TRAN TUAN KHANH
MECHANICAL PROPERTIES OF UNSATURATED SOIL IN SMALL STRAIN RANGE
(小ひずみ領域における不飽和土の力学特性)
Small strain of soils is a great importance in geotechnical engineering practices.
The strain of soil during construction usually does not exceed 0.1%. This situation
has brought out the importance of precise evaluation of stress-strain relationships
and stiffness of soil at small strain to analyze the small deformation of ground.
It is necessary to ensure that reliable measurement of strain is accurately smaller
than 0.01%.
To evaluate the mechanical properties of soils in small strain range, where the
stiffness is varied nonlinearly, the proximity transducers are employed to measure

strain locally using a triaxial apparatus on unsaturated Yoneyama sandy silt. A
series of tests are conducted in the conditions of matric suction constant (CS) in
order of 100, 200,400 and 600 kPa, where drainage is perfectly allowed. These
experimental results were analyzed and compared with the similar testing

condition on saturated soil. Finally, the main conclusions are made as follows:

* The conventional measurement using dial gauge mounted externally could not
estimate for strain smaller than 0.01% and usually underestimated the stiffness of
soil from 49.7% to 29.26% at strain level 0.1%.

* During shearing process, there is no effect due to specimen tilting in the case of

soft clay. The effect of specimen tilting may be occurred in the state before
shearing due to a certain random reason. However, the effect of specimen tilting
could be eliminated during consolidation process.

* The effect of system compliance often occurred in a series of test on saturated
and unsaturated soft clay, while the effects of bedding were not observed in the all
case of soft clay samples.

* The stiffness of soil increased with suction. Moreover, the stiffness increased
rapidly during transition from saturated to unsaturated condition.