As one of the geological prospecting method for civil engineering, electrical prospecting method is used to obtain an information of geological profile for geological structure, basement profile of construction, landslide profile and so on. However, recently, the authors need to develop a new technique which provides a moving profile of resistivity due to the groundwater flow for making clear the mechanism of the nature of groundwater contamination. Utilization of electrical prospecting method for detecting the variation of resistivity for short term range needs the improvement of measuring efficiency and high accuracy. At the point the authors described in the former paper. In this paper, visualization of the movement of an electrolyte tracer in an analogic sand layer equipment is demonstrated by permeability experiment and by means of repeated resistivity measurement of which electrical pole arrangement is dipole-dipole. Sodium chloride solution of which salinity is 1.0 percent for replacement ex-periment or 3.0 percent for injection experiment, respectively, is percolated as an electrolyte tracer into a sand layer in steady state. The effectiveness of this method is ensured with the result of electrical conductivity measurement and measured flow velocity of this method agree well with one calculated from hydraulic gradient. Then this method is proved by the experimental approach. This method provides wide applicability such as detecting of ground water path in landslide or dam basement and analysing of flow direction and velocity of groundwater contaminants which are electrolytic.
Though flow nets offer a valuable means of visualizing groundwater flow fields, accurate drawing of flow nets are generally difficult in complicated hydrogeological structure. A numerical method was developed for automatically generating a flow net, using the finite element method to calculate the stream function and piezometric head. In this paper, a availability of the method is demonstrated in three hypothetical test models and verticalplane models through the granite region of the Kibi Plateau, Okayama Prefecture. Results of the numerical simulation show that a high-permeable zone can converge flow lines, though low-permeable zone can not effectively dam up stream lines. Groundwater flow in the granite region of the Kibi Plateau is approximated by a porous media flow. Flow nets of six cross sections in the region are constructed using the numerical method. Several areas converging flow lines in the basement are detected, but available quantity of water is small. The greater part of groundwater flows in the high-permeable weathering crust (‘Masa’ zone). Flow net analyses can be useful to identify groundwater exploration zones in the granite region.
Applications of data on cracks andcavities in rocks are numerous and varied, in terms of both academic research and practical use. Important current research topics include the precise workings of microcracking processes and the effect of a variety of environmental condition on weathering. The propagation paths in granite, tuff and sandstone and the changes of cracks and cavities produced in specimens of tuff by weathering result, on a microscopic scale, were examined. Microcracks and cavities in specimens of granite, sandstone and weathered tuff were filled with methylmetaacrylate mixed with fluorescent paint, and then microscopically visualized under ultraviolet ray. The image analysis was performed to clarify the state of microcracks and cavities within the rock specimens by coating the specimens with fluorescent resin. Time control on weathering processespresentsclear examples of the stages in the evolution of microcracks, pathways of ground-water, and fillings of microcracks with secondary products. It is observed that the repeated occurrence of microcracks and diffusion enlargement is due to a periodic system dominated by the chemical or mechanical weathering rates. Image analysis using differences in brightness between microcracks or cavities filled with fluorescent resin and other parts of the specimen, was done, and the results showed good agreement with the porosity and the P-wave velocitydetermined by the usual methods. This new method may be useful for assessing the grade of microcracking or weathering.
Dewdrop and evaporation rates were measured in the inner space of an old mound located in the Gifu Prefecture, Japan. The measurement was carried out using five evaporation sensors that were recently developed by the present authors. Spatial temperature variability was observed over the wall surface of the space. It was clearly found that the dewdrop and the evaporation occur at the lower and the higher temperature parts on the wall surface, respectively. The total amount of the dewdrop was almost equal to the total evaporation in the space. This nature indicates that the vapor condensed as dewdrop on the lower temperature part in the space is continuously supplied by the evaporation from the higher temperature part. It can be concluded that the temperature variability is the most important agent that creates dewdrop in the underground space. A numerical simulation technique by which the temperature distribution over the wall surface of an underground spase can be calculated is also proposed in this paper. The main part of the technique is the numerical calculation of the unsaturated groundwater flow and the heat transfer around the space. The spatial distribution of the dewdrop and the evaporation rates over the wall surface and the seasonal change of the distribution were successfully estimated by this technique.
For a long time, the bentonitic drilling mud or the mud based on bentonite and other substances has been used widely. These types of mud have such characteristics as high specific gravity and high viscosity. Bentonite, the main component of the ordinary type of mud, is heavy, so it is hard to transport or to use in the field. A new type of drilling fluid powder have been developed to solve these problems. It is made of polymer which expands enormously when it absorbs water. The powder and water are required to make drilling fluid. Its concentration is about 0.3-0.6%in weight. The specific gravity of this drilling fiuid is close to that of water. But the ability of this new type of drilling fluid is as same as that of ordinary drilling mud. Moreover, thisnew type of drilling fluid has some superior characteristics. The mechanism of lifting drill cuttings with this new type of drilling fluid and some examples of its application are presented in this paper.