The field of geotechnical engineering has often been called more of an art than a science. The materials involved are not manufactured to given specifications (such as the specifications associated with steel and concrete) but are the natural soils and rocks present at the location where the client wants to develop a project; these locations are not always ideal based on soil conditions, but are selected based on access or availability. In addition, the soil and rock materials have properties critical to the design of the structure (e.g., their drainage, settlement, and strength, characteristics) but these properties can vary significantly within just a few meters in any direction. The art of geotechnical engineering involves designing a successful foundation for a structure using a subsurface model based on the geologic history of the site and on limited testing of the subsurface materials. (It is not uncommon to design a structure based on soil and rock samples that represent only 1/1,000,000 of the soil and rock materials that will be affected by the structure.) When the foundations are done well, the structure above can last as long as the aqueducts of Rome. When done poorly, they may collapse (e.g., the Rte. 33 bridge) and leave nothing for the historians except for the occasional tourist attraction (e.g., the Tower of Pisa).
My scholarship activities have primarily focused on improving the reliability of geotechnical designs given limited subsurface information. In the following sections, I give a brief summary of my research areas and a listing of my research funding.
Earth Resistivity as a Geotechnical Site Investigation Tool
Much of my scholarship since 1997 has concentrated on the use of multi-electrode earth resistivity testing as a method to improve subsurface investigations for geotechnical design. In particular, most of my work has involved the use of resistivity to investigate sites that have a potential for the formation of sinkholes. (Areas where sinkholes form are known as karst areas.) On these sites, small subsurface features such as voids or soil-filled fractures may cause sinkholes in the future. Unfortunately, these features are nearly impossible to locate using traditional site investigation methods. Geophysical methods can provide significantly more information, but the experience base for interpretation of these results is limited. A test site I have developed at Metzgar Fields is nearly ideal for this research; the site is close by, it has active sinkholes, and the work done to date has documented a range of subsurface features (open and closed fractures in the bedrock as well as a small cave) that are known to cause sinkholes. Students and I have conducted hundreds of two-dimensional resistivity lines at this site and tried our hand at three-dimensional tests as well.
In addition to my work at the Metzgar site, I have conducted resistivity tests at a number of sites in Pennsylvania and I spent a sabbatical in 2000-2001 in Norway where I worked with the Norwegian Geotechnical Institute using resistivity testing for site investigations related to landslides, hazardous waste plumes, and permafrost among other projects.
Use of Bacteria to Stabilize Loose Sands
In spring 2004, Professor Caslake of the biology department and I started a research program to conduct proof-of-concept testing on the use of bacteria to stabilize loose saturated sands (see grant listed below). Buildings and other structures constructed on loose sands are at high risk of failure during earthquakes because these soil materials rapidly lose strength under seismic loads. We have hypothesized that it may be possible to stabilize these soils using bacteria that will attach to the sand particles. The amount of strength gained from the bacteria may be sufficient to significantly improve the reliability of structures built on these soils. While this research does not deal with limited subsurface information (my typical area of research), it has the potential to improve the reliability of structures built in earthquake-prone areas.
Reliability Analysis of Geotechnical Structures
My M.S. and Ph.D. work used a more theoretical approach and computer modeling to improve the reliability of foundation and retaining wall designs. I have been less active in this area since the mid-1990’s given the challenges of involving undergraduates in the work. However, I continue to serve as a reviewer for papers and research proposals related to this topic.
“MRI: Acquisition of State-of-the-Art Soil Structure Interaction Facility,” National Science Foundation, Major Research Instrumentation Grant No. CMMI-0820640, $222,487, 9/1/08 – 8/31/12.
“Exploratory Research in Microbial Remediation of Liquefiable Soils,” National Science Foundation Small Grant for Exploratory Research Grant No. CMS-0408832, $56,123, 2/1/04-5/31/06.
“MRI/RUI Proposal for Instrumentation of Environmental Research Laboratories,” National Science Foundation, Major Research Instrumentation Grant No. CMS-0215809, $366,364, 8/1/02-7/31/03.
“Collaborative Research: Evaluation of 2D vs 3D Multielectrode Resistivity for the Characterization of Shallow Karst,” National Science Foundation Research Grant No. CMS-0201015, $76,749, 6/1/02 – 5/31/05.
“Evaluation of Potential of Earth Resistivity in Norway,” Fulbright Scholar Program Research Grant, NOK 146,000, 9/1/00-3/1/01.
“Evaluation of Potential of Earth Resistivity in Norway,” National Science Foundation Research Grant No. INT 0071702, $14,000, 8/1/00 – 7/1/01.
“Evaluation of Reliability of Earth Resistivity Method in Thinly Mantled Karst,” National Science Foundation Research Grant No. CMS-9734899, $76,375, 6/1/98 – 5/31/00.
“Risk Assessment of Foundations in Karst Terrain,” National Science Foundation Research Grant No. CMS-9612675, $18,000, 9/1/96 – 2/28/98.