Triaxial test of undisturbed completely decomposed granite under CT monitoring

Abstract

The change and failure are monitored and analyzed of the structures of completely decomposed granite from Hong Kong by CU triaxial tests. The CT scanner and the new triaxial apparatus that can monitor the pore water pressure and control the drainage condition are adopted in the test. The confining pressure of two cylinder specimens is 150 and 300 kPa, respectively. To 4 cross sections of each specimen, scanning is performed at 7 stages, i.e. initial state, after consolidation, and five stages of shearing process. Stress-strain curves and outlook change of specimens after test show that specimen failure is of different features according to different confining pressure and initial structures. Under higher confining pressure, shear failure occurs and under lower confining pressure creep failure occurs. The CT images and CT values are discussed. Five conclusions are gained. (1) The initial structures are extremely inhomogeneous. (2) The pore is compressed and the specimens are densitified after consolidation. (3) The meso-damage is in the form of hole-crack-hole due to the structure of soils and confining pressure. (4) Soil is of a very long plastic strain stage prior to peak value and the crack propagates along the failure plane. (5) Residual strength (creep) stage is steady and lots of hole-failure appear in the soil. In addition, a normal CU triaxial test is performed with one specimen from the same block. The results of CT triaxial tests agree well with those of normal triaxial test.