JP2002139574A - Geological probing method in front of tunnel working face - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a peculiar tunnel HSP method different from a reflection earthquake probing method on measurement and reflecting surface extraction. SOLUTION: One of an oscillation point and a reception point is allocated at fewer positions of three or more, and the other is allocated at more positions. Received seismic wave observed raw data are edited into sets corresponding to the oscillation points or reception points at less positions of three or more, and analytic figures for the edited sets are individually generated from the seismic wave data after a filter-process and the estimated propagation speed of the seismic wave, and the similarity of reflection events is compared and collated between the analytic figures. The reflection events having high similarity and judged to be in common with each other are extracted as a reflecting surface, and the geological structure in front of the tunnel working face is estimated based on the extracted reflecting surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a geological exploration method in front of a tunnel face for exploring the geology in front of the tunnel face.

[0002]

2. Description of the Related Art Prediction of the existence of a fault, a crush zone, or a hydrous layer in front of a tunnel face is extremely important in controlling the tunnel excavation process.

[0003] Generally, as a method of geological survey of the surface or the seabed, a reflection seismic survey method, which is a kind of physical survey utilizing physical phenomena, is employed. This seismic reflection method is used to estimate the distribution and reserves of petroleum and coal, or to grasp the geological composition of sedimentary rocks with a multilayered horizontal structure. .

[0004] In recent years, as a technique for exploring the front of a tunnel face, the equipment of the reflection method seismic exploration and data processing technology have been applied to the tunnel HSP method (tunnel horizontal seismic method).
c Profiling method) has been attempted. This tunnel HSP method aims to detect geological boundaries and fault fracturing zones in tunnel tunnels, and targets mountain tunnels with extremely complex geology that cannot be assumed as horizontal multilayered structures. 3
It must be performed as a dimension, and simply reusing the technique of seismic reflection survey cannot provide the required search results.

[0005] Therefore, efforts have been made to develop a unique technique for exploring the geology ahead of the tunnel face, but the current tunnel HSP method predicts the geological discontinuity in front of the tunnel face. (Hereinafter referred to as "non-conformity"), and it is still at a stage where it cannot be said that it has been fully completed.

An analysis of the types of nonconformities described above reveals that in spite of the fact that a geological discontinuity surface actually exists, its existence cannot be predicted (hereinafter referred to as “no extraction”), and vice versa. In addition, there are two types of cases where the existence of a geological discontinuity surface is predicted even though it does not actually exist (hereinafter referred to as “erroneous extraction”). Geological factors, b, measurement / equipment, c,
Data processing and d, reflective surface extraction are considered to be present. In particular, b, the measurement / instrument and d, and the extraction of the reflection surface are susceptible to noise and artificial influence, and thus often cause a mismatch.

Conventionally, at the stage of preparing an analysis chart to be described later, for example, a method of superimposing a plurality of pieces of seismic wave data has been adopted in order to improve the S / N ratio. The analysis result is not necessarily sufficient because the reflection event appears due to noise and the original reflection event disappears due to noise. Furthermore, in the current situation, the extraction of the reflection event as a reflection surface is based on the validity of the reflection surface from the relative position of the oscillation point and the receiving point, and the validity of the existence as the reflection surface from the geological information, in addition to the above-mentioned polymerization method. However, the rule of extraction as a reflective surface is not necessarily established, and it largely depends on the experience and know-how of the analyst. In such an analysis, the objective basis is not clear, and it is hard to say that the analysis result is satisfactory to everyone.

[0008]

The exploration in front of the tunnel face involves exploration of a mountainous region having a complicated velocity structure.
To measure in a limited space inside the tunnel mine, to interrupt it so as not to affect the tunnel excavation work and to perform it in a short time, or to predict the geological appearance position on the tunnel axis, It is a special exploration.
For this reason, in the tunnel HSP method, it is required to establish a unique technique different from the reflection seismic method in terms of measurement and reflection surface extraction.

Therefore, the present invention solves the above-mentioned problems, eliminates the factors of erroneous extraction and non-extraction as much as possible, and can obtain the same result regardless of who extracts the reflection surface. It is an object of the present invention to provide a geological exploration method in front of a tunnel face, which is capable of extracting a reflection event having a clear pattern, and which is excellent in exploration accuracy.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, a measuring line comprising a plurality of oscillating points separated from each other and a plurality of receiving points separated from each other is arranged in a tunnel pit. In the method of receiving a seismic wave oscillated from a point at a receiving point, and exploring the geology in front of the tunnel face by analyzing the received seismic wave, one of the oscillating point and the receiving point is reduced to a minority of 3 or more. While the other is a large number, each seismic wave sequentially oscillated from a large or small number of oscillation points is simultaneously received at a small number or a large number of receiving points, and the seismic wave data after the filtering is compared with the small number of 3 or more. Edited into a set corresponding to the oscillation point or receiving point that was obtained, calculate the estimated propagation velocity of the seismic wave in front of the face, and all the seismic observation data received at each receiving point,
Filter processing is performed with various filters such as bandpass, FK, deconvolution, etc., and the edited analysis chart for each group is individually created from the seismic wave data after the filtering and the estimated propagation velocity of the seismic wave. Between the analysis diagrams created individually for each, the similarity between the respective reflection events represented there is compared and collated, and the reflection event determined to have a high similarity and common is extracted as a reflection surface, The geological structure ahead of the tunnel face was estimated based on the extracted reflection surface.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on a cracked andesite,
An example of excavating a tunnel in a ground where a crushed zone or a clay layer exists and exploring the geology in front of and behind the tunnel face will be described in detail with reference to the drawings.

(Measurement Line Arrangement) The measurement lines were arranged on the left and right side walls of the tunnel pit, and an oscillation point and a receiving point were provided (FIG. 1). Oscillation points are set at 24 points (total 46 m) of S1 to S24 at 2 m intervals, and three receiving points (R0, R1, R
2) A total of seven points, one point (R3) at the center of the survey line and three points (R4, R5, R6) at 2 m intervals on the entrance side. Of the receiving points, R0 to R2 are used for the analysis of the tunnel face behind,
R6 was used for analysis in front of the tunnel face, and R3 was used for refraction analysis (calculation of ground velocity) together with these geophones.

(Oscillation) The oscillation of the seismic wave is performed by blasting of dynamite, and the oscillation point is formed by a hole having a height of about 20 cm, a diameter of about 45 mm, and a depth of about 2.0 m on the left and right side walls, and a downward inclination of about 30 °. Drilled at ~ 45 ° (Figure 2).

The vibration receiver was set at a vibration receiving point (FIG. 2) having a depth of about 2.0 m and a diameter of about 45 mm from the side wall.
The geophone was sent in a predetermined direction with an insertion rod, and the packer was inflated and pressed into the hole. As the type of the geophone, a two-component in-hole buried geophone manufactured by the present applicant was used. The measurement components were the tunnel axis direction in the horizontal plane and the direction perpendicular to the tunnel axis. The advantage of this type of geophone is that the influence of the slack area is smaller than that of the pit wall type geophone, so that a high frequency region can be observed and the incident direction of the seismic wave becomes accurate.
It is also easy to install and withdraw. Therefore, the type of the geophone is preferably a type buried in the two-component hole.

After the dynamite was oscillated, the signals received by the respective geophones were digitally recorded in a prospecting machine at the observation headquarters via take-out cables and relay lines. An exploration machine with a wide dynamic range was used so that minute reflected waves could be observed with a high S / N ratio. Recording was started by a trigger from a firearm.

(Data Processing / Analysis) FIG. 3 shows a data processing / analysis flow. Hereinafter, the contents of each data processing / analysis item will be described according to the data processing / analysis flow. In the present embodiment, the front and rear of the tunnel face are searched, but in the description of the data processing and analysis, only the contents of the front search will be described.

(Edit) Seismic waves received by the geophone are arranged by editing the raw seismic data for each geophone, which is a small number of the receiving point and the oscillation point. FIG. 4 shows left survey lines R4, R5,
It shows the result of editing for each R6 geophone. FIG.
The upper, middle, and lower figures show the geophone R
4, raw seismic wave data of two components of R5 and R6.

(Analysis by Refraction Method) In the tunnel HSP method, digital records of seismic waves are transferred from a prospecting machine to a computer for processing, but it is necessary to obtain a static correction amount due to ground velocity and loosening. Therefore, the refraction method was analyzed using the Hagitori method. In the analysis of the refraction method, a travel time curve was created by reading the initial movement arrival time at each receiving point from the measurement record in units of 0.1 msec, and plotting the time on the vertical axis and the distance on the horizontal axis. The above-mentioned travel time curve is not shown in the figure because it is generally used in the seismic survey method. The ground speed ahead of the face obtained from the travel time curve was used at 5.0 km / s, and the static correction amount at the time of analysis was
The delay time, which is the time difference between the travel time curve and the Hagitori line, was used.

(Data processing) In order to detect a reflected wave from the measured digital record, a filter test was performed according to the flow of data processing and analysis shown in FIG. The outline of the data processing is as follows. FIG. 5 shows the results of the data processing.

(1) Frequency Analysis This frequency analysis is performed to examine the frequency component of the seismic wave contained in the original waveform (FIG. 4), and is used as a reference for determining the constant of the band-pass filter. This is done in order to make it data.

(2) Bandpass Filter This bandpass filter is used to remove unnecessary frequency component seismic waves from the original waveform and improve the S / N ratio.

(3) Deconvolution filter In this processing, the seismic wave arrives at the geophone through many geological layers, and the resolution is reduced due to the influence of multiple reflection or scattering due to cracks and the like. Therefore, it was carried out in order to remove multiple reflections and to make the waveform into a pulse to increase the resolution.

(4) FK Filter The observed seismic wave contains a mixture of a direct wave from the earthquake and a target reflected wave. A reflected wave can be extracted by the FK filter.

(5) Migration Seismic waves are sampled at fixed time intervals, and as long as this waveform is used, it is a time section. The migration process uses the seismic wave velocity of the ground rock obtained by the refraction analysis to convert it to a depth (distance) section, in other words,
9 illustrates the position of the reflection surface. As a migration method, a diffraction stack method was used (FIG. 6). In the diffraction stack method, when a virtual reflection point set in a grid on a plane coincides with an ellipse having a focal point at an oscillation point and a reception point within a certain range, the amplitude of the waveform at that time is averaged, and this amplitude is calculated. This is a method of finding the reflection surface (point) from the distribution and estimating the geological structure. The time-to-distance conversion is as follows. At time (tn), the distance (Dn) from the blasting point to the reflecting point to the receiving point is represented by Dn = Vp × tn using the P-wave velocity (Vp). When it matches a point on the grid, its amplitude is added. The indication of the diffraction stack (mapping) method is positive (hard to soft) so that the polarity of the amplitude can be understood.
○ and negative (soft → hard) ●. Also, the magnitude of the amplitude was made to be proportional to the diameter of the circle.

(Extraction of Reflection Surface) In tunnel HSP exploration, it is important to extract a reflection surface. The procedure for extracting the reflecting surface is shown below, and FIG. 7 shows an example of extracting the reflecting surface. (1) An analysis result diagram (hereinafter referred to as an “analysis diagram”) of the geophones R4, R5, and R6 (left survey line) is output. (2) Specify the reflection event as a reflection surface from the analysis diagram of each geophone. (3) The specified reflection event is commonly displayed in the analysis diagram of another geophone, and when the similarity of the same reflection event is high, it is extracted as a reflection surface. (4) An analysis diagram having the most common reflection surface is selected, the character of the reflection event as a reflection surface is read on the selected analysis diagram, and an appearance prediction position is drawn. (5) Extend a straight line tangent to the reflecting surface until it intersects the tunnel axis. The point where the straight line intersects with the tunnel axis is
This is the predicted location of the stratum tunnel appearance.

(Notes on Extraction) When extracting each reflection event appearing on each of the geophones as a reflection surface, attention was paid to the following points. (1) The reflection intensity indicates the amplitude intensity at a virtual reflection point by the size of ● or ○. In the above symbols, ● represents the subtraction (minus) of the reflection amplitude,
○ indicates the push (plus) of the reflection amplitude. (2) The reflection surface is a portion which is continuous on a straight line or a circular arc of a reflection point. (3) If the reflection surface is not at the same position in another analysis diagram, it is not specified as a reflection surface. If at least two of the analysis diagrams are common, they are specified as reflection surfaces. (Acquisition of basic evaluation data) (1) Evaluation index for each reflection event Each reflection event in each analysis chart has three levels of evaluation indexes, for example, large, based on the continuity and size of each reflection point in each analysis chart. ,
Give medium and small indicators. The analyst can evaluate the suitability of the reflection surface extraction and the properties of the reflection surface using this index as basic data. (2) Predictability of prediction The evaluation index given in each analysis diagram is converted into a score, for example, three points, two points, and one point for large, medium, and small evaluation indices, respectively.
Points, etc., for each reflection event of each analysis chart extracted as a reflection surface, the points of the three analysis charts are summed, and the reliability of geological structure prediction based on the magnitude of the total points, for example, AA,
Classify according to A, B, C, etc. The analyst can evaluate the suitability of the reflection surface extraction and the properties of the reflection surface using the certainty of the predicted geological structure prediction as basic data.

(Tunnel HSP search result) Tunnel H
FIG. 8 shows the analysis results of the SP method. In this figure, it is predicted that the geological structure exists at the position where a circle is attached to the number and which intersects with the tunnel pit from the extracted reflection surface. The following table summarizes the results of comparing these predictions with the geological structures revealed after excavating the tunnel. As summarized in this table, out of the twelve places where the existence of the geological structure was predicted, there were nine places where the geological structure actually existed and which was suitable for the reflection surface extraction. In addition, although there was actually a geological structure, there was one unextracted point where the existence could not be predicted. Contrary to this, despite the fact that the geological structure did not actually exist, There were two mis-extractions that had been predicted. However, it is probable that no extraction at the 412m point could not be detected as a reflection surface because the fault clay that later appeared on the tunnel face was not distributed and continuous. In addition, the erroneous extraction at the 367m point is presumed that the geological structure is not continuous, and the erroneous extraction at the 436m point incorrectly sets the angle of the reflecting surface and is 3m closer to the actual geological structure appearance position. It is thought that was predicted.

From the above results, it can be said that the prediction of the appearance of the geological structure by the geological survey method in front of the tunnel face is much more suitable than the conventional tunnel HSP method.

(Modification of Embodiment) Regarding the measurement line arrangement In this embodiment, the measurement lines are arranged on the left and right side walls of the tunnel pit. However, the measurement lines may be arranged on the top and bottom of the tunnel mine. In addition, when the running inclination of the geology is known in advance by investigation, or when the geology is not so complicated, one survey line may be used.

In this embodiment, the oscillating source is dynamite. However, an oscillating source other than an explosive, such as a hammer strike, does not affect the exploration result. The order of oscillation is not necessarily S
It is not necessary to perform the steps from 1 to S24, and the steps may be performed in a random manner. However, in order to check the quality of observation data at the data collection site, it is preferable to have a certain order of oscillation.

In the present embodiment, three points (R0 to R2) are provided at 2 m intervals on the face side, one point (R3) is provided at the center of the survey line, and three points are provided at 2 m intervals on the entrance side. A total of 7 points (R4 to R6) are installed, but 3 points on the face side
The number of points may be reduced and only the front of the tunnel face may be searched. In this case, the receiving point is located on the opposite side of the search direction of the oscillation point, so that a directional receiver can be placed far away from the reflecting surface, and the influence of the incident direction of the reflected wave can be further reduced. Is good. Further, the receiving point may be provided only on the search direction side of the oscillation point. In short, it may be arranged so that seismic waves are received at a plurality of receiving points.

Further, in this embodiment, the type of the geophone is a buried type in a pit, but it may be a pit type installed on a pit wall. However, in this case, generally, in the tunnel tunnel, after excavation, a loose area is generated around the tunnel wall due to stress release etc. Therefore, considering the accuracy of analysis and speeding up processing, it is preferable to use the underground type. Is as described above. In addition, there are three types of geophones with respect to the measurement components, namely, a single component, a two component, and a three component. However, it is desirable to measure two or more components so that the incident direction of the seismic wave can be accurately grasped. However, it is sufficient to grasp the two component wave motions in the direction of the tunnel axis and in the direction perpendicular to the tunnel axis in the horizontal plane for the analysis of the actual exploration ahead of the tunnel face. For this reason, the measurement components of the geophone are two components in this embodiment, but may be a single component or three components.

Further, in the present embodiment, the number of the receiving points and the number of the oscillation points are small in the present embodiment, but the number of the receiving points is large and the number of the oscillation points is small. Is also good. In this case, it is necessary to edit the raw seismic data described above for each oscillation point.

[0034]

According to the first aspect of the present invention, the seismic wave data is edited into a set corresponding to the number of oscillation points or reception points having a small number of three or more, and the seismic wave data after filtering and the estimation of the seismic waves are estimated. From the propagation speed, an analysis diagram for each of the edited sets is individually created. Therefore, for example, in the case of the small receiving point / multiple oscillating point system of the present invention, an analysis chart is created for each receiving point. Then, between a plurality of analysis diagrams individually created for each vibration receiving point, the similarity of each reflection event represented there is compared and collated,
Since the reflection events that are determined to have high similarity and are common are extracted as reflection surfaces, the criteria for extraction can be clarified, the variation in results due to differences in analysts is minimized, and who extracts the reflection surfaces Therefore, the reproducibility of obtaining the same result can be improved, and a geological exploration method in front of the tunnel face having excellent exploration accuracy can be achieved.

According to the second aspect of the present invention, for example, two analysis diagrams in which the receiving points are adjacent to each other are similar and the analysis results are similar, so that the similarity between the two reflection events is compared. By performing the collation, the accuracy of extraction as a reflection surface can be further improved as compared with the invention according to claim 1.

According to the third aspect of the present invention, an evaluation index is given to each reflection event of each analysis diagram extracted as a reflection surface based on its continuity and size. The size of the basis extracted as can be objectively and clearly grasped.

According to the fourth aspect of the present invention, the evaluation index given in each analysis diagram is converted into a score, and for each reflection event of each analysis diagram extracted as a reflection surface, the scores of all the analysis diagrams are summed. Since the classification is performed according to the certainty of the prediction based on the magnitude of the total score, the magnitude of the basis for extracting the reflection event as a reflection surface and the certainty of the prediction of the geological structure are compared with those of the invention according to claim 3. And can be more objectively and clearly understood.

The work of setting the oscillation point is lighter than the work of setting the vibration receiving point. Further, there is no difference in the analysis result between the small receiving point / multiple oscillation point method and the multiple receiving point / multiple oscillation point method. Therefore, according to the fifth aspect of the invention, the number of vibration receiving points is reduced, so that the workability is excellent.

According to the sixth aspect of the present invention, since the survey lines are arranged in a plurality of rows, it is possible to perform a search over a wide area in front of the tunnel face, so that the search accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a survey line layout diagram of a tunnel forward exploration according to the present invention.

FIG. 2 is a cross-sectional view orthogonal to a tunnel axis, showing a geophone arranged in a survey line and a state of drilling of an oscillation point.

FIG. 3 is a flowchart of seismic wave data processing / analysis.

FIG. 4 is raw seismic wave component observation data of the geophones R4 to R6 on the left survey line.

FIG. 5 shows a data processing result of raw seismic wave observation data (left surveying geophone R4).

FIG. 6 is a conceptual diagram of a diffraction stack method, which is a kind of migration method.

FIG. 7 shows a geophone R4 on the left survey line in order from the top,
It is an analysis figure of R5 and R6.

FIG. 8 is a diagram showing an analysis result of a geological survey method in front of a tunnel face.

FIG. 9 is a flowchart illustrating a process of extracting each reflection event as a reflection surface and evaluating the extracted reflection surface.

FIG. 10 is a diagram showing a result of evaluating an extracted reflection surface.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akiyoshi Tsuchiya 1-8-9 Kameido, Koto-ku, Tokyo Sanko Consultant Co., Ltd. (72) Koji Morimoto 1-8-9 Kameido, Koto-ku, Tokyo Sanko -Consultant Co., Ltd. F-term (reference) 2D054 GA15 GA17 GA74 GA97

Claims (6)

[Claims] 1. A measuring line composed of a plurality of oscillation points separated from each other and a plurality of vibration receiving points separated from each other is arranged in a tunnel pit, and a seismic wave oscillated from the oscillation point is received at the vibration receiving point and received. In the method of exploring the geology in front of the tunnel face by analyzing a seismic wave, one of the oscillation point and the reception point is set to a small number of 3 or more, and the other is set to a large number, and Sequentially oscillated seismic waves are received simultaneously at a small number or a large number of receiving points, and the received seismic wave observation raw data is edited into a set corresponding to the oscillating points or the receiving points with the minority of 3 or more, The estimated propagation velocity of the seismic wave ahead of the face is obtained, and the edited seismic wave data is filtered by various filters such as bandpass, FK, deconvolution, etc. From the seismic wave data after the data processing and the estimated propagation velocity of the seismic wave, individually create an analysis chart for each of the edited sets, and, among the analysis charts individually created for each of the sets, each represented in the analysis chart. Comparing and comparing the similarities between the reflection events of the above, extracting the reflection events determined to have a high degree of similarity as common as the reflection surface, and estimating the geological structure in front of the tunnel face based on the extracted reflection surface. Characteristic geological exploration method in front of tunnel face. 2. The method according to claim 2, wherein the oscillating point or the receiving point having a small number of 3 or more is adjacent to each other in the edited analysis diagram for each group.
2. The tunnel face according to claim 1, wherein similarities between the respective reflection events shown in the analysis diagrams are compared and collated, and a reflection event determined to have a high degree of similarity and to be common is extracted as a reflection surface. Forward geological exploration method. 3. The suitability of the reflection surface extraction and the properties of the reflection surface are evaluated by giving an evaluation index to each reflection event of each analysis diagram extracted as the reflection surface based on its continuity and size. 3. The geological exploration method in front of a tunnel face according to claim 1, wherein basic data for performing the operation is obtained. 4. The evaluation index given in each analysis chart is converted into a score, and for each reflection event of each analysis chart extracted as the reflection surface, the scores of all the analysis charts are summed, and the total score is calculated. 4. The geological exploration method in front of a tunnel face according to claim 3, wherein basic data for evaluating the suitability of the reflection surface extraction and the properties of the reflection surface are obtained by classifying the reflection surface based on the certainty. 5. A geological exploration method in front of a tunnel face according to claim 1, wherein the number of receiving points is a small number equal to or greater than three. 6. The geological exploration method in front of a tunnel face according to claim 1, wherein said survey lines are arranged in a plurality of rows.