Stress and pore pressure changes in clay during and after the expansion of a cylindrical cavity

The disturbance of a clay mass, due to either the installation of a driven pile or the expansion of a pressuremeter membrane, is often modelled as a cylindrical cavity expansion. In addition, it is usual (and convenient) to assume that the expansion occurs under conditions of plane strain. For this problem a method of analysis is presented which considers the soil to be a saturated two-phase material with a pore fluid which flows according to Darcy's Law. Non-linearity in material behaviour is permitted as long as the effective stress–strain law can be written in an incremental or rate form. The use of a consolidation analysis allows the changes in effective stress and pore pressure to be determined at any stage during both the cavity expansion and the subsequent period of reconsolidation. Expansions may occur at any prescribed rate, including the very fast (undrained) and the very slow (fully drained) case. The technique is illustrated by considering the expansion of a cavity in two different types of elastoplastic soil. It is shown how these solutions may be used to model the disturbance of the soil due to pile driving.     

Current Atmospheric Deposition Loads and Their Trends in the Czech Republic Determined by Mapping the Distribution of Moss Element Contents

Biomonitoring of atmospheric deposition loads of 13, 14 and 35 elements and their compounds through moss analysis was carried out in the Czech Republic (CZ) in 1991, 1995 and 2000, respectively. The last biomonitoring campaign revealed very high contents of typical soil elements and lanthanides in southern Moravia. The variations in current element contents in moss, which can be explained by the action of six factors, were correlated with altitude, with total biennial precipitation, and with the bedrock types in the sampling plots. The element contents in moss samples repeatedly collected from the identical plots showed a steady decrease in atmospheric deposition loads in the CZ in the last decade of the 20th century. The main reasons for this phenomenon are listed. The results of cluster analyses and PCAs have found no substantial changes in the qualitative element composition of atmospheric deposition in CZ in recent years. Isoline maps are presented, which document changes in the distribution of Cd, Pb and S contents in moss in 1995 and 2000. An estimate of absolute deposition loads (g m^–2 year^–1) for given areas of the CZ can be made, using the list of bulk deposition indices.     

Effects of the closure of a major sewage outfall on sublittoral, soft sediment benthic communities

The present study examines the benthos within western inner Swansea Bay (Wales, UK), for the period before, during and immediately after the cessation of a major, sewage discharge from Mumbles Head. There have been significant improvements in seawater quality and changes in the species composition of the benthic communities following the cessation of the sewage discharge. There has been an increase in the diversity of deposit feeders, especially the amphipods, and a decrease in the diversity of the filter feeders, especially the polychaetes. Changes are not attributable either to sediment organic matter content or to gross changes in sediment type, but are related to the significant reduction in suspended particulate organic material and sewage contaminants discharged to the Bay. A recovery model has been proposed to describe how soft sediment benthic communities in a shallow, sublittoral, high tidal energy environment respond to the abrupt cessation of a major sewage discharge.     

Late Pleistocene outburst flooding from pluvial Lake Alvord into the Owyhee River, Oregon

At least one large, late Pleistocene flood traveled into the Owyhee River as a result of a rise and subsequent outburst from pluvial Lake Alvord in southeastern Oregon. Lake Alvord breached Big Sand Gap in its eastern rim after reaching an elevation of 1292 m, releasing 11.3 km³ of water into the adjacent Coyote Basin as it eroded the Big Sand Gap outlet channel to an elevation of about 1280 m. The outflow filled and then spilled out of Coyote Basin through two outlets at 1278 m and into Crooked Creek drainage, ultimately flowing into the Owyhee and Snake Rivers. Along Crooked Creek, the resulting flood eroded canyons, stripped bedrock surfaces, and deposited numerous boulder bars containing imbricated clasts up to 4.1 m in diameter, some of which are located over 30 m above the present-day channel.Critical depth calculations at Big Sand Gap show that maximum outflow from a 1292- to 1280-m drop in Lake Alvord was  10,000 m³ s^− 1. Flooding became confined to a single channel approximately 40 km downstream of Big Sand Gap, where step-backwater calculations show that a much larger peak discharge of 40,000 m³ s^− 1 is required to match the highest geologic evidence of the flood in this channel. This inconsistency can be explained by (1) a single 10,000 m³ s^− 1 flood that caused at least 13 m of vertical incision in the channel (hence enlarging the channel cross-section); (2) multiple floods of 10,000 m³ s^− 1 or less, each producing some incision of the channel; or (3) an earlier flood of 40,000 m³ s^− 1 creating the highest flood deposits and crossed drainage divides observed along Crooked Creek drainage, followed by a later 10,000 m³ s^− 1 flood associated with the most recent shorelines in Alvord and Coyote Basins.Well-developed shorelines of Lake Alvord at 1280 m and in Coyote Basin at 1278 m suggest that after the initial flood, postflood overflow persisted for an extended period, connecting Alvord and Coyote Basins with the Owyhee River of the Columbia River drainage. Surficial weathering characteristics and planktonic freshwater diatoms in Lake Alvord sediment stratigraphically below Mt. St. Helens set Sg tephra, suggest deep open-basin conditions at  13–14 ka (¹⁴C yr) and that the flood and prominent shorelines date to about this time. But geomorphic and sedimentological evidence also show that Alvord and Coyote Basins held older, higher-elevation lakes that may have released earlier floods down Crooked Creek.     

Effects of observed and experimental climate change on terrestrial ecosystems in northern Canada: results from the Canadian IPY program

Tundra and taiga ecosystems comprise nearly 40?% of the terrestrial landscapes of Canada. These permafrost ecosystems have supported humans for more than 4500?years, and are currently home to ca. 115,000 people, the majority of whom are First Nations, Inuit and Métis. The responses of these ecosystems to the regional warming over the past 30?C50?years were the focus of four Canadian IPY projects. Northern residents and researchers reported changes in climate and weather patterns and noted shifts in vegetation and other environmental variables. In forest-tundra areas tree growth and reproductive effort correlated with temperature, but seedling establishment was often hindered by other factors resulting in site-specific responses. Increased shrub cover has occurred in sites across the Arctic at the plot and landscape scale, and this was supported by results from experimental warming. Experimental warming increased vegetation cover and nutrient availability in most tundra soils; however, resistance to warming was also found. Soil microbial diversity in tundra was no different than in other biomes, although there were shifts in mycorrhizal diversity in warming experiments. All sites measured were sinks for carbon during the growing season, with expected seasonal and latitudinal patterns. Modeled responses of a mesic tundra system to climate change showed that the sink status will likely continue for the next 50?C100?years, after which these tundra systems will likely become a net source of carbon dioxide to the atmosphere. These IPY studies were the first comprehensive assessment of the state and change in Canadian northern terrestrial ecosystems and showed that the inherent variability in these systems is reflected in their site-specific responses to changes in climate. They also showed the importance of using local traditional knowledge and science, and provided extensive data sets, sites and researchers needed to study and manage the inevitable changes in the Canadian North.     

Preparing for climate change in Washington State

Climate change is expected to bring potentially significant changes to Washington State’s natural, institutional, cultural, and economic landscape. Addressing climate change impacts will require a sustained commitment to integrating climate information into the day-to-day governance and management of infrastructure, programs, and services that may be affected by climate change. This paper discusses fundamental concepts for planning for climate change and identifies options for adapting to the climate impacts evaluated in the Washington Climate Change Impacts Assessment. Additionally, the paper highlights potential avenues for increasing flexibility in the policies and regulations used to govern human and natural systems in Washington.     

Twentieth century ENSO characteristics in the IPCC database

In this paper, we assess and compare to observations the spatial characteristics of the twentieth Century ENSO SST variability simulated by 23 models of the IPCC-AR4/CMIP3 database. The analysis is confined to the SST anomalies along the equatorial Pacific and is based on the use of a non-linear neural classification algorithm, the Self-Organizing Maps. Systematic biases include a larger than observed proportion for modelled ENSO maximum variability occurring in the Western Pacific. No clear relationship is found between this bias and the characteristics of the modelled mean state bias in the equatorial Pacific. This bias is mainly related to a misrepresentation of both El Niño and La Niña termination phases for most of the models. In contrast, the onset phase is quite well simulated. Modelled El Niño and La Niña peak phases display an asymmetric bias. Whereas the main bias of the modelled El Niño peak is to exhibit a maximum in the western Pacific, the simulated La Niña bias mainly occurs in the central Pacific. In addition, some models are able to capture the observed El Niño peak characteristics while none of them realistically simulate La Niña peaks. It also arises that the models closest to the observations score unevenly in reproducing the different phases, preventing an accurate classification of the models quality to reproduce the overall ENSO-like variability.     

Annual cycles in the interstellar scintillation time-scales of PKS B1519–273 and PKS B1622–253

We have used the University of Tasmania's 30-m radio telescope at Ceduna in South Australia to regularly monitor the flux density of a number of southern blazars. We report the detection of an annual cycle in the variability time-scale of the centimetre radio emission of PKS B1622−253. Observations of PKS B1519−273 over a period of nearly 2 yr confirm the presence of an annual cycle in the variability time-scale in that source. These observations prove that interstellar scintillation is the principal cause of inter-day variability at radio wavelengths in these sources. The best-fitting annual cycle model for both sources implies a high degree of anisotropy in the scattering screen and that it has a large velocity offset with respect to the local standard of rest. This is consistent with a greater screen distance for these 'slow' intra-day variability (IDV) sources than for rapid scintillators such as PKS B0405−385 or J1819+3845.     

Optical and near-infrared colours as a discriminant of the age and metallicity of stellar populations

We present a comprehensive analysis of the ability of current stellar population models to reproduce the optical ( ugriz ) and near-infrared ( JHK ) colours of a small sample of well-studied nearby elliptical and S0 galaxies. We find broad agreement between the ages and metallicities derived using different population models, although different models show different systematic deviations from the measured broad-band fluxes. Although it is possible to constrain simple stellar population models to a well-defined area in age–metallicity space, there is a clear degeneracy between these parameters even with such a full range of precise colours. The precision to which age and metallicity can be determined independently, using only broad-band photometry with realistic errors, is  Δ[Fe/H]≃ 0.18  and  Δlog Age ≃ 0.25  . To constrain the populations and therefore the star formation history further, it will be necessary to combine broad-band optical–IR photometry with either spectral line indices, or else photometry at wavelengths outside this range.     

Simulation of the progressive failure of an embankment on soft soil

A pragmatic strain-softening constitutive model, which is based on Modified Cam Clay, was applied to the simulation of the progressive failure of an embankment constructed on a deposit of sensitive (strain-softening) clay in Saga, Japan. A comparison of the predictions for this case indicates that if softening is ignored, only relatively small deflections and consolidation settlements are predicted, especially after construction. In contrast, for the case where softening is included in the analysis, progressive failure within the clay induces large shear deformations and finally failure of the embankment is predicted. This comparison suggests that softening-induced progressive failure should be considered in the design of embankments on such soils, and the residual strength of the deposit may have an important influence on the overall factor of safety of the construction. Detailed analyses of predicted excess pore water pressures, shear strains and shear stress levels in the ground indicate that considering the strain-softening process: (a) is associated with the buildup of excess pore water pressure; (b) promotes strain localization; and (c) results generally in a larger zone of soil involved in the failure.