Characterization of Transparent Soil for Unsaturated Applications

Abstract

Experimental characterization of unsaturated soils is of primary importance to further understanding of fundamental behavior, as well as allow for accurate modeling and predictions, of constitutive and field behavior. In the laboratory, the most common research methodology used to investigate the hydraulic behavior of unsaturated soils involves placing the unsaturated soil in a column apparatus with measurements of pore pressure and moisture content being made at discrete locations distributed along the elevation of column. These types of tests have provided many valuable insights into unsaturated flow phenomena; however, there are some limitations with this methodology including the discrete nature of the measurement points. In this paper, an alternative method is proposed which aims to combine the use of digital image analysis with a transparent soil to avoid the ambiguity of traditional boundary image measurements of moisture content in column experiments. At 100% saturation, the transparent soil particles appear invisible and allows for the ability to see through the soil mass. Any air bubbles will be visible within the soil voids and as a result, at varying degrees of saturation less than 100%, the soil will become progressively non-transparent. The relationship between pixel intensity of the unsaturated soil and degree of saturation is defined and validated. This relationship allows definition of the degree of saturation throughout the column profile thus giving the opportunity to verify and further develop constitutive models for unsaturated hydraulic behavior.

Thirty-Sixth Canadian Geotechnical Colloquium: Advances in visualization of geotechnical processes through digital image correlation

“…Example applications have been discussed where DIC measurements have been used to visualize failure processes and make quantitative measurements of deformation within physical models, to measure surface heave in the field due to construction processes, to use low-altitude imaging to collect 3D point cloud data of ground movements, and to obtain field measurements of rail track stiffness under dynamic train loading. A great number of other geotechnical applications of the technique can be found in the literature, including applications in transparent soil (e.g., Sadek et al 2003;Ni et al 2009;Ezzein and Bathurst 2011;Peters et al 2011;Sanvitale and Bowman 2012;Stanier et al 2012) and digital volume correlation (e.g., Bay et al 1999;Hall et al 2010). It is expected that the number and breadth of DIC applications in geotechnical engineering will continue to grow due to the versatility of the technique.…”

Physical and numerical modeling of infiltration including consideration of the pore-air phase

“…Infiltration experiments were performed using transparent soil that provides high-resolution locational and temporal measurements of degree of saturation (Peters et al 2011;Siemens et al 2013). Transparent soil is formed by matching the refractive indices of the soil particles and the pore fluid, which are fused quartz and a mineral oil mixture, respectively (Ezzein and Bathurst 2011;Peters et al 2011). Figures 2 and 3 illustrate the change in colour of the unsaturated transparent soil with changes in the degree of saturation (S r ).…”

“…Most apparatuses include point measurements of moisture content and (or) suction along the length of the column. Recently, an optically matched pore fluid -transparent soil was developed, which allows high temporal and locational measurements of degree of saturation (Peters et al 2011). Peters et al (2011) and Siemens et al (2013) used the soil within a column apparatus to examine the effect of air entrapment on degree of saturation and wetting front migration during infiltration.…”

“…Recently, an optically matched pore fluid -transparent soil was developed, which allows high temporal and locational measurements of degree of saturation (Peters et al 2011). Peters et al (2011) and Siemens et al (2013) used the soil within a column apparatus to examine the effect of air entrapment on degree of saturation and wetting front migration during infiltration. The use of unsaturated transparent soil allows for measurement of the degree of saturation to the resolution of a millimetre, which provides for accurate measurements of the wetting front location and direct observation of flow mechanisms captured with digital images.…”

Thirty-Ninth Canadian Geotechnical Colloquium: Unsaturated soil mechanics — bridging the gap between research and practice

“…soil allows for direct observation from within the soil mass of deformations, strains and soil-structure 274 interaction rather then at the boundary of an experiment. Unsaturated transparent soil takes this concept 275 in another direction (Peters et al 2011). Observations in unsaturated experiments are often limited by the 276 number of measurement devices that can be located within an experimental apparatus.…”