Physical Model Tests of the Bearing Behavior of Tongji-1 Lunar Soil Simulant

The new exploration programs of the Moon set up by various countries require a good understanding of the mechanical behavior of lunar soil, especially for the construction of facilities and the soft-landing process of lunar rovers. Plate load tests (PLTs) of lunar soil simulants are routinely used to gain accurate understanding of engineering properties of real lunar soil and to predict the load-settlement behavior of foundation systems on the Moon. In this paper, a test apparatus and testbed are carefully designed to account for the grain-size effect and boundary effect. A series of plate load tests of Tongji-1 lunar soil simulant (TJ-1 simulant) is conducted with a foot pad and four circular plates at different loading velocities using the strain-loading method (soft-landing process of a lunar rover). For comparison, tests using the stress-loading method are also carried out (traditional shallow foundation system). In addition, the experimental results are compared with those predicted by the Terzaghi and the modified Terzaghi methods. The results show that with the same loading method and loading velocity, the bearing capacity of TJ-1 simulant under a foot pad with top diameter Rt and bottom diameter Rb, can be estimated using the data under the plates with diameters Rt and Rb, whereas the deformation modulus is close to the data under the plate with diameter Rb; the values of ultimate bearing capacity and bearing capacity factor using the stress-loading method lie in the range of those using the strain-loading method at different velocities, whereas the values of the deformation modulus using the stress-loading method are larger than those using the strain-loading method; and the Terzaghi method overpredicts the bearing behavior of TJ-1 simulant, whereas the modified Terzaghi method underpredicts it. Hence, more experimental and engineering tests are required to find a better modified method.