1. Ningbo East China Nuclear Industry Engineering Investigation Institute, Province Nuclear Geology 268 Brigade, Ningbo, Zhejiang Province, P. R. China
2. School of Civil Engineering, Sun Yat-Sen University, Guangzhou, Guangdong Province, P. R. China
3. School of Engineering, University of Guam, Mangilao, GU 96923, USA
4. Department of Civil Engineering, University of Texas at Arlington, Arlington, TX 76019, USA