5 research outputs found
The influence of mechanical contrast on industrial and natural hydraulic fracturing
No full textThe heterogeneity of layered systems leads to variation in rock or soil mechanical properties, influencing the resistance to failure. A formation breaks by fracture propagation when the effective stress surpasses the formation strength. The propagation of a fracture through a mechanical interface depends on whether the formation strength of the second formation is overcome. This critical effective stress level could be trespassed by high natural or industrial induced pore pressures. Understanding fracture propagation in multi-layered systems with variable pore pressure regimes has important implications and applications to many industries such as quarrying and hydraulic stimulation. The slope stability of Westerwald Clay Quarries is influenced by inter-bedding of thin sand layers. Surface and slope fractures within the clay formation originated from a high observed hydrostatic head within the sand layers and a reduced confining stress from mining activities. The slopes of the quarry are key in determining the volume of economically mineable clay, these slopes are in turn controlled by the size/extent of fractures and whether they extend through multiple formations. This study examines the effect of fracture continuation from sand layers into the stiff Westerwald Clay Formation. The soil parameters (cohesion and friction angle) of the different lithologies within a Westerwald Clay Quarry are determined for slope stability analysis by shearbox testing. Soil classification has been done in terms of plasticity, grain size and mineralogy by Atterberg Limits, Sieving and XRD & XRF respectively. The results show that fracture initiation within the Westerwald quarries is a combination of mining activities lowering the confining stress and a constant natural hydraulic head. The hydraulic head within the small sand formation lowers slope stability by causing fracture initiation and water infiltration into the clay formation. Slope stabilisation occurs by artificial water pumping or natural water dissipation lowering the hydraulic head. Slope stability is decreased by embankments of low permeability backfill and increased by high permeability backfill. Inter-bedded systems are common target locations for an unconventional reservoir systems and can be found both within source rocks as well as in conventional geological traps. Improvement in recovery from these tight systems often depends on the extent and continuity of fractures through heterogeneous interfaces. This study examines the propagation and continuity of the fractures in an artificial heterogeneous layered system. The fractures will be initiated by hydraulic fracturing in a dried layered system via water injection in a triaxial cell. Fracture propagation is analysed through Micro-CT scans. The mechanical properties such as acoustic wave velocities, unconfined & confined compressive strength and tensile strength are all determined for the analysed layered systems. The results show that hydraulic fractures initiated within the weakest layer are arrested at the interface between a mechanically weak and strong formation, whereas fractures initiated within mechanically stronger layers prograde through the interface. Hydraulic fractures are initiated when local pressure difference at the interface exceeds the formation’s critical tensile stress, the formations critical tensile strength is dependent on the confining pressure
Global distribution map of Rhenish stoneware during the 16th to 18th century
No full textThe dataset provides a distribution map of Rhenish stonewares between the 16th and 18th century. The data was collected from published archaeological data (print and online) available to the author. According the published information the pottery was classified to different wares (Cologne, Frechen, Siegburg, Raeren, Westerwald). Values are given for individual sherd numbers. If no information was given in the publication, the value is set to "1". Bibligraphic reference is given by author - date. Full bibliographic reference can be found in the pdf-file.
The csv-file contains next to location name, bibliographic reference and pottery counts values for longitude and latitude. The coordinate reference is WGS 84 - EPSG:4326
Mobile touristische Anwendungen mit gamebasierten Stationen auf engem Raum
No full textZiel dieser Diplomarbeit ist es, innerhalb von sechs Monaten eine gamebasierte Anwendung für Android-Smartphones zu entwickeln, die durch eng beieinander liegende Stationen historisches Wissen vermittelt. Die einzelnen Spielstationen sollen mit Hilfe von GPS1-Positionen festgelegt und erkannt werden. Als Gelände wurde die Burgruine Reichenstein in der Verbandsgemeinde Puderbach im Westerwald ausgewählt. Es soll untersucht werden, wie viele GPS-Stationen auf engem Raum unterzubringen sind und wie weit sie voneinander entfernt sein müssen, um gute Ergebnisse erzielen zu können. Dazu ist es nötig, sowohl den Grundriss der Burg als auch die Beschaffenheit des Geländes mit einzubeziehen.
An den einzelnen Stationen sollen auf spielerische Art und Weise historische Informationen über die Burgruine Reichenstein vermittelt werden. Neben der Recherche, der Konzepterstellung und der Implementierung umfasst diese Arbeit auch eine Evaluation, die eine Bewertung der Anwendung ermöglicht
Autistic traits and autism spectrum disorders : the clinical validity of two measures presuming a continuum of social communication skills
No full textResearch indicates that autism is the extreme end of a continuously distributed trait. The Social Responsiveness Scale (SRS) and the Social and Communication Disorders Checklist (SCDC) aim to assess autistic traits. The objective of this study was to compare their clinical validity. The SRS showed sensitivities of .74 to .80 and specificities of .69 to 1.00 for autism. Sensitivities were .85 to .90 and specificities .28 to.82 for the SCDC. Correlations with the ADI-R, ADOS and SCQ were higher for the SRS than for the SCDC. The SCDC seems superior to the SRS to screen for unspecific social and communicative deficits including autism. The SRS appears more suitable than the SCDC in clinical settings and for specific autism screening
A Geotechnical Working Plan for a Thorough but Quick Assessment of Existing Slopes in Clay Mines
No full textIn the Westerwald area clay quarries are in production. In order to assess the stability of the slopes the geotechnical characterisation of these quarries needs to be improved. This report provides the justification for a working plan for a thorough but quick assessment of existing slopes in clay mines. Literature is consulted for the information for the types of measuring and monitoring equipment for slopes, what instabilities look like in the field, how the safety factor are calculated, what information can be gathered outside the mine and what a field investigation should concern. To come to a working plan a field investigation was conducted to try out the different measurement equipment. For field testing, the needle penetrometer and hand vane shear came out as useful tools for correlating undrained shear strengths parameters of different layers. For thorough correlations, between layers and a dataset of geotechnical parameters, Atterberg limits are used to minimise the number of geotechnical parameters that have to be tested. The parameters are tested with different machines based on the timespan over which the slope has to be stable. Short-term slopes with insitu conditions are best tested with triaxial tests, but UCS and a theoretical strong shear box can provide useful data as well. Long-term slopes are better tested with either a shear box or ring shear because remoulded or weathered properties are needed. Monitoring is found to be done best by using InSAR monitoring provided a suggestion is added to increase the number of data points inside the mine. The working plan is presented as a flowchart for a good overview
