JP7190015B2

JP7190015B2 - Face forward exploration method

Info

Publication number: JP7190015B2
Application number: JP2021166601A
Authority: JP
Inventors: 匡志中谷; 和弘大沼; 浩之山本
Original assignee: Hazama Ando Corp
Current assignee: Hazama Ando Corp
Priority date: 2017-10-20
Filing date: 2021-10-11
Publication date: 2022-12-14
Anticipated expiration: 2037-10-20
Also published as: JP2022000666A; JP7005272B2; JP2019078549A

Description

本発明は、トンネル等の掘削施工に際し、切羽前方の地質構造の予測に使用する切羽前方探査方法に関する。 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a face front exploration method used for predicting the geological structure in front of a face when excavating a tunnel or the like.

山岳トンネルを掘削するにあたり、切羽前方に拡がる地山の性状を適切かつ高い精度で把握することは、支保工を含めた掘削工事全体を効率よくかつ安全に進めていく上で重要である。 When excavating a mountain tunnel, it is important to properly and accurately grasp the properties of the ground that spreads out in front of the face in order to proceed with the entire excavation work, including the shoring, efficiently and safely.

近時のトンネルの掘削施工では、１点の発振点から地山に弾性波を発生させ、反射面での反射波を坑口近傍に位置する複数の受振点で受振するＨＳＰ（Horizontal Seismic Profiling）法や、探査用の発破を行い、この発破による弾性波を地震計により計測し、この計測した弾性波により切羽前方の地質変化を推定するＴＳＰ（Tunnel Seismic Prediction）法など、弾性波（弾性波反射法）を用いた切羽前方探査の技術が広く利用されている。 In tunnel excavation construction in recent years, the HSP (Horizontal Seismic Profiling) method is used to generate elastic waves in the ground from a single oscillation point and receive the reflected waves at multiple receiving points located near the tunnel entrance. and elastic waves (elastic wave reflection method) is widely used.

この種の弾性波反射法を用いた切羽前方探査方法が特許文献１により提案されている。
この切羽前方探査方法を図１０に示している。この切羽前方探査方法では、複数の受振器がトンネル壁面付近に設けられ、切羽掘削のための発破や掘削ドリル等により生じ、切羽前方の不連続面に反射して戻ってくる波形を測定する。 Japanese Patent Application Laid-Open No. 2002-300000 proposes a method for probing the face forward using this type of elastic wave reflection method.
FIG. 10 shows this face forward searching method. In this face front detection method, a plurality of geophones are installed near the tunnel wall surface to measure waveforms generated by blasting and excavation drills for face excavation and reflected back from the discontinuous surface in front of the face.

この手法では、まず、切羽Ｔ１から離れたトンネルＴの壁面の左右に、ドリル等で穴Ｈを空け、それぞれに複数の受振器Ｓ（受振点）を設置する。この場合、例えば、左右に４個ずつ受振器Ｓを設置する。さらにその後方のトンネルＴの壁面上に複数の受振器Ｓを設置する。この場合、複数の受振器ＳをトンネルＴの壁面の円周上に設置する。例えば、円周上の５個の受振器Ｓは、水平ラインの両端に２個、垂直ラインの上端に１個、その間に２個配置する。また、この場合、受振器Ｓはかぎ型プレートを用いてトンネル壁面に取り付ける。かぎ型プレートは受振器取付部と台部からなり、台部には中央にアンカ用に穴が設けられ、受振器取付部には中央に受振器用の穴が設けられる。トンネルＴの壁面にアンカ用にドリルで穴を空け、かぎ型プレートの台部を穴に合わせて設置し、アンカを穴に設置して、岩盤に連結する。アンカは、アンカの周りの壁面をグラウトで固め、ねじで締め付け、トンネルＴの壁面に固定する。そして、受振器取付部の穴に受振器Ｓを取り付ける。 In this method, first, holes H are drilled on the left and right sides of the wall surface of the tunnel T away from the face T1, and a plurality of geophones S (receiving points) are installed in each hole. In this case, for example, four geophones S are installed on each side. Furthermore, a plurality of geophones S are installed on the wall surface of the tunnel T behind it. In this case, a plurality of geophones S are installed on the circumference of the tunnel T wall surface. For example, the five geophones S on the circumference are arranged two at both ends of the horizontal line, one at the top of the vertical line, and two in between. In this case, the geophone S is attached to the tunnel wall using a hooked plate. The hook-shaped plate consists of a geophone mounting portion and a base portion. The base portion has an anchor hole in the center, and the geophone mounting portion has a geophone hole in the center. A hole for the anchor is drilled in the wall surface of the tunnel T, the pedestal of the hook-shaped plate is placed in alignment with the hole, the anchor is placed in the hole, and connected to the bedrock. The anchor is fixed to the wall of the tunnel T by grouting and screwing the wall around the anchor. Then, the geophone S is attached to the hole of the geophone attachment portion.

次に、切羽掘削のため発破、ブレーカー、掘削ドリル等で振動を与え、振動波を発生させる。この際の発破、ブレーカー、掘削ドリル等の振動が発生するポイントが発振点である。
このようにして切羽掘削により発生する発振点から振動を発生し、切羽前方の断層に反射してトンネルＴ内へ戻ってくる振動波を、トンネルＴの壁面の複数の受振器Ｓで測定する。複数の発振点と複数の受振器Ｓの組み合わせから数多くの測定波を得る。 Next, for face excavation, vibration is applied by blasting, a breaker, an excavating drill, or the like to generate vibration waves. The oscillation point is the point at which vibration occurs in blasting, breaker, excavating drills, and the like.
A plurality of geophones S on the wall of the tunnel T measure vibration waves that are generated from the oscillation point generated by the face excavation in this way, reflected by the fault in front of the face and returned into the tunnel T. A large number of measurement waves are obtained from a combination of a plurality of oscillation points and a plurality of geophones S.

そして、次の処理手順により、切羽前方の地質構造を推定する。
まず、発振点から受振点に伝播した直接波を利用してトモグラフィ解析を行う。受振点で測定された直接波のデータを格納したデータ収集装置は取り外され、パーソナルコンピュータに接続される。パーソナルコンピュータ上でデータ収集装置から読み出された直接波のデータに基づいてトモグラフィ解析を行う。トモグラフィ解析を行うことにより、発振点と受振点間の地盤の速度分布を算出する。トンネルＴの地質状況と、発振点、受振点間の地盤の速度分布から切羽前方地盤の速度分布を仮定する。
次に、発振点と受振点を含む切羽前方に格子点を設定する。
続いて、仮定された速度分布を用いて、発振点から格子点で反射され受振点までの理論的伝播時間を算出する。
次いで、格子点毎に、該格子点を介する複数の前記受振点で測定された波形に対して、前記理論的伝送時間だけシフトさせ、この波形の振幅をすべて足し合わせる。
そして、足し合わせた波形の振幅に基づいて、振幅が正の値でその絶対値が大きい格子点を堅岩部として前記振幅が負の値でその絶対値が大きい格子点を弱層部として、地質を推定する手段と地質を推定する。 Then, the geological structure ahead of the face is estimated by the following procedure.
First, tomographic analysis is performed using the direct wave propagated from the oscillating point to the receiving point. A data acquisition device storing direct wave data measured at the receiving point is removed and connected to a personal computer. Tomographic analysis is performed on a personal computer based on the direct wave data read out from the data acquisition device. By performing tomographic analysis, the velocity distribution of the ground between the oscillation point and the receiving point is calculated. Based on the geological conditions of the tunnel T and the velocity distribution of the ground between the oscillation point and the receiving point, the velocity distribution of the ground ahead of the face is assumed.
Next, grid points are set in front of the face including the oscillation point and the receiving point.
Subsequently, using the assumed velocity distribution, the theoretical propagation time from the oscillating point to the receiving point after being reflected by the grid points is calculated.
Next, for each grid point, the waveforms measured at the plurality of receiving points passing through the grid points are shifted by the theoretical transmission time, and all the amplitudes of the waveforms are summed.
Then, based on the amplitudes of the summed waveforms, grid points with a positive amplitude and a large absolute value are defined as solid rock portions, and grid points with a negative amplitude and a large absolute value are determined as weak layers. Means to estimate and estimate the geology.

このようにこの切羽前方探査方法では、トンネル坑内で人工的に発生させた地震波の切羽前方の反射面で鏡面反射した反射波を検出し、この反射波データを用いて切羽前方の地質変化を推定する。坑壁埋設型の多成分受振器を用いたことで、地震波の入射方向が正確となり、切羽前方の反射面の推定精度を向上させることができる。 In this way, in this face front prospecting method, seismic waves that are artificially generated in the tunnel tunnel are specularly reflected by the reflection surface in front of the face, and the reflected waves are detected. do. By using the tunnel wall-buried multi-component geophone, the incident direction of seismic waves becomes accurate, and the estimation accuracy of the reflection surface in front of the face can be improved.

特開２００１－９９９４５公報Japanese Patent Application Laid-Open No. 2001-99945

しかしながら、上記従来の切羽前方探査方法（以下の説明で、手法３という。）では、切羽から離れたトンネルの壁面の左右にドリル等で穴を空け、左右の岩盤内部に複数の受振器を設置し、また、実際の施工においては、トンネル壁面から深度４ｍ程度の削孔を行い、穴に受振器を設置した後、グラウト等により岩盤と受振器を一体化する必要があり、このため、受振器の設置に際して、大掛かりな準備作業を必要とし、また、切羽周辺が占有されるために、通常のトンネルの施工作業を中断しなければならない、という問題がある。 However, in the above-mentioned conventional face front prospecting method (referred to as method 3 in the following explanation), holes are drilled on the left and right sides of the tunnel wall away from the face, and multiple geophones are installed inside the left and right rock masses. In addition, in actual construction, it is necessary to drill a hole to a depth of about 4m from the tunnel wall, install the geophone in the hole, and then integrate the rock and the geophone with grout. There is a problem that a large amount of preparatory work is required for installation of the vessel, and that normal tunnel construction work must be interrupted due to the occupancy of the face area.

本発明は、このような従来の問題を解決するものであり、この種の切羽前方探査方法において、トンネル坑内に地震計を大掛かりな準備作業を不要として簡易に設置できるようにすること、しかも、地震計の簡単な設置でありながら、切羽前方の反射面の３次元的な分布状況や反射面位置の出現する方向を精度よく推定できるようにすること、を目的としている。 The present invention is intended to solve such conventional problems, and in this kind of face forward prospecting method, it is possible to easily install a seismometer in a tunnel pit without requiring large-scale preparatory work, and furthermore, The objective is to make it possible to accurately estimate the three-dimensional distribution of reflecting surfaces in front of the face and the direction in which the reflecting surfaces appear, while the seismometer is simply installed.

本発明（１）の切羽前方探査方法は、
トンネル内に地震計を設置し、トンネル内で地震波を発生させてトンネル切羽前方の地質境界面で反射した反射波を前記地震計により受振し、前記反射波の波形データを既知の解析処理により解析を行って前記反射波の反射面位置を計測することにより、切羽前方の地質境界面を推定する切羽前方探査方法において、
地震計として、複数の受振センサーを用い、
複数のロックボルトを、少なくともトンネルの坑壁面の天端、左右側壁にそれぞれ、前記各ロックボルトの一端から相互に異なる方向へ前記坑壁面に対して直交又は斜交させて打ち込み、前記各ロックボルトの他端を前記坑壁面上に残して前記ロックボルトの他端の他端面を受振センサー取付部とし、
前記複数の受振センサーを前記坑壁面に打ち込んだ前記各ロックボルトの受振センサー取付部に前記ロックボルトの長軸方向の指向性を有する単成分センサーとして取り付けて、前記各受振センサーの組み合わせにより、多成分受振センサーとして設置し、
前記各受振センサーにより捉える前記各ロックボルトを伝播する地震波から前記各ロックボルトの長軸方向の振動を取得して、当該取得した前記各ロックボルトの長軸方向の一成分の波形データをデータ処理して前記各波形データからフィルタ処理により得られる中心周波数を含む特定の周波数領域に限定して当該特定の周波数領域の計測波形を取り出し、当該個々の計測波形から初動波形と同様の特徴を有する反射波の波形を抽出して、当該各反射波の走時差に基づいて、当該各反射波の反射面位置を計測する、
ことを要旨とする。
本発明（２）の切羽前方探査方法は、
トンネル内に地震計を設置し、トンネル内で地震波を発生させてトンネル切羽前方の地質境界面で反射した反射波を前記地震計により受振し、前記反射波の波形データを既知の解析処理により解析を行って前記反射波の反射面位置を計測することにより、切羽前方の地質境界面を推定する切羽前方探査方法において、
地震計として、複数の受振センサーを用い、
複数のロックボルトを、トンネルの坑壁面の同一地点に、前記各ロックボルトの一端から相互に異なる方向へ前記各ロックボルトを相互に直交させて打ち込み、前記各ロックボルトの他端を前記坑壁面上に残して前記ロックボルトの他端の他端面を受振センサー取付部とし、
前記複数の受振センサーを前記坑壁面に打ち込んだ前記各ロックボルトの受振センサー取付部に前記ロックボルトの長軸方向の指向性を有する単成分センサーとして取り付けて、前記各受振センサーの組み合わせにより、多成分受振センサーとして設置し、
前記各受振センサーにより捉える前記各ロックボルトを伝播する地震波から前記各ロックボルトの長軸方向の振動を取得して、当該取得した前記各ロックボルトの長軸方向の一成分の波形データをデータ処理して前記各波形データからフィルタ処理により得られる中心周波数を含む特定の周波数領域に限定して当該特定の周波数領域の計測波形を取り出し、当該個々の計測波形から初動波形と同様の特徴を有する反射波の波形を抽出して、当該各反射波の走時差に基づいて、当該各反射波の反射面位置を計測する、
ことを要旨とする。 The face forward exploration method of the present invention (1) includes:
A seismometer is installed in the tunnel, a seismic wave is generated inside the tunnel, the reflected wave reflected by the geological interface in front of the tunnel face is received by the seismometer, and the waveform data of the reflected wave is analyzed by a known analysis process. In the face front exploration method for estimating the geological interface in front of the face by measuring the position of the reflection surface of the reflected wave,
Using multiple seismic sensors as seismometers,
A plurality of rock bolts are driven into at least the top end and the left and right side walls of the tunnel wall surface from one end of each of the rock bolts in mutually different directions perpendicularly or obliquely to the tunnel wall surface, and each of the locks leaving the other end of the bolt on the wall surface of the tunnel and using the other end surface of the other end of the rock bolt as a vibration receiving sensor mounting portion;
The plurality of vibration receiving sensors are mounted as single component sensors having directivity in the longitudinal direction of the rock bolts on the vibration receiving sensor mounting portions of the respective rock bolts driven into the wall surface of the tunnel , and the combination of the respective vibration receiving sensors enables multi- component detection. Installed as a component vibration sensor,
Acquiring vibration in the longitudinal direction of each rock bolt from seismic waves propagating through each rock bolt captured by each of the vibration receiving sensors, and processing the acquired waveform data of one component in the longitudinal direction of each rock bolt Then, from each waveform data, a specific frequency region including the center frequency obtained by filtering is extracted, and a measured waveform in the specific frequency region is extracted, and from each measured waveform, a reflection having the same characteristics as the initial waveform extracting the wave waveform and measuring the position of the reflecting surface of each reflected wave based on the travel time difference of each reflected wave;
This is the gist of it.
The face forward exploration method of the present invention (2) is
A seismometer is installed in the tunnel, a seismic wave is generated inside the tunnel, the reflected wave reflected by the geological interface in front of the tunnel face is received by the seismometer, and the waveform data of the reflected wave is analyzed by a known analysis process. In the face front exploration method for estimating the geological interface in front of the face by measuring the position of the reflection surface of the reflected wave,
Using multiple seismic sensors as seismometers,
A plurality of rock bolts are driven into the same point on the wall surface of the tunnel from one end of each of the rock bolts in mutually different directions so that the rock bolts are perpendicular to each other, and the other end of each of the rock bolts is driven into the wall of the tunnel. The other end surface of the other end of the lock bolt left above is used as a vibration receiving sensor mounting portion,
The plurality of vibration receiving sensors are mounted as single component sensors having directivity in the longitudinal direction of the rock bolts on the vibration receiving sensor mounting portions of the respective rock bolts driven into the wall surface of the tunnel, and the combination of the respective vibration receiving sensors enables multi-component detection. Installed as a component vibration sensor,
Acquiring vibration in the longitudinal direction of each rock bolt from seismic waves propagating through each rock bolt captured by each of the vibration receiving sensors, and processing the acquired waveform data of one component in the longitudinal direction of each rock bolt Then, from each waveform data, a specific frequency region including the center frequency obtained by filtering is extracted, and a measured waveform in the specific frequency region is extracted, and from each measured waveform, a reflection having the same characteristics as the initial waveform extracting the wave waveform and measuring the position of the reflecting surface of each reflected wave based on the travel time difference of each reflected wave;
This is the gist of it.

本発明（１）の切羽前方探査方法では、地震計として、複数の受振センサーを用い、複数のロックボルトを、少なくともトンネルの坑壁面の天端、左右側壁にそれぞれ、各ロックボルトの一端から相互に異なる方向へ坑壁面に対して直交又は斜交させて打ち込み、複数の受振センサーをそれぞれロックボルトの長軸方向の指向性を有する単成分センサーとして坑壁面上に残した各ロックボルト他端の他端面の受振センサー取付部に取り付けて、各受振センサーの組み合わせにより、多成分受振センサーとして設置する。そして、各受振センサーにより捉える各ロックボルトを伝播する地震波から各ロックボルトの長軸方向の振動を取得して、当該取得した各ロックボルトの長軸方向の一成分の波形データをデータ処理して各波形データからフィルタ処理により得られる中心周波数を含む特定の周波数領域に限定して当該特定の周波数領域の計測波形を取り出し、当該個々の計測波形から初動波形と同様の特徴を有する反射波の波形を抽出して、当該各反射波の走時差に基づいて、当該各反射波の反射面位置を計測する。このようにしたことで、トンネル坑内に地震計を大掛かりな準備作業を不要として簡易に設置することができ、しかも、この手法によっても、複数の受振器を岩盤内部に埋設して反射波を計測する例えば手法３などのような従来の手法とロックボルトの長軸方向の成分の反射波において概ね同様の挙動が得ることができ、このような地震計のトンネル坑壁面上への簡易な設置でありながら、従来の手法と同様に、切羽前方の反射面の３次元的な分布状況を精度よく推定することができる、という本発明独自の格別な効果を奏する。
本発明（２）の切羽前方探査方法では、地震計として、複数の受振センサーを用い、複数のロックボルトを、トンネルの坑壁面の同一地点に、各ロックボルトの一端から相互に異なる方向へ各ロックボルトを相互に直交させて打ち込み、複数のセンサーをそれぞれロックボルトの長軸方向の指向性を有する単成分センサーとして坑壁面上に残した各ロックボルト他端の他端面の受振センサー取付部に取り付けて、各受振センサーの組み合わせにより、多成分受振センサーとして設置する。そして、各受振センサーにより捉える各ロックボルトを伝播する地震波から各ロックボルトの長軸方向の振動を取得して、当該取得した各ロックボルトの長軸方向の一成分の波形データをデータ処理して各波形データからフィルタ処理により得られる中心周波数を含む特定の周波数領域に限定して当該特定の周波数領域の計測波形を取り出し、当該個々の計測波形から初動波形と同様の特徴を有する反射波の波形を抽出して、当該各反射波の走時差に基づいて、当該各反射波の反射面位置を計測する。このようにしたことで、トンネル坑内に地震計を大掛かりな準備作業を不要として簡易に設置することができ、しかも、この手法によっても、複数の受振器を岩盤内部に埋設して反射波を計測する例えば手法３などのような従来の手法とロックボルトの長軸方向の成分の反射波において概ね同様の挙動が得ることができ、このような地震計のトンネル坑壁面上への簡易な設置でありながら、従来の手法と同様に、切羽前方の反射面の３次元的な分布状況を精度よく推定することができる、という本発明独自の格別な効果を奏する。 In the face front prospecting method of the present invention (1) , a plurality of seismic sensors are used as seismometers, and a plurality of rock bolts are installed at least on the top end of the tunnel wall surface and on the left and right side walls, respectively, from one end of each rock bolt. The other end of each rock bolt left on the well wall as a single-component sensor having directivity in the long axis direction of the rock bolt, driven in mutually different directions perpendicularly or obliquely to the well wall. It is attached to the vibration receiving sensor mounting part on the other end surface of the , and by combining each vibration receiving sensor, it is installed as a multi-component vibration receiving sensor. Then, the vibration in the longitudinal direction of each rock bolt is acquired from the seismic wave propagating through each rock bolt captured by each vibration receiving sensor, and the acquired waveform data of one component in the longitudinal direction of each rock bolt is processed. Restricting to a specific frequency range including the center frequency obtained by filtering from each waveform data, and extracting the measured waveform of the specific frequency range, and extracting the measured waveform of the specific frequency range from the individual measured waveform, the waveform of the reflected wave having the same characteristics as the initial waveform. is extracted, and the position of the reflecting surface of each reflected wave is measured based on the travel time difference of each reflected wave . By doing this , the seismometer can be easily installed in the tunnel without the need for large-scale preparation work.In addition, this method also allows multiple geophones to be embedded in the bedrock to measure the reflected waves. For example, the conventional method such as Method 3 and the reflected wave of the component in the long axis direction of the rock bolt can obtain roughly the same behavior. Nevertheless, the present invention has a unique and special effect that it is possible to accurately estimate the three-dimensional distribution of the reflecting surfaces in front of the face, as in the conventional method.
In the face front prospecting method of the present invention (2), a plurality of seismic sensors are used as seismometers, and a plurality of rock bolts are installed at the same point on the wall surface of the tunnel in different directions from one end of each rock bolt. Rock bolts are driven perpendicular to each other, and multiple sensors are left on the hole wall as single-component sensors with directivity in the longitudinal direction of the rock bolts. It is installed and installed as a multi-component vibration sensor by combining each vibration sensor. Then, the vibration in the longitudinal direction of each rock bolt is acquired from the seismic wave propagating through each rock bolt captured by each vibration receiving sensor, and the acquired waveform data of one component in the longitudinal direction of each rock bolt is processed. Restricting to a specific frequency range including the center frequency obtained by filtering from each waveform data, and extracting the measured waveform of the specific frequency range, and extracting the measured waveform of the specific frequency range from the individual measured waveform, the waveform of the reflected wave having the same characteristics as the initial waveform. is extracted, and the position of the reflecting surface of each reflected wave is measured based on the travel time difference of each reflected wave. By doing this, the seismometer can be easily installed in the tunnel without the need for large-scale preparation work.In addition, this method also allows multiple geophones to be embedded in the bedrock to measure the reflected waves. For example, the conventional method such as Method 3 and the reflected wave of the component in the long axis direction of the rock bolt can obtain roughly the same behavior. Nevertheless, the present invention has a unique and special effect that it is possible to accurately estimate the three-dimensional distribution of the reflecting surfaces in front of the face, as in the conventional method.

本発明の第１の実施の形態による切羽前方探査方法（手法１）を示す図A diagram showing a face front searching method (technique 1) according to the first embodiment of the present invention. 手法１における受振センサーの設置形式を示す図Diagram showing the installation format of the vibration sensor in method 1 手法１の概念を示す図Diagram showing the concept of method 1 本発明の第２の実施の形態による切羽前方探査方法（手法２）を示す図A diagram showing a face front searching method (technique 2) according to a second embodiment of the present invention. 手法２における受振センサーの設置形式を示す図Diagram showing the installation format of the vibration sensor in method 2 手法２の概念を示す図Diagram showing the concept of method 2 手法１、手法２及び従来の手法（手法３）による計測データの周波数特性を示す図Diagram showing frequency characteristics of measurement data by method 1, method 2, and conventional method (method 3) 手法１及び手法３によるｘ方向、ｙ方向及びｚ方向の３成分の地震波の計測データからフィルタ処理により２０－２５０Ｈｚの周波数帯の計測波形を取り出して表示した図Measured waveforms in the frequency band of 20-250 Hz extracted from the measurement data of three components of seismic waves in the x-, y-, and z-directions by Method 1 and Method 3 and displayed. 手法１、手法２及び手法３のｘ方向、ｙ方向及びｚ方向の計測波形から抽出した初動波形（最初の波長（１波長目）の波形）の軌跡を描いた図（リサージュ図形）A diagram (Lissajous figure) depicting the trajectory of the initial waveform (waveform of the first wavelength (first wavelength)) extracted from the measured waveforms in the x, y, and z directions of method 1, method 2, and method 3. 従来の切羽前方探査方法（手法３）を示す図Diagram showing the conventional face forward exploration method (Method 3)

次に、この発明を実施するための形態について図を用いて説明する。
図１、図２及び図３に第１の実施の形態を示している。
図１に示すように、この切羽前方探査方法（以下、手法１という。）は、弾性波反射法を利用したもので、トンネルＴ内に地震計１を設置し、トンネルＴ内で地震波を発生させてトンネル切羽前方の地質境界面で反射した反射波を地震計１により受振し、反射波の波形データを既知の解析処理により解析を行って反射波の反射面位置を計測することにより、切羽前方の地質境界面を推定する。 Next, a mode for carrying out the present invention will be described with reference to the drawings.
1, 2 and 3 show a first embodiment.
As shown in Fig. 1, this face forward prospecting method (hereinafter referred to as method 1) uses the seismic reflection method. The seismometer 1 receives the reflected wave reflected by the geological interface in front of the tunnel face, analyzes the waveform data of the reflected wave by a known analysis process, and measures the position of the reflected wave reflection surface. Estimate the geologic interface ahead.

この手法１では、図２に示すように、地震計１として、中心にロックボルト挿通部１０を有するケース１１内に少なくともｘ方向、ｙ方向及びｚ方向の３次元的方向の受振センサー１２を有する多成分受振センサー１２を配置してなる受振ユニット１２Ｕと、この受振ユニット１２Ｕで取得した波形データを記録するデータロガーなどの記録装置（図示省略）とを用いる。また、この受振ユニット１２ＵをトンネルＴ内に設置するために、ＮＡＴＭ工法の支保工において岩盤に打ち込まれるロックボルトに着目し、ロックボルト２を受振ユニット１２Ｕの設置アンカーとして使用する。
ロックボルト２は、受振ユニット１２Ｕの設置位置とするトンネルＴの坑壁面所定の位置にロックボルト２の一端から打ち込み、ロックボルト２の他端の一部（この場合、３ｃｍ程度）を坑壁面上に受振ユニット取付部２１として残しておく。受振ユニット１２Ｕは中心のロックボルト挿通部１０に坑壁Ｗに打ち込んだロックボルト２の受振ユニット取付部２１を通し、ｘ方向の受振センサー１２をトンネルＴの軸方向に、ｙ方向の受振センサー１２をトンネルＴの鉛直方向に、ｚ方向の受振センサー１２をロックボルト２の軸方向となるようにしてトンネルＴの坑壁Ｗの坑壁面上に設置した後、ロックボルト２の受振ユニット取付部２１にナット３を締め込むことにより、坑壁Ｗに反力を取って、受振ユニット１２Ｕを坑壁面上に圧接して坑壁Ｗに一体的に設置する。そして、この受振ユニット１２Ｕの各受振センサー１２に通信ケーブルを介して又は無線により記録装置を接続し、この記録装置を受振ユニット１２Ｕの近傍に設置する（図示省略）。 In Method 1, as shown in FIG. 2, the seismometer 1 has a vibration sensor 12 in at least the three-dimensional directions of the x, y, and z directions in a case 11 having a lock bolt insertion portion 10 at the center. A vibration receiving unit 12U in which the multi-component vibration receiving sensor 12 is arranged, and a recording device (not shown) such as a data logger for recording waveform data acquired by this vibration receiving unit 12U are used. In addition, in order to install the vibration receiving unit 12U in the tunnel T, attention is paid to the rock bolt driven into the bedrock in the shoring of the NATM construction method, and the rock bolt 2 is used as an installation anchor for the vibration receiving unit 12U.
The rock bolt 2 is driven from one end of the rock bolt 2 into a predetermined position on the wall surface of the tunnel T where the receiving unit 12U is installed, and a part of the other end of the rock bolt 2 (in this case, about 3 cm) is placed on the wall surface of the tunnel T. is left as the vibration receiving unit mounting portion 21. In the vibration receiving unit 12U, the vibration receiving unit mounting portion 21 of the lock bolt 2 driven into the hole wall W is passed through the center lock bolt insertion portion 10, and the vibration receiving sensor 12 in the x direction is inserted in the axial direction of the tunnel T, and the vibration receiving sensor 12 in the y direction is inserted. in the vertical direction of the tunnel T, and the vibration receiving sensor 12 in the z direction in the axial direction of the rock bolt 2 on the wall surface of the tunnel wall W of the tunnel T. By tightening the nut 3 to the hole wall W, a reaction force is applied to the hole wall W, and the vibration receiving unit 12U is pressed against the hole wall W and integrally installed on the hole wall W. Then, a recording device is connected to each vibration receiving sensor 12 of the vibration receiving unit 12U via a communication cable or wirelessly, and this recording device is installed near the vibration receiving unit 12U (not shown).

また、この場合、図１（ａ）に示すように、トンネルＴ内の坑壁面の一点に受振ユニット１２Ｕを設置してこの一点での計測でも坑壁Ｗ（岩盤）の挙動（多成分（３成分）の反射波）を計測して、切羽前方の反射面の分布を推定することが可能であるが、複数のロックボルト２を少なくともトンネルＴの坑壁Ｗの天端、左右側壁にそれぞれ坑壁面に対して直交させて打ち込み、複数の受振ユニット１２Ｕを各ロックボルト２を介して少なくともトンネルＴの坑壁Ｗの天端、左右側壁に圧接して設置することが好ましく、この場合、図３（ｂ）に示すように、３本のロックボルト２を使用し、その１本をトンネルＴの坑壁Ｗの天端壁面に鉛直方向に向けて打ち込み、残りの２本をそれぞれトンネルＴの左右の両側壁面に水平方向に向けて打ち込み、３つの受振ユニット１２Ｕ（以下、多成分受振センサー１２という場合がある。）を各ロックボルト２を介してトンネルＴの天端、左右両側壁の壁面に圧接して設置する。このようにすることにより、合計９チャンネル分の地震波を取ることができ、切羽前方の反射面の推定精度を向上させることができる。 In this case, as shown in FIG. 1(a), the vibration receiving unit 12U is installed at one point on the wall surface of the tunnel T, and the behavior of the wall W (rock mass) (multi-component (3 Although it is possible to estimate the distribution of the reflection surface in front of the face by measuring the reflected wave of the component)), a plurality of rock bolts 2 are installed at least on the top of the hole wall W of the tunnel T, and on the left and right side walls of the hole. It is preferable to drive the plurality of vibration receiving units 12U perpendicularly to the wall surface, and to install the plurality of vibration receiving units 12U in pressure contact with at least the top end and left and right side walls of the well wall W of the tunnel T via each lock bolt 2. In this case, as shown in FIG. As shown in (b), three lock bolts 2 are used, one of which is vertically driven into the top wall surface of the well wall W of the tunnel T, and the remaining two bolts are mounted on the left and right sides of the tunnel T, respectively. , and three vibration receiving units 12U (hereinafter sometimes referred to as multi-component vibration receiving sensors 12.) Install by pressing. By doing so, seismic waves for a total of nine channels can be acquired, and the estimation accuracy of the reflecting surface in front of the face can be improved.

このようにして、図１に示すように、従来と同様に、トンネルＴ内の切羽において切羽掘削のための発破、ブレーカー、掘削ドリル等で振動を与え、地震波を発生させ、受振ユニット１２Ｕの各受振センサー１２により坑壁Ｗ（岩盤）を伝播する地震波を捉え、取得した各地震波の波形データに既知のデータ処理、解析処理を施して、各波形データから反射波の反射面位置を計測する。
各波形データのデータ処理、解析では、図３に示すように、受振ユニット１２Ｕの各受振センサー１２で捉え、記録装置に記録した各地震波の各波形データから特定の低周波領域の計測波形を取り出し、当該個々の計測波形から初動の波形（最初の波長（１波長目））と同様の特徴を有する反射波の波形を抽出して、当該各反射波の波形データに基づいて、当該各反射波の反射面位置を計測する。そして、この計測結果より、切羽前方の地質境界面を推定する。 In this way, as shown in FIG. 1, in the same manner as in the conventional art, vibrations are applied to the face in the tunnel T by blasting for face excavation, a breaker, an excavation drill, etc., to generate seismic waves, and each of the vibration receiving units 12U is generated. The seismic waves propagating through the well wall W (bedrock) are captured by the receiving sensor 12, and known data processing and analysis processing are applied to the obtained waveform data of each seismic wave, and the reflecting surface position of the reflected wave is measured from each waveform data.
In the data processing and analysis of each waveform data, as shown in FIG. 3, a measurement waveform in a specific low frequency region is extracted from each waveform data of each seismic wave captured by each vibration receiving sensor 12 of the vibration receiving unit 12U and recorded in the recording device. , extract the waveform of the reflected wave having the same characteristics as the initial waveform (first wavelength (first wavelength)) from the individual measured waveforms, and based on the waveform data of each reflected wave, each reflected wave Measure the position of the reflective surface of the Then, from this measurement result, the geological interface ahead of the face is estimated.

さて、この手法１のように、手法３など従来の手法において岩盤内部に設置していた多成分受振センサーをトンネルＴの坑壁面にのみ設置して、従来の手法と同様に、反射波データを取得し記録装置に記録する手法では、岩盤内部の多成分受振センサーで取得される波形データと同程度の波形データは取れないというのが一般的な見方であるところ、本願発明者等は、この手法１のような多成分受振センサー１２の設置形式であっても、取得した波形データをバンドパスフィルタに掛けることによって得られるある周波数領域に限っては、岩盤内部の多成分受振センサーで取得される波形データに近似する、そのくらいの信号対ノイズ比（Ｓ／Ｎ比）で波形データを取ることができることを見出した。手法１及び手法３の両手法による計測特性は基礎実験により確認済みであり、その結果を図７、図８、及び図９に示している。 Now, as in Method 1, the multi-component seismic sensor that was installed inside the bedrock in the conventional method such as Method 3 is installed only on the wall of the tunnel T, and the reflected wave data is collected in the same way as in the conventional method. It is a general view that the method of acquiring and recording in a recording device cannot acquire waveform data of the same level as the waveform data acquired by the multi-component seismic sensor inside the rock, but the inventors of the present application Even in the installation format of the multi-component vibration sensor 12 as in Method 1, only a certain frequency range obtained by applying the acquired waveform data to a band-pass filter is obtained by the multi-component vibration sensor inside the bedrock. It has been found that waveform data can be obtained with a signal-to-noise ratio (S/N ratio) that approximates that of waveform data. The measurement characteristics obtained by both method 1 and method 3 have already been confirmed by basic experiments, and the results are shown in FIGS.

図７に図１（ｂ）に示す手法１、後述する手法２、手法３による計測データの周波数特性を示している。この周波数分析により、地震波の原波形に含まれる周波数成分を調べる。なお、手法２による計測データの周波数特性については第２の実施の形態で参照する。
図７に示すように、手法１、３の３成分（ｘ方向、ｙ方向、ｚ方向）の波形データには図示のような特徴が見られ、１００Ｈｚ付近に中心周波数があることが分かる。手法１では、この１００Ｈｚを中心周波数として２０－２５０Ｈｚくらい（好ましくは５０－２００Ｈｚくらい）をターゲットとする。 FIG. 7 shows frequency characteristics of measurement data obtained by method 1 shown in FIG. By this frequency analysis, the frequency components contained in the original waveform of seismic waves are investigated. Note that the frequency characteristics of measurement data obtained by Method 2 will be referred to in the second embodiment.
As shown in FIG. 7, the waveform data of the three components (x-direction, y-direction, and z-direction) of methods 1 and 3 have the characteristics shown in the figure, and it can be seen that the center frequency is around 100 Hz. In Method 1, the target is about 20-250 Hz (preferably about 50-200 Hz) with this 100 Hz as the center frequency.

図８は手法１、手法３によるｘ方向、ｙ方向及びｚ方向の３成分の反射波の計測データからバンドパスフィルタで２０－２５０Ｈｚの周波数帯の計測波形を取り出して表示したグラフであり、上段のグラフに手法１によるｘ方向の計測波形を実線で、手法３によるｘ方向の計測波形を破線でそれぞれ示し、中段のグラフに手法１によるｙ方向の計測波形を実線で、手法３によるｙ方向の計測波形を破線でそれぞれ示し、下段のグラフに手法１によるｚ方向の計測波形を実線で、手法３によるｚ方向の計測波形を破線でそれぞれ示している。
図８に示すように、ｘ方向、ｙ方向及びｚ方向の各計測波形から、手法１により取得したトンネルＴ内の坑壁面の挙動と手法３により取得した坑壁Ｗ（岩盤内部（深部））の挙動が低周波（２０－２５０Ｈｚ）の領域で同じような動きが見られ、とりわけ、手法１の計測波形の初動波形（最初の波長（１波長目）の波形）と手法３の計測波形の初動波形（最初の波長（１波長目）の波形）に同じような波形が取れていることが分かる。この最初の１波長はＰ波であり、手法１の波形でも手法３の波形でも同じ揺れ方をし、この後に続く後続波の波形にはＳ波や表面波が混在されているが、後続のＰ波も同じ動きを取り、反射波のＰ波成分、つまり、一次反射波もまた同じ動きをするものと考えられる。そこで、この手法１では、特に地震波の１波長目にくるＰ波を前方探査のソースとする。 FIG. 8 is a graph showing the measured waveform in the frequency band of 20 to 250 Hz extracted by the band-pass filter from the measured data of the reflected waves of the three components in the x direction, the y direction, and the z direction by the method 1 and method 3. In the middle graph, the measured waveform in the x direction by method 1 is shown by a solid line, and the measured waveform in the x direction by method 3 is shown by a broken line. In the lower graph, the measured waveform in the z-direction by method 1 is shown by a solid line, and the measured waveform in the z-direction by method 3 is shown by a broken line.
As shown in FIG. 8, from the measured waveforms in the x-, y-, and z-directions, the behavior of the wall surface in the tunnel T obtained by method 1 and the wall surface W (inside the bedrock (deep part)) obtained by method 3 behavior is similar in the low frequency (20-250 Hz) region, especially the initial waveform (first wavelength (first wavelength) waveform) of the measurement waveform of method 1 and the measurement waveform of method 3 It can be seen that the initial waveform (the waveform of the first wavelength (first wavelength)) has a similar waveform. This first wavelength is P wave, and it oscillates in the same manner in both method 1 and method 3 waveforms. The P-wave also takes the same motion, and the P-wave component of the reflected wave, that is, the primary reflected wave, is also considered to have the same motion. Therefore, in Method 1, the P wave, which comes to the first wavelength of seismic waves, is used as a source for forward exploration.

図９（手法１）は図８の手法１及び手法３のｘ方向、ｙ方向及びｚ方向の計測波形から抽出した初動波形（最初の波長（１波長目）の波形）の軌跡を描いたリサージュ図形であり、これらの波形が手法１及び手法３の計測特性を表している。図９（手法１）において、実線で表した波形が手法１の波形、破線で表した波形が手法３の波形であり、どちらも同じような波形になっており、手法１が手法３と３成分において同様の計測特性が得られていることが分かる。
このように手法１による計測波形は手法３による計測波形に比べて遜色がなく、手法１によっても、手法３と概ね同様の、３次元的な指向性を持った計測が可能であることを確認した。 FIG. 9 (Method 1) shows Lissajous trajectories of initial waveforms (waveforms of the first wavelength (first wavelength)) extracted from the measured waveforms in the x-, y-, and z-directions of Method 1 and Method 3 in FIG. These waveforms represent the measurement characteristics of method 1 and method 3. FIG. In FIG. 9 (Method 1), the waveform represented by the solid line is the waveform of Method 1, and the waveform represented by the dashed line is the waveform of Method 3. It can be seen that similar measurement characteristics are obtained for the components.
In this way, the waveform measured by method 1 is comparable to the waveform measured by method 3, and it was confirmed that method 1 can also perform measurement with three-dimensional directivity, which is roughly the same as method 3. did.

かくして既述の低周波領域の個々の計測波形から初動波形（最初の波長（１波長目））を取り出し、同個々の計測波形から初動波形と同様の特徴を有する後続波、つまり一次反
射波の波形を抽出すれば、これら反射波の波形データについて既知の解析処理（スタッキング処理、マイグレーション処理など）を施すことにより、各反射波の反射面のイメージングを行なうことができる。 Thus, an initial waveform (first wavelength (first wavelength)) is extracted from the individual measured waveforms in the low-frequency region described above, and a subsequent wave having the same characteristics as the initial waveform is obtained from the individual measured waveforms, that is, the primary reflected wave. Once the waveforms are extracted, the reflection surface of each reflected wave can be imaged by subjecting the waveform data of these reflected waves to known analysis processing (stacking processing, migration processing, etc.).

そこで、この手法１では、図３に示すように、多成分受振センサー１２によりトンネルの坑壁Ｗを伝播する３成分の地震波を捉え、取得した各地震波の波形データ（原波形）に、まず、バンドパスフィルタによりフィルタ処理を施して３成分の各波形データから２０－２５０Ｈｚの低周波領域の計測波形を取り出し、当該個々の計測波形から初動波形（最初の波長（１波長目））と同様の特徴を有する反射波の波形を抽出する。次いで、複数の測定データを重ね合わせる所謂スタッキング処理を行ない、同一成分の波形データを重ね合わせて、波形データの分解能を向上させ、このようにして３成分の個々の計測波形から初動波形（最初の波長（１波長目））と同様の特徴を有する一次反射波の波形を抽出する。そして、以上の処理により求めた時間断面を、マイグレーション処理（例えば、ディフラクション・スタック法）により、距離断面に変換して、３成分の各反射波の到来方向及び反射位置を算出し、各反射波の反射点を抽出して反射面を３次元的に予測する。かくして、トンネル掘削時にトンネルＴ内に上下左右に出現する地質境界面を推定する。 Therefore, in this method 1, as shown in FIG. 3, seismic waves of three components propagating through the tunnel wall W are captured by the multi-component seismic sensor 12, and the acquired waveform data (original waveform) of each seismic wave is first: A measurement waveform in a low frequency range of 20-250 Hz is extracted from each waveform data of three components by filtering with a band-pass filter, and the initial waveform (first wavelength (first wavelength)) is extracted from each measurement waveform. A characteristic reflected wave waveform is extracted. Next, a so-called stacking process is performed to superimpose a plurality of measured data, and waveform data of the same component are superimposed to improve the resolution of the waveform data. The waveform of the primary reflected wave having the same characteristics as the wavelength (first wavelength) is extracted. Then, the time section obtained by the above processing is converted into a distance section by migration processing (for example, diffraction stack method), the arrival direction and reflection position of each reflected wave of the three components are calculated, and each reflection Reflection points of waves are extracted and reflection surfaces are predicted three-dimensionally. In this way, the geological interface that appears in the vertical and horizontal directions in the tunnel T during tunnel excavation is estimated.

以上説明したように、この手法１によれば、地震計１として多成分受振センサー１２をトンネルＴの坑壁面に設置したものであっても、多成分受振センサー１２をトンネルＴの坑壁面にロックボルト２及びナット３により圧接して一体的に設置し、この多成分受振センサー１２により坑壁Ｗを伝播する地震波を捉え、取得した各地震波の波形データをデータ処理して各波形データから低周波領域の計測波形を取り出し、当該個々の計測波形から初動波形と同様の特徴を有する反射波の波形を抽出して、当該各反射波の波形データに基づいて、取得した各反射波の到来方向及び反射面位置を計測するようにしたので、トンネルＴ内に地震計１を大掛かりな準備作業を不要として簡易に設置することができ、しかも、この手法１によっても、複数の受振器を坑壁内部に埋設して反射波を計測する例えば手法３などのような従来の手法と３成分の反射波において概ね同様の計測特性を得ることができ、このような地震計１のトンネル坑壁面上への簡易な設置でありながら、従来の手法と同様に、切羽前方の反射面の３次元的な分布状況、すなわち、切羽前方の地質境界面を精度よく推定することができる。
そして、この手法１では、特に、受振センサー１２の設置アンカーに支保工に使用するロックボルト２を利用するので、手法３など従来の手法に比べて準備作業を簡易に短時間で行うことができ、また、施工設備を利用して計測するため、測定しやすく安価である。
また、トンネル切羽前方の地質境界面を３次元的に把握できるため、トンネルの掘削時に地質の変化が始まる部位（天端か踏前か、右側か左側か）を予測することができ、トンネルの掘削時の施工管理、安全管理に活用することができる。 As described above, according to Method 1, even if the multi-component seismic sensor 12 is installed on the wall surface of the tunnel T as the seismometer 1, the multi-component seismic sensor 12 is locked on the wall surface of the tunnel T. The multi-component seismic sensor 12 captures the seismic waves propagating through the well wall W, processes the acquired waveform data of each seismic wave, and converts each waveform data into a low-frequency wave. Take out the measured waveform of the area, extract the waveform of the reflected wave having the same characteristics as the initial waveform from the individual measured waveform, and based on the waveform data of each reflected wave, the acquired arrival direction and direction of each reflected wave Since the position of the reflecting surface is measured, the seismometer 1 can be easily installed in the tunnel T without requiring large-scale preparation work. It is possible to obtain roughly the same measurement characteristics for the three-component reflected wave as for the conventional method such as Method 3, which measures the reflected wave by embedding the seismometer 1 on the wall of the tunnel pit. Although it is a simple installation, it is possible to accurately estimate the three-dimensional distribution of reflecting surfaces in front of the face, that is, the geological interface in front of the face, as in the conventional method.
In method 1, the rock bolts 2 used for shoring are used as anchors for installing the vibration receiving sensor 12. Therefore, compared to conventional methods such as method 3, preparation work can be performed easily and in a short time. In addition, since it is measured using construction equipment, it is easy to measure and inexpensive.
In addition, since the geological boundary surface in front of the tunnel face can be grasped three-dimensionally, it is possible to predict the part where geological changes will start when the tunnel is excavated (crown top or front side, right side or left side). It can be used for construction management and safety management during excavation.

図４、図５及び図６に第２の実施の形態を示している。
図４に示すように、この切羽前方探査方法（以下、手法２という。）は、手法１と同様に、弾性波反射法を利用したもので、トンネルＴ内に地震計１を設置し、トンネルＴ内で地震波を発生させてトンネルＴの切羽前方の地質境界面で反射した反射波を地震計１により受振し、反射波の波形データを既知の解析処理により解析を行って反射波の反射面位置を計測することにより、切羽前方の地質境界面を推定する。 4, 5 and 6 show a second embodiment.
As shown in Fig. 4, this face forward exploration method (hereinafter referred to as method 2) uses the elastic wave reflection method, as in method 1. A seismometer 1 is installed in the tunnel T, and the tunnel A seismic wave is generated in T, and the reflected wave reflected at the geological interface in front of the face of the tunnel T is received by the seismometer 1, and the waveform data of the reflected wave is analyzed by a known analysis process to determine the reflection surface of the reflected wave. By measuring the position, the geological interface in front of the face is estimated.

この手法２では、図５に示すように、地震計１として、複数の受振センサー１３と、これらの受振センサー１３で取得した波形データを記録する記録装置（図示省略）とを用いる。また、これらの受振センサー１３をトンネルＴ内に設置するために、ＮＡＴＭ工法の支保工において岩盤に打ち込むロックボルト２に着目し、ロックボルト２を受振センサー１３の設置アンカーとして使用する。
複数のロックボルト２は、各受振センサー１３の設置位置とするトンネルＴの坑壁Ｗの坑壁面所定の位置にそれぞれロックボルト２の一端から相互に異なる方向に打ち込み、ロックボルト２の他端側の一部を坑壁面上に残してロックボルト２の他端面を受振センサー取付部２２とする。
各受振センサー１３は、坑壁面に打ち込んだ各ロックボルト２の受振センサー取付部２２にロックボルト２の長軸方向の指向性を有する単成分センサーとして取り付ける。ロックボルト２は後述するとおり長軸方向に振動しやすい性質を有することから、受振センサー１３をロックボルト２の挿入方向の単成分センサーとして取り扱い、複数の受振センサー１３を組み合わせることで、多成分受振センサーとして機能させることが可能である。そして、各受振センサー１３に通信ケーブルを介して又は無線により記録装置を接続し、この記録装置をトンネルＴ内に設置する（図示省略）。
この手法２では、トンネル断面が探査範囲に対して十分小さく無視できる場合、反射波を３次元的に計測するには、図４（ａ）に示すように、複数のロックボルト２を少なくともトンネルＴの坑壁Ｗの天端、左右側壁にそれぞれ坑壁面に対して直交又は斜交（好ましくは側壁に対して±４５°方向に斜交）させて打ち込み、複数の受振センサー１３を各ロックボルト２を介して少なくともトンネルＴの坑壁Ｗの天端、左右側壁に設置することが好ましい。なお、ロックボルト２を坑壁面に斜交させて打ち込む場合は、ロックボルト２の一端（先端）を切羽方向に向けて打ち込むことが望ましい。また、図４（ｂ）に示すように、３本以上の複数のロックボルト２をトンネルＴの坑壁面の同一地点に各ロックボルト２を相互に直交させて打ち込み、複数の受振センサー１３を各ロックボルト２を介してトンネルＴの坑壁面の同一箇所に設置するようにしてもよい。このようにすることにより全体として多成分受振センサーとして取り扱うことが可能である。なお、この場合も、ロックボルト２を坑壁面にロックボルト２の一端（先端）を切羽方向に向けて打ち込むことが望ましい。 In Method 2, as shown in FIG. 5, a plurality of vibration sensors 13 and a recording device (not shown) for recording waveform data acquired by these vibration sensors 13 are used as the seismometer 1 . In addition, in order to install these vibration receiving sensors 13 in the tunnel T, attention is paid to the rock bolts 2 that are driven into the bedrock in the shoring of the NATM construction method, and the rock bolts 2 are used as installation anchors for the vibration receiving sensors 13 .
A plurality of rock bolts 2 are driven from one end of the rock bolt 2 in mutually different directions to predetermined positions on the wall surface of the tunnel wall W of the tunnel T where each vibration receiving sensor 13 is to be installed. is left on the hole wall surface, and the other end surface of the rock bolt 2 is used as a vibration receiving sensor mounting portion 22 .
Each vibration sensor 13 is attached as a single-component sensor having directivity in the longitudinal direction of the rock bolt 2 to the vibration sensor mounting portion 22 of each rock bolt 2 driven into the wall surface of the pit. As will be described later, the rock bolt 2 tends to vibrate in the longitudinal direction. Therefore, by treating the vibration receiving sensor 13 as a single component sensor in the insertion direction of the rock bolt 2 and combining a plurality of vibration receiving sensors 13, a multi-component vibration receiving sensor can be obtained. It is possible to function as a sensor. Then, a recording device is connected to each vibration receiving sensor 13 via a communication cable or wirelessly, and this recording device is installed in the tunnel T (not shown).
In Method 2, if the tunnel cross section is sufficiently small relative to the exploration range and can be neglected, a plurality of rock bolts 2 should be placed at least in the tunnel T as shown in FIG. A plurality of vibration receiving sensors 13 are driven into the top end and left and right side walls of the well wall W, respectively perpendicularly or obliquely to the well wall (preferably oblique to the side wall in the direction of ±45°), and a plurality of vibration receiving sensors 13 It is preferable to install at least on the top of the tunnel wall W of the tunnel T and the left and right side walls thereof. When the rock bolt 2 is driven obliquely into the hole wall surface, it is desirable to drive the rock bolt 2 with one end (tip) facing the face direction. Further, as shown in FIG. 4(b), three or more rock bolts 2 are driven into the same point on the wall surface of the tunnel T so that the rock bolts 2 are perpendicular to each other, and the plurality of vibration receiving sensors 13 are installed on each side. They may be installed at the same location on the wall surface of the tunnel T via the rock bolts 2 . By doing so, it is possible to treat the whole as a multi-component vibration receiving sensor. Also in this case, it is desirable to drive the rock bolt 2 into the hole wall with one end (tip) of the rock bolt 2 facing the face direction.

このようにして、図４に示すように、手法３と同様に、トンネルＴ内の切羽において切羽掘削のための発破、ブレーカー、掘削ドリル等で振動を与え、地震波を発生させる。
そして、各受振センサー１３によりトンネルＴの坑壁Ｗに打ち込まれた各ロックボルト２を伝播する地震波を捉え、取得した各地震波の波形データをデータ処理して各波形データから特定の低周波領域の計測波形を取り出し、当該個々の計測波形から初動波形と同様の特徴を有する反射波の波形を抽出して、当該各反射波の走時（到来時間）から当該各反射波の走時差（到来時間の時間差）を算出し、当該各反射波の走時差に基づいて、当該各反射波の反射面位置を計測する。 In this way, as shown in FIG. 4, the face in the tunnel T is vibrated by blasting, a breaker, an excavation drill, etc. for excavating the face, and seismic waves are generated in the same manner as in Method 3.
Then, the seismic waves propagating through the rock bolts 2 driven into the tunnel wall W of the tunnel T are captured by the seismic sensors 13, and the acquired waveform data of the seismic waves are processed to obtain specific low-frequency regions from the waveform data. Take out the measured waveform, extract the waveform of the reflected wave having the same characteristics as the initial waveform from the individual measured waveform, and calculate the travel time difference (arrival time) of each reflected wave from the travel time (arrival time) of each reflected wave ) is calculated, and the position of the reflecting surface of each reflected wave is measured based on the travel time difference of each reflected wave.

さて、本願発明者等は、手法２のように、ロックボルト２をトンネルＴの坑壁面に打ち込んでロックボルト２の頭部（ロックボルト２の他端部の端面）にｚ方向の単成分受振センサー１３を取り付ける受振センサーの設置形式でも、受振センサー１３でロックボルト２の振動を取り、得られるロックボルト２の長軸方向の一成分の波形データについて、波形データをバンドパスフィルタに掛けることによって得られるある周波数領域に限っては、岩盤内部の多成分受振センサーで取得されるｚ方向の一成分の波形データに近似する波形データを取ることができることを見出した。手法２及び手法３の両手法による計測特性は基礎実験により確認済みであり、その結果を図７、図９に示している。なお、この場合、ロックボルト２の頭部周囲に、第１の実施の形態と同様に、ｘ方向、ｙ方向の受振センサー１３を併せて取り付けてある。 Now, the inventors of the present application, as in method 2, drive the rock bolt 2 into the wall surface of the tunnel T, and the head of the rock bolt 2 (the end surface of the other end of the rock bolt 2) receives a single-component vibration in the z direction. In the installation form of the vibration receiving sensor in which the sensor 13 is installed, the vibration of the rock bolt 2 is detected by the vibration receiving sensor 13, and the obtained waveform data of one component of the rock bolt 2 in the longitudinal direction is filtered by applying the waveform data to a band-pass filter. It was found that, limited to a certain frequency range obtained, it is possible to obtain waveform data that approximates one-component waveform data in the z direction obtained by a multi-component vibration sensor inside the rock. The measurement characteristics of both method 2 and method 3 have already been confirmed by basic experiments, and the results are shown in FIGS. 7 and 9. FIG. In this case, vibration sensors 13 in the x and y directions are attached around the head of the lock bolt 2 as in the first embodiment.

図７（手法２）に図４（ａ）に示す手法２による計測データの周波数特性を示している。この周波数分析により、地震波の原波形に含まれる周波数成分を調べる。図７（手法２）に示すように、手法２による計測データの周波数特性は、ｘ方向、ｙ方向、ｚ方向のどの波形データも他の手法１、３のものより大きく表れ、ピークの形も特徴的で、１００Ｈｚ付近に中心周波数があり、特にｚ方向の波形データに最も大きな反応が見られる。そこで、この手法２でもまた、この１００Ｈｚを中心周波数として２０－２５０Ｈｚくらい（好ましくは、５０－２００Ｈｚくらい）をターゲットとする。なお、手法２の周波数特性には５００Ｈｚ当たりに手法３の周波数特性には見られないピークがある。これはロックボルト２の共振（３００Ｈｚ－５００Ｈｚ）によるものとみられる。この手法２では、ターゲットとしている周波数帯域と異なるため、ロックボルト２の共振は大きく影響しない。
そして、第１の実施の形態と同様に、手法２、手法３によるｘ方向、ｙ方向及びｚ方向の３成分の反射波の実際の計測データからバンドパスフィルタで２０－２５０Ｈｚの周波数帯の計測波形を取り出したところ、手法２では、ｘ方向の成分、ｙ方向の成分は適正に取れない結果となったが、ｚ方向の波形データは手法３のｚ方向の波形データと概ね同様の動きが見られ、とりわけ、両手法２、３の計測波形の初動波形の最初の２分の１波長内の範囲に同じような波形が取れており、ｚ方向の反応は適正に取れることが分かった。この初動波形はＰ波であり、手法２の波形でも手法３の波形でも同じ揺れ方をし、この後に続く後続波の波形にはＳ波や表面波が混在されているが、後続のＰ波も同じ動きを取り、反射波のＰ波成分、すなわち、一次反射波もまた同じ動きをするものと考えられる。そこで、この手法２では、特に地震波の２分の１波長目にくるＰ波を前方探査のソースとする。 FIG. 7 (Method 2) shows the frequency characteristics of measurement data obtained by Method 2 shown in FIG. 4A. By this frequency analysis, the frequency components contained in the original waveform of seismic waves are investigated. As shown in FIG. 7 (Method 2), the frequency characteristics of the measurement data obtained by Method 2 appear larger than those of the other Methods 1 and 3 in all of the x-, y-, and z-direction waveform data, and the peak shape is Characteristically, there is a center frequency around 100 Hz, and the largest reaction is seen especially in the waveform data in the z direction. Therefore, in this method 2 as well, the target is about 20-250 Hz (preferably about 50-200 Hz) with this 100 Hz as the center frequency. Note that the frequency characteristics of Method 2 have a peak around 500 Hz, which is not seen in the frequency characteristics of Method 3. This is considered to be due to the resonance (300Hz-500Hz) of the rock bolt 2. In Method 2, since the target frequency band is different, the resonance of the rock bolt 2 does not have a large effect.
Then, in the same manner as in the first embodiment, measurement of a frequency band of 20 to 250 Hz is performed using a bandpass filter from actual measurement data of reflected waves of three components in the x direction, the y direction, and the z direction by method 2 and method 3. When the waveforms were taken out, it was found that the x-direction component and the y-direction component could not be obtained properly with method 2, but the z-direction waveform data showed roughly the same movement as the z-direction waveform data of method 3. In particular, similar waveforms were obtained in the range within the first half wavelength of the initial waveforms of the waveforms measured by both methods 2 and 3, and it was found that the reaction in the z direction was appropriately obtained. This initial waveform is the P wave, and the waveform of method 2 and the waveform of method 3 sway in the same way, and the waveform of the subsequent wave that follows is mixed with the S wave and the surface wave, but the subsequent P wave , and the P-wave component of the reflected wave, ie, the primary reflected wave, also follows the same motion. Therefore, in method 2, the P-wave, which comes at the 1/2 wavelength of the seismic wave, is used as the source for forward exploration.

図９（手法２）は手法２及び手法３のｘ方向、ｙ方向及びｚ方向の計測波形から抽出した初動波形（１波長目の波形）の軌跡を描いたリサージュ図形で、これらの波形が手法２及び手法３の計測特性を表している。図９において、実線で表した波形が手法２の波形、破線で表した波形が手法３の波形であり、手法２と手法３とではｘ成分、ｙ成分ともに異なる波形になっているものの、どちらもｚ成分については同じような波形が見られ、手法２がｚ成分（ロックボルトの長軸方向の成分）で手法３と同様の挙動が得られていることが分かる。
このように手法２による計測波形はｚ成分については手法３による計測波形に比べて遜色がなく、ロックボルト２頭部の受振センサー１３で、ロックボルト２の振動の伝播特性を使って、ｚ方向（ロックボルトの長軸方向）の波形データを計測できることを確認した。 FIG. 9 (method 2) is a Lissajous figure depicting the trajectory of the initial waveform (waveform at the first wavelength) extracted from the measured waveforms in the x, y, and z directions of method 2 and method 3, and these waveforms are the methods. 2 and method 3 are shown. In FIG. 9, the waveform represented by the solid line is the waveform for Method 2, and the waveform represented by the dashed line is the waveform for Method 3. A similar waveform is seen for the z component in both, and it can be seen that method 2 obtains the same behavior as method 3 in the z component (component in the long axis direction of the rock bolt).
As described above, the waveform measured by method 2 is comparable to the waveform measured by method 3 in terms of the z component. It was confirmed that the waveform data in (long axis direction of the rock bolt) can be measured.

したがって、既述の低周波領域の個々の計測波形から初動波形を取り出し、同個々の計測波形から初動波形と同様の特徴を有する後続波を抽出することで、反射波を推定することができる。つまり、初動波形と同様の特徴を有する後続波が一次反射波となる。これらの一次反射波は、図４（ａ）に示すように、異なる計測位置の受振センサ１３で計測されるので、反射面から戻ってくる時間が異なり、各反射波間で到来時間の差が生じる。この時間差、つまり走時差を利用して、各一次反射波の到来方向及び位置を求めることができる。
また、図４（ｂ）に示すように、複数のロックボルト２を同一地点において異なる方向に打ち込む場合でも同様で、各反射波の各受振センサー１３に到達する時間が違うので、この時間差から、各反射波の到来方向及び位置を求めることができる。この場合、例えば、切羽前方の右側に地質境界面があると見込まれるときは、複数のロックボルト２を右側の坑壁Ｗに集中してそれぞれ異なる方向に向けて打ち込み、各ロックボルト２の頭部に受振センサー１３を取り付けておけば、各反射波の到来方向及び位置をより適切に求めることができる。また、この場合、各ロックボルト２をトンネルＴの坑壁Ｗに切羽方向に向けて差し込むことで、より強い反応を取ることができる。 Therefore, the reflected wave can be estimated by extracting the initial waveform from the individual measured waveforms in the low-frequency region described above and extracting subsequent waves having the same characteristics as the initial waveform from the individual measured waveforms. That is, the subsequent wave having the same characteristics as the initial wave becomes the primary reflected wave. As shown in FIG. 4(a), these primary reflected waves are measured by the vibration sensors 13 at different measurement positions, so the time to return from the reflecting surface differs, and a difference in arrival time occurs between the reflected waves. . The arrival direction and position of each primary reflected wave can be determined using this time difference, that is, the travel time difference.
Also, as shown in FIG. 4(b), the same applies when a plurality of rock bolts 2 are driven in different directions at the same point. The arrival direction and position of each reflected wave can be obtained. In this case, for example, when it is expected that there is a geological interface on the right side in front of the face, a plurality of rock bolts 2 are concentrated on the right hole wall W and driven in different directions. By attaching the vibration receiving sensor 13 to the portion, the arrival direction and position of each reflected wave can be obtained more appropriately. Further, in this case, by inserting each rock bolt 2 into the wall W of the tunnel T facing the face direction, a stronger reaction can be obtained.

かくして既述の低周波領域の個々の計測波形から初動波形を取り出して、同個々の計測波形から初動波形と同様の特徴を有する後続波、つまり一次反射波の波形を抽出し、これら一次反射波の異なる走時からこれら一次反射波の走時差を算出すれば、各一次反射波の走時差に基づいて、各一次反射波の反射面位置を計測することができる。 Thus, the initial waveform is extracted from the individual measured waveforms in the low-frequency region described above, and the subsequent waves having the same characteristics as the initial waveform, that is, the waveforms of the primary reflected waves, are extracted from the individual measured waveforms, and these primary reflected waves are extracted. If the travel time differences of these primary reflected waves are calculated from different travel times, the reflecting surface position of each primary reflected wave can be measured based on the travel time difference of each primary reflected wave.

そこで、この手法２では、図６に示すように、複数の受振センサー１３により坑壁Ｗに打ち込まれた各ロックボルト２を伝播する地震波を捉え、取得した各地震波の波形データをフィルタ処理して各波形データから２０－２５０Ｈｚの特定の低周波領域の計測波形を取り出し、当該個々の計測波形から初動波形と同様の特徴を有する一次反射波の波形を抽出して、これら一次反射波の走時から各一次反射波の走時差を算出し、各一時反射波の走時差に基づいて、各一次反射波の反射位置を計測し、各反射波の反射点を抽出して反射面を予測する。かくして、トンネルＴの掘削時にトンネルＴ内に上下左右に出現する地質境界面を推定する。 Therefore, in this method 2, as shown in FIG. 6, seismic waves propagating through each rock bolt 2 driven into the tunnel wall W are captured by a plurality of receiving sensors 13, and the obtained waveform data of each seismic wave is filtered. A measurement waveform in a specific low frequency range of 20 to 250 Hz is extracted from each waveform data, a primary reflected wave waveform having the same characteristics as the initial waveform is extracted from each measured waveform, and the travel time of these primary reflected waves Based on the travel time difference of each primary reflected wave, the reflection position of each primary reflected wave is measured, the reflection point of each reflected wave is extracted, and the reflecting surface is predicted. Thus, the geological interface that appears in the tunnel T in the vertical and horizontal directions during excavation of the tunnel T is estimated.

以上説明したように、手法２によれば、地震計１として複数の受振センサー１３をロックボルト２を介してトンネルＴの坑壁面に設置したものであっても、トンネルＴの坑壁面所定の位置に複数のロックボルト２を相互に異なる方向に打ち込み、複数の受振センサー１３を坑壁面上に残したロックボルト２他端の他端面の受振センサー取付部２２にロックボルト２の長軸方向の指向性を有する単成分センサーとして取り付けて、各受振センサー１３により各ロックボルト２を伝播する地震波を捉え、取得した各地震波の波形データをデータ処理して各波形データから特定の低周波領域の計測波形を取り出し、当該個々の計測波形から初動波形と同様の特徴を有する反射波の波形を抽出して、当該各反射波の走時差に基づいて、当該各反射波の反射面位置を計測するようにしたので、トンネルＴ坑内に地震計１を大掛かりな準備作業を不要として簡易に設置することができ、しかも、この手法２によっても、複数の受振器１３を岩盤内部に埋設して反射波を計測する例えば手法３などのような従来の手法とロックボルトの長軸方向の成分の反射波において概ね同様の挙動が得ることができ、このような地震計１のトンネルＴの坑壁面上への簡易な設置でありながら、従来の手法と同様に、切羽前方の反射面の３次元的な分布状況、すなわち、切羽前方の地質境界面を精度よく推定することができる。
そして、この手法２においても、特に、受振センサー１３の設置アンカーに支保工に使用するロックボルト２を利用するので、手法３など従来の手法に比べて準備作業を簡易に短時間で行うことができ、また、施工設備を利用して計測するため、測定しやすく安価である。
また、トンネル切羽前方の地質境界面を３次元的に把握できるため、トンネルの掘削時に地質の変化が始まる部位（天端か踏前か、右側か左側か）を予測することができ、トンネルの掘削時の施工管理、安全管理に活用することができる。 As described above, according to Method 2, even if a plurality of seismic sensors 13 are installed on the wall of the tunnel T through the rock bolts 2 as the seismometer 1, the predetermined position on the wall of the tunnel T can be detected. A plurality of rock bolts 2 are driven in directions different from each other, and a plurality of vibration receiving sensors 13 are left on the hole wall surface. The seismic waves propagating through each rock bolt 2 are captured by each receiving sensor 13, and the acquired waveform data of each seismic wave is processed to obtain a specific measured waveform in a low frequency region from each waveform data. is extracted from each of the measured waveforms, the waveform of the reflected wave having the same characteristics as the initial waveform is extracted, and the position of the reflection surface of each reflected wave is measured based on the travel time difference of each reflected wave. Therefore, it is possible to easily install the seismometer 1 in the tunnel T tunnel without the need for large-scale preparation work. For example, the conventional method such as method 3 and the reflected wave of the component in the long axis direction of the rock bolt can obtain roughly the same behavior. Despite the installation, it is possible to accurately estimate the three-dimensional distribution of reflection surfaces in front of the face, that is, the geological interface in front of the face, as in the conventional method.
Also in this method 2, since the rock bolts 2 used for shoring are used as the installation anchors of the vibration receiving sensor 13, the preparation work can be performed easily and in a short time compared to the conventional methods such as method 3. In addition, since it is measured using construction equipment, it is easy to measure and inexpensive.
In addition, since the geological boundary surface in front of the tunnel face can be grasped three-dimensionally, it is possible to predict the part where geological changes will start when the tunnel is excavated (crown top or front side, right side or left side). It can be used for construction management and safety management during excavation.

Ｔトンネル
Ｗ坑壁
１地震計
１０ロックボルト挿通部
１１ケース
１２受振センサー（多成分受振センサー）
１２Ｕ受振ユニット
１３受振センサー（Ｚ方向の単成分受振センサー）
２ロックボルト
２１受振ユニット取付部
２２受振センサー取付部
３ナット T Tunnel W Pit wall 1 Seismometer 10 Rock bolt insertion portion 11 Case 12 Seismic sensor (multi-component seismic sensor)
12U vibration receiving unit 13 vibration receiving sensor (single-component vibration receiving sensor in Z direction)
2 lock bolt 21 vibration receiving unit mounting portion 22 vibration receiving sensor mounting portion 3 nut

Claims

A seismometer is installed in the tunnel, a seismic wave is generated inside the tunnel, the reflected wave reflected by the geological interface in front of the tunnel face is received by the seismometer, and the waveform data of the reflected wave is analyzed by a known analysis process. In the face front exploration method for estimating the geological interface in front of the face by measuring the position of the reflection surface of the reflected wave,
Using multiple seismic sensors as seismometers,
A plurality of rock bolts are driven into at least the top end and the left and right side walls of the tunnel wall surface from one end of each of the rock bolts in mutually different directions perpendicularly or obliquely to the tunnel wall surface, and each of the locks leaving the other end of the bolt on the wall surface of the tunnel and using the other end surface of the other end of the rock bolt as a vibration receiving sensor mounting portion;
The plurality of vibration receiving sensors are mounted as single component sensors having directivity in the longitudinal direction of the rock bolts on the vibration receiving sensor mounting portions of the respective rock bolts driven into the wall surface of the tunnel , and the combination of the respective vibration receiving sensors enables multi- component detection. Installed as a component vibration sensor,
Acquiring vibration in the longitudinal direction of each rock bolt from seismic waves propagating through each rock bolt captured by each of the vibration receiving sensors, and processing the acquired waveform data of one component in the longitudinal direction of each rock bolt Then, from each waveform data, a specific frequency region including the center frequency obtained by filtering is extracted, and a measured waveform in the specific frequency region is extracted, and from each measured waveform, a reflection having the same characteristics as the initial waveform extracting the wave waveform and measuring the position of the reflecting surface of each reflected wave based on the travel time difference of each reflected wave;
A face forward exploration method characterized by:

A seismometer is installed in the tunnel, a seismic wave is generated inside the tunnel, the reflected wave reflected by the geological interface in front of the tunnel face is received by the seismometer, and the waveform data of the reflected wave is analyzed by a known analysis process. In the face front exploration method for estimating the geological interface in front of the face by measuring the position of the reflection surface of the reflected wave,
Using multiple seismic sensors as seismometers,
A plurality of rock bolts are driven into the same point on the wall surface of the tunnel from one end of each of the rock bolts in mutually different directions so that the rock bolts are perpendicular to each other, and the other end of each of the rock bolts is driven into the wall of the tunnel. The other end surface of the other end of the lock bolt left above is used as a vibration receiving sensor mounting portion,
The plurality of vibration receiving sensors are mounted as single component sensors having directivity in the longitudinal direction of the rock bolts on the vibration receiving sensor mounting portions of the respective rock bolts driven into the wall surface of the tunnel, and the combination of the respective vibration receiving sensors enables multi-component detection. Installed as a component vibration sensor,
Acquiring vibration in the longitudinal direction of each rock bolt from seismic waves propagating through each rock bolt captured by each of the vibration receiving sensors, and processing the acquired waveform data of one component in the longitudinal direction of each rock bolt Then, from each waveform data, a specific frequency region including the center frequency obtained by filtering is extracted, and a measured waveform in the specific frequency region is extracted, and from each measured waveform, a reflection having the same characteristics as the initial waveform extracting the wave waveform and measuring the position of the reflecting surface of each reflected wave based on the travel time difference of each reflected wave;
A face forward exploration method characterized by :