Surface structure and mechanical properties of the lunar maria

Strain gage and television data from Surveyor 1, as well as earlier measurements from earth and spacecraft, are consistent with the following characteristics for undisturbed mare surface: a structure composed of individual particles, for the most part 100 micron or less in diameter, and with a small percentage at millimeter-to-meter sizes. The density of the top few centimeters is about 0.7 g/cm³, corresponding to about 25% solid. Static bearing capacity is about 4 × 105 dynes/cm² on a 25-cm bearing diameter with no sinkage, increasing at the rate of about 2 × 104 dynes/cm³ with sinkage. Cohesion is between 10² and 105 dynes/cm², most probably about 10³ dynes/cm². Coefficient of internal friction is most probably about 1.5 but may be somewhat lower. The failure mode under bearing load is primarily local shear.