Volume 7, Issue 3 (September 1984)
Measurement of Lateral Stress Around Multihelix Anchors in Sand
The lateral stress regime around a one-quarter scale model triple-helix anchor was measured with diaphragm-type soil stress cells. Laboratory anchor pullout tests were run in a dry, uniformly graded sand at two different depths and relative densities. Lateral stresses were measured before and after installation of the helical anchor, at anchor failure, and continuously during the application of the uplift load. Results indicated that helical anchor installation causes increase in lateral stress around the anchor. Large increases in stress were observed in dense soils. In addition, lateral stresses increased as the anchor was loaded to failure. This behavior was attributed to arching stresses and soil dilatancy developing in the sand as it was sheared by the anchor. The magnitude of these increases was found to depend on the relative density of the sand. Based on the test results, values of the coefficient of lateral stress at failure kF were calculated for several densities and depths. The calculated kF values were found to be 30 to 40% lower than those proposed by Meyerhof and Adams for buried foundations. These lower values are due to the shearing disturbance during anchor installation.