Study On Simulating Lunar Soil Arching Test And Three-dimensional Discrete Element Simulation

At present, the human face the situation that the traditional energy sources such as coal, oil and natural gas are depleting. As a result, people turn their attention to rich resources such as the moon. In order to develop and use lunar resources, the United States, Russia and other countries rise a new round of "return to the moon" boom. China has also developed a lunar exploration project, "three-step" plan, the third step and at the course of building the future lunar base involving testing samples of lunar soil in-situ investigation. In order to ensure a smooth and complete in-situ sampling on the Moon, associated simulation must be done in advance on Earth. According to in-situ sampling experience on Earth, there will always be earth drilling device, you can not remove all the drilling depth of undisturbed soil, or even simply did not get a soil sample situation. Through the analysis of the mechanism of soil mechanics, it is probably impacted by Soil Arching in the process of drilling.This paper select Jingyu ash as original material to simulate lunar soil, which have the relatively similar chemical composition of mineral volcanic eruptions as lunar soil samples, and obtain volcanic ash samples .The volcanic ash samples are tested for basic physical and mechanical property. The results showed that: Raymond crushing, over 0.5mm sieve of ash samples and emery complexes, have the similar shape as lunar soil , the proportion of soil particles slightly smaller than the typical sample of the soil particles on moon, the average particle size and internal friction angle is close to lunar soil, could be simulated lunar soil.Then by simulating Soil Arching tests on Moon showed: it is very vulnerable to emerge soil arching phenomenon, during simulating lunar soil, And the ease of the formation of soil arching depend on sampling tube aperture, the relative density of simulated lunar soil. Overall: when in the same aperture, the bigger relative density, the more easily into the arch; in the same relative density, the smaller aperture, the more easily into the arch. When the density is relatively large, the arch height is about hole radius.Through the soil arching effect on the in-situ sampling from the Experimental Study, it can be explained from the mechanism that the possible reasons for in-situ sampling failure: effected by soil arching, the soil samples below soil arching were blocked outside the pipe, it is difficult to access to the test tube. At the same time, the soil samples already entered the tube become more loose because of soil arching effected by test tube is pressured,so that the friction between soil sample and test tube is not sufficient to remove the soil sample when extracting the test tube, resulting in the failure of drilling original soil samples.Finally, using three-dimensional discrete element software PFC3D analog-pressure tests showed, in the course of cylinder wall is depressed, there is a clear soil arching phenomenon in Soil.This study shows that it is easier to produce soil arching effect in the process of conducting in-situ sampling, especially on lunar soil sampling. In order to ensure the smooth completion of in situ sampling, it is necessary to strengthen the study on soil arching effect.