Highly organic soil is widely distributed and deposited with large thickness at southeastern area of Suwa Lake in Nagano prefecture, where is known as one of Japan’s softest ground. The ground settlement has been accumulated more than 3 m in this area, hence exposed pile foundations can be found out everywhere the area. Also, it has been known that this area is much susceptible to earthquake shaking. Then, general site investigation tests were conducted on July 2015 at Konami in Suwa city, in order to evaluate the possibility of ground settlement in highly organic soil, and to discover the correlation between results of different sounding test. This paper presents results obtained from the borehole survey, Swedish ram sounding test and Swedish weight sounding test as well as the examination on the correlation between each sounding testing result. Further, the possibility of ground settlement of surveyed ground due to loading a new fill is considered, which was calculated based on results of laboratory physical, chemical and mechanical soil tests. As a result, we found that there is still the possibility of large ground settlement on this site.
