Lateral Pressure Measurements During 2.5 Years of Consolidation and Setup (1998)

Abstract A complete suite of lateral pressure data was taken during installation of tile test pile. followed by frequent observations of the changes with time during reconsolidation. Detailed recordings were made during static and cyclic load testing and thus provide a basis for fundamental interpretation of the soil resistance and its changes with time and with cyclic loading. One of the primary objectives of the test program was obtaining data that could be used to develop or verify axial pile design methods based on the principles of effective stress. While the behavior observed early in the consolidation process held promise. the severe effects of cyclic loading on the lateral pressures led to the conclusion that the interrelationships among the lateral pressures and the shear transfer were more complex than had been anticipated. The nature of the changes in the lateral pressures with time after cyclic loading was also significantly different than that predicted using current hypotheses of pile-soil interaction. Examination of the thick layer of clay that adhered to the pile after its removal however provides a clear framework for understanding the observed behavior. The results of the laboratory strength and moisture content determinations. combined with the x-ray and SEM studies. provide a benchmark by which future analytical techniques can be tested and refined. Introduction During the years prior to this research program a number of studies had been performed with the aim of developing design procedures for axially loaded piles based on then-current concepts of effective stress (Refs 1,2,3,4,4,5,6,7). The research efforts were confined to numerical analysis of the stress changes in clays adjacent to driven piles and had not been guided nor confirmed by field or laboratory experiments. One of the principal goals of this research therefore became the observation of the lateral total and pore pressures adjacent to a driven pile with the goal of obtaining experimental evidence upon which to found a reliable effective stress design method. In order to investigate the relationships between the lateral pressures and the axial capacity parallel manual and automatic digital records were kept during pile installation. reconsolidation and setup and static and cyclic axial loading. Data were recorded continuously during installation using the automatic data acquisition system. The total pressures were also read at intervals using the manual system. During installation of the pile the driving process was stopped for a few minutes each time the lowest set of pressure transducers were near an e1eyation at which a set of transducers would reside at the end of pile installation. A number of records were then obtained at a high sampling rate with manual data also being recorded at selected penetrations. After the pile, vas driven data were recorded at frequent intervals during the first twelve days while eight parallel experiments, were performed with instrumented pile segment models (Refs 8. 9). Data were then recorded periodically until the first major load test program in April 1984. Following the load testing program data was collected at intervals. primarily for the purpose of verifying the continued performance of the instruments.