Greg Siemens

A Column Apparatus for Investigation of 1-D Unsaturated-Saturated Response of Sand-Geotextile Systems

This paper is focused on the details of an experimental device that was used to investigate the transient unsaturated-saturated hydraulic response of sand-geotextile layers under conditions of 1-D constant head surface infiltration. The column was instrumented with inexpensive tensiometer-transducer devices to measure pore water pressures and conductivity probes to measure wetting front migration. The results of two tests are presented to demonstrate the use of the apparatus. One test was carried out using a sand column and the second test was nominally identical but included a horizontal woven geotextile layer at about mid-depth. The test results demonstrate that the apparatus can detect differences in the unsaturated response of the two systems. For example, transient ponding of water was measured above the surface of the geotextile layer commencing from an initial unsaturated condition despite the relatively high saturated permeability of the woven material. In addition, there was a small but detectable delay in the hydraulic flow after the wetting front reached the geotextile layer.

Characterization of Transparent Soil for Use in Heat Transport Experiments

Heat transport in the geosphere is important in applications of geothermal energy systems, thermal remediation technologies, and design of energy foundations. The study of these applications would benefit significantly from the ability to collect temperature data from within the porous media system, and at high spatial and temporal resolutions. Temperature measurements made using conventional probes have high temporal resolution but are limited in their spatial resolution. Higher-resolution methods, such as thermal imaging, are limited to measurements of an exposed face of an experiment. This paper presents the development of a technique for measuring temperature using transparent soil. In typical transparent soil, the refractive indices of the soil particles and the pore fluid are matched, creating invisible soil particles when saturated. However, because the refractive indices of the soil particles and pore fluid are different functions of temperature, the degree of transparency decreases as the temperature increases or decreases from the transparency temperature. As such, changes in transparency are detected by digital photographs and can be calibrated and used to measure temperature. This paper presents relationships between temperature and normalized pixel intensity for two oil-fused silica combinations. One combination used an oil mixture with a transparency temperature of 25°C and the other, which was constructed using one of the oils in the mixture, has a transparency temperature of 4°C. The results show that there must be at least a 10°C differential from the transparency temperature to ensure a linear relationship between temperature and normalized pixel intensity. The capabilities of transparent soil constructed with the second oil are displayed in two laboratory experiments, which provide direct comparisons between transparent soil, conventional temperature probes, and thermal imaging. The results show the transparent soil provides reliable temperature fields across the experimental domain at high spatial and temporal resolutions.

An Unconfined Swelling Test for Clayey Soils That Incorporates Digital Image Correlation

A new laboratory test apparatus and methodology have been developed for characterizing the swelling potential of expansive soil under free stress conditions. Soil specimens are given access to water under true free swell conditions, and the maximum swelling potential is determined experimentally. Real-time deformation measurements and interpretation are obtained through digital image correlation using GeoPIV. The capabilities of the new test are illustrated using a remolded natural swelling soil. Both primary and secondary swelling behavior were observed during testing. The effect of the aspect ratio was assessed, and it was found that smaller specimens achieved equivalent swelling strains with significantly shorter test durations. The non-contact deformation results agree with the end-of-test hand measurements. The non-contact method also provides additional valuable information regarding the time-dependent swell behavior and evaluation of the end-of-test criterion. The results are interpreted using the Swell Equilibrium Limit, which is a unifying framework for the analysis and prediction of swelling soil deformations under defined initial and boundary conditions.

Influence of Specimen Geometry on Sample Disturbance Observed in Oedometric Testing of Clay Shales

There has been a significant amount of research investigating the relationship between sample disturbance and laboratory test results in soft soils. As a result of this research, the general rule adopted is that using larger specimens results in less sample disturbance. When testing these larger specimens in the laboratory, the results are more representative of in situ behavior of the materials. In contrast, there has been relatively little corresponding research performed on hard soils whose behavior typically lies on the boundary between rock and soil. Extensive unloading in hard soils, from sampling, results in large suctions (negative pore pressures) and the formation of fractures that are uncharacteristic of the material in its natural state. This poses the question of whether the use of small specimens would produce more reliable laboratory results. This paper investigates the following two hypotheses within the context of oedometric testing: (1) testing smaller diameter specimens will produce results more representative of the in situ behavior of the material, and (2) an aspect ratio of 2.5 may reduce disturbance to the specimen during preparation are tested. The results of this testing program, including the intact material properties, and a characterization of the compression behaviour of clay shale from the Bearpaw Formation is also presented herein. Results show that a reduced specimen size, when working with a hard clay shale, minimizes the effect of disturbance and produces results that are the most representative of the intact material. Decreased specimen size also aids in determining preconsolidation pressure by not only reducing the disturbance to the sample resulting from unloading, but also by enabling these high stresses to be achieved in conventional testing equipment. Two criteria from the literature were used to assess disturbance within the oedometer specimens. Overall, the methods provide a good baseline of assessing disturbance, however, there is less gradation to the quality of a specimen in a hard soil. Parameters Cc and σ′p were sensitive to sample disturbance, however, other parameters such as cv and K were less dramatically affected by disturbance. Therefore, care must be taken when assessing the compression of a hard soil as failing to achieve sufficiently higher stresses and the presence of disturbed specimens may lead to misleading Cc and σ′p values.

Examination of Unsaturated Conductivity Curves Using Transparent Soil

Numerical simulations of unsaturated flow require the retention curve and unsaturated conductivity curve as inputs. Except in research or in the case of large projects these material properties are estimated to some degree. This manuscript examines the accuracy of unsaturated conductivity estimations for an unsaturated transparent soil. Using transparent soil allows accurate measurement of degree of saturation along the soil profile as well as the spatial measurements of conductivity. The estimations show the correct trend and are found to be within one order of magnitude compared with the experimental data.

Impact of pore fluid chemistry on the thermal conductivity of bentonite–sand mixture

Thermal conductivity is an important parameter to consider when designing clay-based barriers for use in deep geological repositories (DGR). In the DGR environment, the infiltration of local saline groundwater can potentially change the pore fluid chemistry of a barrier over its lifetime. This change in chemistry is known to alter the thermal properties of the barrier materials. In order to examine the impact of pore fluid salinity on thermal conductivity, experiments were conducted under both distilled water and saline pore fluid conditions. The material mixtures were prepared at two different dry densities using two different salt types. Furthermore, five different thermal conductivity prediction models were selected and evaluated on their performance with respect to the experimental outcomes. In general, these results indicated that an increase in the constituent pore fluid’s salt concentration leads to a decrease in the thermal conductivity of the material. Additionally, the thermal conductivity values of the materials prepared at a high dry density were greater than of those compacted at a low dry density.