Publication Abstract

Proceedings of the 43rd Annual Conference on Deep Foundations, 2018, Anaheim, CA, USA, (DFI)

Pore Water Pressure Response and Effect on Installation Torque of Large Diameter Helical Piles in Soft Soils
M. Mae Benvenga, P.E., Howard A. Perko, Ph.D., P.E., Heather H. Trantham, Ph.D., P.E., P.Eng., D.GE. and P.M.P.

Displacement of soil and groundwater during helical pile installation can produce excess pore water pressures (PWP) in fine-grained soils. Pore water pressure reduces effective stress in the soil immediately adjacent to the helical pile shaft and near the helical piles. Previous studies have shown generation of PWP may affect the capacity to torque ratios of the helical bearing elements. Large diameter helical piles that generate much of their torque and capacity from shaft adhesion are affected by PWP and therefore exhibit significant pile "freeze" after installation. Computer modeling is used herein to evaluate PWP immediately adjacent to helical pile shafts during installation in various soil types. The models show the degree and distance from the shaft that is influenced by PWP during installation and the amount of time required for the PWP to dissipate. Pile freeze has been measured on several project sites by re]torque measurements. These re-torque data are compared with computer modeling and correlations between saturated hydraulic conductivity and dissipation time are presented and discussed.

 article #3091; publication #1045 (AM-2018)