NEWS 2009

Posted October 14, 2009 (Updated October 20, 2009)

Event: October 27, 2009

CGS/GSE: Cross Canada Lecture Tour, Prof. Kyle Rollins - Drilled Shaft Side Friction in Gravelly Soils

Location: NREF 1-001, U of A Campus

Time: 5:00pm

The CCLT is organized by the Canadian Geotechnical Society, with funding through the Canadian Foundation for Geotechnique.

Sponsorship provided by:

• AMEC Earth "&" Environmental
• BGC Engineering
• Golder Associates
• Reinforced Earth Company

To evaluate side friction, 28 axial tension (uplift) load tests were performed on drilled shafts in soil profiles ranging from uniform medium sand through well graded sandy gravel. Typical load-displacement (t-z) curves for skin friction in gravelly soils were developed. Measured load capacities were compared with capacities computed using equations proposed by Reese and O'Niell, Meyerhof, and Kulhawy. Reasonable agreement between measured and computed capacities was generally found for sandy profiles. However, measured capacities were typically two to four times higher than predicted at sites where the gravel fraction was over 50 percent. The increased capacity appears to result from increased lateral pressure due to dilation during shearing. Additional load test data for gravelly soils were collected and combined with the data from Utah load tests. Similar response was observed for denser gravel, but looser gravel layers were found to have about the same capacity as that of sands. Based on this data set, modifications to design equations were developed to predict ulitmate side friction capacity better while still maintaining a margin of safety.

Dr. Kyle M. Rollins is a professor of Civil and Environmental Engineering at Brigham Young University in Provo, Utah. He received his BS degree from BYU and his Ph.D. from the University of California at Berkeley working under Harry Seed. After working with his father as a geotechnical consultant, he joined the faculty at BYU in 1987 and was promoted to full-professor in 1998. His research has involved geotechnical earthquake engineering, deep foundation behavior, collapsible soils and soil improvement techniques. He has published over 120 technical papers and supervised over 80 graduate students. The full biography of Dr. Rollins can be found on this page.