Methods concerning the Subsurface Study of a Littoroal Lowland viewed from an Applied Geologic Stand Point

Abstract

It is difficult for an engineering geologist who participates in exploitation on a large scale to learn an underground condition of alluvial plains, without plenty knowledge of soil mechanics, hydrodynamics, geophysical prospecting, boring techniques and so on. Practical utility is the most significant essence for the establishment of engineering geology. The writer intends to approach to the aim at this stage, having a perfect command of geology, together with fundamental knowledge of geophysics, geochemistry and civil engineering.
The writer has investigated the 25 areas among the extensive littoral lowland in Japan by way of boring method during these seven years, in order to learn the underground condition. He has known the fact that the bore hole attains to the Tertiary formation within the average depth of 150 200 meters even in the deepest case ; that is an unconsolidated deposit has accumulated from the earth surface down to the depth, underneath which a harder formation has been found. These researches have utilized the newer method of prospecting, such as electric prospecting, lifting-up subterranean water, soil mechanic test and chemical analysis of pore water of boring cores etc. He describes the nature of the underground structure of the districts surveyed, illustrating a few examples.
Then the writer explains means for study necessary for the localization of industry upon a littoral lowland. It is a important problem whether the ground of sites can be borne against the weight of the building of factories or not. There are soft grounds, the bearing-power of which are less than 10t per m², everywhere in a littoral plain. An engineering geologist has tried to search for various kinds of prospecting methods, which occupy an indispensable part. The writer explains a few techniques for prospecting bearing-power of grounds, viz, standard penetration test (N-value method) and sounding method of Sweedish mode etc.
Measurement of void water-pressure in a stratum can determine stability of grounds or solve land subsidence. The writer recommends and explains an instrument named Sakata P. P. R. void pressure meter fitting for in situ test, introducing a few instances of success.
Engineering geologist must make efforts for counter-measures in the prevention of disasters in a littoral lowland, such as land subsidence in the main industrial regions and quick sand phenomenon after a severe earthquake. Since the writer has touched on the character and origin of the two phenomena previously, he has been able to account for a detail status quo of the studies in Japan.