The feasibility of using sediments from the Theewaterskloof, Greater Brandvlei and Waterzicht Dams as construction materials

Dorfling, Johannes Adolf (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Between 2014 and 2018, the Western Cape experienced the worst drought that the province has faced since 1904. The drought led to numerous water restrictions being applied by municipalities to regulate water use by their respective communities. From the exposed surfaces caused by the receding dam water levels, it was clear that thick layers of sediment have been deposited in the dams over the years, decreasing the storage capacities of these dams. The removal of these reservoir sediments will assist in maintaining optimal water storage capacity. The aim of this study was to determine the practical and economic feasibility of removing sediments out of the Western Cape's two largest dams namely the Theewaterskloof and Greater Brandvlei Dams as well as the smaller Waterzicht farm dam, and the possible use of these sediments as construction materials such as road building materials, fine aggregates, lightweight aggregates, bricks and landfill clay liners. Field investigations were conducted on the exposed dam surfaces of these three reservoirs. During this fieldwork, zones were demarcated based on sediment type and location and samples were gathered from each zone. Subsequently, laboratory analyses were performed on these samples to determine their engineering and chemical properties. These properties were used to classify each sample according to the Unified Soil Classification System (USCS) and related to the specific criteria for the various construction materials under investigation. The data from field analyses were used, together with sediment types, to determine the volume of each sediment zone. Where the sediments in a mapped zone were found suitable to be used as construction materials, cost models were prepared based on the type of construction material to be removed to estimate the removal cost per unit volume. Based on the laboratory results, two cost models for the two zones were calculated. These zones included the poorly graded sands (SP) from zone B5 of the Greater Brandvlei Dam that is suitable for use as fine aggregate and clayey sands (CS) of the Waterzicht Dam that can be used for landfill liners in Class B and Class C type landfills. Three samples from the Theewaterskloof Dam and one sample from the Greater Brandvlei Dam can be used as lower layers of the pavement or in construction of fills, however the low cost, low quality and abundance of such road materials made it not feasible to be recovered for road construction unless such construction occurs adjacent to the sediment zones. The methods used in the cost models for the removal of sediment from zone B includes dry excavation with and without sheet piling and dredging if the zone is submerged by an increase in dam levels. The removal costs for dry excavation without sheet piling and dredging methods were considered feasible if no more than five sediment removal units are used. For dry excavation to be feasible the minimum proportion of the sediment reserve to be removed ranges from 26% to 100% if one to five excavators are used respectively. The cost model created for removing clayey sands (CS) from the Waterzicht farm dam estimated that if 100% of the sediment reserve is removed, it will be feasible to use the sediment for compacted clay liners for Class B and Class C landfills if the transport distances are 1 km and 25 km respectively. From the cost models, it was concluded that the sediments from the Greater Brandvlei Dam and Waterzicht farm dam may be feasibly mined, however the volume estimations indicate that removal of these mapped sediments will result in only a minor increase in storage capacity and will have only a small impact on lessening the effects on future droughts.

AFRIKAANSE OPSOMMING: Vanaf 2014 tot 2018, het die Weskaap die die ergste droogte ervaar sedert die 1904-droogte. Die droogte het veroorsaak dat daar menige waterbeperkings deur munisipaliteite ingestel is. Die laer damvlakke het dik lae sedimente op die oppervlakkte blootgelê. Dit was duidelik dat hierdie sedimente deur menige jare neergeset is en dat die stoorkapasiteit van die damme verlaag het. Die verwydering van hierdie sedimente sal help met die handhawing van optimale waterbergingskapasiteit van hierdie damme. Die doel van hierdie studie was om the bepaal of dit prakties en ekonomies lewensvatbaar sal wees om die sedimente van the Weskaapse twee grootste damme genaamd Theewaterskloofdam en die Groot Brandvleidam te verwyder asook die van die kleiner Waterzichtplaasdam. Daar sal ook bepaal word of hierdie sedimente dan gebruik kan word vir konstruksiemateriale. Die konstruksiemateriale waarvoor sedimente getoets is, sluit in padboumateriaal, fyn aggregate, liggewig-aggregate, bakstene en kleiverseëlings in stortingsterreine. Veldondersoeke is op die blootgestelde damoppervlaktes van hierdie drie damme uitgevoer. Tydens hierdie veldwerk is sones afgebaken op grond van die sedimentstipe en ligging. Monsters uit elke sone is versamel. Vervolgens is laboratoriumontledings op hierdie monsters uitgevoer om hul ingenieursmoontlikhede en chemiese eienskappe te bepaal. Die data van die veldanalises is saam met die sedimenttipes gebruik om die volume van elke sedimentsone te bepaal. Waar die sedimente in 'n gekarteerde sone geskik gevind is om as konstruksiemateriaal gebruik te word, is daar kostemodelle opgestel volgens die tipe konstruksiemateriaal om te bepaal of die kostes verwant aan die verwydering van die materiale lewensvatbaar sal wees. Op grond van die laboratoriumresultate is twee kostemodelle vir twee sones bereken. Hierdie sones sluit in die swak gegradeerde sand vanaf sone B5 van die Groot Brandvleidam wat geskik is vir die gebruik as fyn aggregaat en die klei sand van die Waterzichtdam wat gebruik kan word as ‘n kleiverseëling in Klas B en Klas C stortingsterreine. Drie monsters van die Theewaterskloofdam en een monster uit die Groot Brandvleidam kan gebruik word as onderste lae van die sypaadjie of in die konstruksie van vullings, maar die lae koste, lae gehalte en die oorvloed van hierdie tipe padmateriaal maak die ontginning van hierdie materiale nie winsgewend nie, tensy sodanige konstruksie langs die sedimentsones plaasvind. Die metodes wat gebruik word in die kostemodelle vir die verwydering van sediment uit sone B, sluit droë uitgrawing met en sonder plaatmure en baggering indien die sone onder water is deur 'n toename in damvlakke. Die verwyderingskoste vir droë opgrawings sonder die plaatmure en met baggermetode word as haalbaar beskou as nie meer as vyf sedimentverwydering masjiene gebruik word nie. Vir die uitvoer van droë grawe met behulp van plaatmure, wissel die minimum persentasie van die sedimentreserwe wat verwyder moet word, van 26% tot 100% indien onderskeidelik een tot vyf graafmasjiene gebruik word. Vanaf die kostemodel wat vir die verwydering van klei sand uit die Waterzichtplaasdam, word dit beraam dat indien 100% van die sedimentreserwe ontgin word, dit die uitvoerbare sediment as klei verseëling vir die stortingsterreine van Klas B en Klas C kan gebruik as die afstande 1 km en 25 km onderskeidelik is. Uit die kostemodelle is die gevolgtrekking gekom dat die sedimente van die Groot Brandvleidam en die Waterzichtplaasdam moontlik haalbaar ontgin kan word, maar die volume-ramings dui daarop dat die verwydering van hierdie gekarteerde sedimente slegs 'n geringe toename in die bergingskapasiteit sal veroorsaak en slegs 'n klein impak op die vermindering van die gevolge vir toekomstige droogtes.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107215
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