A brief state-of-the-art review is given on backfill materials and laboratory tests. A new system developed for testing backfill material in the laboratory is described. In this system, most of the limitations of previously applied techniques have been eliminated. In performing unconfined-deformability tests (UDT) and confined-deform ability tests (CDT), large cylindrical specimens having a diameter of 600 mm are used. The specimens were prepared from riverbed sand and gravel mixed with cement. A total of 135 UDT and 127 CDT specimens were tested in order to investigate the strength and deformability characteristics of 40 different combinations of backfill mixture. Calculation methods are evaluated in terms of stress-strain plots and are illustrated with examples. Typical results are presented. Two sets of deformation data can be obtained during testing: one from between the top and bottom plates, and the other from between the rings peripherally fixed onto the specimen. It is shown in this study that ring-to-ring readings provide more reliable modulus results.