Physical and mechanical properties of decomposed granite soils sampled in Cheongju, Korea

Decomposed granite soils are in a wide range of conditions depending on the degrees of weathering. This paper is intended to examine laboratory tests, such as consolidation tests and conventional triaxial compression (CTC) tests conducted in order to find out the mechanical properties of Cheongju granite soil. Along with the foregoing, the results of basic physical tests conducted in order to grasp the physical properties of Cheongju granite soil were described and based on the results, methods to calculate the mechanical parameters of numerical approaches using Lade’s single and double surface work-hardening constitutive model were examined. Finally, this study is intended to explain the stress properties of Cheongju granite soil used as a geotechnical material based on its shear behavior and critical state concept using the results of isotropic consolidation tests and triaxial compression tests. As a conclusion, it can be seen that in the relationship between confining stress and maximum deviator stress, the slope is maintained at a constant value of 2.95. In the drained CTC test, maximum deviator stress generally existed in a range of axial strain of 6 to 8% and larger dilatancy phenomena appeared when confining stress was smaller. Finally, based on the results of the CTC tests on Cheongju granite soil, although axial strain, deviator stress and pore water pressure showed mechanical properties similar to those of over consolidated soil, Cheongju granite soil showed behavior similar to that of normally consolidated soil in terms of volumetric strain.   Key words: Granite soil, stress-strain relation, single and double surface work-hardening model, soil parameter.