Geotechnical properties and foundation requirements for the Satellite and Lunar Laser Ranger at the Matjiesfontein Space Geodesy Observatory
Thesis (MEng)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The basic idea of Satellite and Lunar Laser Ranging (S/LLR) is to improve our understanding of gravity. The earth-moon system is a good workspace to test the theories of gravity. By measuring the distance between the earth and the moon, the precise orbital shape of the path can be determined with millimetre precision. This enables scientists to test general relativity (GR), which is the predicted deviation from the Newtonian gravity and is supposed to exactly predict the correct orbital path of the moon. With the measurements obtained from S/LLR experiments, scientists can compare the values to those predicted by GR and this will help them to understand and prove the GR theorem. The intention of this thesis is to identify, analyse and evaluate the required aspects for the emplacement of an S/LLR at the Matjiesfontein Space Geodesy Observatory (MSGO). The 7 ton S/LLR needs a very stable foundation to ensure accurate measurements as well as pointing to the exact location on the satellite/lunar surface. The aspects evaluated is the bearing capacity of the rock mass, settlement of the foundation, slope stability, excavatability of materials, the wind loads on the shed as well as the management of risks. The following data is needed to complete the evaluation: Field survey and tests: o Geometric data capturing; o Joint survey; o DCP tests (Dynamic Cone Penetrometer); and o Core Drilling. Laboratory tests: o UCS tests (Unconfined Compression Strength); o Point load tests; and o Petrographic analyses. It was calculated that the applied bearing pressure is much smaller than the bearing capacity of the rock and thus a safe assumption can be made that the rock mass is more than sufficient to withstand the load of the structure. From the result of the settlement calculation it is clear that settlement would not be a factor influencing the operation of the S/LLR. It is recommended that the level of the foundation should be calibrated after the hardening of the concrete and before the instrument is placed. Slope stability analyses were done for potential circular failure, wedge failure, planar failure and toppling. All of the slope stability analyses have shown that the areas are safe against slope instability and no extra precautions need to be taken to keep the area safe. It is however important to do new analyses if any cuts or excavations are made to build a road or building. Bedrock can be found within 500 mm to 600 mm below ground level. The assessment of the excavatability of materials yielded that the method of ripping should be used to excavate the material on site. This indicates that the topsoil can be removed without the need for blasting to reach deep intact rock. Thin sections were prepared from the core samples and petrographic analyses were done to determine the origin, composition, distribution and structure of the rocks. It is important to establish which clay minerals are present to determine if the rock mass could be expansive and have a resultant destabilising effect on the foundation. The petrographic studies have shown that clay minerals such as kaolinite and chlorite are present in the samples. It can thus be concluded that, as these are nonexpansive minerals, it can be assumed to be a non-expansive rock mass. The conclusion that can be drawn from this study is that the design of the foundations of the S/LLR at MSGO will be the same as at HartRAO. This conclusion can be made as none of the factors that were evaluated have shown a potential destabilising effect on the S/LLR.
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