Masters Degrees (Civil Engineering)

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Browsing Masters Degrees (Civil Engineering) by Subject "Aggregates (Building materials)"

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    Geotechnical investigation for the emplacement of radio telemetry dishes at the Matjiesfontein Space Geodesy observatory
    (Stellenbosch : Stellenbosch University, 2020-03) Coetzee, Jaco; Croukamp, Leon; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: A secondary site area at the Matjiesfontein Space Geodesy Observatory (MSGO) has provisionally been selected for the emplacement of large radio telemetry dishes. While several investigations have been performed for the geotechnical characterization of the main MSGO site area, similar data that pertains to the newly selected site area is mostly unavailable. Since telemetry dishes are sensitive structures that require very stable founding conditions, a geotechnical investigation was performed to determine the suitability of the new site area for emplacement. Furthermore, the procurement and transportation of materials from external sources is typically among the highest expenditures of construction projects. In addition, unutilized materials leave a larger footprint on the environment. Therefore, tests were performed to determine the suitability of local material for use as coarse aggregate in concrete. Two variations of the predominant underlying rock type, namely slightly and highly weathered Dwyka tillite, were collected for coarse aggregate tests. Sample characteristics were tested as follows: particle size distribution and dust content through grading analyses; particle shape through Flakiness Index (FI) tests; crushing resistance and water absorption through a full set of dry and soaked Aggregate Crushing Value (ACV) and 10 % Fines Aggregate Crushing Value (10%FACT) tests; and durability through a modified slake durability test. All requirements were met comfortably by slightly weathered tillite. On the other hand, the dust content, soaked crushing resistance, water absorption and slake durability of highly weathered tillite indicated that it may adversely affect the workability and water requirement of fresh concrete as well as the durability of hardened concrete. While slightly weathered tillite is deemed suitable for use as coarse aggregate in concrete, the use of highly weathered tillite is not recommended. Furthermore, a basic feasibility study indicated that the local production of aggregate can reduce construction costs significantly. Rock mass characterization was performed through geophysical electro-resistivity tests, drilling and core logging, the Rock Quality Designation (RQD) and Rock Mass Rating (RMR) systems and Unconfined Compressive Strength (UCS) tests. Electro-resistivity imaging along the length of the site area indicated that competent rock can be found within a few metres below the surface. Furthermore, no distinct problem areas were identified. Recovered core consisted predominantly of unweathered and slightly weathered tillite, while medium weathered tillite was encountered in subordinate amounts. The overall rock quality was classified as “good to fair rock” according to the RQD and RMR systems. Based on the results of numerous UCS tests, unweathered and slightly weathered tillite were classified as “hard to very hard rock” according to standard core logging guidelines, while medium weathered tillite was classified as “medium hard rock”. Finally, a preliminary foundation design was performed to determine the minimum foundation diameter and indicate potential governing factors. The design indicated that the minimum foundation diameter would ultimately be governed by the size of the superstructure and the space required inside the pedestal for the housing and operation of telemetry equipment, since safety against the verified failure modes was satisfied at relatively small diameters. Therefore, local founding conditions are indeed suitable for the emplacement of large telemetry dishes.