Bentonite homogenisation during the closure of void spaces

Harrington, J.F.; Daniels, Katherine A.; Wiseall, A.C.; Sellin, Patrik

doi:10.1016/j.ijrmms.2020.104535

Cited by 21 publications

(23 citation statements)

References 27 publications

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“…FieldPoint™ and cRIO logging hardware combined with the LabVIEW™ data acquisition software (National Instruments Corporation, Austin, TX, USA) were used to record the total stress, pore pressures and pump flow rates at intervals of 2 min, providing detailed time series information. The total testing duration was 101.7 days, which was long enough to ensure that the swelling response of the clay was observed [47,48].…”

Section: Methodsmentioning

confidence: 99%

“…In addition, half of each sample slice was hand-crushed in a pestle and mortar and half of the crushate was ball-milled to a fine powder for whole-rock X-ray diffraction (XRD) and 2-ethoxyethanol (EGME) surface area analyses. The same set of tests was also run on a sample of MX80 bentonite that had experienced the same experimental history (the Test 4 sample from Harrington et al [47]), to provide a reference for comparison with the Bulgarian Ca bentonite. To provide a finer and uniform particle-size for powder XRD analysis, a 2.7 g portion of each sample was micronised under acetone for 10 min with 10% (0.3 g) corundum (American Elements-PN:AL-OY-03-P).…”

Section: Samplementioning

confidence: 99%

“…Errors for the surface area values are ±3%. The Bulgarian Ca bentonite sample data were compared against the same set of analyses conducted on the sliced sample of MX80 bentonite used in Test 4 presented in Harrington et al [47]. This sample was analysed for comparison because it was manufactured to the same sample size and dry density, had undergone the same experimental procedure and was removed from the test vessel and dried in the same manner as the Bulgarian Ca bentonite sample.…”

Section: Samplementioning

confidence: 99%

“…There was as much as 15 days difference in the arrival times, observed as a change in the recorded pore pressure (Figure 1). An overview of the swelling and pore pressure data is also available from Harrington et al [47], where the swelling and pore pressure data from this test have been compared to tests conducted using a different composition of bentonite and in a vertical orientation.…”

Section: Development Of Swelling and Pore Pressurementioning

confidence: 99%

“…Studies have looked at the material behaviour at ambient and elevated temperatures, examining the swelling capacity [9][10][11]34] and swelling (or suction) pressure, both at steady-state and over time [33,[35][36][37][38][39][40][41][42][43][44][45][46][47][48]. The most recent studies [47,48] have investigated the development and evolution of swelling pressure within the barrier, looking at a case where the void space is nearly equivalent in size to that of the clay material. These large void spaces are especially likely to occur at the edges of the engineered barrier [33], where the availability of water is also likely to be high as it migrates away from the waste canister and heat source (e.g., [49]).…”

Section: Introductionmentioning

confidence: 99%

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Gel Formation at the Front of Expanding Calcium Bentonites

et al. 2021

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The removal of potentially harmful radioactive waste from the anthroposphere will require disposal in geological repositories, the designs of which often favour the inclusion of a clay backfill or engineered barrier around the waste. Bentonite is often proposed as this engineered barrier and understanding its long-term performance and behaviour is vital in establishing the safety case for its usage. There are many different compositions of bentonite that exist and much research has focussed on the properties and behaviour of both sodium (Na) and calcium (Ca) bentonites. This study focusses on the results of a swelling test on Bulgarian Ca bentonite that showed an unusual gel formation at the expanding front, unobserved in previous tests of this type using the sodium bentonite MX80. The Bulgarian Ca bentonite was able to swell to completely fill an internal void space over the duration of the test, with a thin gel layer present on one end of the sample. The properties of the gel, along with the rest of the bulk sample, have been investigated using ESEM, EXDA and XRD analyses and the formation mechanism has been attributed to the migration of nanoparticulate smectite through a more silica-rich matrix of the bentonite substrate. The migration of smectite clay out of the bulk of the sample has important implications for bentonite erosion where this engineered barrier interacts with flowing groundwater in repository host rocks.

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Section: Methodsmentioning

confidence: 99%

Section: Samplementioning

confidence: 99%

Section: Samplementioning

confidence: 99%

Section: Development Of Swelling and Pore Pressurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Gel Formation at the Front of Expanding Calcium Bentonites

et al. 2021

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Heterogeneous Swelling of an Isotropically Compacted Bentonite-Based Material: Experimental Observations and Modelling

et al. 2023

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This paper presents a comprehensive investigation of the swelling behaviour of a compacted bentonite–sand mixture subjected to hydration under constant volume conditions. Contrary to previous studies, the tested sample was isotropically compacted before being hydrated under constant volume conditions until full saturation was reached. The total axial pressure, total radial pressures at four different heights of the sample, and injected water volume were recorded over time. The experimental data reveal a complex and non-uniform evolution of the axial and radial stresses over time, as well as anisotropy of the total stresses, which persist at the saturated equilibrated state. To gain further insights, a numerical analysis was performed using an advanced hydromechanical framework for partially saturated porous media, accounting for the evolving microstructure of the material. The complex evolution of the total axial and radial pressures with time is attributed to the advancing hydration and swelling front in the sample, along with the development of irreversible strains. The good agreement between the numerical results and the experimental data enables validation of the developed framework. Implications for engineered barriers in deep geological disposal of radioactive waste are discussed.

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