Regional Spotlight – Intro to the Mid-South
Geotechnical engineers and constructors working in the states of Kentucky, Tennessee, Arkansas, southern parts of Missouri, and northern parts of Alabama and Mississippi must be familiar with a wide variety of geology. These geo-professionals need to be part engineer, part geologist and part historian, because soil conditions across this part of America vary widely. If you’re working in the eastern extreme of the area, you’d better be skilled in identifying kart risks. Moving into Middle Tennessee, extremely hard bedrock can be found as shallow as the ground surface, so you could be blasting bedrock and country music at the same time. If your work takes you near the Mississippi River, you can probably leave your rock-coring equipment behind and spend your time understanding loess and deep alluvial deposits. While you’re enjoying your BBQ in Graceland, it’s probably a good idea to brush up on your liquefaction and seismic analysis methods, since the New Madrid Seismic Zone affects nearly everything in the area. Venturing further west into Central Arkansas is a geologist’s dream (or nightmare). The Diamond state will provide a true mixed bag of soil conditions left over from the Gulf of Mexico’s historic northern reach including sand, clay, cobbles, sandstone, shale and limestone….and that’s just in a few blocks of downtown Little Rock!
The versatile Ductile Iron Pile (DIP) system has helped solve foundation challenges on projects throughout the region over the past 7 years. Since DIPs can be designed for end-bearing on bedrock or can be installed with exterior grouting shoes to create a friction pile, the system is highly adaptable to the many different geologic challenges in this Mid-South region of the U.S. This versatility gives geotechnical engineers and constructors another high-value tool in their arsenal when challenging subsurface conditions complicate your deep foundation plans.
In this month’s DuroTerra Dialogue, we’re featuring a few projects throughout the Mid-South region, each with unique challenges that were addressed by using Ductile Piles. Have a project in the Mid-South (or beyond) that may be a candidate for DIPs, reach out to us for a feasibility assessment to know your options.
PROJECT EXPERIENCE – DAL-TILE SILO FOUNDATION
The addition of a new raw-product storage silo within the existing manufacturing facility required a solution to work within the limited access area. The silo was supported on 4 legs bearing on a common mat with axial loads of 800 kips and uplift loads of 200 kips. In addition, the silo would bear adjacent to an existing 13-ft deep pit. Ground conditions consisted of soft to very stiff clay extending to rock near 60 feet. The project team needed a deep foundation solution to transfer the silo loads below the pit to a competent strata. Ductile Iron Piles were selected and installed within the narrow work area to support the mat. Series 118/9.0 piles were installed to penetrate the clay and achieve set on rock at 52 to 58 feet below grade. A #8 thread bar was wet-set in many of the piles to provide tension resistance. Nearly 1,000 LF of piles were installed in less than two days. For more information, check out the project summary.
PROJECT EXPERIENCE – CARTI CANCER CENTER LINEAR ACCELERATOR
Construction of a new Linear Accelerator (LINAC) vault at the existing medical facility required support for the heavy structure. The vault consisted of 4-ft thick concrete walls and a concrete roof supported on a mat foundation with an applied pressure of 5,000 psf. Soil conditions included fill underlain by very soft to stiff clay extending between 55 and 70 feet. Exterior grouted Ductile Iron Piles were designed for capacities of 100 kips (compression) and 15 kips (tension). A Series 118/9.0 Ductile Iron Pile with a 220 mm (8.7 inch) diameter grout shoe was installed for load testing to a depth of 44 feet. The test was performed up to 250 kips (250% of the design load) with less than 0.6 inches of deflection. A total of 49 piles were installed in 6 working days on the constrained site. For more information, check out the project summary.
PROJECT EXPERIENCE – ENTERGY SUBSTATION RENOVATION
After a failing helical pile load test, the project team was scrambling to find an alternative foundation solution to avoid significant cost and schedule impacts to the piling scope. The expansion of the existing substation included support of isolated, small foundations and numerous larger mat foundations subjected to compression, tension and lateral loads. Peterson Contractors, Inc. proposed a combined solution using Geopier® ground improvement for lightly loaded foundations and Ductile Iron Piles to support larger mats. The piles were driven approximately 45 to 50 feet through the soft clay to develop frictional capacity in the medium-dense sand below. Full-scale load testing confirmed design capacities of 67 kips (compression) and 37 kips (tension). A total of 94 friction piles were installed to 65 feet in less than 2 weeks. The combined solution of Ductile Iron Piles and ground improvement prevented significant delays and change orders due to foundation cost overruns. For more information, check out the project summary.
