SuperPile 2017 Online Proceedings, (DFI)
Driven Displacement Pile Ground Improvement for Liquefaction Mitigation
Armin W Stuedlein, Ph.D., P.E.
Conventional driven timber pile ground improvement can provide a cost-effective liquefaction mitigation method, as it provides densification and reinforcement to an improved subgrade. The potential for drained timber piles to improve densification and potentially reduce in-earthquake pore pressures could allow densification, reinforcement, and drainage in one mitigation method. However, the soil densification possible with timber pile ground improvement is rarely incorporated into stability analyses of supported geostructures because of the current lack of understanding of the amount of densification possible. This study focuses on a field trial of driven conventional and drained timber piles to investigate the effect of pile spacing, time-since-installation, and drainage on the amount of soil densification. The test site consisted of clean to silty sands with a relative density ranging from 40 to 50 percent prior to installation. Following installation of the timber piles spaced at two, three, four, and five pile diameters, cone penetration tests were conducted to evaluate the degree of densification. These tests were performed at approximately 10, 50, 120, and 250 days following installation to evaluate the effect of time and to understand the role of fines content on the degree of densification. In general, the relative density of the soils improved to approximately 60 to 100 percent depending on the pile spacing and the presence of drainage elements. A controlled blasting test plan was also conducted at an un-improved control zone and in the improved timber pile test area to evaluate the effectiveness of this ground improvement alternative to reduce the excess pore-water pressures and mitigate liquefaction. The treated zones were shown to mitigate liquefaction by reducing the peak residual ru values 10 to 25 percent and lowering the soil settlements by approximately 75 percent compared to the un-improved zone.
|article #2658; publication #1031 (SP-2017)|