The results obtained through the further study on the subject are described hereunder. An unconfied aquifer model as shown in Fig. 1 has been clarified to be a depletion model of exponential function type as given by the following equation;h (t)=h(O)e-(α/λ)/t (7). A slope of depletion part of semilogarithmic time-series plot of groundwater head, A, is defined to beA=α/λ (8). Thus the real depletion coefficient, α, can be known when the specific yield, λ, becomes clear. The specific yield of a basin can be known through a proper pumping test. Otherwise an approximation may be made by an apparent depletion coefficient, A, and rainfall depth within a period. The manner of approximation are given in the equations (9) to (15). When the α and λ are properly defined a recharge other than from rainfall may be evaluated. Some of representative models under various hydrogeological conditions are illustrated in Fig. 3. One of time-series plots of observed and simulated hydrographs made for a verification purpose of a model is given in Fig. 4. Excluding major exceptions, the α and λ concentrate an order of n×10-4 day-1 and several percents respectively. Two kinds of recharge structure are described through the model adopted to a coral island that there are a slow structure for usual input and a rapid one for input in high intensity.
One of the purposes of this study is to get the internal information of slope, such as a thickness and profile of surface layer, from the information of landform and baserock geology. Another purpose is to investigate a fundamental method required to estimate the stability potential of slope when the surface layer thickness is known. All data required for these purposes were derived from the reports of elastic wave prospecting carried out for public works. The results of statistical analysis of surface layer data may be summarized as follows: The profile form of surface layer is in many cases either of uniform layer type or upper thicker layer type, depending on the vertical section form of slope. The thickness of surface layer is affected by the slope angle and baserock geology. From a large number of data on the relation between surface layer thickness and slope angle, the ultimate thickness and the mode thickness could be obtained in each slope angle. Assuming that the slope failure occurs preferentially at the surface layer with the mode thickness, the strength constant of the layer can be obtained by the reverse calculation based on the analytical method of slope stability. As a result of this calculation, it was proved that C' has an influence on the mode thickness of surface layer.
Surface textures of quartz grains from about 250 fault gouge samples with various types of fault in Japan are examined by means of the scanning electron microscope. It is disclosed that the surface morphology of the grains is variable, but quartz grains extracted from one fault gouge sample commonly show a type of texture different from those observed on the grains from the other samples. The surface textures observed under the microscope are tentatively classified into eight types; subconcoidal, orange peel-like, fish scale-like, moss-like, motheaten, stalactitic, pot-hole, and coral-like textures. These textures can be classified into four groups of I to IV. Arranged in the order of their apparent features, it is interpreted that the progressive corrosion of quartz grains by ground water has taken place after faulting. The change of this surface feature can assist in estimating the time elapsed since the last fault activity.
Proper idealization of geologic succession at the depth of Neogene sedimentary basin is indespensable to solve many problems in the field of Engineering Geology such as land subsidence, groundwater flow and stress distribution around deep excavation. A new procedure to idealize the succession by means of Markov matrix and its entropy of stratigraphic columns obtained from bore hole logs is given. As an application of this procedure, Markov matrix and its entropy are calculated from many stratigraphic columns obtained from two core boring logs and non core boring logs of over 300 in the east plain area of Saitama prefecture, Japan, with following results. (1) Markov matrix and its entropy represent well the regularity in the stratigraphic columns. (2) Some regional differences of the regularity are found in the area, and these differences seem to be caused by the regional variation of sedimentary environments. (3) Geologic succession in this area can be simply idealized as the alternation of some thick layers of coarse sediments and those of fine sediments. It has been clear that the procedure is quite useful to idealize the geologic succession under Neogene sedimentary basin.
In the previous paper, the author summarized results of geotechnical investigation for Ohnaruto Bridge foundation in planning and design stages. In this paper, results of engineering geological survey are described briefly during construction stage of Ohnaruto Bridge. Inspection of excavated foundation rock was carried out on the basis of geotechnical rock classification by geologist. Some in-situ rock tests were also performed in order to confirm geomechnical parameters used for foundatlon design. As multi-column foundation is selected for tower pier of Ohnaruto Bridge, a large diameter rotary drilling machine is adopted and it is shown that the drillability is fairly affected by such index properties as rock class and RQD. Field measurements of foundation rock behaviour during construction are planned for the purpose of construction control and improvements of geological investigation and stability analysis method. Main items of monitoring are vertical and horizontal displacements, and contact pressure of foundation rock. Some considerations are presented based on the preliminary measuring results.