scholarly journals Desiccation-Induced Volumetric Shrinkage of Compacted Metakaolin-Treated Black Cotton Soil for a Hydraulic Barriers System

2016 ◽  
Vol 24 (1) ◽  
pp. 1-5 ◽  
Author(s):  
George Moses ◽  
Oriola F. O. Peter ◽  
Kolawole J. Osinubi
Keyword(s):  
Shrinkage Strain ◽  
West African ◽  
Degree Of Saturation ◽  
Volumetric Shrinkage ◽  
Black Cotton Soil ◽  
Waste Containment ◽  
Intermediate Energies ◽  
Volumetric Shrinkage Strain ◽  
Water Contents ◽  
Hydraulic Barriers

AbstractBlack cotton soil treated with up to 24% metakaolin (MCL) content was prepared by molding water contents of −2, 0, 2, 4 and 6% of optimum moisture content (OMC) and compacted with British Standard Light (BSL) and West African Standard (WAS) or ‘Intermediate’ energies. The specimens were extruded from the compaction molds and allowed to air dry in a laboratory in order to assess the effect of desiccation-induced shrinkage on the compacted mix for use as a hydraulic barrier in a waste containment application. The results recorded show that the volumetric shrinkage strain (VSS) values were large within the first 10 days of drying; the VSS values increased with a higher molding of the water content, relative to the OMC. The VSS generally increased with a higher initial degree of saturation for the two compactive efforts, irrespective of the level of MCL treatment. Generally, the VSS decreased with an increasing MCL content. Only specimens treated with a minimum 20% MCL content and compacted with the WAS energy satisfied the regulatory maximum VSS of 4% for use as a hydraulic barrier.

scholarly journals Experimental study on the influence of preliminary desiccation on the swelling pressure and hydraulic conductivity of compacted bentonite

Clay Minerals ◽  
2018 ◽  
Vol 53 (4) ◽  
pp. 733-744 ◽  
Author(s):  
Lin Zhi Lang ◽  
Wiebke Baille ◽  
Snehasis Tripathy ◽  
Tom Schanz
Keyword(s):  
Hydraulic Conductivity ◽  
Swelling Pressure ◽  
Shrinkage Strain ◽  
Volumetric Shrinkage ◽  
Barrier Materials ◽  
Compacted Bentonite ◽  
Swelling Capacity ◽  
Pressure Tests ◽  
Volumetric Shrinkage Strain ◽  
Volume Swelling

ABSTRACTIn deep geological repositories, compacted bentonites have been proposed for use as barrier materials for isolating nuclear waste. The prevailing thermo-hydro-mechanical boundary conditions in the repositories may affect the swelling capacity and permeability of the compacted bentonites. In this study, the effect of preliminary desiccation on the subsequent hydro-mechanical behaviour (swelling pressure and hydraulic conductivity) of compacted Calcigel bentonite was investigated experimentally at 22°C and 80°C. In the first stage of the test, the compacted specimens were subjected to suction-controlled desiccation at 22°C and 80°C using the vapour-equilibrium technique. After the water content reached equilibrium at a given suction, the axial, radial and volumetric shrinkage strains were measured. Afterwards, constant-volume swelling-pressure tests were performed on the desiccated specimens (second test stage) by saturating the dried specimens with deionized water at 22°C and 80°C. At the end of the swelling-pressure test, the hydraulic conductivities of four saturated specimens were measured at each temperature. The volumetric shrinkage strain of the compacted bentonite during desiccation is controlled by suction instead of temperature. In addition, the preliminary desiccation increases both the swelling pressure and hydraulic conductivity of compacted bentonite, particularly if compacted bentonite undergoes extreme desiccation at an applied suction of >700 MPa.

Desiccation Induced Shrinkage of Compacted Lateritic Soil Treated via Enzymatic Induced Calcium Carbonate Precipitation Technique

2021 ◽  
Vol 1030 ◽  
pp. 110-123
Author(s):  
Muttaqa Uba Zango ◽  
Khairul Anuar Kassim ◽  
Abubakar Sadiq Muhammed ◽  
Kamarudin Ahmad ◽  
Jodin Makinda
Keyword(s):  
Calcium Carbonate ◽  
Shrinkage Strain ◽  
Engineering Properties ◽  
Volumetric Shrinkage ◽  
Natural Soil ◽  
Residual Soil ◽  
Carbonate Precipitation ◽  
Calcium Carbonate Precipitation ◽  
British Standard ◽  
Volumetric Shrinkage Strain

Exploring the biological process to enhance the engineering properties of soil have received enormous recognition in recent years. Enzymatic induced calcium carbonate precipitation (EICP) is one of the bio-inspired methods of utilizing free urease to precipitates calcite from urea and calcium ions for bettering the geotechnical properties of poor soils. In this research, the EICP technique was used to improve the volumetric shrinkage strain of compacted soil liner. In this work, the residual soil was treated with various concentrations of cementations ranging from 0.25 to 1.0 M, and the soil was subjected to Atterberg limit tests, compaction test using British standard light (BSL) and reduced British standard light (RBSL) and desiccation drying volumetric shrinkage strain test. The study's findings revealed a remarkable improvement in the liquid limit and plasticity index of the treated residual soils compared to natural soil. It was also found that the volumetric shrinkage strain of the treated soil reduces progressively from 5.24% of natural to 1.49% at 1.0 M cementation solution when the soils were prepared at 0% OMC and BSL compaction effort. Based on the consideration of permissible VSS of less than 4%, the best treatment was obtained at 1.0 M for both BSL and RBSL prepared samples. Similarly, the best compaction plane is found in the treated with 1.0 M cementation solution.

Influence of clod size and water content on gas permeability of a compacted loess

2014 ◽  
Vol 51 (12) ◽  
pp. 1468-1474 ◽  
Author(s):  
T.L.T. Zhan ◽  
Y.B. Yang ◽  
R. Chen ◽  
C.W.W. Ng ◽  
Y.M. Chen
Keyword(s):  
Water Content ◽  
Power Function ◽  
Soil Structure ◽  
Gas Permeability ◽  
High Water ◽  
Degree Of Saturation ◽  
Northwestern Region ◽  
Water Contents ◽  
Compacted Loess ◽  
Compaction Degree

The northwestern region of China is mainly semi-arid to arid and loess is ubiquitous. This natural resource has considerable potential to be transformed into earthen final covers for local landfills, but first its suitability must be ascertained through extensive tests. In this study, a device was developed to measure the gas permeability of unsaturated compacted loess specimens. Experiments were carried out to investigate the influence of clod size, compaction water content, and post-compaction water content on the gas permeability of the compacted loess. To maintain an identical soil structure, the post-compaction water content was changed using the osmotic technique. It was found that the compaction water content and resultant soil clod size exerted a combined effect on the gas permeability such that, at low water contents, the gas permeability remained fairly constant, but at high water contents the clods became relatively large, and the effect of the clod size dominated the water blockage effect from increasing water content. For specimens with identical soil structure, the gas permeability decreased with the increasing post-compaction degree of saturation at an accelerated rate. A power function is proposed to predict the relationship between the gas permeability normalized by the porosity function of the Kozeny–Carmen model and the post-compaction degree of saturation. Analysis of the experimental data indicates that the parameters for the power function still depend on the porosity of the compacted loess, particularly at high degrees of saturation.

The influence of degree of saturation on the coefficient of aqueous diffusion

1998 ◽  
Vol 35 (5) ◽  
pp. 811-827 ◽  
Author(s):  
P C Lim ◽  
S L Barbour ◽  
D G Fredlund
Keyword(s):  
Diffusion Coefficient ◽  
Effective Diffusion ◽  
Theoretical Models ◽  
Chloride Ions ◽  
Model Verification ◽  
Degree Of Saturation ◽  
Best Fit ◽  
Coefficient Of Diffusion ◽  
Water Contents

The role of degree of saturation on the coefficient of diffusion of contaminants in the aqueous phase is presented and theoretical models for predicting the coefficient of diffusion at any degree of saturation are described. Three predictive models were developed based on three different diffusion modes: diffusion in parallel and series arrangements and combination of both. Diffusion tests were conducted on a sand at various water contents ranging from saturation to the residual degree of saturation using potassium and chloride ions as tracers to verify the applicability of the models. Results from the diffusion tests showed a decrease in effective diffusion coefficient of potassium with a decrease in degree of saturation. The functional relationship between the normalized diffusion coefficient for potassium and the degree of saturation is slightly nonlinear. The results for chloride also showed a decreasing trend, although the data were quite scattered and further verification is needed. Model verification based on the results for potassium showed that among the three models proposed, the model which combines the diffusion pathways in parallel and series arrangements provides the best fit to the experimental data.Key words: unsaturated, contaminant transport, aqueous diffusion, degree of saturation.

scholarly journals Modelling evaporation processes of cement-bentonite mixtures

2020 ◽  
Vol 195 ◽  
pp. 02029
Author(s):  
Vincenzo Sergio Vespo ◽  
Gabriele Della Vecchia ◽  
Guido Musso
Keyword(s):  
Water Vapour ◽  
Liquid Water ◽  
Coupled Model ◽  
Degree Of Saturation ◽  
Physical Processes ◽  
Coupled Process ◽  
Model Predictions ◽  
Real Scale ◽  
Water Contents ◽  
Good Agreement

Upon drying, matter and energy are exchanged between the atmosphere and porous media through evaporation, which is a coupled process that involves the simultaneous transport of liquid water, water vapour and heat. At shallow depths, evaporation controls the water content and suction of both natural soils and earthworks, affecting their hydraulic response. This impact is particularly relevant when the earthworks are aimed at the containment of aqueous or non-aqueous pollutants, as in the case of cement bentonite cut-off walls. A coupled model for the transport of liquid water, water vapour and heat through cement bentonite mixtures upon evaporation was formulated. The model considers flow of water driven by both total suction and temperature gradients. Model predictions were compared to experimental results obtained in the laboratory on samples having different sizes and imposed boundary conditions. A good agreement between predicted and measured volumetric water contents was obtained, once defined a suitable dependency of the relative permeability of the mixture on degree of saturation. The results suggest that the proposed formulation correctly accounts for the underlying physical processes, and that it might be used to model the real scale behaviour of cut-off walls.

scholarly journals Mixed formulation for an easy and robust numerical computation of sorptivity

2021 ◽  
Author(s):  
Laurent Lassabatere ◽  
Pierre-Emmanuel Peyneau ◽  
Deniz Yilmaz ◽  
Joseph Pollacco ◽  
Jesús Fernández-Gálvez ◽  
...  
Keyword(s):  
Soil Water ◽  
Water Pressure ◽  
Pressure Head ◽  
Mixed Formulation ◽  
Water Infiltration ◽  
Degree Of Saturation ◽  
Soil Water Retention ◽  
Initial Water ◽  
Hydraulic Diffusivity ◽  
Water Contents

Abstract. Sorptivity is one of the most important parameters for the quantification of water infiltration into soils. Parlange (1975) proposed a specific formulation to derive sorptivity as a function of the soil water retention and hydraulic conductivity functions, as well as initial and final soil water contents. However, this formulation requires the integration of a function involving the hydraulic diffusivity, which may be undefined or present numerical difficulties that cause numerical misestimations. In this study, we propose a mixed formulation that scales sorptivity and splits the integrals into two parts: the first term involves the scaled degree of saturation while the second involves the scaled water pressure head. The new mixed formulation is shown to be robust and well-suited to any type of hydraulic functions - even with infinite hydraulic diffusivity or positive air-entry water pressure heads - and any boundary condition, including infinite initial water pressure head, h → −∞.

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