For the past 35 years, Dr. Nadim Fuleihan has built his expertise in geotechnical engineering and soft ground construction as part of the renowned team at Tetra Tech subsidiary Ardaman and Associates, Inc., where he serves as president.

Educated in the French baccalaureate system in Lebanon, Dr. Fuleihan went on to earn his Bachelor’s degree in Engineering, with distinction, from the American University of Beirut. He received his Master of Science degree in Civil Engineering and Doctor of Science degree in geotechnical engineering at MIT, where he was involved with innovative soil stabilization and soft ground construction research.

Dr. Fuleihan continues to work on breakthrough solutions in the areas of geo-environmental, water resources, foundation systems, earthen dams, mining, solid and industrial waste, facilities engineering, and construction materials testing.

What are some of the current important issues with geotechnical engineering?

In order to be a successful geotechnical engineer, you have to be able to bridge the fields of science and art, to assess the geology and soil-structure as well as soil-water interaction, and rely on gut feeling moderated with local experience and expertise.The soil profile, geology and groundwater vary significantly from one area to the next, so standardization is not a formula for success as it is in other fields of engineering. You need to investigate, understand and become familiar with the soil properties within each locality and at each specific site. The profession has evolved and matured since the 1920s when it was largely art, without any formal technology or basic theory. It has become very sophisticated, more science than art, but individual judgment still plays a crucial role.

Tetra Tech has recently completed some very interesting and challenging work with the USACE on design of flood protection levees, flood walls and pump foundations in the U.S. Gulf Coast, using our in-house soft ground construction expertise.

What challenges does soft ground construction create?

Soft ground is basically unstable ground. It could consist of loose sand that would liquefy when subjected to earthquake vibrations, or very plastic wet clay that deforms easily even when subjected to very small loads. In geotechnical engineering, soft-ground typically refers to foundation conditions consisting of soft organic clays characterized by elevated in-situ water contents.

Soft ground is highly compressible, and is characterized by very low shear strengths and poor drainage characteristics—so, very low hydraulic conductivity. It creates very challenging construction problems, such as excessive time-dependent foundation settlements, as well as bearing capacity and slope stability-type foundation failures.

A soft clay behaves like a relatively stiff, wet, non-porous, non-linear sponge. It compresses rather easily under load, but it takes time to deform, as the compression is largely dependent on the rate at which water can be expelled from the non-porous structure of such a sponge. As the non-linear sponge compresses, it becomes stiffer and less deformable, and it gains strength. This concept of strength gain was developed at MIT by Professor Charles C. Ladd, a worldwide recognized expert in soft ground construction. My own doctorate research at the institute dealt with construction of levees on soft ground.

What industries are affected by soft ground conditions?

Any structure constructed on soft ground—whether it be a house, bridge abutment, runway, solid waste disposal facility, industrial plant, or flood protection levee—is affected by the soft conditions, which have to be mitigated. In other words, all industrial facilities located on soft ground present challenges that the geotechnical engineer needs to overcome. The cost of the design or mitigative or remedial measures needed to address the challenge is largely dependent on the expertise of the engineer to solve the specific problem.

For clients facing soft ground issues, what are the benefits of getting Tetra Tech involved early in the process?

Tetra Tech can provide clients with the most cost-effective design resulting in significant savings in construction costs. We use our in-house field, lab, and engineering capabilities to thoroughly investigate foundation conditions, relying on the predicted strength gain of the clay over time, combining the breadth of various possible solutions with local expertise and specialized soft ground experience.

Can you describe a particularly interesting or challenging situation you faced on a project?

The owners of a major phosphoric acid fertilizer plant on the west bank of the Mississippi River in Louisiana wanted to optimize the storage capacity of their waste phosphogypsum stack (a by-product generated during the process of reacting phosphate rock with sulfuric acid). This project relied on our expertise in a niche area, phosphogypsum disposal, and also our expertise in soft ground construction.

The client retained three geotechnical engineering firms to independently perform this assessment. The storage life that we projected using predicted strength gains was 4 to 5 years greater than recommended by the other two local consultants, resulting in a $2 million savings for the client, who has retained us ever since. We regularly monitored lateral movements and pore water pressures as the stack was being raised. It has since achieved its maximum design height without any problem.

What sets Tetra Tech apart from other engineering firms when it comes to soft ground construction?

Our soft ground expertise relies on our expert staff. Many of our key personnel graduated from MIT and trained with Dr. Ladd. Tetra Tech is also a leader in soft ground field exploration and sampling, in-situ and laboratory testing, and instrumentation monitoring, so we are a one-stop shop when it comes to soft ground construction.