Initial Tangent Modulus and its Variation due to Water Content in Granitic Rock

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  • WADA Chiharu
    Research Institute for Strength and Fracture of Materials, Faculty of Engineering, Tohoku Univ.
  • TAKAHASHI Hideaki
    Research Institute for Strength and Fracture of Materials, Faculty of Engineering, Tohoku Univ.

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Other Title
  • コンプライアンス法による花崗岩の初期接線縦弾性係数の測定とその水分飽和度依存性について
  • コンプライアンスホウ ニ ヨル カコウガン ノ ショキ セッセン タテダンセ

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This paper describes an effect of water content on initial tangent modulus (elastic constant) of granitic rock sample in tension.Rock samples containing various levels of water content were prepared, where water-saturated or vacuum-dried samples are made through the procedures in accordance with ASTM recommendation (ASTM C97).A degree of water saturation, Sr, is determined for each sample by use of the equation.<BR>Sr=Wi-Wd/Ws-Wd × 100 (%)<BR>where Ws is a weight of a water-saturated sample, Wd weight of a completely dry sample and WZ is a weight under air-dry or vacuum-dry condition.<BR>Based upon linear elastic fracture mechanics, elastic moduli could be precisely measured for these rock samples by means of compliance calibration technique.The experimental results obtained indicate a strong dependece of elastic modulus on degree of water saturation.Water contained in rock sample can be divided into three kinds of water, pore water, capillary water and adsorbed water (physisorption and chemisorption).The elastic modulus changes as a function of Sr-values.When Sr is below 35%, the elastic modulus increases abruptly.These increases in the elastic modulus are due to the reduction of capillary water in the rock sample.<BR>It is also considered that significant effect of water content on the elastic modulus can be interpreted as the results of frictional force acting on a microcrack plane in rock samples.

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