DMT-Based Estimation of Mechanical Properties for Subsurface Lunar Soil Simulant

Abstract

In the third phase of the Chang’E project, a drilling and coring device mounted on a lunar probe will be sent to the moon to acquire samples of lunar soil within a certain depth (subsurface lunar soil). Interaction between the sampling drill and lunar soil simulant must be investigated to evaluate the drilling load and coring rate on the Earth in advance. It is necessary to measure the mechanical properties that are distributed in a vertical direction in the preparation of the lunar soil simulant. Until now, only a few preliminary attempts based on a simple penetrometer for measurement estimation are reported in the literature. The flat dilatometer test (DMT) is an in situ civil empirical method for soil type identification and settlement prediction that analyzes the test results by depth. Because the empirical formulas used in the standard DMT method aimed to cover various soil types, the accuracy of mechanical properties estimation for a specific soil type was limited, especially for well-distributed artificial soil, such as lunar soil simulant. This paper proposes a modified DMT method considering relations of compressibility, shear strength, and bulk density as additional information for the DMT results analysis. Based on the relationship between the DMT constrained modulus (MDMT) and depth, the distributions of bulk density and shear strength could be derived accurately for the subsurface lunar soil simulant. The test results were consistent with both theoretical analysis and Apollo estimation in bulk density. The contribution of this paper is to provide a feasible approach to obtain the vertical distribution of the mechanical properties for the subsurface lunar soil simulant.