Think about what makes a person have such a strong foundation in life: family, friends, positive mindset, and more. The foundation of a person’s life leads to who that person becomes just like how the foundation of a structure will affect how that structure exists. Without this proper foundation, the risk of experiencing issues such as cracking or collapsing of the structure increases.
Civil engineering doctoral student Jorge Orozco-Herrera worked mostly in the construction vibrations field before expanding his interests into the field of auger cast piles, a type of deep foundation element constructed by drilling an auger into the ground and then pumping concrete through the same hallow stem auger. He has been involved with three research projects, one of those projects being the effect of horizontal center-to-center spacing between auger cast piles in the capacity of groups of piles, which is very relevant in Florida. The other two projects he is involved in include road compaction and blasting induced liquefaction.
The auger cast piles project is intended to provide recommendations for the bridge design manuals at the state level.
This two-year project is funded by the Florida Department of Transportation and is led by two principal investigators (PI): Associate Professor Luis Arboleda and Co-PI Professor Kevin Mackie. Two doctoral students, Camilo Correa and Jackson Gil, are assisting them with this work.
“For this project, it’s about coming up with more efficient engineering designs. If they [the pile foundations] are too close to each other, engineers expect them to have lower resistance, and therefore you need more of them for design,” Mackie said. “The project is looking at exactly what the penalty is for spacing, if at all, so that the fewest piles can be used in a project.”
In this project, there are two things happening: numerical simulation in the computer running finite element models to analyze the response and a large-scale experiment in the structural lab. There is a box full of soil in the lab where they are installing and testing those elements under vertically applied loads similar to the weight from a structure above. The lab testing is at a reduced scale, and in geotechnical land, it is called a physical model test.
“This project started from scratch. We didn’t have the equipment, so we had to develop it. We designed the container where we have the soil, the equipment that we used to install these elements, and we had to rearrange a lot of the things in the structural lab,” Orozco-Herrera says. “It was quite a challenge to start.”
Along with those challenges was dealing with the suppliers to coordinate with the building and lab manager and learning how to model these on the computer. To install these foundations, they would use an auger to drill into the soil and pump concrete inside of the borehole.
The main data they want to collect is the displacement of groups of piles with different spacings and the load at which that displacement may occur. A linear variable differential transformer sensor was used to measure the displacement of the pile. Secondary data they wanted to see and collect includes pressure cells to know what the pressures in the soil are and strain gauges to measure the deformations at different locations in the pile.
“What we are looking for is that when they [the pile foundation] are far away, they’re going to fail at a larger load than if they are more closely spaced,” Orozco-Herrera says. ” We want all of them to fail during the experiment, so that we can understand the capacity.”
Failing means that they measure excessive deformations when they apply the loads. Since the structure shouldn’t move that much, applying a load that makes the piles go down excessively means they reach failure.
Further studies are needed to analyze what happens when they apply horizontal loads similar to wind load.
“The idea will be, for example, that the large-scale container we have can be used by the university,” Orozco-Herrera says. “All the experiments we have is applying a vertical load, but you can also analyze it by loading them horizontally. Hopefully, [we] can get a project like that.”
- Written by Sydney Ford