Browsing by Author "Uwimana, Aimable"
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- ItemInvestigation of factors affecting the load carrying capacity of driven solar panel support posts(Stellenbosch : Stellenbosch University, 2015-12) Uwimana, Aimable; Day, Peter; De Wet, Marius; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: A number of large “solar farms” have already been built in South Africa and more are under construction. Many of these make use of banks of photovoltaic panels mounted on a frame-work supported on columns known as posts. Various methods of founding are used for these posts. One of the founding methods involves driving the post into a predrilled hole filled with granular material. In South Africa, this method is used in semi-arid areas where the sites are frequently underlain by clacretes or by shallow rock. However, there are no clear design guidelines for such foundations. When the installation is not done correctly and the solar panel support structure is subjected to the action of wind and water, the driven posts could settle or be pulled-out of the ground creating failure. Therefore, an investigation of factors affecting the shaft pull-out capacity of driven post is vitally important. In order to provide a better understanding of load bearing capacity of driven posts in both compression and tension, research has been carried out into the effect of backfill material type, compaction density, compaction moisture content, backfill saturation, post-to-hole area ratio and aging of the backfill. An experimental programme using three types of backfill material, three degrees of compaction, three area ratios and two compaction moisture con-tents was carried out to assess the influence of these variables on axial and oblique pull-out loading capacity of predrilled driven posts. In addition, the moisture content at the time of loading and the effect of aging of the backfill was considered. Each material was evalu-ated in terms of particle size distribution, particle shape, and shearing resistance using di-rect shear tests. The pull-out resistance was evaluated using an Instron load-testing ma-chine on experimental driven posts at half scale. The results from the direct shear tests revealed an increase in shear strength with an in-crease in the degree of compaction and normal stress. It also shows that the crusher dust material has higher shear strength than Malmesbury and Philippi sands. However, shear strength reduces with saturation while dilation reduces with an increase of both normal stress and moisture content. The shaft pull-out capacity results from the experimental model tests confirm the findings of the direct shear tests on material performance. The pull-out resistance increases with both degree of compaction and area ratio. It reduces with saturation. In addition, the pull-out capacity of the post increases significantly with time. Comparing the axial and oblique pull-out capacity, a higher resistance was observed under oblique pull-out loads than for axial pull-out. This helps to explain why posts have been observed to settle under very modest dead loading but are, nevertheless, able to resist significant wind loading on the underside of the panels. This study contributes to understanding the effect of material type, compaction density, area ratio, water content and aging on the shaft pull-out capacity of driven post foundations for solar panels. Practical specifications and technical guidelines are developed to ensure an improved installation of foundations using this predrilled driven post method.