scholarly journals Application of single-board computers in experimental research on unsaturated soils

2020 ◽  
Vol 195 ◽  
pp. 02022
Author(s):  
Marius Milatz
Keyword(s):  
Uniaxial Compression ◽  
Mechanical Behaviour ◽  
Unsaturated Soils ◽  
Water Retention ◽  
University Teaching ◽  
Water Retention Curve ◽  
Raspberry Pi ◽  
Granular Soils ◽  
Compression Tests ◽  
Unsaturated Granular Soils

In this contribution, the application of single-board computers for the investigation of the hydro-mechanical behaviour of unsaturated granular soils is presented. Single-board computers, such as the Raspberry Pi or Arduino, have recently experienced a hype of applications in school and university teaching, in the maker scene, amongst hobbyists, but also in research. In combination with easy to learn and open programming languages, such as Python, individual experimental set-ups for research in unsaturated soil mechanics, using actuators and sensors can be easily developed with the help of different programmable hardware, such as stepper motors, analog-to-digital converters and other controller boards. For the experimental application in imaging of unsaturated granular soils by computed tomography (CT), we present a miniaturized uniaxial compression device for the measurement of unsaturated shear strength and capillary cohesion in CT-experiments. The device has already been applied for CT-imaging of the development of water distribution and capillary bridges in between different shear steps. Furthermore, a new fully programmable hydraulic experimental set-up for the automated investigation of transient hydraulic paths of the water retention curve of granular media is presented. Both devices have been developed in the framework of the Raspberry Pi single-board computer and Python programming language with simple and relatively inexpensive hardware components. In addition to the technical development of the testing devices, experimental results of the hydro-mechanical behaviour of unsaturated sand and glass beads, derived from uniaxial compression tests and water retention tests, will be presented.

Predicting the unsaturated hydraulic conductivity of granular soils from basic geotechnical properties using the modified Kovács (MK) model and statistical models

2006 ◽  
Vol 43 (8) ◽  
pp. 773-787 ◽  
Author(s):  
M Mbonimpa ◽  
M Aubertin ◽  
B Bussière
Keyword(s):  
Hydraulic Conductivity ◽  
Statistical Models ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Geotechnical Properties ◽  
Water Retention Curve ◽  
Granular Soils ◽  
Retention Curve ◽  
Unsaturated Hydraulic Conductivity ◽  
Preliminary Validation

The water retention curve (WRC) is often used to define the relative hydraulic conductivity, kr, of unsaturated soils. In this paper, the authors propose the use of the modified Kovács (MK) model, developed to predict the WRC using basic geotechnical properties, combined with some existing statistical models to estimate the kr function. The proposed equations are implemented in MATLAB®. After a preliminary validation based on comparisons with existing solutions, predictive results are presented for granular soils. These indicate a relatively good agreement with experimental results from drainage tests taken from the literature. A discussion follows on the advantages and limitations of the proposed approach.Key words: water retention curve, unsaturated hydraulic conductivity, predictive models, granular soils.

scholarly journals Micro- and macro-scale water retention properties of granular soils: contribution of the X-Ray CT-based voxel percolation method

Soil Research ◽  
2019 ◽  
Vol 57 (6) ◽  
pp. 575
Author(s):  
Erika Shiota ◽  
Toshifumi Mukunoki ◽  
Laurent Oxarango ◽  
Anne-Julie Tinet ◽  
Fabrice Golfier
Keyword(s):  
Water Retention ◽  
Drainage Water ◽  
Transport Processes ◽  
Water Retention Curve ◽  
Granular Soils ◽  
Pore Scale ◽  
Micro Computed Tomography ◽  
X Ray ◽  
Percolation Method ◽  
Macro Scale

Water retention in granular soils is a key mechanism for understanding transport processes in the vadose zone for various applications from agronomy to hydrological and environmental sciences. The macroscopic pattern of water entrapment is mainly driven by the pore-scale morphology and capillary and gravity forces. In the present study, the drainage water retention curve (WRC) was measured for three different granular materials using a miniaturised hanging column apparatus. The samples were scanned using X-ray micro-computed tomography during the experiment. A segmentation procedure was applied to identify air, water and solid phases in 3D at the pore-scale. A representative elementary volume analysis based on volume and surface properties validated the experimental setup size. A morphological approach, the voxel percolation method (VPM) was used to model the drainage experiment under the assumption of capillary-dominated quasi-static flow. At the macro-scale, the VPM showed a good capability to predict the WRC when compared with direct experimental measurements. An in-depth comparison with image data also revealed a satisfactory agreement concerning both the average volumetric distributions and the pore-scale local topology. Image voxelisation and the quasi-static assumption of VPM are likely to explain minor discrepancies observed at low suctions and for coarser materials.

scholarly journals The influence of rates of drying and wetting on measurements of soil water retention curves

2020 ◽  
Vol 195 ◽  
pp. 03005
Author(s):  
Arash Azizi ◽  
Ashutosh Kumar ◽  
Mwajuma Ibrahim Lingwanda ◽  
David Geoffrey Toll
Keyword(s):  
Unsaturated Soils ◽  
Water Retention ◽  
Continuous Measurement ◽  
High Capacity ◽  
Water Retention Curve ◽  
Testing System ◽  
Soil Water Retention ◽  
Comprehensive Description ◽  
Retention Curve ◽  
Lower Saturation

The water retention curve is fundamental for a comprehensive description of the hydro-mechanical behaviour of unsaturated soils. The water retention testing system developed at Durham University allows direct and continuous measurement of suction using a high capacity tensiometer, water content determined from mass readings of a digital balance and measurements of volume change. The system was modified to accommodate an additional tensiometer to measure suction at the top besides the existing one at the bottom of the soil specimen. Soil specimens were subjected to drying and wetting following two procedures: discrete measurements carried out in stages to ensure equalisation and continuous measurement at different rates. All suctions measured during continuous and discrete measurements were very close at high saturation degrees. At lower saturation degrees, the suction values from the top and bottom of the specimen deviated from suctions observed in discrete measurements. This deviation in suction values was more evident in accelerated drying and wetting patterns. This can be explained by the fact that water permeability reduces with the decrease in saturation levels.

scholarly journals Evolution of the soil water retention curve based on plastic volumetric strain

2020 ◽  
Vol 195 ◽  
pp. 02016
Author(s):  
J. Kodikara ◽  
C. Jayasundara
Keyword(s):  
Soil Water ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Void Ratio ◽  
Volumetric Strain ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Retention Curve ◽  
Plastic Volumetric Strain

The water retention behaviour of soil can be defined as the relationship between the degree of saturation (or water content) and suction at a constant temperature, which characterises the hydraulic behaviour of unsaturated soils, normally represented as the soil water retention curve (SWRC). The SWRC is commonly measured at nominal net stress by initially saturating a soil specimen and then subjecting it to drying and wetting paths, resulting in major drying and wetting curves. However, there is evidence that during these major drying and wetting paths and initial saturation, soil can undergo volumetric deformation with changes in void ratio, sometimes plastically. Therefore, for coupling the SWRC with mechanical behaviour, the dependency of SWRC on other state variables such as void ratio has been proposed. In this paper, an approach to defining SWRC for a particular plastic volumetric strain is presented within the generalised MPK model. The SWRC evolves as soil is subjected to wet/dry cycles, eventually approaching drying and wetting curves relevant to an environmentally-stabilised state. The performance of this model is demonstrated by the simulation of the loading/unloading/drying/wetting paths followed in a laboratory experiment. In addition, the evolution of the commonly-considered major drying and wetting curves is simulated, highlighting key features of the environmentally-stabilised line..

Experiments and interpretations on unsaturated hydraulic properties using water retention tests based on the membrane in Korea

2020 ◽  
Author(s):  
Seboong Oh ◽  
Sungjin Kim ◽  
Kwang Ik Son
Keyword(s):  
Unsaturated Soils ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Void Ratio ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Huge Amount ◽  
Retention Curve ◽  
Hydraulic Behavior

<p>In unsaturated soils, the soil water retention curve (SWRC) is most important in the fundamental hydraulic properties. In order to measure SWRCs through an alternative method in Korea, high air entry disks were replaced by micro membranes. Micro membranes are thin in which the air entry value is around 100kPa. Tests with the membrane are fast to reduce the duration of infiltration through the high air entry disk.</p><p>The water retention curves using the membrane were compared with the data using high air entry disks from the volumetric pressure plate extractor and Tempe pressure cell for samples of various sites. As a result, the SWRCs using the membrane were very similar for most cases and the micro membrane was verified as a useful tool to measure SWRCs.</p><p>The unsaturated hydraulic behavior could be measured easily using the membrane than ceramic disks and the huge amount of data could have been obtained in Korea. Using DB of SWRCs, the hydraulic properties were interpreted based on the parameters of the van Genuchten SWRC model. The void ratio and density are correlated to SWRCs under the same classification soil.</p><p><strong>Acknowledgements</strong> This research is supported by grant from Korean NRF (2019R1A2C1003604) and MOE (79608), which are greatly appreciated.</p>

scholarly journals Implementation of biocementation for a partially saturated problematic soil of the UK railway network

2020 ◽  
Vol 195 ◽  
pp. 05006
Author(s):  
Muhammad Umair Safdar ◽  
Maria Mavroulidou ◽  
Michael J. Gunn ◽  
Christopher Gray ◽  
Diane Purchase ◽  
...  
Keyword(s):  
Unsaturated Soils ◽  
Water Retention ◽  
Degree Of Saturation ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Railway Network ◽  
Foundation Soil ◽  
The Uk ◽  
Problematic Soil

This paper refers to biocementation of a problematic soil of the UK railway network as a potential stabilisation technique of this soil using indigenous ureolytic bacteria. The soil is peat, a soft foundation soil also subject to oxidation wastage. As the peat is under existing embankments, electrokinetics (EK) is proposed as a promising technique to implement treatments. In the context of unsaturated soils the paper thus focuses on two particular aspects relevant for the implementation of treatments and the stability of this soil, namely: a) the effect of degree of saturation of the peat on the bio-electrokinetic treatment ; b) the soil water retention curve of the soil affecting flow and transport; these are relevant as we focus on understanding and modelling the implementation of treatments through electrokinetics; moreover for the peat it is of importance to understand moisture exchange in the vadose zone and control groundwater table levels (e.g. during electrokinetics) in order to prevent further oxidation. After isolation and screening of indigenous microorgansisms Bacillus licheniformis was selected for further testing. The results in terms of unconfined compressive strength, CaCO3 content, swelling and compression behaviour and water retention proved the feasibility of biocementation using this indigenous microorganism. Ongoing work is assessing the required treated soil characteristics and related required biocementation degree to solve UK rail's peat foundation problems. Upscaling of the techniques towards in situ implementation is also planned in the next stage of the research.

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