JP6936751B2 - Ground information acquisition method and equipment - Google Patents

Description

The present invention relates to a method and device for acquiring ground information, and is particularly suitable for use when acquiring ground information of ground into which a chemical solution has been injected for ground improvement, such as under an existing airport runway. Regarding the acquisition method and equipment of ground information. The ground information refers to the hardness of the ground, the formation structure, the formation classification, the range of ground improvement, underground cavities and underground obstacles, cracks in the bedrock, gravel layers and boulders, underground gas, etc.

One predecessor of the applicant has proposed in Patent Documents 1 and 2 a method of acquiring ground information by tomography between two holes arranged vertically using acoustic tomography.

As illustrated in FIGS. 1 (cross-sectional view in the ground) and FIG. 2 (perspective view in the ground), a plurality of vertical boring holes (hereinafter, simply referred to as vertical holes) 20 perpendicular to the surface of the ground 10. Is provided, an in-hole oscillator 30 such as a piezoelectric element is arranged in a part thereof, and a plurality of receivers 32 such as hydrophones are arranged in the remaining vertical holes 20 to form a receiver array, and acoustics between the two holes. Ground information is acquired by tomography. In the figure, 10A is a turbulent stratum near the ground surface, and 12 is a ground improvement body (hereinafter referred to as an improvement body) by, for example, chemical injection.

On the other hand, a chemical injection method is known as a ground improvement method for measures against liquefaction of the ground due to an earthquake. Since there are some parts that cannot be dealt with by straight drilling when improving the area directly under the existing structure, a curved drilling method as proposed by one of the applicants in Patent Document 3 has been developed.

Special Fair 8-20438 Gazette Japanese Patent No. 2862171 Japanese Unexamined Patent Publication No. 2016-196805

Toshifumi Matsuoka et al. "Geographical Exploration Method Using Seismic Interferometry" Journal of the Geotechnical Society, 57-5 (616), pp. 8-11 (May 2009)

However, in the acoustic tomography between two holes arranged vertically, it is necessary to increase the number of vertical holes for measurement in order to expand the investigation range in the horizontal direction, and boring cost is required. In addition, since the number of lines to be measured is large and the number of oscillations is large, the on-site work time becomes long. There is also a problem that the accuracy in the horizontal direction may not be sufficient.

On the other hand, as illustrated in FIG. 3, it is also conceivable to dispose the in-hole oscillator 30 and the receiver 32 in the horizontal boring holes (hereinafter, simply referred to as horizontal holes) 22 and 24 formed by, for example, the curved hole drilling method. Be done. In this case, even if the survey range is widened, it can be dealt with simply by lengthening the horizontal boring, and the number of survey lines is reduced, but since the number of oscillations is large, the on-site work time for data acquisition becomes long.

Further, in any of the vertical holes 20, the horizontal holes 22, and 24, the in-hole oscillator 30 has a problem that the size is restricted, the output is limited, and the investigation range may be narrow.

On the other hand, as illustrated in FIG. 4, the receiver arrays 32R1, 32R2, 32R3 in which the oscillator (also referred to as the ground oscillator) 40 is arranged on the ground and a plurality of receivers are arranged in the horizontal hole 22 can be received. Conceivable. In this case, even if the survey range becomes wide, it can be dealt with simply by lengthening the horizontal boring. In addition, the number of survey lines and the number of oscillations can be reduced, and the on-site work time for data acquisition can be shortened. Further, since the ground oscillator 40 arranged on the ground surface has no restrictions on the dimensions, it has an advantage that a large output can be used and the investigation range can be widened, but the ground is disturbed near the ground surface. In many cases, the oscillation energy becomes non-uniform due to the influence of the non-uniform ground surface, and the oscillating sound pressure cannot be made constant, so that there is a problem that it is difficult to calculate the attenuation factor.

Using the seismic wave interferometry described in Non-Patent Document 1, as shown in FIG. 5 (A), the vibration wave R 1 ( _{vibration wave R 1) received by the receiver 32 R 1 of the receiver array 42 R1 in which a plurality of receivers are arranged.} The correlation function C _{1 * 2} (t) = R ₁ (t) * R ₂ (t) of the vibration wave R _{2 (t) received by the receiver 32 R 2} of the receiver array 42 R2 is shown in FIG. 5 (t). as shown in B), it is oscillated though a receiver 32R ₁ of receiver array 42R1, result that is equal to the received vibration waves R _'2 (t) at a receiver 32R ₂ of receiver array 42R2 can be obtained .. This seismic interferometry can also use natural earthquakes and construction noise as a virtual oscillation source.

The present invention utilizes this seismic wave interference method, and as illustrated in FIG. 6A, when this seismic wave interference method is used in the depth direction, for example, in two horizontal holes 22 and 24, it is arranged on the ground surface. _{The vibration wave R 1} (t) received by each receiver of the receiver array 44R1 and the vibration wave R ₂ received by each receiver of the receiver array 44R2 are oscillated from the oscillation point S by using the generated oscillator 40. _{Correlation functions of -1} (t), R _2-2 (t), R _2-3 (t) C _{1 * 2-1} (t), C _{1 * 2-2} (t), C _{1 * 2-3} (t) is, as shown in FIG. 6 (B), and oscillated from the receiving point of the receiver array 44R1, vibration wave R received by the receiver of the receiver array _{44R2 '2-1 (t), R} ' 2 _It is equal to -2 (t) and _R'2-3 (t). This is shown in equations (1) to (3).
C _{1 * 2-1} (t) = R ₁ (t) * R _2-1 (t) = _R'2-1 (t)… (1)
C _{1 * 2-2} (t) = R ₁ (t) * R _2-2 (t) = _R'2-2 (t)… (2)
C _{1 * 2-3} (t) = R ₁ (t) * R _2-3 (t) = _R'2-3 (t)… (3)

The present invention utilizes this measurement principle, and as illustrated in FIG. 7 (A), a plurality of receivers 32R _1-1 , 32R _1-2 , 32R _{1- of the receiver array 44R1 (four in the figure).} Oscillation waves R _1-1 (t), R _1-2 (t), R _1-3 (t), R _{1-4 (t) received by 3} , 32R _1-4 , and receiver array 44R2, for example. Correlation function C of vibration waves R _2-1 (t), R _2-2 (t), R _2-3 (t) received by three receivers 32R _2-1 , 32R _2-2 , 32R _{2-3 When (1 to 4) * (2-1 to 2-3)} (t) are obtained, as shown in FIG. 7 (B), the receiver oscillates from _{a plurality of points S 1 to} S _{4 of the receiver array 44R1 to receive the receiver.} each receiver in the array 44R2 32R _2-1, 32R _2-2, vibration wave R received at _{32R 2-3 '2-1 (t),} R' 2-2 (t), R '2-3 (t ).

The present invention has been made in view of the above points, provided in the ground in the depth direction, the horizontal holes in a plurality of stages of different depths, a plurality of receivers disposed a receiver array, respectively Vibration in the ground by detecting the vibration wave received by each receiver array when the vibration wave is oscillated by the oscillator arranged on the ground surface and calculating the correlation coefficient between the receiver arrays. The above-mentioned problem is solved by obtaining the wave velocity distribution or the attenuation rate distribution.

The present invention also provided in the ground in the depth direction, the horizontal holes in a plurality of stages of different depths, are disposed respectively, a receiver array having a plurality of receivers are disposed, on the surface By detecting the arranged oscillator and the vibration wave received by each receiver array when the vibration wave is oscillated by the oscillator, and calculating the correlation coefficient between the receiver arrays, the vibration wave in the ground Similarly, the above-mentioned problem is solved by a ground information acquisition device characterized by comprising an arithmetic control means for obtaining a velocity distribution or a damping rate distribution.

Here, the horizontal hole may be formed by bending a hole in order to inject a chemical solution for ground improvement into the ground.

Further, a receiver array in which a plurality of receivers are arranged is also arranged in the vertical hole, and the vibration wave detected by the receiver array in the vertical hole can also be used.

According to the present invention, the problems of the prior art can be solved with respect to the following points.
(I) Since vertical boring is not required, the number of boring does not change even if the survey range is widened. When applied to ground improvement work using horizontal boring, a boring hole for injection can be used, so that it is not necessary to perform new boring.
(Ii) Since the same information as oscillating from a plurality of points in the ground can be obtained only by oscillating from one point on the ground surface, the work time for data acquisition can be shortened.
(Iii) Since it is not necessary to dispose the oscillator in the boring hole and the size is not restricted, an oscillator having a large energy, for example, a vibrator can be used, and the investigation range can be expanded.

A cross-sectional view in the ground schematically showing an acoustic tomography technique between two holes using vertical holes proposed by one of the applicants. Similarly, a perspective view in the ground An underground perspective view showing a comparative example in which an oscillator and a receiver are arranged in a horizontal boring hole. An underground perspective view showing a comparative example using a ground oscillator and a receiver arranged in a horizontal hole. Underground cross-sectional view showing the principle of seismic interferometry using vertical holes A cross-sectional view in the ground showing the measurement principle of the present invention for one point of the receiver array. Underground cross-section, also showing all points in the receiver array Underground perspective view showing the first embodiment of the present invention Longitudinal cross-sectional view of the ground seen from the direction of arrow IX in FIG. Cross-sectional view of the ground seen from the direction X of the arrow in FIG. Underground perspective view showing a second embodiment of the present invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments and examples. Further, the constituent requirements in the embodiments and examples described below include those that can be easily assumed by those skilled in the art, those that are substantially the same, that is, those in a so-called equal range. Further, the components disclosed in the embodiments and examples described below may be appropriately combined or appropriately selected and used.

The first embodiment of the present invention includes FIG. 8 (horizontal view in the ground), FIG. 9 (longitudinal sectional view in the ground seen from the direction of arrow IX in FIG. 8), and FIG. 10 (direction of arrow X in FIG. 8). As shown in the cross-sectional view of the ground as seen from above), a receiver in which a plurality of receivers are arranged in horizontal holes 22 and 24 provided in the ground in two stages in the depth direction and three rows in the horizontal direction. Vibration waves received by each of the receiver arrays 44R1 to R6 when the instrument arrays 44R1 to R6 are arranged respectively and the vibration waves are oscillated by the ground oscillator 40 arranged on the ground surface according to the command of the computer 50 which is the arithmetic control means. Is detected, and the correlation coefficient between the receiver arrays 44R1 to R6 is calculated to obtain the velocity distribution and the attenuation rate distribution of the vibration waves between the receiver arrays.

As the horizontal hole 22, one formed by bending a hole can be used in order to inject a chemical solution for ground improvement into the ground. In this case, it is not necessary to make a new measuring hole.

As the ground oscillator 40, for example, a vibrator can be used.

As each receiver of the receiver arrays 44R1 to R6, for example, a hydrophone can be used.

From the ground oscillator 40, for example, a vibration wave according to a pseudo-random code as described in Patent Documents 1 and 2 can be generated.

Each of the receivers of the receiver arrays 44R1 to R6 identifies the corresponding vibration wave from the received vibration wave by the correlation calculation by the computer 50, calculates the velocity of the vibration wave from the propagation time, and generates the vibration wave. The attenuation rate between each receiver array can be calculated from the ratio of the generated vibration wave to the sound pressure of the received vibration wave.

Specifically, for example, the correlation function C _{1 * 2-1} reception recording R _2-1 (t) of the received record R ₁ (t) and the reception point R _2-1 reception point R ₁ is receiving point R _Since it oscillates from 1 and becomes equal to the received waveform received at the _{receiving point R 2-1.} Therefore, the arrival time t of the vibration wave and the received sound pressure A are read from _{the calculation result C 1 * 2-1 (t), and the speed V is} It can be calculated by the following equation (4).
V = d / t ... (4)

ここで、ｄは伝播距離、ｔは到達時間、Ａは受信音圧、Ａ_Oは発振音圧、ｆは発振周波数、αは減衰定数である。なお、式（７）の減衰定数αは自然対数で表される減衰定数(neper)であり、式（８）の減衰定数αは音圧レベル(ｄＢ)で表される定数である。 ^{Further, the attenuation factor Q -1,} which is the reciprocal of the dimensionless quantity Q value representing the attenuation characteristic of the medium, is calculated by obtaining equations (7) and (8) from the following equations (5) and (6). Can be done.

Here, d is the propagation distance, t is the arrival time, A is the received sound pressure, A _O is the oscillation sound pressure, f is the oscillation frequency, and α is the attenuation constant. The attenuation constant α in the equation (7) is a decay constant (neper) represented by the natural logarithm, and the attenuation constant α in the equation (8) is a constant represented by the sound pressure level (dB).

Therefore, using the calculated velocity and attenuation rate of the vibration wave, the velocity distribution and attenuation rate distribution of the vibration wave in the ground can be obtained and displayed by a computer 50 or the like.

According to this embodiment, as shown in FIG. 9, since measurement can be performed three-dimensionally using a plurality of receivers at one oscillation point, the number of survey lines and the number of oscillations can be significantly reduced, and data acquisition can be performed. On-site work time can be significantly reduced. For example, when the survey lines are measured using the six receiver arrays 44R1 to R6 as in the present embodiment, as shown in FIG. 10, the measurement of 9 survey lines can be performed at one time, so that the working time is 1. It becomes / 9. As shown in FIG. 9, the accuracy can be improved by moving the position of the ground oscillator 40 and repeating the measurement.

In the first embodiment, the ground information was acquired using only the receiver arrays 44R1 to R6 arranged in the horizontal holes 22 and 24, but as in the second embodiment shown in FIG. 11, it is vertical. It is also possible to improve the resolution in the vertical direction by providing the holes 20 and using the vibration waves detected by the receiver arrays 42R1 to R6 arranged in the vertical holes 20.

In the above embodiment, the present invention has been applied to the ground of an airport into which a chemical solution has been injected, but the scope of application of the present invention is not limited to this, and investigation of obstacles and / or cavities in shallow places is performed. It can also be applied to other ground such as inspection of tunnels near the surface of the earth.

The type of horizontal hole is not limited to that formed by the curved hole drilling method. The number of steps in the depth direction of the horizontal hole and the number of rows in the horizontal direction are not limited to two steps and three rows, and may be, for example, two steps and one row.

Vertical holes and horizontal holes do not need to be newly formed by boring if there are available holes.

10 ... Ground 12 ... Improved body 20 ... Vertical (boring) holes 22, 24 ... Horizontal (boring) holes 32, 32R ₁ , 32R _{2 , 32R 1-1} , 32R _1-2 , 32R _1-3 , 32R _1-4 , 32R _2-1 , 32R _2-2 , 32R _2-3 ... Receiver 40 ... Ground oscillator 42R1-R6, 44R1-R6 ... Receiver array 50 ... Computer

Claims (6)

Provided in the ground in the depth direction, the horizontal holes in a plurality of stages of different depths, a plurality of receivers disposed a receiver array disposed respectively,
When the vibration wave is oscillated by the oscillator arranged on the ground surface, the vibration wave received by each receiver array is detected.
A method for acquiring ground information, which comprises obtaining a velocity distribution or an attenuation factor distribution of vibration waves in the ground by calculating a correlation coefficient between the receiver arrays. The method for acquiring ground information according to claim 1, wherein the horizontal hole is formed by bending a hole in order to inject a chemical solution for ground improvement into the ground. According to claim 1 or 2, a receiver array in which a plurality of receivers are arranged is also arranged in the vertical hole, and the vibration wave detected by the receiver array in the vertical hole is also used. How to get the described ground information. Provided in the ground in the depth direction, the horizontal holes in a plurality of stages of different depths, are disposed respectively, a receiver array having a plurality of receivers are disposed,
Oscillators placed on the surface of the earth
By detecting the vibration wave received by each receiver array when the vibration wave is oscillated by the oscillator and calculating the correlation coefficient between the receiver arrays, the velocity distribution or attenuation rate distribution of the vibration wave in the ground And the arithmetic control means to obtain
A device for acquiring ground information, which is characterized by being equipped with. The device for acquiring ground information according to claim 4, wherein the horizontal hole is formed by bending a hole for injecting a chemical solution for ground improvement into the ground. 4. A device for acquiring the described ground information.

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