Closure to “Three-Dimensional Responses of a Tied-Back Excavation through Clay” by Richard J. Finno and Jill F. Roboski

In regard to the magnitude of the preload, the authors note that quantification of the relative merits of prestressing the ground anchors at either 75% or 100% of the design load is difficult. In their paper, the authors report that the first two level of ground anchors, located in beach sand, were nearly at the same elevation. This was physically possible only because the contractor horizontally staggered the anchors in these two rows. The authors further state that in order to evaluate response differences that are strictly the result of differences in the prestress, one would need excessively detailed three-dimensional numerical analyses. The authors cite Finno et al. (2002) regarding presentation of data from instrumented anchors collected at a different Chicago excavation. Results show that the anchors, locked off at 100% of the design loads, remained essentially constant throughout the excavation. As for the discusser's query about optimal prestress value, the authors are unaware of any supporting numerical studies or performance data.