JP4743416B2 - Geological boundary judgment method around existing tunnel - Google Patents

Description

  The present invention relates to a method for estimating a geological boundary of a ground around a tunnel using an elastic wave (S wave) using an existing tunnel mine. Although this technology is not particularly limited, it is useful for estimating the geological structure around shield tunnels of medium and small diameters (diameters of about 5 m or less) for electric power and communication embedded in unconsolidated ground. .

  When constructing a tunnel, a boring survey is carried out from the ground surface at the planning and design stages to understand the geological structure around the tunnel. If the existing tunnel has deteriorated over time, geological information in the vicinity of the deformed part is required, but it may not match the location where the boring survey was conducted at the planning or design stage. In such a case, it is necessary to confirm the geological properties in the vicinity of the deformed portion. Also, in tunnels with an older construction year, the results of geological surveys at the planning or design stage may not necessarily match the current technical level, so in order to obtain the information necessary for maintenance, a new geological survey will be conducted after operation. It may be necessary to do so. In such a case, as for the method of grasping the geology around the tunnel, the current technology has only a boring survey, and in some cases, it is necessary to carry out a boring survey even after the tunnel is used.

  Boring surveys can grasp the exact geological properties, but the geology between the drilled points must be supplemented in consideration of the surrounding topography. For this reason, it cannot be said that the small buried valleys are accurately grasped. If the interval between the boring positions is reduced, the accuracy of the survey will increase, but the cost will increase significantly. Boring surveys need to be conducted from the ground surface. Depending on the surrounding environment such as traffic conditions on the road and the presence of existing buried objects, construction may not be possible at the necessary points. Also, in the case of a submarine tunnel, boring may not be possible, and even if boring is carried out, the survey cost increases greatly and is difficult to implement. For this reason, there is a need for the development of a technology that enables accurate geological surveys of buried valleys, etc., without being affected by environmental conditions such as on the road, and enables easy geological surveys of the seabed.

An elastic wave exploration method has been proposed as a method other than boring for investigating the geological situation around an existing tunnel (see Patent Document 1). In general, the elastic wave exploration method is a method in which a large number of geophones are arranged in an array along a survey line on the ground surface, and the reflected waves from the underground are measured and analyzed by hitting the ground. In this case, since only the reflected wave from the underground, the underground structure can be explored accurately. The method described in the above-mentioned Patent Document 1 applies this technique to measurement in a tunnel. A large number of geophones are arranged in the tunnel tunnel, and the tunnel tunnel is struck by a vibration device. Certainly, in principle, the reflected wave can be detected by the geophone. However, it is difficult to efficiently propagate elastic waves to the surrounding ground by simply hitting the tunnel mine with a seismic device. Also, since the tunnel is surrounded by the ground unlike the ground, there are not only reflections from the formation below the tunnel but also reflections from the formation above the tunnel. It is difficult to specify the position of the reflecting surface only by arranging them. Under these circumstances, it is generally difficult to correctly grasp the formation status.
Japanese Patent Laid-Open No. 2002-156459

  The problem to be solved by the present invention is to make it possible to accurately and continuously estimate the geological boundary of the ground around the tunnel using an elastic wave (S wave) using an existing tunnel mine. Another problem to be solved by the present invention is to provide a new geological survey method capable of easily grasping the geological condition around the tunnel without performing a costly boring survey, and thus even in a submarine tunnel.

In the present invention, a large number of upper and lower geophones are arranged in an array at predetermined intervals along both the upper and lower sides of the tunnel mine buried in the unconsolidated ground , An S-wave seismic device that generates elastic waves containing low-frequency components is installed in the lower part of the tunnel pit, and a vibrator is vibrated at one point of the tunnel using the S-wave seismic device. Elastic waves are propagated to the ground, and the reflected waves from the upper and lower strata boundaries around the tunnel are detected and recorded simultaneously by both the upper and lower geophones, and the upper and lower geophones analyzing the position of the reflecting surface from the arrival time of the detected reflected wave by, the reflective surface is a tunnel by arrival time difference corresponding to the same vibration to the upper geophones and lower geophone and tunnel diameter portion of the reflected wave detected by the To estimate the position in any of the upper and lower portions, an existing tunnel near geologic boundary determination method characterized by identifying a geologic boundary position.

  As the S-wave seismic device, for example, a seismic device that generates S waves mainly including a frequency component of 30 to 40 Hz is used. The existing tunnel is, for example, a shield tunnel having a diameter of about 5 m or less embedded in unconsolidated ground for electric power or communication.

  The geological boundary determination method around the existing tunnel according to the present invention is that the entire tunnel becomes a source of vibration by causing one point of the tunnel to vibrate with an S-wave seismic device, and elastic waves are efficiently generated in a concentric circle around the tunnel. Can be propagated in. Then, the reflected waves from the ground around the tunnel are detected and recorded by both the upper and lower geophones, and the geology above and below the tunnel is analyzed by analyzing the arrival times of the reflected waves detected by the upper and lower geophones. The boundary can be specified accurately.

  FIG. 1 shows an example of a method for determining a geological boundary around an existing tunnel according to the present invention. The existing tunnel shown in this example is typically a shielded tunnel having a diameter of about 5 m or less for power or communication embedded in unconsolidated ground such as soft ground on the seabed. A large number of upper geophones 12a and lower geophones 12b are arranged in an array at predetermined intervals along both the upper and lower sides of the tunnel 10 tunnel. Here, for example, the upper geophone 12a and the lower geophone 12b are arranged over about 100 m at intervals of 2 m. At the same time, an S-wave seismic device 14 for generating an elastic wave including a low-frequency component is installed in the lower part of the tunnel 10 well. As the S wave seismic device 14, a seismic device that generates an S wave that can sweep the frequency in the range of 10 to 100 Hz is used.

When the S-wave shaking device 14 vibrates a vibrator at one point in the shield tunnel 10 at a low frequency (mainly 30 to 40 Hz, depending on the size of the tunnel and the surrounding ground, etc.), the entire tunnel is raised. It becomes an epicenter, and elastic waves propagate through the ground around the tunnel concentrically through a strong segment from inside the tunnel. This has been confirmed by simulation. It is considered that such elastic waves propagate outside the tunnel because the surrounding area of the tunnel is unconsolidated ground and the ground is in close contact with the strong segment of the shield tunnel. By the way, in the hitting earthquake using kayak, vibration of a relatively high frequency is mainly used, and even if the segment is hit directly, the elastic wave hardly propagates outside the tunnel.

  If there is a geological boundary in the ground around the tunnel, the elastic wave is reflected at the geological boundary, and the reflected wave reaches a large number of the upper geophone 12a and the lower geophone 12b, and the upper geophone 12a and the lower geophone 12b Both are detected and recorded simultaneously. In the present invention, by analyzing the arrival times of the reflected waves detected by the large number of upper geophones 12a and lower geophones 12b, it is specified where and how the geological boundary is located.

  As shown in FIG. 2A, when a horizontal invert 16 (portion where an operator etc. walks) is provided at the lower part of the tunnel 10 tunnel, an S-wave seismic device 14 is installed on the invert 16. do it. If a horizontal invert or the like is not provided in the lower part of the tunnel tunnel, it is difficult to install the S-wave seismic device as it is. Therefore, as shown in FIG. 2B, a wooden plate 20 is horizontally passed to the lower part of the tunnel 10 tunnel via rubber plates 18 on both sides, and the S-wave seismic device 14 is installed thereon. There may be a space below the wooden plate 20. In this manner, when the earthquake is generated by the S-wave vibration device 14, the entire shield tunnel 10 is shaken as indicated by the arrow, and an elastic wave can be generated from the inside through a strong segment, and the reflected wave from the geological boundary Can be observed clearly. These things have been confirmed experimentally.

  By the way, unlike the elastic wave exploration on the ground surface as described above, it is difficult to specify the position and state of the geological boundary because the shield tunnel is surrounded by the ground. However, as in the present invention, if geophones are installed at both the upper and lower parts in the shield tunnel and the reflected waves from the surrounding geological boundary are received by both the upper and lower geophones, By using these two methods, the arrival direction of the reflected wave can be specified.

  The geophone installed in the upper part of the shield tunnel is sensitive to the reflected wave from the upper part of the shield tunnel, and the geophone installed in the lower part of the shield tunnel is sensitive to the reflected wave from the lower part of the shield tunnel. High sensitivity. As shown in FIG. 3, in the vicinity of the experimental site, the geological structure is almost the Heisei layer, and the shield tunnel has an upward slope from the start point to the end point. Under these geological conditions, the time section created by recording the upper geophone (the vertical axis is the cross-sectional view expressed by the arrival time of the reflected wave from the reflecting surface) is the arrival time of the reflected wave from the origin side to the end point side. In the time section created by recording the lower geophone, it is assumed that the arrival time of the reflected wave is longer on the end point side than on the start point side.

  FIG. 4 shows the result of actual measurement by simultaneous vibrations of the upper and lower geophones. A is a time section created by recording the upper geophone, and B is a time section created by recording the lower geophone. Each has a clear reflecting surface (indicated by an arrow). In the time section created by recording the upper geophone (A in FIG. 4), the arrival time of the reflected wave is shorter from the start side to the end point side. On the other hand, in the time section (B in FIG. 4) created by the recording of the lower geophone, the arrival time of the reflected wave is longer from the start side to the end point side. From these results, the relative inclination between the reflecting surface and the shield tunnel can be obtained from the analysis of the time section created by recording the upper and lower geophones.

  The geophone installed in the upper part of the shield tunnel receives the reflected wave from the upper part of the shield tunnel earlier than the geophone installed in the lower part of the shield tunnel by the tunnel diameter. The measured results are shown in FIG. A is a time section created by recording the upper geophone, and B is a time section created by recording the lower geophone. Each reflecting surface indicated by an arrow has an arrival time difference Td corresponding to the tunnel diameter. Therefore, as shown in FIG. 5, the reflecting surface corresponding to the geological boundary is a time section (A in FIG. 5) created by the recording of the upper geophone and a time section (B in FIG. 5) created by the recording of the lower geophone. ) If found earlier, it can be assumed that this reflective surface is due to a geological boundary located above the shield tunnel.

  As described above, the geological boundary position can be specified from the analysis of the time section by the upper and lower geophones. In particular, if the upper and lower geophones are detected at the same time during an S-wave earthquake, the exact same vibration will be observed by another geophone array, and even the phase difference of the reflected waves can be measured, resulting in measurement accuracy. Will improve.

  FIG. 6 is an explanatory diagram showing an analysis procedure for discriminating the geological boundary around the tunnel from the time section by the upper and lower geophones. By operating the S-wave seismic device in the shield tunnel, the entire tunnel becomes a source of vibration, and elastic waves propagate concentrically around the tunnel into the surrounding ground. The reflected waves from the ground around the tunnel are detected simultaneously by both the upper and lower geophones, and a time section is created by recording the waves. According to the results of the experiment, it was found that a unique reverberation sound that hinders exploration was generated due to the shape of the tunnel. However, it has also been found that this reverberant sound can be removed by appropriate filtering (two-dimensional filter, frequency filter (LPF), etc.), thereby improving the quality of the time section. 6A is a time section created by recording the upper geophone after filtering, and FIG. 6B is a time section created by recording the lower geophone after filtering. The reflective surface becomes clear by the filtering process.

  First, in consideration of the positional relationship of the reflecting surface, the vertical axis of the time section of the upper and lower geophones is converted into depth (distance from the shield tunnel) using the existing S wave velocity. C in FIG. 6 is a depth cross section recorded by the upper geophone. Here, since the shield tunnel is inclined, the reflection surface from the horizontal geological boundary is observed to be inclined. In FIG. 6C, since the depth represents the distance from the shield tunnel (that is, the distance from the tunnel upward), the upper and lower sides are inverted (D in FIG. 6). E in FIG. 6 is a depth cross section recorded by the lower geophone. Also in this case, since the shield tunnel is tilted, the reflection surface from the horizontal geological boundary is tilted and observed.

  Therefore, considering the shape of the shield tunnel, a depth sectional view of the entire tunnel periphery is created from D and E in FIG. 6 (F in FIG. 6). In FIG. 6F, ground information (soil name and S wave velocity) based on past data is shown side by side. From the created depth cross-sectional view, the geological boundary located at the top and bottom of the shield tunnel is considered as a clear reflection surface, and the reflection surface is horizontal considering the inclination of the shield tunnel. It is confirmed that it is consistent with the existing geological structure.

  The above embodiment is an example applied to a shield tunnel having a small and medium diameter, but the present invention can also be applied to the identification of a geological structure around other general tunnels.

Explanatory drawing which shows an example of the geological boundary discrimination method around the existing tunnel which concerns on this invention. Sectional drawing which shows the example of the installation condition of the S wave seismic device in a tunnel mine. Explanatory drawing which shows the example of the arrival path | route of a reflected wave. The figure which shows an example of the time cross section created by the recording of the upper and lower geophone. The figure which shows the other example of the time cross section created by the recording of the upper and lower geophone. Explanatory drawing of the analysis procedure which discriminates the geological boundary around a tunnel from a time section.

Explanation of symbols

10 Tunnel 12a Upper geophone 12b Lower geophone 14 S wave vibration device

Claims (3)

A large number of upper and lower geophones are arranged in an array at predetermined intervals along both the upper and lower parts of the tunnel mine buried in the unconsolidated ground, and the lower part of the tunnel mine acoustic waves in the S wave OkoshiShin device for generating an elastic wave including a low-frequency component is installed, the ground of the tunnel near the entire tunnel as caused hypocenter by vibrator OkoshiShin one point of the tunnel by the S-wave OkoshiShin device , And the reflected waves from the upper and lower strata boundaries around the tunnel are detected and recorded simultaneously by both the upper and lower geophones, and the reflection detected by the upper and lower geophones. analyzing the position of the reflecting surface from the wave arrival time, the same vibration by arrival time difference corresponding to the upper geophones and lower geophone and tunnel diameter portion of the reflected wave detected by the reflective surface of the upper and lower portion of the tunnel To estimate the position on the shift, geological boundary determination methods around existing tunnels and identifies a geological boundary position. As S-wave OkoshiShin device, geological boundary determination method of the existing tunnel near claim 1 Symbol placement using OkoshiShin device that generates S wave including mainly the frequency components of the 30～40Hz. The method of determining a geological boundary around an existing tunnel according to claim 1 or 2 , wherein the tunnel buried in the unconsolidated ground is a shield tunnel.

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