to evaluate the risk of failure of the fault or the like by comparing the stress state with the yield stress at which the crack or the fault or the like causes sliding failure, or to evaluate the risk of the occurrence of a crack in the rock. It becomes extremely easy to evaluate the risk of occurrence of destruction such as the above. In addition, by analyzing the crustal deformation data and the strain energy accumulated around the fault, etc., the time-dependent rise characteristics of the stress acting on this fault, etc., are analyzed, and the slip fracture yield stress is used as an index to determine the relation to earthquakes, etc. It is also possible to specify the location and predict the timing of the occurrence of slip failure.

[0022]

As is apparent from the above description, according to the present invention, a displacement measuring device is installed on a discontinuous surface in a rock mass or in the vicinity thereof, or a portion where no discontinuous surface exists, and this device is installed by over-coring. Is measured before and after release from the restrained state, and the stress acting on the portion is detected from the difference between the measured values before and after.

Therefore, a discontinuous surface or the like in a rock mass, which is difficult with the conventional method, is specified and the stress at that location is reduced by three.
Dimensional and high-accuracy detection is possible, and by utilizing the obtained data, the stress state inside the rock can be properly grasped to evaluate the risk of, for example, the collapse of discontinuous surfaces in the rock. In addition, it becomes easy to predict the time of occurrence of slip failure related to an earthquake or the like.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an implementation state of a first invention.

FIG. 2 is an explanatory diagram of an implementation state of a second invention.

FIG. 3 is a schematic sectional view showing an example of a displacement measuring device used in the present invention.

[Explanation of symbols]

 Reference Signs List 1 rock 2 borehole 3 discontinuous surface 4 overcoring portion 10 displacement measuring device 11 front structure 12 rear structure 13 plane 14 displacement sensor 15, 16 fixing pin

────────────────────────────────────────────────── ─── Continuation of the front page Examiner Yuji Fukuda (56) References JP-A-1-199130 (JP, A) JP-A-9-26386 (JP, A) JP-A-9-145849 (JP, A) JP-A-5-180709 (JP, A) JP-A-11-37866 (JP, A) JP-A-8-327746 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01L5 / 00 E02D 1/00

Claims (2)

(57) [Claims] 1. A method for measuring a stress state acting on a discontinuous surface such as a crack or a fault existing inside a rock, comprising a structure capable of measuring a relative three-dimensional displacement between at least two points. The displacement measuring device is inserted into the well formed in the rock across the discontinuous surface, and the displacement measuring device is installed in the well while being restrained by both rocks sandwiching the discontinuous surface. The stress acting on the discontinuous surface is detected by using the measured value of the displacement obtained when the drilling is performed and the measured value of the displacement obtained when the inner wall of the borehole is released from the restrained state against the rock by drilling the core of the borehole A method for measuring stress in a rock mass, characterized in that: 2. A method for measuring a stress state acting inside a rock mass having no discontinuous surface such as a crack or a fault, wherein the structure is capable of measuring a relative three-dimensional displacement between at least two points. A displacement measurement device equipped with a rock is inserted into a well formed in the rock, and the displacement measurement value obtained when the displacement measurement device is installed in the well while being restrained with respect to the rock, Using the measured value of the displacement obtained when the inner wall is cored and released from the constraint state against the rock,
A method for measuring stress inside a rock mass, comprising detecting stress acting inside the rock mass.