Centrifuge modeling of energy foundations – effect of seasonal temperature fluctuation and soil state

Energy foundations can reduce carbon footprint and lead to energy savings. Understanding the process of heat migration in soil is therefore of great interest in the field of geotechnical engineering. However, limited literature exists on the thermo-dynamic interaction and structural performance of an energy foundation and the surrounding soil. Lab testing of energy foundations remains inexpensive compared to field tests; however lab tests cannot easily simulate representative in-situ stress conditions. This can be resolved by using a geotechnical centrifuge to correctly mimic the stress gradient of the self-weight of the soil. A series of centrifuge models of energy foundations in different soil states (dense and loose) have been tested. Representative seasonal temperature fluctuations in the UK are used as the benchmark in this study. A total of three years of heating/cooling cycles are modelled and foundation response is captured by means of embedded temperature sensors at different distances away from the thermal foundation

Development and calibration of a sand pluviation device for preparation of model sand bed for centrifuge tests

A bespoke 0.068m3 (18.5 gallon) sand hopper is employed at the newly established 50gTon centrifuge facility at the University of Sheffield. The sand hopper employs a series of mesh inserts of different diameters which control the flow rate and thus the relative density of the model. A series of calibration tests on equivalent Fraction E and Fraction C sands were performed to calibrate the mesh diameter and drop height for a desired relative density. Result showed that the sand hopper is capable of delivering repeatable relative densities in the range of 30% to above 90%, for both kinds of sand grades. This wide range relative density is considered sufficient to satisfy the needs of researchers preparing dry sand models for testing in the center

Development of a 25ton consolidation press at the Centre for Energy and Infrastructure Ground Research

1d consolidation frame has been designed and manufactured at the Centre for Energy and Infrastructure Ground Research (CEIGR), University of Sheffield. The consolidation frame allows static consolidation of soil beds. This system comprises of a 25 ton rated press that can accommodate a range of centrifuge payload strong box configurations. The consolidation force is delivered via a hydraulic piston rated to deliver 80 kN force at 10bar supply pressure with a stroke of 500mm. A series of vertical draw-wire transducers are implemented which monitor consolidation settlement. Combined with pore pressure transducers, the user can measure the pore water pressure at the top and at the bottom of the clay sample. A bespoke LabVIEW VI visual display is implemented which offers visual/graphical feedback to the user on the range of sensor information and a live update of consolidation progress; it also incorporates data entry to capture test specific in-formation

Shear Strength of Transparent Gelita-The Effect of the Mixture Ratio, Displacement Rate, and Over-Consolidation Ratio

Transparent soils combined with non-invasive imaging techniques allow internal visualization of geotechnical processes. Oil-based transparent silica has been traditionally used for measurements of deformation patterns, soil structure interaction (SSI), flow pattern, and permeability. New water based environmentally friendly transparent material, Gelita, can be used as a transparent soil to model fine grain clay soils. Gelita has been extensively used in applied mechanics as a standard target to test bullets or to simulate human tissue. However, the potential of this material to serve as a soil surrogate and its correlation to basic geotechnical properties have not yet been investigated. Material properties and transparency of Gelita depend on its mixture ratio with water. For example, a 5% by mass Gelita mixture offers high optical transparency; however, it exhibits extremely low strength characteristics. As the mixture ratio (density) of Gelita increases, its transparency is reduced, but it offers a higher strength. This paper investigates the effect of Gelita mixture ratio, confinement, displacement rate and over-consolidation ratio on the resulting shear strength, for the purpose of being used as a soil surrogate for modeling applications

Centrifuge modelling of shallow foundations on firm over soft layered clay

In practice shallow foundations are rarely simply founded on a homogenous soil beds hence there are uncertainties surrounding the mode of failure that will prevail and the bearing capacity factor that should be adopted in design. A series of centrifuge model tests on surface strip footings resting on a layered soil bed having firm clay overlying soft clay of varying thickness are presented. Plane strain test conditions enabled the use of Digital Image Correlation (DIC) to determine the relative displacement of the soil and reveal the foundation failure mechanics. Complementary numerical modelling is also conducted which verifies the model experimental data. General shear and punch failure were observed and the dominant failure mechanism shown to depend on the ratio of the upper layer thickness and footing width

Optical Characterization of Transparent Gelita Using the Modulation Transfer Function

Visualization of internal geotechnical processes in physical modelling is possible through the use of transparent soils. These materials rely on optical clarity hence a systematic impartial user-independent assessment framework for visual quantification is necessary. The visual quantification of transparent soil models have been traditionally done by Snellen eye charts. Black and Take (2015) introduced an independent method called Modulation Transfer Function (MTF) to quantify the visual quality of transparent soil models. This method incorporates optical calibration charts consisting of black and white grids of different spatial frequency (pixel intensity). A new transparent material named Gelita is introduced to model clay and assessed using this standardized framework Different mixture ratios of transparent Gelita (5% to 20%) are produced and visually tested. Viewing depth is varied from 50 mm to 150 mm and tests are repeated to quantify this effect on the visual transparency of Gelita. It is found that smaller mixture ratios of Gelita have the highest MTF and therefore offer the highest optical quality. The effect of viewing depth is more pronounced in samples of Gelita of larger mixture ratios. RE-use of the material by secondary melting does not significantly affect transparency regardless of the mixture ratio

Immunofluorescent labeling of CD20 tumor marker with quantum dots for rapid and quantitative detection of diffuse large B-cell non-Hodgkin's lymphoma

Fluorescent semiconductor quantum dots (QDs) are newfound nanocrystal probes which have been used in bioimaging filed in recent years. The purpose of this study is to evaluate the diagnostic value of specific QDs coupled to rituximab monoclonal antibody against CD20 tumor markers for patients with diffuse large B-cell lymphoma (DLBCL). In current study rituximab-conjugated quantum dots (QDs-rituximab) were prepared against CD20 tumor markers for detection of CD20-positive cells (human Raji cell line) using flowcytometry. A total of 27 tumor tissue samples were collected from patients with DLBCL and 27 subjects with negative pathological tests as healthy ones, which stained by QD-rituximab. The detection signals were obtained from QDs using fluorescence microscopy. The flowcytometry results demonstrated a remarkable difference in fluorescent intensity and FL2-H + (CD20-positive cells percentage) between two groups. Both factors were significantly higher in Raji in comparison with K562 cell line (P < 0.05). Lot of green fluorescence signals was observed due to the selectively binding of QD-rituximab to CD20 tumor markers which overexpressed in tumor tissues and a few signals observed on the defined healthy ones. Based on these observations the cut-off point was 46.8 dots and the sensitivity, specificity, positive predictive value, and negative predictive value were 100, 89.5, 91.3, and 100, respectively (LR+, 9.52; LR�, 0). The QD -rituximab could be beneficial as a bioimaging tool with high sensitivity to provide an accurate molecular imaging technique for identifying CD20 tumor markers for early diagnosis of the patients with DLBCL. © 2018 Wiley Periodicals, Inc