Phenomenological fractional stress–dilatancy model for granular soil and soil-structure interface under monotonic and cyclic loads

The stress–dilatancy relation is of critical importance for constitutive modelling of geomaterial. A novel fractional-order stress–dilatancy equation had been developed for granular soil, where a nonlinear stress–dilatancy response was always predicted. However, it was experimentally observed that after a certain extent of shearing, an almost linear response between the stress ratio and the dilatancy ratio, rather than the nonlinear response, usually existed. To capture such stress–dilatancy behaviour, a new fractional stress–dilatancy model is developed in this study, where an apparent linear response of the stress–dilatancy behaviour of soil after sufficient shearing is obtained via analytical solution. As the fractional order varies, the derived stress–dilatancy curve and the associated phase transformation state stress ratio keep changing. But, unlike existing researches, no other specific parameters, except the parameter related to fractional order, concerning such shift are required. Then, the developed stress–dilatancy model is applied to constitutive modelling of granular soil and soil–structure interface, for further validation. A series of test results of different granular soils and soil–structure interfaces under different loading conditions are simulated and compared, where a good model performance is observed.

     

Seasonal and spatial changes in the zooplankton community of Kongsfjorden, Svalbard

Seasonal changes in the zooplankton composition of the glacially influenced Kongsfjorden, Svalbard (79°N, 12°E), and its adjacent shelf were studied in 2002. Samples were collected in the spring, summer and autumn in stratified hauls (according to hydrographic characteristics), by means of a 0.180-mm Multi Plankton Sampler. A strong front between the open sea and the fjord waters was observed during the spring, preventing water mass exchange, but was not observed later in the season. The considerable seasonal changes in zooplankton abundance were related to the seasonal variation in hydrographical regime. The total zooplankton abundance during the spring (40–2010 individuals m⁻³) was much lower than in the summer and autumn (410–10 560 individuals m⁻³). The main factors shaping the zooplankton community in the fjord include: the presence of a local front, advection, the flow pattern and the decreasing depth of the basin in the inner fjord. Presumably these factors regulate the gross pattern of zooplankton density and distribution, and override the importance of biological processes. This study increased our understanding of seasonal processes in fjords, particularly with regard to the strong seasonal variability in the Arctic.     

Advantages and limitations of an α-plasticity model for sand

Acta Geotechnica - The stress–strain response of sand was observed to depend on its material state, i.e., pressure and density. Successful modelling of such state-dependent response of sand...     

Non‐normality and induced plastic anisotropy under fractional plastic flow rule: a numerical study

In this paper, an implementation of fractional plastic flow rule in the framework of implicit and explicit procedures is under consideration. The fractional plastic flow rule is obtained from a generalisation of the classical plastic flow rule utilising fractional calculus. The key feature of this new concept is that in general, the non‐associative flow is obtained without necessity of additional potential assumption. If needed, the model can cover the anisotropy induced by plastic deformation. Illustrative examples showing the unusual flexibility of this model are also presented. Copyright © 2015 John Wiley & Sons, Ltd.     

On the bulk parameterization of snow and its application to the quantitative studies of precipitation growth

Appropriate formulation of bulk parameterization of snow growth and evaporation based on observational characteristics of snow particles is presented. The parameterization is compared to that of S. A. Rutledge and P. V. Hobbs and to detailed treatment in which snow particles are assumed to grow or evaporate in each size bin separately. On the contrary to bulk parameterization of rain, snow diffusional growth or evaporation is accurately represented in the suggested bulk formulation, but growth by riming is overpredicted. Integrations of water budget equations in a one-dimensional updraft have shown that quantitative results, e.g., precipitation intensity, cloudwater content, supersaturation with respect to ice, depend on the parameterization scheme employed, which suggests that comparisons of field measurements with parameterized model outputs is usually not straightforward.     

A Model to Simulate Pumping Tests in Wells with High Loss and Backflow

Traditional methods of analyzing pumping tests in single wells fail when the well loss is very high due to a low transmissivity skin. Because of the restricted rate at which water can enter a high loss well from the aquifer, well casing storage becomes a significant factor. Additionally, if a slug of water enters the well from the pump column immediately after the pump is switched off, it has a long‐lasting significant effect on the recovering water level in the well because it cannot be absorbed rapidly by the aquifer. A theoretical model is derived here that simulates the water level in a well in these circumstances. In the model, the continuously changing rate of water inflow from the aquifer to the well is approximated by a step function with a finite difference time step. It is demonstrated by a real example that the model can be applied easily to analyze pumping tests, including tests with a varying pumping rate. The analysis confirms suspected high well loss, calculates the unknown rate of backflow, and determines the aquifer's transmissivity.     

Airborne Fungal Spores of Subalpine Zone of the Karkonosze and Izerskie Mountains （Poland）

The incidence of the airborne fungal spores was determined in the air of subalpine zone of the Karkonosze Mountains and of the Izerskie Mountains in the borderland between Poland and the Czech Republic. The experiment was conducted in 2011 and 2012 at three to four week intervals from May to October. Air samples were taken from three locations in the Karkonosze Mts. and one from the Izerskie Mts. To examine the air, the Air Ideal 3P sampler and acidified PDA medium were used. The results show that Cladosporium cladosporioides was the most abundant spore type in all the sampling locations （up to 30%）, followed by Alternaria alternata （16%-20%）, Fusarium （up to 10%） and Sclerotinia sclerotiorium （up to 6%）. The lower spore counts were recorded in May samples, compared to the other months. In this case the snow cover, that was still present in the area at the beginning of May, may be the reason for the lower, compared to June, July and August samplings, CFU （Colony Forming Unit） counts in that month.. The influx of air masses from SE, S and SW sectors in the area under study may affect dissemination of the plant-pathogenic fungi from the Czech Republic and from the South of Europe in general.     

Modelling of hydrogeochemical potential of three lake catchments in Polesie region (Eastern Poland)

Total dissolved solids (TDS) in lake and catchment water is a result of geological structure, as well as duration of rock and water contact and human activity. In this paper, a potential dissolved solids (PtDS) in three ??czna–W?odawa Lake catchments was determined using extraction and computer software (GIS and AquaChem). Human pressure on water quality was estimated as a difference of the TDS and a catchment hydrogeochemical potential (TPtDS, total potential dissolved solids). TPtDS coefficient included hydrogeological features of the aquifer, soil cover impact on infiltrated water quality, and sediments susceptibility to denudation. The main advantage of the model is a possibility of its employment for every catchment or other areas (e.g. administrative) on both microscale and mesoscale. The highest TPtDS occurred in the catchment, favoured with underground supply, which was located in the vicinity of the Cretaceous mesoregional unit (Che?m Hills). The lowest value was observed in the catchment built with organogenic sediments and coarse material. A seasonal constancy of TPtDS values proved a stability of the lake‐catchment systems under study. Copyright © 2012 John Wiley & Sons, Ltd.