ポアスケールモデリングによる豊浦砂の毛管圧曲線の推定
室内試験をコンピューター上で行うデジタルラボラトリー技術の開発
地盤など多孔質媒体中における二相流体の流動を数値解析する場合，毛管圧曲線などの二相流パラメータを室内試験で求める必要がある。しかし，対象とする流体や温度圧力条件によっては，試験の実施自体が困難となる場合も考えられる。本研究では，そのような場合でも数値解析によって二相流パラメータを推定または試験結果を補完する技術の開発を目的に，X線CTを用いて豊浦砂の空隙を抽出・モデル化し，ナビエ・ストークス式による数値解析（ポアスケールモデリング）を行い検討した結果を示す。流体が水のみの単相流解析から透水係数を求めた結果，既往研究による実験値とオーダーレベルで等しい値が得られた。水-空気二相流解析から毛管圧曲線を推定した結果，残留体積含水率やS字状の曲線が得られた点で，既往研究の室内試験結果の特徴を再現できた。水と土粒子との接触角を変えた同検討から，豊浦砂における水と土粒子の接触角は約60°と推察された。
キーワード：ポアスケールモデリング，X線CT，二相流解析，毛管圧曲線，不飽和流
＊１ 技術センター 社会基盤技術研究部 地盤研究室
Estimation for Capillary Pressure Curve of Toyoura Sand Using Pore Scale Modeling
Development of a Digital Laboratory Which Conducts a Laboratory Test on a Virtual Space
When simulating two-phase fluid flow in a porous medium, such as soil or rock, it is necessary to obtain two-phase flow parameters such as the capillary pressure curve by laboratorial experiments. However, performing such experiments may be difficult depending on the target fluid and temperature and pressure conditions. In this study, in order to develop a technology for estimating two-phase flow parameters using numerical simulation or supplementing experiment results in such cases, pores in the Toyoura sand were extracted and modeled using X-ray CT for pore scale modeling by the Navier-Stokes equation, and the results are reported here. As a result of a single-phase flow analysis for water, the hydraulic conductivity obtained was found to be equal to the experimental values obtained in previous studies in the same order of magnitude. Moreover, two-phase flow simulation of water and air was conducted to estimate the capillary pressure curve, and the characteristics of the laboratory tests in the past studies were successfully reproduced judging from the fact that the residual volumetric water content and S-shaped curve were obtained. In this study, contact angles between water and soil particles were changed, which led to the estimation that the contact angle between water and soil particles of the Toyoura sand is about 60˚.
Keywords: pore scale modeling, X-ray computed tomography, two-phase flow analysis, capillary pressure curve, unsaturated flow
*1 Geotechnical Research Section, Infrastructure Technology Research Department, Taisei Advanced Cwnter of Technology