Abstract
In many cases, slide surfaces are observable in testpits, but hardly on the boring cores. This paper describes the results of exploration of slide surfaces in a few testpits in some study areas.
In the testpits, a state of a slide surface is not always visible to the naked eye. But it is possible to collect cohesive soil samples containing a slide surface. Therefore, the position and shape of a slide surface is determined when the constants of shear strength of cohesive soil is measured.
There is broad difference among the constants of shear strength on a slide surface. In application of the method of slices for the stability analysis of a landslide, testpits are necessary as many as possible for determination of those constants. In order to obtain exactly the safety factor of a landslide, we must know correctly the distribution of φ′ along the slide surface, in which constants of shear strength are C′=0 and φ′>0 in the moving landslide.
