K..M. Hafez1 ,. M..M. Soltan2
1 Fac. of Eng., Aswan, South Valley Univ.
2 Fac. of Science, Aswan, South Valley Univ.
Suction stress characteristic curve (SSCC) is a relation between shear strength of soil and its
matric suction. It provides a potentially simple and practical way to describe the state of stress in
unsaturated soil. This relation is highly affected by the degree of saturation and texture of soil.
Mohr-Coulomb failure and critical state failure can be well represented by the SSCC concept.
For unsaturated soil, the shear strength theory proposed by Fredlund et al, 1978 can be used to
interpret the meaning of undrained shear strength in terms of two stress state variables, net
normal stress, (σ − ua) and matric suction, (ua – uw), assuming both linear and nonlinear failure
envelopes with respect to matric suction. However, it is the matric suction which holds the soil
specimen together during an unconfined compression test. The nonlinear variation of shear
strength of the soil with the friction angle with respect to suction, tan φb is predicted for the
tested compacted sand. The shear strength behavior of compacted sandy soil in unsaturated
condition is significantly influenced by physical and mechanical properties such as the initial
moulding water content, stress state and soil structure.