Compilation of published experimental data, a) k versus ϕ, b) F versus ϕ and c) k versus F, in unconsolidated monodisperse glass beads (Glover and Walker, 2009; Glover and Déry, 2010; black dots), well-sorted, rounded sands (Biella and Tabacco, 1981; Biella et al., 1983; blue dots), sintered glass beads (Wong et al., 1984; Guyon et al., 1987; Li et al., 1995; Blair et al., 1996; purple, red and orange squares corresponding to different grain sizes as indicated in the inset) and Fontainebleau sandstone (Doyen, 1988; Fredrich et al., 1993; Zamora, unpublished data; black diamonds; Revil et al., 2014; grey diamonds). The colored lines are inserted to highlight power-law trends in the various materials (note that the three families of sintered glass obey fairly similar power laws). The values of the exponents are given when necessary.