Shear strength and stiffness characterization of lunar simulant GRC-3

Physical modeling experiments related to lunar in situ resource utilization activities use suitable soil simulants such as GRC-3. Only the index properties (e.g., specific gravity, particle size distribution, and maximum and minimum densities) compression indices, and shear strength parameters (peak angle of internal friction) of GRC-3 are currently available in the literature. In addition to the shear strength parameters, this work determined other important mechanical parameters such as critical state angle of internal friction, dilatancy angle, elastic modulus, and Poisson’s ratio using triaxial compression tests conducted at three different confining stresses of 25, 50, and 100 kPa. An additional set of triaxial specimens incorporated bender elements, which were used to determine small-strain shear wave velocity and shear modulus of GRC-3 at confining stresses ranging between 12.5 and 150 kPa. The confining stresses used in this work were lower than those used in other works on GRC-3 found in the literature. For extrapolating the behavior of terrestrial simulants to in situ surface lunar regolith, results obtained at smaller confining stresses are generally more relevant. The shear strength parameters of GRC-3 determined as part of this investigation compared well with those for GRC-3 and lunar regolith found in the literature, as well as lunar simulants GRC-1 and JSC-1A. Simple empirical correlations relating mechanical properties (angle of internal friction, dilatancy angle, elastic modulus, small-strain shear wave velocity, and maximum shear modulus) of GRC-3 as a function of its relative density or void ratio and confining stress are provided, so these properties can be readily estimated to support further analytical studies involving GRC-3.