JP5128912B2 - Groundwater exploration method in the ground in front of the tunnel - Google Patents

Groundwater exploration method in the ground in front of the tunnel Download PDF

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JP5128912B2
JP5128912B2 JP2007297644A JP2007297644A JP5128912B2 JP 5128912 B2 JP5128912 B2 JP 5128912B2 JP 2007297644 A JP2007297644 A JP 2007297644A JP 2007297644 A JP2007297644 A JP 2007297644A JP 5128912 B2 JP5128912 B2 JP 5128912B2
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浩之 山本
哲夫 猪狩
慎司 宇津木
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株式会社間組
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Description

本発明は、トンネル掘削方向における地盤内の地下水を探査する方法に関する。   The present invention relates to a method for exploring groundwater in the ground in the direction of tunnel excavation.

トンネルを構築する際に、地下断層や地下水状況の情報を得るため、比抵抗法等の電気探査が実施されている。例えば、特許文献１には、地表面に複数の地表電極を配置し、トンネル坑内に複数の坑内電極を配置し、一方の遠電極と坑内電極の１つを通電し、他方の遠電極と各地表電極間の電位差を測定した後、一方の遠電極と他の坑内電極を順次通電し、その都度、他方の遠電極と各地表電極間の電位差を測定し、比抵抗の分布状況から地盤性状を推定する探査方法が記載されている。
この従来方法は、地表面とトンネル坑内とで挟まれた範囲を探査するものであり、この探査以降に掘削する予定の地盤、すなわち、トンネル切羽前方の地盤については探査範囲外となってしまい、したがって、地下深部の地下水状況について必要とされる情報が得られないという欠点がある。 When constructing a tunnel, electrical exploration such as the resistivity method has been carried out to obtain information on underground faults and groundwater conditions. For example, in Patent Document 1, a plurality of ground electrodes are arranged on the ground surface, a plurality of underground electrodes are arranged in a tunnel mine, one far electrode and one of the underground electrodes are energized, and the other far electrode and various locations After measuring the potential difference between the surface electrodes, sequentially energize one far electrode and the other underground electrode, measure the potential difference between the other far electrode and each surface electrode each time, and determine the ground properties from the distribution of specific resistance. The exploration method to estimate is described.
This conventional method is for exploring the area sandwiched between the ground surface and the tunnel mine, and the ground to be excavated after this exploration, that is, the ground in front of the tunnel face is out of the exploration area, Therefore, there is a drawback that required information about the groundwater condition in the deep underground cannot be obtained.

他の従来技術としては、地上から複数の鉛直ボーリング孔を形成し、それぞれの鉛直ボーリング孔内に等間隔で測定点を設定し、任意の鉛直ボーリング孔の測定点から電流を流したり、又は弾性波を発信し、他のボーリング孔内の各測定点で電位を測定したり、又は弾性波を受信し、比抵抗分布や弾性波速度分布から地盤性状を推定する探査方法がある。この従来方法では、少なくとも二本の鉛直ボーリング孔を地表面からトンネル基面まで設ける必要があり、そのため膨大なコストが掛かるという問題がある。   As another conventional technique, a plurality of vertical boring holes are formed from the ground, measurement points are set at equal intervals in each vertical boring hole, and an electric current is passed from the measuring point of any vertical boring hole or elastic There is an exploration method for transmitting a wave and measuring a potential at each measurement point in another borehole or receiving an elastic wave to estimate the ground properties from a specific resistance distribution or an elastic wave velocity distribution. In this conventional method, it is necessary to provide at least two vertical boring holes from the ground surface to the tunnel base surface.

また他の従来技術としては、トンネルの切羽前方の地質性状を予測する方法が特許文献２に記載されている。これは、トンネル前方地盤に向けて斜めに一対のボーリング孔を穿設し、各ボーリング孔内に等間隔に電極を設置すると共に、切羽面にも等間隔に電極を設置し、各電極で電位を測定して比抵抗を求め、これら比抵抗値から二次元比抵抗断面分布図を作成するものである。
しかしながら、トンネル前方地盤に地下水流が存在する場合、ボーリング孔からトンネル内に多量の地下水が流入し、この水処理に多大な労力を要してしまうため、トンネルの斜め前方地盤にボーリング孔を形成することは、あまり合理的ではない。また比較的遠距離である５０〜１００ｍ程度前方の探査は短時間で行うことができず、さらに、最も情報が必要であるトンネル基面での比抵抗値と地下水の関係が不明であるという欠点もある。
特開平１０−２６０２６４号公報 特開２００１−１６６０６１号公報 As another conventional technique, Patent Document 2 describes a method for predicting the geological properties in front of a tunnel face. This is because a pair of boring holes are drilled obliquely toward the ground in front of the tunnel, electrodes are installed at equal intervals in each boring hole, and electrodes are also installed at equal intervals on the face of the tunnel. Is measured to obtain the specific resistance, and a two-dimensional specific resistance cross-sectional distribution map is created from these specific resistance values.
However, when there is a groundwater flow in the ground in front of the tunnel, a large amount of groundwater flows into the tunnel from the borehole, and this water treatment requires a lot of labor. It is not very reasonable to do. In addition, exploration in front of a relatively long distance of about 50 to 100 m cannot be performed in a short time, and furthermore, the relationship between the specific resistance value at the tunnel base where information is most needed and the groundwater is unknown. There is also.
JP-A-10-260264 JP 2001-166061 A

以上のような現状を鑑みて本発明の課題は、トンネル坑内から前方５０〜１００ｍ程度の比較的長距離に及ぶ範囲で短時間且つ低コストで地下水を探査することが可能なトンネル前方地盤内の地下水探査方法を提供することである。   In view of the current situation as described above, the problem of the present invention is that in the ground in front of the tunnel capable of exploring groundwater in a short time and at a low cost within a range of a relatively long distance of about 50 to 100 m ahead from the tunnel tunnel. It is to provide groundwater exploration methods.

また本発明の別の課題は、トンネル基面での地下水と比抵抗値の関係が明らかであり、高い測定精度が可能なトンネル前方地盤内の地下水探査方法を提供することである。   Another object of the present invention is to provide a groundwater exploration method in the ground in front of the tunnel in which the relationship between the groundwater at the tunnel base and the specific resistance value is clear and high measurement accuracy is possible.

上記課題を解決するために、本発明では、地上においては、トンネル切羽前方の地盤内に向けて地表面からほぼ鉛直のボーリング孔を形成し、当該ボーリング孔内の複数箇所に電極を設置するか、または地表面からトンネル切羽前方の地盤内に向けてほぼ鉛直に予め形成されている既存のボーリング孔内の複数箇所に電極を設置し、トンネル坑内においては、切羽付近又は切羽から離間した所定長後方でトンネル軸にほぼ直交する上下方向にボーリング孔を形成し、各ボーリング孔内の複数箇所に電極を設置し、地表面から形成されたボーリング孔内の電極と、トンネル坑内から形成されたボーリング孔内の電極との間で比抵抗値を求めてトンネル掘削方向の前方地盤における地下水状況を予測することを特徴とするトンネル前方地盤内の地下水探査方法が提供される。   In order to solve the above problems, in the present invention, on the ground, a substantially vertical borehole is formed from the ground surface toward the ground in front of the tunnel face, and electrodes are installed at a plurality of locations in the borehole. Alternatively, electrodes are installed at multiple locations in the existing boreholes that are pre-formed almost vertically from the ground surface into the ground in front of the tunnel face, and within the tunnel mine, a predetermined length near the face or apart from the face Boring holes are formed in the vertical direction that is substantially perpendicular to the tunnel axis at the rear, and electrodes are installed at multiple locations in each boring hole. The electrodes in the boring holes formed from the ground surface and the boring formed from the tunnel tunnel The ground in the ground ahead of the tunnel is characterized by predicting the groundwater condition in the ground in front of the tunnel excavation direction by obtaining the specific resistance value with the electrode in the hole Water exploration method is provided.

ここで、前記予め形成されている既存のボーリング孔としては、例えば、トンネル掘削を実際に開始する以前に、地表面からトンネル予定線に向けて形成された調査ボーリング孔であって、未だ埋め戻されていない調査ボーリング孔を挙げることができる。   Here, as the existing borehole formed in advance, for example, before actually starting the tunnel excavation, it is an investigation borehole formed from the ground surface toward the planned tunnel line, and is still backfilled. An unexamined drilling hole can be mentioned.

本発明において、トンネル坑内でボーリング孔を形成する位置は、例えば、トンネル坑内で湧水が比較的多い場合には、切羽から離間したほぼ１０ｍ程度後方地点が好ましく、この地点における天端及びインバートからトンネル軸にほぼ直交する上下方向に比較的短いボーリング孔を形成する。このほぼ１０ｍ程度後方地点とする根拠は、切羽の湧水処理作業スペース、もしくは安全を確保できる位置として１Ｄ（Ｄ：トンネルの幅）程度離れた位置が望ましいからである。
一方、トンネル坑内で湧水が比較的少ない場合には、トンネル坑内でボーリング孔を形成する位置は切羽付近、すなわち、切羽とほぼ同地点又は切羽からほぼ２ｍ以内の後方の地点が好ましく、この地点において同様に天端及びインバートからトンネル軸にほぼ直交する上下方向に比較的短いボーリング孔を形成する。
ここで、トンネル坑内から上下方向に形成するボーリング孔は、少なくとも２０ｍ〜３０ｍ程度の長さに形成すれば良い。この長さの根拠は、一般的にトンネル施工に使用するドリルジャンボ機の削孔能力として、２０〜３０ｍ程度のボーリング孔であれば、１本を１〜２時間程度で効率良く孔曲がりせずに削孔できるからである。 In the present invention, the position where the borehole is formed in the tunnel mine, for example, when the spring water is relatively large in the tunnel mine, is preferably a rear point of about 10 m away from the face, from the top and invert at this point. A relatively short boring hole is formed in the vertical direction substantially perpendicular to the tunnel axis. The grounds for the rear point of about 10 m are because it is desirable to have a working water treatment space at the face, or a position separated by about 1D (D: tunnel width) as a position that can ensure safety.
On the other hand, when there is relatively little spring water in the tunnel mine, the position where the borehole is formed in the tunnel mine is preferably near the face, that is, approximately the same point as the face or a position behind the face within about 2 m. Similarly, a relatively short boring hole is formed in the vertical direction substantially perpendicular to the tunnel axis from the top and invert.
Here, the boring hole formed in the vertical direction from the tunnel pit may be formed to a length of at least about 20 m to 30 m. The basis of this length is that the drilling ability of a drill jumbo machine generally used for tunnel construction is a drilling hole of about 20 to 30 m, and one hole can be efficiently bent in about 1 to 2 hours. This is because drilling is possible.

また地表面からほぼ鉛直に形成するボーリング孔と、トンネル切羽との相対的な位置は、例えば、トンネル坑内の湧水が比較的多い場合には、トンネル切羽から４０〜９０ｍ程度離間した位置とするのが好ましい。
一方、トンネル坑内の湧水が比較的少ない場合には、トンネル切羽から５０〜１００ｍ程度離間した位置とするのが好ましい。
以上のようなトンネル切羽からの離間位置にする根拠は、一般的に比抵抗トモグラフィの探査距離の限界として地山条件が良ければ１００ｍ程度、悪ければ５０ｍ程度であり、トンネル坑内の測線が切羽後方１０ｍを考慮しているからである。 In addition, the relative position between the boring hole formed almost vertically from the ground surface and the tunnel face is, for example, a position that is separated from the tunnel face by about 40 to 90 m when there is a relatively large amount of spring water in the tunnel tunnel. Is preferred.
On the other hand, when there is relatively little spring water in the tunnel mine, the position is preferably about 50 to 100 m away from the tunnel face.
The grounds for the distance from the tunnel face as described above are generally about 100 m if the ground condition is good and 50 m if the ground condition is good as the limit of the exploration distance of specific resistance tomography. This is because the rear 10 m is taken into consideration.

本発明のトンネル前方地盤内の地下水探査方法では、前記上下方向のボーリング孔を切羽付近に設けた場合には、これら上下方向のボーリング孔に加えて、切羽からトンネル掘削方向の地盤に向けて水平方向にボーリング孔を形成し、当該水平方向のボーリング孔内の複数箇所に電極を設置して探査精度を向上させても良い。
ここで、水平方向のボーリング孔は、トンネル切羽から３０ｍ程度の長さに形成すれば良い。この長さの根拠は、一般的にトンネル施工に使用するドリルジャンボ機の削孔能力として、２０〜３０ｍ程度のボーリング孔であれば、１本を１〜２時間程度で効率良く孔曲がりせずに削孔できるからである。
以上のように水平方向のボーリング孔内に設置した各電極で比抵抗値を求め、この比抵抗値と、水平方向にボーリング孔を形成したときの湧水状況とを比較し、これにより、切羽前方の得られた比抵抗値から、切羽前方の湧水量を予測することにより、極めて精度の高い地下水探査が可能になる。 In the groundwater exploration method in the ground in front of the tunnel according to the present invention, when the vertical boring holes are provided in the vicinity of the face, in addition to the vertical boring holes, a horizontal direction from the face to the ground in the tunnel excavation direction is provided. A boring hole may be formed in the direction, and electrodes may be installed at a plurality of locations in the horizontal boring hole to improve the search accuracy.
Here, the horizontal boring hole may be formed with a length of about 30 m from the tunnel face. The basis of this length is that the drilling ability of a drill jumbo machine generally used for tunnel construction is a drilling hole of about 20 to 30 m, and one hole can be efficiently bent in about 1 to 2 hours. This is because drilling is possible.
As described above, the specific resistance value is obtained for each electrode installed in the horizontal borehole, and the specific resistance value is compared with the spring water condition when the horizontal borehole is formed. By predicting the amount of spring water in front of the face from the specific resistance value obtained in front, groundwater exploration with extremely high accuracy becomes possible.

また本発明のトンネル前方地盤内の地下水探査方法では、前記上下方向のボーリング孔を切羽から離間した所定長後方に設けた場合には、これら上下方向のボーリング孔に加えて、上下方向のボーリング孔が設けられた付近から切羽までのトンネル坑壁面に複数箇所に電極を設置しても良い。   Further, in the groundwater exploration method in the ground in front of the tunnel according to the present invention, when the vertical boring hole is provided at a predetermined length behind the face, the vertical boring hole is added to the vertical boring hole. Electrodes may be installed at a plurality of locations on the wall surface of the tunnel tunnel from the vicinity where the is provided to the face.

本発明のトンネル前方地盤内の地下水探査方法では、予め形成されている調査ボーリング孔を１本使用するか、又は、地上からトンネル切羽前方の地盤に向けてほぼ鉛直のボーリング孔を新たに１本形成すれば、トンネル坑内では、坑壁からは上下方向に短いボーリング孔を形成するだけで、ボーリング孔間の比抵抗値の測定が可能となり、地下水状況を精度良く、比較的安いコストで探査することができる。
また本発明では、トンネル切羽から５０〜１００ｍ程度前方地盤の地下水探査を比較的短時間で終了させることができるため、トンネル施工の遅延を防止することができる。
さらに、本発明によれば、トンネル切羽から前方地盤に水平方向に形成した水平ボーリング孔又はトンネル坑壁面の地下水状況と比抵抗値との関係から探査を検証することにより、非常に精度のよい地下水探査が可能となる。 In the groundwater exploration method in the ground in front of the tunnel according to the present invention, one pre-formed survey boring hole is used, or one new almost vertical boring hole is formed from the ground toward the ground in front of the tunnel face. If it is formed, it is possible to measure the specific resistance value between the boreholes by simply forming a short borehole in the vertical direction from the wall in the tunnel mine, and the groundwater situation can be surveyed accurately and at a relatively low cost. be able to.
Further, in the present invention, since groundwater exploration in the ground approximately 50 to 100 m from the tunnel face can be completed in a relatively short time, delay in tunnel construction can be prevented.
Furthermore, according to the present invention, by examining the exploration from the relationship between the ground boring hole formed in the horizontal direction from the tunnel face to the front ground or the ground water situation of the tunnel pit wall surface and the specific resistance value, the groundwater with very high accuracy can be obtained. Exploration becomes possible.

以下、本発明の実施の形態を説明するが、本発明はこれに限定されるものではない。
図１乃至図３は、本発明にかかるトンネル前方地盤内の地下水探査方法の一実施形態を示している。 Hereinafter, although embodiment of this invention is described, this invention is not limited to this.
1 to 3 show an embodiment of the groundwater exploration method in the ground in front of the tunnel according to the present invention.

本発明をトンネル坑内の湧水が比較的多い地盤に適用する場合、図１に示したように、トンネル切羽１１からほぼ１０ｍ程度後方の地点で天端１２及びインバート１３からトンネル軸にほぼ直交する上下方向に２０〜３０ｍ程度の比較的短いボーリング孔１４，１５（以下、短尺ボーリング孔１４，１５という）を形成する。この短尺ボーリング孔１４，１５は、多くのトンネル施工において採用されているドリルジャンボなどの削岩機により形成可能である。
一方、地上１６からは、トンネル切羽前方の地盤１７に向けてほぼ鉛直のボーリング孔１８を形成する。この鉛直ボーリング孔１８は、本発明を実施するに際して新たに形成するか、またはトンネルの掘削開始以前にトンネル予定線に向けて予め形成された調査ボーリング孔を使用することが可能である。鉛直ボーリング孔１８は、トンネル切羽１１からほぼ４０〜９０ｍ程度離間した位置に設けることが好ましい。 When the present invention is applied to the ground having a relatively large amount of spring water in the tunnel mine, as shown in FIG. 1, it is substantially orthogonal to the tunnel axis from the top 12 and the invert 13 at a point about 10 m behind the tunnel face 11. Relatively short boring holes 14 and 15 (hereinafter referred to as short boring holes 14 and 15) of about 20 to 30 m are formed in the vertical direction. The short boring holes 14 and 15 can be formed by a rock drill such as a drill jumbo that is employed in many tunnel constructions.
On the other hand, a substantially vertical boring hole 18 is formed from the ground 16 toward the ground 17 in front of the tunnel face. The vertical boring hole 18 can be newly formed when the present invention is carried out, or an investigation boring hole formed in advance toward the planned tunnel line before the start of tunnel excavation can be used. The vertical boring hole 18 is preferably provided at a position approximately 40 to 90 m away from the tunnel face 11.

以上のように形成した短尺ボーリング孔１４，１５及び鉛直ボーリング孔１８に、ほぼ２ｍ間隔でそれぞれ電極１４ａ，１５ａ，１８ａを配置する。短尺ボーリング孔１４，１５内の電極１４ａ，１５ａのうち選択した一つの電極と、鉛直ボーリング孔１８内の電極１８ａのうち選択した一つの電極との間で通電し、一方の電極に接続された測定機（図示せず）により比抵抗を測定する。短尺ボーリング孔１４，１５内及び鉛直ボーリング孔１８内の全ての電極において、このような一対一の電極の全ての組み合わせで比抵抗を順次測定する。   Electrodes 14a, 15a and 18a are respectively arranged in the short boring holes 14 and 15 and the vertical boring hole 18 formed as described above at intervals of about 2 m. A current was passed between one electrode selected from the electrodes 14a and 15a in the short boring holes 14 and 15 and one electrode selected from the electrodes 18a in the vertical boring hole 18 and connected to one electrode. The specific resistance is measured with a measuring machine (not shown). In all the electrodes in the short boring holes 14 and 15 and in the vertical boring hole 18, the specific resistance is sequentially measured by all the combinations of such one-to-one electrodes.

次に、トンネル切羽１１から短尺ボーリング孔１４，１５までの区間の坑壁面１９におけるトンネル基面に近い高さに、ほぼ２ｍ間隔で電極１９ａを配置する。
坑壁面１９に設置した電極１９ａに関しても、鉛直ボーリング孔１８の電極１８ａとの間で、一対一の電極の全ての組み合わせで比抵抗を順次測定する。また電極１９ａを設置した坑壁面１９からの湧水量と、坑壁面１９の比抵抗値とを比較し、湧水量と比抵抗値との関係が得られることにより、探査範囲の地下水胚胎状態を定量的に評価する。 Next, the electrodes 19a are arranged at intervals of about 2 m at a height close to the tunnel base surface in the pit wall surface 19 in the section from the tunnel face 11 to the short boring holes 14,15.
With respect to the electrode 19 a installed on the well wall 19, the specific resistance is sequentially measured with all the combinations of one-to-one electrodes with the electrode 18 a of the vertical boring hole 18. In addition, the amount of spring water from the well wall 19 where the electrode 19a is installed is compared with the specific resistance value of the well wall 19, and the relationship between the spring water amount and the specific resistance value is obtained. To evaluate.

最後に、既にパッケージソフトとして販売されている解析ソフトウェアを使用し、比抵抗値から、例えば、図３に示したようなトモグラフィにより出力する。これは、図１において点線で囲った計測範囲２０、すなわち、上下方向の短尺ボーリング孔１４，１５と、鉛直ボーリング孔１８と、上端の電極どうしを接続する線と、下端の電極どうしを接続する線とで囲まれたほぼ垂直な平面における比抵抗の修正値の分布である。比抵抗は、岩盤中に含まれている水分量により変化するものであり、比抵抗が高い場合には、堅硬な岩盤もしくは風化層等のように間隙率が大きいが含水率の低い部分であり、また比抵抗が低い場合には、岩盤は堅硬だが粘土層や石墨等の導電性鉱物を挟在する部分、著しく低比抵抗の水を含む部分、もしくは断層・破砕帯等のように間隙率が大きくて且つ地下水で飽和されている部分、粘土帯である。   Finally, using analysis software already sold as package software, the specific resistance value is output by, for example, tomography as shown in FIG. This is a measurement range 20 surrounded by a dotted line in FIG. 1, that is, a vertical boring hole 14, 15, a vertical boring hole 18, a line connecting upper electrodes, and a lower electrode are connected. It is a distribution of correction values of specific resistance in a substantially vertical plane surrounded by a line. The specific resistance varies depending on the amount of water contained in the rock mass. When the specific resistance is high, the porosity is large but the moisture content is low, such as hard rock or weathered layer. When the resistivity is low, the bedrock is hard, but the porosity is such as a part where conductive minerals such as clay layers and graphite are sandwiched, a part containing extremely low resistivity water, or a fault / fracture zone. This is a clay zone, which is large and saturated with groundwater.

次に、図２は、本発明をトンネル坑内の湧水が比較的少ない地盤に適用した探査状況の断面図である。この場合、図２に示したように、トンネル切羽１１とほぼ同地点又は切羽から数センチ程度後方の地点で天端１２及びインバート１３からトンネル軸にほぼ直交する上下方向に１０〜３０ｍ程度の比較的短い短尺ボーリング孔２４，２５を削岩機等により形成する。また短尺ボーリング孔２４，２５に加えて、切羽１１からトンネル切羽前方地盤１７に向けて水平方向に２０〜３０ｍ程度の比較的短い水平ボーリング孔２６を形成する。
一方、地上１６からは、トンネル切羽前方地盤１７に向けてほぼ鉛直のボーリング孔１８を形成する。この鉛直ボーリング孔１８は、新たに形成するか、または既設の調査ボーリング孔を使用し、鉛直ボーリング孔１８とトンネル切羽１１との離間距離はほぼ５０〜１００ｍ程度とすることが好ましい。 Next, FIG. 2 is a cross-sectional view of an exploration situation in which the present invention is applied to the ground having relatively little spring water in the tunnel mine. In this case, as shown in FIG. 2, a comparison of about 10 to 30 m in the vertical direction almost perpendicular to the tunnel axis from the top 12 and the invert 13 at the same point as the tunnel face 11 or a point about several centimeters behind the face. Short short boring holes 24 and 25 are formed by a rock drill or the like. Further, in addition to the short boring holes 24 and 25, a relatively short horizontal boring hole 26 of about 20 to 30 m is formed in the horizontal direction from the face 11 toward the front face 17 of the tunnel face.
On the other hand, a substantially vertical boring hole 18 is formed from the ground 16 toward the ground 17 in front of the tunnel face. It is preferable that the vertical boring hole 18 is newly formed or an existing survey boring hole is used, and the distance between the vertical boring hole 18 and the tunnel face 11 is about 50 to 100 m.

次に、図１の態様と同様に、短尺ボーリング孔２４，２５及び鉛直ボーリング孔１８にほぼ２ｍ間隔でそれぞれ電極２４ａ，２５ａ，１８ａを配置し、短尺ボーリング孔２４，２５内の電極２４ａ，２５ａと、鉛直ボーリング孔１８内の電極１８ａとから、一対一の全ての組み合わせで通電し、一方の電極に接続された測定機（図示せず）により比抵抗を順次測定する。また水平ボーリング孔２６にもほぼ２ｍ間隔でそれぞれ電極２６ａを配置し、これらの電極２６ａに関しても、鉛直ボーリング孔１８の電極１８ａとの間で、一対一の全ての組み合わせで比抵抗を順次測定する。また水平ボーリング孔２６を形成するときに、ボーリング孔の深さが２ｍずつ増加する毎に湧水量を、水平ボーリング孔２６の比抵抗値と比較することで、湧水量と比抵抗値との関係が得られることにより、探査範囲の地下水胚胎状況を定量的に評価する。
最後に、これらの比抵抗値からトモグラフィ（図示せず）により結果を出力する。 Next, as in the embodiment of FIG. 1, the electrodes 24a, 25a, 18a are arranged in the short boring holes 24, 25 and the vertical boring hole 18 at intervals of about 2 m, respectively, and the electrodes 24a, 25a in the short boring holes 24, 25 are arranged. The electrodes 18a in the vertical boring holes 18 are energized in all one-to-one combinations, and the specific resistance is sequentially measured by a measuring machine (not shown) connected to one of the electrodes. Electrodes 26a are also arranged in the horizontal boring holes 26 at intervals of approximately 2 m, and the specific resistances of these electrodes 26a are sequentially measured in all one-to-one combinations with the electrodes 18a of the vertical boring holes 18. . Further, when the horizontal borehole 26 is formed, each time the depth of the borehole increases by 2 m, the amount of spring water is compared with the specific resistance value of the horizontal borehole 26, so that the relationship between the spring water amount and the specific resistance value. To obtain a quantitative assessment of the groundwater embryo status in the exploration area.
Finally, a result is output from these specific resistance values by tomography (not shown).

トンネル坑内における湧水が多い場合の探査状況を示す断面図である。It is sectional drawing which shows the search condition in case there are many springs in a tunnel mine. トンネル坑内における湧水が少ない場合の探査状況を示す断面図である。It is sectional drawing which shows the search condition in case there is little spring water in a tunnel mine. 図１の断面図に解析結果のトモグラフィを重ねて示した図である。FIG. 2 is a diagram in which the tomography of the analysis result is superimposed on the sectional view of FIG.

符号の説明Explanation of symbols

１１ トンネルの切羽
１２ 天端
１３ インバート
１４ 短尺ボーリング孔
１４ａ 短尺ボーリング孔１４内に設置された電極
１５ 短尺ボーリング孔
１５ａ短尺ボーリング孔１５内に設置された電極
１６ 地上
１７ トンネル切羽前方の地盤
１８ 鉛直ボーリング孔
１９ トンネルの坑壁面
１９ａ 坑壁面１９に設置された電極
２４ 短尺ボーリング孔
２４ａ 短尺ボーリング孔２４に設置された電極
２５ 短尺ボーリング孔
２５ａ 短尺ボーリング孔２５に設置された電極
２６ 水平ボーリング孔
２６ａ 水平ボーリング孔２６に設置された電極 DESCRIPTION OF SYMBOLS 11 Tunnel face 12 Top end 13 Invert 14 Short boring hole 14a Electrode installed in the short boring hole 15 15 Short boring hole 15a Electrode installed in the short boring hole 16 16 Above ground 17 Ground in front of the tunnel face 18 Vertical boring Hole 19 Tunnel wall surface 19a Electrode installed on the tunnel wall 19 24 Short boring hole 24a Electrode installed on the short boring hole 25 Short boring hole 25a Electrode installed on the short boring hole 26 Horizontal boring hole 26a Horizontal boring Electrode installed in hole 26

Claims (3)

地上においては、トンネル切羽前方の地盤内に向けて地表面からほぼ鉛直のボーリング孔を形成し、当該ボーリング孔内の複数箇所に電極を設置するか、または地表面からトンネル切羽前方の地盤内に向けてほぼ鉛直に予め形成されている既存のボーリング孔内の複数箇所に電極を設置し、
トンネル坑内においては、切羽付近又は切羽から離間した所定長後方でトンネル軸にほぼ直交する上下方向にボーリング孔を形成し、各ボーリング孔内の複数箇所に電極を設置し、
地表面から形成されたボーリング孔内の電極と、トンネル坑内から形成されたボーリング孔内の電極との間で比抵抗値を求めてトンネル掘削方向の前方地盤における地下水状況を予測することを特徴とするトンネル前方地盤内の地下水探査方法。 On the ground, bore holes that are almost vertical from the ground surface toward the ground in front of the tunnel face, and install electrodes at multiple locations within the borehole, or from the ground surface into the ground in front of the tunnel face. Electrodes are installed at multiple locations within the existing boreholes that are pre-formed almost vertically toward
In the tunnel pit, boring holes are formed in the vertical direction approximately perpendicular to the tunnel axis in the vicinity of the face or behind a predetermined length away from the face, and electrodes are installed at a plurality of locations in each bore hole,
It is characterized by predicting the groundwater condition in the front ground in the tunnel excavation direction by obtaining the specific resistance value between the electrode in the borehole formed from the ground surface and the electrode in the borehole formed from the tunnel tunnel. Groundwater exploration method in the ground ahead of the tunnel. 前記上下方向のボーリング孔を切羽付近に設けた場合には、これらに加えて、切羽からトンネル掘削方向の地盤に向けて水平方向にボーリング孔を形成し、当該水平方向のボーリング孔内の複数箇所に電極を設置することを特徴とする前記請求項１に記載のトンネル前方地盤内の地下水探査方法。   In the case where the vertical boring hole is provided near the face, in addition to these, a boring hole is formed in the horizontal direction from the face to the ground in the tunnel excavation direction, and a plurality of locations in the horizontal boring hole are formed. 2. The groundwater exploration method in the tunnel front ground according to claim 1, wherein an electrode is installed on the ground. 前記上下方向のボーリング孔を切羽から離間した所定長後方に設けた場合には、これらに加えて、上下方向のボーリング孔が設けられた付近から切羽までのトンネル坑壁面に複数箇所に電極を設置することを特徴とする前記請求項１に記載のトンネル前方地盤内の地下水探査方法。   When the vertical boring hole is provided at a predetermined length behind the face, in addition to this, electrodes are installed at multiple locations on the tunnel well wall from the vicinity where the vertical boring hole is provided to the face. The groundwater exploration method in the tunnel front ground according to claim 1, characterized in that:
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