1. Division Director, Norwegian Geotechnical Inst., P.O. Box 3930 Ullevaal Stadion, N-0806 Oslo, Norway (corresponding author).
2. Expert Advisor, Norwegian Geotechnical Inst., P.O. Box 3930 Ullevaal Stadion, N-0806 Oslo, Norway.
3. Technical Director, Norwegian Geotechnical Inst., P.O. Box 3930 Ullevaal Stadion, N-0806 Oslo, Norway.