scholarly journals A model for hydraulic conductivity of compacted bentonite – inclusion of microstructure effects under confined wetting

Géotechnique ◽  
2020 ◽  
pp. 1-14 ◽  
Author(s):  
Tian Chen ◽  
Majid Sedighi ◽  
Andrey P. Jivkov ◽  
Suresh C. Seetharam
Keyword(s):  
Hydraulic Conductivity ◽  
Compacted Bentonite ◽  
Microstructure Effects

scholarly journals Evolution of Hydraulic Conductivity of Unsaturated Compacted Na-Bentonite under Confined Condition—Including the Microstructure Effects

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 219
Author(s):  
Tian Chen ◽  
Mao Du ◽  
Qiangling Yao
Keyword(s):  
Hydraulic Conductivity ◽  
Network Evolution ◽  
Saturated Hydraulic Conductivity ◽  
Constitutive Relationship ◽  
Pore System ◽  
Compacted Bentonite ◽  
Hydraulic Behaviour ◽  
Unsaturated Hydraulic Conductivity ◽  
Microstructure Effects ◽  
Microstructure Effect

Compacted bentonite is envisaged as engineering buffer/backfill material in geological disposal for high-level radioactive waste. In particular, Na-bentonite is characterised by lower hydraulic conductivity and higher swelling competence and cation exchange capacity, compared with other clays. A solid understanding of the hydraulic behaviour of compacted bentonite remains challenging because of the microstructure expansion of the pore system over the confined wetting path. This work proposed a novel theoretical method of pore system evolution of compacted bentonite based on its stacked microstructure, including the dynamic transfer from micro to macro porosity. Furthermore, the Kozeny–Carman equation was revised to evaluate the saturated hydraulic conductivity of compacted bentonite, taking into account microstructure effects on key hydraulic parameters such as porosity, specific surface area and tortuosity. The results show that the prediction of the revised Kozeny–Carman model falls within the acceptable range of experimental saturated hydraulic conductivity. A new constitutive relationship of relative hydraulic conductivity was also developed by considering both the pore network evolution and suction. The proposed constitutive relationship well reveals that unsaturated hydraulic conductivity undergoes a decrease controlled by microstructure evolution before an increase dominated by dropping the gradient of suction during the wetting path, leading to a U-shaped relationship. The predictive outcomes of the new constitutive relationship show an excellent match with laboratory observation of unsaturated hydraulic conductivity for GMZ and MX80 bentonite over the entire wetting path, while the traditional approach overestimates the hydraulic conductivity without consideration of the microstructure effect.

Influence of Temperature on Hydraulic Conductivity in Compacted Bentonite

1997 ◽  
Vol 506 ◽  
Author(s):  
W. J. Cho ◽  
J. O. Lee ◽  
K. S. Chun
Keyword(s):  
Hydraulic Conductivity ◽  
Influence Of Temperature ◽  
Temperature Range ◽  
Compacted Bentonite ◽  
Influence Of Temperature On ◽  
Water Saturated ◽  
Increasing Temperature ◽  
Good Agreement

ABSTRACTThe hydraulic conductivities in water saturated bentonites at different densities were measured within temperature range of 20 to 80 °C. The results show that the hydraulic conductivities increase with increasing temperature. The hydraulic conductivities of bentonites at the temperature of 80 °C increase up to about 3 times as high as those at 20 °C. The measured values are in good agreement with those predicted. The change in viscosity of water with temperature contributes greatly to increase of hydraulic conductivity.

Influence of alkalinity on the hydraulic conductivity of bentonite-sand liners

1998 ◽  
Vol 38 (2) ◽  
pp. 151-157 ◽  
Author(s):  
David G. Wareham ◽  
Arman Farajollahi ◽  
Mark W. Milke
Keyword(s):  
Hydraulic Conductivity ◽  
Charge Density ◽  
Liquid Limit ◽  
Permeability Test ◽  
Clay Particles ◽  
Sand Mixture ◽  
Compacted Bentonite ◽  
Limit Test ◽  
The Impact

The aim of this research is to record the impact of specific changes in the molding water alkalinity on the hydraulic conductivity of a compacted bentonite-sand mixture. Adding alkalinity to the molding water influences the charge density existing on the clay particles. This can increase the amount of separation of the bentonite particles which causes a decrease in the hydraulic conductivity of the compacted mixture. At the optimum alkalinity the mixture possesses the smallest hydraulic conductivity. In this research an optimum alkalinity (pH=10.1) for a compacted bentonite-sand mixture (7.5% bentonite) was derived from the liquid limit test and the falling-head permeability test.

Laboratory Experiments on the Alteration of Highly-Compacted Bentonite by Alkaline Solution and the Effects on Physical Properties

2011 ◽  
Author(s):  
Satoru Miyoshi ◽  
Shinya Morikami ◽  
Yukinobu Kimura ◽  
Tomoko Jinno ◽  
Shuichi Yamamoto
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Solution ◽  
Sodium Hydroxide Solution ◽  
Mineral Dissolution ◽  
Alkali Solution ◽  
Exchangeable Cation ◽  
High Concentration ◽  
Compacted Bentonite ◽  
Aqueous Silicon ◽  
The Difference

The laboratory experiment was done that 1.0mol/L sodium hydroxide solution was injected to the compacted bentonite whose density is the same as the prospected value in the concept of the intermediate-level disposal in Japan in the circumstance of 70°C temperature. After the injection of the alkali solution for approximately 600 days, the bentonite was taken out of the apparatus and some sorts of analysis were done. The accompanying minerals in the bentonite, calcedony and quartz, were dissolved and disappeared in XRD charts. Then analcime was precipitated as a secondary mineral. Although montmorillonite was dissolved, the mass fraction of it was kept approximately. The hydraulic conductivity of the bentonite calculated using the flow rate at the end of the injection of alkali solution was smaller than the prospected value based on a widely-used empirical model of the hydraulic conductivity of compacted bentonite as a function of the equivalent concentration of pore solution, montmorillonite partial void ratio, and the ratio of sodium ion equivalent to the exchangeable cation equivalent. The reasons for the difference were supposed to be the decrease of pore size brought by mineral dissolution and the large viscosity of pore solution involving high concentration aqueous silicon.

Modeling Hydraulic Conductivity and Swelling Pressure of Several Kinds of Bentonites Affected by Salinity of Water

2010 ◽  
Author(s):  
Yukihisa Tanaka ◽  
Takuma Hasegawa ◽  
Kunihiko Nakamura
Keyword(s):  
Hydraulic Conductivity ◽  
Radioactive Waste ◽  
Ground Water ◽  
Quantitative Evaluation ◽  
Coastal Area ◽  
Evaluation Method ◽  
Saline Water ◽  
Swelling Pressure ◽  
Compacted Bentonite ◽  
Swelling Characteristics

In case of construction of repository for radioactive waste near the coastal area, the effect of salinity of water on hydraulic conductivity as well as swelling pressure of bentonite as an engineered barrier should be considered because it is known that the hydraulic conductivity of bentonite increases and swelling pressure decreases with increasing salinity of water. Though the effect of salinity of water on hydraulic conductivity and swelling pressure of bentonite has been investigated experimentally, it is necessary to elucidate and to model the mechanism of the phenomenon because various kinds of bentonites may possibly be placed in various salinities of ground water. Thus, in this study, a model for evaluating hydraulic conductivity as well as swelling pressure of compacted bentonite is proposed considering the effect of salinity of water as follows: a) Change in number of flakes of a stack of montmorillonite because of cohesion. b) Change in viscosity of water in interlayer between flakes of montmorillonite. Quantitative evaluation method for hydraulic conductivity and swelling characteristics of several kinds of bentonites under saline water is proposed based on the model mentioned above.

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.

Influence of Salinity on The Hydraulic Conductivity of Compacted Bentonite

2002 ◽  
Vol 713 ◽  
Author(s):  
Won-Jin Cho ◽  
Jae-Owan Lee ◽  
Chul-Hyung Kang
Keyword(s):  
Hydraulic Conductivity ◽  
Fresh Water ◽  
Water Solution ◽  
Salinity Range ◽  
Dry Density ◽  
Nacl Solution ◽  
Compacted Bentonite ◽  
Insignificant Effect ◽  
Solution Increase

ABSTRACTThe effect of salinity on hydraulic conductivities of compacted bentonites with various dry densities was studied. The hydraulic conductivities increase with increasing salinity only when the dry density of bentonite is relatively low. The degree of increase becomes more remarkable at a lower dry density of bentonite. For bentonites with densities of 1.0 Mg/m3 and 1.2 Mg/m3, the hydraulic conductivities associated with the 0.4 M NaCl solution increase beyond those associated with the fresh water solution by factor of 7 and 3 times, respectively. However, for the bentonite with dry density higher than 1.4 Mg/m3, the salinity has an insignificant effect on the hydraulic conductivities, and the hydraulic conductivity is nearly constant within the salinity range of 0 to 0.4 M NaCl.

Sign in / Sign up

Export Citation Format

Share Document