1. Research Engineer, Mexican Institute of Water Technology, Paseo Cuauhnahuac 8532, Jiutepec, Mor. 62550, Mexico.
2. Head of Geotechnical Dept., Mexican National Water Commission, Insurgentes Sur 2416, Coyoacan, 04340, Mexico D.F.
3. Dean of Engineering and Computer Science, California State Univ., Sacramento 6000 J St., Riverside Hall, Suite 2014, Sacramento, CA 95819-6023 (corresponding author).