Assessment of Liquefaction Potential
Resistance of sand against liquefaction is determined by running undrained cyclic triaxial tests on undisturbed soil specimens (Sect. 18.15). Cyclic stress with a constant amplitude is loaded repeatedly (similar to torsion shear tests in Sect. 18.8), and the number of cycles are counted until 1) excess pore water pressure equal to the initial effective stress (σ′c) and (2) peak-to-peak (i.e., double amplitude) axial strain equal to 2.5%, 5%, 10%, etc. The 100% development of excess pore water pressure is called “initial liquefaction” and the strain upon initial liquefaction may not yet be as large as those mentioned above. Thus, liquefaction in laboratory tests are defined in different ways; by pore pressure rise or development of strain. When sand is loose, the number of cycles needed for pore pressure rise and large strain amplitude are not much different.
KeywordsStress Ratio Simple Shear Triaxial Test Excess Pore Water Pressure Liquefaction Potential
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