In Korea, granite is occupied around one - third of the country, and granite weathered residual soils are widely distributed. Most of the research on this soil has been performed using reconstituted specimens because of the extreme difficulty of undisturbed sampling due to the sensitive particle structures. Therefore, the comparisons of deformational characteristics, which is expressed in terms of shear and Young′s moduli and damping ratio, obtained from the undisturbed and reconstituted specimens are important for the reliable understanding of soil behavior.
The overall purpose of this research is to study the deformational characteristics of Korean granite weathered residual soils at small ($10^{-5}$% to $10^{-3}$%) to medium ($10^{-3}$% to $10^{-1}$%) shearing strains using modified triaxial compression, resonant column, and torsional shear tests. Triaxial testing equipment was modified to employ the internal and local measurements, which can eliminate the bedding, seating and compliance errors. Proximity transducers were used for internal measurement whereas the LVDTs were used for local measurement. The resolution of both systems were achieved as small as $5×10^{-4}$% and the data acquisition system was constructed by using LabVIEW. System compliance of the developed system was evaluated by performing calibration tests using synthetic specimens of known stiffnesses.
Undisturbed samples are obtained at Hongsung by using a special undisturbed sampling device developed at KAIST and the reconstituted specimens are prepared at a similar density by using under-compaction method. Deformational characteristics determined by triaxial tests are compared well with those determined by resonant column and torsional shear tests. The effects of confining pressure, and loading frequency on small-strain shear modulus and damping ratio are investigated on both undisturbed and reconstituted specimens. Apparent consolidation pressure of undisturbed granite weathered residual soil was determined at a pressure of about 180kPa, but it was difficult to determine the apparent consolidation pressure distinctly on reconstituted specimens. The variations in modulus reduction and damping curves determined by undisturbed and disturbed specimens are also investigated and the elastic and cyclic threshold strains are defined and correlated with confining pressure.
