Chad Alexander Victoria CARRETAS

Development of In-situ Shear Apparatus

Hirofumi TOYOTA

Strength coefficients c and are determined using two methods: by measuring the
soil resistance to penetration (N) from in-situ shear tests, and by performing indoor
tests. In the former, they cannot be measured directly so one has to rely on estimating
them from N based on experience. In the latter, the stress condition of the soil changes
during sampling, influencing test results. Given the above factors, determining c and
directly by means of in-situ shear tests would yield more reliable results. Consequently,
by utilizing the bottom of boreholes, it is possible to directly and more easily obtain their
values. On this research, I investigated the usability of Borehole Torsional Shear Test
(BTST) apparatus by performing constant pressure and constant volume tests, and by
comparing the results with those from standard indoor tests. Toyoura sand and Kaolin
clay were used as the specimens. Judging from the test results, I conclude that for
testing sandy soils, the installation of a confining ring is required and the length of the
edge should be set to 22mm to obtain a good result. The purpose of the confining ring is
to prevent the particles of sand from moving away from the shear blade, and thus
preventing decrease in density. For clayey soils, results show that a hollow shear edge
with a 2mm blade is best to use.