Issue contains 4 papers, presented at Symposium on ″Excavation Techniques ″held on Nov. 28-29, 1973 at Luxemburg. Listing of titles and authors follows: EXAMEN DES DIFFERENTS PROCEDES CLASSIQUES DE DETERMINATION DE LA NOCIVITE DES ROCHES VIS-A-VIS DE L'ABATTAGE MECANIQUE. left bracket Investigation of Conventional Methods for Determining Resistance of Rocks to Mechanical Excavation right bracket . By A. Valantin. L'EMPLOI DE MACHINES A PERCUSSION POUR LES CREUSEMENTS ET LES BOSSEYEMENTS. left bracket Application of Percussive Machines for Tunneling and Ripping right bracket . By W. J. W. Bourne, and K. Moore. L'IMPORTANCE DE L'ORGANISATION ET DE LA SPECIFICATION POUR UN CREUSEMENT DE GALERIE EFFICACE ET RAPIDE. left bracket Importance of Planning and Organization for Efficient and Rapid Tunneling right bracket . By W. R. Cheetham. PROBLEMES SPECIAUX DE CREUSEMENT. PROBLEMES D'ENVIRONNEMENT. left bracket Special Environmental Problems of Rock Excavation right bracket . By G. Dracon.