R. Katzenbach and S. Leppla. (2014) Challenging Construction Projects Related to Urban Tunnels. <i>The Geotechnical Engineering Journal of the SEAGS & AGSSEA</i>, <i>45</i>(3), pp 71-77.R. Katzenbach and S. Leppla. "Challenging Construction Projects Related to Urban Tunnels". The Geotechnical Engineering Journal of the SEAGS & AGSSEA 45 (2014):pp 71-77.R. Katzenbach and S. Leppla. Challenging Construction Projects Related to Urban Tunnels. Southeast Asian Geotechnical Society:ม.ป.ท. 2014.