Discrete Element Modeling of Cone Penetration in JSC-1A Lunar Regolith Simulant

NASA plans to return back to the Moon for a long term presence and use of the Moon as a launch station for further space exploration to other planets. This scenario increases the importance of determining the geotechnical properties of the lunar surface. However, due to the limited availability of lunar regolith and its high scientific value, a simulant material which closely matches the composition and grain size distribution and other characteristics of the lunar regolith has become an indispensable need to benefit in hardware development as well as estimating lunar regolith properties. Therefore, JSC-1A lunar regolith simulant, which was produced by Orbitec Company under the guidance of NASA, was provided for researchers to investigate soil parameters. Previous studies about JSC-1A utilized from conventional laboratory experiments. This thesis aims to examine the behavior of JSC-1A and auxiliary Ottawa sand against cone penetration testing (CPT). CPT is a fast and reliable method to characterize soil properties. Experimental work is augmented with numerical simulation to take advantage of powerful capabilities of discrete element method (DEM). Experimental work is mainly composed of two sets of tests. Firstly, CPT is conducted on JSC-1A in the field using a CPT truck and soil classification and internal friction angle analyses were estimated based on the test results. However, the limited data and high boundary effects on the container made a strong case to provide reliable reference for DEM simulations. Therefore, miniature CPT experiments were conducted for JSC-1A and Ottawa sand with distinctive densities using two size cylindrical containers. Ottawa sand which is a uniform silica sand is also included in the analysis to obtain supplementary data. Finally, DEM in 3D was used to model the response of two soils to cone penetration. Microscale changes such as contact force, displacement, velocity and stress variation of individual soil particles were monitored throughout the simulation process. In conclusion, CPT results show that each soil exhibits a characteristic response to cone penetration under different conditions. Its response is affected by various parameters such as soil density, boundary conditions, homogeneity, grain size and shape. It was found that boundary condition influence the results significantly. DEM results have a good agreement with laboratory experiments except the fluctuations in simulation data. The penetration of the cone produces a considerable variation in velocity and displacement field. Contact forces and deformation pattern of the granular material are mainly governed by the relative position of particles

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