Site characterization and foundation design for the emplacement of radio telescope antennas at the Matjiesfontein Space Geodesy Observatory

Janse van Rensburg, Cornelius Johannes Theodorus (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The suitability of the Matjiesfontein Space Geodesy Observatory (MSGO) site for hosting radio telescope antennas is partially dictated by certain civil engineering considerations. These include the investigated geotechnical and hydrological site characteristics. The engineering properties of different soil and rock types in the surrounding area were also investigated as their use as construction material may have cost implications for the project. A GPS survey was carried out on the area earmarked for radio telescopes, which gave the researcher an opportunity to familiarize himself with the terrain and use the data for creating a digital terrain model (DTM) of the area. The geotechnical investigation followed and has shown encouraging results indicating shallow bedrock generally of hard to very hard rock consistency. This is a favourable founding condition for structures, but is particularly important in geodesy where instruments rely on stability to produce accurate results. The hydrological investigation has shown that, with even a very conservative steady flow analysis, the discharge in channels will not put infrastructure at risk of flooding in the event of heavy rainfall. Standard tests performed on local soil indicated a variety of soil types, mostly due to the different geomorphic processes in their origin as well as the varying geology in the area. Six disturbed samples of colluvial, alluvial and residual material were tested using the TMH1 (Technical Methods for Highways) to produce indicative characteristics of untreated local soil. They were then classified using the Unified Soil Classification System and the three main samples were classified for quality using TRH14 (Technical Recommendations for Highways). The materials were also evaluated as fine aggregate for concrete, selected fill for services and patching material for improving eroded sections of the access road. Petrographic results from a previous study indicated the presence of strained quartz in quartzitic sandstone from the site, rendering aggregate potentially susceptible to alkali-silica reaction. Tillite (Diamictite) of the Dwyka Formation in KwaZulu-Natal has also been identified as potentially reactive by laboratory testing. Quartzitic sandstone and tillite samples were subsequently collected from site and tested for alkali-silica reaction (ASR), resulting in almost none to innocuous expansion. These rocks were also tested for compressive strength, yielding strengths in excess of 70MPa. Based on these results and if found to be feasible, the possibility exists for loose boulders to be sourced, crushed and sorted locally for use as coarse aggregate in concrete, without causing any aesthetically displeasing affects to the environment. A limit state design (LSD) approach for a SKA-type radio telescope foundation was undertaken using nominal loads obtained from the organization and characteristic material properties obtained from this study. The foundation was designed as a circular spread gravity footing with a diameter of 5.5m, the size being governed by equilibrium at the ultimate limit state (ULS). The most important conclusion is that the site is, in terms of its engineering properties, certainly suitable for conducting radio astronomy and geodetic experiments.

AFRIKAANSE OPSOMMING: Die geskiktheid van die “Matjiesfontein Space Geodesy Observatory” (MSGO) terrein vir die huisvesting van radioteleskoop antennas word gedeeltelik bepaal deur sekere siviele ingenieursoorwegings. Dit sluit die ondersoekde geotegniese en hidrologiese eienskappe van die terrein in. Die ingenieurseienskappe van verskillende grond- en rotstipes in die omliggende gebied was ook ondersoek aangesien die gebruik daarvan as konstruksiemateriaal koste-implikasies vir die projek mag inhou. ’n “GPS” opname was uitgevoer in die area geoormerk vir radioteleskope, wat die navorser die geleentheid gebied het om homself te vergewis met die terrein en die data te gebruik om ’n digitale terrein model (DTM) van die terrein te skep. Die geotegniese ondersoek het daarna gevolg en het goeie resultate opgelewer wat dui op ’n goeie gehalte vlak rotsbedding van harde tot baie harde materiaal. Dit is 'n gunstige toestand vir strukture, maar is veral belangrik vir geodesie waar instrumente staatmaak op stabiliteit om akkurate resultate op te lewer. Die hidrologiese ondersoek het getoon dat, selfs met ’n baie konserwatiewe bestendige vloei analise, die afloop in kanale nie infrastruktuur in gevaar van oorstroming sal plaas in die geval van swaar reënval nie. Standaard toetse op plaaslike grond het gedui op ’n verskeidenheid van grondtipes, as gevolg van die verskillende geomorfologiese prosesse sowel as die wisselende geologie in die gebied. Ses versteurde monsters van kolluviale, alluviale en residuele grond is getoets met behulp van die TMH1 (“Technical Methods for Highways”) om voorlopige eienskappe van onbehandelde plaaslike grond te verkry. Daarna was dit geklassifiseer met behulp van die “Unified Soil Classification” sisteem en die drie belangrikste monsters is verder geklassifiseer met behulp van die TRH14 (“Technical Recommendations for Highways”). Die materiaal was geëvalueer as fyn aggregaat vir beton, opvulmateriaal vir dienste en pleister-materiaal vir die verbetering van geërodeerde dele van die toegangspad. Petrografiese resultate uit ’n vorige studie het die teenwoordigheid van gespanne kwarts aangedui in die sandsteen van die terrein, wat aggregaat moontlik vatbaar maak vir alkali-silika reaksie. Tilliet (Diamiktiet) van die Dwyka Formasie in KwaZulu-Natal is in die literatuur geïdentifiseer as potensieel reaktief. Kwartsitiese sandsteen en tilliet monsters is gevolglik versamel en getoets vir alkali-silika reaktiwiteit (ASR), met byna geen tot weglaatbare uitsetting. Dié rots was ook getoets vir druksterkte, met sterktes bo 70MPa. Op grond van hierdie resultate en indien dit uitvoerbaar is, kan los rotse plaaslik versamel, gebreek en sorteer word vir gebruik as growwe aggregaat in beton, sonder enige negatiewe ongewensde effekte op die omgewing. ’n Limietstaat ontwerp (LSD) benadering vir die fondasie van ’n SKA-tipe radioteleskoop was gedoen met behulp van nominale laste verkry vanaf die organisasie en karakteristieke materiaaleienskappe vanuit dié studie. Die fondasie is ontwerp as ’n ronde plat voetstuk met 'n diameter van 5.5m, bepaal deur ewewig by die uiteindelike limietstaat (ULS). Die hoof gevolgtrekking is dat die terrein geskik is, in terme van sy ingenieurseienskappe, vir die uitvoer van radio-astronomie en geodetiese eksperimente.

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