Crushed Salt Research Articles

Laboratory tests and analysis of mathematical models of deformation of crushed salt rocks

Relevance of the work. For a qualitative prediction of the stress-strain state of host rock massifs during the development of potash and salt mines with chamber-pillar mining systems with the backfilling of the excavated space, as well as in other cases of the use of crushed salts as the backfilling masses, it is necessary to take into account the influence of the backfill massive, which determines the relevance of the study devoted to the laboratory tests and analysis of mathematical models of deformation of crushed salt rocks, which usually represent the backfilling massifs used in these cases. The purpose of the work is to analyze situation in the field of mathematical and numerical modeling of deformation of crushed salt rock and investigation of mechanical response of crushed salt rock under hydrostatic conditions. Methods. As the main method of theoretical research, the analysis of modern sources of information related to the subject of the study was used. Laboratory tests were carried out using a standard set of sieves and universal test machine MTS 815. Results. The paper considers the following deformation models used to describe the mechanical response of crushed salt rocks, as well as examples of their use: the Mohr-Coulomb model, the model of double plastic hardening, the S. A. Konstantinova model, the S. Olivella and A. Gens model, and the WIPP Salt model. As part of laboratory studies, data were obtained on the material size modulus, as well as the dependence of the medium pressure on volumetric deformations and volumetric deformations on time, in addition, creep rates for the studied material were obtained at various levels of average stresses under hydrostatic compression conditions. Conclusions. It is proposed to carry out further development of models of crushed salt rocks for mining conditions based on the description of plastic flow surfaces with a hardening/softening area obtained as a result of extensive laboratory and field surveys.

Compaction of crushed salt for safe containment – a summary of the KOMPASS projects

Abstract. For the underground disposal of high-level nuclear waste in rock salt formations, the safety concept includes the backfilling of open cavities with crushed salt. For the prognosis of the sealing function of the backfill for the safe containment of the radioactive waste, it is crucial to have a comprehensive process understanding of the crushed-salt compaction behavior. The crushed-salt compaction process is influenced by internal properties (e.g., grain size, mineralogy, and moisture content) and boundary conditions (e.g., temperature, stress state, and compaction rate) and, therefore, involves several coupled thermal–hydro–mechanical (THM) processes (Hansen et al., 2014; Kröhn et al., 2017). With the paradigm shift from the limited release of radionuclides to safe containment due to the German Repository Site Selection Act passed in 2017, the importance of crushed salt as geotechnical barrier has increased, with a focus on the evolution of its hydraulic properties. Based on the knowledge gaps in the current process understanding, the “Compaction of crushed salt for safe containment” (KOMPASS) projects were initiated to improve the scientific basis behind using crushed salt for the long-term isolation of high-level nuclear waste within rock salt repositories. The efforts to improve the prediction of crushed-salt compaction begun during the first phase of the KOMPASS projects (Czaikowski et al., 2020) and were followed up in a second phase ending in June 2023. The primary achievements of the projects are as follows (Czaikowski et al., 2020; Friedenberg et al., 2022): specification of the KOMPASS reference material, an easily available and reproducible synthetic crushed-salt material, for generic investigations; development of pre-compaction methods and successful production of samples in the short term and under in situ loading conditions; formulation of an extended laboratory program addressing the isolated investigation of known relevant factors influencing the compaction behavior of crushed salt (Düsterloh et al., 2022); execution of long-term compaction tests addressing isotropic and deviatoric load changes, temperature, and compaction state; construction of a backfill body using the KOMPASS reference material in the Sondershausen mine through collaboration with the SAVER (Entwicklung eines salzgrusbasierten Versatzkonzepts unter der Option Rückholbarkeit) project (Schaarschmidt and Friedenberg, 2022); advancement of the tools for microstructure investigation methods (Svensson and Laurich, 2022); generation (first stages) of a microphysical process list combining literature research with our own findings; benchmarking of long-term compaction test for model development and optimization of various existing models as well as the development of new models; application of a virtual demonstrator (2D model representing a backfilled drift in rock salt) for the visualization of developments and the quantification of the models (Rabbel, 2022). In summary, the KOMPASS projects contributed to the reduction of uncertainties and the strengthening of the safety case for using crushed salt within rock salt repositories.

Compaction of crushed salt for safe containment – overview of the KOMPASS project

Abstract. In Germany, rock salt formations are possible host rock candidates for a repository for heat-emitting radioactive waste. The safety concept of a repository in salt bases on a multibarrier system consisting mainly of the geological barrier salt and geotechnical seals ensuring safe containment. Crushed salt will be used for backfilling of cavities and sealing measures in drifts and shafts due to its favourable properties and its easy availability (mined-off material). The creep of the rock salt leads to crushed salt compaction with time. Thereby, the crushed salts' porosity is reduced from the initial porosity of 30 %–40 % to a value comparable to the porosity of undisturbed rock salt (≤1 %). In such low porosity ranges, technical impermeability is assumed. The compaction behaviour of crushed salt is rather complex and involves several coupled THM processes (Kröhn et al., 2017; Hansen et al., 2014). It is influenced by internal properties like humidity and grain size distribution, as well as boundary conditions such as temperature, compaction rate or stress state. However, the current process understanding has some important gaps referring to the material behaviour, experimental database and numerical modelling. It needs to be extended and validated, especially in the low porosity range. The objective of the KOMPASS project was development of methods and strategies for the reduction of deficits in the prediction of crushed salt compaction leading to an improvement of the prognosis quality. Key results are as follows (KOMPASS Phase 1, 2020): selection of an easily available and permanently producible synthetic crushed salt mixture, acting as a reference material for generic investigations; development and proof of different techniques for producing pre-compacted samples for further investigations; establishment of a tool of microstructure investigation methods to demonstrate the comparability of grain structures of pre-compacted samples with in-situ compacted material for future investigations; execution of various laboratory experiments using pre-compacted samples, e.g. long-term creep tests which deliver reliable information about time- and stress-dependent compaction behaviour; development of a complex experimental investigation strategy to derive necessary model parameters considering individual functional dependencies. Its technical feasibility was successfully verified; benchmarking with various existing numerical models using datasets from three different triaxial long-term tests. The result was not entirely satisfactory; however, the number of influencing factors is small and further validation work has to be done. Overall, the KOMPASS project has made significant progress in the approaches to solving the outstanding question, building the basis for further investigations.

Methodology of structured development and validation of multiphysical constitutive models using the example of crushed salt compaction under 3D THM load conditions

Abstract. The conceptual plans for the final underground disposal of radioactive waste in rock salt formations are based on extensive backfilling with crushed salt of the residual cavities left after waste deposition. It is therefore of particular importance for the historical and prognostic analysis of the load-bearing behavior and impermeability of a final repository in rock salt to demonstrate that compaction of the crushed salt backfill, which progresses over time, is suitable to seal the breaches in the geological barrier created during the underground excavation of the cavity in the long term such that safe containment of the waste is ensured. Relevant investigations on the thermal-hydraulic-mechanical (THM) behavior of crushed salt revealed that the constitutive models for the description of crushed salt compaction, which have regularly been based on the evaluation of oedometer tests, are not suitable for a sufficiently realistic representation of the essentially three-dimensional stress-strain behavior of crushed salt depending on the external load in space and time. Evidence for the above statement lies in particular in the fact that even when standardized mixtures of crushed salt are used, a computational reanalysis of compaction tests using a standardized set of parameters has hitherto been unsuccessful when different loading scenarios were specified for these laboratory tests. This means that deformations and porosities measured in the context of one individual laboratory tests can currently only be reanalyzed in sufficient quantity, irrespective of the choice of constitutive model, if the model parameters are determined in relation to this test. As a result, it must be stated that, on the one hand, the compaction behavior of crushed salt in space and time is not yet definitively understood, while, on the other hand, to ensure reliable, robust and sufficiently realistic statements to be made on compaction behavior, and thus to prove the safe containment of radioactive waste in rock salt, the availability of extensive systematically and sufficiently validated constitutive models is indispensable. This presentation introduces a methodological approach for the systematic and structured development and validation of multiphysical constitutive models, an approach that has meanwhile been successfully tested many times. The practical application of this methodology will be presented here using the example of a constitutive model that takes into account the triaxial stress-strain behavior of crushed salt. The individual development and validation steps are documented for the crushed salt model, EXPO-COM, newly developed at the Chair for Waste Disposal Technologies and Geomechanics. Validation of the constitutive model is performed by means of a back-analysis of triaxial long-term crushed salt compaction tests as follows: Test TK-031 of the German Federal Institute for Geosciences and Natural Resources (Bundesanstalt für Geowissenschaften und Rohstoffe, BGR) for isotropic load conditions Tests V1 (dry), V2 (w=0.1 %), and V3 (wet) of the German Society for Plant and Reactor Safety (Gesellschaft für Anlagen- und Reaktorsicherheit gGmbH, GRS) for different stresses and temperature levels as well as humidity Test TUC_V2 of the Clausthal University of Technology (TUC) for isotropic and deviatoric stress conditions. The TUC_V2 test characterizes, in the context of the methodology for the structured development and validation of multiphysical constitutive models, an innovative test method geared towards constitutive model development, in which the loading boundary conditions specified in the test guarantee the isolated analysis of individual factors influencing compaction behavior (Fig. 1). A description of the tests and test techniques that are still required for the full development and validation of the EXPO-COM constitutive model planned as part of the KOMPASS II research project is given together with a description of methodological guidelines relating to requirements on reliability, functionality, practicability, and validity ranges of the EXPO-COM constitutive model (Fig. 2). As a result of the subsequently possible comparison of experimentally validated and not yet validated dependencies or process variables, a validation status is defined for the constitutive model EXPO-COM. This validation status shows which factors influencing the THM-coupled material behavior of crushed salt are currently sufficiently realistically taken into account, and which influencing factors cannot yet be validated by the constitutive model. The main objectives of the tests to be carried out as part of the KOMPASS II research project include: Continued validation based on the systematized database to be created in KOMPASS II. Testing of the constitutive model in the context of numerical analyses of the predictive quality and numerical stability of the constitutive model for in situ relevant stress boundary conditions, prediction times and material properties.

The challenge in measuring low-permeability materials: a comparison of different approaches

Abstract. The German repository site selection procedure calls for a radioactive waste containment zone with a low-permeability host rock (kf<10-10 m s−1, StandAG §23, 5) and long-term sealing by barrier materials (EndlSiAnfV, 2020; ESK, 2019). The potential host rocks, clay and rock salt, as well as the considered barrier materials, bentonite and compacted crushed salt, show permeability in the range of kf∼10-16 m s−1 (K∼10-21 m2). These low values suggest that advective flow is as slow as diffusive mass flux. Measuring such low permeability with adequate accuracy challenges measurement setups and respective error evaluation. Methodologies. Several low-permeability measurements are carried out by transient tests, e.g. by monitoring controlled fluid pressure changes in: (1) pressure decay and (2) oscillating pulse tests. The first method (1) deviates permeability from the time needed to compensate pressure differences through the sample. The latter (2) monitors phase shift and amplitude attenuation of controlled pressure pulses passing through the sample. Any permeability measurement needs to be post-processed, e.g. for: (1) material-intrinsic controls (saturation state, storativity, the fluids' compressibility, etc.), (2) environmental controls (temperature, confining pressures, etc.) and (3) theoretical considerations (Klinkenberg correction, multi-phase wetting angles, etc.). Salts. A porosity-permeability relation was found down to K=10-19 m2 (e.g., Popp et al., 2007). Testing fluids were NaCl brine, oils, He and N2 as a fluid. As a matter of current research, a critical, low-permeability value might be associated with the so-called “percolation threshold” that defines the minimal requirements for an interconnected pore system (e.g., DAEF, 2016). Clays. A major challenge is the long duration of sample saturation (up to several months) and pressure equilibration (often days), as well as precise, temperature-compensated measuring and the determination of the samples' storativity (e.g., Winhausen et al., 2021). Testing fluids are commonly designed mixtures mimicking the rocks' pore waters. Geotechnical barrier materials. The permeability testing performed is similar to that of salt and clays mentioned above. However, both barrier materials, crushed salt and bentonite, have significant permeability early after emplacement. This is beneficial, as it allows the outflow of unwanted canister corrosion gases. Eventually, the permeability drops by orders of magnitude and the barriers become tight seals in the long-term. Here, identifying the gas entry/breakthrough pressure has been valuable (e.g., Rothfuchs et al., 2007). Figure 1 shows a preliminary sensitivity analysis as an example of pressure decay measurements. It suggests that the pressure equilibration term (c), and hence the test duration, is most sensitive to the calculation of low permeability. However, the large variation of (representative) material and environmental controls make permeability measurements complex. This workshop aims to encourage discussions on uncertainty and sensitivity of the influencing controls, such that it may lead to a “best-practice” guide for permeability measurements.

Influence of crushed maize and soybean cake on the growth of crossbred female calves

The present research work was conducted to develop a balanced ration for crossbred high yielding calves in farm condition. For this purpose, seventy days long feeding trial was conducted with nine crossbred female calves having nearly similar body weight and age. Nine crossbred calves were equally divided into three groups such as T1 (1 kg concentrate mixture of crushed maize, wheat bran, mustard oil cake, molasses, DCP and salt at a ratio of 25:45:22:5:1:2, respectively), T2 (1 kg concentrate mixture of crushed maize, wheat bran, soybean cake, molasses, DCP and salt at a ratio of 27:45:20:5:1:2, respectively) and T3 (Wheat bran, rice polish, mustard oil cake, DCP, Salt were supplied according to BAU routine farm feeding at a ratio of 65:18:14:1:2, respectively). All calves were supplied with ad libitum green grasses (German and Para) and fresh clean drinking water. From the research finding, it was observed that the average total dry matter intake, total body weight gain, body length gain and heart girth gain were in T1 (2.68a±0.000 kg, 2.51a±0.21 kg, 1.83a±0.12 cm, 1.29a±0.07 cm, respectively) and T2 (2.65a±0.001 kg, 2.55a±0.21 kg, 1.67a±0.12 cm, 1.25a±0.07 cm, respectively) groups significantly (p<0.05) higher than that of the T3 (2.34b±0.002 kg, 0.96b±0.21 kg, 0.81b±0.12 cm, 0.64b±0.07 cm, respectively) group. The result showed that the body weight gain of T2 group was higher by supplementation of balanced ration. Therefore, the feed supplementation of crushed maize, wheat bran, soybean cake, molasses, DCP and salt at a ratio of 27:45:20:5:1:2, respectively should be supplied to crossbred calves for the future development of dairy herd replacement stock for profitable dairy business.
 Asian J. Med. Biol. Res. September 2020, 6(3): 499-506

A study on estimate of Iodine Deficiency Disorders and adequacy of Iodized Salt Consumption in Begusarai district of Bihar, India

Background: Iodine Deficiency Disorder is major public health problem causing increased perinatal mortality, mental retardation and goiter and all these morbidities are preventable. Most effective and inexpensive mode to prevent IDD is consumption of iodized salt. Objectives: To estimate the proportion of households using adequately iodized salt in Begusarai district, to assess the knowledge of households on consumption and storage of salt and to estimate Total Goitre Rate (TGR). Material and Methods: Community- based cross sectional study carried out on 412 household from 30 cluster in Begusarai district using cluster sampling technique. Children (6-12 years) were examined clinically for goitre status and sample of household salt was collected for testing iodine content. Iodine content estimation was done both quantitatively by titration and qualitatively by MBI kit. Statistical analysis was performed using SPSS version 22. Result: The respondents were mainly female (92.8%) of mean age 34 years. Three- fifth (61.6%) participants used packaged crushed salt for cooking purpose, followed by packaged crystal (30.5%). Only 12.1 % of the respondents gave affirmative answer for presence of label and logo. Storage of salt in container with lid was 78.5%. The proportion of household using adequately iodized salt was 78%. The sensitivity MBI kit was 61% and the Total goiter rate was 9.3%. Conclusion: The Begusarai district falls in mild public health problem for IDD as TGR is more than 5% and even after many decades of effort towards achieving an adequately salt iodization of more than 90%, it is 79% only.

Coupled Processes Modeling in Rock Salt and Crushed Salt Including Halite Solubility Constraints: Application to Disposal of Heat-Generating Nuclear Waste

This paper presents numerical modeling of coupled thermal, hydraulic and mechanical processes in rock salt and crushed salt considering halite solubility constraints. The TOUGH-FLAC simulator is used, with a recently enhanced Equation-Of-State module that includes the thermodynamic properties of aqueous fluids of variable salinity. Laboratory and field scale tests performed on rock salt and crushed salt under temperature gradients are modeled first to evaluate the capabilities of the simulator to reproduce important features, such as porosity changes induced by halite dissolution/precipitation, and brine and heat migration. Since the results are quite satisfactory, the simulator is used to predict the long-term response of a generic salt repository for heat-generating nuclear waste. To evaluate the impacts of halite solubility on the predictions, two simulations that respectively consider or neglect solubility constraints are performed. In the scenario studied, the results are not significantly affected by dissolution/precipitation, and only some differences are observed due to changes in porosity, but the dominating processes remain the same. With the new provisions, TOUGH-FLAC is more complete in terms of processes occurring around a heat-releasing nuclear waste package and can therefore provide more accurate predictions of the long-term performance of a nuclear waste repository in salt formations.

An adaptation for exhaled breath condensate collection in rabbits

ABSTRACTAim: To set up and test the feasibility of a handmade apparatus adapted for exhaled breath condensate (EBC) collection in medium-sized animals. Materials and Methods: The apparatus was produced using an 18-mm thick u-shaped borosilicate glass. The u-shaped tube body is 25 cm in diameter, and the horizontal portions are 12 cm in diameter. The base consists of a tube joint 14/20 or 14 mm thick by 20 cm in diameter, and has a length of 5 cm. This has a hole that is plugged for condensate flow to a 1.5 mL polypropylene microtube that stores the condensate during collection. Was placed inside a styrofoam box and immersed in crushed ice and salt to ensure cooling. The temperature was monitored and maintained throughout the collection at −10°C. One of the outputs of the u-shaped tube was connected to the expiratory limb of the ventilator. Results: An experimental model of ALI, induced by oleic acid (OA) was adopted to determine the concentration of biomarkers of oxidative stress: malondialdehyde (MDA), glutathione (GSH), and nitrite/nitrate (NOx). The proposed model allows measurement of NOx, MDA, and GSH. However, the NOx and MDA levels in the EBC were not significant. It was only possible to observe an upward trend, which suggests a temporal evolution of the presence of these markers in the EBC. Conclusion: The EBC collection method adapted is effective to generate sufficient content that allows to determine the levels of different biomarkers, such as NOx, MDA, and GSH, that are involved in oxidative and inflammatory stress processes during respiratory diseases.

Experimental determination of single-crystal halite thermal conductivity, diffusivity and specific heat from −75 °C to 300 °C

The thermal properties of halite have broad practical importance, from design and long-term modeling of nuclear waste repositories to analysis and performance assessment of underground natural gas, petroleum and air storage facilities. Using a computer-controlled transient plane source method, single-crystal halite thermal conductivity, thermal diffusivity and specific heat were measured from -75°C to 300°C. These measurements reproduce historical high-temperature experiments and extend the lower temperature extreme into cryogenic conditions. Measurements were taken in 25-degree increments from -75°C to 300°C. Over this temperature range, thermal conductivity decreases by a factor of 3.7, from 9.975 to 2.699 W/mK , and thermal diffusivity decreases by a factor of 3.6, from 5.032 to 1.396 mm²/s. Specific heat does not appear to be temperature dependent, remaining near 2.0 MJ/m³K at all temperatures. This work is intended to develop and expand the existing dataset of halite thermal properties, which are of particular value in defining the parameters of salt storage thermophysical models. The work was motivated by a need for thermal conductivity values in a mixture theory model used to determine bulk thermal conductivity of reconsolidating crushed salt.

Implementation of a viscoplastic model for crushed salt in the ADINA program

This paper presents the numerical modeling of the thermomechanical behavior of crushed salt using a viscoplastic constitutive model. In the ADINA finite element code the viscoplastic model that considers both volumetric and deviatoric strain rates under hydrostatic and shear stress conditions proposed by Hein (Hein HJ. Ein stoffgesetz zur Beschreibung des thermomechanischen Verhaltens von Salzgranulat. Dissertation, RWTH Aachen, 1991) is implemented. A series of exercises were designed to verify the numerical implementation and the theoretical formulation of the proposed model. The applicability of the model to predicting the consolidation of a crushed salt specimen with step-wise stress increase and decrease, performed in laboratory tests, is examined. Finally, a benchmark problem taking into account the interaction between crushed salt and rock salt under nuclear waste repository conditions is analyzed. The calculated temperature, porosity and compaction pressure in crushed salt correspond to a large degree with the results of other numerical codes.

Constitutive behavior of reconsolidating crushed salt

The constitutive model used to describe deformation of crushed salt is presented in this paper. Two mechanisms--dislocation creep and grain boundary diffusional pressure solutioning--are combined to form the basis for the constitutive model governing deformation of crushed salt. The constitutive model is generalized to represent three-dimensional states of stress. Recently completed creep consolidation tests are combined with an existing database that includes hydrostatic consolidation and shear consolidation tests conducted on Waste Isolation Pilot Plant (WIPP) and southeastern New Mexico salt to determine material parameters for the constitutive model. Nonlinear least-squares model fitting to data from shear consolidation tests and a combination of shear and hydrostatic tests produces two sets of material parameter values for the model. Changes in material parameter values from test group to test group indicate the empirical nature of the model but show significant improvement over earlier work. To demonstrate the predictive capability of the model, each parameter value set was used to predict each of the tests in the database. Based on fitting statistics and ability of the model to predict test data, the model appears to capture the creep consolidation behavior of crushed salt quite well.

Physical modelling of sand production

The proposed use of crushed salt as a functional seal element in the Waste Isolation Pilot Plant (WIPP) shafts has given rise to several technological advances. A large-scale dynamic compaction demonstration using mine-run salt produced a compacted mass having a fractional density of 0.9 and a permeability of 9×10 −14 m 2 . To model evolution of crushed salt from these initial conditions to a high-density, low-permeability seal requires implementation of a suitable constitutive model. Candidate models were evaluated, generalized, and fit to limited data. Refinement of model parameters and definition of the relationship between permeability and density necessitate further experimental work as discussed in this paper. Implementation of a proper constitutive model, inclusion of a reliable permeability/density relationship for reconsolidating crushed salt, and a fundamental understanding of micromechanical processes assure credible design and analyses of the WIPP shaft seal system.

Reconsolidating salt: Compaction, constitutive modeling, and physical processes

Abstract The proposed use of crushed salt as a functional seal element in the Waste Isolation Pilot Plant (WIPP) shafts has given rise to several technological advances. A large-scale dynamic compaction demonstration using mine-run salt produced a compacted mass having a fractional density of 0.9 and a permeability of 9×10 −14 m 2 . To model evolution of crushed salt from these initial conditions to a high-density, low-permeability seal requires implementation of a suitable constitutive model. Candidate models were evaluated, generalized, and fit to limited data. Refinement of model parameters and definition of the relationship between permeability and density necessitate further experimental work as discussed in this paper. Implementation of a proper constitutive model, inclusion of a reliable permeability/density relationship for reconsolidating crushed salt, and a fundamental understanding of micromechanical processes assure credible design and analyses of the WIPP shaft seal system.

In situ tests on backfilling and surrounding host-rock in the case of a radioactive waste disposal in a layered salt formation

In situ experiments carried out by ANDRA in a deep and homogeneous salt layer of a French mine (Amélie mine — Alsace Potash Mines S.A.) tested the behavior of the different components of a multibarrier system, designed for high-level waste disposal and particularly for heat-generating wastes. Canisters were placed in blind boreholes. The experimental field is located at a depth of 520 m where two major tests have been carried out since 1987. The first test (1987–1989) tested the backfilling by heating different types of crushed salt (max. 130°C) emplaced in large-diameter boreholes. One hole remained empty as a control. The second experiment started in 1989 with the opening of a gallery and the boring of three different boreholes (7 m depth, 250 mm diameter) where the annulus between the cylindrical heating cell and the salt mass differs fundamentally in configuration: as tight as possible, empty, or backfilled with crushed salt. The first configuration was tested at the end of 1991. In both test fields, a complete series of measurements has been carried out to record temperatures, pressures and deformations on the heating devices, as well as in the surrounding media. Backfill and host rock are monitored with sensors placed in different boreholes. High-resolution tiltmeters and accurate levelling complete the field of investigations. Thermo-mechanical behavior and the properties of the materials have been considered in detail using laboratory test results. Calculations showed how thermo-mechanical interactions behave and generally agreed in a satisfactory manner with the measurements of the test field. Finally, after cooling and dismantling of the experiment, the microscopic change of the different crushed salts used for the backfilling is analysed.