JP2014106075A - Method for geological survey during tunnel excavation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately survey geology in front of the working face 101 during execution in excavation construction of a tunnel 100 without requiring the use of a dedicated artificial seismic source.SOLUTION: A plurality of vibration receiving means 1 are installed at a predetermined interval in the inside of a tunnel 100, noise vibration of the ground generated by works accompanying the execution of tunnel excavation construction is used as a seismic source, a direct wave from this seismic source and a reflection wave reflected by the boundary surface due to geological change in front of the working face is received by the vibration receiving means 1, the vibration reception records are analyzed by seismic interferometry, and the direct wave is subtracted from the reflection wave, thereby predicting a geological situation in front of the working face.

Description

  The present invention relates to a method for exploring geology in front of a working face during construction in tunnel excavation work for roads, railways, and waterways.

  In tunnel excavation, the geology in front of the face is properly explored to investigate in advance whether there are faulty areas due to faults, crushing zones, or hydrous layers, and with appropriate equipment and construction methods according to the exploration results. It is important to work on the face.

  Conventionally, as a geological exploration method in front of the face of the tunnel, a boring method (see, for example, Patent Document 1) or a large hydraulic drill is used to horizontally drill a ground in front of the face, and the striking force and torque at that time There are methods called exploration fleas that predict geological firmness and softness, groundwater conditions, etc., and methods using elastic wave exploration. As a geological exploration method in front of the face by elastic wave exploration, a method using VSP (vertical seismic profile) processing is known, which includes artificial seismic sources (blasting and mechanical seismic sources), geophones and records Using a device, etc., generate an elastic wave from the excitation source to the ground, receive the reflected wave from the boundary surface of the geology, and apply waveform processing such as filtering to the received data to the ground in front of the face This is a method for relatively determining changes (see, for example, Patent Documents 2 and 3).

  However, in such elastic wave exploration, in order to explore the tunnel geology (mainly the geology ahead of the face) during tunnel construction, the exploration equipment occupies the mine, so select a day without mine work such as holidays, It has been pointed out that it is necessary to carry exploration equipment (such as geophones, blast and mechanical seismic sources, recording devices, etc.) into the mine and occupy the vicinity of the face (exploration is 1.5 Days). Elastic wave exploration is always performed by a combination of an artificial seismic source and a geophone (including a recording device). For this reason, blasting with dynamite or a mechanical seismic source with a vibrator or a hydraulic impactor has to be used as an artificial seismic source.

  On the other hand, as a technology for imaging underground structures of ground, the underground reflected waves reflected by the ground reflection point at the ground or at the ground surface are reflected at the same time using geophones at two different points on the ground surface. And by performing cross-correlation processing on the waveforms of the measured data, a synthetic shot record of the pseudo reflected wave created by synthesizing the vibration waveform as observed with one as the epicenter and the other as the receiving point In addition, seismic interferometry is known (see Non-Patent Document 1 below) that can be integrated by adding predetermined processing to obtain visualization data of the underground structure in the measurement area.

JP-A-8-177380 JP 2001-141835 A JP 2000-170478 A

Kazuya Shiraishi, Toshifumi Matsuoka, Taku Kawanaka: Overview of Seismic Interferometry, Geographical Journal, Vol. 117, No. 5, pp. 863-869, 2008.

  However, a technique for exploring the geology ahead of the tunnel face under construction using seismic interferometry has not been established.

  The present invention has been made in view of the above points, and the technical problem is that the geology in front of the working face during tunnel excavation work can be obtained without using a dedicated artificial seismic source. The purpose is to enable exploration with high accuracy.

  As a means for effectively solving the technical problem described above, the geological exploration method during tunnel excavation according to the invention of claim 1 is the work accompanying the construction of the tunnel excavation work by installing the vibration receiving means in the tunnel pit. The ground vibration generated by the ground is used as the epicenter, and the direct wave from this epicenter and the reflected wave reflected by the boundary surface due to the geological change ahead of the face are received by the receiving means, and the received records are autocorrelation (auto- The geology ahead of the face is obtained by superimposing a plurality of reflected waves with the hypocenter as a virtual receiving point, which is obtained by removing the direct wave travel time from the reflected waves by analyzing by seismic wave interferometry using correlation) It is characterized by predicting the situation.

  In the method described above, seismic wave interferometry is a vibration that is observed at another receiving point using one receiving point position as a virtual source, based on the cross-correlation of vibration records observed at different receiving points. This is a signal processing technique capable of synthesizing waveforms. According to this method, the presence of a boundary surface due to a geological change ahead of the face can be imaged by superimposing a plurality of reflected waves with the hypocenter as a virtual receiving point. Therefore, by effectively utilizing the vibration record, which has been regarded as noise in the past, for ground exploration, a special dedicated epicenter for geological exploration can be eliminated.

  The geological exploration method during tunnel excavation according to the invention of claim 2 is the method according to claim 1, wherein the noise vibration of the ground is blasting in the construction of the blasting excavation tunnel, shear transport by dump, It is generated by any one of the drilling holes, or generated by any one of machine excavation in the construction of the machine excavation tunnel, shear transport by dump, and drilling holes for rock bolts.

  In the construction of tunnels, there are many operations involving the occurrence of ground vibration such as blasting, machine excavation, and dumping. In the present invention, noise caused by such vibration is effectively used for exploration ahead of the face. Here, “shear” refers to rocks and earth and sand generated by tunnel excavation, and “sakuku” refers to the work of dropping float stones that appear on the face and shaping the face.

  A geological exploration method during tunnel excavation according to a third aspect of the invention is the method according to the first or second aspect, wherein the waveform amplitude is leveled as a pre-processing for analysis by seismic interferometry using autocorrelation. It is.

  Here, the leveling of the waveform amplitude is a process of dividing the original amplitude value by the root mean square amplitude within a unit time that is set shorter than the length of the observation record for all times of the observation record. That is. When using observation recordings of stage blasting and various vibration noise recordings, if leveling processing is not applied, the correlation coefficient between those with large waveform amplitudes is high, while extraction of reflected waves from the front of the face that is the original target The effect may be reduced. By equalizing the amplitude energy of observation records by leveling processing, the efficiency of extracting reflected waves from the front of the face by correlation processing can be improved.

  According to the geological exploration method during tunnel excavation according to the present invention, it is possible to effectively utilize noise vibration due to work for geological exploration, thereby eliminating the need for a special dedicated epicenter for geological exploration, and the face during tunnel excavation. The geological exploration ahead can be performed with high accuracy.

It is explanatory drawing which shows the construction procedure of the tunnel excavation work by a blasting method, and the operation | work accompanied by generation | occurrence | production of the ground vibration which can be utilized for this invention. It is explanatory drawing which shows the construction procedure of the tunnel excavation work by a mechanical excavation method, and the operation | work accompanying generation | occurrence | production of the ground vibration which can be utilized for this invention. It is explanatory drawing which shows roughly preferable embodiment of the geological exploration method in the tunnel excavation based on this invention. In preferred embodiment of the geological exploration method during tunnel excavation concerning this invention, it is explanatory drawing which shows the analysis method at the time of setting a step blast as an epicenter. It is explanatory drawing which shows the concept of the reflected wave at the time of assuming excavation blasting in a face position as a receiving point (autocorrelation process) in preferable embodiment of the geological exploration method in the tunnel excavation which concerns on this invention. It is explanatory drawing which represented the concept shown in FIG. 5 with the travel time (time for a wave to reach) of an elastic wave. It is explanatory drawing which shows the concept of the superimposition of the autocorrelation processing waveform obtained in several receiving points by one blasting in preferable embodiment of the geological exploration method in the tunnel excavation which concerns on this invention. It is explanatory drawing which shows the case where the anti-slope by a geological change part inclines. In a preferred embodiment of the geological exploration method during tunnel excavation according to the present invention, when an anti-slope due to a geological change portion is inclined, superposition of autocorrelation processing waveforms obtained at a plurality of receiving points by one blasting It is explanatory drawing which shows the concept of. As an Example, it is explanatory drawing which shows the received waveform by stage blasting, and the waveform after a leveling process. It is explanatory drawing which compares and shows the processing waveform of the reflected wave by a prior art (VSP process), and the processing waveform by the seismic wave interferometry (autocorrelation) based on this invention.

  Hereinafter, preferred embodiments of a geological exploration method during tunnel excavation according to the present invention will be described with reference to the drawings.

  Tunnel excavation includes a blasting method in which excavation is performed using an explosive such as dynamite, and a mechanical excavation method in which excavation is performed using a free-section excavator, a large breaker, a tunnel boring machine (TBM), or the like.

  Among them, in the construction of a blast excavation tunnel by the blasting method, as shown in FIG. 1, first, a blast hole is drilled (S01), charged (S02), and blasted (blasted) (S03). On the other hand, “sludge” such as sediment and rocks generated by this blast excavation is transported to the outside of the mine with a heavy dumper (S04), or floats that appear on the face by excavation are dropped or the face is shaped. (S05) is performed. At the rear of the face, in order to prevent the collapse of the inner wall of the mine, the construction of steel (S06), the lining by spraying concrete (S07), and many bore holes from the lining wall to the ground are drilled. A lock bolt is inserted and fixed therein, and tightened with a nut to support and reinforce the surrounding ground around the mine wall (S08). And the excavator including the work of S01-S05 and the support work including the work of S06-S08 are repeated alternately.

  Further, in the construction of the machine excavation tunnel by the machine excavation method, as shown in FIG. 2, machine excavation is performed by a free section excavator, a large breaker, TBM, or the like (S11). Excavation by transporting "sludge" to the outside of the mine with a wheel loader or heavy dumper (S12), and in order to prevent the collapse of the inner wall of the mine behind the face, the construction of steel (S13) or the spraying of concrete A large number of bore holes are drilled from the lining wall surface to the natural ground, and lock bolts are inserted and fixed in the lining (S14), and the surrounding natural ground on the inner wall is supported and reinforced by tightening with nuts. The support work including the work (S15) is repeated alternately.

  And in the construction of blasting excavation tunnels, drilling of blasting holes (S01), blasting (S03), shear transport by heavy dumping (S04), scraping (S05), drilling of rock bolt bore holes (S08), etc. Noise vibration is generated, and even in the construction of a mechanical excavation tunnel, mechanical excavation (S11), shear transport by a wheel loader or heavy dumper (S12), and drilling of a rock bolt borehole (S15), etc. generate noise vibration of the ground. It is accompanied by.

  In FIG. 3, reference numeral 100 is a tunnel constructed in a natural ground, and 101 is a face (tunnel cutting surface). In the construction of the blast excavation tunnel, as shown in FIG. 3 (A), a hydraulic rock drill (jumbo) 201 or the like excavates the required number of blast holes 102 from the face 101 to the ground in front of the explosive. And explode the explosive by the blasting device 4 as shown in FIG. Then, as shown in FIG. 3 (C), using the hydraulic breaker 202 or the like, “crush” is performed to remove or shape the float on the face 101, and the “shear” generated by blasting is shown in FIG. As shown to (D), it conveys outside a mine with the wheel loader 203, the heavy dumping 204, etc. FIG. Note that reference numeral 103 in FIG. 3A denotes a bore hole for driving a lock bolt that supports the inner wall of the mine.

  Further, in the construction of the mechanical excavation tunnel, the face 101 was excavated by using a free section excavator 205 as shown in FIG. 3E or a TBM 206 as shown in FIG. As in FIG. 3D, the “shear” is transported to the outside of the mine by the wheel loader 203 and the heavy dump 204.

  The ground noise vibration data generated in these processes is received by the required number of geophones 1 and loaded into the recording device 2, and the data is stored in the personal computer 3 installed in the field office outside the mine, Analysis is performed by waveform processing using seismic wave interferometry (autocorrelation), and the geology ahead of the face 101 is predicted.

  Here, seismic interferometry is the one in which the reflection record in a one-dimensional model was derived from auto-correlation by Claerbout in 1968, and began to attract attention in the field of geophysical exploration from around 2006 As described in Non-Patent Document 1 “Outline of Seismic Interferometry” mentioned above, it is possible to use the position of one receiving point as a hypothetical hypocenter due to mutual interference of vibration records observed at different receiving points. This is a signal processing method capable of synthesizing a vibration waveform as observed at the receiving point. In other words, according to the seismic wave interferometry, since the vibration waveform can be synthesized using the hypocenter as a virtual seismic point or the seismic point as a hypothetical seismic point, the above-mentioned noise, which has been conventionally considered as noise, without using a special seismic source Such vibration records can be effectively used for ground exploration.

  Autocorrelation is a mathematical technique often used in signal processing to analyze functions or sequences, such as time-domain signals or spatial-domain signals, and how well the signal matches itself with a time-shifted signal Is a measure of the time shift, and is a maximum when the shift amount is zero. In other words, autocorrelation is a cross-correlation with a signal itself and is useful for searching for a repetitive pattern included in the signal. If it has periodicity, the value increases for each period. For example, it is used to determine the presence of a periodic signal buried in noise or to identify a lost fundamental frequency in the signal based on suggestions by harmonic frequencies.

  In a preferred embodiment of the geological exploration method during tunnel excavation according to the present invention, autocorrelation analysis is performed with data of one focal point in excavation blasting (current data is 2.5 seconds, around 10 rounds) as input. . The vibration pattern generated by excavation blasting is basically included in the reflected waveform as a pattern, so by calculating the autocorrelation for the observed waveform at the time of excavation blasting, the same pattern will be reflected. The value of the pattern corresponding to the reflected wave becomes large, and the arrival time from the face 101 to the receiving point is canceled out, so that it can be converted into a waveform indicating the arrival time from the face 101.

  In a preferred embodiment of the geological exploration method during tunnel excavation according to the present invention, as shown in FIG. 4, the shallow seismic reflection survey for tunnels (SSRT) previously developed by the inventors of the present application. ), The analysis is performed by seismic interferometry using autocorrelation in a continuous SSRT in which vibration is continuously observed in the mine using a step blast at the face 101 as an epicenter.

  That is, the tunnel 100 shown in FIG. 4 is constructed in a mountainous area and can be dug by blasting the face 101 at intervals of several meters. The geophone 1 that captures data of noise vibration of the natural ground generated by the blasting is composed of a small seismometer such as a geophone, for example, and is installed in the mine, for example, along the longitudinal direction of the underground ground of the tunnel 100. Are installed at intervals of about 1.5 m to 3 m along the longitudinal direction, and are connected to the recording apparatus 2 respectively.

  Further, the blasting device 4 for blasting and excavating the face 101 is configured such that a detection signal for detecting the initiation current to the stage detonator for detonating the explosive is output to the recording device 2, that is, in stage blasting. The first blast time is recorded in the recording device 2 as the earthquake time.

  Therefore, in the above configuration, in order to blast and excavate the face 101 of the tunnel 100, the explosive loaded in the blast hole 102 drilled in the ground in front of the face 101 shown in FIG. When the explosion occurs from the detonator to the detonator, the blasting point P becomes the source of the earthquake, and the resulting elastic waves are received by the plurality of geophones 1, and each received data is recorded in the recording device 2 and the first occurrence time ( Blast time) is recorded in the recording device 2.

  The vibration reception data received by the vibration receiver 1 is recorded in the recording device 2 and sent to a personal computer 3 installed in a field office outside the mine. In the personal computer 3, the propagation time of the elastic wave is calculated from the vibration receiving data and the blast time recorded in the recording device 2.

  At this time, as shown in FIG. 4, when a geological change portion Q due to a crush zone or a fault exists in the natural ground, a part of the elastic wave having the blasting point P as a source is the boundary of the geological change portion Q. Since the surface is reflected, the geophone 1 can receive the reflected wave from the geological change portion Q in addition to the direct wave from the blasting point P. And the vibration receiving data of the geophone 1 in this case includes distance information from the blasting point P to each reflecting surface as shown in FIG.

Specifically, in FIG. 5, T ₁ is the traveling time of the direct wave until the elastic wave generated at the blasting point P on the face 101 reaches the downhole geophone 1 B, and T ₂ is the blasting point P. It is the travel time of the reflected wave until the elastic wave generated in step b is reflected by the reflection surface by the geological change portion Q in the ground in front of the face 101 and reaches the downhole geophone 1B.

From Figure 5, travel time T ₂ of the reflected wave, the travel time T ₃ to acoustic waves generated by the blast point P on the working face 101 is returned to the working face 101 is reflected by the reflecting surface by geological change portion Q, directly Sum of wave travel times T ₁ , ie T ₂ = T ₁ + T ₃
It can be seen that it is.

Therefore, as shown in FIG. 6, the autocorrelation function at time 0 (blast time) is expressed by the following equation:
The maximum value (arrow A ₀ ) can be calculated. In addition, the autocorrelation function at the time T _{3 has} elapsed from the blasting time to the running time t (the time when the reflected wave is received by the downhole geophone 1B) is expressed by the following equation:
When the calculation is performed, the value again becomes a large value (arrow A _t ) at the travel time T ₃ . By removing the travel times T ₁ of the direct wave from the traveltime T ₂ of the reflected wave, since the time corresponds to the time run of the reflected wave on the assumption blasting point P on the working face 101 and geophone point , so that T ₃ is obtained reciprocating run times of the reflected waves. Therefore, if the propagation velocity of the elastic wave is V, the distance L from the blasting point P shown in FIG.
L = V × _T 3/2
It can be obtained as

FIG. 7 shows the concept of superposition of autocorrelation processing waveforms obtained at a plurality of receiving points by one blast. That is, as shown in FIG. 7, when many geophones 1 (1 ₁ , 1 ₂ ,... 1 _n−1 , 1 _n ) are installed at predetermined intervals along the longitudinal direction of the underground ground of the tunnel 100. , The arrival time of the direct wave and the reflected wave to each of the geophones 1 ₁ , 1 ₂ ,... 1 _n−1 , 1 _n by blasting the face 101 is the superposition of the received waveforms of FIG. As shown in the figure, the geophone that is farther away from the epicenter is slower (running time is longer).

Therefore, by performing the autocorrelation process as described above, the traveling time of the direct wave from the received waveforms of the receivers 1 ₁ , 1 ₂ ,... 1 _n−1 , 1 _n shown in FIG. As shown in FIG. 7 (II), the vibration record with the face 101 (blasting point) as a virtual receiving point is obtained, as shown in FIG. This reflects the reflection structure of the geologically changing portion Q such as a belt.

  Therefore, according to this method, it is not necessary to record the blasting time, and even with one blasting, it is possible to obtain a plurality of reflection records from the front of the face by a plurality of receiving points and to superimpose them. By using it, there is an advantage that it is possible to analyze even at one receiving point.

  In the basic model shown in FIG. 7, it is assumed that the anti-slope due to the geological change portion Q forms a plane substantially orthogonal to the tunnel 100 excavation direction. Q is usually inclined as shown in FIG.

That is, as shown in FIG. 8, when the geological change portion Q forms an inclination angle θ with respect to a plane orthogonal to the tunnel 100 excavation direction, the blasting point is O, a straight line extending from the blasting point O to the tunnel 100 excavation direction and the geology F is the intersection with the opposite slope due to the change portion Q, and the position of the geophone 1 ₁ closest to the face 101 out of the geophones 1 ₁ , 1 ₂ ,... 1 _n−1 , 1 _n installed in the tunnel 100 Is A, and the position of the geophone 1 _n on the most wellhead side is B, the elastic wave reflected from the blasting point O by the anti-slope of the geological change portion Q and reaching A or B blasts with the anti-slope as the symmetry axis. It can be assumed that the wave is a direct wave from a point O ′ symmetrical to the point O. Therefore, the line segments AB, CB, O′A, O′B, O′C are
O'A + AB>O'B
= O'C + CB
= O'A + CB
∴AB> CB
It is.

And as shown in FIG. 9, the arrival time of the direct wave and the reflected wave to each geophone 1 ₁ , 1 ₂ ,... 1 _n−1 , 1 _n by blasting the face 101 is shown in FIG. As shown in the received waveform of I), the farther away from the epicenter position, the slower the receiver (running time becomes longer), but by performing the autocorrelation process as described above, it is shown in (I) of FIG. If the traveling time of the direct wave is subtracted from the received waveform of each of the geophones 1 ₁ , 1 ₂ ,... 1 _n−1 , 1 _n , as shown in the received waveform of (II) in FIG. The vibration record with the virtual receiving point at the blasting point) was obtained, which is the difference between the travel time of the reflected wave due to only the slope of the geological change part Q such as the fault or crush zone existing in front of the face Therefore, the inclined structure of the geological change portion Q can be estimated from this received waveform.

  In the case of tunnel excavation, we tried to analyze the reflected wave from the geological change part in front of the face with the step blast at the face as the epicenter, and analyzed the seismic interferometry using the autocorrelation of the present invention. . The geology of the applied tunnel is made of granodiorite, and the elastic wave velocity of the fresh ground is assumed to be 4,000-4,500 m / s. Faults develop at several places mainly from lineament observation by aerial photo interpretation. It is a place that has been pointed out.

  FIG. 10A shows the vibration recording waveforms (original waveforms) of the blast management numbers SP1, SP12, SP25 obtained at the 12ch receiving points, corresponding to almost the entire blasting time with the traveling time aligned. 5 seconds are shown. SP1 and SP12, and SP12 and SP25 are both separated by a face position of about 18 m, and SP12 is located at an intermediate point between SP1 and SP25. The stage blasting is 10 stages using DS detonator, and the loadings of SP1, SP12 and SP25 are 106.6kg, 72.4kg and 128.5kg, respectively, and the back split is the whole section construction method with auxiliary bench It is. The nominal interstage time of the DS detonator is 250 ms for the 1st to 9th stages and 300 ms for the 10th and subsequent stages.

  Referring to (A) of FIG. 10, it can be seen that the vibration recording waveform has a remarkable recording of the direct wave from the blasting point. Therefore, since there is a possibility of detecting a direct wave from the blasting point as a similar waveform in the autocorrelation processing, waveform amplitude leveling processing by AGC processing was performed. FIG. 10B shows the waveform after the leveling process. From this figure, it can be seen that the influence of the direct wave is considerably reduced, and the waveform in the time domain where the distribution of the reflected wave is assumed is relatively raised.

  FIG. 11 shows a waveform obtained by performing autocorrelation processing on a vibration recording waveform by excavation blasting of SP1, SP12, and SP25 after leveling processing by AGC, and converting it into a distance cross section (Vp = 4,000 m / s is adopted). It shows in contrast with the reflection waveform by the VSP processing of the continuous SSRT by the technology and the reflection waveform by the VSP processing of the underground SSRT. The record extracted from the autocorrelation waveform is displayed as a shading bar by superimposing the 12ch received records by the superposition method shown in FIG. Moreover, the arrow displayed in FIG. 11 marks and shows the location where strong reflection was extracted.

  In continuous SSRT, the reflection record of the excavation blast section used for the analysis cannot be obtained, but in the autocorrelation processing waveforms SP1, SP12, SP25, the reflection record with the face position due to the blast as the origin is obtained. Therefore, the origin position of the autocorrelation waveform in each blasting is 18 m apart.

  The autocorrelation processing waveforms SP1, SP12, and SP25 are processing waveforms that substantially reflect the structure of the reflection surface due to the geological change portion of the natural ground in front of the face when compared with the reflection waveforms by the VSP processing of the conventional continuous SSRT and underground SSRT. I understand that.

1 geophone 2 recording device 3 personal computer (analysis means)
DESCRIPTION OF SYMBOLS 100 Tunnel 101 Face 201 Hydraulic rock drill 202 Hydraulic breaker 203 Wheel loader 204 Heavy dump P Explosion point Q Geological change part

Claims (3)

  A vibration receiving means is installed in the tunnel tunnel, and the ground noise generated by the work accompanying the tunnel excavation work is used as the epicenter, and the direct wave from this epicenter and the reflection reflected at the boundary due to the geological change in front of the face. A hypocenter is obtained by receiving a wave by the receiving means, analyzing the received record by seismic interferometry using autocorrelation, and removing the direct wave travel time from the reflected wave. A geological exploration method during tunnel excavation, wherein a geological situation in front of the face is predicted by superimposing a plurality of reflected waves.   Noise generated by ground noise is generated by either blasting in excavation tunnel construction, shear transfer by dumping, drilling for rock bolts, or excavation by mechanical excavation tunnel, shearing transport by dump, 2. The geological exploration method during tunnel excavation according to claim 1, wherein the geological exploration method is generated by any one of rock bolt drilling holes.   The geological exploration method during tunnel excavation according to claim 1 or 2, characterized in that the waveform amplitude is leveled as preprocessing of analysis by seismic interferometry using autocorrelation.