Driving from Lake City to Chipley, Dr. Mike Rodgers recalls his first involvement with Dr. Bloomquist, Dr. Crowley, and this instrument laying in the backseat of his car. Almost ten years ago, he was just an ambitious assistant researcher on the team. Now, with a Ph.D. under his belt and years of research toward improving soil permeability testing, he is finally delivering a polished and improved product of his team’s work to FDOT. And there is still more work to be done.
Despite researcher turnover and taking a step or two backward in scoping, this research moved from only a concept to a physical, proven tool in each FDOT District office. The perseverance to improve soil permeability testing is evident throughout the life of this work started by University of Florida’s Dr. David Bloomquist. This research is worth being proud of; the team is persisting toward the ultimate goal while simultaneously reassessing their process and creating small victories – actual products – along the way.
A Rundown of Permeability
Hydraulic conductivity, or soil permeability, is the rate at which water moves through a soil. It is widely tested by engineering and geotechnical consultants throughout Florida. Soil permeability is important throughout design and construction phases to understand how water will seep through the ground. For example, retention pond development critically relies on permeability to understand how much additional capacity is available for stormwater that runs off roads, buildings, and other impervious infrastructure.
There are many factors that contribute to soil permeability, not only from within the soil itself, but also from the methodology and tools used to measure permeability. Testing in the field, in-situ, is technically the best approach because you are reducing the amount of manipulation to the tested soil as compared to extracting and then testing in the laboratory.
Even though soil permeability testing is best performed in the field, there are still limitations to existing technology. FDOT Project Manager David Horhota describes, “A borehole test would typically be performed, with a static measurement taken at the depth of the borehole opening; however, if the elevation of the retention pond happens to change during the life of the project, you are stuck with that permeability or the added cost of going back out to the site to retest at the correct depth.” In addition to receiving a static measurement, permeability is only measured for water released in the vertical direction, even though there are changes to permeability when water is released in the horizontal direction. On top of these limitations, the process is time-consuming and expensive. So, in 2004, Dr. David Bloomquist decided to dig deep into methods and tool development for testing permeability.
VAHIP or VIP? In-Situ Permeameter Development
Dr. Bloomquist’s initial research has evolved in many ways since his initial involvement and subsequent retirement in 2012. University of Florida researchers Dr. Mike Rodgers and Dr. Ana Mohseni and University of North Florida researcher Dr. Raphael Crowley have all served as Principal Investigator throughout these projects.
In 2007, Dr. Crowley started working with Dr. Bloomquist on the development of a new tool to measure soil permeability, called the Vertical and Horizontal In-Situ Permeameter (VAHIP). The VAHIP was intended to measure both permeability from the vertical and horizontal directions, instead of only measuring permeability in the vertical direction. While this capability was new and exciting, certain soils distorted the probe readings, defeating the accuracy of the instrument. Dr. Rodgers, at the time serving under Dr. Bloomquist, worked alongside the two professors to improve the VAHIP design. He reflects on the design, saying, “It was this highly mechanical, complex probe that we designed, and after some time we determined it was just too complex. Too much rotation, too many moving pieces. But the geotechnical engineers we shared this research with liked the idea of the probe, and they asked us to create a simplified version.”
So Dr. Crowley, Dr. Mohseni, and Dr. Rodgers took a step back and began improving the design for the Vertical In-Situ Permeameter (VIP), removing the horizontal capabilities, and focusing on improving the average measurement capabilities of the probe.
Testing, Testing: A VIP Pilot Program
Fast forward to today, and the VIP has been designed and modified to meet the researchers’ satisfaction. The latest project task is underway, led by Dr. Rodgers, to get eight VIP units into the hands of FDOT. Soils are currently being tested across the state in each District to see how the tool performs in different geological conditions. The testing and training are not only for District engineers, but also the geotechnical consultants who desired a simple design of the VAHIP, as Dr Rodgers explains, “One of the things we like to do is invite consultants around the area to come on-site and go through the learning process, asking as many questions as possible. Our main priority is to distribute a probe to the Districts, along with the accompanying head vessel and all the equipment necessary to complete the testing, then provide internal training and invite consultants that do this kind of work.” As of publication, Dr. Rodgers has delivered four probes to Districts 1/7, 2, 3, and 5, with the rest to follow shortly.
Dr. Rodgers is currently developing videos and recordings in place of field training, as well. “It will be used throughout the pilot program for training anyone who needs a refresher or who has questions outside of what we did.”
The pilot program has also led to the development of shop drawings for the VIP probe, which just recently became a formal Florida Test Method, FM 5-614. This means Districts and geotechnical consultants can now send these drawings to any machine shop to build their own VIP probe.
A Test Method Toward Opportunity
There is a lot of promise with the new and improved VIP probe, including potential use in non-DOT jobs and in other states. With its compactness resulting in a quicker set-up and less material, the VIP is more repeatable and more reliable. Much more data is available from a single test because it measures permeability profiles. David Horhota explains, “Instead of running a test at 15 feet, it’s easy to run one at 5, 10, 15, and 20 feet so you have a profile in case things change during the design, you already have the material properties.” Dr. Crowley adds, “You can run more tests for the same site investigation cost. And in terms of permeability, more tests are better to measure the variability.”
So, where did the VAHIP leave off? Well, it has a new design based on Dr. Harald Klammler’s alternative approach to delineating vertical and horizontal permeability. The new probe developed by Drs. Mohseni, Klammler, and Rodgers showed great promise in a controlled laboratory setting, but there is still a desire to make it less complicated for use in the field.
Reflecting on the process and what it took to get here, David Horhota shares, “The VIP was not our end goal, but there was an advantage to testing what could be tested in the short-term. Yes, if you can get a better VAHIP probe measuring vertical and horizontal permeability, that is great. But it would not be to the benefit of the Department or public if we waited for that ultimate end goal. Let’s take advantage of the research results and develop a pilot study from what we can right now. It still has its advantages!”