Deformation mechanisms and their microstructural indicators in the compaction of crushed salt as a geotechnical barrier

Abstract. Following 30 years of research, it is common sense that crushed salt is the most suitable geotechnical material for encapsulating radioactive waste in a rock salt repository (e.g., Chaikowski et al., 2020). After emplacement, it provides sufficient permeability to allow outflow of unwanted canister-corrosion gases. In the long term, however, when it becomes compacted by converging cavity walls, it safely hinders any fluid flow from and to the waste. Hence, it is essential to know the evolution of (1) the material's key parameters during compaction, such as porosity and permeability, backfill resistance and viscosity; (2) the material's response to environmental controls, such as temperature, humidity, and stress; and (3) the material's long-term rheology. Here we align microstructural deformation indicators with physical processes that underlie compaction (Mills et al., 2018a). We strive to identify and – where feasible – to quantify the dominant deformation mechanisms (Blenkinsop, 2002; Jackson and Hudec, 2017). As a preliminary result, we show that the abundancy of deformation indicators increases with increasing compaction state. In early compaction, we observe more brittle mechanisms, such as grain fracturing (Fig. 1a) and cataclastic flow. At later stages, especially in the presence of moisture, plastic deformation overtakes. Therein, we observe an increased presence of indicators for pressure solution precipitation (grain boundary seams) and dislocation creep (subgrain formation, Fig. 1b), with progressing deformation. In our upcoming work, we aim at linking the observed indicators to environmental controls, such as moisture content, temperature, and strain rate by applying our approach to larger suits of samples compacted under best-known controlled conditions. Final goal is the joint interpretation with findings from in situ-compacted material (Mills et al., 2018b). Do lab tests mimic in situ processes of crushed salt compaction adequately? Can we learn how to do better by means of microstructural investigations?

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Over 30 years of research on crushed salt as a barrier material: fundamental findings and open questions

Safety of Nuclear Waste Disposal ◽

10.5194/sand-1-137-2021 ◽

2021 ◽

Vol 1 ◽

pp. 137-139

Author(s):

Kornelia Zemke ◽

Kristoff Svensson ◽

Ben Laurich ◽

Johanna Lippmann-Pipke

Keyword(s):

Radioactive Waste ◽

Rock Salt ◽

Radioactive Waste Disposal ◽

Test Series ◽

Triaxial Tests ◽

Barrier Material ◽

Environmental Controls ◽

History Of

Abstract. Repositories for high-level radioactive waste in geological formations require knowledge on thermal, mechanical and fluid transport properties of the whole repository system, including the engineered barriers and backfill materials. For about 30 years, crushed salt has been considered the most suitable geotechnical barrier material to backfill cavities and encapsulate radioactive waste in rock salt repository sites (e.g., Czaikowski et al., 2020). Over time, when the surrounding cavity walls converge by the creep of salt, it can become strongly compacted and safely encapsulates radioactive waste from any fluid flow. Hence, crushed salt has been characterized in detail for its physical material properties and its response to environmental controls (stress, temperature and moisture). This characterisation provides a basis for long-term numerical simulations (e.g., Liu et al., 2018), which verify so-called safety cases in radioactive waste disposal. Displacement-controlled oedometric compaction tests mimic the long-term in situ behaviour of crushed salt. The tests show that it can be compacted to a state comprising physical rock properties similar to natural rock salt. In general, compaction is easier with an increase in humidity and temperature (e.g., Stührenberg, 2007; Kröhn, et al., 2017). Triaxial test series address the compactions' response to differing confining pressures and help to identify generalized constitutive equations for crushed salt. Both BGR procedures, the oedometric and the triaxial compaction, are verified by the German accreditation body (DAkkS). Figure 1 illustrates the history of oedometric tests at the BGR laboratory since 1993, which examined crushed salt from various origins and differing temperature conditions. Most tests focused on material from the Asse mine, revealing the compactions' response to the materials' humidity and to brine flow. Moreover, systematic test series with synthetic grain size distributions and bentonite additives provided a basis for barrier material design. More recent tests on bedded salt formations (e.g., Teutschenthal and Sondershausen mines) allow the differentiation from characteristics from domal salt deposits (e.g. Gorleben). The current research continues the history of oedometric and triaxial tests, but has a new focus on late compaction stages with marginal remaining porosities (<5 %). The approach of systematic material characterization under best-controlled conditions essentially benefits from the international research collaboration in the KOMPASS project (Czaikowski et al., 2020). The aim of its current phase two is to synthetically generate, identify and quantify dominant grain-scale deformation processes in response to changes in environmental controls. Subsequently, these laboratory results will be embedded in numerical models on the long-term in situ rheology of crushed salt.

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Global analysis of short- versus long-term drainage basin erosion rates

10.5194/esurf-2021-7 ◽

2021 ◽

Author(s):

Shiuan-An Chen ◽

Katerina Michaelides ◽

Michael Bliss Singer ◽

David A. Richards

Keyword(s):

Suspended Sediment ◽

Global Analysis ◽

Sediment Flux ◽

Anthropogenic Activity ◽

Drainage Basins ◽

Erosion Rates ◽

Environmental Controls ◽

Short And Long Term

Abstract. Measuring erosion rates, analysing their temporal variations, and exploring environmental controls are crucial in the field of geomorphology because erosion through sediment transport in drainage basins shapes landforms and landscapes. Thus, important insights into landscape controls can be gleaned from analyses of erosion rates measured over different timescales. Suspended sediment flux and in situ cosmogenic radionuclides have been widely used for estimating short- and long-term erosion rates of drainage basins, respectively. Even though analyses of erosion rates have been conducted across the globe, there are still gaps in understanding of the links between environmental controls and erosion rates between timescales, especially the influence of climate, which is complex and covaries with other factors. To begin unpicking controls on landscape evolution across the globe, we compiled short- and long-term erosion rates (estimated from suspended sediment yield and in situ beryllium-10, 10Be, respectively) and analysed their relationships with climate, topography, and anthropogenic activity. The results show that: 1) A non-linear relationship exists between aridity and long-term erosion rates, resulting from the balance between precipitation and vegetation cover; 2) Long-term erosion rates are higher in mid- and high-latitude regions with high humidity, reflecting glacial processes during ice ages; 3) Long-term erosion rates are positively related to the steepness of drainage basins, showing that both climate and topography are the common factors; 4) Human activities increase short-term erosion rates which outweigh natural controls; and 5) The ratios of short- to long-term erosion rates are negatively related to basin area, reflecting the buffering capacity of large basins. These results highlight the complex interplay of controlling factors on land surface processes and reinforce the view that timescale of observation reveals different erosion rates and principal controls.

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Global soil moisture data derived through machine learning trained with in-situ measurements

Scientific Data ◽

10.1038/s41597-021-00964-1 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Sungmin O. ◽

Rene Orth

Keyword(s):

Machine Learning ◽

Soil Moisture ◽

Large Scale ◽

Short Term Memory ◽

Temporal Dynamics ◽

Soil Moisture Data ◽

Wide Range ◽

Global Soil

AbstractWhile soil moisture information is essential for a wide range of hydrologic and climate applications, spatially-continuous soil moisture data is only available from satellite observations or model simulations. Here we present a global, long-term dataset of soil moisture derived through machine learning trained with in-situ measurements, SoMo.ml. We train a Long Short-Term Memory (LSTM) model to extrapolate daily soil moisture dynamics in space and in time, based on in-situ data collected from more than 1,000 stations across the globe. SoMo.ml provides multi-layer soil moisture data (0–10 cm, 10–30 cm, and 30–50 cm) at 0.25° spatial and daily temporal resolution over the period 2000–2019. The performance of the resulting dataset is evaluated through cross validation and inter-comparison with existing soil moisture datasets. SoMo.ml performs especially well in terms of temporal dynamics, making it particularly useful for applications requiring time-varying soil moisture, such as anomaly detection and memory analyses. SoMo.ml complements the existing suite of modelled and satellite-based datasets given its distinct derivation, to support large-scale hydrological, meteorological, and ecological analyses.

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A Study of UVER in Santiago, Chile Based on Long-Term In Situ Measurements (Five Years) and Empirical Modelling

Energies ◽

10.3390/en14020368 ◽

2021 ◽

Vol 14 (2) ◽

pp. 368

Author(s):

Lisdelys González-Rodríguez ◽

Amauri Pereira de Oliveira ◽

Lien Rodríguez-López ◽

Jorge Rosas ◽

David Contreras ◽

...

Keyword(s):

Urban Areas ◽

Solar Spectrum ◽

Sun Exposure ◽

Great Accuracy ◽

In Situ Measurements ◽

Uv Index ◽

Empirical Modelling ◽

The People

Ultraviolet radiation is a highly energetic component of the solar spectrum that needs to be monitored because is harmful to life on Earth, especially in areas where the ozone layer has been depleted, like Chile. This work is the first to address the long-term (five-year) behaviour of ultraviolet erythemal radiation (UVER) in Santiago, Chile (33.5° S, 70.7° W, 500 m) using in situ measurements and empirical modelling. Observations indicate that to alert the people on the risks of UVER overexposure, it is necessary to use, in addition to the currently available UV index (UVI), three more erythema indices: standard erythemal doses (SEDs), minimum erythemal doses (MEDs), and sun exposure time (tery). The combination of UVI, SEDs, MEDs, and tery shows that in Santiago, individuals with skin types III and IV are exposed to harmfully high UVER doses for 46% of the time that UVI indicates is safe. Empirical models predicted hourly and daily values UVER in Santiago with great accuracy and can be applied to other Chilean urban areas with similar climate. This research inspires future advances in reconstructing large datasets to analyse the UVER in Central Chile, its trends, and its changes.

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In-Situ Annealed Ti3C2Tx MXene Based All-Solid-State Flexible Zn-Ion Hybrid Micro Supercapacitor Array with Enhanced Stability

Nano-Micro Letters ◽

10.1007/s40820-021-00634-2 ◽

2021 ◽

Vol 13 (1) ◽

Author(s):

La Li ◽

Weijia Liu ◽

Kai Jiang ◽

Di Chen ◽

Fengyu Qu ◽

...

Keyword(s):

High Energy ◽

High Rate ◽

High Energy Density ◽

Electrochemical Performances ◽

Integrated Electronics ◽

Long Term Stability ◽

Hybrid Supercapacitors ◽

Portable Electronics

AbstractZn-ion hybrid supercapacitors (SCs) are considered as promising energy storage owing to their high energy density compared to traditional SCs. How to realize the miniaturization, patterning, and flexibility of the Zn-ion SCs without affecting the electrochemical performances has special meanings for expanding their applications in wearable integrated electronics. Ti3C2Tx cathode with outstanding conductivity, unique lamellar structure and good mechanical flexibility has been demonstrated tremendous potential in the design of Zn-ion SCs, but achieving long cycling stability and high rate stability is still big challenges. Here, we proposed a facile laser writing approach to fabricate patterned Ti3C2Tx-based Zn-ion micro-supercapacitors (MSCs), followed by the in-situ anneal treatment of the assembled MSCs to improve the long-term stability, which exhibits 80% of the capacitance retention even after 50,000 charge/discharge cycles and superior rate stability. The influence of the cathode thickness on the electrochemical performance of the MSCs is also studied. When the thickness reaches 0.851 µm the maximum areal capacitance of 72.02 mF cm−2 at scan rate of 10 mV s−1, which is 1.77 times higher than that with a thickness of 0.329 µm (35.6 mF cm−2). Moreover, the fabricated Ti3C2Tx based Zn-ion MSCs have excellent flexibility, a digital timer can be driven by the single device even under bending state, a flexible LED displayer of “TiC” logo also can be easily lighted by the MSC arrays under twisting, crimping, and winding conditions, demonstrating the scalable fabrication and application of the fabricated MSCs in portable electronics.

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A long-term, gridded, subsurface physical oceanography dataset and average annual cycles derived from in situ measurements off the Western Australia coast during 2009–2020

Data in Brief ◽

10.1016/j.dib.2021.106812 ◽

2021 ◽

Vol 35 ◽

pp. 106812

Author(s):

Miaoju Chen ◽

Ming Feng

Keyword(s):

Western Australia ◽

In Situ Measurements ◽

Physical Oceanography ◽

Annual Cycles

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Poly(ethylene glycol)-b-poly(1,3-trimethylene carbonate) Copolymers for the Formulation of In Situ Forming Depot Long-Acting Injectables

Pharmaceutics ◽

10.3390/pharmaceutics13050605 ◽

2021 ◽

Vol 13 (5) ◽

pp. 605

Author(s):

Marie-Emérentienne Cagnon ◽

Silvio Curia ◽

Juliette Serindoux ◽

Jean-Manuel Cros ◽

Feifei Ng ◽

...

Keyword(s):

Ethylene Glycol ◽

Surface Erosion ◽

Sustained Delivery ◽

Trimethylene Carbonate ◽

Poly Ethylene Glycol ◽

In Situ Forming ◽

Poly Ethylene ◽

Long Acting

This article describes the utilization of (methoxy)poly(ethylene glycol)-b-poly(1,3-trimethylene carbonate) ((m)PEG–PTMC) diblock and triblock copolymers for the formulation of in situ forming depot long-acting injectables by solvent exchange. The results shown in this manuscript demonstrate that it is possible to achieve long-term drug deliveries from suspension formulations prepared with these copolymers, with release durations up to several months in vitro. The utilization of copolymers with different PEG and PTMC molecular weights affords to modulate the release profile and duration. A pharmacokinetic study in rats with meloxicam confirmed the feasibility of achieving at least 28 days of sustained delivery by using this technology while showing good local tolerability in the subcutaneous environment. The characterization of the depots at the end of the in vivo study suggests that the rapid phase exchange upon administration and the surface erosion of the resulting depots are driving the delivery kinetics from suspension formulations. Due to the widely accepted utilization of meloxicam as an analgesic drug for animal care, the results shown in this article are of special interest for the development of veterinary products aiming at a very long-term sustained delivery of this therapeutic molecule.

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In Situ Tests on Creep Behavior of Rock Mass with Joint or Shearing Zone in Foundation of Large-Scale Hydroelectric Projects

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.261-263.1097 ◽

2004 ◽

Vol 261-263 ◽

pp. 1097-1102 ◽

Cited By ~ 2

Author(s):

Jian Liu ◽

Xia Ting Feng ◽

Xiu Li Ding ◽

Huo Ming Zhou

Keyword(s):

Rock Mass ◽

Creep Behavior ◽

Large Scale ◽

Time Dependent ◽

Three Gorges Project ◽

Three Gorges ◽

The Three Gorges ◽

The Three Gorges Project

The time-dependent behavior of rock mass, which is generally governed by joints and shearing zones, is of great significance for engineering design and prediction of long-term deformation and stability. In situ creep test is a more effective method than laboratory test in characterizing the creep behavior of rock mass with joint or shearing zone due to the complexity of field conditions. A series of in situ creep tests on granite with joint at the shiplock area of the Three-Gorges Project and basalt with shearing zone at the right abutment of the Xiluodu Project were performed in this study. Based on the test results, the stress-displacement-time responses of the joints and basalt are analyzed, and their time-dependent constitutive model and model coefficients are given, which is crucial for the design to prevent the creep deformations of rock masses from causing the failure of the operation of the shiplock gate at the Three-Gorges Project and long-term stability of the Xiluodu arc dam.

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