JPH10153665A - Bedrock survey method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily and exactly surveying brittle part of ground by using elastic wave. SOLUTION: By using reflection wave of excited wave of elastic wave reflecting in the ground to be surveyed, the positions of reflection planes 21 to 25 in the ground are defined, estimating the interval where the reflection planes 22 to 24 are densely existing as the brittle parts 26 of the ground and estimating the interval where the reflection plane does not exist as intact part (hard rock part), exact survey of the bedrock is easily done regardless of the kind of the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for exploring a rock mass, and more particularly to a method for exploring a fragile portion of a ground using elastic waves.

[0002]

2. Description of the Related Art It is very advantageous from the viewpoint of safety, economy, construction period and the like if geological information in front of a face is obtained in advance in tunnel excavation. When constructing tunnels, geological surveys are often performed in advance, but the information is often insufficient. Therefore, as one of the methods for exploring the geological condition in front of the face during excavation work, there is known an exploration method using elastic waves from inside the tunnel, and a method for exploring the face in front of a multi-point oscillation one-point vibration receiving system is known. I have.

[0003] In the method for exploring a face in front of a face, an elastic wave (seismic wave) due to small blasting is oscillated in a tunnel pit, and a reflected wave from a changing surface property of the ground in front of the face is caught and its position is estimated.

In this method, the information finally obtained by the exploration relates to the reflection surface of the elastic wave representing the change in the physical properties of the ground in front of the face, and is determined by the position, the property, and the intensity of the reflected signal. is there. Of these, the properties of the reflecting surface represent how the physical properties of the ground change,
It is either a change of "soft" or a change of "soft → hard". When estimating the geology, we predict the hardness of the ground from this combination, that is, the section between each of the reflecting surfaces that appeared in the order of “hard → soft” and “soft → hard” is called the weak part of the ground. As expected.

[0005]

SUMMARY OF THE INVENTION Incidentally, the present inventors, in order to verify the prospect of the ground by the above-mentioned front face exploration method, examined the actual geological conditions revealed by tunnel excavation and the results of the exploration results. Comparison and collation were performed. As a result, as shown in FIG. 4, it became clear that the actual geology may be different.

That is, in FIG. 4, the one-dot chain lines indicated by reference numerals 1 and 2 are the reflecting surfaces where the change of “hard → soft” appears, and the ones indicated by the reference numerals 3, 4 and 5 are “soft → hard”. "On the reflective surface. Therefore, in this figure, the portions between the reflecting surfaces 1 and 3 and the portions between the reflecting surfaces 2 and 5 are predicted (estimated) as the weak portions 6 and 7 of the ground, respectively. On the other hand, in FIG.
The portions indicated by are crushed zones (fragile portions) that appeared by actual excavation, and 9a, 9b, 9c are small cracks. Therefore,
The actual vulnerable part 8 is the vulnerable part 6,
It can be seen that the position is different from 7. In FIG. 4, reference numeral 11 denotes an oscillation hole, and 15 denotes a vibration receiving hole.

[0007] The present inventors have compared and collated the results of the exploration with the front face exploration method with the results of actual underground geological surveys, and performed diligent analysis. They found that the denser parts corresponded relatively well with the fragile parts of the ground.

[0008]

According to a first aspect of the present invention, there is provided a rock exploration method for exploring a rock using an elastic wave.
By the reflected wave reflected in the ground to be explored by the excitation wave that is an elastic wave, the position of the reflection surface in the ground is determined, and the dense section of the reflection surface is estimated as the fragile portion of the ground. Features.

[0009] The denseness of the reflecting surfaces refers to a state in which two or more reflecting surfaces are in close contact with each other, and is used as a guide when the distance between the reflecting surfaces is about 5 meters or less. In addition, the section where the reflection surface does not exist can be estimated as a healthy part (hard rock part) of the ground. In addition, when the reflection signal of the densely reflecting surface is high, the rock strength is very low and the degree of crushing is strong, and the rock is fragile. On the other hand, when the reflection signal of the dense reflecting surface is low, the rock strength is slightly lower than that of the healthy part of the ground,
It is a fragile part of the mountain where the degree of crushing is weak. However, this does not apply when it is recognized that the elastic wave is attenuated. Furthermore, if the obtained reflecting surfaces are not dispersed and dense within the exploration area, the geological geology of the exploration area is generally sound, and the reflecting surface that exists alone has small changes such as small cracks. Represents

As described above, according to the rock exploration method of the first aspect, the section where the reflection surface is dense is estimated as the fragile portion of the ground, and the section where the reflection surface does not exist is sound. By estimating it as a part (hard rock part), accurate rock exploration becomes possible.

In the above-mentioned rock exploration method, when analyzing an elastic wave recorded by measurement, there are several parameters, such as coefficients of various filters, which must be determined. One of them is the elastic wave propagation velocity in front of the tunnel face. In the case where the elastic wave propagation velocity in the section in front of the face is considered to be almost the same as the survey line section, the elastic wave propagation velocity obtained in the survey line section can be used for analysis. The method cannot be used for cases that are considered to be significantly different from those in the survey line section.

Therefore, when the elastic wave propagation velocity of the ground to be searched for is significantly different from that of the survey line section or when there are a plurality of velocity bands having different elastic wave propagation velocities in the ground, accurate rock search is performed. , The propagation velocity must be separately estimated, and it is difficult to estimate the propagation velocity.

According to a second aspect of the present invention, there is provided a rock exploration method according to the first aspect, wherein a plurality of velocity bands having different elastic wave propagation velocities are obtained in advance in the ground to be explored. Assuming a typical reciprocating wavy line path for the excitation wave and the reflected wave propagating in these velocity bands, the ratio of the length of the excitation wave and the reflected wave on the wavy line in each of the speed bands to the reciprocating wave line path The average elastic wave propagation velocity of the ground to be searched is obtained by the sum of the values obtained by multiplying the average by the elastic wave propagation velocity in each velocity band.

When finding a plurality of velocity zones having different elastic wave propagation velocities in the ground to be searched, use the result of refraction elastic wave exploration from the surface, which is often performed in a preliminary survey of tunnel excavation work. I do. Then, according to the result, the speed zone is described on the geological profile, and in the geological profile in which the speed zone is described, a typical reciprocating ray line path for the excitation wave and the reflected wave is assumed by drawing,
The average elastic wave propagation velocity is obtained from the sum of values obtained by multiplying the ratio of the length of the excitation wave and the reflected wave on the wavy line in the velocity band to the reciprocating wave line path by the elastic wave propagation velocity in each velocity band.

In this way, the average elastic wave propagation velocity at the ground to be searched can be easily and quickly obtained. Then, by analyzing the elastic waves (excitation waves and reflected waves) based on the average elastic wave propagation velocity, the elastic wave propagation velocity of the ground to be explored greatly differs from that of the survey line section, Even if there are multiple velocity zones with different elastic wave propagation velocities, accurate rock exploration can be performed.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a rock exploration method according to an embodiment of the present invention. FIG.
FIG. 1 is a conceptual diagram of an apparatus for implementing a rock exploration method of the present invention. At the time of measurement, a measurement line of about 60 meters is provided in a straight line on the tunnel side wall in front of the face. Then, a small-scale explosion for exploration is performed in about 30 oscillation holes 11 on the survey line, and an elastic wave (earthquake wave) is measured by a vibration sensor 12 behind the survey line. Blasting uses a high-performance explosive and an exploration detonator 13.

The vibration sensor 12 is compactly assembled and inserted into one rod 14, and three sets of two-component accelerometers in the axial direction and the vertical direction of the tunnel are mounted. The rod 14 into which the vibration sensor 12 is inserted is used by inserting it into a vibration hole 15 for reducing the influence of the loose area. Further, the rod 14 is inserted into a dedicated guide casing 16 in order to enhance the adhesion to the ground,
The guide casing 16 is fixed to the ground with non-shrink mortar. In FIG. 1, reference numeral 17 denotes a blaster, 18 denotes a trigger box, and 19 denotes a recording device.

Elastic waves (seismic waves) generated by the rock exploration apparatus
Is performed in two major steps. The wave field processing process, which is the first stage, removes and reduces noise such as a direct P wave, a direct S wave, a back reflection wave, and a surface wave from the recording wave, and amplifies only the reflection wave reflected by the front reflection surface 20.・ This is the process of extraction. The event extraction process, which is the second stage, is a process of performing a migration process on the reflected wave obtained in the wave field processing process, extracting a reflection surface, and three-dimensionally displaying the reflection surface.

In the case of analyzing the elastic wave, in the case where the elastic wave propagation velocity in the section in front of the face is considered to be significantly different from that in the search line section, the reflection surface can be obtained by using the elastic wave propagation velocity in the search line section. Is extracted with the position shifted, the average value of the elastic wave propagation velocity in the section in front of the face is obtained from the existing geological information, and analysis is performed using this average elastic wave propagation velocity.

The average elastic wave propagation velocity is determined, for example, as follows. That is, as shown in FIG. 2, when the exploration range is a valley in terms of topography,
The direction from the tunnel axis direction to the upward direction θ is used as the reflected wave enhancement direction, and the reflected wave from the ground near the tunnel axis is amplified.
In FIG. 2, S1 to S4 are ground velocity zones obtained by refraction elastic wave exploration from the surface of the ground, which were performed in a preliminary survey of tunnel excavation work, and respective elastic wave propagation in these velocity bands S1 to S4. The speeds V1 to V4 are V1 <V
2 <V3 <V4. The speed zone S1
Is a fragile portion near the ground surface due to strong weathering, etc., and is a portion where the elastic wave is significantly attenuated.

In the geological profile showing the speed bands S1 to S4, a typical reciprocating wavy line path for the excitation wave and the reflected wave is assumed by drawing as follows. First, a right triangle △ DBC is drawn with the analysis range extending from a receiver (vibration sensor 12) to a predetermined distance in front. Here, the line segment DB is appropriately set, but is, for example, about 150 meters. The line segment DC is a straight line passing through the contact point of the boundary curve between the speed bands S1 and S2,
The speed zone S1 is not included in C. Further, the line segment CB is a line segment connecting the point C and a point C where a perpendicular extending vertically upward from the point B intersects the line segment DC.

Next, a typical reciprocating trajectory of the oscillating wave and the reflected wave propagating in the △ DBC is assumed as follows. First, the intersection between the bisector of the angle θ formed by the line segment DB and the line segment DC and the line segment CB is R (assumed reflection point of the wavy line), and the line segment RD is represented by the wavy line of the reflected wave (return path). Wavy line). On the other hand, the middle point of a straight line connecting the large number (for example, 30) of the oscillation holes 11 is defined as A, and the line segment AR connecting this point A and the intersection R is defined as a wavy line of the excitation wave (outgoing wavy line). Then, the line segment AR and the speed bands S2 to S4
Are defined as p1, p2, and p3, and the intersections between the line segment RD and the boundaries of the speed bands S2 to S4 are defined as q1, q2, and q3.

Next, the elastic wave propagation in each speed band is determined by the ratio of the length of the oscillating wave to the reflected wave in each of the speed bands S2 to S4 with respect to the reciprocating wave line path (line segment AR + line segment RD). The average elastic wave propagation velocity V of the ground to be searched is obtained from the sum of the values multiplied by the velocity. This average elastic wave propagation velocity V is obtained by the following equation.

(Equation 1)

Thus, by drawing and simple calculation,
The average elastic wave propagation velocity in the ground to be searched can be obtained easily and in a short time. Then, by analyzing the elastic waves (excitation waves and reflected waves) based on the average elastic wave propagation velocity, the elastic wave propagation velocity of the ground to be explored greatly differs from that of the survey line section, Even if there are multiple velocity bands with different elastic wave propagation velocities,
Accurate rock exploration can be performed.

FIG. 3 shows a result of analysis of an elastic wave (seismic wave) by the rock exploration method of the present embodiment using the average elastic wave propagation velocity. In this figure, the position of the reflecting surface is shown. , Direction, and the nature of the reflective surface are indicated. That is, in FIG. 3, dashed lines indicated by reference numerals 21 and 22 indicate reflection surfaces where the change of “hard → soft” appears, and dashed lines indicated by reference numerals 23, 24 and 25 indicate change of “soft → hard”. Indicates the reflective surface where appears. In addition,
A portion indicated by reference numeral 8 indicates a crush zone (fragile portion) that has appeared by actual excavation, and 9a, 9b, and 9c indicate small cracks.

In the rock exploration method of this example,
A section where the reflection surface is dense is estimated as a fragile portion of the ground. That is, as shown in FIG.
22 are dense, so this section is
, The section where there is no reflective surface is estimated as a sound part (hard rock) of the ground, and the reflective surfaces 21 and 25 that exist alone are estimated as small changes such as small cracks.

As is apparent from FIG.
And the actual position of the crush zone (fragile portion) 8 almost coincides. In the section where the reflection surfaces are not dense, although there are small cracks 9a and 9c, Is sound, and it can be seen that the positions of the reflecting surfaces 21 and 25 that exist alone and the positions of the small cracks 9a and 9c substantially coincide with each other.

As described above, in the rock exploration method of the present embodiment, the section where the reflection surfaces 23, 24, and 22 are dense is estimated as the weak portion 26 of the ground, and the section where the reflection surface does not exist is the ground. By estimating it as a healthy part of the mountain (hard rock), accurate rock exploration can be easily performed regardless of the type of rock at the ground. In the above example, an example was described in which the rock mass exploration method of the present invention was applied to the case where a front face exploration method of a multi-point oscillation single-point vibration receiving system using elastic waves from the inside of the tunnel was used. Of course, the present invention can be similarly applied to the exploration in front of a face using elastic waves and the exploration of other grounds other than the exploration in front of the face.

[0029]

As described above, according to the first aspect of the present invention,
The rock mass exploration method of (1) finds the position of the reflection surface in the ground by the reflected wave in which the exciting wave which is an elastic wave is reflected in the ground to be searched, and makes the section where the reflection surface is densely fragile Since it is estimated as a part, accurate rock exploration can be easily performed regardless of the type of rock at the ground.

Further, according to the rock exploration method of claim 2, in the rock exploration method of claim 1, a plurality of velocity bands having different elastic wave propagation velocities are obtained in advance in the ground to be investigated, and these velocity zones are determined. A typical reciprocating wavy path is assumed for the elastic waves (excitation waves and reflected waves) propagating in the band, and the ratio of the length of the elastic wave on the wavy line in each of the velocity bands to the reciprocating wavy path is calculated by Since the average elastic wave propagation velocity of the ground to be searched is determined by the sum of the values multiplied by the elastic wave propagation velocity in the band, the elastic wave propagation velocity of the ground to be searched is larger than that of the survey line section. Even when the ground is different or when there are a plurality of velocity bands having different elastic wave propagation velocities in the ground, accurate rock exploration can be performed.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of an exploration apparatus for implementing a rock exploration method of the present invention.

FIG. 2 is a longitudinal sectional view showing an example of a ground used in the rock exploration method of the present invention.

FIG. 3 is a sectional view of a tunnel showing a comparison between a result obtained by the rock exploration method of the present invention and actual geology.

FIG. 4 shows the results obtained by the conventional rock exploration method,
It is sectional drawing of the tunnel which shows the comparison of actual geology.

[Explanation of symbols]

 8 Actual crush zone (fragile part) 9a-9c Actual small crack 21, 25 Reflecting surface that exists alone 22, 23, 24 Reflecting surface that is dense 26 Vulnerable part estimated by exploration

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshihisa Nawa 1 Higashi-ku, Higashi-ku, Nagoya City, Aichi Prefecture Inside (72) Inventor Fumio Kawajiri 1 Higashi-Shimmachi, Higashi-ku, Nagoya City, Aichi Chubu Electric Power Company (72) Inventor Takeshi Akashi 2570-4 Shimotsuruma, Yamato-shi, Kanagawa Prefecture Nishimatsu Construction Co., Ltd.Technical Research Institute (72) Inventor Riki Inaba 2570-4 Shimotsurumama, Yamato-shi, Kanagawa Prefecture Nishimatsu Construction Co., Ltd.Technology Research Institute (72) Inventor Koji Ishiyama 2570-4 Shimotsuruma, Yamato-shi, Kanagawa Prefecture Nishimatsu Construction Co., Ltd. (72) Inventor Takashi Hirano 2570-4 Shimotsuruma, Yamato-shi, Kanagawa Prefecture Nishimatsu Construction Co., Ltd. 2570-4 Shimotsuruma, Yamato City, Kanagawa Prefecture Nishimatsu Construction Co., Ltd. (72) Inventor Horiba Natsumine Yamato, Kanagawa Prefecture 2570-4 Shimotsuruma, Nishimatsu Nishimatsu Construction Co., Ltd.

Claims (2)

[Claims] 1. A rock mass exploration method for exploring a rock mass using an elastic wave, wherein an exciting wave, which is an elastic wave, is reflected by the reflected wave in the ground to be searched, and a reflection surface in the ground is detected. A rock mass exploration method comprising: determining a position of a reflection surface; and estimating a section where the reflection surface is dense as a fragile portion of the ground. 2. The rock exploration method according to claim 1, wherein a plurality of velocity bands having different elastic wave propagation velocities are obtained in advance in the ground to be searched, and vibrations propagating through these velocity bands are obtained. Assuming a typical reciprocating wavy line path for the wave and the reflected wave, the elastic wave propagation velocity in each speed band is determined by the ratio of the length of the vibrating wave and the reflected wave on the wavy line in each speed band to the reciprocating wave line path. A rock exploration method, wherein an average elastic wave propagation velocity in a ground to be searched is obtained from a sum of multiplied values.