Influence of loading conditions on mechanical behaviors of lunar regolith simulant WHU-1 based on Chang’e-5 returned samples

Abstract

As lunar exploration and development missions advance, understanding the geomechanical properties of lunar regolith becomes essential for supporting future lunar engineering and in situ resource utilization. This study investigates the effects of loading conditions on the mechanical behavior of the lunar regolith simulant WHU-1, which was prepared based on particle size distribution data from samples returned by the Chang’e-5 mission. Key factors influencing the mechanical response of WHU-1, including confining medium, lateral constraint conditions, and ambient pressure, are analyzed through back pressure-controlled triaxial compression and direct shear tests. The results indicate that water pressure loading during triaxial tests leads to underestimated cohesion and overestimated internal friction angles compared to air pressure loading conditions. Decreasing ambient pressure alters the relationship between shear strength and radial stress from linear to quadratic. Radial stress and ambient pressure significantly affect the interactions among irregular particles, leading to the formation of various shear bands that influence post-peak failure behaviors. Direct shear tests exhibit a distinct nonlinear strength response with increasing load, whereas triaxial tests yield more consistent values for cohesion and internal friction angles under higher stress, attributed to differences in lateral confinement. Our study, combined with existing experimental results, suggests that the lunar soil returned by Chang’e-5 may exhibit higher shear strength compared to Apollo samples, likely due to its finer particle size distribution and more favorable grading characteristics.