[en] Terra Tek Research has conducted a testing program on a variety of backfill mixtures to evaluate their thermal and hydraulic properties under conditions expected to be representative of a nuclear waste repository in a deep salt formation. Backfill mixtures were produced by combining bentonite clay with a number of different solid materials, primarily silica sand and crushed salt, in a variety of proportions. Generally, samples were compacted to specified densities, after which appropriate properties were determined. Thermal conductivity and hydraulic conductivity as functions of composition, density and temperature were the principal material properties determined in this program. Additional measurements were performed to determine gas permeability of several mixtures, time-dependent axial deformation of bentonite, water loss from bentonite at elevated temperatures, viscosity of synthetic heavy brines used, and grain size distribution of sands used in the program. Program tests are shown in tabular form which include backfill mixture compositions, test conditions and descriptions of data collected during each test. Measured sand size grain distributions are presented in Appendix A. A discussion of gas (nitrogen) permeability theory and data collected is in Appendix B. A detailed technical discussion of the transient technique of thermal conductivity measurement is given in Appendix C. Brine viscosity data are presented in Appendix D