Mechanical and hydraulic properties of the excavation damaged zone (EDZ) in the Opalinus Clay of the Mont Terri rock laboratory, Switzerland

Construction of cavities in the subsurface is always accompanied by excavation damage. Especially in the context of deep geological nuclear waste disposal, the evolving excavation damaged zone (EDZ) in the near field of emplacement tunnels is of utmost importance concerning safety aspects. As the EDZ differs from the intact host rock due to enhanced hydraulic transmissivity and altered geomechanical behavior, reasonable and location-dependent input data on hydraulic and mechanical properties are crucial. Thus, in this study, a hydromechanical characterization of an EDZ in the Mont Terri underground rock laboratory, Switzerland, was performed using three different handheld devices: (1) air permeameter, (2) microscopic camera and (3) needle penetrometer. The discrete fracture network (DFN), consisting of artificially induced unloading joints and reactivated natural discontinuities, was investigated by a portable air permeameter and combined microscopic imaging with automatic evaluation. Geomechanical and geophysical characterization of the claystone was conducted based on needle penetrometer testing at the exposed rock surface. Within the EDZ, permeable fractures with a mean hydraulic aperture of 84 ± 23 µm are present. Under open conditions, self-sealing of fractures is suppressed, and cyclic long-term fracture aperture oscillations in combination with closure resulting from convergence processes is observed. Based on measured needle penetration indices, a uniaxial compressive strength of 30 ± 13 MPa (normal to bedding) and 18 ± 8 MPa (parallel to bedding) was determined. Enhanced strength and stiffness are directly related to near-surface desaturation of the claystone and a sharp decrease in water content from 6.6 wt % to 3.7 wt %. The presented methodological approach is particularly suitable for time-dependent monitoring of EDZs since measurements are nondestructive and do not change the actual state of the rock mass. This allows for a spatially resolved investigation of hydraulic and mechanical fracture apertures, fracture surface roughness, and physico-mechanical rock parameters and their intra-facies variability

Determination of the hydraulic conductivities of a sandstone using an air permeameter [Bestimmung der hydraulischen Durchlässigkeiten eines Sandsteins mithilfe eines Luftpermeameters]

Ziel dieser Studie ist die Bestimmung der hydraulischen Durchlässigkeiten eines Sandsteins unter Berücksichtigung der Gesteinsmatrix sowie einer Einzelkluft unter Verwendung eines tragbaren Luftpermeameters. Hierfür wurde der fluviatil-äolisch abgelagerte Bebertaler Sandstein des Oberen Rotliegenden in Sachsen-Anhalt untersucht. Es wurden die Matrixpermeabilitäten der unterschiedlichen Faziesbereiche sowie die Kluftöffnungsweiten entlang einer Schichtfuge bestimmt. Die ermittelten hydraulischen Durchlässigkeiten der Sandsteinmatrix liegen dabei zwischen 1,0 · 10$^{-7}$ und 9,2 · 10$^{-7}$ m/s, allerdings weisen nur 3 von insgesamt 298 Messpunkten einen kf-Wert von > 7,4 · 10$^{-7}$ m/s bzw. eine Permeabilität von > 10 mD auf. Diese gehören zur homogenen und höher durchlässigen äolischen Fazies. Die bestimmte mittlere Öffnungsweite der Schichtfuge liegt bei 82 ± 12 µm. Mithilfe der ermittelten hydraulischen Eigenschaften konnte somit die effektive hydraulische Durchlässigkeit des untersuchten Sandsteins bestimmt werden. Unsere Ergebnisse verdeutlichen die praktische und robuste Anwendbarkeit des verwendeten Luftpermeameters zur Bestimmung der hydraulischen Durchlässigkeiten von Sandsteinen sowohl im Labor als auch im Gelände

Quantification of Fracture Roughness by Change Probabilities and Hurst Exponents

The objective of the current study is to utilize an innovative method called “change probabilities” for describing fracture roughness. In order to detect and visualize anisotropy of rock joint surfaces, the roughness of one-dimensional profiles taken in different directions is quantified. The central quantifiers, change probabilities, are based on counting monotonic changes in discretizations of a profile. These probabilities, which usually vary with the scale, can be reinterpreted as scale-dependent Hurst exponents. For a large class of Gaussian stochastic processes, change probabilities are shown to be directly related to the classical Hurst exponent, which generalizes a relationship known for fractional Brownian motion. While related to this classical roughness measure, the proposed method is more generally applicable, therefore increasing the flexibility of modeling and investigating surface profiles. In particular, it allows a quick and efficient visualization and detection of roughness anisotropy and scale dependence of roughness

Upscaling calcite dissolution rates in a tight reservoir sandstone

Calcite is a highly abundant mineral in the Earth’s crust and occurs as a cement phase in numerous siliciclastic sediments, where it often represents the most reactive component when a fluid percolates through the rock. Hence, the objective of this study is to derive calcite dissolution rates on different scales in a reservoir sandstone using mineral surface experiments combined with vertical scanning interferometry (VSI) and two types of core plug experiments. The 3D geometry of the calcite cement phase inside the rock cores was characterized by X-ray micro-computed tomography (µXCT) and was used to attempt dissolution rate upscaling from the mineral surface to the core scale. Initially (without upscaling), our comparison of the far-from-equilibrium dissolution rates at the mineral surface (µm-mm-scale, low fluid residence time) and the surface normalized dissolution rates obtained from the core experiments (cm-scale, high fluid residence time) revealed differences of 0.5–2 orders of magnitude. The µXCT geometric surface area connected to the open pore space (GSA$_{Cc,open}$) considers the fluid accessibility of the heterogeneously distributed calcite cement that can largely vary between individual samples, but greatly affects the effective dissolution rates. Using this parameter to upscale the rates from the µm- to the cm-scale, the deviation of the upscaled total dissolution rates from the measured total dissolution rates was less than one order of magnitude for all investigated rock cores. Thus, GSA$_{Cc,open}$ showed to be reasonably suitable for upscaling the mineral surface rates to the core scale

Simulating permeability reduction by clay mineral nanopores in a tight sandstone by combining computer X-ray microtomography and focussed ion beam scanning electron microscopy imaging

Computer X-ray microtomography (µXCT) represents a powerful tool for investigating the physical properties of porous rocks. While calculated porosities determined by this method typically match experimental measurements, computed permeabilities are often overestimated by more than 1 order of magnitude. This effect increases towards smaller pore sizes, as shown in this study, in which nanostructural features related to clay minerals reduce the permeability of tight reservoir sandstone samples. Focussed ion beam scanning electron microscopy (FIB-SEM) tomography was applied to determine the permeability effects of illites at the nanometre scale, and Navier–Stokes equations were applied to calculate the permeability of these domains. With these data, microporous domains (porous voxels) were defined using microtomography images of a tight reservoir sample. The distribution of these domains could be extrapolated by calibration against size distributions measured in FIB-SEM images. For this, we assumed a mean permeability for the dominant clay mineral (illite) in the rock and assigned it to the microporous domains within the structure. The results prove the applicability of our novel approach by combining FIB-SEM with X-ray tomographic rock core scans to achieve a good correspondence between measured and simulated permeabilities. This methodology results in a more accurate representation of reservoir rock permeability in comparison to that estimated purely based on µXCT images

Effect of sedation level on the prevalence of delirium when assessed with CAM-ICU and ICDSC

Purpose: We hypothesized that reduced arousability (Richmond Agitation Sedation Scale, RASS, scores −2 to −3) for any reason during delirium assessment increases the apparent prevalence of delirium in intensive care patients. To test this hypothesis, we assessed delirium using the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) and Intensive Care Delirium Screening Checklist (ICDSC) in intensive care patients during sedation stops, and related the findings to the level of sedation, as assessed with RASS score. Methods: We assessed delirium in 80 patients with ICU stay longer than 48h using CAM-ICU and ICDSC during daily sedation stops. Sedation was assessed using RASS. The effect of including patients with a RASS of −2 and −3 during sedation stop ("light to moderate sedation”, eye contact less than 10s or not at all, respectively) on prevalence of delirium was analyzed. Results: A total of 467 patient days were assessed. The proportion of CAM-ICU-positive evaluations decreased from 53 to 31% (p<0.001) if assessments from patients at RASS −2/−3 (22% of all assessments) were excluded. Similarly, the number of positive ICDSC results decreased from 51 to 29% (p<0.001). Conclusions: Sedation per se can result in positive items of both CAM-ICU and ICDSC, and therefore in a diagnosis of delirium. Consequently, apparent prevalence of delirium is dependent on how a depressed level of consciousness after sedation stop is interpreted (delirium vs persisting sedation). We suggest that any reports on delirium using these assessment tools should be stratified for a sedation score during the assessmen

Hessische Forschungsdateninfrastrukturen HeFDI

Das Projekt „Hessische Forschungsdateninfrastrukturen“ (HeFDI) setzt auf die kooperative Entwicklung einer gemeinsamen Forschungsdatenstrategie und den Aufbau vernetzter Services. Durch den Zusammenschluss von zehn hessischen Hochschulen baut der so entstandene Verbund auf Kooperation durch institutionelle Arbeitsteilung

The host response to the probiotic Escherichia coli strain Nissle 1917: Specific up-regulation of the proinflammatory chemokine MCP-1

BACKGROUND: The use of live microorganisms to influence positively the course of intestinal disorders such as infectious diarrhea or chronic inflammatory conditions has recently gained increasing interest as a therapeutic alternative. In vitro and in vivo investigations have demonstrated that probiotic-host eukaryotic cell interactions evoke a large number of responses potentially responsible for the effects of probiotics. The aim of this study was to improve our understanding of the E. coli Nissle 1917-host interaction by analyzing the gene expression pattern initiated by this probiotic in human intestinal epithelial cells. METHODS: Gene expression profiles of Caco-2 cells treated with E. coli Nissle 1917 were analyzed with microarrays. A second human intestinal cell line and also pieces of small intestine from BALB/c mice were used to confirm regulatory data of selected genes by real-time RT-PCR and cytometric bead array (CBA) to detect secretion of corresponding proteins. RESULTS: Whole genome expression analysis revealed 126 genes specifically regulated after treatment of confluent Caco-2 cells with E. coli Nissle 1917. Among others, expression of genes encoding the proinflammatory molecules monocyte chemoattractant protein-1 ligand 2 (MCP-1), macrophage inflammatory protein-2 alpha (MIP-2α) and macrophage inflammatory protein-2 beta (MIP-2β) was increased up to 10 fold. Caco-2 cells cocultured with E. coli Nissle 1917 also secreted high amounts of MCP-1 protein. Elevated levels of MCP-1 and MIP-2α mRNA could be confirmed with Lovo cells. MCP-1 gene expression was also up-regulated in mouse intestinal tissue. CONCLUSION: Thus, probiotic E. coli Nissle 1917 specifically upregulates expression of proinflammatory genes and proteins in human and mouse intestinal epithelial cells