JP7587884B2 - Method for evaluating the permeability of underground dam cut-off walls - Google Patents
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Description
本発明は、地下に止水壁を設けて地盤の空隙に地下水を蓄える地下ダム止水壁の透水性評価方法に関する。 The present invention relates to a method for evaluating the permeability of underground dam cutoff walls, which are installed underground and store groundwater in voids in the ground.
地下ダム止水壁は、我が国では、土木技術の発達により大規模なものが施工可能となった１９８０年代後半以降、沖縄県や鹿児島県の南西諸島において、地表水の利用が困難な離島における貴重な農業用水源として施工され、２０１９年２月現在では１０基が既に工事を完了し、３基が建設中、１基が計画されている。
最初に施工された地下ダム止水壁は、完成してから既に２０年以上が経過しており、施設の老朽化が懸念される時期に差し掛かってきている。２０１５年に閣議決定された食料・農業・農村基本計画では、農業水利施設の点検、機能診断、及び監視を通じた適切なリスク管理の下で、施設の徹底した長寿命化とライフサイクルコストの低減を図ることとされており、地下ダムについてもこのようなストックマネジメント手法の導入が必要と考えられる。
しかし、地下ダム止水壁は、地中深くに造られており、目視で漏水の有無や劣化の程度を確認することができない。延長数ｋｍ、深度５０ｍ以上の止水壁を掘削によって露わにして点検することは、工事費を考慮すると現実的ではなく、経済的でかつ有効な止水壁の機能診断技術の確立が求められている。
図１を用いてこの診断方法について説明する。
図１（ａ）は漏水が無い状態を示し、図１（ｂ）は漏水時の状態を示している。
この診断方法は、地下ダム止水壁１の上流に地下水観測孔２ａを、地下ダム止水壁１の下流に地下水観測孔２ｂをそれぞれ設けて地下水位を観測する。そして、下流に設けた地下水観測孔２ｂで観測される地下水位の上昇が検知されると、上流に設けた地下水観測孔２ａで観測される地下水位以下の位置において漏水が発生したと推定する。
なお、特許文献１には、地下水観測孔２ａおよび地下水観測孔２bに検出器を設置し、両者の検出値を比較することによって、壁材の水理学的性質を推定する方法が記載されている。
In Japan, since the late 1980s, when developments in civil engineering technology made it possible to construct large-scale underground dam cut-off walls, they have been constructed as valuable agricultural water sources in remote islands where using surface water is difficult, such as in the southwestern islands of Okinawa Prefecture and Kagoshima Prefecture. As of February 2019, construction of 10 dams has already been completed, with three under construction and one planned.
More than 20 years have passed since the first underground dam cut-off wall was constructed, and the time has come when the deterioration of the facility is a concern. The Basic Plan for Food, Agriculture, and Rural Areas, approved by the Cabinet in 2015, calls for thorough extension of the facility's lifespan and reduction of its life cycle costs under appropriate risk management through inspection, functional diagnosis, and monitoring of irrigation facilities, and it is considered necessary to introduce such a stock management method for underground dams as well.
However, because underground dam water cutoff walls are constructed deep underground, it is not possible to visually check for leaks or the degree of deterioration. Considering the cost of construction, it is not realistic to inspect water cutoff walls that are several kilometers long and over 50 meters deep by excavating them, so there is a need to establish an economical and effective technology for diagnosing the function of water cutoff walls.
This diagnostic method will be explained with reference to FIG.
FIG. 1(a) shows a state where there is no water leakage, and FIG. 1(b) shows a state where there is water leakage.
In this diagnostic method, the groundwater level is observed by providing a groundwater observation hole 2a upstream of the underground dam water cut-off wall 1 and a groundwater observation hole 2b downstream of the underground dam water cut-off wall 1. When a rise in the groundwater level observed in the downstream groundwater observation hole 2b is detected, it is presumed that a leak has occurred at a position below the groundwater level observed in the upstream groundwater observation hole 2a.
Patent Document 1 describes a method of estimating the hydraulic properties of the wall material by installing detectors in the groundwater observation holes 2a and 2b and comparing the detected values of both.
しかし、地下ダム止水壁が建設される地域は、透水性が高い地質であることから、漏水が発生しても、その水は速やかに下流に流れ去ってしまい、下流での地下水位の上昇は小さい。
一例として、日本で最初に完成した大規模地下ダムである沖縄県宮古島砂川地下ダムでは、漏水箇所から観測孔までの距離が２０ｍであり、５００ｍ３／日の漏水があった場合でも水位上昇は３ｃｍ程度である。また、止水壁下流での地下水位は降雨によって大きく変動する。従って、３ｃｍ程度の僅かな水位上昇によって漏水を推定することは事実上不可能であった。
However, because the area where the underground dam cut-off wall will be constructed has highly permeable geology, even if a leak occurs, the water will quickly flow away downstream, and the rise in the groundwater level downstream will be small.
As an example, at the Sunagawa Underground Dam in Miyakojima, Okinawa Prefecture, the first large-scale underground dam completed in Japan, the distance from the leak point to the observation hole is 20 m, and even if there was a leak of 500 m3 /day, the water level would only rise by about 3 cm. In addition, the groundwater level downstream of the cutoff wall fluctuates greatly with rainfall. Therefore, it was virtually impossible to estimate the leak based on a slight water level rise of about 3 cm.
そこで本発明は、地下水位の変化によらずに漏水を判定できる地下ダム止水壁の透水性評価方法を提供することを目的とする。 Therefore, the present invention aims to provide a method for evaluating the permeability of underground dam cut-off walls that can determine leakage without relying on changes in the groundwater level.
請求項１記載の本発明の地下ダム止水壁１の透水性評価方法は、水圧により相違が生じる物質濃度を用い、地下ダム止水壁１によって形成される貯水域３ａにある上流側地下水４ａに含まれる前記物質濃度と、前記地下ダム止水壁１の下流域３ｂにある下流側地下水４ｂに含まれる前記物質濃度とを比較することで前記地下ダム止水壁１の漏水を判定することを特徴とする。
請求項２記載の本発明は、請求項１に記載の地下ダム止水壁１の透水性評価方法において、前記物質濃度として、空気の濃度を用いることを特徴とする。
請求項３記載の本発明は、請求項１に記載の地下ダム止水壁１の透水性評価方法において、前記物質濃度として、窒素又はネオンの濃度を用いることを特徴とする。
The method for evaluating the permeability of an underground dam waterstop wall 1 of the present invention described in claim 1 is characterized in that it uses a substance concentration that differs depending on water pressure and judges leakage from the underground dam waterstop wall 1 by comparing the substance concentration contained in upstream groundwater 4a in a water storage area 3a formed by the underground dam waterstop wall 1 with the substance concentration contained in downstream groundwater 4b in a downstream area 3b of the underground dam waterstop wall 1.
The present invention as set forth in claim 2 is characterized in that in the method for evaluating the permeability of a water cutoff wall 1 of an underground dam as set forth in claim 1, the concentration of air is used as the substance concentration.
The present invention as set forth in claim 3 is characterized in that in the method for evaluating the permeability of a water cutoff wall 1 of an underground dam as set forth in claim 1, a concentration of nitrogen or neon is used as the substance concentration.
本発明の地下ダム止水壁の透水性評価方法によれば、地下水年代や水圧により上流側地下水と下流側地下水とで相違が生じる物質濃度を用いることで、地下水位の変化によらずに漏水を判定できる。 The method for evaluating the permeability of an underground dam cutoff wall of the present invention uses the concentration of substances that differ between the upstream and downstream groundwater due to groundwater age and water pressure, making it possible to determine leakage regardless of changes in the groundwater level.
本発明の第１の実施の形態による地下ダム止水壁の透水性評価方法は、水圧により相違が生じる物質濃度を用い、地下ダム止水壁によって形成される貯水域にある上流側地下水に含まれる物質濃度と、地下ダム止水壁の下流域にある下流側地下水に含まれる物質濃度とを比較することで地下ダム止水壁の漏水を判定するものである。
本実施の形態によれば、地下水年代や水圧により上流側地下水と下流側地下水とで相違が生じる物質濃度を用いることで、地下水位の変化によらずに漏水を判定できる。
The method for evaluating the permeability of an underground dam cut-off wall according to the first embodiment of the present invention uses substance concentrations that differ due to water pressure, and determines leakage from the underground dam cut-off wall by comparing the substance concentrations contained in the upstream groundwater in the reservoir area formed by the underground dam cut-off wall with the substance concentrations contained in the downstream groundwater in the area downstream of the underground dam cut-off wall.
According to this embodiment, by using the substance concentrations that differ between the upstream and downstream groundwater due to groundwater age and water pressure, it is possible to determine a water leak regardless of changes in the groundwater level.
本発明の第２の実施の形態は、第１の実施の形態による地下ダム止水壁の透水性評価方法において、物質濃度として、空気の濃度を用いるものである。
地下ダム止水壁によって形成される貯水域にある上流側地下水には、水圧が加わっているために下流側地下水に比較して空気の溶け込み量が多くなるため、本実施の形態によれば、地下水に含まれる空気の濃度によって、地下水位の変化によらずに漏水を判定できる。
A second embodiment of the present invention is a method for evaluating the permeability of a cut-off wall of an underground dam according to the first embodiment, in which the concentration of air is used as the substance concentration.
Since the upstream groundwater in the reservoir area formed by the underground dam water cut-off wall is subjected to water pressure, the amount of air dissolved in the upstream groundwater is greater than that in the downstream groundwater. Therefore, according to this embodiment, leakage can be determined based on the concentration of air contained in the groundwater, regardless of changes in the groundwater level.
本発明の第３の実施の形態は、第１の実施の形態による地下ダム止水壁の透水性評価方法において、物質濃度として、窒素又はネオンの濃度を用いるものである。
地下ダム止水壁によって形成される貯水域にある上流側地下水には、水圧が加わっているために下流側地下水に比較して空気の溶け込み量が多く、更に空気に含まれる窒素又はネオンは地下水中において岩石との反応による増減が少ないため、本実施の形態によれば、地下水に含まれる窒素又はネオンの濃度によって、地下水位の変化によらずに漏水を判定できる。
A third embodiment of the present invention is a method for evaluating the permeability of a cutoff wall of an underground dam according to the first embodiment, in which a concentration of nitrogen or neon is used as a substance concentration.
The upstream groundwater in the reservoir area formed by the underground dam water cut-off wall has a greater amount of dissolved air than the downstream groundwater due to the application of water pressure, and furthermore the nitrogen or neon contained in the air does not increase or decrease much due to reaction with rocks in the groundwater. Therefore, according to this embodiment, a leak can be determined based on the concentration of nitrogen or neon contained in the groundwater, regardless of changes in the groundwater level.
以下本発明の一実施例による地下ダム止水壁の透水性評価方法について説明する。
図１に示すように、地下ダム止水壁１は、難透水性基盤１１に至る深度まで、透水性が高い地質１２に形成する。
地下ダム止水壁１によって、地下ダム止水壁１の上流には、貯水域３ａが形成される。
貯水域３ａにある上流側地下水４ａは地下水観測孔２ａから採取し、地下ダム止水壁１の下流域３ｂにある下流側地下水４ｂは地下水観測孔２ｂから採取する。
A method for evaluating the permeability of a cut-off wall of an underground dam according to one embodiment of the present invention will be described below.
As shown in FIG. 1 , an underground dam cutoff wall 1 is formed in highly permeable geology 12 down to a depth reaching a low-permeability bedrock 11 .
The underground dam water cutoff wall 1 forms a water storage area 3 a upstream of the underground dam water cutoff wall 1 .
Upstream groundwater 4a in the reservoir area 3a is sampled from a groundwater observation hole 2a, and downstream groundwater 4b in the downstream area 3b of the underground dam water cut-off wall 1 is sampled from a groundwater observation hole 2b.
図１（ｂ）では、地下ダム止水壁１に透水性劣化部位１ｘが生じた状態を示している。
本発明による地下ダム止水壁の透水性評価方法は、地下ダム止水壁１によって形成される貯水域３ａにある上流側地下水４ａの上流側地下水年代と、地下ダム止水壁１の下流域３ｂにある下流側地下水４ｂの下流側地下水年代とを比較することで地下ダム止水壁１の漏水を判定するものである。
上流側地下水年代及び下流側地下水年代は、上流側地下水４ａ及び下流側地下水４ｂに含まれる物質濃度によって推定する。なお、本発明において地下水年代とは、水が地下に浸透してからの経過年である。
物質濃度として、温室効果ガスの濃度を用いることができる。
FIG. 1( b ) shows a state in which a permeability-deteriorated portion 1 x has occurred in the underground dam water cut-off wall 1 .
The method for evaluating the permeability of an underground dam water cut-off wall according to the present invention determines leakage from the underground dam water cut-off wall 1 by comparing the upstream groundwater age of the upstream groundwater 4a in the water storage area 3a formed by the underground dam water cut-off wall 1 with the downstream groundwater age of the downstream groundwater 4b in the downstream area 3b of the underground dam water cut-off wall 1.
The upstream groundwater age and the downstream groundwater age are estimated based on the concentrations of substances contained in the upstream groundwater 4a and the downstream groundwater 4b. In the present invention, the groundwater age refers to the number of years since water infiltrated underground.
The concentration of a greenhouse gas can be used as the substance concentration.
図１（ａ）に示すように地下ダム止水壁１に漏水が無い場合には、例えば貯水域３ａにある上流側地下水４ａは、地下ダム建設時から現在までの地下水が混合して貯留されているため比較的古い年代を持ち、下流域３ｂにある下流側地下水４ｂは、降水が涵養された後に速やかに下流に流れ去るため常に新しい年代を持つ。また、上流側地下水４ａの汲み上げ量や流れ込み量が多く、下流側地下水４ｂが流れにくい場合には、下流側地下水４ｂが上流側地下水４ａに対して比較的古い年代を持つ場合もある。
しかし、図１（ｂ）に示すように地下ダム止水壁１に透水性劣化部位１ｘが生じた場合には、比較的古い年代の上流側地下水４ａが下流側地下水４ｂとして流れ込むため、下流側地下水４ｂの地下水年代が古くなる。
このように、上流側地下水４ａの上流側地下水年代と下流側地下水４ｂの下流側地下水年代とを比較することで、下流側地下水年代が上流側地下水年代と同じ年代又は近い年代の場合には漏水と判定でき、又は、下流側地下水年代を経時的に比較することで、下流側地下水年代が古い年代に変化した場合には漏水と判定できる。
As shown in Figure 1(a), when there is no leakage from the underground dam cutoff wall 1, for example, the upstream groundwater 4a in the reservoir area 3a is relatively old because it is a mixture of groundwater stored from the time of the construction of the underground dam to the present, while the downstream groundwater 4b in the downstream area 3b is always newer because it flows downstream quickly after being recharged with precipitation. Also, when the amount of pumping or inflow of the upstream groundwater 4a is large and the downstream groundwater 4b does not flow easily, the downstream groundwater 4b may be relatively old compared to the upstream groundwater 4a.
However, when a deteriorated permeability site 1x occurs in the underground dam water cut-off wall 1 as shown in Figure 1(b) , relatively old upstream groundwater 4a flows in as downstream groundwater 4b, causing the downstream groundwater 4b to have an older age.
In this way, by comparing the upstream groundwater age of the upstream groundwater 4a with the downstream groundwater age of the downstream groundwater 4b, it is possible to determine that a leak has occurred if the downstream groundwater age is the same age or close to the upstream groundwater age, or by comparing the downstream groundwater age over time, it is possible to determine that a leak has occurred if the downstream groundwater age has changed to an older age.
図２はＳＦ６濃度の変化を示すグラフであり、図２（ａ）はアメリカ海洋大気庁（ＮＯＡＡ）が公表している北半球８箇所でのモニタリング値であり年度別大気中のＳＦ６濃度の変化を示し、図２（ｂ）はＳＦ６濃度による地下水年代の推定を示している。
温室効果ガスの一つであるＳＦ６（六フッ化硫黄）は、１９６０年代から電気及び電子機器の分野で絶縁材などとして広く使用されている化学物質であり、図２（ａ）に示すように大気中の濃度は年間約７％の割合で上昇を続けている。降水中のＳＦ６濃度は、その時の大気中の濃度と平衡しており、地下水として涵養された後は大気との接触が断たれるため浸透時の濃度を保つ。
従って、図２（ｂ）に示すように、地下水中のＳＦ６濃度を測定することによって、その地下水の涵養年、言い換えれば地下水年代を推定することができる。
Figure 2 is a graph showing changes in SF6 concentration. Figure 2(a) shows the annual change in SF6 concentration in the atmosphere based on monitoring values published by the National Oceanic and Atmospheric Administration (NOAA) at eight locations in the Northern Hemisphere, and Figure 2(b) shows an estimate of the age of groundwater based on SF6 concentration.
SF6 (sulfur hexafluoride), one of the greenhouse gases, is a chemical substance that has been widely used since the 1960s as an insulating material in the fields of electrical and electronic equipment, and its concentration in the atmosphere has been increasing at a rate of about 7% per year, as shown in Figure 2 (a). The concentration of SF6 in precipitation is in equilibrium with the concentration in the atmosphere at that time, and after it is recharged as groundwater, it maintains the concentration at the time of infiltration because it is cut off from contact with the atmosphere.
Therefore, as shown in FIG. 2(b), by measuring the SF6 concentration in groundwater, the year of recharge of the groundwater, in other words, the groundwater age, can be estimated.
図３は沖縄県砂川地下ダムにおける地下水年代を示す図である。
図中に示すダム軸の下に地下ダム止水壁１が形成されている。貯水域３ａは、地下ダム止水壁１の上流に、貯留域境界までの間に形成される。
貯水域３ａにおいて１５箇所で採取した上流側地下水４ａの平均地下水年代は６年であった。
Figure 3 shows the groundwater age at the Sunagawa Underground Dam in Okinawa Prefecture.
An underground dam cutoff wall 1 is formed below the dam axis shown in the drawing. A reservoir area 3a is formed upstream of the underground dam cutoff wall 1 up to the reservoir area boundary.
The average age of the upstream groundwater 4a sampled at 15 locations in the reservoir area 3a was 6 years.
図４は気象庁ＨＰ（https://ds.data.jma.go.jp/ghg/kanshi/ghgp/cfcs_trend.html）で公表されている温室効果ガスの大気中における濃度変化を示すグラフである。
図４（ａ）はＳＦ６、図４（ｂ）はＨＦＣ－１３４ａ、図４（ｃ）はＣＦＣ－１１、図４（ｄ）はＣＨ３ＣＣｌ３の濃度変化を示している。
このように、温室効果ガスとして、ＳＦ６、ＨＦＣ－１３４ａ、ＣＦＣ－１１、及びＣＨ３ＣＣｌ３の少なくともいずれか一つ又はこれらを組み合わせて用いることで、地下水年代を推定することができる。
Figure 4 is a graph showing changes in greenhouse gas concentrations in the atmosphere, published on the Japan Meteorological Agency website (https://ds.data.jma.go.jp/ghg/kanshi/ghgp/cfcs_trend.html).
FIG. 4(a) shows the concentration change of SF 6 , FIG. 4(b) shows the concentration change of HFC-134a, FIG. 4(c) shows the concentration change of CFC-11, and FIG. 4(d) shows the concentration change of CH 3 CCl 3 .
In this way, the age of groundwater can be estimated by using at least one of SF 6 , HFC-134a, CFC-11, and CH 3 CCl 3 or a combination of these as the greenhouse gas.
図５は地下ダム止水壁によって形成される貯水域での過剰大気を示す図であり、図５（ａ）は沖縄県糸満市の米須地下ダムにおける過剰大気を示す図、図５（ｂ）は沖縄県八重洲町の慶座地下ダムにおける過剰大気を示す図である。
図中に示すダム軸の下に地下ダム止水壁１が形成されている。貯水域３ａは、地下ダム止水壁１の上流に形成される。
図５（ａ）に示すように、米須地下ダムにおける貯水域３ａでの過剰大気（大気開放状態で水に溶け込む空気量を越えた溶存空気量）は４．２～４．３ｃｃ／ｋｇ、図５（ｂ）に示すように、慶座地下ダムにおける貯水域３ａでの過剰大気（大気開放状態で水に溶け込む空気量を越えた溶存空気量）は２．２～４．３ｃｃ／ｋｇであった。
このように、地下ダム止水壁１によって形成される貯水域３ａにある上流側地下水４ａには、水圧が加わっているために下流側地下水に比較して空気の溶け込み量が多くなる。
従って、物質濃度として空気の濃度を用い、地下ダム止水壁１によって形成される貯水域３ａにある上流側地下水４ａに含まれる物質濃度と、地下ダム止水壁１の下流域３ｂにある下流側地下水４ｂに含まれる物質濃度とを比較することでも、水圧により上流側地下水４ａと下流側地下水４ｂとで物質濃度に違いが生じ、地下水位の変化によらずに漏水を判定できる。
空気に含まれる窒素又はネオンは地下水中において岩石との反応による増減が少ない。従って、物質濃度として、窒素又はネオンの濃度を用いることで、地下水位の変化によらずに更に正確に漏水を判定できる。
Figure 5 shows excess air in a reservoir area formed by an underground dam water cut-off wall, where Figure 5(a) shows excess air at the Yonezu underground dam in Itoman City, Okinawa Prefecture, and Figure 5(b) shows excess air at the Keiza underground dam in Yaesu Town, Okinawa Prefecture.
An underground dam cutoff wall 1 is formed below the dam axis shown in the drawing. A water storage area 3a is formed upstream of the underground dam cutoff wall 1.
As shown in Figure 5(a), the excess air (the amount of dissolved air in excess of the amount of air that dissolves in the water when open to the atmosphere) in the reservoir area 3a of the Yonezu subsurface dam was 4.2 to 4.3 cc/kg, and as shown in Figure 5(b), the excess air (the amount of dissolved air in excess of the amount of air that dissolves in the water when open to the atmosphere) in the reservoir area 3a of the Keiza subsurface dam was 2.2 to 4.3 cc/kg.
In this way, the upstream groundwater 4a in the reservoir area 3a formed by the subsurface dam water cutoff wall 1 is subjected to water pressure, and therefore has a greater amount of air dissolved therein than the downstream groundwater.
Therefore, by using the concentration of air as the substance concentration and comparing the substance concentration contained in the upstream groundwater 4a in the water storage area 3a formed by the underground dam waterstop wall 1 with the substance concentration contained in the downstream groundwater 4b in the downstream area 3b of the underground dam waterstop wall 1, it is possible to determine whether there is a difference in substance concentration between the upstream groundwater 4a and the downstream groundwater 4b due to water pressure, and therefore it is possible to determine whether there is a leak, regardless of changes in the groundwater level.
Nitrogen or neon contained in air does not increase or decrease much due to reaction with rocks in groundwater, so by using the concentration of nitrogen or neon as the substance concentration, water leakage can be detected more accurately regardless of changes in the groundwater level.
本発明の地下ダム止水壁の透水性評価方法によれば、地下水年代を用いることで、地下水位の変化によらずに漏水を判定できる。
なお、上流側地下水年代及び下流側地下水年代を、経時的に推定して監視することで、更に精度良く漏水を判定できる。
また、上流側地下水年代が上流側地下水４ａの深度によって異なる場合には、深度によって異なる上流側地下水年代を用いて地下ダム止水壁１の漏水深度を判定することで、補修工事を容易にすることができる。
また本発明の地下ダム止水壁の透水性評価方法によれば、地下水年代や水圧により上流側地下水と下流側地下水とで相違が生じる物質濃度を用いることで、地下水位の変化によらずに漏水を判定できる。
According to the method for evaluating the permeability of a cut-off wall of an underground dam of the present invention, by using groundwater age, leakage can be determined regardless of changes in the groundwater level.
Furthermore, by estimating and monitoring the upstream groundwater age and the downstream groundwater age over time, leakage can be detected with even greater accuracy.
In addition, if the upstream groundwater age varies depending on the depth of the upstream groundwater 4a, repair work can be facilitated by determining the leakage depth of the underground dam water cut-off wall 1 using the upstream groundwater age, which varies depending on the depth.
Furthermore, according to the method for evaluating the permeability of an underground dam water cut-off wall of the present invention, by using the concentration of substances that differ between the upstream and downstream groundwater due to the groundwater age and water pressure, leakage can be determined regardless of changes in the groundwater level.
本発明による地下ダム止水壁の透水性評価方法によれば、定期的な地下水年代の判定を行うことで、地下水位の変化によらずに漏水を的確に判定できる。 According to the method for evaluating the permeability of underground dam cutoff walls of the present invention, by periodically determining the age of groundwater, leakage can be accurately determined regardless of changes in the groundwater level.
１ 地下ダム止水壁
１ｘ 透水性劣化部位
２ａ、２ｂ 地下水観測孔
３ａ 貯水域
３ｂ 下流域
４ａ 上流側地下水
４ｂ 下流側地下水
１１ 難透水性基盤
１２ 透水性が高い地質
1 Underground dam cut-off wall 1x Permeability deterioration area 2a, 2b Groundwater observation hole 3a Reservoir area 3b Downstream area 4a Upstream groundwater 4b Downstream groundwater 11 Low-permeability basement 12 Highly permeable geology
Claims (3)
ことを特徴とする地下ダム止水壁の透水性評価方法。 A method for evaluating the permeability of a water cut-off wall of an underground dam , characterized by using a substance concentration that differs due to water pressure and comparing the substance concentration contained in upstream groundwater in a water storage area formed by the water cut-off wall of the underground dam with the substance concentration contained in downstream groundwater in a downstream area of the water cut-off wall of the underground dam to determine leakage from the water cut-off wall of the underground dam.
ことを特徴とする請求項１に記載の地下ダム止水壁の透水性評価方法。 2. The method for evaluating the permeability of a cut-off wall of an underground dam according to claim 1, wherein the substance concentration is a concentration of air.
ことを特徴とする請求項１に記載の地下ダム止水壁の透水性評価方法。 2. The method for evaluating the permeability of a cut-off wall of an underground dam according to claim 1, wherein the substance concentration is a concentration of nitrogen or neon.
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