Geotechnical investigation for the emplacement of radio telemetry dishes at the Matjiesfontein Space Geodesy observatory

Coetzee, Jaco (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

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.

AFRIKAANSE OPSOMMING: ’n Nuwe sekondêre terrein by die Matjiesfontein “Space Geodesy Observatory” (MSGO) is voorlopig geselekteer vir die plasing van groot radiotelemetrie-skottels. Hoewel verskeie ondersoeke in die verlede uitgevoer is vir die geotegniese karakterisering van die van die MSGO-hoofterrein, is soortgelyke inligting met betrekking tot die nuwe terrein grotendeels onbeskikbaar. Aangesien telemetrie-skottels sensitiewe strukture is wat besonder stabiele grondvestingstoestande verg, is ’n geotegniese ondersoek uitgevoer om die geskiktheid van die nuwe terrein te bepaal. Verder word die aankoop en vervoer van boumateriaal vanaf eksterne bronne tipies getel onder die grootste uitgawes van ‘n konstruksieprojek. Onbenutte materiaal laat boonop ’n groter voetspoor op die omgewing. Daarom is toetse uitgevoer om die geskiktheid van plaaslike materiaal te bepaal vir gebruik as growwe aggregaat in beton. Twee variasies van die oorheersende onderliggende gesteentetipe, naamlik effens en hoogs verweerde Dwyka tilliet, is vir toetse versamel. Die eienskappe van growwe aggregaat is as volg bepaal: partikel-grootte verdeling en stofinhoud deur middel van graderings; partikel vorm deur “Flakiness Index” (FI) toetse; breekweerstand en waterabsorpsie deur ’n volledige stel droë en deurweekte “Aggregate Crushing Value” (ACV) en “10 % Fines Aggregate Crushing Value” (10%FACT) toetse; en duursaamheid deur middel van ’n aangepasde blusbaarheidstoets. Hoewel effens verweerde tilliet aan alle vereistes voldoen, het die stofinhoud, deurweekte breekweerstand, waterabsorpsie en blusbaarheid van hoogs verweerde tilliet aangedui dat dit die bewerkbaarheid en waterbehoefte van ‘n betonmengsel nadelig mag beïnvloed. Gevolglik, terwyl effens verweerde tilliet as geskik beskou word vir gebruik as growwe aggregaat in beton, word die gebruik van hoogs verweerde tilliet nie aanbeveel nie. Verder het ’n basiese itvoerbaarheidstudie aangedui dat die plaaslike produksie van growwe aggregaat konstruksiekostes aansienlik kan verminder. Rotsmassa-karakterisering is uitgevoer deur middel van geofisiese elektro-resistiwiteitstoetse, kernmonster-ontleding, die “Rock Quality Designation” (RQD) en “Rock Mass Rating” (RMR) stelsels asook onbeperkte druksterkte (UCS) toetse. Elektro-resistiwiteitsbeelding oor die lengte van die terrein het aangedui dat geskikte rots binne enkele meters onder die oppervlak aangetref word. Daar is ook geen duidelike probleemareas geïdentifiseer nie. Herwonne kernmonsters bestaan hoofsaaklik uit onverweerde en effens verweerde tilliet, terwyl medium verweerde tilliet in kleiner hoeveelhede voorkom. Die algehele rotsgehalte is volgens die RQD en RMR stelsels geklassifiseer as “billike tot goeie rots”. Op grond van die resultate van talle UCS toetse, is onverweerde en effens verweerde tilliet volgens standaard riglyne geklassifiseer as “harde tot baie harde rots”, terwyl medium verweerde tilliet geklassifiseer is as “medium harde rots”. Laastens is ’n preliminˆere fondasie-ontwerp uitgevoer om die minimum diameter van die fondasie te bepaal om as ‘n aanduiding te dien van potensiële beherende faktore. Die ontwerp het aangedui dat die minimum diameter van die fondasie uiteindelik bepaal sal word deur die grootte van die superstruktuur en die ruimte wat benodig word in die voetstuk vir die behuising en bediening van telemetrie-toerusting, aangesien veiligheid teen alle oorwoë swigtingsmeganismes reeds by kleiner diameters bevestig is. Dus is plaaslike grondvestingstoestande inderdaad geskik vir die plasing van groot telemetrie-skottels.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107807
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