This paper begins with a review about electrical property of soil and rock, anisotropy of ground, electrical measurement for resistivity data. And it presents a result of resistivity tomography in order to investigate electrode array effects. Next, the authors have evaluated the electrode array effects in reconstructed resistivity image for predictive design in resources and environment and ground investigation technique by using water tank electrical model experiment for Wenner and Eltran electrode arrangement systems. Furthermore the detailed relation between resistivity anisotropy and electrode arrays has been investigated for high resolution/high density resistivity prospecting as an aid to obtain reliable geophysical and geological information.
Ground water flow in fracture developing rock mass seems to be more complicate than porous sedimentary rocks due to the geometry of fractures and characteristics of fracture filling minerals. To understand the ground water flow in the fracture developimg rock mass, the ground water surveying system was proposed. The system was established by three points of view, i.e. Where the ground water flows?(geological structures), How the rock permeability is?(rock mass permeability), How the ground water flows?(ground water flow property). The system was constituted by the newly developed methods and the existing ones. The system was applied to the granitic rock site, 100 m×100 m wide and 100 m deep to verify the system. Major conclusion obtained at the application site was as follows; Core-logging, BHTV logging, and geo-tomography were rather instrumental in making a geological model. Single-hole and cross-hole hydraulic test could obtain 2-D distribution of the hydraulic conductivity, showing the close relationship with the geological structures and geophysical parameters. Radon logging and spiner logging is useful to detect the permeable fractures.
CSAMT (Controlled Source Audio Frequency Magnet-Telluric) and TDEM (Time Domain Electromagnetic) survey were carryed out at Mikata area, northern part of Hyogo Prefecture. The joint inversion with CSAMT and TDEM was conducted, and the result is summarized as follows: (1) The resistivity structure of the Mikata area to 2000-3000m below the surface was analyzed. (2) The resistivity structure to 500m below the surface was analyzed with CSAMT. TDEM data was used to analyze the deeper structure. (3) In a shallow zone to 250m below the surface the high resistivity zone with more than 200Ω-m is distributed around the northwest of Yatagawa River. And the low resistivity zone with less than 200Ω-m is around the southeast side. This resistivity structure corresponds to the Utaosa rhyolite lava around the northwest side of the river and Haruki mudstone member around southeast side. (4) The low resistivity zone with less than 50Ω-m, intersecting this structures, under 500m below the sea level, is stretching from east-northeast to west-southwest. (5) That low resistivity zone corresponds to the discharge area of the hot water at Mikata area, and is considered to indicates the presence of the fractured rock (granitic rock) in deep underground. The points of the hot springs may be controlled by the presence of the deep low local resistivity zone.
Stereographic solution is applicable to evaluate the sliding frictional angle of discrete surface in rockmass. In case of rock slope with discrete surface, the possibility of failure is attributed to relationship between the following factors:(1) plunge of the rock slope, (2) plunge of the discrete surface, and (3) sliding frictional angle of the discrete surface. Therefore, in the failed rock slope, sliding frictional angle of discrete surface is evaluated from geometric relationship between the plunges of discrete surface and rock slope. It is easy to examine the geometric relationship of those plunges by using equalangle stereonet. Tow examples of stereographic solution, which apply to rock slopes within Gifu Prefecture, are discussed in this report.
The new type Helicopter-borne Electro-Magnetic (HEM) system, which has been improved the frequencyrange of measurement to meet the needs in civil engineering fields, has been applied to the landslides of Sarukuyoji in Niigata prefecture and Yachi in Akita prefecture. The results of HEM survey show that both landslides correspond to the anomalous low resistivity zones, which shows that HEM method is effective to detect and delineate the landslides accompanied with cohesive soil, collapse soil or weathered zone.
Recently, the variety of utilization of underground rock cavern requires the increase of problem of underground water in a rock mass. Especially, at the construction of the repository of high level radioactive waste, it is nessesary to exactly evaluate deep and regional groundwater flow in order to keep safety of the rock mass as natural barrier if harmful nuclides are leaked because of some accident. For these needs, one of the suitable methods is geochemical method, which gives information about real groundwater flow recharge area, residence time, source and so on by means of dissolved ions and environmental isotopes. In this report, the result was shown to apply this geochemical method to groundwater flow in a granitic rock mass at the tunnel site under construction. To evaluate regional groundwater flow in detail, this investigation was focused on these points, (1) principal component analysis for major dissolved ions, (2) altitude effect of stable isotope 18Oin water, (3) dissolved 222Rn gas, (4) stable isotope 13C in dissolved carbonate. From these results, it was concluded that regional groundwater flow in this site can be modeled as a flow in porous medium, and that changes of groundwater flow because of tunnelling can be evaluated by geochemical method.