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Influence of cyclic loading on axially loaded piles in clay
2 volumes (xxix, 454 leaves) : illustrations ; 29 cm
This research work is related to the influence of cyclic loading on axially loaded piles in clay. A literature survey of cyclic laboratory shear tests on clay shows that: 1. slow undrained cyclic loading is more damaging than rapid loading, 2. cyclic soil behavior is related to a decrease in effective stress, 3. the threshold cyclic stress ratio beyond which large and rapid degradation occurs is generally below 60% of the ultimate static strength, and 4. cyclic loading does not produce significant reduction of undrained shear strength. For piles under cyclic vertical loads, the literature shows that: 1. excess pore pressures at the pile-soil interface do not increase during cyclic loading, 2. the degradation process is probably due mainly to the destruction of the soil structure at the soil pile interface, 3. a cyclic load threshold exists above which failure occurs, 4. this cyclic threshold averages 80% of the ultimate static capacity, and 5. Cyclic loading below the threshold does not produce a significant decrease in ultimate static capacity. Thirteen simple shear tests were performed on a low plasticity clay. These test confirmed most of the finding form the literature review and showed that: 1. a power law model for soil degradation in shear is appropriate up to the number of cycles tested (2000), 2. the power law exponent may be linearly related to the cyclic shear strain, 3. creep creates more damage than relaxation, and 4. relaxation creates more damage than strain controlled cyclic loading. Fifty eight rod shear test were performed on a low plasticity clay. These tests showed that: 1. at cyclic levels less than 0.4 times the static ultimate friction, stiffening of the load transfer curve occurs, 2. at cyclic levels between 0.4 and the cyclic threshold, limited degradation occurs followed by a stable behavior, 3. the cyclic threshold has a very precise value, 4. The cyclic threshold seems to correspond directly to the value of the residual soil pile friction, 5. beyond the cyclic threshold failure occurs in less than 30 cycles, and 6. displacement controlled test are less damaging than stress controlled tests. A theoretical approach is proposed based on the radial integration of the power law hyperbolic load transfer model. The integration bridges the gap between the simple shear test and the rod shear test and shows their compatibility. The model allows to predict the degradation and the cyclic threshold for the load transfer curves. The gap between the rigid rod shear test and the flexible long pile is bridged by proposing the flow chart of a computer program which would encompass both cyclic loading and rate of loading effects.
Includes bibliographical references (leaves 446-453).