Packing states of ideal reservoir sands: Insights from simulation of porosity reduction by grain rearrangement

The question being tackled in this study is to which extent grain rearrangement contributes to porosity reduction in very well sorted quartzose sands (ideal reservoir sands). A numerical model, RAMPAGE (an acronym of random packing generator), has been developed to address this long-standing problem. RAMPAGE represents a synthesis of various algorithms designed to simulate packing of equal-sized spheres, which have been used to represent ideal solids, liquids, and gases, as well as natural porous media. The results of RAMPAGE simulations compare favourably to theoretical and experimental data from various disciplines and allow delineation of the field of gravitationally stable random packing of equal-sized spheres in the 2-D state space of porosity (P) versus mean coordination number (N). Three end-member packing states have been identified: random loose packing (RLP: P = 45.4%, N = 5.2), random close packing (RCP: P = 36.3%, N = 7.0), and bridged random close packing (Bridged RCP: P = 39.5%, N = 5.2). Unlike previously proposed models, RAMPAGE can simulate the transition from RLP to any other point in the stability field. The RLP state is fully consistent with wet-packed porosities of synthetic sands with lognormal mass-size distributions reported in the literature. The much higher in-situ porosity values reported for modern (air-packed) sands are unlikely to be preserved at depth on geological time scales. Data on the relation between intergranular volume and burial depth indicate that the observed intergranular volume reduction in the upper ~ 800 m of the sediment column corresponds to the evolution of RLP to RCP, and is thus fully explained by non-destructive grain rearrangement.     

Rock displacement and thermal expansion study at historic heritage sites in Slovakia

The paper discusses the results of the research devoted to the preservation of cultural heritage carried out within last two decades in Slovakia. The aim of the study depended on monitoring of selected castle rocks showing instability problems due to extremely slow displacements of creep character. Apart from traditional methods of investigation at one test site (Spis Castle), authors implemented in their work the study of thermal expansion of the rocks as a result of seasonal periodic temperature changes having potential influence on displacements and numerical modeling in order to understand better the landslide failure mechanism. The results obtained from all study sites confirmed that even slow movements have to be implemented into preservation and stabilization works in order to safeguard the sites of great historic value.     

Late Pleistocene stratigraphy and sedimentary environments of the Severnaya Dvina‐Vychegda region in northwestern Russia

The Late Pleistocene stratigraphy from the Severnaya Dvina‐Vychegda region of northwestern Russia is revised based on investigations of new localities, revisiting earlier localities, introduction of about 110 new OSL dates and burial depth corrections of earlier published OSL dates, in addition to six new radiocarbon dates. Most of the OSL samples studied here are from fluvial and subaquaeous sediments, which we found to be well bleached. Six chronostratigraphical units and their sedimentary environment are described, with the oldest unit consisting of pre‐Eemian glacial beds. For the first time, Early Weichselian sediments are documented from the region and a fluvial environment with some vegetation and permafrost conditions is suggested to have persisted from the end of the Eemian until at least about 92 ka ago. The period in which a Middle Weichselian White Sea Lake could have existed is constrained to 67?62 ka, but as the lake level never reached the thresholds of the drainage basin, the lake probably existed only for a short interval within this time‐span. Blocking and reversal of fluvial drainage started again around 21?20 ka ago when the Fennoscandian Ice Sheet advanced into the area, reaching its maximum 17?15 ka ago. At that time, an ice‐dammed lake reached its maximum water level, which was around 135 m above present sea level. Drainage of the lake started shortly after 15 ka ago, and the lake was emptied within 700 years. Severe periglacial conditions, with permafrost and aeolian activity, prevailed in the area until about 10.7 ka.     

Comparison of volumetric and remote sensing methods (TLS) for assessing the development of a permanent forested loess gully

The gully systems develop a compact network dissecting the loess cover of the NW part of the Lublin Upland. They are overgrown by dense and multi-storey forest assemblages. It is very difficult to apply teledetection techniques, GPS positioning, and geodesic tools, such as a laser rangefinder or total station, for monitoring of gully development. The detailed research, involving the comparison of traditional and modern methods, was conducted in a gully with a secondary erosional dissection, developing in the gully bottom with varied intensity for the last 15 years. In the period of comparative research (2012/2013), the rate of development of the erosional dissection was measured by means of traditional methods as well as a Leica HDS 7000 laser scanner. 3D laser scanning permitted precise terrain modelling and the assessment of qualitative and quantitative spatial changes. This paper compares the results of three measurement campaigns. The analysis showed intensive development of the dissection, manifested in an increase in its volume (37 %), retreat of the erosion scarp (32 m), deep erosion (19 %), and lateral erosion (27 %). Registered moderate snowmelt in 2013 caused the volume dissection to increase by 57 m³, mainly as a result of the gully bottom scouring. During heavy rainfalls in June, the landforms were widened by a further 217 m³ and observed deepening and widening of erosive potholes. The prevalence of deep erosion resulted in the transformation back into a V-shaped cross section. A total of 37.3 Mg km⁻² of material was discharged from the gully catchment during snowmelt runoffs in 2013. A precipitation event in June 2013 caused the discharge of 856.9 Mg km⁻² of material from the catchment. The obtained results confirm that snowmelt erosion determines the spatial development of perennial gullies, but the volume of material discharged from the catchment depends on the occurrence of extreme precipitation during the warm season.

     

Spalling Experiments on Large Hard Rock Specimens

Specimens of coarse-grained Äspö diorite were axially compressed to observe stress-induced spalling. The specimens had a novel design characterized by two manufactured large radius notches on opposite sides. The tangential stress occurring in the notches aimed to represent the tangential loading around a circular opening. Fracture stages were monitored by acoustic emission measurements. Rock chips were formed similar to those found in situ, which indicates a similar fracture process. Slabs were cut out from the specimens and impregnated using a fluorescent material to visualize the cracks. The cracks were subsequently examined by the naked eye and by means of microscopy images, from which fracture paths could be identified and related to different minerals and their crystallographic orientations. The microscopy analyses showed how the stress field and the microstructure interact. Parallel cracks were formed 2–4 mm below the surface, sub-parallel to the direction of the maximum principal stress. The crack initiation, the roles of minerals such as feldspar, biotite and quartz and their grain boundaries and crystallographic directions are thoroughly studied and discussed in this paper. Scale effects, which relate to the stress gradient and microstructure, are discussed.     

Magnetism of natural pyrrhotite,haematite and ilmenite

Summary The paper deals with the magnetic properties of the natural minerals haematite, ilmenite and pyrrhotite. The natural remanent magnetization J_n, the volume susceptibility , the specific magnetization of saturation _so, the Curie temperature , the A.C. demagnetization of natural remanent magnetization, the thermal demagnetization J_n, the temperature dependence of the specific magnetization of saturation, and several other parameters were determined for the individual sets of minerals. Since natural minerals can and do contain various heterogeneous and isomorphic admixtures, their magnetic properties may change depending on the content and type of these admixtures. Therefore, all the investigations of the magnetic properties described in this paper were carried out with extensive sets of minerals, representing various Czechoslovak and world localities. A number of interesting results were obtained from the executed experiments, e.g., the different stability of the natural remanent magnetization of haematite with respect to A.C. demagnetization, the presence and type of heterogeneous inclusions in ilmenite, the phase changes connected with the -transition in natural pyrrhotites, etc. The types of distributions of the investigated values of the magnetic properties were also determined.     

Comment on some relations between the shape of streamlines and frontal interface in the proximity of a cyclonic vortex

Zusammenfassung Es wird ein einfaches Modell des zykolnalen Wirbels vorgeschlagen und die Beziehung zwischen seiner Intensität, der Form der Stromlinien und der Deformation der frontalen Grenzoberfläche in seiner Nähe diskutiert. Die Arbeit verfolgt das Ziel, die Kriterien der sogenannten dynamischen Klassifikation der aus den meteorologischen Satelliten photographierten Bewölkung zu finden.     

On the problem of frequency calibration of induction variometers with large air-core loops

Zusammenfassung Es wird eine Methode für experimentelle Untersuchung der Frequenzkennlinien von Induktionsvariometern mit Aufnahmeschleifen nichttraditioneller Ausmasse beschrieben. Die Grundlage des beschriebenen Verfahrens bildet eine genaue Bestimmung jenes Teils des magnetischen Kraftflusses, der durch die Aufnahmeschleife durchgeht.