For the purpose of improving Hydro p ulse Tomography technique which is a method of identifying hydraulic property distribution in rock mass by using multi-well testing data, the authors propose new 3-D inversion algorithm that treats objective function consisting of both pressure performance data and their derivatives. Extended optimal control theory is developed for new objective function that includes the squared sum of differances between observed pressure change rate and calculated one at every observation point and every timestep. With this algorithm, approximated pressure derivative can be matched simultaneously without increasing computing time for every inversion step. Numerical case studies show us that the new algorithm is very useful to reduce the total number of inversion steps.

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When a Dense Nonaqueous Phase Liquid (DNAPL) can penetrate into the saturated zone, two types of liquid form in either discrete drops or continuous flows will be observed. In order to understand their dynamics, the mechanism of formation of immiscible fluid drops in saturated pore space has to be enlightened. This study deals with the snap-off of immiscible drops in different constriction (pore) models. Snap-off experiments of DNAPL are carried out in models of (1) single capillary tubes; (2) single constrictions built of glass beads; and (3) successive constrictions built of glass beads. All models are submerged in pure water. According to the experimental results, the snap-off unconditionally occurs as the protruding DNAPL passes an equilibrium position below the neck of a single constriction owing to the effect of gravitational force. Dynamics of snap-off depend on both the properties of the fluids and geometry of the constriction. Structure and size of pore space under the constriction where the DNAPL is passing has a dominant influence on the possibility of snap-off formation. An unfavorable condition of the pore space can resist snap-off not to occur, and the DNAPL may achieve a filament flow in such a case. It is also observed that the snap-off-generated drops break again into two or more smaller drops as collision with solid phase in the successively underlying constrictions. This process results in different sizes of discrete drops flowing in the porous medium.

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In the accompanying paper (Fujinawa,1997), new methods were proposed to evaluate hysteretic relationships of soil water characteristics θ(h) and unsaturated hydraulic conductivity k(h) and its applicability was verified by using experimental results conducted by Vachaud & Thony (1971). This paper deals with a finite element method with the aid of smoothing B-spline functions which enable to eliminate numerical oscillations associated with solving infiltration problems with abrupt seepage fronts and to search for correct scanning curves. The proposed method was applied to a Vachaud & Thony's redistribution experiment and the simulated results were favorably compared with the experimental results in terms of suction and volumetric water content.

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