JP6418387B2 - Forward exploration method of tunnel face - Google Patents

Description

  The present invention relates to a forward exploration method of a tunnel face that is mainly used when excavating a natural mountain of a mountain tunnel.

When excavating a mountain tunnel, grasping the nature of the natural ground spreading ahead of the face with appropriate and high accuracy is very important for efficiently and safely proceeding with the entire excavation work including supporting works and auxiliary works. is important.

  Drilling exploration by non-core drilling using drill jumbo (percussion drilling machine) and non-core advanced boring machine (rotary percussion drilling machine) has been put to practical use as a technology for exploring tunnel face front, and a striking piston The drilling energy generated in step 1 is transmitted to the excavation bit at the tip via a rod, and the rock is drilled with the bit, thereby measuring parameters during drilling such as drilling speed and feed pressure. The magnitude of drilling energy is evaluated using the time parameter, and the quality of the front ground can be judged.

JP 2013-142659 A JP 2001-249186 A

  However, exploration of natural ground in front of the face is not enough to target weak layers such as faults, and the location of springs is extremely important in terms of safety and work efficiency in excavation work. The above-mentioned drilling exploration by non-core drilling has a problem that it is difficult to predict a spring location without causing flooding even though a weak layer existing in the front ground can be predicted. It was.

  By the way, as for the prediction method of spring location, advanced boring without water, electric survey or electromagnetic survey of natural ground are known, but the former method forced a lot of cost and long tunnel excavation interruption, In the latter method, sufficient accuracy cannot be secured.

  On the other hand, so-called underground seismic wave exploration is also known, which uses the reflected waves of elastic waves such as TSP (Tunnel Seismic Prediction), HSP (Horizontal Seismic Profiling), and reflection tomography (TRT) to detect the front of the face. (Patent Documents 1 and 2).

  However, in such underground elastic wave exploration, after excitement at the excitation point installed in the tunnel mine, the reflected wave is received at the receiving point installed in the same tunnel mine, so that it exists in the ground in front of the tunnel face. Although it is possible to estimate the reflecting surface to some extent, it is not always easy to specify the reflecting surface in a form corresponding to the quality of the actual ground.

  In addition, in the point of predicting spring locations, there has also been a problem that conventional underground mine wave exploration is difficult as well as drilling exploration by non-core drilling.

  The present invention has been made in consideration of the above-described circumstances, and the front surface of the tunnel face that can identify the reflecting surface existing in the front ground of the tunnel face in a form corresponding to the quality of the actual ground. The purpose is to provide exploration methods.

  Another object of the present invention is to provide a forward exploration method for a tunnel face capable of predicting not only a weak layer such as a fault but also a spring location.

In order to achieve the above object, a tunnel face forward exploration method according to the present invention operates a plurality of vibration generating means installed on the inner surface of a tunnel, as described in claim 1, and The elastic wave propagated to the ground surrounding the tunnel is received as reflected wave data by the receiving means installed on the inner surface, and the reflected wave data is analyzed, thereby exploring a natural ground spreading in front of the face of the tunnel. In the forward exploration method of the tunnel face,
Evaluating the elastic wave velocity in the ground in the vicinity of the tunnel to be a reference elastic wave velocity,
Create a reflection intensity distribution in the ground using the reflected wave data and the reference elastic wave velocity,
The reflection intensity distribution is divided into a zone in which points with a large reflection intensity are densely distributed and a zone in which points with a large reflection intensity are not densely distributed, respectively, to be a heterogeneous zone and a homogeneous zone,
In the case of the boundary where the reflection intensity at the boundary between the inhomogeneous zone and the homogeneous zone changes from the inhomogeneous zone to the homogeneous zone as seen from the face, the waveform polarity has advanced in the soft material. In the case of a boundary that changes from the homogeneous zone to the inhomogeneous zone as viewed from the face, while calculating for only those that match the waveform polarity when the elastic wave reflects at the boundary with the hard material, The waveform polarity is calculated only for those that match the waveform polarity when the elastic wave that has traveled through the hard material is reflected at the boundary with the soft material,
By comparing the reflection intensity at each boundary calculated in the intensity calculation step with the corresponding relationship obtained between the reflection coefficient and the reflection intensity, the reflection coefficient at each boundary is obtained,
Using the reflection coefficient at each boundary, the elastic wave velocity in the inhomogeneous zone and the homogeneous zone is calculated as a modified elastic wave velocity,
The position of each boundary on the tunnel axis is corrected using the corrected elastic wave velocity.

Also, the forward exploration method of the tunnel face according to the present invention calculates the ratio V _p / V _s of the corrected elastic wave velocities using the P wave velocity V _p and the S wave velocity V _s. .

  Also, the forward exploration method of the tunnel face according to the present invention is configured such that the vibration receiving means can measure three components orthogonal to each other, and one of the three components is orthogonal to the vertical direction or the tunnel axis and the The vibration receiving means is arranged so that the remaining two are not parallel to the tunnel axis so as to be parallel to the vertical plane including the tunnel axis.

  Among the well-known underground elastic wave exploration, HSP is intended for the exploration of resources such as oil exploration. The wave analysis procedure is also based on the assumption that the ground has a water stratified structure, so it is inherently difficult to apply it to mountainous areas where fault fracture zones and crack concentration zones are intricately crossed vertically and horizontally.

  In addition, although mine seismic surveys can be applied to mountainous areas, there are many cases where a large number of reflective surfaces can be obtained. In practice, it is difficult to identify whether it is a boundary with a concentrated zone.

  The applicant has conducted research and development focusing on this point, and divides the reflection intensity distribution into zones where the points with high reflection intensity are densely distributed and zones where the points with high reflection intensity are not densely distributed. As a result, we have obtained new knowledge that fragile layers such as fault fracture zones and crack concentration zones can be found more appropriately by using heterogeneous zones and homogeneous zones, respectively.

  That is, in the forward exploration method of the tunnel face according to the present invention, a plurality of vibration generators installed on the inner surface of the tunnel are operated, and the elastic waves propagated to the ground surrounding the tunnel by each of the vibration generators are described above. In order to explore the natural ground spreading in front of the tunnel face by receiving the reflected wave data by the receiving means installed on the inner surface of the tunnel and analyzing the reflected wave data, first, the elastic wave in the ground near the tunnel The velocity is evaluated and set as a reference elastic wave velocity.

  The reference elastic wave velocity can be evaluated by receiving the elastic wave propagated by each vibration generating means as a direct wave by the vibration receiving means.

  Next, a reflection intensity distribution in the ground is created using the reflected wave data and the reference elastic wave velocity.

  The reflected wave received by the receiving means is on an ellipse with the focal point at the position where the receiving means is installed and the position where the exciting means is installed, and the propagation distance of the reflected wave is the sum of the distances from each focal point. The propagation distance can be obtained by multiplying the elapsed time from the vibration by the reference elastic wave velocity.

  That is, the point where the elastic wave may have been reflected can be represented as a number of positions on an ellipse with different diameters drawn around the tunnel using the time history observation waveform of the reflected wave, Furthermore, it can handle similarly about the elastic wave each propagated from several excitation means.

  Therefore, after creating an analysis model in which the ground around the tunnel is divided into a mesh or lattice, the amplitude of the reflected wave at each time is used as an index indicating the reflection intensity, and the lattice points and ellipses of the analysis model described above are By stacking (stacking) on the matching points and performing this stack for all the vibration generating means, at the lattice point corresponding to the point where the reflection actually occurs, the amplitude is added to become a large value. At a lattice point corresponding to a point where no reflection occurs, a reflection intensity distribution having a small value is obtained by canceling the amplitude.

  The procedure for creating the reflection intensity distribution itself can be implemented by the underground elastic wave exploration concept and other known techniques, and a detailed description thereof will be omitted here.

  Next, the reflection intensity distribution is divided into a zone in which the points with high reflection intensity are densely distributed and a zone in which the points with high reflection intensity are not densely distributed.

As described above, the reflected intensity distribution is obtained by superimposing the amplitude of the reflected wave on each lattice point as the reflected intensity. As a result, it was confirmed that the entire zone where the areas with high reflection intensity are densely distributed is the fault crushing zone or the crack concentration zone, rather than treating the linear series of areas with high reflection intensity as the reflecting surfaces. It was found that it was closer to the quality of an actual natural ground to treat the boundary with a zone that was not so as a geological reflection surface, that is, a geological boundary such as a lithology, weathered alteration zone, or fault.
In addition, in the prior art, for example, TSP, although a large number of reflection surfaces with high reflection intensity are automatically detected, it is difficult to evaluate the elastic wave velocity before and after the reflection surface. Since the elastic wave velocity can be increased / decreased by using the reflecting surface obtained by zoning as a boundary, more accurate forward exploration becomes possible.

  Here, the zone where the reflection intensity points are not densely distributed is a zone where the reflection intensity is high but the density is rough, the points where the reflection intensity is low are only densely distributed, and It means a case where only a point having a low reflection intensity is present at a coarse density (including a case where no substantial reflection is observed).

Next, the reflection intensity at the boundary between the heterogeneous zone and the homogeneous zone is calculated as follows. That is,
(a) When the boundary changes from the heterogeneous zone to the homogeneous zone when viewed from the face, the waveform polarity matches the waveform polarity when the elastic wave traveling in the soft material is reflected at the boundary with the hard material Calculate only for
(b) When the boundary changes from the homogeneous zone to the inhomogeneous zone as seen from the face, the waveform polarity matches the waveform polarity when the elastic wave traveling inside the hard material is reflected at the boundary with the soft material For example, in the case of (a), the reflection intensity is calculated only for the reflected wave whose amplitude polarity is positive, and in the case of (b), only the reflected wave whose amplitude polarity is negative is calculated. The reflection intensity is calculated for. The reflection intensity may be calculated, for example, in the form of an average of amplitude values at each boundary.

  Next, the reflection coefficient at each boundary is obtained by collating the reflection intensity at each boundary calculated as described above with the correspondence previously obtained between the reflection coefficient and the reflection intensity.

  The reflection coefficient mainly depends on the ratio of the hardness of the two ground constituent materials that sandwich the boundary, and no clear correspondence has been found between the reflection intensity and the energy of the vibration generating means. In addition, if the construction materials of each place constituting the homogeneous zone and the inhomogeneous zone are substantially constant, it is possible to use the correspondence relationship between the reflection coefficient and the reflection intensity obtained at other tunnel sites.

  Next, the elastic wave velocity in the inhomogeneous zone and the homogeneous zone is calculated as a corrected elastic wave velocity using the reflection coefficient at each boundary. As the calculation procedure, a known one can be adopted, and for example, an approximate expression by Yoshinori Ishii can be used.

  Next, the position of each boundary on the tunnel axis is corrected using the calculated corrected elastic wave velocity.

If the procedure described above is followed, the position of the fragile layer existing in front of the face of the tunnel can be appropriately predicted. Among the modified elastic wave velocities, the P wave velocity V _p and the S wave velocity V _s are used. If the ratio V _p / V _s is calculated, if the water content increases, the P wave velocity will be affected and the magnitude will decrease, so that the position where V _p / V _s becomes the minimum value will be detected. It can be specified as a water spot.

  For this reason, large-scale springs are predicted in advance without interrupting tunnel excavation and without generating springs like draining boring, and such predictions are added to ensure the addition of wastewater muddy water treatment facilities and the stability of the face. Or it becomes possible to reflect in prior measures, such as preparation of a water drainage shaft.

  As long as the elastic means can propagate the elastic wave to the ground around the tunnel, the specific configuration is arbitrary, and a hammering operation may be performed, but blasting with explosives is typically used as the vibration means. An example.

  The vibration receiving means can receive the waveform data by receiving a reflected wave, and in some cases, a direct wave in addition to this, and is typically a seismometer, particularly a hole-buried type whose outer shape is cylindrical. Although it can be constituted by an earthquake sensor, the vibration receiving means is constituted so that three components orthogonal to each other can be measured, and one of the three components is perpendicular to the vertical direction or the tunnel axis and the tunnel axis is If the vibration receiving means is arranged so that the other two are not parallel to the tunnel axis so that they are parallel to the vertical plane, it is possible to appropriately explore the vulnerable layer and springs located in front of the face. it can.

  That is, since the vibration receiving means and the plurality of vibration generating means are typically arranged on the inner wall of the tunnel along the tunnel axis direction, as can be understood by considering the propagation path from the vibration generating means to the vibration receiving means, A reflective surface parallel to the axial direction is relatively easy to search, but a reflective surface that is not parallel to the tunnel axial direction is less likely to be searched as it is closer to a right angle.

  On the other hand, in tunnel excavation, it is meaningless unless the reflection surface that exists in front of the face, that is, the reflection surface that intersects the tunnel axis, can be explored, so that the reflected wave from the reflection surface that is not parallel to the tunnel axis direction is as sensitive as possible. It is necessary to receive the vibration.

  However, when a hole-embedded seismic sensor capable of measuring three components x, y, and z orthogonal to each other is embedded so that the x direction, which is the material axis direction, is orthogonal to the inner wall of the tunnel as in the past, Since the reflected wave propagating from the reflecting surface extending obliquely with respect to the axis greatly intersects with the x direction and the y direction, the S / N ratio is inevitably deteriorated.

  Therefore, when the vibration receiving means is arranged as described above, the reflected wave propagating from the reflection surface extending obliquely with respect to the tunnel axis can be directly captured by the x component or the y component, and the S / N ratio can be increased. it can.

The flowchart which showed the implementation procedure of the forward exploration method of the tunnel face which concerns on this embodiment. It is an arrangement plan of gunpowder 5 and seismographs 6a-6e, (a) is a top view and (b) is a transverse section which meets an AA line. It is a conceptual diagram regarding the reflected wave, (a) is a diagram showing an example in which the elastic wave reflected in the natural ground reaches the seismometer 6d as a reflected wave, (b) is an ellipse and lattice points in the analysis model The figure which showed the relationship. The figure which showed an example of reflection intensity distribution. The conceptual diagram which showed the zoning which divides reflection intensity distribution into a homogeneous zone and a heterogeneous zone. It is the figure which showed the result of zoning the reflection intensity distribution of FIG. 4, (a) is a general view, (b) is an enlarged view of the upper left part. The figure which showed a mode that the reflection intensity in the boundary of a heterogeneous zone and a homogeneous zone was calculated. A graph depicting V _p / V _s .

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a tunnel face forward exploration method according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a flowchart showing an implementation procedure of a forward search method for a tunnel face according to the present embodiment. As shown in FIG. 2, the forward exploration method of the tunnel face according to the present embodiment is applied when exploring the front ground of the face 3 exposed in the hollow space 2 of the tunnel 1. First, as shown in the figure, the inner wall 4 of the tunnel 1 is horizontally drilled so as to have a height of 1 m and a depth of 1.5 m, for example. The explosive 5 constituting the vibration generating means is loaded on the inner wall 4 and the face 3 in the same manner so that the height is 2 m and the depth is 1.5 m, and the seismometer 6 a is placed in the hole. ~ 6e are buried (step 101).

  The explosives 5 may be arranged at an equal pitch over a length of about 50 m, for example, so that the total number is 20 to 30.

  The seismometers 6a to 6e are each composed of a cylindrical seismic sensor configured to measure three components orthogonal to each other, and the face 3 so that the x direction as the material axis direction is parallel to the tunnel axis. And the seismometers 6b to 6e installed on the inner wall 4 on the same side as the side on which the explosive 5 is disposed.

  Here, the seismometer 6e is arranged so that the x direction is orthogonal to the inner wall 4. However, the seismometers 6b to 6d propagate reflected waves of elastic waves generated in the ground by detonating the gunpowder 5. In consideration of the coming direction, the x direction and the y direction are arranged to form 45 ° with the tunnel axis direction. In the z direction, all the seismometers 6a to 6e are positioned vertically downward.

  Next, the explosive 5 is detonated, and the elastic waves generated by the detonation are received by the seismometers 6a to 6e (step 102).

Next, by analyzing the observation waveforms received by the seismometers 6a to 6e, the elastic wave velocity in the ground in the vicinity of the tunnel 1 is calculated and set as the reference elastic wave velocity V ₀ (step 103).

The reference elastic wave velocity V ₀ is calculated using a wave directly propagating from the loading position of the explosive 5 among the observed waveforms described above, that is, a direct wave.

Next, out of the elastic waves generated by the explosion of the explosive 5, the reflected waves reflected in the ground are taken out from the observed waveforms of the seismometers 6 a to 6 e, and these reflected wave data and the above-mentioned reference elastic wave velocity V ₀ are obtained. Using this, a reflection intensity distribution in the ground is created (step 104).

FIG. 3A is a conceptual diagram showing an example in which the elastic wave generated by the explosive of the gunpowder 5 is reflected in the natural ground and reaches the seismometer 6d as a reflected wave. As shown in the figure, the reflected wave received by the seismometer 6d is focused on the position where the seismometer is installed and the position where the gunpowder 5 is loaded, and the propagation distance L of the reflected wave is the focus. Is a wave reflected at any point on the ellipse 32 as the sum of the distances from, and the propagation distance L is a value obtained by multiplying the elapsed time T after the vibration by the reference elastic wave velocity V ₀ , T -It can be _calculated as V0.

  That is, the point where the elastic wave may be reflected is on a large number of ellipses 32 having different diameters drawn around the tunnel 1 using the time history observation waveform 31 of the reflected wave received by the seismometer 6d. It can be expressed as a position.

  And the above-mentioned handling is similarly realized about the vibration by the other explosives 5. FIG.

  Therefore, as shown in FIG. 5B, the analysis model 33 in which the ground around the tunnel 1 is divided into a mesh shape or a lattice shape is created, and the amplitude of the reflected wave at each time is used as an index indicating the reflection intensity. By stacking (stacking) on the lattice points that coincide on the ellipse 32 described above, and performing this stack on the vibrations of all the gunpowder 5, the amplitude at the lattice point corresponding to the point where the reflection actually occurs is increased. When added, a large value is obtained, and at a lattice point corresponding to a point where no reflection actually occurs, a reflection intensity distribution having a small value is obtained by canceling the amplitude.

  As for the lattice size of the analysis model, when the elastic wave velocity is 3,000 m / s and the frequency is 300 Hz, the wavelength is 10 m. Therefore, if the lattice size is set to about 2 m, the reflection intensity distribution is sufficient. It is possible to create with accuracy.

  FIG. 4 shows an example of the reflection intensity distribution. In the example of FIG. 4, the amplitude value along the x direction (arrow direction) of the seismometer 6a installed on the face 3 is positive. It is drawn so that the dark color and the negative color are light, and the excavation direction of the tunnel 1 is leftward. In the present embodiment, for the sake of convenience of drawing, the positive value is drawn in dark color and the negative value is drawn in light color. However, for example, if the color display is made so that positive is black and negative is red, the positive / negative of the amplitude value is clear. Can be visually recognized.

  Next, the reflection intensity distribution is divided into a zone where the points having a large reflection intensity are densely distributed and a zone where the points having a large reflection intensity are not densely distributed, which are defined as a heterogeneous zone and a homogeneous zone, respectively (step 105).

  FIG. 5 is a conceptual diagram showing such zoning, in which the homogeneous zone is indicated by a graphic 51 and the inhomogeneous zone is indicated by a graphic 52. FIG. 6 (a) shows the result of applying the above zoning to the reflection intensity distribution described in FIG. 4, and FIG. 6 (b) shows the upper left part of FIG. 6 (a). It is an enlarged one.

  As can be seen well in FIG. 6 (b), in the reflection intensity distribution created in step 104, there is a zone in which plots indicating points having a high reflection intensity are gathered densely and a blank where there is almost no such plot. Zones exist alternately, and the former is a heterogeneous zone and the latter is a homogeneous zone.

  As described above, the reflection intensity distribution is obtained by superimposing the amplitude of the reflected wave on each lattice point as a reflection intensity. In this embodiment, as shown in FIG. 5 (b), the linear series extending from the lower left to the upper right is not treated as a reflecting surface. The entire zone with dense distribution is considered as a fault fracture zone or a crack concentration zone, and this zone is set as a heterogeneous zone, and a blank zone where there is almost no plot showing a portion with high reflection intensity is set as a homogeneous zone. Are treated as geological boundaries such as lithofacies, weathered alteration zones, and faults.

  Whether the zone is a homogeneous zone or a non-homogeneous zone is determined by, for example, binarizing the reflection intensity distribution by image processing to convert a plot where the reflection intensity is large into black pixels, and then black pixels for the total number of pixels. Determination can be made by calculating the ratio of the number of pixels and comparing and comparing with an appropriate threshold value.

  Next, as shown in FIG. 7, the reflection intensity at the boundary between the heterogeneous zone and the homogeneous zone is calculated as follows (step 106).

In particular,
(a) In the case of a boundary that changes from the inhomogeneous zone to the homogeneous zone as seen from the face 3, the elastic wave whose waveform polarity has propagated through the soft material out of the reflected intensity of the plot existing near the boundary. Only those that match the waveform polarity when reflecting at the boundary with the hard material are calculated, and the average value thereof is calculated.
(b) In the case of a boundary that changes from the homogeneous zone to the heterogeneous zone as seen from the face 3, the elastic wave whose waveform polarity has traveled through the hard material out of the reflection intensity of the plot existing near the boundary. Only those that match the waveform polarity when reflecting at the boundary with the soft material are calculated, and the average value thereof is calculated.

  For example, in the case of (a), the average value of the reflection intensity is calculated only for the reflected wave whose amplitude polarity is positive, and in the case of (b), only the reflected wave whose amplitude polarity is negative is targeted. The average value of the reflection intensity is calculated.

  Next, the reflection coefficient at each boundary is obtained by collating the reflection intensity at each boundary calculated as described above with the correspondence obtained in advance between the reflection coefficient and the reflection intensity (step 107).

  A clear correspondence between the reflection coefficient and the reflection intensity is not necessarily found, but the condition of the energy of the vibration by the gunpowder 5 and the constituent materials of each board constituting the homogeneous zone and the heterogeneous zone are almost constant. If it is below, the correspondence between the reflection coefficient and the reflection intensity obtained at another tunnel site can be used.

  Next, the elastic wave velocity in the inhomogeneous zone and the homogeneous zone is calculated as a corrected elastic wave velocity using the reflection coefficient at each boundary (step 108).

  As the calculation procedure, a known one can be adopted, and for example, an approximate expression by Yoshinori Ishii can be used.

  On the other hand, the boundary position between the heterogeneous zone and the homogeneous zone on the tunnel axis is obtained by extending the boundary between the heterogeneous zone and the homogeneous zone obtained at step 105 in the tunnel axis direction (step 109).

  Specifically, as shown in FIG. 6 (a), the tangent line of the ellipse at the boundary between the inhomogeneous zone and the homogeneous zone obtained in step 105 is extended in the tunnel axis direction, and the intersection with the tunnel axis line ( In the same figure, a square-shaped plot) may be a boundary position between the heterogeneous zone and the homogeneous zone on the tunnel axis.

  Next, the position of each boundary on the tunnel axis obtained in step 109 is corrected using the corrected elastic wave velocity calculated in step 108 (step 110).

In correcting each boundary position, first, using the analysis diagram of the initial diffraction stack analysis, the section length from the face 3 to the first reflecting surface is read as D ₁ ,
D _i = (1 + 2r ₁ ) (1 + 2r ₂ ) (1 + 2r _(i−1) ) D ′ _i
here,
D _i : section length from the i-th reflecting surface to the (i−1) -th reflecting surface
D ′ _i : Section length from the i-th reflection surface to the (i−1) -th reflection surface read from the analysis diagram of the original diffraction stack analysis
r _i : reflection coefficient of the i-th reflecting surface
t _i : Wave propagation time from the i-th reflecting surface to the (i−1) -th reflecting surface
Then, D _i is obtained sequentially, and finally, these are expressed by the following equation:
ΣD _i = D ₁ + D ₂ +... D _i
By summing up like this, the distance from the face to the i-th reflecting surface may be obtained.

  As described above, according to the forward exploration method of the tunnel face according to the present embodiment, the reflection intensity distribution obtained by the analysis of the reflected wave is divided into the zone where the points where the reflection intensity is high and the reflection intensity are large. By dividing the points into zones where the points are not densely distributed and forming the inhomogeneous zone and the homogeneous zone, respectively, and treating the boundary as a geological reflecting surface, the reflecting surface existing in the front ground of the face 3 is It becomes possible to specify in a form corresponding to the quality of natural ground.

  Moreover, according to the forward exploration method of the tunnel face according to the present embodiment, the seismometers 6b to 6d take into account the direction in which the reflected wave of the elastic wave generated in the ground by propelling the gunpowder 5 propagates. Since the x direction and the y direction form 45 ° with the tunnel axis direction, the fragile layer located in front of the face can be appropriately probed.

  That is, when the material is embedded so that the x direction, which is the material axis direction, is orthogonal to the inner wall 4 of the tunnel 1 as in the prior art, the reflected wave propagating from the reflecting surface extending obliquely with respect to the tunnel axis is the x direction and the y direction. However, the S / N ratio is inevitably deteriorated because it intersects greatly with the above, but if configured as described above, the reflected wave propagating from the reflecting surface extending obliquely with respect to the tunnel axis is directly captured by the x component or the y component. And the S / N ratio can be greatly increased.

Although not specifically mentioned in the present embodiment, the ratio V _p / V _s may be calculated using the P wave velocity V _p and the S wave velocity V _s among the corrected elastic wave velocities.

FIG. 8 is a graph depicting the calculated V _p / V _s . About the P wave velocity V _p and the S wave velocity V _s , the direction from the side where the gunpowder 5 and the seismometers 6a to 6e are installed among the directions oblique to the tunnel axis orthogonal direction (hereinafter referred to as an oblique front direction). In the case of the reflected wave arriving from the seismometers 6b and 6d, the waveform observed by the x-axis component of the seismometers 6b and 6d and the y-axis component of the seismometer 6c are mainly P-waves. In many cases, the waveform observed in the x-axis component of 6c is mainly an S-wave, and is opposite to the side where the gunpowder 5 and the seismometers 6a to 6e are installed in the direction oblique to the tunnel axis orthogonal direction. In the case of a reflected wave coming from the direction from the side (hereinafter referred to as an oblique back direction), the waveforms observed in the x-axis component of the seismometers 6b and 6d and the y-axis component of the seismometer 6c are mainly S waves. Observed with the y-axis component of 6b and 6d and the x-axis component of seismometer 6c In many cases, the P wave is mainly a P wave, so that the P wave velocity V _p and the S wave velocity V _s can be obtained by analyzing the observed waveform for each component in consideration of the arrival direction of the reflected wave. Is possible.

According to such a configuration, when the water content is increased, the P wave is affected and the magnitude thereof is reduced. Therefore, the position where V _p / V _s becomes the minimum value can be specified as the spring site.

  Therefore, large-scale springs can be predicted in advance without interrupting tunnel excavation and without generating springs like draining boring. It is possible to reflect this in advance measures such as ensuring stability or preparing drainage shafts.

  In this embodiment, the seismometers 6b to 6d are arranged so that the z direction faces vertically downward so that the x direction and the y direction form 45 ° with the tunnel axis direction. The angle formed between the y direction and the tunnel axis direction does not necessarily need to be 45 °. Considering the arrival direction of the reflected wave, the angle is larger than 0 ° and smaller than 90 °, that is, the x direction and the y direction are the tunnel axis. It may be installed so that it is non-parallel.

  If the tunnel axis is not horizontal, the seismometers 6b to 6d may be installed so that the z-axis direction is orthogonal to the tunnel axis and parallel to the vertical plane including the tunnel axis.

  In the present embodiment and the above-described modification, the seismometers 6b to 6d are arranged so that the x direction and the y direction are not parallel to the tunnel axis direction. If there is no problem, how to install each seismometer is arbitrary, and it may be arranged so that the x direction and the y direction are parallel to the tunnel axis direction as in the conventional case.

1 tunnel 3 face 4 inner wall (tunnel inner surface)
5 Gunpowder (vibration means)
6a-6e Seismometer (vibration means)
51 Homogeneous zone 52 Heterogeneous zone

Claims (3)

A plurality of vibration generators installed on the inner surface of the tunnel are actuated, and the elastic waves propagated to the ground surrounding the tunnel by each of the vibration generators are received as reflected wave data by the vibration receivers installed on the inner surface. In the forward exploration method of the tunnel face that explores a natural mountain spreading in front of the face of the tunnel by analyzing the reflected wave data,
Evaluating the elastic wave velocity in the ground in the vicinity of the tunnel to be a reference elastic wave velocity,
Create a reflection intensity distribution in the ground using the reflected wave data and the reference elastic wave velocity,
The reflection intensity distribution is divided into a zone in which points with a large reflection intensity are densely distributed and a zone in which points with a large reflection intensity are not densely distributed, respectively, to be a heterogeneous zone and a homogeneous zone,
In the case of the boundary where the reflection intensity at the boundary between the inhomogeneous zone and the homogeneous zone changes from the inhomogeneous zone to the homogeneous zone as seen from the face, the waveform polarity has advanced in the soft material. In the case of a boundary that changes from the homogeneous zone to the inhomogeneous zone as viewed from the face, while calculating for only those that match the waveform polarity when the elastic wave reflects at the boundary with the hard material, The waveform polarity is calculated only for those that match the waveform polarity when the elastic wave that has traveled through the hard material is reflected at the boundary with the soft material,
By comparing the reflection intensity at each boundary calculated in the intensity calculation step with the corresponding relationship obtained between the reflection coefficient and the reflection intensity, the reflection coefficient at each boundary is obtained,
Using the reflection coefficient at each boundary, the elastic wave velocity in the inhomogeneous zone and the homogeneous zone is calculated as a modified elastic wave velocity,
A forward search method for a tunnel face, wherein the position of each boundary on the tunnel axis is corrected using the corrected elastic wave velocity. The tunnel face forward exploration method according to claim 1, wherein the ratio V _p / V _s is calculated using the P wave velocity V _p and the S wave velocity V _s among the modified elastic wave velocities. The vibration receiving means is configured to measure three components orthogonal to each other, and one of the three components remains in a vertical direction or perpendicular to the tunnel axis and parallel to a vertical plane including the tunnel axis. The tunnel face forward exploration method according to claim 1 or 2, wherein the vibration receiving means is arranged so that two of them are not parallel to the tunnel axis.