Shear Strength of Soils on Slopes

Surface mobility is one of the most critical problems in design of a lunar roving vehicle, and tests of vehicle models in frictional soils were initiated early in our program. Tests on grades produced anomalous results, and it was found that conventional assumptions for predicting grade performance from results of testing at zero grade were as much as 20% in error. No simple trigonometric predictive relationship between grade angle and the angle of internal friction of the soil could be applied with certainty.

Tests were run on a simplified interface consisting of a weighted grouser plate operating on frictional soil, and the results are presented in detail in the paper. Since it was determined that shear behavior does not follow common simple theory even at zero grade, this test series is now considered a single step in a comprehensive research study that will include tests of grouser plates and models in a variety of frictional soils. The goal of this program is development of a general expression for predicting grade capability from performance data obtained on level soil.