JPH08327746A - Measuring method of mechanical characteristics and initial stress of rock-bed - Google Patents

Abstract

PURPOSE: To enable simultaneous measurement of the mechanical characteristics and the initial stress of a discontinuous rock-bed by emitting an elastic wave at different depths in a bored hole and by detecting the elastic wave in the other bored hole. CONSTITUTION: Elastic wave generating-seizing devices are set at three points in the depth direction respectively in two holes (a) and (b) made by boring or the like. Then, elastic waves are emitted sequentially from arbitrary elastic wave generating devices 1, 2 and 3 in one of the holes (a) and (b) and seized by seismometers 1, 2 and 3 in the other of the holes (b) and (a). The results of the seized elastic waves are put in an equation Vij=f (d, ds, θ) in which V denotes the velocity of the elastic wave, (d) an initial stress, (ds) an interval of discontinuous planes, θ a tilt angle of the discontinuous plane and (i) and (j) numbers of measuring places in the holes (a) and (b), and by establishing simultaneous equations thereof, the initial stress, the interval of the discontinuous plane and the tilt angle of the discontinuous plane can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical property of a discontinuous rock mass and a method for measuring initial stress. More specifically, the present invention relates to a mechanical property of a discontinuous rock mass and a method for measuring initial stress, which are useful in the fields of construction, civil engineering, and the like.

[0002]

[Prior Art and Problems] In constructing a building, investigating the initial stress of the bedrock that is the foundation of the building and the mechanical properties of the bedrock are from the viewpoint of ensuring the safety of the disaster prevention or construction process. Very important from. The initial stress of bedrock has long been a major problem in the fields of geotechnical engineering and earthquake engineering. This is because the conventional method for measuring rock mass stress is to embed a volumetric strain gauge in the rock mass. With this method, changes in rock mass stress can be known, but initial stress can be measured directly. Because there was a problem that they could not do it. In addition to this, geophysical rock stress measurement methods such as the hydraulic fracture method and the stress release method are also known, but the stress release has already occurred to some extent before the measurement, and correct measurement is not possible. Can not.

With respect to the measurement of mechanical properties of rock mass, conventionally, seismic wave exploration method (acoustic wave exploration method) is used to artificially generate vibration in the rock mass and observe the propagation of the wave to estimate the condition of the rock mass. Is generally adopted. This seismic wave exploration method has two methods, a refraction method and a reflection method, depending on the type of wave to be measured. The refraction method is a method of estimating the condition of the rock mass by using a surface wave transmitted to the ground surface and a refraction wave transmitted by being refracted in the rock mass to the seismic wave generated from the artificial hypocenter. In addition, the refraction wave is a wave that once entered the bedrock, if there is a part where the physical properties have changed in the bedrock,
It is transmitted to the boundary surface and returns to the ground again. Since this refraction wave varies depending on the depth of the layer in the bedrock, its inclination, the propagation velocity, etc., it is possible to estimate the boundary of the layer existing in the bedrock by using its properties.

On the other hand, the reflection method is a method of estimating the underground structure by recording the fact that the seismic wave emitted from the artificial hypocenter is reflected at the boundary of layers in the bedrock and reaches the ground again. However, the refraction method and the reflection method cannot investigate the joint characteristics (striking, rigidity, spacing) that influence the behavior of rock mass, nor can they investigate deep underground. The present invention has been made in view of the above circumstances, solves the drawbacks of the conventional method, enables the measurement of the initial stress of the rock mass, and provides the mechanical properties of the rock mass and the initial stress measurement method independent of the depth. The purpose is to do.

[0005]

In order to solve the above problems, the present invention is a method for simultaneously measuring the mechanical properties and initial stress of a discontinuous rock mass, which is elastic at different depths in a drill hole. A method for measuring mechanical characteristics of rock mass and a method for measuring initial stress, which is characterized in that waves are emitted and the elastic waves are detected in another drill hole.

[0006]

That is, the present invention is based on the following knowledge derived from the result of the study by the inventor of the relationship between the elastic wave and the rock body having the discontinuous surface and the like. 1) Elastic wave velocity depends on normal stress on discontinuous plane. 2) The elastic wave velocity depends on the density of the discontinuous surface (joint). 3) The elastic wave velocity depends on the intersection angle between the line and the discontinuity (joint).

The present inventor has found that these can be expressed by one relational expression. That is, let us consider two drill holes a and b by boring or the like. Arbitrary numbers of elastic wave generators and absorptive devices are respectively set in these excavations a and b in the depth direction.

Next, an elastic wave is emitted from the device at an arbitrary point in the excavation hole a, and the elastic wave is captured by the device in the excavation hole b. In this case, the device can both be fired and requisitioned, and may be relocated in one hole as one device. The device may alternate firing and confiscation. The waves emitted from the elastic wave emitting devices in the drill holes a and b are detected by the device in the drill holes b and a. At this time, the relationship between the wave emitted and the wave received is: V is the elastic wave velocity, σ is the initial stress, ds is the distance between the discontinuous surfaces, and θ is the inclination angle of the discontinuous surface.
It is expressed by the following equation 1.

[0009]

[Equation 1] Here, i and j are the numbers of the locations in the excavation hole a and excavation hole b where measurement is performed. Since the relational expressions of the measuring lines connecting the measurement locations in both holes are independent of each other, the initial stress, the discontinuity spacing, and the discontinuity inclination angle can be obtained by making these relations simultaneous.

As described above, the method of the present invention has been established, and the drawbacks of the conventional methods have been resolved.
It is possible to measure the mechanical properties (particularly the properties of joints) and initial stress of bedrock. Hereinafter, the present invention will be described in more detail with reference to examples.

[0011]

EXAMPLE As shown in FIG. 1, for example, three elastic wave generating / accepting devices are set in the depth direction in two excavation holes a and b formed by two borings or the like. Next, from the arbitrary elastic wave generators 1, 2, and 3 in one of the drill holes a and b,
The elastic wave is emitted, and the elastic wave is captured by the seismographs 1, 2, and 3 in the other drill holes b and a. At this time, the elastic wave is emitted even from the elastic wave emitting device on the upper side of the drill hole.
It may be from the elastic wave emitting device at the bottom of the drill hole, but the elastic waves emitted from two or more elastic wave emitting devices should not be at the same time or overlap.

Since the captured elastic wave satisfies the above-mentioned formula 1, these results are put into the formula 1 and by making them simultaneous, the initial stress, the distance between the discontinuities and the inclination angle of the discontinuities are obtained. Can be obtained. Of course, regarding the excavation hole (3), a plurality of holes may be provided and the measurement may be performed in the same manner as above, in consideration of the state prediction of the target rock mass. It enables the elucidation of more complicated situations.

[0013]

As described above in detail, according to the present invention, the initial stress and the discontinuity (joint) which could not be achieved in the past can be obtained.
It is possible to identify the distribution of and its mechanical properties. Also,
In addition, since the rock survey work can be performed in parallel with the boring, the survey time can be shortened.

[Brief description of drawings]

FIG. 1 is a schematic view of a rock mass mechanical property and an initial stress measuring method according to an embodiment of the present invention.

[Explanation of symbols]

 1, 2, 3 Elastic wave emission / reception device a, b Drill hole

Claims (1)

[Claims] 1. A method for simultaneously measuring mechanical properties and initial stress of a discontinuous rock mass, which comprises emitting elastic waves at different depths in a drill hole and detecting the elastic wave in another drill hole. Characteristics of rock mass and method of measuring initial stress.