1. Professor, Dept. Civil Engineering, Federal Univ. of Rio Grande do Norte, Campus Universitário, Natal-RN, Brazil 59072-970 (corresponding author).
2. Fluor Centennial Associate Professor, Dept. Civil Engineering, The Univ. of Texas at Austin, 1 University Station, C1792, Austin, TX 78712-0280.
3. Professor, Dept. of Geotechnical Engineering, Univ. of São Paulo at São Carlos, Av. Trabalhador São-Carlense, 400, São Carlos-SP, Brazil 13566-590.
4. Professor, Federal Institute of Education, Science and Technology of Rio Grande do Norte, Av. Salgado Filho, 1559, Natal–RN, Brazil 59015-000.