The Stress-Strain-Strength Behaviour of a Completely Decomposed Granite Soil Using a New Advanced True Triaxial Testing System

Completely decomposed granite (CDG) soil is the most common type of soils found in more than 90% of the land area in Hong Kong. The measurement of the stress-strain-strength behaviour of the CDG soil is very important for deformation and stability analysis of slopes, retaining walls, excavations, deep and shallow foundations related to the CDG soil ground. As most of these geotechnical structures are in a three-dimensional (3-D) stress state or approximately in a plane strain condition, the measurement of the behaviour of the CDG soil in a 3-D stress state or a plane strain condition is necessary. In this paper, first, a new true triaxial loading device and its setup for testing are introduced. Second, typical test results from a series of true triaxial tests on the CDG soil with different b-values are presented and discussed. These tests are used to study the influence of intermediate principal stress on the mechanical behaviour of the re-compacted completely decomposed granite soil. Third, typical test results from a series of plane strain tests on the same soil are presented and discussed. These test results are used to study the stress-strain-strength characteristics of the soil in a plane strain condition.