Background
Drilled shafts are deep foundation elements constructed in soil to resist compressive, uplift and lateral loads. This process involves drilling a hole to a design depth, and filling the hole with reinforcing steel and concrete. Tip resistance is not usually accounted for when estimating the overall capacity of drilled shafts and bored piles due to the excess deformation needed to achieve resistance. Instead of lengthening the shaft/pile, post-grouting techniques are typically implemented to improve the stiffness and load carrying capacity of the end bearing soil, but incur several limitations such as the lack of reliability and repeatability of the results. Researchers at the University of Nevada, Reno have developed an improved method to increase drilled shaft/pile end-bearing resistance.
Description
Our researchers have developed a system, method, and loading module which accounts for the tip resistance of overall pile/drilled shaft capacity, resulting in increased stiffness of the end bearing soil. This method improves upon post-grouting techniques utilizing a mechanical mechanism to preload the soil under the shaft tip, conferring the ability to account for the gained resistance at an acceptable level of movement. Each shaft/pile is preloaded during construction to verity its load carrying capability. The disclosed module comprises varying modifications to the associated shaft construction including positioning of anchors for a movable reaction frame, positioning of loading rod tubes, cement slurry tubes, and a tip loading module within the hole, where the tip loading module is comprised of a base plate with a lip and a seat opening for positing and securing the loading rod and reaction frame to the pile/shaft body. This module may also be coupled with a porewater pressure dissipater to dissipate water pressure generated during earthquakes.
Advantages
- This module increases the stiffness of the end bearing soil
- This module allows designers to confidently and systematically account for the forfeited tip resistance component in the overall pile/shaft capacity
- This module load tests every production shaft allowing designers to use higher resistance factors in LRFD design of shafts.
- This module allows users will be able to reduce shaft lengths and or diameters, thus reducing the foundation cost of a project
Patent and Publications:
UNR16-007
