Department of Soil Science

Permanent URI for this community

https://scholar.sun.ac.za/handle/10019.1/23

Browse

Browsing Department of Soil Science by browse.metadata.advisor "Du Plessis, Anton"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Assessing the potential of using microcomputerized tomography to determine the physical properties of different textured soils
    (Stellenbosch : Stellenbosch University, 2020-12) Hartnick, Emke Kim; Du Plessis, Anton; Lategan, Eugene; Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science.
    ENGLISH ABSTRACT: The physical properties of soil, particularly the structure, texture, and pore geometry affect hydraulic conductivity in soils. The hydraulic conductivity is an important parameter for understanding the flow of water through different soil types for determining irrigation rates, monitoring of groundwater, and runoff. The hydraulic conductivity is a highly variable soil property and there are several methods for determining the hydraulic conductivity in soils. Each has its advantages and limitations. Traditional methods are time-consuming and the application of X-ray micro-computer tomography (microCT) offers fast and effective analysis and results. The additional use of microCT for this purpose might improve the accuracy of laboratory constant hydraulic head tests if these methods are used in combination. The application of microCT technology can visualize the internal pore geometry of a soil sample without destroying the soil sample. Thus, the microCT technology can examine the porosity and the pore connectivity in soils, which influence the hydraulic conductivity. The purpose of this study was to apply microCT technology to examine the range within it can be used to determine the saturated hydraulic conductivity (Ksat) and porosity of homogeneous and heterogeneous soils. This was done in the context of considering if the advantages of this application (fast and efficient analysis) exceed the disadvantages (cost). The investigation of an effective sampling method for soil samples for X-ray microCT scans and associated image-based analysis were examined. The saturated hydraulic conductivity (Ksat) and porosity of five different soil types (homogeneous and heterogeneous soil) will be obtained through standard laboratory methods (constant hydraulic head test and calculating the porosity from the bulk and particle density) and microCT image-based simulations and analysis. Additional calculation of the Ksat based on grain size theoretical equations such as Hazen and Kozenzy & Carman equation will be used. The results showed that the Ksat of the homogeneous soil very coarse, coarse, and medium sand were underestimated by the microCT simulations. The Ksat of the fine and very fine sand determined through microCT simulations and constant hydraulic head tests compared well. MicroCT simulations underestimated the Ksat of the heterogeneous soil. The porosity values for the homogeneous soil were overestimated by microCT image-based analysis. The porosity values of the heterogeneous soil obtained from microCT image-based analysis for the coarse and pure fine sand were higher than the sandy clay loam, sandy loam and sandy clay soils. The sandy clay loam, sandy loam and sandy clay soils porosity were measured inaccurately by microCT due to resolution limitations. The Ksat of the homogeneous soil analysed by microCT simulation, however, fell within the same order of magnitude as the Ksat obtained from the constant hydraulic head test. Fundamentally, the microCT technology demonstrated great capabilities for analysing both the Ksat and porosity of homogeneous soils. The microCT application is best used for soils with larger particle sizes due to image resolution limits. The 2D visualization of the microCT scans can be useful for investigating structural changes within a soil sample caused by laboratory analysis. Such analysis may include constant hydraulic head tests or the examination of soil samples after sample preparations.