JP6024960B2 - Measurement test method for water absorption expansion characteristics - Google Patents
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本発明は、ベントナイトなどの吸水膨張特性を試験する吸水膨張特性の測定試験方法に関する。 The present invention relates to a method for measuring and measuring water absorption expansion characteristics for testing water absorption expansion characteristics such as bentonite.
高レベル放射性廃棄物の地層処分では、図１−１および図１−２に示すように、廃棄体Ｐのまわりを吸水膨張性粘土Ｂで囲繞し、まわりからの地圧を緩衝するとともに、地下水の浸入を抑制し、廃棄体Ｐからの放射性物質の漏洩を抑止することが考えられている（たとえば、非特許文献１参照）。 In the geological disposal of high-level radioactive waste, as shown in FIGS. 1-1 and 1-2, the waste P is surrounded by water-absorbing expansive clay B, and the ground pressure from the surroundings is buffered. It is considered that the intrusion of the radioactive material is suppressed and the leakage of the radioactive substance from the waste body P is suppressed (for example, see Non-Patent Document 1).
廃棄体Ｐのまわりを吸水膨張性粘土Ｂで囲繞するのは、（１）吸水膨張性粘土Ｂの透水係数（１Ｅ−１０〜１Ｅ−１３）が一般的な地盤材料の透水係数（１Ｅ−５〜１Ｅ−８ｍ／ｓ）よりも格段に小さく、難透水性に優れていること、（２）吸水膨張性粘土Ｂは、コンクリートに比べて柔軟性があるため、ひび割れが発生しにくく、かつ、発生したひび割れはまわりから地下水が浸入した時点で吸水膨張挙動によりシールされるので、卓越した水みちとならないこと、（３）吸水膨張性粘土Ｂ（たとえば、ベントナイト）は、天然に存在するものであるから、数万年以上の長期間を経ても材料劣化が生じにくいこと、によるものである。 Surrounding the waste P with the water-swellable clay B is that (1) the water-swelling coefficient of the water-swelling clay B (1E-10 to 1E-13) is the water-swelling coefficient (1E-5) of a general ground material. ~ 1E-8m / s), which is much smaller and excellent in poor water permeability, (2) Since the water-absorbing expansive clay B is more flexible than concrete, it is difficult to generate cracks, and The generated cracks are sealed by the water absorption expansion behavior when groundwater enters from the surroundings, so that it does not become an excellent water channel, and (3) water expansion expandable clay B (for example, bentonite) is naturally present. Therefore, it is because material deterioration hardly occurs even after a long period of tens of thousands of years.
ところで、放射性物質を吸着したコロイド粒子は、吸水膨張性粘土Ｂを通過して、施設外に漏出することが懸念され、コロイドが通過しない密実な緩衝材であることの担保として、吸水膨張性粘土Ｂの膨潤圧を指標にする例がある。 By the way, colloidal particles that have adsorbed radioactive substances are likely to leak out of the facility through the water-absorbing expansive clay B. There is an example using the swelling pressure of clay B as an index.
また、吸水膨張性粘土Ｂの膨潤圧が周囲の岩盤に与える影響も懸念される。このことから、吸水膨張性粘土Ｂについて複数の膨潤圧計測例が報告されている。 There is also a concern about the influence of the swelling pressure of the water-absorbing expandable clay B on the surrounding rock mass. For this reason, a plurality of swelling pressure measurement examples have been reported for the water-absorbing expandable clay B.
一方、吸水膨張性粘土Ｂの挙動として、吸水膨張現象に伴う膨張変形挙動についての実現象を予測評価したいというニーズがある。たとえば、廃棄体Ｐを地下に埋設した後に地下水が浸入することにより、緩衝材が膨張し、その密度が変化することや内部に定置した廃棄体Ｐの位置がずれる等の挙動が懸念される。 On the other hand, as the behavior of the water-swellable clay B, there is a need to predict and evaluate the actual phenomenon regarding the expansion and deformation behavior associated with the water-absorption and expansion phenomenon. For example, if the waste water P is buried in the ground and then the groundwater infiltrates, the buffer material expands, and its density changes, and the behavior of the waste body P placed inside is shifted.
たとえば、図２は、模擬岩盤（砂岩製）の竪穴にベントナイト系の土質材料Ｂ（ベントナイト７０％と砂３０％の配合で、乾燥時の密度が１．６Ｍｇ／ｍ３相当の材料）を装填した後に、淡水が浸入しやすいように浸漬させた場合の、緩衝材天端部の膨張による膨出量を時間の経過とともに測定した事例を示している。図３に示すように、時間の経過とともに、次第に吸水して膨張していることがわかる。また、吸水膨張したベントナイト系の土質材料Ｂは、若干密度の低いゲル（ベントナイトゲル）となって、緩衝材の周囲にある岩盤の割れ目に浸入していく現象も予測されている（たとえば、非特許文献２参照）。
For example, Figure 2 is loaded with simulated rock soil material B (the formulation of 70% bentonite and
したがって、吸水膨張性粘土Ｂの吸水膨張特性を把握し、その挙動を予測し、周囲への影響を評価することが、放射性廃棄物の処分の安全性の評価に必要となる。吸水膨張性粘土Ｂの吸水膨張特性は、所定密度の吸水膨張粘土（試験体）に吸水させたときに発生する圧力（膨潤圧）を測定することにより把握されてきた。膨潤圧の測定は、比較的簡便な装置で比較的短期間で可能であるため、多くの測定例が報告されている。それらを総括した例として、図４に示すように、吸水膨張性粘土Ｂの密度と膨潤圧との関係が報告されている（たとえば、非特許文献３参照）。なお、図４は、さまざまな種類の吸水膨張性粘土Ｂ（ベントナイト）の測定例を統一的に整理するために、横軸を吸水膨張する粘土鉱物であるモンモリロナイトの乾燥密度に換算した有効モンモリロナイト密度で整理している。 Therefore, it is necessary to evaluate the safety of disposal of radioactive waste by grasping the water-swelling characteristics of the water-swelling clay B, predicting its behavior, and evaluating the influence on the surroundings. The water-absorbing expansion property of the water-absorbing expandable clay B has been grasped by measuring the pressure (swelling pressure) generated when water-absorbing expanded clay (test body) having a predetermined density is absorbed. Since the measurement of the swelling pressure can be performed with a relatively simple apparatus in a relatively short period of time, many measurement examples have been reported. As an example summarizing them, as shown in FIG. 4, the relationship between the density of the water-swellable clay B and the swelling pressure has been reported (for example, see Non-Patent Document 3). FIG. 4 shows the effective montmorillonite density converted to the dry density of montmorillonite, which is a clay mineral that absorbs and expands the horizontal axis, in order to unify the measurement examples of various types of water-swellable clay B (bentonite). Organize with.
しかしながら、膨潤圧は、周囲を拘束した一定密度の吸水膨張性粘土Ｂが吸水したときに発生させる圧力であり、吸水膨張初期の変形をさせない状態での反力を計測するので、図４に示すように、測定された膨潤圧力は、一桁程度のバラツキを有する。バラツキの原因の一つとして、微妙な実験装置の違いによって、測定する反力が異なる値となるからであると考えられる。このように、膨潤圧の測定法におけるバラツキでは、過大な膨潤圧が測定されやすい、という欠点がある。 However, the swelling pressure is a pressure generated when the water-absorbing expandable clay B having a constant density with confined surroundings absorbs water, and the reaction force is measured in a state in which the deformation at the initial stage of water-absorbing expansion is not performed. Thus, the measured swelling pressure has a variation of about one digit. One of the causes of the variation is considered to be that the reaction force to be measured becomes a different value due to subtle differences in the experimental apparatus. As described above, the variation in the measurement method of the swelling pressure has a drawback that an excessive swelling pressure is easily measured.
本発明は、上記に鑑みてなされたものであって、吸水膨張性粘土の吸水膨張特性を正確に評価できる吸水膨張特性の測定試験方法を提供することを課題とする。 This invention is made | formed in view of the above, Comprising: It aims at providing the measurement test method of the water absorption expansion | swelling characteristic which can evaluate the water absorption expansion | swelling characteristic of a water absorption expansible clay correctly.
上述した課題を解決し、目的を達成するために、本発明は、吸水膨張する粘土の周囲を拘束するとともに該粘土の上に荷重を載荷した状態で該粘土に吸水させ、該粘土の吸水膨張が終息した時点で該粘土の密度を求め、該粘土に作用する圧力を求めた密度における吸水膨張ポテンシャルとする吸水膨張特性の測定試験方法であって、粘土に載荷する荷重を段階的に小さくし、各段階において粘土の吸水膨張が終息した時点で該粘土の密度と該粘土の密度おける吸水膨張ポテンシャルを求めることを特徴とする。 In order to solve the above-described problems and achieve the object, the present invention constrains the periphery of clay that absorbs and expands water, and absorbs water in a state where a load is loaded on the clay, thereby absorbing and expanding the clay. Is a test method for measuring the water-absorbing expansion characteristics by determining the density of the clay at the time of termination of the pressure, and the water- absorbing expansion potential at the density at which the pressure acting on the clay is determined, wherein the load loaded on the clay is reduced stepwise. In each stage, the density of the clay and the water absorption expansion potential at the density of the clay are obtained when the water absorption expansion of the clay ends .
また、本発明は、上記発明において、飽和度を９５％以上に調整した粘土を試験体とすることを特徴とする。 Further, the present invention is characterized in that, in the above invention, a clay whose saturation is adjusted to 95% or more is used as a test specimen.
また、本発明は、上記発明において、粘土に含まれる水の電解質濃度を予め定めた濃度に調整するとともに、吸水させる水の電解質濃度を前記予め定めた濃度に調整したことを特徴とする。 Further, the present invention is characterized in that, in the above invention, the electrolyte concentration of water contained in the clay is adjusted to a predetermined concentration, and the electrolyte concentration of water to be absorbed is adjusted to the predetermined concentration.
本発明にかかる吸水膨張特性の測定試験方法は、吸水膨張する粘土の周囲を拘束するとともに該粘土に圧力を作用させた状態で粘土に吸水させ、該粘土の吸水膨張が終息した時点で該粘土の密度を求め、該粘土に作用させた圧力を求めた密度における吸水ポテンシャルとするので、吸水膨張性粘土の吸水膨張特性を正確に評価できる。 The test method for measuring the water absorption and expansion characteristics according to the present invention is to restrain the surroundings of the clay that absorbs and expands water and allow the clay to absorb water while pressure is applied to the clay, and when the water absorption and expansion of the clay ends, the clay Thus, the pressure applied to the clay is taken as the water absorption potential at the obtained density, so that the water absorption and expansion characteristics of the water expansion clay can be accurately evaluated.
また、本発明にかかる吸水膨張特性の測定方法は、粘土に作用させる圧力を段階的に小さくし、各段階において粘土の吸水膨張が終息した時点で該粘土の密度と該粘土の密度における吸水膨張ポテンシャルを求めるので、試験体の数が少なくても多数のデータを取得できる。これにより、試験体および試験装置が少なくて済むので、少ないコストで多数のデータを効率的に取得できる。さらに、一つの試験体から複数のデータを取得できるので、試験体の個体差によるデータのバラツキを小さくできる。 In addition, the method for measuring the water absorption expansion characteristic according to the present invention is such that the pressure acting on the clay is reduced stepwise, and when the water absorption expansion of the clay ends in each step, the density of the clay and the water absorption expansion at the density of the clay Since the potential is obtained, a large number of data can be acquired even if the number of test specimens is small. As a result, the number of test bodies and test devices can be reduced, and a large number of data can be efficiently acquired at a low cost. Furthermore, since a plurality of data can be acquired from one specimen, the variation in data due to individual differences among specimens can be reduced.
以下に、本発明にかかる吸水膨張特性の測定試験方法の実施の形態を図面に基づいて詳細に説明する。なお、この実施の形態によりこの発明が限定されるものではない。 Embodiments of a water absorption expansion characteristic measurement test method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.
本発明の実施の形態である吸水膨張特性の測定試験方法は、上述した膨潤圧を測定する方法と異なり、膨張変形量を測定することにより、吸水膨張特性を把握するものである。 Unlike the method of measuring the swelling pressure described above, the water absorption expansion characteristic measurement test method according to the embodiment of the present invention grasps the water absorption expansion characteristic by measuring the amount of expansion deformation.
図５は、吸水膨張性粘土に荷重を載荷した状態で膨張高さを計測する吸水膨張特性の測定試験の概要を説明するための模式図であり、図６は、図５に示した測定試験の試験結果を示す図である。図５に示すように、吸水膨張性粘土Ｂに荷重を載荷した状態で膨張量を計測する吸水膨張特性を測定する試験は、吸水膨張性粘土Ｂ（たとえば、ベントナイト７０％と砂３０％の配合で、乾燥密度が１．６Ｍｇ／ｍ３相当のベントナイト系の土質材料）に荷重を載荷した状態で吸水させた場合の時間経過と膨張高さを測定するものである。図６に示すように、吸水膨張性粘土Ｂに作用する圧力Ｐｓが膨張圧力よりも小さい場合には膨張挙動が生じる。また、吸水膨張性粘土Ｂに作用する圧力Ｐｓが膨張圧力よりも小さいほど膨張高さが高くなる。すなわち、吸水膨張の駆動力は、その吸水膨張性粘土Ｂが有している膨張能力と拘束されている拘束力の差で決まる。このような吸水して膨張変形する現象における膨張能力に相当するポテンシャルを本発明および本発明の実施の形態では「吸水膨張ポテンシャル」と称することにする。 FIG. 5 is a schematic diagram for explaining an outline of a measurement test of a water absorption expansion characteristic in which an expansion height is measured in a state where a load is loaded on the water expansion clay, and FIG. 6 is a measurement test shown in FIG. It is a figure which shows the test result of. As shown in FIG. 5, the test for measuring the water-absorbing expansion characteristic of measuring the amount of expansion in a state where a load is applied to the water-absorbing expansive clay B is a combination of water-absorbing expansive clay B (for example, 70% bentonite and 30% sand) Then, the time lapse and the expansion height are measured when water is absorbed in a state where a load is loaded on a bentonite-based soil material having a dry density equivalent to 1.6 Mg / m 3 . As shown in FIG. 6, the expansion behavior occurs when the pressure P s which acts on the water-swellable clay B is less than the inflation pressure. Further, as the expansion height pressure P s which acts on the water-swellable clay B is less than the inflation pressure is increased. That is, the driving force for water absorption expansion is determined by the difference between the expansion capability of the water expansion expandable clay B and the restraining force restrained. Such a potential corresponding to the expansion capability in the phenomenon of water deformation and expansion deformation is referred to as “water absorption expansion potential” in the present invention and the embodiment of the present invention.
このように、吸水膨張性粘土Ｂに荷重を載荷した状態で吸水膨張性粘土Ｂに吸水させ、吸水膨張性粘土Ｂの吸水膨張が終息した時点の吸水膨張性粘土Ｂの密度ρｄは、吸水前の密度ρｄ０に対して下記の数式１に示す関係を有している。この式において、δは、図６の縦軸の値に相当しており、膨張高さの元の高さに対する百分率である。 In this way, the density ρ d of the water-swellable clay B when the water-swellable clay B absorbs water while the water-swellable clay B is loaded and the water-swellable clay B ends its water-swelling expansion. It has the relationship shown in the following formula 1 with respect to the previous density ρ d0 . In this equation, δ corresponds to the value on the vertical axis in FIG. 6 and is a percentage of the original height of the inflated height.
(数１)
ρｄ＝ρｄ０／（１＋δ／１００）
(Equation 1)
ρ d = ρ d0 / (1 + δ / 100)
言い換えると、吸水膨張が終息した時点の密度ρｄにおける吸水膨張性粘土Ｂ（ベントナイト）の吸水膨張ポテンシャルは、載荷した荷重に対応する。これにより、吸水膨張性粘土Ｂに作用する圧力Ｐｓ（上載圧力）は、吸水膨張が終息した時点の密度ρｄにおける吸水ポテンシャルに等しい。 In other words, the water-absorbing expansion potential of the water-expandable clay B (bentonite) at the density ρ d when the water-absorbing expansion ends corresponds to the loaded load. Thereby, the pressure P s (upload pressure) acting on the water-absorbing expandable clay B is equal to the water-absorbing potential at the density ρ d when the water-absorbing expansion ends.
別の言い方をするならば、吸水膨張ポテンシャルは、吸水膨張現象が終息した時点における吸水膨張性粘土Ｂの拘束応力（載荷した荷重を試験体の断面積で除した値）である。実際の測定試験では、載荷する荷重により生じる圧力Ｐｓ（上載圧力）を測定した後、吸水膨張性粘土Ｂに荷重を載荷した状態で吸水膨張させ、吸水膨張性粘土Ｂの吸水膨張が終息した時点で吸水膨張性粘土Ｂの密度（終息密度）を求める。そして、吸水膨張性粘土Ｂに作用する圧力Ｐｓ（上載圧力）の圧力値と密度が「所定密度の吸水膨張性粘土の吸水膨張ポテンシャル」として記録される。たとえば、図６に示す結果からは、乾燥密度０．６９６Ｍｇ／ｍ３（ｇ／ｃｍ３）のベントナイト（商品名：クニゲルＶ１）の吸水膨張ポテンシャルの値は１９．６ｋＰａである。同様に、乾燥密度０．４５７Ｍｇ／ｍ３（ｇ／ｃｍ３）の吸水膨張ポテンシャルの値は４．９ｋＰａである。 In other words, the water absorption expansion potential is the restraining stress (the value obtained by dividing the loaded load by the cross-sectional area of the test specimen) when the water absorption expansion phenomenon ends. In an actual measurement test, after measuring the pressure P s (upload pressure) generated by the loaded load, the water-absorbing expandable clay B was subjected to water-absorbing expansion while the load was loaded, and the water-absorbing expansion of the water-absorbing expandable clay B was terminated. At the time, the density (final density) of the water-absorbing expandable clay B is obtained. Then, the pressure value and density of the pressure P s (upload pressure) acting on the water-absorbing expandable clay B are recorded as “the water-absorbing expansion potential of the water-absorbing expandable clay having a predetermined density”. For example, from the results shown in FIG. 6, the value of the water absorption expansion potential of bentonite (trade name: Kunigel V1) having a dry density of 0.696 Mg / m 3 (g / cm 3 ) is 19.6 kPa. Similarly, the value of the water absorption expansion potential at a dry density of 0.457 Mg / m 3 (g / cm 3 ) is 4.9 kPa.
吸水膨張性粘土Ｂに作用する圧力を吸水膨張ポテンシャルと称する理由は、吸水膨張性粘土Ｂが載荷した荷重を支持する圧力Ｐｓを有するとともに、吸水現象による水を引き込むポテンシャルをも有すると解釈できるからである。すなわち、吸水膨張ポテンシャルは、力学的な力（圧力）であると同時に、水を引き込む吸水力でもある。 The reason why the pressure acting on the water-absorbing expansive clay B is referred to as the water-absorbing expansive potential can be interpreted as having a pressure P s that supports the load on which the water-absorbing expansive clay B is loaded and also having the potential to draw water due to the water absorption phenomenon. Because. That is, the water absorption expansion potential is not only a dynamic force (pressure) but also a water absorption force for drawing water.
吸水膨張性粘土Ｂの吸水膨張現象が完全な可逆反動であるならば、上述した膨潤圧と吸水膨張ポテンシャルとは同じ値になるが、実際には膨張挙動に粒子間の摩擦力等の影響が加わるために、膨潤圧に比べて吸水膨張ポテンシャルのほうが小さくなり、膨潤圧と吸水膨張ポテンシャルとは一致しない。 If the water-absorbing expansion phenomenon of the water-absorbing expansive clay B is a completely reversible reaction, the above-mentioned swelling pressure and water-absorbing expansion potential will be the same value. Therefore, the water absorption expansion potential becomes smaller than the swelling pressure, and the swelling pressure and the water absorption expansion potential do not match.
図７は、図６に示した試験結果を図４に示した測定例に加えた図である。なお、図６に示した試験結果は、図４に示した測定例と同様、吸水膨張性粘土Ｂ（ベントナイト系の土質材料）の乾燥密度を吸水膨張する粘土鉱物であるモンモリロナイトの乾燥密度に換算した有効モンモリロナイト密度で整理している。 7 is a diagram in which the test results shown in FIG. 6 are added to the measurement example shown in FIG. The test results shown in FIG. 6 are converted to the dry density of montmorillonite, which is a clay mineral that absorbs and expands water, in the same way as the measurement example shown in FIG. 4. Sorted by effective montmorillonite density.
上述したように、乾燥密度０．６９６Ｍｇ／ｍ３のベントナイト（商品名：クニゲルＶ１）の吸水膨張ポテンシャルの値は、１９．６ｋＰａである。ベントナイト（商品名：クニゲルＶ１）の中には、吸水膨張性の粘土鉱物であるモンモリロナイトが６０％含有されているため、有効モンモリロナイトの乾燥密度は、約０．４２Ｍｇ／ｍ３である。同様に、乾燥密度０．４５７Ｍｇ／ｍ３（ｇ／ｃｍ３）の有効モンモリロナイトの乾燥密度は、約０．２７Ｍｇ／ｍ３であり、その吸水膨張ポテンシャルの値は、４．９ｋＰａである。 As described above, the value of the water absorption expansion potential of bentonite (trade name: Kunigel V1) having a dry density of 0.696 Mg / m 3 is 19.6 kPa. Bentonite (trade name: Kunigel V1) contains 60% of montmorillonite, which is a water-swellable clay mineral, and therefore the dry density of effective montmorillonite is about 0.42 Mg / m 3 . Similarly, the dry density of effective montmorillonite having a dry density of 0.457 Mg / m 3 (g / cm 3 ) is about 0.27 Mg / m 3 , and the value of its water absorption expansion potential is 4.9 kPa.
図７に示した直線は、上記の二点を考慮した回帰線であり、吸水膨張ポテンシャルは、バラツキの中間値に相当していることを示唆していることから、バラツキの小さい測定方法である。 The straight line shown in FIG. 7 is a regression line considering the above two points, and suggests that the water absorption expansion potential corresponds to an intermediate value of the variation, and is therefore a measurement method with a small variation. .
上述したように、吸水膨張性粘土Ｂの吸水膨張特性を把握する際には、膨潤圧を測定するよりも、吸水膨張ポテンシャルを測定するほうが好ましい。しかしながら、吸水膨張ポテンシャルを測定するには吸水膨張が終息するまで待たなければならないので、一つの吸水膨張ポテンシャルを測定するのにも著しく長い時間がかかる。また、複数の吸水膨張ポテンシャルを測定する場合には、吸水膨張性粘土Ｂ（試験体）ごとに荷重を設定し、吸水膨張が終息するまで待たなければならないので、さらに長い時間がかかる。複数の吸水膨張性粘土Ｂを同時に測定すれば、測定にかかる時間を短縮できるが、試験装置が複数必要となり、試験コストが嵩む。また、複数の吸水膨張性粘土Ｂは密度や飽和度に微少な個体差があるので、個体差がデータにバラツキをもたらすことも懸念される。 As described above, when grasping the water-absorbing expansion characteristic of the water-absorbing expandable clay B, it is preferable to measure the water-absorbing expansion potential rather than measuring the swelling pressure. However, in order to measure the water absorption expansion potential, it is necessary to wait until the water absorption expansion ends, so it takes a very long time to measure one water absorption expansion potential. Further, when measuring a plurality of water absorption expansion potentials, it is necessary to set a load for each water expansion expandable clay B (test body) and wait for the water absorption expansion to end. If a plurality of water-swellable clays B are measured at the same time, the time required for the measurement can be shortened, but a plurality of test devices are required, and the test cost increases. In addition, since the plurality of water-absorbing expandable clays B have slight individual differences in density and saturation, there is a concern that individual differences may cause variation in data.
図８は、吸水膨張性粘土の吸水膨張特性を示す図である。本発明の実施の形態では、吸水膨張性粘土Ｂに載荷する荷重を段階的に小さくし、各段階において吸水膨張が終息した時点で、吸水膨張性粘土Ｂの密度と吸水膨張ポテンシャルを求める。 FIG. 8 is a diagram showing the water absorption expansion characteristics of the water expansion expandable clay. In the embodiment of the present invention, the load loaded on the water-absorbing expandable clay B is decreased stepwise, and the density and water-absorbing expansion potential of the water-absorbing expandable clay B are obtained when the water-absorbing expansion ends in each step.
具体的には、吸水膨張性粘土Ｂに第１段階の上載圧力Ｐｓが作用するように、吸水膨張性粘土Ｂに荷重を載荷し、吸水膨張性粘土Ｂの膨張高さを計測する。そして、この計測した膨張高さから元の高さ（吸水前の高さ）に対する膨張高さの割合δ（％）を求める（図８参照）。 More specifically, as acts on the mounting pressure P s of the first stage water-swellable clay B, and loading a load to water-swellable clay B, and measure the expansion height of the water-swellable clay B. Then, the ratio δ (%) of the expansion height with respect to the original height (the height before water absorption) is obtained from the measured expansion height (see FIG. 8).
その後、上述した数式１を用いて吸水膨張が終息した時点の吸水膨張性粘土Ｂの密度を求める。これにより、第１段階の上載圧力Ｐｓが求めた吸水膨張性粘土Ｂの密度における吸水膨張ポテンシャルとなる。 Thereafter, the density of the water-swellable clay B at the time when the water-swelling expansion ends is obtained using the above-described formula 1. Thus, the hygroscopic expansion potential in the density of the water-swellable clay B the pressure P s placement on the first phase is determined.
つぎに、吸水膨張性粘土Ｂに第１段階の上載圧力Ｐｓよりも小さな第２段階の上載圧力Ｐｓが作用するように、吸水膨張性粘土Ｂに荷重を載せ換えて、吸水膨張性粘土Ｂの膨張高さを計測する。そして、この計測した膨張高さから元の高さに対する膨張高さの割合、吸水膨張が終息した時点の吸水膨張性粘土Ｂの密度を求める。これにより、第２段階の上載圧力Ｐｓが求めた吸水膨張性粘土Ｂの密度における吸水膨張ポテンシャルとなる。 Then, so as to act pressure P s placement on a small second stage than the pressure P s placement on the first stage water-swellable clay B, and instead put a load on the water-swellable clay B, water-swellable clay The expansion height of B is measured. And the ratio of the expansion | swelling height with respect to the original height from this measured expansion | swelling height and the density of the water-absorbable expansive clay B at the time of water absorption expansion | swelling are calculated | required. Thus, the hygroscopic expansion potential in the density of the water-swellable clay B the pressure P s placement on the second phase is determined.
このように、吸水膨張性粘土Ｂに載荷する荷重を段階的に小さくし、各段階において吸水膨張が終息した時点で、吸水膨張性粘土Ｂの密度と吸水膨張ポテンシャルを求めるが、その段階数は、限られるものではなく、図８に示すように、３段階であっても良いし、それ以上あるいはそれ以下の段階数であってもよい。 Thus, the load loaded on the water-swellable clay B is reduced stepwise, and when the water-swelling expansion ends at each stage, the density and water-swelling expansion potential of the water-swellable clay B are obtained. However, it is not limited, and as shown in FIG. 8, there may be three stages, or more or less stages.
本発明の実施の形態のように、吸水膨張性粘土Ｂに載荷する荷重を段階的に小さくし、各段階において吸水膨張が終息した時点で、吸水膨張性粘土Ｂの密度と吸水膨張ポテンシャルを求めれば、一つの吸水膨張性粘土Ｂ（試験体）から複数の密度（終息密度）における吸水膨張ポテンシャルを求めることができる。測定試験開始から測定試験終了までの期間は、一つの吸水膨張性粘土Ｂで一つの密度（終息密度）における吸水膨張ポテンシャルを求める場合に比べて長くなるが、第１段階における吸水膨張が終息した時点（状態）がわかれば、第２段階以降における吸水膨張が終息した時点の判定が容易になる。これにより、つぎの段階、すなわち、荷重を小さくすること、に進みやすくなる。 As in the embodiment of the present invention, the load loaded on the water-swelling clay B is reduced stepwise, and the water-swelling clay B density and water-swelling expansion potential can be obtained when the water-swelling expansion ends at each stage. For example, the water absorption expansion potential at a plurality of densities (final density) can be obtained from one water absorption expandable clay B (test body). The period from the start of the measurement test to the end of the measurement test is longer than the case of obtaining the water absorption expansion potential at one density (final density) with one water absorbent expansive clay B, but the water absorption expansion at the first stage has ended. If the time point (state) is known, it becomes easy to determine the time point when the water-absorbing expansion in the second stage and thereafter ends. This makes it easier to proceed to the next stage, that is, to reduce the load.
また、一つの吸水膨張性粘土Ｂから複数のデータ（複数の密度における吸水膨張ポテンシャルのデータ）を取得するので、吸水膨張性粘土Ｂの数、試験装置の数が少なくて済み、コストや試験スペースを削減できる。さらに、一つの吸水膨張性粘土Ｂから複数のデータを取得するので、吸水膨張性粘土Ｂの個体差によるデータのバラツキを小さくできる。 Moreover, since a plurality of data (data of water absorption expansion potential at a plurality of densities) are acquired from one water-swellable clay B, the number of water-swellable clays B and the number of test devices can be reduced, and the cost and test space can be reduced. Can be reduced. Furthermore, since a plurality of data are acquired from one water-absorbing expandable clay B, the data variation due to individual differences in the water-absorbing expandable clay B can be reduced.
図８には、６つのデータをとるために、２つの吸水膨張性粘土Ｂ（試験体）を用いる例を示した。この例によれば、６つのデータを取るために、２つの吸水膨張性粘土Ｂと２つの試験装置を用いればよいので、６つの吸水膨張性粘土Ｂと６つの試験装置を用いる必要はない。これにより、コストや試験スペースを削減できる。 FIG. 8 shows an example in which two water-swellable clays B (test bodies) are used to obtain six data. According to this example, since it is sufficient to use two water-swellable clays B and two test devices in order to obtain six data, it is not necessary to use six water-swellable clays B and six test devices. Thereby, cost and test space can be reduced.
本発明の実施の形態では、飽和度を９５％以上に調整した吸水膨張性粘土Ｂを試験体とする。 In the embodiment of the present invention, the water-swellable clay B having a saturation adjusted to 95% or more is used as a test specimen.
図９は、不飽和状態の吸水膨張性粘土に吸水させた状態を示す概念図であり、図１０は、飽和状態の吸水膨張性粘土に吸水させたときの途中段階の状態を示す概念図である。 FIG. 9 is a conceptual diagram showing a state in which water is absorbed by an unsaturated water-absorbing expandable clay, and FIG. 10 is a conceptual diagram showing a state at an intermediate stage when water is absorbed by a saturated water-absorbing clay. is there.
吸水膨張性粘土Ｂが不飽和状態から吸水を始めると、図９に示すように、注水側の底部付近だけが吸水膨張して膨張挙動が始まる。時間の経過とともに、試験体全体に水が行き渡ると考えられるが、その間は、試験体の飽和度は均質ではないため、均質で安定した膨張変形挙動とならない懸念がある。また、終息密度に至るまでに要する時間も大きくなるという懸念がある。飽和度を事前に９５％に調整した吸水膨張性粘土Ｂを試験体とすることにより、図１０に示すように、均質に湿潤化した吸水膨張性粘土Ｂの膨張挙動を観測できる。吸水膨張性粘土Ｂの飽和度を初めから水で飽和した状態（飽和度９５％以上）にしておくことにより、吸水膨張性粘土Ｂに均質な吸水膨張特性が生じるので、膨張挙動が安定して進む結果、精度の良い測定ができる。なお、飽和度の高い吸水膨張性粘土の試験体の作成方法としては、特許第４２１７９５３号がある。 When the water-absorbing expandable clay B starts to absorb water from the unsaturated state, only the vicinity of the bottom portion on the water injection side absorbs water and expands, as shown in FIG. Although it is considered that water spreads over the entire test body over time, there is a concern that the degree of saturation of the test body is not homogeneous during that time, and thus a homogeneous and stable expansion deformation behavior is not obtained. There is also a concern that the time required to reach the end density will also increase. By using the water-swellable clay B whose saturation is adjusted to 95% in advance as a test specimen, the expansion behavior of the water-swellable clay B wetted uniformly can be observed as shown in FIG. By making the water-absorbing expandable clay B saturated with water from the beginning (saturation level of 95% or more), the water-absorbing expandable clay B has uniform water-absorbing expansion characteristics, so that the expansion behavior is stable. As a result, accurate measurement can be performed. In addition, as a method for preparing a specimen of water-swellable clay having a high degree of saturation, there is Japanese Patent No. 4217953.
ところで、吸水膨張性粘土鉱物であるモンモリロナイトの吸水膨張特性は、粘土鉱物の結晶層の間に存在する陽イオンが周囲の水に比べて電解質濃度が高い故の浸透圧現象であるとされている。このことから、吸水膨張性粘土Ｂに含まれる水（以下「間隙水」という）の電解質濃度が高い場合には吸水膨張特性は小さくなるはずである。その観点で図４を見ると、人工海水環境における膨潤圧は蒸留水環境における膨潤圧に比べて小さいプロットが多い。一方で、低密度領域では、蒸留水環境での値に比べて大きい傾向が認められ、バラツキが大きい。試験体は、半乾燥状態（たとえば、飽和度６０％程度）で作成し、その後、所定の電解質濃度の水を通水させて行く方法をとるため、実際に吸水膨張性粘土Ｂに含まれる間隙水は均質な電解質濃度ではないことがバラツキが大きいことの原因として考えられる。 By the way, the water absorption and expansion characteristics of montmorillonite, which is a water-swellable clay mineral, are considered to be an osmotic pressure phenomenon because the cation existing between the crystal layers of the clay mineral has a higher electrolyte concentration than the surrounding water. . From this, when the electrolyte concentration of the water (hereinafter referred to as “pore water”) contained in the water-absorbing expansive clay B is high, the water-absorbing expansion characteristic should be small. When FIG. 4 is seen from that viewpoint, there are many plots in which the swelling pressure in the artificial seawater environment is smaller than the swelling pressure in the distilled water environment. On the other hand, in the low density region, a large tendency is recognized compared with the value in the distilled water environment, and the variation is large. The test specimen is prepared in a semi-dry state (for example, a saturation degree of about 60%), and then a method of allowing water having a predetermined electrolyte concentration to flow therethrough, so that the gap actually contained in the water-absorbing expandable clay B is used. It is considered that water is not a homogeneous electrolyte concentration, which is a cause of the large variation.
本発明の実施の形態では、吸水膨張性粘土Ｂに含まれる間隙水の電解質濃度を予め定めた濃度に調整するとともに、吸水させる水の電解質濃度を吸水膨張性粘土に含まれる水の濃度（予め定めた濃度）に調整する。 In the embodiment of the present invention, the electrolyte concentration of pore water contained in the water-swelling clay B is adjusted to a predetermined concentration, and the electrolyte concentration of water to be absorbed is adjusted to the concentration of water contained in the water-swelling clay (preliminary). Adjust to the specified concentration).
図１１は、間隙水の電解質濃度が０に近い吸水膨張性粘土に吸水させた状態を段階的に示す概念図であり、図１２は、間隙水の電解質濃度が予め定めた濃度の吸水膨張性粘土に間隙水の電解質濃度と同じ濃度の水を吸水させた状態を示す概念図である。 FIG. 11 is a conceptual diagram showing stepwise a state in which the water-swelling clay having an electrolyte concentration of pore water close to 0 is absorbed, and FIG. 12 is a water-swelling property having a predetermined concentration of the electrolyte concentration of pore water. It is a conceptual diagram which shows the state which made water absorb the water of the same density | concentration as the electrolyte density | concentration of pore water in clay.
たとえば、図１１（ａ）に示すように、吸水膨張性粘土Ｂに含まれる間隙水の電解質濃度が０に近い場合には、吸水膨張性粘土Ｂの底部から一定濃度の水を注水してから、試験体全体が同じ濃度の間隙水に置き換わる。図１１（ｂ）から（ｃ）に至る時間は、当該電解質濃度環境における膨張挙動を呈することができない。これが、図４に示す人工海水環境条件でのプロットがばらついた値となっている原因の一つとなっている。 For example, as shown in FIG. 11 (a), when the electrolyte concentration of pore water contained in the water-swelling clay B is close to 0, water having a constant concentration is poured from the bottom of the water-swelling clay B. The whole specimen is replaced with pore water of the same concentration. The time from FIG. 11 (b) to (c) cannot exhibit the expansion behavior in the electrolyte concentration environment. This is one of the reasons why the plots in the artificial seawater environmental conditions shown in FIG.
これに対して、吸水膨張性粘土に含まれる間隙水の電解質濃度を予め定めた濃度に調整するとともに、吸水させる水の電解質濃度を吸水膨張性粘土Ｂに含まれる間隙水の電解質濃度に調整すると、図１２に示すように、吸水膨張性粘土Ｂの間隙には所定の電解質濃度の間隙水が最初から存在するので、測定開始時点で当該電解質濃度環境における正しい膨張挙動を呈することになる。その結果、より短時間でより均質な電解質濃度環境条件での吸水膨張挙動を観測できる。なお、試験体を事前に所定の電解質濃度で間隙を満たされた状態にして作成する方法については、特許第５０４１２３９号の方法がある。 On the other hand, when the electrolyte concentration of pore water contained in the water-swelling clay is adjusted to a predetermined concentration, and the electrolyte concentration of water to be absorbed is adjusted to the electrolyte concentration of the pore water contained in the water-swellable clay B. As shown in FIG. 12, pore water having a predetermined electrolyte concentration is present in the gap between the water-absorbing expansive clay B from the beginning, so that the correct expansion behavior in the electrolyte concentration environment is exhibited at the start of measurement. As a result, it is possible to observe the water absorption expansion behavior under a more homogeneous electrolyte concentration environment condition in a shorter time. In addition, there exists a method of patent 5041239 about the method of making a test body in the state by which the space | gap was filled with predetermined electrolyte concentration beforehand.
Ｂ 吸水膨張性粘土 B Water-absorbing expansive clay
Claims (3)
粘土に載荷する荷重を段階的に小さくし、各段階において粘土の吸水膨張が終息した時点で該粘土の密度と該粘土の密度おける吸水膨張ポテンシャルを求めることを特徴とする吸水膨張特性の測定試験方法。 Constrain the periphery of the clay that absorbs water and absorb the water in a state where a load is loaded on the clay, and determine the density of the clay when the water absorption and expansion of the clay ceases, and the pressure acting on the clay Is a water absorption expansion characteristic measurement test method , characterized in that the water absorption expansion potential at the obtained density ,
A test for measuring the water-absorbing expansion characteristic, characterized in that the load loaded on the clay is reduced stepwise and the density of the clay and the water-absorbing expansion potential at the density of the clay are determined at each stage when the water-absorbing expansion of the clay ends. Way .
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| JP4217953B2 (en) * | 2003-02-03 | 2009-02-04 | 清水建設株式会社 | Test method for poorly water-permeable soil materials |
| JP2005024347A (en) * | 2003-06-30 | 2005-01-27 | Ibaraki Univ | Simple measurement tool for infiltrating volume and swelling volume of bentonite material, measurement method therefor, and simple calculation method for infiltrating speed and swelling rate of the bentonite material by using the tool |
| US7240545B1 (en) * | 2003-12-31 | 2007-07-10 | Saudi Arabian Oil Company | Test apparatus for direct measurement of expansion and shrinkage of oil well cements |
| JP3923954B2 (en) * | 2004-03-31 | 2007-06-06 | 飛島建設株式会社 | Consolidation permeability test apparatus and test method |
| JP5041239B2 (en) * | 2008-05-13 | 2012-10-03 | 清水建設株式会社 | Buffering material and disposal method of waste |
| JP5416661B2 (en) * | 2010-06-30 | 2014-02-12 | 鹿島建設株式会社 | Swelling test method |
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