Determination of Shear Strength Index of Completely Decomposed Granite in Macao

Based on the basic physical parameters and triaxial consolidation undrained shear test results of 31 groups of completely decomposed granite (CDG) in Macao, the shear characteristics and the value of the shear strength index of completely decomposed granite were analyzed. The test results show that the stress-strain curve of the completely decomposed granite in Macao is generally strain-softening, the pore water pressure reaches a peak before the maximum deviatoric stress occurs and then begins to decrease, with the decrease of the clay content, the rate of decrease accelerates, and eventually a negative value may appear. It is inappropriate to take the peak value of the principal stress difference as the shear strength failure standard of Macao completely decomposed granite because of the shear expansion problem. 3 value methods were summarized, and the clay content was selected as a guiding index for the value of the shear strength. A new idea is provided for the selection of strength parameters of completely decomposed granite and is helpful to improve the reliability of the value.