1. a Department of Civil and Natural Resources Engineering , University of Canterbury , Christchurch, New Zealand, Private Bag 4800, Christchurch , 8140 , New Zealand E-mail:
2. b Department of Civil and Natural Resources Engineering , University of Canterbury , Christchurch, New Zealand, Private Bag 4800, Christchurch , 8140 , New Zealand
3. c Department of Civil and Natural Resources Engineering , University of Canterbury , Christchurch, New Zealand, Private Bag 4800, Christchurch , 8140 , New Zealand E-mail: