Altunbas, A., Gezgin, A.T., Soltanbeigi, B., Cinicioglu, O., “Influences of backfill properties and stress state on ultimate earth pressure coefficients”, XV Danube-European Conference on Geotechnical Engineering, 2014, Viyana, Avusturya, Geotechnics of Roads and Railways, 2, 997-1002, 2014.