As shown in Fig. 4, the most unique feature of the apparatus
is that two parallel specimens of the same soil are tested simultaneously,
instead of just one. Such a special configuration,
in conjunction with very stiff components of the device and
the high-precision noncontact displacement transducers, enables
almost complete elimination of problems associated with
false deformations, system compliance, and friction. As a result,
very small strains and stresses can be applied and measured
in a controlled manner. Typical records of a test on Clay
A are presented in Fig. 5.
In Fig. 6, four loops obtained for Clay B at four different
levels of 'Ye are presented. The figure illustrates the smallest
'Ye for which the cyclic stress-strain curve, and thus the area
aW and A, can be accurately measured in the DSDSS device.
It can be seen that for the largest 'Ye .... 0.011% [Fig. 6(d»), the
shape of the loop is well defined and aW can be determined
precisely. For the smallest 'Ye .... 0.002% [Fig. 6(a»), the shape
of the loop is less well defined, but aW can still be determined
approximately. This indicates that the smallest 'Ye for which A
can be measured in the DSDSS device with an acceptable
accuracy is around 0.002%.