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News Archive 2001 - 2010

Soil Enhancement Studies to Improve Structure of Local Dams

October 14, 2010

Joe Pool Lake, which straddles the Dallas and Tarrant county line, was constructed in the late 1980s, but earlier this year extensive repairs were required along more than a quarter mile of its dam’s north slope because of soil slippage. Similar problems have been encountered at Grapevine Lake. However, investigations being conducted by civil engineering researchers at The University of Texas at Arlington are leading to ways to reduce or eliminate these soil problems, which can cost millions of dollars annually to fix.

Professor Anand Puppala is leading a team of post-doctorate researchers and graduate students in exploring several field stabilization methods in test areas at the upper embankment soils of dams at Joe Pool Lake and Grapevine Lake, which are owned, maintained and operated by the U.S. Army Corps of Engineers’ Fort Worth District. Jose Hernandez, P.E., with the Corps of Engineers’ Geotechnical Section, is the director of the stabilization project.

“These surface failures in earth dams are predominantly rainfall-induced,” said Dr. Puppala. “Extended dry periods cause deep cracks in the soil, allowing rainwater to penetrate several feet into the structure and increase the saturation of soil mass in the upper layers. As a result, a drastic decrease of shear strength occurs, allowing the top three-to-five feet of soil to slide away in what is called a ‘skin slide.’ We’re investigating ways to keep the top layer of soil from cracking, thereby mitigating water intrusion and eventual slope failure.”

In this five-year, $493,000 project, Dr. Puppala and his team are conducting long-term evaluations of four forms of stabilizing additives to native soil: compost, lime, and different proportions of lime and polypropylene fibers. Only the top 18 inches of soil need to be treated. Five test sections, including four treated and one control without any surface treatment, were constructed at each dam site. The test sections were instrumented with moisture and temperature probes and inclinometers; measurements are being taken at regular intervals to record the continuous performance of each section.

“Our goal is to develop a better model for slope stability,” said Dr. Puppala. “Moreover, what we learn here about soil treatments can be applied to any earthen dam, and the Corps of Engineers’ Fort Worth District maintains more than 20 just in Texas alone. There must be hundreds across the U.S.” Dr. Puppala's research team includes post-doctoral fellow Bhaskar Chittoori and graduate students Varagorn Puljan and Le Minh.

Dr. Puppala’s understanding of soil stability issues is well known in civil engineering circles. In September, he deliver an invited talk to dam safety experts gathered for a national meeting in Seattle.