JP4164747B2

JP4164747B2 - Magnetic exploration method

Info

Publication number: JP4164747B2
Application number: JP2003096384A
Authority: JP
Inventors: 英俊西岡; 洋羽矢
Original assignee: Railway Technical Research Institute
Current assignee: Railway Technical Research Institute
Priority date: 2003-03-31
Filing date: 2003-03-31
Publication date: 2008-10-15
Anticipated expiration: 2023-03-31
Also published as: JP2004301745A

Description

【０００１】
【発明の属する技術分野】
本発明は、磁気探査方法に関し、特に基礎杭の先端位置を検出する磁気探査方法に関する。
【０００２】
【従来の技術】
施行年度の古い構造物の耐震性判定のためや、老朽化した構造物の更新のためには、基礎杭の杭長を確認しておく必要があるが、図面等が存在しない場合には、基礎杭の杭長を調査しなければならない。
【０００３】
従来、基礎杭の杭長の調査には、両コイル型磁気傾度計を用いた磁気探査方法が行われている。磁気探査方法は、基礎杭の残留磁気や地球磁場による感応磁気を測定することによって杭長を特定するもので、ロータリーボーリング等によって測定対象の基礎杭の近傍に探査孔を掘削し、当該探査孔に両コイル型磁気傾度計を挿入して一定速度で移動させることによって磁気傾度、すなわち磁場の強さの変化率を測定し、杭長を特定する（例えば、非特許文献１参照）。
【０００４】
【非特許文献１】
「磁気探査を用いた橋梁基礎の形状調査法マニュアル」建設省土木研究所、平成１１年３月
【０００５】
【発明が解決しようとする課題】
しかしながら、従来技術の両コイル型磁気傾度計のような磁場強さの勾配を測定する手法では、コイルを一定速度で移動させて生じる起電圧の変化から磁気傾度、すなわち磁場の強さの変化率を測定しているため、Ｈ型鋼杭等の比較的鋼材量が多く、残留磁気量が大きい物に対しては実績が得られているものの、場所打ち杭等のように鉄筋量が少ない杭や、フーチングによって探査孔を杭から離れたところに配置しなければならない場合には、高い検知精度が期待できないという問題点があった。
【０００６】
本発明は斯かる問題点を鑑みてなされたものであり、その目的とするところは、場所打ち杭等のように鉄筋量が少ない杭や、フーチングによって探査孔を杭から離れたところに配置しなければならない場合にも、杭長を正確に検出することができる磁気探査方法を提供する点にある。
【０００７】
【課題を解決するための手段】
本発明は上記課題を解決すべく、以下に掲げる構成とした。
請求項１記載の発明の要旨は、鋼材を含む基礎杭の近傍の磁気探査を行って、基礎杭の先端位置を非接触で検出する磁気探査方法であって、互いに直交するｘ軸、ｙ軸およびｚ軸の磁気量を測定可能な３次元磁気センサをｚ軸が前記基礎杭と平行になるように位置決めした状態でｚ軸方向に移動させ、前記３次元磁気センサによってｚ軸方向の複数の箇所でそれぞれｘ軸方向の磁気量ＢＸ、ｙ軸方向の磁気量ＢＹおよびｚ軸方向の磁気量ＢＺを測定し、前記磁気量ＢＸと前記磁気量ＢＹとから前記基礎杭に対して垂直な面上の磁気量ＢＨを算出し、当該磁気量ＢＨと前記磁気量ＢＺとから予め測定しておいた地磁気をそれぞれ除去して地磁気を除去した前記基礎杭に対して垂直な面上の磁気量Ｂｈと地磁気を除去したｚ軸方向の磁気量Ｂｚとをそれぞれ算出し、前記磁気量Ｂｈと前記磁気量Ｂｚとに基づく形状解析結果を前記ｚ軸方向の複数の箇所毎に出力することを特徴とする磁気探査方法に存する。
また請求項２記載の発明の要旨は、鋼材を含む基礎杭の近傍の磁気探査を行って、前記基礎杭の先端位置を非接触で検出する磁気探査方法であって、互いに直交するｘ軸、ｙ軸およびｚ軸の磁気量を測定可能な３次元磁気センサをｚ軸が前記基礎杭と平行になると共にｘ軸およびｙ軸が変位しないように位置決めした状態でｚ軸方向に移動させ、前記３次元磁気センサによってｚ軸方向の複数の箇所でそれぞれｘ軸方向の磁気量ＢＸ、ｙ軸方向の磁気量ＢＹおよびｚ軸方向の磁気量ＢＺを測定し、前記磁気量ＢＸ、前記磁気量ＢＹおよび前記磁気量ＢＺとから予め測定しておいた地磁気をそれぞれ除去して地磁気を除去したｘ軸方向の磁気量Ｂｘ、地磁気を除去したｙ軸方向の磁気量Ｂｙおよび地磁気を除去したｚ軸方向の磁気量Ｂｚをそれぞれ算出し、前記磁気量Ｂｘと前記磁気量Ｂｙとから前記基礎杭に対して垂直な面上の磁気量Ｂｈを算出し、前記磁気量Ｂｈと前記磁気量Ｂｚとに基づく形状解析結果を前記ｚ軸方向の複数の箇所毎に出力することを特徴とする磁気探査方法に存する。
また請求項３記載の発明の要旨は、前記形状解析結果は、前記磁気量Ｂｈと前記磁気量Ｂｚとの比を表す情報であることを特徴とする請求項１又は２記載の磁気探査方法に存する。
また請求項４記載の発明の要旨は、前記３次元磁気センサは、互いに直交する向きに配置された３つのホール素子からなることを特徴とする請求項１乃至３のいずれかに記載の磁気探査方法に存する。
また請求項５記載の発明の要旨は、鋼材を含む基礎杭の近傍の磁気探査を行って、前記基礎杭の先端位置を非接触で検出する磁気探査方法であって、互いに直交するｘ軸およびｚ軸の磁気量を測定可能な２次元磁気センサをｚ軸が前記基礎杭と平行になると共にｘ軸が変位しないように位置決めした状態でｚ軸方向に移動させ、
前記２次元磁気センサによってｚ軸方向の複数の箇所でそれぞれｘ軸方向の磁気量ＢＸおよびｚ軸方向の磁気量ＢＺを測定し、前記磁気量ＢＸと前記磁気量ＢＺとから予め測定しておいた地磁気をそれぞれ除去して地磁気を除去したｘ軸方向の磁気量Ｂｘと地磁気を除去したｚ軸方向の磁気量Ｂｚとをそれぞれ算出し、前記磁気量Ｂｘと前記磁気量Ｂｚとに基づく形状解析結果を前記ｚ軸方向の複数の箇所毎に出力することを特徴とする磁気探査方法に存する。
また請求項６記載の発明の要旨は、前記形状解析結果は、前記磁気量Ｂｘと前記磁気量Ｂｚとの比を表す情報であることを特徴とする請求項５記載の磁気探査方法に存する。
また請求項７記載の発明の要旨は、前記２次元磁気センサは、互いに直交する向きに配置された２つのホール素子からなることを特徴とする請求項５又は６記載の磁気探査方法に存する。
【０００８】
【発明の実施の形態】
以下、本発明の実施の形態を図面に基づいて詳細に説明する。
【０００９】
図１は、本発明に係る磁気探査方法の実施の形態で使用する機器構成を示す図であり、図２は、図１に示す形状解析装置の構成を示すブロック図であり、図３は、図２に示す水平磁界算出部における水平磁界の算出方法を説明するための図であり、図４は、図２に示す探査結果算出部において算出された探査結果を説明するための図である。
【００１０】
本実施の形態では、互いに直交する向き（ｘ軸、ｙ軸、ｚ軸）の磁界の強さを測定可能な３次元磁気センサ４を使用して磁場の分布を測定する。本実施の形態で使用する３次元磁気センサ４は、例えば互いに直交する向きに配置された３つのホール素子からなるもので、静止状態で互いに直交する向きの磁界の強さを測定することが可能な構成となっている。なお、ホール素子の替わりにフラックスゲート型センサやＳＱＵＩＤ型センサ等を用いることもできる。
【００１１】
図１を参照すると、測定対象の基礎杭１の近傍に基礎杭１と平行（鉛直）な探査孔２を掘削し、探査孔２の全長にわたってアルミや塩化ビニール等の非磁性ガイド管３を挿入する。次に非磁性ガイド管３に３次元磁気センサ４を挿入し、基礎杭１の軸方向に深さを変えながらｘ軸方向、ｙ軸方向、ｚ軸方向の磁界の強さをそれぞれ測定していく。なお、測定対象の基礎杭１としては、具体的には、杭（鋼杭，場所打ち杭）の他、ケーソン（鋼製，鉄筋コンクリート製）、井筒（鉄筋コンクリート製）等が考えられる。
【００１２】
３次元磁気センサ４は、図１に示すようにｚ軸が基礎杭１に平行（鉛直）になるように位置決めされ、ｘ軸およびｙ軸がｚ軸と垂直な平面（水平面）上に位置する。なお、３次元磁気センサ４は、吊り下げることによって鉛直方向がｚ軸になるように構成されており、図１に示すように吊り下げるだけでも各軸の位置決めが可能であるが、より精度良く位置決めする場合には、探査孔２内に基礎杭１と平行なガイド棒を設置し、当該ガイド棒でガイドしながらｚ軸方向を移動させるようにすれば良い。
【００１３】
３次元磁気センサ４からの出力は、増幅器６で増幅され、プーリー５に接続されたカウンタ７からの深さ情報と共にデータ収集器８に入力される。従って、データ収集器８には、深さ毎のｘ軸方向、ｙ軸方向およびｚ軸方向の磁界の強さが探査データとして収集されることになる。
【００１４】
形状解析装置９は、図２を参照すると、データ収集器８からの探査データが入力される探査データ入力部９１と、予め測定しておいた地磁気データが記憶される地磁気記憶部９２と、地磁気記憶部９２に記憶されている地磁気データに基づいて探査データから地磁気を除去する地磁気除去部９３と、水平磁界算出部９４と、探査結果算出部９５と、データ出力部９６とからなる。
【００１５】
探査データ入力部９１には、データ収集器８から探査データとして深さ毎のｘ軸方向の磁界の強さＢＸと、ｙ軸方向の磁界の強さＢＹと、ｚ軸方向の磁界の強さＢＺとが入力される。
【００１６】
地磁気記憶部９２に記憶される地磁気は、周囲の磁性体から十分離れた位置に３次元磁気センサ４を置き、ｚ軸が鉛直方向になるように調整し、ｘ軸方向、ｙ軸方向、ｚ軸方向の３方向成分の磁界の強さ（μＴ）をそれぞれ測定し、当該測定結果をそれぞれ地磁気Ｂｘ_０、Ｂｙ_０、Ｂｚ_０として記憶させておく。
【００１７】
水平磁界算出部９４は、以下に示す式によって水平成分の磁界の強さＢＨを算出する。すなわち、図３に示すように、３次元磁気センサ４が回転してｘ軸およびｙ軸が変化しても、ｘ軸方向の磁界の強さＢＸと、ｙ軸方向の磁界の強さＢＹとから正確な水平成分の磁界の強さＢＨを算出する。
【００１８】

【００１９】
地磁気除去部９３は、以下に示す式によって水平成分の地磁気Ｂｈ_０を算出し、地磁気を除去した水平成分の磁界の強さＢｈ＝ＢＨ−Ｂｈ_０と、地磁気を除去した鉛直方向の磁界の強さＢｚ＝ＢＺ−Ｂｚ_０を算出する。
【００２０】

【００２１】
探査結果算出部９５は、地磁気を除去した水平成分の磁界の強さＢｈと、地磁気を除去した鉛直方向の磁界の強さＢｚとからｔａｎθ＝Ｂｈ／Ｂｚを算出する。
このようにして深さ毎のｔａｎθ＝Ｂｈ／Ｂｚを算出してプリンタ等のデータ出力部９６にグラフや表として出力する。
【００２２】
基礎杭１を磁石してみなすと、基礎杭１からは、図４に示すような磁力線がでていることになり、ｔａｎθ＝Ｂｈ／Ｂｚを算出して水平成分の磁界の強さＢｈと鉛直方向の磁界の強さＢｚとの比として捉えることにより、磁力線の角度の変化を検出できるため、データ出力部９６から出力されるグラフや表には、基礎杭１の先端位置を中心とした明らかな変動が確認でき、基礎杭１の杭長を検出することが可能になる。
【００２３】
また、鉛直方向の磁界の強さＢｚのみでは、基礎杭１と３次元磁気センサ４との離隔が大きいときに誤差が大きくなるが、水平成分の磁界の強さＢｈ、鉛直方向の磁界の強さＢｚとも同じレベルで磁気量が低下するため、ｔａｎθ＝Ｂｈ／Ｂｚとすれば、磁気量が小さくても精度が良く基礎杭１の先端位置を検出することが可能になる。さらに、ｔａｎθ＝Ｂｈ／Ｂｚとすることで、θ＝０で正負が入れ替わり、検出の信頼性が向上する。
【００２４】
なお、本実施の形態では、３次元磁気センサ４の回転を考慮して水平成分の磁界の強さＢＨを、ｘ軸方向の磁界の強さＢＸと、ｙ軸方向の磁界の強さＢＹとから算出するように構成したが、ｚ軸（鉛直方向）の移動に際して３次元磁気センサ４が回転しないように、すなわちｘ軸およびｙ軸が動かないように位置決めすると、地磁気の除去をより正確に行うことができる。
【００２５】
この場合には、地磁気除去部９３によって、成分毎に地磁気を除去し、地磁気を除去したｘ軸方向の磁界の強さＢｘ＝ＢＸ−Ｂｘ_０と、地磁気を除去したｙ軸方向の磁界の強さＢｙ＝ＢＹ−Ｂｙ_０と、地磁気を除去したｚ軸方向（鉛直方向）の磁界の強さＢｚ＝ＢＺ−Ｂｚ_０をそれぞれ算出し、水平磁界算出部９４によって、地磁気を除去したｘ軸方向の磁界の強さＢｘと、地磁気を除去したｙ軸方向の磁界の強さＢｙとから以下に示す式によって水平成分の磁界の強さＢｈを算出するようにすれば良い。
【００２６】

【００２７】
また、ｘ軸およびｙ軸が動かないように位置決めした場合には、水平成分の磁界の強さＢｈを算出することなく、探査結果算出部９５において、地磁気を除去したｘ軸方向の磁界の強さＢｘもしくは地磁気を除去したｙ軸方向の磁界の強さＢｙを用いてｔａｎθ＝Ｂｘ／Ｂｚもしくはｔａｎθ＝Ｂｙ／Ｂｚを算出するようにしても良く、この場合には、３次元磁気センサ４の替わりに互いに直交する向き（ｘ軸もしくはｙ軸、ｚ軸）の磁界の強さを測定可能な２次元磁気センサを用いることができる。
【００２８】
以上説明したように、本実施の形態によれば、互いに直交する向き（ｘ軸、ｙ軸、ｚ軸）の磁界の強さを測定可能な３次元磁気センサ４を使用して磁場の分布を測定し、測定結果を水平成分の磁界の強さＢｈと鉛直方向の磁界の強さＢｚとの比として捉えることにより、場所打ち杭等のように、鋼杭と比べて鋼材量が少ない杭や、フーチングによって探査孔を杭から離れたところに配置しなければならない場合にも、杭長を正確に検出することができるという効果を奏する。
【００２９】
さらに、本実施の形態によれば、ｘ軸方向の磁界の強さＢｘと、ｙ軸方向の磁界の強さＢｙとから水平成分の磁界の強さＢｈを算出することにより、３次元磁気センサ４の複雑な位置決めを必要とせず、簡易な装備で磁気探査を行うことができるという効果を奏する。
【００３０】
【実施例】
（実施例１）
図５は、本発明に係る磁気探査方法の実施例１の測定条件を示す図であり、（ａ）は、側面図であり、（ｂ）は、正面図であり、（ｃ）は、上面図である。図６および図７は、本発明に係る磁気探査方法の実施例１の探査結果を示すグラフである。
【００３１】
図５に示すように、横に寝かせた鉄筋篭１０から距離Ｌを離して、３次元磁気センサ４（ホール素子）を固定するセンサ固定用治具１１を設置し、当該センサ固定用治具１１上を５０ｍｍピッチで３次元磁気センサ４を移動させながら、各位置での磁界強さを測定した。この測定を鉄筋篭１０から３次元磁気センサ４までの距離ＬがＬ＝１０ｃｍ、Ｌ＝５０ｃｍ、Ｌ＝１００ｃｍに３ケースについてそれぞれ行った。３次元磁気センサ４によって測定する磁界の座標は、３次元磁気センサ４の移動軸をｚ軸、鉛直方向をｘ軸、水平方向がｙ軸となるようにし、各位置でｘ軸方向、ｙ軸方向、ｚ軸方向の３方向成分をそれぞれ測定し、各測定結果から地磁気を除去した結果をＢｘ、Ｂｙ、Ｂｚ（μＴ）とした。地磁気としては、鉄筋篭１０がない状態でｘ軸方向、ｙ軸方向、ｚ軸方向の３方向成分（μＴ）の磁界の強さ（μＴ）をそれぞれ測定し、当該測定結果をそれぞれ地磁気Ｂｘ_０、Ｂｙ_０、Ｂｚ_０として地磁気の除去を行った。なお、同一位置では、２回以上計測を行い、磁場の定常性を確認した。
【００３２】
このようにして測定したＢｘ、Ｂｙに基づいて、
処理Ａ：鉄筋篭軸方向（z軸方向）の磁気量分布勾配（ｄＢｚ／ｄｚ）、
処理Ｂ：鉄筋篭軸方向（ｚ軸方向）の磁界の強さ／鉄筋篭直角軸方向水平成分（ｙ軸方向）の磁界の強さ、の２通りの形状解析処理を行い、両者を比較した。
ここで処理Ａは、鉄筋篭軸方向成分の一階微分であり、磁気傾度計を用いた従来方式の計測で得られる値と同等のものとなり、処理Ｂは、本実施の形態において、３次元磁気センサ４のｘ軸およびｙ軸を位置決めして測定し、水平成分中のｙ軸成分に基づいて探査結果を算出した場合に相当する。
【００３３】
その結果、図６（ａ）に示すようにＬ＝１０ｃｍでは、処理Ａおよび処理Ｂのいずれにおいても鉄筋篭１０の先端位置を中心とした明らかな変動が確認できるが、Ｌ＝５０ｃｍおよびＬ＝１００ｃｍでは、図６（ｂ）および図７にそれぞれ示すように、処理Ｂのみ鉄筋篭１０の先端位置を中心とした明らかな変動が確認できる。
【００３４】
（実施例２）
図８は、本発明に係る磁気探査方法の実施例２の測定条件を示す図であり、（ａ）は、側面図であり、（ｂ）は、上面図である。図９は、本発明に係る磁気探査方法の実施例２の測定結果を示すグラフである。
【００３５】
図８に示すように、土中に鉄筋１２（Ｄ３２）と計測用パイプ１３（アルミ製）とを埋設し、計測用パイプ１３内に３次元磁気センサ４（ホール素子）を固定するセンサ固定用治具１１を設置し、当該センサ固定用治具上で３次元磁気センサ４を移動させながら、各位置での磁界強さを測定した。鉄筋１２から３次元磁気センサ４までの距離Ｌは、Ｌ＝１２ｃｍに設定した。３次元磁気センサ４によつて測定する磁界の座標は、３次元磁気センサ４の移動軸（鉛直方向）をｚ軸に、水平面は、南北方向がｙ軸、東西方向がｘ軸になるようにし、各位置でｘ軸方向、ｙ軸方向、ｚ軸方向の３方向成分をそれぞれ測定し、各測定結果から地磁気を除去した結果をＢｘ、Ｂｙ、Ｂｚ（μＴ）とした。地磁気としては、鉄筋篭がない状態でｘ軸方向、ｙ軸方向、ｚ軸方向の３方向成分（μＴ）でそれぞれ測定し、当該測定結果をそれぞれ地磁気Ｂｘ_０、Ｂｙ_０、Ｂｚ_０として地磁気の除去を行った。なお、同一位置では、２回以上計測を行い、磁場の定常性を確認した。
【００３６】
このようにして測定したＢｘ、Ｂｙ、Ｂｚに基づいて、
処理Ａ：鉄筋軸方向（z軸方向）の磁気量分布勾配（ｄＢｚ／ｄｚ）、
処理Ｂ：鉄筋直角軸方向水平成分の磁界の強さＢｈ／鉄筋軸方向（z軸方向）の磁界の強さＢｚ、の２通りの形状解析処理を行い、両者を比較した。
ここで処理Ａは、鉄筋軸方向成分の一階微分であり、磁気傾度計を用いた従来方式の計測で得られる値と同等のものとなり、処理Ｂは、本実施の形態において、３次元磁気センサ４のｘ軸およびｙ軸を位置決めして測定し、水平成分中のｘ軸成分およびｙ軸成分に基づいて探査結果を算出した場合に相当する。
【００３７】
その結果、図９に示すように、処理Ｂでは、鉄筋１２の先端位置を中心とした明らかな変動が確認できるが、処理Ａでは、明確な違いは得られなかった。
【００３８】
なお、本発明が上記各実施の形態に限定されず、本発明の技術思想の範囲内において、各実施の形態は適宜変更され得ることは明らかである。また、上記構成部材の数、位置、形状等は上記実施の形態に限定されず、本発明を実施する上で好適な数、位置、形状等にすることができる。なお、各図において、同一構成要素には同一符号を付している。
【００３９】
【発明の効果】
本発明の磁気探査方法は、互いに直交する向き（ｘ軸、ｙ軸、ｚ軸）の磁界の強さを測定可能な３次元磁気センサを使用して磁場の分布を測定し、測定結果を水平成分の磁界の強さと鉛直方向の磁界の強さとの比として捉えることにより、場所打ち杭等のように、鋼杭と比べて鋼材量が少ない杭や、フーチングによって探査孔を杭から離れたところに配置しなければならない場合にも、杭長を正確に検出することができるという効果を奏する。
【００４０】
さらに、本発明の磁気探査方法は、ｘ軸方向の磁界の強さと、ｙ軸方向の磁界の強さとから水平成分の磁界の強さを算出することにより、３次元磁気センサの複雑な位置決めを必要とせず、簡易な装備で磁気探査を行うことができるという効果を奏する。
【図面の簡単な説明】
【図１】本発明に係る磁気探査方法の実施の形態で使用する機器構成を示す図である。
【図２】図１に示す形状解析装置の構成を示すブロック図である。
【図３】図２に示す水平磁界算出部における水平磁界の算出方法を説明するための図である。
【図４】図２に示す探査結果算出部において算出された探査結果を説明するための図である。
【図５】本発明に係る磁気探査方法の実施例１の測定条件を示す図であり、（ａ）は、側面図であり、（ｂ）は、正面図であり、（ｃ）は、上面図である。
【図６】本発明に係る磁気探査方法の実施例１の探査結果を示すグラフである。
【図７】本発明に係る磁気探査方法の実施例１の探査結果を示すグラフである。
【図８】本発明に係る磁気探査方法の実施例２の測定条件を示す図であり、（ａ）は、側面図であり、（ｂ）は、上面図である。
【図９】本発明に係る磁気探査方法の実施例２の測定結果を示すグラフである。
【符号の説明】
１基礎杭
２探査孔
３非磁性ガイド管
４３次元磁気センサ
５プーリー
６増幅器
７カウンタ
８データ収集器
９形状解析装置
１０鉄筋篭
１１センサ固定用治具
１２鉄筋
１３計測用パイプ
９１探査データ入力部
９２地磁気記憶部
９３地磁気除去部
９４水平磁界算出部
９５探査結果算出部
９６データ出力部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic exploration method, and more particularly to a magnetic exploration method for detecting a tip position of a foundation pile.
[0002]
[Prior art]
It is necessary to confirm the pile length of the foundation pile for the seismic assessment of the old structure in the year of enforcement or for the replacement of an aged structure. The pile length of the foundation pile must be investigated.
[0003]
Conventionally, in order to investigate the pile length of a foundation pile, a magnetic exploration method using a double-coil magnetic inclinometer has been performed. The magnetic exploration method specifies the pile length by measuring the residual magnetism of the foundation pile and the sensitive magnetism due to the earth's magnetic field. The exploration hole is excavated in the vicinity of the foundation pile to be measured by rotary boring, etc. The magnetic gradient, that is, the rate of change in the strength of the magnetic field is measured by inserting a double coil type magnetic inclinometer and moving at a constant speed, and the pile length is specified (for example, see Non-Patent Document 1).
[0004]
[Non-Patent Document 1]
"Manual of shape survey method for bridge foundation using magnetic exploration", Ministry of Construction, Public Works Research Institute, March 1999 [0005]
[Problems to be solved by the invention]
However, in the method of measuring the gradient of the magnetic field strength, such as the conventional double-coil magnetic inclinometer, the magnetic gradient, that is, the rate of change of the magnetic field strength, from the change in electromotive force generated by moving the coil at a constant speed. However, piles with a small amount of rebar, such as cast-in-place piles, have been used for items with a relatively large amount of steel, such as H-shaped steel piles, and a large amount of residual magnetism. When the exploration hole must be arranged away from the pile by footing, there is a problem that high detection accuracy cannot be expected.
[0006]
The present invention has been made in view of such problems. The purpose of the present invention is to place the exploration hole away from the pile by footing such as a cast-in-place pile or the like with a small amount of reinforcing bars. It is in providing a magnetic exploration method capable of accurately detecting the pile length even when it is necessary.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention has the following configuration.
The gist of the invention described in claim 1 is a magnetic exploration method for detecting the tip position of a foundation pile in a non-contact manner by conducting a magnetic exploration in the vicinity of the foundation pile including the steel material, the x axis and the y axis being orthogonal to each other. And a three-dimensional magnetic sensor capable of measuring the magnetic amount of the z-axis is moved in the z-axis direction while being positioned so that the z-axis is parallel to the foundation pile, and a plurality of z-axis directions are moved by the three-dimensional magnetic sensor. Measure the magnetic quantity BX in the x-axis direction, the magnetic quantity BY in the y-axis direction, and the magnetic quantity BZ in the z-axis direction at each location, and a plane perpendicular to the foundation pile from the magnetic quantity BX and the magnetic quantity BY The upper magnetic amount BH is calculated, and the magnetic amount Bh on the plane perpendicular to the foundation pile from which the geomagnetism is removed by removing the geomagnetism measured in advance from the magnetic amount BH and the magnetic amount BZ. And the magnetic quantity Bz in the z-axis direction from which the geomagnetism is removed, Each calculated resides in magnetic survey method and outputting the magnetic charge Bh and the magnetic charge Bz and shape analysis results based on each of a plurality of positions of the z-axis direction.
The gist of the invention described in claim 2 is a magnetic exploration method for detecting the tip position of the foundation pile in a non-contact manner by conducting a magnetic exploration in the vicinity of the foundation pile including the steel material. moving the three-dimensional magnetic sensor capable of measuring the magnetic quantity of the y-axis and the z-axis in the z-axis direction in a state where the z-axis is parallel to the foundation pile and the x-axis and the y-axis are not displaced, A magnetic quantity BX in the x-axis direction, a magnetic quantity BY in the y-axis direction, and a magnetic quantity BZ in the z-axis direction are measured at a plurality of locations in the z-axis direction by a three-dimensional magnetic sensor, and the magnetic quantity BX and the magnetic quantity BY are measured. And the magnetic quantity Bx in the x-axis direction from which the previously measured geomagnetism is removed from the magnetic quantity BZ to remove the geomagnetism, the magnetic quantity By in the y-axis direction from which the geomagnetism is removed, and the z-axis direction from which the geomagnetism is removed Magnetic quantity Bz of it Is calculated, the calculated magnetic quantity Bh on a plane perpendicular to the foundation piles from magnetic quantity Bx and the magnetic charge By, the said magnetic charge Bh and the magnetic charge Bz and shape analysis results based on The present invention resides in a magnetic exploration method characterized by outputting data at a plurality of locations in the z-axis direction.
The gist of the invention according to claim 3 is the magnetic exploration method according to

claim

1 or 2, wherein the shape analysis result is information representing a ratio between the magnetic quantity Bh and the magnetic quantity Bz. Exist.
According to a fourth aspect of the present invention, in the magnetic exploration according to any one of the first to third aspects, the three-dimensional magnetic sensor includes three Hall elements arranged in directions orthogonal to each other. Lies in the way.
The gist of the invention of claim 5 is a magnetic exploration method for detecting the tip position of the foundation pile in a non-contact manner by conducting a magnetic exploration in the vicinity of the foundation pile including the steel material, A two-dimensional magnetic sensor capable of measuring the magnetic amount of the z-axis is moved in the z-axis direction in a state where the z-axis is parallel to the foundation pile and the x-axis is not displaced,
The two-dimensional magnetic sensor measures a magnetic quantity BX in the x-axis direction and a magnetic quantity BZ in the z-axis direction at a plurality of locations in the z-axis direction, and measures in advance from the magnetic quantity BX and the magnetic quantity BZ. The magnetic quantity Bx in the x-axis direction from which the geomagnetism was removed by removing the existing geomagnetism and the magnetic quantity Bz in the z-axis direction from which the geomagnetism was removed are respectively calculated, and shape analysis based on the magnetic quantity Bx and the magnetic quantity Bz The present invention resides in a magnetic exploration method characterized by outputting a result for each of a plurality of locations in the z-axis direction.
The gist of the invention according to claim 6 resides in the magnetic exploration method according to claim 5, wherein the shape analysis result is information representing a ratio between the magnetic quantity Bx and the magnetic quantity Bz.
The gist of the invention according to claim 7 resides in the magnetic exploration method according to claim 5 or 6, wherein the two-dimensional magnetic sensor comprises two Hall elements arranged in directions orthogonal to each other.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0009]
FIG. 1 is a diagram showing a device configuration used in an embodiment of a magnetic exploration method according to the present invention, FIG. 2 is a block diagram showing a configuration of the shape analysis apparatus shown in FIG. 1, and FIG. FIG. 4 is a diagram for explaining a horizontal magnetic field calculation method in the horizontal magnetic field calculation unit shown in FIG. 2, and FIG. 4 is a diagram for explaining a search result calculated in the search result calculation unit shown in FIG.
[0010]
In the present embodiment, the distribution of the magnetic field is measured using the three-dimensional magnetic sensor 4 that can measure the strength of the magnetic field in directions (x axis, y axis, z axis) orthogonal to each other. The three-dimensional magnetic sensor 4 used in the present embodiment is composed of, for example, three Hall elements arranged in directions orthogonal to each other, and can measure the strength of magnetic fields in directions orthogonal to each other in a stationary state. It has become a structure. Note that a fluxgate type sensor, a SQUID type sensor, or the like can be used instead of the Hall element.
[0011]
Referring to FIG. 1, an exploration hole 2 parallel (vertical) to the foundation pile 1 is excavated in the vicinity of the foundation pile 1 to be measured, and a nonmagnetic guide tube 3 such as aluminum or vinyl chloride is inserted over the entire length of the exploration hole 2 To do. Next, the three-dimensional magnetic sensor 4 is inserted into the nonmagnetic guide tube 3, and the magnetic field strengths in the x-axis direction, the y-axis direction, and the z-axis direction are respectively measured while changing the depth in the axial direction of the foundation pile 1. Go. As the foundation pile 1 to be measured, specifically, a pile (steel pile, cast-in-place pile), a caisson (made of steel, reinforced concrete), a well (made of reinforced concrete), and the like can be considered.
[0012]
As shown in FIG. 1, the three-dimensional magnetic sensor 4 is positioned so that the z axis is parallel (vertical) to the foundation pile 1, and the x axis and the y axis are located on a plane (horizontal plane) perpendicular to the z axis. . The three-dimensional magnetic sensor 4 is configured such that the vertical direction becomes the z-axis by being suspended, and each axis can be positioned by simply suspending as shown in FIG. When positioning, a guide bar parallel to the foundation pile 1 may be installed in the exploration hole 2 and moved in the z-axis direction while being guided by the guide bar.
[0013]
The output from the three-dimensional magnetic sensor 4 is amplified by the amplifier 6 and input to the data collector 8 together with the depth information from the counter 7 connected to the pulley 5. Therefore, the data collector 8 collects the strength of the magnetic field in the x-axis direction, the y-axis direction, and the z-axis direction for each depth as exploration data.
[0014]
Referring to FIG. 2, the shape analysis device 9 includes an exploration data input unit 91 for inputting exploration data from the data collector 8, a geomagnetic storage unit 92 for storing previously measured geomagnetic data, and a geomagnetism. It comprises a geomagnetism removing unit 93 that removes geomagnetism from exploration data based on the geomagnetic data stored in the storage unit 92, a horizontal magnetic field calculating unit 94, an exploration result calculating unit 95, and a data output unit 96.
[0015]
In the search data input unit 91, the magnetic field strength BX in the x-axis direction at every depth, the magnetic field strength BY in the y-axis direction, and the magnetic field strength in the z-axis direction as the search data from the data collector 8. BZ is input.
[0016]
For the geomagnetism stored in the geomagnetism storage unit 92, the three-dimensional magnetic sensor 4 is placed at a position sufficiently away from the surrounding magnetic body and adjusted so that the z-axis is in the vertical direction, and the x-axis direction, y-axis direction, z The magnetic field strengths (μT) of the three-direction components in the axial direction are measured, and the measurement results are stored as geomagnetisms Bx ₀ , By ₀ , and Bz ₀ , respectively.
[0017]
The horizontal magnetic field calculation unit 94 calculates the magnetic field strength BH of the horizontal component by the following equation. That is, as shown in FIG. 3, even if the three-dimensional magnetic sensor 4 rotates and the x-axis and the y-axis change, the magnetic field strength BX in the x-axis direction and the magnetic field strength BY in the y-axis direction From the above, the magnetic field strength BH of an accurate horizontal component is calculated.
[0018]

[0019]
The geomagnetism removing unit 93 calculates the horizontal component geomagnetism Bh ₀ by the following formula, and the horizontal component magnetic field strength Bh = BH−Bh _{0 from} which the geomagnetism has been removed and the vertical magnetic field strength from which the geomagnetism has been removed. Bz = BZ−Bz ₀ is calculated.
[0020]

[0021]
The exploration result calculation unit 95 calculates tan θ = Bh / Bz from the horizontal component magnetic field strength Bh from which the geomagnetism has been removed and the vertical magnetic field strength Bz from which the geomagnetism has been removed.
In this way, tan θ = Bh / Bz for each depth is calculated and output to the data output unit 96 such as a printer as a graph or a table.
[0022]
When the foundation pile 1 is regarded as a magnet, magnetic lines of force as shown in FIG. 4 are generated from the foundation pile 1, and tan θ = Bh / Bz is calculated to calculate the horizontal component magnetic field strength Bh and vertical Since the change in the angle of the magnetic lines of force can be detected by grasping it as a ratio with the magnetic field strength Bz in the direction, the graph and table output from the data output unit 96 are clearly centered on the tip position of the foundation pile 1 Therefore, it is possible to detect the pile length of the foundation pile 1.
[0023]
Further, when the magnetic field strength Bz in the vertical direction alone is used, the error increases when the separation between the foundation pile 1 and the three-dimensional magnetic sensor 4 is large. However, the magnetic field strength Bh in the horizontal component and the magnetic field strength in the vertical direction are large. Since the magnetic amount decreases at the same level as the height Bz, if tan θ = Bh / Bz, the tip position of the foundation pile 1 can be detected with high accuracy even if the magnetic amount is small. Furthermore, by setting tan θ = Bh / Bz, positive and negative are switched at θ = 0, and the detection reliability is improved.
[0024]
In the present embodiment, considering the rotation of the three-dimensional magnetic sensor 4, the horizontal component magnetic field strength BH is set to x-axis direction magnetic field strength BX and y-axis direction magnetic field strength BY. If the positioning is performed so that the three-dimensional magnetic sensor 4 does not rotate during the movement of the z-axis (vertical direction), that is, the x-axis and the y-axis do not move, the removal of the geomagnetism can be performed more accurately. It can be carried out.
[0025]
In this case, the geomagnetism removing unit 93 removes the geomagnetism for each component, and the magnetic field strength in the x-axis direction Bx = BX−Bx _{0 from} which the geomagnetism is removed and the strength of the magnetic field in the y-axis direction from which the geomagnetism is removed. By = BY−By ₀ and the magnetic field strength Bz = BZ−Bz ₀ in the z-axis direction (vertical direction) from which geomagnetism is removed are calculated, respectively, and the horizontal magnetic field calculation unit 94 removes the geomagnetism. The horizontal component magnetic field strength Bh may be calculated from the following magnetic field strength Bx and the magnetic field strength By in the y-axis direction with the earth magnetism removed.
[0026]

[0027]
Further, when positioning is performed so that the x axis and the y axis do not move, the search result calculation unit 95 does not calculate the strength Bh of the horizontal component magnetic field, and the magnetic field strength in the x axis direction from which the geomagnetism is removed is calculated. Tan θ = Bx / Bz or tan θ = By / Bz may be calculated using the strength Bx or the magnetic field strength By in the y-axis direction from which geomagnetism is removed. In this case, the three-dimensional magnetic sensor 4 Instead, it is possible to use a two-dimensional magnetic sensor capable of measuring the strength of the magnetic field in the directions orthogonal to each other (x axis, y axis, z axis).
[0028]
As described above, according to the present embodiment, the distribution of the magnetic field is determined by using the three-dimensional magnetic sensor 4 that can measure the strength of the magnetic field in the directions orthogonal to each other (x axis, y axis, z axis). By measuring and capturing the measurement result as the ratio of the horizontal component magnetic field strength Bh and the vertical magnetic field strength Bz, a pile with less steel material than a steel pile, such as cast-in-place piles, etc. Even when the exploration hole must be arranged away from the pile by footing, the pile length can be accurately detected.
[0029]
Furthermore, according to the present embodiment, the three-dimensional magnetic sensor is obtained by calculating the horizontal component magnetic field strength Bh from the magnetic field strength Bx in the x-axis direction and the magnetic field strength By in the y-axis direction. Thus, there is an effect that magnetic exploration can be performed with simple equipment without requiring the complicated positioning of 4.
[0030]
【Example】
(Example 1)
FIG. 5 is a diagram showing measurement conditions of Example 1 of the magnetic exploration method according to the present invention, (a) is a side view, (b) is a front view, and (c) is an upper surface. FIG. 6 and 7 are graphs showing the search results of Example 1 of the magnetic search method according to the present invention.
[0031]
As shown in FIG. 5, a sensor fixing jig 11 for fixing the three-dimensional magnetic sensor 4 (Hall element) is installed at a distance L from the reinforcing bar 10 laid sideways, and the sensor fixing jig 11 is installed. The magnetic field strength at each position was measured while moving the three-dimensional magnetic sensor 4 at a pitch of 50 mm. This measurement was performed for the three cases with the distance L from the reinforcing bar 10 to the three-dimensional magnetic sensor 4 being L = 10 cm, L = 50 cm, and L = 100 cm. The coordinates of the magnetic field measured by the three-dimensional magnetic sensor 4 are such that the moving axis of the three-dimensional magnetic sensor 4 is the z-axis, the vertical direction is the x-axis, and the horizontal direction is the y-axis. The three direction components in the direction and the z-axis direction were measured, and the result of removing the geomagnetism from each measurement result was defined as Bx, By, Bz (μT). As the geomagnetism, the magnetic field strength (μT) of the three-direction component (μT) in the x-axis direction, the y-axis direction, and the z-axis direction is measured in the absence of the reinforcing bar 10, and the measurement results are respectively represented by the geomagnetism Bx _0. , By ₀ and Bz ₀ were used to remove the geomagnetism. In addition, at the same position, the measurement was performed twice or more to confirm the continuity of the magnetic field.
[0032]
Based on Bx and By measured in this way,
Process A: Magnetic quantity distribution gradient (dBz / dz) in the rebar vertical axis direction (z-axis direction),
Process B: Two types of shape analysis processing were performed: the strength of the magnetic field in the rebar saddle axis direction (z-axis direction) / the strength of the magnetic field in the horizontal direction of the reinforcing steel bar perpendicular axis direction (y-axis direction). .
Here, the process A is a first-order derivative of the rebar axial direction component and is equivalent to a value obtained by the conventional measurement using the magnetic inclinometer, and the process B is three-dimensional in the present embodiment. This corresponds to the case where the x-axis and y-axis of the magnetic sensor 4 are positioned and measured, and the search result is calculated based on the y-axis component in the horizontal component.
[0033]
As a result, as shown in FIG. 6 (a), when L = 10 cm, clear fluctuations centering on the tip position of the rebar rod 10 can be confirmed in both the processing A and the processing B, but L = 50 cm and L = At 100 cm, as shown in FIG. 6B and FIG. 7, only the processing B can be confirmed to have a clear fluctuation centered on the tip position of the reinforcing bar rod 10.
[0034]
(Example 2)
8A and 8B are diagrams showing measurement conditions of Example 2 of the magnetic exploration method according to the present invention, in which FIG. 8A is a side view and FIG. 8B is a top view. FIG. 9 is a graph showing measurement results of Example 2 of the magnetic exploration method according to the present invention.
[0035]
As shown in FIG. 8, the reinforcing bar 12 (D32) and the measurement pipe 13 (made of aluminum) are buried in the soil, and the three-dimensional magnetic sensor 4 (Hall element) is fixed in the measurement pipe 13. The jig 11 was installed, and the magnetic field strength at each position was measured while moving the three-dimensional magnetic sensor 4 on the sensor fixing jig. The distance L from the reinforcing bar 12 to the three-dimensional magnetic sensor 4 was set to L = 12 cm. The coordinates of the magnetic field measured by the three-dimensional magnetic sensor 4 are such that the moving axis (vertical direction) of the three-dimensional magnetic sensor 4 is the z-axis, and the horizontal plane is the y-axis in the north-south direction and the x-axis in the east-west direction. The three-direction components in the x-axis direction, the y-axis direction, and the z-axis direction were measured at each position, and the result of removing the geomagnetism from each measurement result was defined as Bx, By, Bz (μT). The geomagnetism is measured with three components (μT) in the x-axis direction, the y-axis direction, and the z-axis direction in the absence of reinforcing bar rods, and the measurement results are indicated as geomagnetism Bx ₀ , By ₀ , Bz ₀ , respectively. Removal was performed. In addition, at the same position, the measurement was performed twice or more to confirm the continuity of the magnetic field.
[0036]
Based on Bx, By, Bz measured in this way,
Process A: Magnetic quantity distribution gradient (dBz / dz) in the rebar axis direction (z-axis direction),
Process B: Two types of shape analysis processes were performed, ie, the strength Bh of the horizontal component in the direction perpendicular to the rebar and the strength Bz of the magnetic field in the direction of the rebar (z-axis), and the two were compared.
Here, the process A is a first-order derivative of the rebar axial direction component, which is equivalent to a value obtained by the conventional measurement using a magnetic inclinometer, and the process B is a three-dimensional magnetic field in the present embodiment. This corresponds to the case where the x-axis and y-axis of the sensor 4 are positioned and measured, and the search result is calculated based on the x-axis component and the y-axis component in the horizontal component.
[0037]
As a result, as shown in FIG. 9, in Process B, a clear fluctuation centered on the tip position of the reinforcing bar 12 can be confirmed, but in Process A, a clear difference was not obtained.
[0038]
Note that the present invention is not limited to the above-described embodiments, and it is obvious that the embodiments can be appropriately changed within the scope of the technical idea of the present invention. In addition, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to a suitable number, position, shape, and the like in practicing the present invention. In each figure, the same numerals are given to the same component.
[0039]
【The invention's effect】
In the magnetic exploration method of the present invention, the magnetic field distribution is measured using a three-dimensional magnetic sensor capable of measuring the magnetic field strengths in the directions orthogonal to each other (x-axis, y-axis, z-axis), and the measurement result is leveled. By looking at the ratio of the strength of the magnetic field of the component to the strength of the magnetic field in the vertical direction, the place where the exploration hole is separated from the pile by footing, such as cast-in-place piles, etc. Even if it is necessary to arrange the piles, it is possible to accurately detect the pile length.
[0040]
Furthermore, the magnetic exploration method of the present invention calculates the strength of the horizontal component magnetic field from the strength of the magnetic field in the x-axis direction and the strength of the magnetic field in the y-axis direction, thereby performing complex positioning of the three-dimensional magnetic sensor. There is an effect that magnetic exploration can be performed with simple equipment without the need.
[Brief description of the drawings]
FIG. 1 is a diagram showing a device configuration used in an embodiment of a magnetic exploration method according to the present invention.
FIG. 2 is a block diagram showing a configuration of the shape analysis apparatus shown in FIG.
3 is a diagram for explaining a horizontal magnetic field calculation method in a horizontal magnetic field calculation unit shown in FIG. 2; FIG.
4 is a diagram for explaining a search result calculated by a search result calculation unit shown in FIG. 2; FIG.
5A and 5B are diagrams showing measurement conditions of Example 1 of the magnetic exploration method according to the present invention, in which FIG. 5A is a side view, FIG. 5B is a front view, and FIG. FIG.
FIG. 6 is a graph showing a search result of Example 1 of the magnetic search method according to the present invention.
FIG. 7 is a graph showing a search result of Example 1 of the magnetic search method according to the present invention.
8A and 8B are diagrams showing measurement conditions of Example 2 of the magnetic exploration method according to the present invention, wherein FIG. 8A is a side view and FIG. 8B is a top view.
FIG. 9 is a graph showing measurement results of Example 2 of the magnetic exploration method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Foundation pile 2 Search hole 3 Nonmagnetic guide pipe 4 Three-dimensional magnetic sensor 5 Pulley 6 Amplifier 7 Counter 8 Data collector 9 Shape analyzer 10 Rebar rod 11 Sensor fixing jig 12 Rebar 13 Measurement pipe 91 Search data input part 92 Geomagnetism storage unit 93 Geomagnetism removal unit 94 Horizontal magnetic field calculation unit 95 Search result calculation unit 96 Data output unit

Claims

A magnetic exploration method for detecting the tip position of a foundation pile in a non-contact manner by conducting a magnetic exploration in the vicinity of the foundation pile containing steel,
A three-dimensional magnetic sensor capable of measuring the magnetic amounts of the x-axis, y-axis and z-axis orthogonal to each other is moved in the z-axis direction in a state where the z-axis is positioned parallel to the foundation pile ,
The three-dimensional magnetic sensor measures a magnetic quantity BX in the x-axis direction, a magnetic quantity BY in the y-axis direction, and a magnetic quantity BZ in the z-axis direction at a plurality of locations in the z-axis direction,
A magnetic amount BH on a surface perpendicular to the foundation pile is calculated from the magnetic amount BX and the magnetic amount BY,
The magnetic quantity Bh on the surface perpendicular to the foundation pile from which the geomagnetism was removed by removing the geomagnetism measured in advance from the magnetic quantity BH and the magnetic quantity BZ and the z-axis direction from which the geomagnetism was removed. Calculate the magnetic quantity Bz,
A magnetic exploration method comprising outputting a shape analysis result based on the magnetic quantity Bh and the magnetic quantity Bz for each of a plurality of locations in the z-axis direction.

A magnetic exploration method for detecting the tip position of the foundation pile in a non-contact manner by conducting a magnetic exploration in the vicinity of the foundation pile including the steel material,
A z-axis with a three-dimensional magnetic sensor capable of measuring the magnetic quantities of the x-axis, y-axis, and z-axis orthogonal to each other positioned so that the z-axis is parallel to the foundation pile and the x-axis and y-axis are not displaced Move in the direction,
The three-dimensional magnetic sensor measures a magnetic quantity BX in the x-axis direction, a magnetic quantity BY in the y-axis direction, and a magnetic quantity BZ in the z-axis direction at a plurality of locations in the z-axis direction,
The magnetic quantity BX, the magnetic quantity BY, and the magnetic quantity BZ, respectively, the magnetic quantity Bx in the x-axis direction obtained by removing the geomagnetism previously measured from the magnetic quantity BZ and the magnetic quantity in the y-axis direction obtained by removing the geomagnetism. Calculate a magnetic quantity Bz in the z-axis direction from which By and geomagnetism are removed,
A magnetic amount Bh on a surface perpendicular to the foundation pile is calculated from the magnetic amount Bx and the magnetic amount By,
A magnetic exploration method comprising outputting a shape analysis result based on the magnetic quantity Bh and the magnetic quantity Bz for each of a plurality of locations in the z-axis direction.

The magnetic exploration method according to claim 1, wherein the shape analysis result is information representing a ratio between the magnetic quantity Bh and the magnetic quantity Bz.

The magnetic exploration method according to claim 1, wherein the three-dimensional magnetic sensor includes three Hall elements arranged in directions orthogonal to each other.

A magnetic exploration method for detecting the tip position of the foundation pile in a non-contact manner by conducting a magnetic exploration in the vicinity of the foundation pile including the steel material,
A two-dimensional magnetic sensor capable of measuring the magnetic quantities of the x-axis and z-axis orthogonal to each other is moved in the z-axis direction in a state where the z-axis is parallel to the foundation pile and the x-axis is not displaced,
The two-dimensional magnetic sensor measures a magnetic quantity BX in the x-axis direction and a magnetic quantity BZ in the z-axis direction at a plurality of locations in the z-axis direction,
From the magnetic quantity BX and the magnetic quantity BZ, the magnetic quantity Bx in the x-axis direction and the magnetic quantity Bz in the z-axis direction from which the geomagnetism is removed are respectively calculated by removing the previously measured geomagnetism. And
A magnetic exploration method characterized by outputting a shape analysis result based on the magnetic quantity Bx and the magnetic quantity Bz for each of a plurality of locations in the z-axis direction.

6. The magnetic exploration method according to claim 5, wherein the shape analysis result is information representing a ratio between the magnetic quantity Bx and the magnetic quantity Bz.

The magnetic exploration method according to claim 5 or 6, wherein the two-dimensional magnetic sensor includes two Hall elements arranged in directions orthogonal to each other.