Abstract
The drilling survey of soft rocks, which are thickly distributed in the subsurface of coastal area of Japanese islands, has a lot of task to be solved. Among the various drilling methods, the wire-line core drilling method has the advantage of being the most efficient, and it is generally adopted for conducting drilling surveys at depths of over 200 m. However, wire-line drilling method leads to an excessive increase in water pressure and to a low core collection rate of soft rocks because in wire-line drilling, the space between the tools and the borehole walls is very narrow. Therefore, we developed wire-line drilling tools that are larger than the standard-size tools. In addition, the new wire-line type single core tube was developed due to remove cuttings or debris quickly and keeps a high core collection rate. As the result, we succeeded in achieving a high core collection rate and obtaining good quality core while maintaining a high operational efficiency.
