STRAIN AND PORE PRESSURE BEHAVIOR OF FINE GRAINED SOILS SUBJECTED TO CYCLIC SHEAR LOADING

This study investigated the behavior of fine grained soils subjected to cyclic loading. Consolidated, constant volume (CCV), static (monotonic) and cyclic laboratory shear tests were performed using the Norwegian Geotechnical Institute (NGI) Direct Simple Shear Device, which has been modified for cyclic loading capabilities. All cyclic tests were performed with stress-controlled square wave loading and most with complete and symmetric stress reversal.; Two marine clays were studied: a clay from the Gulf of Mexico and an illite from the Pacific Ocean. The Gulf of Mexico clay sample was an undisturbed core and the Pacific Illite sample was reconstituted from dredged material. A few shear tests were also performed on a sand sample from the Yukon River Prodelta in Norton Sound, Alaska.; All tests included lateral stress measurements taken during consolidation and shear. The lateral stresses acting on the soil specimen were measured with the use of calibrated, wire reinforced rubber membranes acting as strain gauges. Detailed procedures for obtaining and interpreting lateral stress readings are presented. The additional information provided by the lateral stress measurements greatly increases the knowledge of the state of stress within the soil specimen being tested.; The calibrated membranes enabled the coefficient of lateral stress at rest, K(,0), to be determined experimentally during consolidation. The measured values of K(,0) agree very well with various indirect determinations (empirical correlations) of K(,0) for both clays.; The Mohr's Circle state of stress could be established for an infinetesimal soil element at the center of the specimen during consolidation and shear. The change in the coefficient of lateral stress, in the orientation of failure planes, in the principal planes and planes of maximum shear stress, as well as q-p plots (stress paths), could also be determined for the shear phase of the tests.; Knowing the monotonic stress-strain and lateral stress behavior during monotonic shear allows one to construct von Mises type nested yield surfaces which define the initial anisotropy of the soil specimen. These yield surfaces can be used to compare or predict the stress-strain behavior of a triaxial test performed at similar conditions (K(,0) consolidated).; The range of shear stresses in the cyclic tests was chosen such that the highest cyclic shear stress level produced failure in 100 to 200 cycles and the lowest such that failure did not occur in 3000 cycles (cyclic equilibrium). The cyclic tests were typically performed at 0.25 Hz. All soil specimens were normally consolidated with a final vertical confining stress of 0.518 kg/cm('2) (on a 50 cm('2) specimen). The shear device and calibrated membranes performed well at this low stress level and was considered an extreme test of the procedure and system capabilities.; Pore pressure was found to be a basic indication of the degradation of a soil specimen subjected to shear. Pore pressure can be used directly in predicting the behavior of soil specimens subjected to varying cyclic stress levels. A unique relationship between modulus and pore pressure for a particular soil subjected to cyclic loading was observed. If the cyclic shear strain at any test parameter combination (cyclic shear stress level and number of cycles) can be determined (through constitutive relations or graphically), the resulting pore pressure can also be determined from this unique relationship.; No soil testing equipment is without its problems and limitations, and the NGI device is no exception. These problems and testing errors were identified and evaluated.