Load Transfer Behavior of Full-Scale Instrumented Screw Anchors

A research program was undertaken to study the load-transfer behavior of full-scale multi-helix screw anchors installed in natural soils. Four triple-helix screw anchors were instrumented with strain gauges at incremental distances along the inside of each anchor shaft. The test anchors were installed in glacio-lacustrine clay and aeolian sand deposits, and statically loaded in uplift and compression. Strain gauge readings collected during the load testing were used to delineate the stress transfer along the length of the test anchors to the surrounding soil. The resulting load distribution curves are compared to values predicted by the published "cylindrical shear" model, and discrepancies between the model and measured values are discussed. The results provide a context for the engineering design of screw anchors based on their interaction with the surrounding soil.