Experimental Investigations On Small-strain Stiffness Properties Of Partially Saturated Soils Via Resonant Column And Bender Element Testing
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A comprehensive series of resonant column (ASTM D 2325-68), bender element (ASTM C 778), pressure plate (ASTM D 4015-92), and filter paper (ASTM D 5298) tests were conducted on compacted specimens of poorly graded sand (SP) and high plasticity clay (CH) in order to assess the influence of key environmental factors, namely compaction-induced matric suction and Ko stress state, on small-strain stiffness properties of partially saturated soils. Compaction-induced matric suction in all test specimens was estimated via soil-water characteristic curves (SWCC) for each type of soil. The research work was accomplished in six broad stages. During Stage I, a modified pressure plate extractor device was developed for assessing SWCC under anisotropic stress sates. Results from a series of SWCC tests on SP and CH specimens were used to assess the Fredlund and Xing's SWCC model parameters for each type of soil. During Stage II, resonant column (RC) tests were conducted on SP and CH specimens, at different compaction-induced suctions and isotropic confinements, in order to devise correlations between small-strain stiffness properties, shear modulus (Gmax) and material damping (Dmin), and matric suction. During Stage III, bender element (BE) tests were conducted on SP and CH specimens for the same experimental variables as in Stage II. Results were used to investigate the influence of suction on bender element performance as compared to resonant column testing. During Stage IV, bender element (BE) tests were conducted on SP and CH specimens at different compaction-induced suctions and Ko stress states. Results were used to devise a correction factor for RC results, on the basis of initial compaction-induced suction, for any given Ko stress condition. During Stage V, a series of RC and BE tests were conducted on SP and CH specimens using a resonant column device with self-contained bender elements. Results were used to further substantiate the experimental findings and correlations devised in Stages II, III and IV. Finally, during Stage VI, bender element tests were conducted on SP and CH specimens sheared at different vertical strain levels in order to assess the influence of vertical strain level on suction loss and menisci regeneration patterns.