FIELD STUDY OF PILE GROUP ACTION

Abstract

This report is the final report for a study involving the static vertical load test- ing of a full scale, instrumented pile group.The test group consisted of nine pipe piles instrumented for settlement, load transfer, pore pressures, total pressures and inclination.Two similarly instrumented reference (control) piles were also in- stalled.Two smaller subgroups within the main group were also tested, and uplift tests were conducted on several of the individual piles.The soils at the test site consisted of clays that were overconsolidated by desiccation.It was determined that the efficiency of the main group and of the subgroups was essentially unity.Set- tlement ratios in the working load range were found to vary from about 1 .2 to about 1.7, depending on the number of piles that were loaded.Failure was observed to be by plunging of the individual piles .Unit side load transfer varied essentially linearly with depth.Some dependence of load transfer patterns on residual stresses that remained after driving the piles was observed.The measured behavior of the group and subgroups was modeled by the "hybrid" algorithm, by means of Program PILGP1 , which was developed for this study and documented in Appendixes A and B. Good agreement between computed and measured results were achieved when the unit load transfer curves from the reference piles were^sedand when the soil modulus of deformation was appropriately adjusted to account forpTTe"gfiff#9*pement of the soil and the presence of very small strains in the| maSr^j&ST&tEMT f^uild the group.TRANSPORTATION A description of the mathematical model, the rationale for its selection and a prior analysis of group behavior is presented in|FHV|a/]MH81/0pi^Ab analysis of dynamic measurements taken during driving the 11 test piles is"'xn FfljwA/RD-81/009.Analyses and data obtained during the conduct of jthis study are in Appendixes A-F, FHWA/RD-81/003-008.