Publication Abstract

Proceedings of the 39th Annual Conference on Deep Foundations, 2014, Atlanta, GA, USA, (DFI)

Evaluating Installation Disturbance of Helical Anchors in Clay from Field Vane Tests
Alan J. Lutenegger, John Erikson and Nicholas Williams, University of Massachusetts

In order to evaluate the level of disturbance produced in clays during installation, a series of single-helix and multi-helix anchors were installed at a test site consisting of a stiff overconsolidated clay crust overlying softer near normally consolidated clay. Field vane tests were then conducted over the top of the helical plates at various depths to determine the undrained shear strength after installation and were compared with undrained shear strength measured in adjacent undisturbed ground. The tests represent the first time that the degree of installation disturbance has been evaluated directly and show that even with perfect installation practice the clay is disturbed as a result of rotation of the helices during installation. The results show that the soil is not completely remolded but that the strength is below the peak undrained strength of the adjacent undisturbed ground. Measurement of the installation torque and the rate of advance are used to define an “Installation Disturbance Factor” which may help to evaluate the quality of the installation by the Contractor and degree of soil disturbance.

 article #1993; publication #1011 (AM-2014)