VLF-MT survey was performed over the volcanic ejecta zone in northern foot of Mt. Fuji (Tateishi, Kamiyoshida, Fujiyoshida city, prefecture Yamanashi), and the geological structure is estimated, and the limitationof VLF-MT survey is discussed. This area is characterized by volcanic ejecta (tuff breccia, scoria and so on) resulted from the eruption of Mt. Fuji volcano. The instrument used in this survey is TeraTecnica VL-101equipment. VLF-MT measurments were made along 14 lines using 50 m station interval, apparent resistivity, phase anglebetween magnetic field and electric field, magnetic field strength and electric field strength are measured ateach station. The value of apparent resistivity of this area ranged in magnitude from 200 ohm-m to 1000 ohm-m.The electric field have considerable variation in value throughout the area, but the magnetic field have little variation.For this reason, the variation of the apparent resistivity has been considered to be due to the variation in theelectric field. When interpreting the structure by two-layer model, evaluation of the resistivity of the top layer pimust to be done. The resistivity of the top layer pi is evaluated by the following manner: value for apparentresistivity at station where has value for phase angle between 43-47 degree is regarded as the value for pi, andthis value is used as pi near the station. The result of the VLF-MT survey is compared with known electrical prospecting data from the same localities. The result is as follows: (1) The VLF-MT resistivity profiles are in general agreement with the profiles obtained from the electricalprospecting, (2) In the VLF-MT survey, multilayer which each layer have similar resistivity value is interpreted as theuniform layer.The result of survey indicate that VLF-MT method is useful for estimating the geological structure in the volcanicarea where no outcrops are present.
In the cold region of Japan, many roads constructed under steep slopes are in danger of rock falls. In thiswork, the occurrence mechanism of rock fall was considered theoretically to find the proper prevention measure. Practically, the thermal deformation of a rock plate on slope was calculated on the basis of the mechanicalmodel. In this model there was a cohesive joint between the rock plate and the slope, and a length of crack propagatedalong the joint from the upper end. There was no or a piece of rock in the crack. Next, the energy releaserate was calculated by applying the method of linear fracture mechanics, and the stress intensity factor was investigatedby changing a temperature gradient, an angle of slope and a thickness of the rock plate as a parameter. Consequently, it was proved that the occurrence condition of rock fall was satisfied more easily correspondingto an increase of the above parameters. Furthermore, it was clarified that the occurrence frequency of rockfall became highest at the term when the temperature gradient became steepest.
It has been pointed out that ground water in a fractured rock mass is mainly flowing in a three dimensionalnetwork of channels. A technique for modeling this network on the basis of the geologic structures of the majorfractures is proposed in this paper. It is assumed that the channel is defined as the open part and/or the part inwhich many small fractures are concentrated on these major fractures. Some geologic structures that can formthose parts are also studied. A new computer code named “Don-Chan” was newly developed for analysis of theground water flow and the tracer migration in the 3-D channel network. The largest advantage of this computercode is the short calculation time. Because the trial calculation using a 3-D channel network model can be rapidlycarried out, this code is fit for the trial-and-error analysis used for improving the network model. The groundwater flow around a tunnel in an idealized fractured rock was successfully calculated within a short time.