Method of Investigating Groundwater-vein Streams by Measuring One-meter-depth Temperature in Landslide Areas Part 1

Abstract

The occurrence of a landslide is very often correlated with topographical and geological characteristics of the landslide area as well as the existence of groundwater in the area. Therefore, overall information about surface and underground water in the landslide area is required in order to elucidate the mechanism of the slide, to predict its activity, and to design construction works for its prevention. On the basis of various findings and observations hitherto accumulated on groundwater in and outside landslide areas, the water may be divided into two categories ; the one flowing at a low filtration velocity through strata which are regarded hydrogeologically as aquifers, and the other flowing at considerably high filtration velocities through stratum portions, water veins which are distinguished in permeability from their surroundings. When the water veins postulated above are supplied with a large quantity of water at a stretch by a heavy rain or meltwater, or when abnormal effects are exercised on the veins by an earthquake, banking, or other causes, a possibility of landslide occurrence is developed. Therefore, in order to elucidate the above-mentioned mechanism etc., it is necessary to grasp the routes and scales of these water veins. The conditions of existence of groundwater in and outside landslide areas used to be investigated mainly by seismic and/or electrical methods which utilize either elastic or electrical properties of soil mass including water, respectively. These methods are useful to detect places where water may exist in a relatively large quantity. However, the both methods have furnished little information with regard to water existing in a vein form. Considering circumstances in summer that many landslide areas are rich in cold spring water and on the other hand the earth's surface is heated to a warmer temperature by solar radiation, the utilization of the temperature difference between them could offer useful information on the location and size of water vein. Reflecting upon the methods so far used, the author found out that methods utilizing thermal properties of water and soil are not included among them. Prospecting methods applying underground temperature measurement at shallow depth have been studied and employed mainly in the field of hot-spring exploration. YUHARA (1955) presented a method by which the scale and existence depth of a hot-spring vein are estimated theoretically from a temperature-distance curve obtained by measuring 1-m-depth underground temperature. Except for the field of hot-springs, NOMURA and MAKINO (1958) carried out preliminary investigations for mining by measuring temperature of shallow depth up to 60 cm, and examined the accuracy of ther-