We explore the relationship between mechanical, transport, and critical state characteristics of coal-biomass mixtures by evaluating mixture composition, stress, strength, rhelogy, and permeability of coal-biomass mixtures. We report measurements of strength and permeability evolution for uniformly graded (passing no. 200 mesh) granular mixtures of coal-biomass in the proportions (a) 10096 sub-bituminous coal, (b) 75-25% sub-bituminous coal-biomass, and (c) 100% biomass. We observe response at confining stresses in the range 5 and 25 MPa and at strain rates of similar to 10(-4)/s. The pure biomass is the most compliant and weakest of the three mixtures, and the coal is the stiffest and strongest. The samples stiffen with compaction as confining stress increases. Results show strain hardening for all sample mixtures resulting from grain breakage. Work hardening behavior is characterized using a CAP model. In all samples, permeability reduces with an increase in axial strain and yields permeabilities in the range 10(-14)-10(-16) m(2) (10-0.1 mD). We define the evolution of permeability as a function of changes in both porosity and grain breakage and link this to a model representing the harmonic mean of the particle diameters, as they evolve. This characterization works well and the harmonic mean of the particle size distribution is the best predictor of permeability evolution. These measurements are important in characterizing feed characteristics of dry-fed coal-biomass mixtures to prevent gas-flow back and to maintain feed rates into pressurized gasifiers.