Abstract: With special geotechnical properties, the soft bedrocks such as, muddy and silty sandstone and slate, are widely deposited in the regions of low hill and rolling hill of east Hunan Province. In this paper, several key technical points in the geotechnical investigations are analyzed and discussed. For the broken and strongly weathered layer, the double casing coring along with the vegetable jell as the drilling method should be adopted to improve the drilling quality; when the strongly weathered bedrock is thick, and it can be divided into several sub layers so that the detailed variation of the geotechnical characteristics in the rock mass can be captured. Mudstone lenses are frequently encountered in the soft bedrock and its influence on the stability of the day-lighted rock slopes should be fully investigated. Drainage ditches and French drains should be provided in order to reduce the groundwater level and minimize the cost for the buoyancy construction.

Key words: rolling hill region, soft rock, geotechnical investigation, day-lighted rock slopes, buoyancy design elevation