JP6584010B2 - Tunnel face forward exploration method - Google Patents

Description

  The present invention relates to a tunnel face forward exploration method, for example, a tunnel face forward exploration method for exploring a fault zone or the like in front of a tunnel face using seismic waves generated by vibration during tunnel blasting excavation.

  Because the tunnel is a linear structure built deep underground, it is difficult to conduct a full survey over the entire length of the tunnel for technical and economic reasons. In most of the preliminary surveys of mountain tunnels, refracted elastic wave exploration is carried out in most cases, and the natural mountains are classified by comprehensively evaluating the obtained elastic wave velocity, etc., and prepared according to the classification. The standard design (standard support pattern, etc.) is applied.

  However, the design support pattern and the support pattern during construction often differ. One reason for this is that conventional elastic wave exploration from the surface of the earth does not reach the tunnel excavation point deep in the ground, and it is difficult to improve the exploration accuracy and the elastic wave velocity cannot be evaluated correctly. The point is mentioned. In such a case, it is effective to investigate the front of the face from the tunnel pit during construction.

  The inventors also measured the blasting during excavation with a geophone installed on the ground surface on the tunnel route, and combined the travel time with the elastic wave exploration data of the previous survey to perform tomographic analysis. A method has been developed to predict the elastic wave velocity distribution in the ground in front of the face. In this case, in order to accurately predict the elastic wave velocity distribution, it is necessary to increase the number of installed geophones and the number of oscillation points (blasting positions) to increase the number of wavy lines. It may be difficult to install a sufficient prediction accuracy. In such a case, a reflection elastic wave exploration in which a geophone is installed in the tunnel mine and the ground in front of the face is explored from the tunnel mine during construction is effective as another method. Typical reflection method elastic wave exploration methods include TSP (Tunnel Seismic Prediction) method and HSP (Horizontal Seismic Profiling) method.

  In addition, about the exploration technique ahead of a tunnel face, there exists description in patent documents 1-5, for example. Patent Document 1 discloses a technique for estimating the geology in front of a tunnel face based on an elastic wave whose epicenter is blasting for tunnel excavation.

  Patent Document 2 discloses a technique for exploring the geology in front of the tunnel face by measuring seismic waves with the blast of each stage in tunnel excavation as the epicenter using a seismometer in the tunnel.

  Patent Document 3 discloses that the internal clock of the outside recording apparatus installed outside the tunnel and the internal clock of the underground recording apparatus installed inside the tunnel are synchronized with the GPS time. A technique for predicting the geology ahead of the tunnel face based on the vibration receiving data recorded in each of the out-of-hole recording device and the down-hole recording device when blasting at the face is disclosed.

  Patent Document 4 discloses a technique for predicting geological conditions in front of a tunnel face by receiving blast vibration generated by blasting the face in tunnel excavation by a geophone installed on the ground surface in front of the face. Is disclosed.

  Patent Document 5 discloses a technique for judging the collapse of a tunnel by receiving and measuring the acoustic emission generated in the ground of the tunnel through a lock bolt driven from the anti-wall surface of the tunnel toward the ground. Has been.

JP 2013-174580 A JP-A-10-31880 Japanese Unexamined Patent Publication No. 2011-43409 Japanese Patent Application Laid-Open No. 2015-190789 JP-A-2001-355384

  By the way, in order to carry out tunnel excavation work safely and economically, information on the position and width of the fault zone in front of the face of the tunnel must be grasped in advance, and support changes and auxiliary construction methods can be It is important to take measures such as application. In particular, near the tunnel entrance, the topography and geological structure are complex, and unexpected deformations may be encountered, so it is necessary to grasp the state quickly and accurately. However, in the above-described exploration methods such as the TSP method and the HSP method, when a wide fault zone exists in front of the face of the tunnel, the reflection position may be greatly different between actual and predicted. There is a problem.

  The present invention has been made from the technical background described above, and an object of the present invention is to provide a technique capable of improving the search accuracy in front of the face of the tunnel.

In order to solve the above-mentioned problem, a tunnel face forward exploration method according to the present invention as set forth in claim 1 is: (a) an earthquake wave generated by blasting for excavating a tunnel to a natural ground in front of the tunnel face; A step of measuring a reflected wave reflected from a fault zone in front of the face by a plurality of first vibration receiving means installed on a tunnel wall of the tunnel; and (b) reflection based on a measurement value of the first vibration receiving means. Extracting a waveform; (c) measuring a seismic wave generated by the blasting by a plurality of second receiving means installed on the ground surface; and (d) based on a measurement value of the second receiving means. Calculating the elastic wave velocity of the ground in front of the face of the tunnel by the tomography method analysis process, creating a velocity model, and then calculating the theoretical travel time of the reflected wave based on the velocity model (E) After forming the reflected energy distribution using the reflected waveform data obtained in the step (b) and the theoretical travel time obtained in the step (d), a velocity boundary surface is obtained from the reflected energy distribution. (F) The position of the velocity boundary surface obtained in the step (e) is subjected to a convergence judgment, and if it does not converge, it is obtained in the step (e) until convergence. Performing the step (d) using the data of the position of the velocity boundary surface, and repeating the step (e) using the calculation result of the theoretical travel time obtained there. It is characterized by.

Further, the invention of claim 2, in the invention according to the first aspect, after the step (e), prior to the convergence determination, the position of the (e) the velocity boundary surface calculated in step When the data is the first calculation data, the (d) step is performed using the data of the position of the speed boundary surface calculated in the (e) step without performing the convergence determination. The step (e) is performed using the calculation result of the theoretical running time.

The present invention according to claim 3 is the invention according to claim 1 or 2 , wherein the steps (a) to (f) are performed every time the face of the tunnel is blasted, and the fault zone is The optimal velocity boundary surface position and elastic wave velocity data are calculated, and the calculated data is updated each time the blasting is performed.

  According to the present invention, it is possible to improve the measurement accuracy of the velocity boundary position of the fault zone in front of the face of the tunnel and the elastic wave velocity of the natural ground, so it is possible to improve the exploration precision in front of the face of the tunnel. .

It is a top view in the tunnel mine at the time of the tunnel face front exploration which concerns on one embodiment of this invention. It is a principal part expanded side view of the geophone which comprises the search apparatus used at the time of the tunnel face front search of FIG. It is a wave form diagram of an example of the blasting earthquake waveform measured by the tunnel face front exploration of FIG. It is a flowchart which shows the process sequence of the waveform data obtained by the tunnel face front search of FIG. It is explanatory drawing of the imaging process with respect to the waveform data obtained by the tunnel face front search of FIG. It is a tunnel face front exploration flow figure concerning one embodiment of the present invention. (A) is explanatory drawing which shows the arrangement | positioning of a geophone and a wavy path in a reflection method, (b) is explanatory drawing which shows the arrangement of a geophone and a wavy path in a tomography method. It is explanatory drawing which shows the analysis result by a reflection method. It is explanatory drawing which shows the analysis result by a tomography method. (A) is explanatory drawing which shows the analysis result by the tomography method following FIG. 9, FIG.10 (b) is a graph which shows the speed distribution of the II line cross section of Fig.10 (a). It is explanatory drawing which shows the analysis result by the tomography method following Fig.10 (a). It is explanatory drawing which shows the analysis result by the reflection method following FIG. It is explanatory drawing which shows the analysis result by the tomography method following FIG. It is explanatory drawing which shows the analysis result by the reflection method following FIG. It is a graph which shows the geological structure external appearance of a numerical calculation model. It is a graph which shows the positional relationship of a speed boundary surface and a tunnel. It is a calculated waveform diagram of the receiving point closest to the oscillation point obtained from the numerical simulation of wave propagation. FIG. 9 is a reflection waveform diagram obtained by calculating the calculation waveform of FIG. 8 by the data processing shown in FIG. 4. It is a graph which shows the distribution of the reflected energy calculated | required using the elastic wave velocity which is a conventional method and is a propagation velocity of a search area. It is a tunnel face front exploration method of this embodiment, and is a graph which shows the result of having calculated reflection energy using travel time by a difference method using the elastic wave velocity ahead of a tunnel face. It is a geological profile of the experiment site. It is a wave form diagram for 10 m of face movement (10 times of exploration blasting) measured with a geophone 46.2 m away from the face of the tunnel. It is evaluation sectional drawing of reflected energy. It is the distribution of reflected energy by a conventional method. It is the distribution of reflected energy using the travel time of the differential method using the elastic wave velocity of elastic wave exploration. It is explanatory drawing which expanded and showed a part of state of the cell which divided the natural ground in FIG.

  Hereinafter, an embodiment as an example of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  Exploration method ahead of tunnel face using vibration during blast excavation

  Reflection method measurement overview

  FIG. 1 is a plan view of a tunnel during forward exploration of a tunnel face according to the present embodiment, and FIG. 2 is an enlarged side view of the main part of a geophone that constitutes the exploration device used during forward exploration of the tunnel face of FIG.

  In the tunnel face forward exploration method of the present embodiment, for example, the blast for excavating the tunnel H is used as the oscillation point, and the face K of the tunnel H is used by both the reflection method and the tomography method. The low-velocity layer (fault zone) D etc. in front of is searched. In this case, since the blast for excavation of the tunnel H is used as the oscillation point, the excavation efficiency of the tunnel H can be improved as compared with the case where the oscillation point for the exploration in front of the face of the tunnel H is separately provided. Further, by using the analysis data of both the reflection method and the tomography method, the search accuracy in front of the face of the tunnel H can be improved.

  In the exploration processing by the reflection method, for example, multipoint oscillation-multipoint reception is performed, and a geophone is placed on each head of each of the plurality of lock bolts RB in the range between the positions P1 and P2 behind the face K of the tunnel H. S1 is attached and blast vibration is measured. Note that the distance from the position Pk to the position P1 of the face K is 45 m, for example, and the distance from the position P1 to the position P2 is 15 m, for example.

  For example, the geophone S1 is mounted on the head of each of the twelve lock bolts RB arranged in a line at predetermined intervals along the tunnel axis direction on one side surface of the tunnel wall of the tunnel H. The rock bolt RB is a support tool for the tunnel H, and is installed at the intersection of a plurality of tunnel axial lines and a plurality of tunnel circumferential lines within the tunnel H wall surface. Each lock bolt RB is driven on the ground G of the natural ground in a state orthogonal to the tunnel wall of the tunnel H, and by a nut N1 (see FIG. 2) screwed to the head of each lock bolt RB. It is fixed. Note that the arrangement of the geophone S1 is not limited to the above-described one, and can be variously changed. For example, the geophone S1 is arranged at positions 90 degrees apart along the circumferential line on the tunnel wall surface of the tunnel H, and You may arrange | position at predetermined intervals along an axial direction. Thereby, since a receiving point can be increased, a receiving accuracy can be improved.

  The reason why the geophone S1 is mounted on the head of the lock bolt RB is that, for example, since the material of the lock bolt RB is generally iron that easily transmits vibration, the function as a waveguide (waveguide rod) can be expected. This is because there is no need to newly drill holes in the tunnel wall of the tunnel H to install the geophone S1, so that the measurement preparation work can be reduced. Therefore, the geophone S1 was installed by attaching the geophone S1 fixed to the nut N2 to the head of the lock bolt RB as shown in FIG. In addition, in order to measure the vibration in the axial direction of the lock bolt RB with high sensitivity, for example, a 28-Hz movable linear ring type (MC type) velocity seismometer having a high resonance frequency was used as the geophone S1. The sensitivity of each geophone S1 is, for example, 35.4 V / m / s. Each geophone S1 is electrically connected to the recording apparatus M through a communication cable or the like.

  The recording device M is a device that records the waveform data obtained by the geophone S1. As this recording apparatus M, for example, an earthquake wave recording apparatus having 16 channels of input channels, 24 bits of AD (Analog / Digital) resolution, and a sampling frequency of 12 kHz is used. The recording device M is electrically connected to a blaster (not shown) through a trigger box TB. When the power is turned on, the recording software M starts up, and the recording apparatus M enters a state of waiting for a trigger under preset measurement conditions. When a trigger signal is acquired from the blasting device at the time of blasting, waveform acquisition is started, and for example, measurement data for 7 seconds is recorded at a sampling frequency of 12 kHz. After recording measurement data, the recording device M is connected to the computer of the exploration device through a USB cable or the like, and the measurement data is stored in the memory of the computer.

  The exploration is performed by inserting a small amount of explosives (parent die) using a flashing detonator into the explosive charge hole drilled in the center of the face K of the tunnel H, and blasting ahead of the excavation blast. Generate vibration used for exploration.

  FIG. 3 is a waveform diagram of an example of a blast earthquake waveform measured by forward exploration of the tunnel face in FIG.

  In the present embodiment, a small-scale blast for exploration is performed in the center of the face using an instantaneous detonator before the time T1 of the core blasting for tunnel excavation, and the vibration of the second stage core blasting is performed. Among the seismic waveforms at the time T2 (about 180 ms) until it reaches the geophone S1, the waveform data at the time T3 (about 100 ms) necessary for ground prediction about 100 m ahead of the face is used for exploration. The blasting vibration for the 10 face movements is continuously recorded, the exploration blasting waveform data is cut out from the recorded data, and the reflected wave data processing and tomography data processing are performed.

  Reflection method data processing

  FIG. 4 is a flowchart showing a processing procedure for extracting a reflected waveform from the waveform data obtained by the tunnel face forward search in FIG.

  After the exploration is completed, the waveform data stored in the memory of the computer in the exploration device is transferred to the computer for analysis, and the waveform data processing is performed by the processing procedure shown in FIG. 4 to extract the reflected waveform. This is because the waveform data recorded by the recording device M includes not only the reflected wave from the velocity boundary surface in front of the face of the tunnel H but also the direct wave from the oscillation point to the receiving point, the reflected wave from the back of the exploration point, Furthermore, since noise and the like are included, these are removed by the data processing shown in FIG. Hereinafter, the data processing of FIG. 4 will be described.

  First, an elastic wave velocity (Vp) propagating from the oscillation point through the tunnel wall of the tunnel H is calculated by extracting the initial rising from the waveform data recorded by the recording device M (step 102a). Here, the elastic wave velocity is, for example, 4.6 km / s.

  Subsequently, after removing noise from the waveform data recorded by the recording apparatus M by a bandpass filter (step 102b), the amplitude of the reflected wave is attenuated in accordance with the distance from the oscillation point, and depends on the distance. The amplitude of the reflected wave is increased by spherical divergence correction so that there is no attenuation (step 102c).

  Subsequently, after removing the direct wave (primary wave (hereinafter referred to as P wave) and second wave (hereinafter referred to as S wave)) by the median filter, the FK filter, or the like (steps 102d and 102e). ) In order to clarify the waveform of the reflected wave, the amplitude of the reflected wave is increased (extracted) (step 102f).

  Subsequently, since the noise also increases due to the increase in amplitude in step 102f, the noise is removed by the bandpass filter (step 102g), and then the amplitude of the reflected wave is superimposed by overlapping the waveforms with the time axis of each waveform corrected. Is increased (step 102h).

  Using the reflected waveform thus obtained, the position of the velocity boundary surface (reflecting surface) of the low velocity layer D in front of the face of the tunnel H is specified by the method described later.

  Reflection energy evaluation using travel time by finite difference method

  FIG. 5 is an explanatory diagram of the imaging process for the waveform data obtained by the forward search of the tunnel face in FIG.

  For the imaging process, a diffraction stack (Diffraction Stack: hereinafter referred to as DS) method shown in FIG. 5 was used. In the DS method, virtual lattice points GP are provided at regular intervals in a three-dimensional coordinate space including the front face of the tunnel H and surrounding surrounding mountains, and a wave spread from the oscillation point SP is reflected at the lattice point GP to receive the receiving point RP. Suppose that it returns to (location where geophone S1 was installed).

  When an elastic wave generated from one oscillation point SP is reflected at a lattice point GP and reaches the receiving point RP, the propagation path of the elastic wave is obtained according to the elastic wave velocity of the natural ground from the wave line theory. Travel time (propagation time) is calculated as travel time TSR (travel time TS + travel time TR) that is the sum of travel time TS from oscillation point SP to grid point GP and travel time TR from receiving point RP to grid point GP. it can. From this propagation time, the position on the waveform trace corresponding to the lattice point GP can be specified. The sum of the waveform amplitudes (single amplitudes) at those positions is made dimensionless, and the reflected energy (the square of the reflected wave amplitude) is obtained and given to the lattice point GP. Here, one reflected energy is predominantly distributed on the locus of an elliptical curved surface having the oscillation point SP and the receiving point RP as the focal points.

  If a certain lattice point GP corresponds to an actual reflection point, the reflection energy of this lattice point GP shows a large value. A plane in contact with these lattice points GP can be specified as the velocity boundary surface. Furthermore, the change in physical properties before and after the boundary can be seen from the sign of the reflected energy. That is, when the reflected energy is positive, the physical property changes from hard to soft before and after the boundary surface, and when it is negative, the physical property changes from soft to hard.

  Here, since the conventional method predicts the position of the velocity boundary surface using only the elastic wave velocity of the blasted natural ground section, if there is a layer with different elastic wave velocity in the natural ground in front of the face of the tunnel H, the velocity The position of the boundary surface cannot be obtained with high accuracy. Therefore, in the present embodiment, using both the information on the position of the velocity boundary surface obtained by the reflection method and the information on the velocity distribution obtained by the tomography method or the like, the ground in front of the face of the tunnel H is used. Explore the state. A specific example will be described below with reference to FIGS. 7 to 14 along the flowchart of FIG.

  Explanation of observation state by reflection method and tomography method

  FIG. 7 shows the placement of the geophone and the wavy line path in the forward exploration of the tunnel face according to the present embodiment. In the tunnel face forward exploration method of the present embodiment, blasting for excavation of tunnel H is used as an oscillation point used in both the reflection method and tomography method, and a plurality of geophones S1 in tunnel H are used in the reflection method. As a receiving point, a plurality of receiving devices S2 on the ground surface of the ground mountain Y are used as the receiving points used in the tomography method.

  First, Fig.7 (a) has shown the arrangement | positioning and wavy path | route of the geophone in the reflection method. In the measurement of the reflection method, as explained in FIG. 1, the blasting performed at the face for excavation of the tunnel H is used as an oscillation point, and a plurality of reflected waves from the velocity boundary surface of the low velocity layer D are reflected in the tunnel H. Measured with the geophone S1.

  On the other hand, FIG.7 (b) has shown the arrangement | positioning and wavy line path | route of the geophone in the tomography method. In the tomography measurement, the blasting performed at the face for excavation of the tunnel H is used as the oscillation point, and the elastic waves generated by the blasting at the face of the tunnel H are measured by a plurality of geophones S2 on the ground surface of the ground Y. To do.

  In the excavation work of the tunnel H by blasting, the installation positions of the geophones S1 and S2 are moved toward the excavation direction of the tunnel H every time the excavation length reaches a predetermined length (for example, 50 m).

  Explanation of specific examples of forward exploration methods for tunnel face

  First, since the reflection method requires a predetermined number of prior measurements, blasting a predetermined number of times (for example, 10 times) for excavation of the tunnel H prior to the exploration processing using both the reflection method and the tomography method. Each time, the reflected wave is measured by the reflection method. At this time, the measurement by the tomography method may be performed or may not be performed.

  Subsequently, in the processing of the reflection method on the right side of FIG. 6, the blasting seismic wave generated by the first blasting for excavation of the tunnel H (the first blasting that implements both the reflection method and the tomography method) is performed on the tunnel H. Measured by the geophone S1 and transferred to the computer for analysis, and the reflected waveform is extracted from the observed waveform data (steps 100 to 102 in FIG. 6). At the same time, the position coordinate data of the oscillation point and the receiving point are input to the computer for analysis (step 103 in FIG. 6). The reflection waveform extraction process has been described with reference to FIG.

  Subsequently, it is determined whether or not the elastic wave velocity of the natural ground in front of the face of the tunnel H is known (step 104 in FIG. 6). If it is already known, such as refraction elastic wave exploration or tomography, etc., the theoretical travel time is calculated using the elastic wave velocity (step 105 in FIG. 6), and the theoretical travel time is calculated. A reflection energy distribution is created by imaging processing using the result (step 107 in FIG. 6), and a velocity boundary surface of the ground mountain Yb (low velocity layer D) is extracted from the reflection energy distribution (step 108 in FIG. 6). On the other hand, if it is not known in step 104, it is assumed that the entire front of the face of the tunnel H is the speed Va of the natural mountain Ya near the face as shown in FIG. 8 (step 106 in FIG. 6). Is used to calculate the theoretical travel time (step 105 in FIG. 6), and a reflection energy distribution is created by imaging processing using the calculation result of the theoretical travel time (step 107 in FIG. 6). The speed boundary surfaces RS1 and RS2 of the natural ground Yb (low speed layer D) are extracted (step 108 in FIG. 6). In addition, FIG. 8 is explanatory drawing which shows the analysis result by a reflection method.

  Thereafter, it is determined whether or not the reflection measurement is the first time (step 109 in FIG. 6). If it is not the first time, the process proceeds to the determination (step 110 in FIG. 6) of whether or not it has converged (the reflection boundary surfaces RS1 and RS2 of the ground mountain Yb (low speed layer D) are the same as the previous time). Then, since it is the first time, the process proceeds to # 1 in the tomography analysis processing flow on the left side of FIG. 6, and information on the position of the velocity boundary surfaces RS1 and RS2 of the natural mountain Yb (low velocity layer D) obtained by the reflection method is obtained. It is used as information for creating an initial velocity model in the tomography method.

  On the other hand, in the tomography analysis process on the left side of FIG. 6 (left side of FIG. 6), the seismic wave generated by the first blast for excavation of the tunnel H is measured by the geophone S2 on the ground surface of the natural ground Y and analyzed. It is transferred to a computer, and the initial running time is read from the observed waveform data to create a running curve (steps 200 to 202 in FIG. 6). At the same time, the position coordinate data of the oscillation point and the receiving point are input to the computer for analysis (step 203 in FIG. 6).

  Subsequently, a data set of input data of analysis conditions is created (step 204 in FIG. 6), and the data and information on the position of the velocity boundary surfaces RS1 and RS2 of the natural mountain Yb obtained by the reflection method are used. Then, the analysis region is divided into grid-like cells, and an initial velocity model (hereinafter simply referred to as velocity model) in which the elastic wave velocity is set for each cell is created (step 205 in FIG. 6). As shown in FIG. 9, in the velocity model, the elastic wave velocity of the natural ground Ya obtained with blasting as the vibration source was fixed to Va, and the velocities of the natural mountain Yb and the natural mountain Yc were determined by the reflection method. A tomographic analysis is performed by estimating from the result of the reflected energy (position information of the velocity boundary surfaces RS1 and RS2), and elastic wave velocities of the cells of the natural ground Yb and the natural ground Yc are obtained. In this case, the elastic wave velocities of the natural grounds Yb and Yc may be estimated from other refraction methods, but if the other refraction methods are not performed, the elastic wave velocities of the natural grounds Yb and Yc are obtained. Since the value of is not known, the elastic wave velocity Va of the natural ground Ya is assumed.

  As a result of this tomography analysis, the elastic wave velocity of each cell of the natural ground Yb and the elastic wave velocity of each cell of the natural ground Yc shown in FIG. Thereby, as shown in FIG.10 (b), the velocity distribution in the natural mountain Y ahead of the face of the tunnel H is obtained. In addition, the elastic wave velocity of each cell of natural ground Ya is Va mentioned above. FIG. 10A is an explanatory diagram showing the analysis result by the tomography method following FIG. 9, and FIG. 10B is a graph showing the velocity distribution of the cross section taken along the line II of FIG. 10A.

Subsequently, as shown in FIGS. 11 and 26, the elastic wave velocity for each section (cell) of the natural ground Y is obtained. That is, the average elastic wave velocity Vb ′ in the area of the natural ground Yb is obtained from the result of tomography analysis by the following mathematical formula.

  Where Vb (i) is the elastic wave velocity of each cell i in the ground mountain Yb region, Ab (i) is the area of the cell i in the ground mountain Yb region, and n is the number of cells i in the ground mountain Yb region. is there.

Further, the average elastic wave velocity Vc ′ in the area of the natural ground Yc is obtained by the following mathematical formula.

  Where Vc (i) is the elastic wave velocity of each cell i in the area of the natural ground Yc, Ac (i) is the area of the cell i in the area of the natural ground Yc, and n is the number of cells i in the area of the natural ground Yc. is there.

  In addition, FIG. 11 is explanatory drawing which shows the analysis result by the tomography method following Fig.10 (a). FIG. 26 is an explanatory diagram showing, in an enlarged manner, a part of the state of the cell in which the natural ground is divided in FIG. The symbol SF in FIG. 26 is the ground surface. In FIG. 26, Va (i) is the elastic wave velocity of each cell i in the region of the natural ground Ya, Aa (i) is the area of the cell i in the natural mountain Ya region, and n is the cell in the natural mountain Ya region. The number of i.

  Subsequently, the theoretical travel time, which is the theoretical value at the time of the initial motion that will be observed for all oscillation point (blasting position) and receiving point (receiver S2) pairs, is calculated for the speed model (see FIG. 6 step 206). Subsequently, the difference between the observed travel time and the theoretical travel time of each oscillation point and receiving point pair is calculated (step 207 in FIG. 6). Then, the convergence determination is performed based on the difference between the observed travel time and the theoretical travel time (step 208 in FIG. 6). That is, the speed model is updated by repeating inversion and ray tracing so that the difference between the theoretical travel time and the observation travel time is minimized (step 209 in FIG. 6). Then, Steps 206 to 209 are repeated until the running time difference between the observed running time and the theoretical running time becomes smaller than the allowable value. On the other hand, if the travel time residual between the observed travel time and the theoretical travel time is smaller than the allowable value, the speed distribution cross section obtained up to that point is considered to be almost satisfied with the observed travel time, and it is repeated. End the calculation. Note that the final velocity distribution section representation in this tomography method is to divide the target section into rectangular cells, assign a speed value to each cell, and color-coded in shade or color display according to the speed value of each cell By doing so, the velocity distribution may be easily grasped visually.

  Next, when the convergence determination is made in step 208 of the tomography analysis as described above, the reflected energy is obtained by imaging processing using the theoretical travel time obtained there and the data of the reflected waveform obtained by the waveform processing of the reflection method. A distribution is created (step 107 in FIG. 6), a velocity boundary surface is extracted from the reflected energy distribution (step 108 in FIG. 6), and new velocity boundary surfaces RS3 and RS4 of the natural ground Yb are obtained as shown in FIG. Find the position of. FIG. 12 is an explanatory view showing the analysis result by the reflection method subsequent to FIG.

  Subsequently, it is determined whether or not the reflection method is measured for the first time (step 109 in FIG. 6). Here, since it is not the first time, the convergence determination of the newly obtained velocity boundary surface is performed (step 110 in FIG. 6). Here, for example, it is assumed that the convergence is not performed in step 110 of the reflection method convergence determination. In that case, a velocity model for tomography analysis using information on the positions of the new velocity boundary surfaces RS3 and RS4 obtained by the reflection method and information on the input data set of the tomography method (step 204 in FIG. 6). Is created (step 205 in FIG. 6). At this time, the speed of each natural mountain divided by the new speed boundary surfaces RS3 and RS4 is set as the average speed in each region (step 210 in FIG. 6).

  Subsequently, with respect to the velocity model obtained here, the theoretical value at the time of initial motion that will be observed for all pairs of oscillation points (blasting positions) and receiving points (receiver S2) in the same manner as described above. Is calculated (step 206 in FIG. 6), and the difference between the observed travel time and the theoretical travel time of each oscillation point and receiving point pair is calculated (step 207 in FIG. 6). Convergence is determined based on the difference from the theoretical travel time (step 208 in FIG. 6). That is, as described above, when the speed does not converge, the speed model is corrected (step 209 in FIG. 6), and step 206 is performed until the running time residual between the observed running time and the theoretical running time becomes smaller than the allowable value. On the other hand, when it converges, it is considered that the velocity distribution cross section obtained up to that point almost satisfies the observation travel time, and the iterative calculation is terminated. As a result of this tomography analysis, the elastic wave velocities of the natural ground Yb and natural ground Yc cells shown in FIG. 13 are obtained. FIG. 13 is an explanatory view showing the analysis result by the tomography method following FIG. Note that the final velocity distribution cross section at this stage may be color-coded by grayscale display or color display according to the velocity value of each cell, as described above.

  Next, when the convergence determination is made in step 208 of tomography analysis as described above, the theoretical travel time of the reflected wave is calculated based on the velocity model obtained there (step 105 in FIG. 6), and the reflected wave is calculated. A reflection energy distribution is created by imaging processing using the theoretical travel time of the above and the reflection waveform data obtained by the waveform processing of the reflection method (step 107 in FIG. 6), and the velocity boundary surface is extracted from the reflection energy distribution. (Step 108 in FIG. 6), as shown in FIG. 14, the positions of the velocity boundary surfaces Rs5 and Rs6 of the natural ground Yb are newly obtained.

  Subsequently, convergence determination is performed (step 110 in FIG. 6), and the positions of the speed boundary surfaces RS5 and RS6 obtained at this time and the positions of the speed boundary surfaces RS3 and RS4 obtained in FIG. 12 (width between lattice points). If not, the process is terminated. Otherwise, as described above, the position information of the new velocity boundary surfaces RS5 and RS6 obtained by the reflection method and the input data set of the tomography method (in FIG. 6) Using the information in step 204), the process returns again to step 205 in which a velocity model is created by tomographic analysis, and the same processing as described above is repeated. FIG. 14 is an explanatory view showing the analysis result by the reflection method following FIG.

  In the analysis of the conventional reflection method, since the elastic wave velocity of the natural ground is constant, a straight propagation path is used. Therefore, if the layer thickness of the low velocity layer D increases or the velocity change increases, a prediction error occurs. On the other hand, in the tunnel face front exploration according to the present embodiment, the traveling time can be calculated by using the differential method to calculate the traveling time and the propagation path refracting at the velocity boundary surface can be considered. Even in the structure, the measurement accuracy of the velocity boundary surface position and the elastic wave velocity of the low velocity layer D can be improved. Therefore, the search accuracy in front of the face of the tunnel H can be improved.

  Further, in the present embodiment, the exploration method in front of the face of the tunnel H as described above is performed for each blasting (each face) for excavation of the tunnel H, and the optimum low-velocity layer D at that time is determined. Data is updated by obtaining the velocity boundary surface position and elastic wave velocity. Thereby, every time the tunnel H is dug, the oscillation point can be increased and the measurement data can be increased. Therefore, the measurement accuracy of the velocity boundary surface position and the elastic wave velocity of the low velocity layer D in front of the face of the tunnel H can be increased. Can be improved. Therefore, the search accuracy in front of the face of the tunnel H can be further improved.

  Verification of exploration performance by numerical simulation

  Here, a numerical simulation of the three-dimensional wave propagation phenomenon of the P wave by the difference method is performed using the numerical model, the velocity boundary surface is predicted using the waveform obtained by calculation, and the comparison with the velocity boundary surface of the analysis model is performed. The exploration method of this embodiment is verified.

  Calculation model

  FIG. 15 is a graph showing the outer appearance of the stratum structure of the numerical calculation model, and FIG. 16 is a graph showing the positional relationship between the velocity boundary surface and the tunnel.

  As shown in FIG. 15 and FIG. 16, for example, the analysis is performed using a range of 100 m in the tunnel cross-sectional direction (x), 140 m in the tunnel axis direction (y), and 100 m in the height direction (z) as an analysis region. The number of divisions was determined so that the interval was 1 m in all directions.

  A low-velocity layer (elastic wave velocity Vp = 3.0 km / s) D with a layer thickness of 20 m is moved forward from the face K of the tunnel H on the ground where the elastic wave velocity around the tunnel H is 4.6 km / s. A three-dimensional model that intersects at a distance L1 (e.g., 57 m) toward the tunnel at a crossing angle θ1 of about 30 degrees in the horizontal direction and an inclination angle θ2 of 60 degrees in the vertical direction is used. . Of the velocity boundary surfaces where the difference in elastic wave velocity occurs, the face K side is defined as a first velocity boundary surface RSa, and the velocity boundary surface separated from the face K is defined as a second velocity boundary surface RSb. The receiving points RP (see FIG. 5) are, for example, 12 points at 1 m intervals in the range of 15 to 26 m from the face K on the tunnel wall of the tunnel H having a width of 10 m. Further, the oscillation point SP (see FIG. 5) is, for example, 25 points corresponding to blasting (1-m intervals) in the range of 1 to 25 m from the face K of the tunnel H in the direction of excavation. In order to suppress the generation of reflected waves at the calculation model boundary, a transmission boundary condition was given to the model boundary. The calculation time step is set to 80 μs, which is the same as the measurement sample time of the search, for example. This time step satisfies the stability condition for the difference calculation.

  The calculation waveform data processing method is shown below.

  FIG. 17 is a calculated waveform diagram of the receiving point closest to the oscillation point obtained from the numerical simulation of wave propagation. In the calculated waveform, the direct wave DW that directly reaches the receiving point RP from the oscillation point SP can be confirmed, but the reflected waves (the first reflected wave RW1 and the second reflected wave RW2) from the velocity boundary surface in front of the face of the tunnel H are Since the amplitude becomes smaller due to distance attenuation, it cannot be clearly confirmed. The direct wave DW, the first reflected wave RW1, and the second reflected wave RW2 are all P waves.

  18 is a reflection waveform diagram obtained by calculating the calculation waveform of FIG. 17 by the data processing shown in FIG. The direct wave DW is removed, and the reflected waves (first reflected wave RW1 and second reflected wave RW2) can be clearly confirmed. Of these, the first reflected wave RW1 is a reflection from the first velocity boundary surface RSa of 57 m from the running time toward the front of the face. On the other hand, the second reflected wave RW2 propagates in the opposite phase to the direct wave DW, and is a reflected wave by the second velocity boundary surface RSb. A reflected wave having a small amplitude can also be confirmed in the following, but it can be inferred that the reflected wave overlaps at these velocity boundary surfaces.

  Reflected wave imaging and velocity interface identification

  Using the 120 reflected waveforms (12 (number of receiving points) × 10 (number of oscillation points)) obtained from the data processing of the calculated waveform, imaging processing of reflected energy is performed in the three-dimensional coordinate space by the DS method.

  FIG. 19 is a graph showing the evaluation of the reflected energy obtained by using the elastic wave velocity (= 4.6 km / s) of the direct wave which is the conventional method and is the propagation velocity in the exploration section. In the figure, the positions of the first velocity boundary surface RSa and the second velocity boundary surface RSb of the analysis model are shown. In the predicted Ea of the first velocity boundary surface RSa where the elastic wave velocity near the face K of the tunnel H changes from 4.6 km / s to 3.0 km / s (that is, changes from hard to soft), a plot with a large reflected energy Are concentrated in the vicinity of the first speed boundary surface RSa and evaluated at the correct position. On the other hand, in the prediction Eb of the second velocity boundary surface RSb where the elastic wave velocity away from the face K of the tunnel H changes from 3.0 km / s to 4.6 km / s (that is, changes from soft to hard), an analysis model is used. The plots are concentrated at a position away from the position set in (1) by a distance L2 (for example, 10.6 m), and the low-speed layer width W of 20 m is erroneously evaluated as 30.6 m.

  On the other hand, FIG. 20 is a graph showing the result of obtaining the reflected energy using the traveling time by the differential method using the elastic wave velocity in front of the tunnel face in the tunnel face forward search method of the present embodiment. is there. The prediction Ea of the first speed boundary surface RSa that changes from hard to soft near the front face of the face K of the tunnel H has the same evaluation as the conventional method. On the other hand, in the prediction Ec of the second speed boundary surface RSb that changes from soft to hard away from the face K of the tunnel H, the plot is concentrated in the vicinity of the position of the second speed boundary surface RSb and is evaluated at the correct position.

  From the above, in the tunnel face front exploration method of this embodiment, which uses reflected time to calculate reflected energy, the reflected energy concentrates near the velocity boundary surface of the analysis model, and the position of the velocity boundary surface is accurately evaluated. I confirmed that I can do it. For this reason, since the information regarding the position, width, elastic wave velocity, etc. of the low-velocity layer D in front of the face K of the tunnel H can be accurately grasped beforehand, such as change of support or application of auxiliary construction method, etc. It is possible to take sufficient measures. Further, the search work ahead of the face K of the tunnel H does not significantly hinder excavation work itself. Therefore, the tunnel H can be excavated safely and economically in a short period of time.

  Applicable site and surrounding geological conditions

  FIG. 21 is a geological profile of the experiment site.

  A field experiment was conducted in a road tunnel. The geology is based on the Paleozoic Permian Kita Suzuka Group, and igneous rocks (green rocks), chert and slate are distributed. The experiment was carried out in the tunnel H of the tunnel H 140 m before the position Pp of the end point side wellhead shown in FIG. The position Pp of the wellhead from the position Pk of the face K of the tunnel H is the exploration range. The position of the oscillation point SP moves forward (to the right in FIG. 21) as the face moves.

  In the figure, the results of elastic wave velocity distribution obtained by prior refraction method exploration are shown. In the low earth covering portion extending to the wellhead portion, 2.6 km / s and 1.0 km / s low speed layers D1 and D2 are present in order from the lower layer on the ground G. Reference sign SF denotes the ground surface, reference sign RSc denotes a lower speed boundary face (lower speed boundary face), and reference sign RSd denotes an upper speed boundary face (upper speed boundary face). The ground G is composed of, for example, a CM rock having a elastic wave velocity of 4.6 km / s and a CH grade rock.

  Reflection from the upper face of the face because the position Pk of the face K of the tunnel H is closer to the speed boundary surface of the upper part of the face than the speed boundary face in front of the face (in the tunnel axis direction) due to the relationship between the geological structure position of the tunnel H and the tunnel mouth The wave effect is expected to increase. Therefore, in the experiment, the performance of the tunnel face front exploration method is verified by comparing the velocity boundary surface above the tunnel H and the reflected energy distribution.

  Waveform data processing

  FIG. 22 is a waveform diagram for 10 m (10 exploration blasts) of the face travel measured by a geophone 46.2 m away from the face of the tunnel. Exploration blasting was performed using, for example, an explosive amount (200 g). It can be seen that the waveform shapes are the same and the blasting conditions were the same. The elastic wave velocity Vp obtained from the initial running time is 4.6 km / s, which coincides with the elastic wave velocity obtained by the refraction method.

  Exploration results

  FIG. 23 is an evaluation cross-sectional view of reflected energy. For the evaluation of the velocity boundary surface, as shown in FIG. 23, the reflection energy is obtained at lattice points obtained by discretizing a space (for example, 100 m × 160 m × 140 m) at intervals of 1 m. The reflected energy was evaluated by a vertical section passing through the center of the tunnel H.

  FIG. 24 shows the distribution of reflected energy according to the conventional method, and FIG. 25 shows the distribution of reflected energy using the travel time of the differential method using the elastic wave velocity of the elastic wave exploration. Actually the color is shown. Although the color is not shown here, the reflection that changes from hard to soft becomes stronger as the color becomes warmer, and the reflection that changes from soft to hard becomes stronger as the color becomes colder. In the figure, velocity boundary surfaces (lower velocity boundary surface RSc and upper velocity boundary surface RSd) obtained by elastic wave exploration are shown superimposed.

  As shown in FIG. 24, the reflected energy by the conventional analysis method is distributed in an elliptical shape with the oscillation point SP and the receiving point RP as the focal points, and the velocity boundary (lower velocity boundary surface RSc and upper velocity boundary). It is not consistent with the plane RSd). On the other hand, as shown in FIG. 25, the reflected energy distribution using the travel time of the difference method is the velocity of the ground surface SF around the face of the tunnel H, the lower velocity boundary surface RSc, the upper velocity boundary surface RSd, and the like. The distribution matches the boundary surface, and it can be seen that the velocity boundary surface can be predicted at the correct position even when there are grounds with different elastic wave velocities. As a result, it is possible to accurately evaluate the position of the velocity boundary surface even when the tunnel H, which is difficult to predict with the conventional method, intersects the velocity boundary surface at an acute angle.

  From the above, the developed tunnel face front exploration method is effective for predicting the velocity boundary even in the ground where the elastic wave velocity changes due to the complicated geological structure. For this reason, even if the topography or geological structure is complex, such as near the tunnel head of the tunnel H (low earth covering), it is possible to quickly and accurately grasp the state in advance, so changes in support And measures such as the application of auxiliary construction methods can be taken. Therefore, the tunnel H can be excavated safely and economically in a short period of time.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the embodiment disclosed in this specification is an example in all respects and is limited to the disclosed technology. It is not a thing. That is, the technical scope of the present invention should not be construed restrictively based on the description in the above-described embodiment, but should be construed according to the description of the scope of claims. All modifications are included without departing from the technical scope equivalent to the described technique and the gist of the claims.

  For example, using the vibration of excavation blasting, based on GPS (Global Positioning System) time information, the travel time is obtained from the oscillation time in the mine and the vibration receiving time of the geophone installed on the ground surface, and the elastic wave exploration It is also possible to perform tomographic analysis in combination with the measurement data and to obtain the elastic wave velocity of the ground in front of the face of the tunnel. By applying this elastic wave velocity to the exploration method of the present embodiment, it is possible to grasp the ground in front of the tunnel face with high reliability.

  In the above description, the tomography method for measuring the seismic wave with the geophone provided on the surface of the ground using blasting in the tunnel as an oscillation source has been described. However, the present invention is not limited to this. You may use the tomography method in the refraction method which measures a seismic wave with the geophone provided on the surface of the ground using the blast on the surface as the oscillation source.

  As described above, in the tunnel face forward exploration method according to the present invention, when excavating a tunnel by blasting to a natural ground, the tunnel face that explores a fault zone in front of the tunnel face using elastic waves generated by blasting. It is effective when applied to the forward exploration method.

Y Ground mountain G Ground H Tunnel K Face D, D1, D2 Low speed layer S1, S2 Geophone RB Lock bolt N1, N2 Nut M Recording device TB Trigger box SP Oscillation point RP Vibration point GP Grid point RS1-RS6 Speed boundary surface RSa First velocity boundary surface RSb Second velocity boundary surface RSc Lower velocity boundary surface RSd Upper velocity boundary surface RW1 First reflected wave RW2 Second reflected wave

Claims (3)

(A) A plurality of reflection waves reflected from a fault zone in front of the tunnel face by a seismic wave generated by blasting for excavating the tunnel to the ground in front of the tunnel face are installed on the tunnel wall of the tunnel. Measuring by the first vibration receiving means;
(B) extracting a reflected waveform based on the measured value of the first vibration receiving means;
(C) measuring the seismic waves generated by the blasting using a plurality of second receiving means installed on the ground surface;
(D) Based on the measured value of the second vibration receiving means, the elastic wave velocity of the ground in front of the face of the tunnel is calculated by the tomographic analysis process, and the velocity model is created. And calculating the theoretical travel time of the reflected wave,
(E) After forming the reflected energy distribution using the reflected waveform data obtained in the step (b) and the theoretical travel time obtained in the step (d), the velocity boundary surface is calculated from the reflected energy distribution. Extracting a position;
(F) The speed boundary surface position data obtained in the step (e) is subjected to convergence determination. If the data does not converge, the speed boundary surface position data obtained in the step (e) is converged. Repeating the step (d) using the calculation result of the theoretical travel time obtained using the step (e),
A method for exploring forward of a tunnel face, comprising: After the step (e), before the convergence determination, when the data of the position of the velocity boundary surface calculated in the step (e) is the first calculation data, the convergence determination is not performed and the (e ) Step (d) is performed using the velocity boundary surface position data calculated in step, and the step (e) is performed using the theoretical travel time calculation result obtained there. The tunnel face forward exploration method according to claim 1. The steps (a) to (f) are performed every time the tunnel face blasts, and the optimum velocity boundary surface position and elastic wave velocity data of the fault zone are calculated for each blast, and the calculated data is used as the blasting. tunnel face forward exploration method according to claim 1 or 2, wherein the updating every time but is implemented.

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