The cross section of fill dams is generally triangular or trapezoidal in shape. If the analytical system contains such geometry, the finite difference or finite element procedure is the most effective for analyzing such problems for handling the boundary condition. However, it is inevitable that the computational efforts need to be increased for obtaining more precise solutions using these procedures. For that reason, a more simplified analytical method is proposed in this paper. It is characteristic to sum the finite difference equation of a given equation under boudary conditions. Basically, this approach is similar to the procedure from which the closed-form analytical solution is derived, whereas, solutions obtained are reduced to a discrete function. Applying this method to a two-dimensional probrem of seepage, the flow net in the impervious dam sections can be computed. To ascertain the validity of this method, the forward finite difference metod is employed here. It is indicated that the computational results by this procedure agree with the one by the conventional finite difference method with a reasonable degree of accuracy in the case of the impervious zone section and the homogeneous type of dam with isotropic and anisotropic conditions. In addition, the determination of phreatic lines is also proposed by fitting a power function of a third-order equation.

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A series of laboratory tests were performed in this paper on the shear strength characteristics of volcanic ash cohesive soils, to investigate the mechanism of strength reduction (softening) due to roller compaction and thixotropic strengh regain (hardening) after placement, referring to field observation records of an existing earthfill dam under construction. Emphasis was placed on the significance of quality control on strength and its relationships with deformation of earthfill and trafficability during construction.
On the overall slope stability of earthfills, the effective stress analysis of introducing variations of pore water pressure and shear strength in the softening process was found available for discussing the possibility of crack generation by examining the relationship between safety factor and deformation of earthfills.

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The borehole scanner system (BSS) has been recently developed to shorten the time of observing borehole wall. Shortend time makes it possible to process the large amount of data such as cracks. The panoramic images of the entire borehole wall improved the accuracy of borehole informations such as geologic structure, distribution of opening cracks. And hydraulic fracturing during Lugeon test is also clarified.

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An arch dam is a structure which, by a horizontal arch action, transmits a considerable portion of external load to the foundation rock on both sides. Accordingly the stability depends directly on the bearing capacities of the rock masses for the arch thrusts. The authors have investigated PS-anchor behavior on the shoulder of arch dam. As a result, it was found that the arch thrust due to thermal effect influences behavior of the foundation rock prestressed by the anchors.

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The development of new dam sites is decreasing recently by geological and environmental problems.
On the contrary, redevelopment of existing dams by raising their height will increse in the future, since this method has outstanding merits; for example, high ratio of storage volume/raised-height (high economical feasibility), and easiness of purchase of new land area (small impact on environment).
Design and construction of rasing dam height should take into account of functions of exising dams; flood control, irrigation, and water supply, etc.
Kayaze dam, of concrete gravity type, 51.0m high, built in 1962 by Nagasaki prefecture, is now under construction by raising its height by 14.5m.

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