1. Senior Research Fellow, Institute for Underground Infrastructure, Exterbruch 1, D-45886 Gelsenkirchen, Germany.
2. Senior Research Fellow, Institute for Underground Infrastructure, Exterbruch 1, D-45886 Gelsenkirchen, Germany (corresponding author).
3. Professor, Univ. of Applied Science Munster, Corrensstraße 25, 48149 Münster, Germany.
4. Professor and Scientific Director, Institute for Underground Infrastructure, Exterbruch 1, D-45886 Gelsenkirchen, Germany.