JP4283985B2 - Geological exploration method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a geological exploration method in front of a tunnel face using an elastic wave reflection method.
[0002]
[Prior art]
Conventionally, as a search method in front of a tunnel face using an elastic wave reflection method, there is a search method as shown in FIG. In this method, 24 blast holes 110 having a depth of 1.5 m are usually installed behind the face 100 at intervals of 1.5 m, and further receiving holes 120 having a depth of 2.4 m are positioned 15 to 16 m behind the blast holes 110. One 121 is installed on each side of the tunnel, and a vibration meter is inserted and fixed in the casing embedded in it. Then, a small amount of dynamite is loaded into the first blast hole near the face side and detonated with an electric detonator. The recording device 140 records the direct wave of the elastic wave generated at this time and the reflected wave reflected by the reflecting surface 130 in front of the face.
Similarly, a small amount of dynamite loaded in each blast hole is sequentially detonated, direct waves and indirect waves are recorded, and the same operation is performed for all 24 blast holes. In this way, a waveform as shown in FIG. 9 is obtained.
[0003]
The waveform obtained in this manner is subjected to various waveform processing such as a median filter and the position of the formation boundary surface is predicted from the traveling time of each reflected wave.
However, the conventional exploration methods as described above have the following many problems.
(1) Since the vibration receiving position is about 50 m behind the face, the actual exploration distance in front of the face is at most 100 m, and the exploration distance is relatively short.
(2) Since the vibration receiving position is about 50m behind the face, the tunnel cavity has a strong influence on the propagation characteristics of the generated elastic wave, leading to a decrease in the sensitivity of detection of the reflecting surface, and an error factor in the measurement results. .
[0004]
(3) In order to predict the position of the reflective surface in front of the face by measuring the speed of the elastic wave in the ground behind the face, if the speed of the elastic wave is different before and after the face, There is a problem that the error becomes large.
(4) Since the section from the vibration receiving position to the face is an already excavated section, there is no need for exploration, and there is a problem that such a useless exploration section is long.
[0005]
Therefore, the present invention provides a geological exploration method in which the position of the blast hole and the position of the vibrometer can be changed from the conventional positions in the geological exploration method by the elastic wave reflection method, and the position of the geological boundary surface can be predicted more accurately. It was made for the purpose of providing.
[0006]
[Means for Solving the Problems]
According to the geological exploration method of claim 1 of the present invention, one vibration meter is embedded in a natural ground near the face of a tunnel, and a plurality of blast holes are provided at predetermined intervals in the natural ground on the tunnel well side from the vibration meter. Reflection of reflected elastic waves generated by sequentially detonating explosives loaded in the blast holes and reflected from the boundary of the stratum in front of the face by each vibration meter, and reflecting the received elastic waves It is characterized by exploring the geological structure of the natural ground in front of the face by analyzing the waves.
According to the geological exploration method of claim 2, one vibration meter is buried in each of the left and right grounds near the face of the tunnel, and a plurality of blast holes are respectively defined in the left and right grounds on the tunnel well side from the vibration meter. The elastic wave generated by sequentially detonating the explosive loaded in the blast hole and reflected from the formation boundary surface in front of the face is received by each vibration meter, and is received at each interval. The geological structure of the natural ground in front of the face is explored by analyzing the reflected waves .
[0007]
In the present invention, since the vibrometer is located behind the blast hole, analysis processing using a median filter as in the prior art cannot be performed, so the traveling time of each reflected wave is determined based on the initial motion of each reflected wave. It is good to measure.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a geological exploration method according to the present invention will be described in detail with reference to the drawings showing embodiments thereof.
[0009]
As shown in FIG. 1, the receiving holes 41 and 42 are drilled on both the left and right sides 2 m behind (the wellhead side) from the face 10 of the tunnel 1, and a casing is embedded in the receiving hole. Insert and fix the vibrometers 51 and 52.
Then, 24 blast holes L1, L2,..., L24 and R1, R2,. .., R24 is drilled, and each blasting hole is embedded with a detonator loaded with dynamite.
[0010]
Next, the dynamite in the rear blast hole L1 is detonated by the electrical signal from the igniter 61 to generate an elastic wave (P wave) accompanying the expansion of the hole wall, and hits the reflective surface (stratum boundary surface) 9 in front of the face. The reflected wave and the direct wave reflected are received by the left vibrometer 51 and recorded by the recording device 7. Similarly, based on the signal from the switch box 62, the dynamite of the second, third,... Blast holes L2, L3,. Recording is performed by the recording device 7.
Similarly, for the right blast holes R1, R2,..., R24, the dynamite is sequentially detonated, and the direct wave and the reflected wave received by the right vibrometer 52 are recorded by the recording device 7.
[0011]
Then, the analysis device 8 analyzes the direct wave and the reflected wave recorded in the recording device 7 by an analysis method to be described later, predicts the position of the reflection surface three-dimensionally, and determines the reflected wave amplitude ( Alternatively, the hardness of the reflecting surface is predicted from the reflected energy.
[0012]
Next, an analysis method for predicting the position of the reflecting surface based on the direct wave and the reflected wave will be described.
FIG. 2 schematically shows a face, a blast hole, a vibrometer, and a reflecting surface orthogonal to the tunnel axis in front of the face.
The time td (i) indicates the time until the seismic wave generated from the (i) th blast hole R (i) directly reaches the vibrometer 52, and the time tr (i) is the (i) th blast hole R ( The time until the seismic wave generated from i) is reflected by the reflecting surface 9 in front of the face 10 and reaches the vibration meter 52 is shown.
[0013]
Since the amplitude of the seismic wave from the blast hole attenuates in inverse proportion to the propagation distance, the amplitude of the reflected wave that returns after being reflected by the reflecting surface is considerably small. For this reason, the blasting holes are sequentially shifted to perform blasting a plurality of times (for example, 24 times), and the reflected waves are amplified by superimposing (superimposing) seismic waves received by a vibrometer by waveform analysis described later.
[0014]
Next, a waveform analysis method will be described.
When reflected in front of the face 10, since the traveling time of the direct wave is td (i) and the traveling time of the reflected wave is tr (i), if the propagation speed of the seismic wave in the natural ground is V The distance L from the vibrometer 52 to the front reflecting surface is expressed as V (tr (i) −td (i)) / 2.
Since the amplitude of the seismic wave attenuates in inverse proportion to the propagation distance R, the amplitude attenuation is corrected by multiplying the amplitude of the received seismic wave by the propagation distance R. Actually, since the relationship between the propagation velocity V, the propagation distance R, and the observation time t can be expressed as R = V · t, the received waveform is corrected by multiplying the observation time t.
Explosives are exploded in order from the first blast hole to the 24th blast hole, and 24 seismic waves are received and the distance from the 24 data to the reflecting surface is predicted, so that the prediction can be made with high accuracy.
[0015]
When observing a plurality of waveform data obtained in this way, the arrival time of the direct wave and the reflected wave becomes faster as the blast hole approaches as shown in FIG.
Next, attenuation correction is performed by multiplying the amplitude of each waveform data in FIG. 3A by the observation time t. Thereafter, the arrival time td (i) of the direct wave is added to align the direct wave in a line as shown in FIG. 3B, and the direct wave is removed by the velocity filter.
Then, the arrival time td (i) is subtracted from each waveform data of FIG. 3C to align the timing of initial movement of each waveform data, and the distance from the vibration meter to the reflecting surface is obtained from the running time. It becomes possible.
As described above, the influence of the direct wave can be sufficiently reduced by performing the amplitude correction.
The above is a description of the schematic case of FIG.
[0016]
Next, the result by the numerical simulation method in the general case (when the reflecting surface is inclined) as shown in FIG. 4 will be described. The calculation of the data for 24 times in the numerical simulation was performed by discretizing the three-dimensional scalar wave equation with a difference approximation and setting the transmission boundary condition at the boundary of the analysis region.
In FIG. 5 showing the contour diagram of the reflected energy based on the simulation result for the three-dimensional model with either one of the vibrometers, the X axis corresponds to the horizontal direction in FIG. 4, and the Y axis in the vertical direction in FIG. The Z axis corresponds to the tunnel axis direction of FIG. The simulation was performed on the assumption that the position of the reflecting surface crossed forward (Z-axis direction) from the position of the vibrometer on a 100 m tunnel axis at a horizontal angle of 110 ° and an inclination angle of 60 °.
[0017]
The simulation results are shown in FIGS. 5 (A) and 5 (B). 5A shows a plan view, and FIG. 5B shows an elevation view. The reflected energy corresponding to the reflected wave of the three-dimensional model is dominated by one elliptical curved surface with the position of the blast hole and the position of the vibrometer as the focal point. And since each elliptical curved surface which makes each blast hole and the position of a vibrometer a focus overlaps, the reflective energy in the position equivalent to reflective surface vicinity becomes high, and the image 9A of a reflective surface appears.
However, a virtual image 9B that is different from the image 9A of the original reflection surface also appears on the opposite side to the tunnel axis in both the plan view (A) and the elevation view (B). Therefore, it is not possible to determine which image shows the reflecting surface.
This is because when the positions of the blast hole and the vibrometer are on one straight line, the elliptical curved surface group is distributed to the target with the straight line as an axis.
[0018]
Next, in the case of using two vibrometers 51 and 52 that are spaced apart in the horizontal direction, as shown in FIG. 6A, the virtual image in the horizontal plane becomes thin and can be eliminated. In this way, virtual images in the horizontal plane can be eliminated by using two horizontal vibrometers. As shown in FIG. 7, if two vibrometers are added and arranged in the vertical direction, a virtual image in the elevation view can be eliminated as shown in FIG. 6B. .
In FIGS. 6A and 6B, the reflecting surface is estimated from the real image 9A, and the position where the straight line 9C extending along the reflecting surface intersects the tunnel axis is determined, so that the reflecting surface is in front of the tunnel axis. It is possible to assume at which position of. In the case of FIGS. 6A and 6B, it can be assumed that the position of the reflecting surface is 100 m ahead of the tunnel axis.
[0019]
Note that the number of blast holes is not limited to 24, and a recording device, an analysis device, or the like may be adapted according to the number. Further, the angle of the blast hole or the receiving hole may be slightly inclined.
The technology of the present invention is not limited to tunnel excavation and is a technology that can be applied in various ways. For example, a plurality of blast holes are drilled on the exposed surface of the ground, and vibration is generated on the exposed surface of the ground around the blast hole. It is also possible to explore the geology by installing a meter.
[0020]
【The invention's effect】
According to the geological exploration method of the present invention, the following effects can be obtained.
(1) Since the position of the vibrometer is closer to the face than the blasting position, the attenuation of the reflected wave is reduced, so that the effective search distance can be made longer than before.
(2) Since the tunnel cavity does not exist in the propagation path until the generated elastic wave enters the vibrometer, the influence of the tunnel cavity can be suppressed, and the detection sensitivity of the reflecting surface is reduced and the measurement result error is small. .
(3) Since the velocity of the elastic wave to be used is a rock bed closer to the exploration position than before, the measurement error can be reduced.
(4) Since an unexcavated front area is a main measurement area, a useless exploration section can be shortened.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an embodiment of a geological exploration method according to the present invention.
FIG. 2 is a schematic diagram for explaining the operation of the present invention.
FIG. 3 is an explanatory diagram of the processing status of the waveform data in FIG. 2;
FIG. 4 is a schematic diagram showing a state of a tunnel and a reflecting surface used for simulation.
FIG. 5 is an explanatory diagram of an assumed situation of the reflecting surface in FIG. 4;
FIG. 6 is an explanatory diagram of an assumed situation of a reflecting surface when a plurality of vibrometers are used.
FIG. 7 is a perspective view of an arrangement example of a plurality of vibrometers.
FIG. 8 is an explanatory diagram of a conventional exploration method.
FIG. 9 is an explanatory diagram of a conventional exploration method.
[Explanation of symbols]
1 tunnel
10 face
51, 52 Vibrometer 9 Reflecting surface, formation boundary surface L1, L2,..., L24 Blasting hole R1, R2,.

Claims (2)

While burying one vibrometer in the ground near the face of the tunnel,
A plurality of blast holes are provided at predetermined intervals in the ground on the tunnel well side from the vibration meter,
A reflected wave reflected acoustic wave generated by sequentially detonate explosive loaded into the blasting hole from the formation boundary of the working face forward, and geophone In each vibrometer,
A geological exploration method characterized by exploring the geological structure of a natural ground in front of the face by analyzing the reflected waves of the received elastic waves. One vibrometer is buried in each of the left and right grounds near the face of the tunnel,
A plurality of blast holes are provided at predetermined intervals in the ground on the left and right sides of the tunnel well side from the vibration meter,
Resonant waves generated by sequentially detonating the explosives loaded in the blast holes and reflected from the stratum interface in front of the face are received by the vibration meters,
A geological exploration method characterized by exploring the geological structure of a natural ground in front of the face by analyzing the reflected waves of the received elastic waves .

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