Geotechnical properties and foundation requirements for the Satellite and Lunar Laser Ranger at the Matjiesfontein Space Geodesy Observatory

[摘要] 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 distancebetween the earth and the moon, the precise orbital shape of the path can be determined withmillimetre precision. This enables scientists to test general relativity (GR), which is the predicteddeviation from the Newtonian gravity and is supposed to exactly predict the correct orbital path of themoon. With the measurements obtained from S/LLR experiments, scientists can compare the values tothose 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 emplacementof an S/LLR at the Matjiesfontein Space Geodesy Observatory (MSGO). The 7 ton S/LLR needs a verystable foundation to ensure accurate measurements as well as pointing to the exact location on thesatellite/lunar surface. The aspects evaluated is the bearing capacity of the rock mass, settlement of thefoundation, slope stability, excavatability of materials, the wind loads on the shed as well as themanagement 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); ando Core Drilling. Laboratory tests:o UCS tests (Unconfined Compression Strength);o Point load tests; ando Petrographic analyses.It was calculated that the applied bearing pressure is much smaller than the bearing capacity of the rockand thus a safe assumption can be made that the rock mass is more than sufficient to withstand the loadof the structure.From the result of the settlement calculation it is clear that settlement would not be a factor influencingthe operation of the S/LLR. It is recommended that the level of the foundation should be calibrated afterthe hardening of the concrete and before the instrument is placed.Slope stability analyses were done for potential circular failure, wedge failure, planar failure andtoppling. 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 newanalyses 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 theexcavatability of materials yielded that the method of ripping should be used to excavate the materialon site. This indicates that the topsoil can be removed without the need for blasting to reach deep intactrock.Thin sections were prepared from the core samples and petrographic analyses were done to determinethe origin, composition, distribution and structure of the rocks. It is important to establish which clayminerals are present to determine if the rock mass could be expansive and have a resultantdestabilising effect on the foundation. The petrographic studies have shown that clay minerals such askaolinite and chlorite are present in the samples. It can thus be concluded that, as these are nonexpansiveminerals, 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 atMSGO will be the same as at HartRAO. This conclusion can be made as none of the factors that wereevaluated have shown a potential destabilising effect on the S/LLR.

[发布机构] Stellenbosch University