Abstract: As a kind of special soil, granite residual soil is widely distributed in the southeastern part of China and usually leads to engineering accidents due to its special structure. In this paper, a series of triaxle tests was conducted on the slope residual soil from Bozhi County, Zhaoqing City, Guangdong Province, to study the strain and pore pressure characteristics of structural granite residual soil under triaxial stress state as well as the structural yield characteristics of granite residual soil, which could provide useful reference for corresponding projects. Triaxial compression tests were conducted on undisturbed soil, remolded normal consolidated soil and remolded over-consolidated soil. The results showed that both undisturbed soil and remolded over-consolidated soil had certain structural characteristics, and had an obvious dilatancy during the drained shear test. The stress-strain curves of both undisturbed soil and remolded over-consolidated soil showed strain softening. The excess pore pressure of both undisturbed soil and remolded over-consolidated soil increased first and then decreased during the undrained shear test, while the excess pore pressure of undisturbed soil decreased more. The undrained shear strength of over-consolidated soil was consistent with the SHANSEP theory and the test constant was 0.67. The normalized stiffness of remolded normal consolidated soil decreased slowly with loading process going on, and it yielded completely when =15%. The normalized stiffness curves of undisturbed soil and remolded over-consolidated soil were not consistent with each other, and the structural yielding occurs at =1.5% and =1% respectively, and the overall failure occurs at =15%. In addition, the larger the confining pressure was, the more similar the structural curve of the structural soil was to the disturbed soil.

Key words: granite residual soil, triaxial test, tangent stiffness, structural characterization