Centrifuge modelling of cone penetration tests in layered soils

Penetration problems are important in many areas of geotechnical engineering, such as the prediction of pile capacity and interpretation of in situ test data. The cone penetration test is a proven method for evaluating soil properties, yet relatively little research has been conducted to understand the effect of soil layering on penetrometer readings. This paper focuses on the penetration of a probe within layered soils and investigates the layered soil effects on both penetration resistance and soil deformation. A series of centrifuge tests was performed in layered configurations of silica sand with varying relative density in a 180° axisymmetric model container. The tests allowed for the use of a half-probe for observation of the induced soil deformation through a poly(methyl methacrylate) window as well as a full-probe for measurement of penetration resistance within the central area of the container. The variations of penetration resistance and soil deformation characteristics as they relate to penetration depth, soil density and soil layering are examined. The results of deformation are also compared with previous experimental data to examine the effect of the axisymmetric condition. The effects of soil layering on both resistance and soil deformation are shown to be dependent on the relative properties between soil layers

Associations between stratospheric variability and tropospheric blocking

There is widely believed to be a link between stratospheric flow variability and stationary, persistent “blocking” weather systems, but the precise nature of this link has proved elusive. Using data from the ERA-40 Reanalysis and an atmospheric general circulation model (GCM) with a well-resolved stratosphere (HadGAM), it is shown that there are in fact several different highly significant associations, with blocking in different regions being related to different patterns of stratospheric variability. This is true in both hemispheres and in both data sets. The associations in HadGAM are shown to be very similar to those in ERA-40, although the model has a tendency to underestimate both European blocking and the wave number 2 stratospheric variability to which this is related. Although the focus is on stratospheric variability in general, several of the blocking links are seen to occur in association with the major stratospheric sudden warmings. In general, the direction of influence appears to be upward, as blocking anomalies are shown to modify the planetary stationary waves, leading to an upward propagation of wave activity into the stratosphere. However, significant correlations are also apparent with the zonal mean flow in the stratosphere leading the occurrence of blocking at high latitudes. Finally, the underestimation of blocking is an enduring problem in GCMs, and an example has recently been given in which improving the resolution of the stratosphere improved the representation of blocking. Here, however, another example is given, in which increasing the stratospheric resolution unfortunately does not lead to an improvement in blocking

Interpretation of cone penetration test data in layered soils using cavity expansion analysis

Cavity expansion theory plays an important role in many geotechnical engineering problems, including the cone penetration test (CPT). One of the challenges of interpreting CPT data is the delineation of interfaces between soil layers and the identification of distinct thin layers, a process which relies on an in-depth understanding of the relationship between penetrometer readings and soil properties. In this paper, analytical cavity expansion solutions in two concentric regions of soil are applied to the interpretation of CPT data, with a specific focus on the layered effects during penetration. The solutions provide a large-strain analysis of cavity expansion in two concentric regions for dilatant elastic-perfectly plastic material. The analysis of CPT data in two-layered soils highlights the effect of respective soil properties (strength, stiffness) on CPT measurements within the influence zones around the two-soil interface. Results show good comparisons with numerical results and elastic solutions. A simple superposition method of the two-layered analytical approach is applied to the analysis of penetration in multilayered soils. A good comparison with field data and numerical results is obtained. It is illustrated that the proposed parameters effectively capture the influence of respective soil properties in the thin-layer analysis. It is also shown that results based on this analysis have better agreement with numerical results compared with elastic solutions

Cavity expansion-contraction based method for tunnel-soil-pile interaction in a unified clay and sand model: drained analysis

This paper proposes an analytical method based on drained solutions of cavity expansion and contraction in a unified clay and sand model to investigate tunnel-soil-pile interactions. Cavity expansion analyses are used to evaluate the effects of pile installation on ground stresses and to determine pile end bearing capacity and the distribution of shaft friction. Cavity contraction methods were adopted to replicate the tunnel convergence-confinement response using the singularity and image method for ground loss and ovalization of a shallow tunnel in a semi- infinite medium. A 2D model was developed which evaluates changes in mean stress and specific volume during pile installation and tunnel excavation. Outcomes from the developed analytical approach are compared against data from centrifuge tests in silica sand; results demonstrate that trends in pile load capacity degradation, mobilized safety factor, and tunneling induced pile settlement can be satisfactorily predicted for the case of a tunnel excavated beneath a pile with a constant service load. Criteria based on pile capacity, safety factor, and settlement are proposed which can be used to determine a critical tunnel volume loss or evaluate pile safety level. The paper contributes to the understanding of tunnel-soil-structure interaction mechanisms and provides an efficient means of conducting a preliminary risk assessment of tunnel-pile interaction

Interannual variability of the tropical Atlantic independent of and associated with ENSO: Part I. The North Tropical Atlantic

The interannual variability of the tropical Atlantic ocean-atmosphere system is examined using 50 years of sea-surface temperature (SST) and re-analysis data, and satellite data when available. A singular value decomposition analysis of 12- to 72-month bandpass filtered SST and zonal wind stress reveals two dominant modes of interannual variability. The SST anomalies are confined to the North Tropical Atlantic (NTA) in the first mode and extend over the equatorial and South Tropical Atlantic in the second mode. No evidence is found for an Atlantic SST dipole. The structure of the first (NTA) mode is examined in detail here, while the second mode has been described in a companion paper. In particular, the relationship of the NTA mode with El Nino-Southern Oscillation (ENSO) is investigated. There are 12 NTA events (seven warm and five cold) that are associated with ENSO, and 18 NTA events (seven warm and 11 cold) that are independent of ENSO. The ENSO-associated NTA events appear to be a passive response to remote ENSO forcing, mainly via a Pacific-North America (PNA)-like wave train that induces SST anomalies over the NTA through changes in the surface wind and latent heat flux. The NTA anomalies peak four months after ENSO. There does not appear to be an atmospheric response to the NTA SST anomalies as convection over the Atlantic is suppressed by the anomalous Walker circulation due to ENSO. The ENSO-independent NTA events also appear to be induced by an extratropical wave train from the Pacific sector (but one that is independent of Pacific SST), and forcing by the North Atlantic Oscillation (NAO) also contributes. As the event matures, the atmosphere does respond to the NTA SST anomalies, with enhanced convection over the Caribbean and a wave train that propagates northeastward to Europe

A Station-Based Southern Annular Mode Index from 1884 to 2005

Atmospheric pressure observations from the Southern Hemisphere are used to estimate monthly and annually averaged indexes of the southern annular mode (SAM) back to 1884. This analysis groups all relevant observations in the following four regions: one for Antarctica and three in the subtropical zone. Continuous surface pressure observations are available at a number of locations in the subtropical regions since the end of the nineteenth century. However, year-round observations in the subpolar region near the Antarctic continent began only during the 1940-60 period. The shorter Antarctic records seriously compromise the length of a traditionally estimated SAM index. To improve the situation "proxy'' estimates of Antarctic sea level pressure anomalies are provided based on the concept of atmospheric mass conservation poleward of 208S. This allows deriving a longer SAM index back to 1884. Several aspects of the new record, its statistical properties, seasonal trends, and the regional pressure anomaly correlations, are presented

Cosmological constraints from clustering properties of galaxy clusters

In this paper, we discuss improvements of the Suto et al. (2000) model, in the light of recent theoretical developments (new theoretical mass functions, a more accurate mass-temperature relation and an improved bias model) to predict the clustering properties of galaxy clusters and to obtain constraints on cosmological parameters. We re-derive the two-point correlation function of clusters of galaxies for OCDM and LambdaCDM cosmological models, and we compare these results with the observed spatial correlation function for clusters in RASS1 (ROSAT All-Sky Survey 1), and in XBACs (X-RAY Brighest Abell-Type) samples. The comparison shows that the best agreement is obtained for the LambdaCDM model with Omega=0.3. The values of the correlation length obtained, (r_\simeq 28.2 \pm 5.2 \rm h^{-1}} Mpc for LambdaCDM), are larger than those found in the literature and comparable with the results found in Borgani, Plionis & Kolokotronis (1999). (REST IN THE PAPER ABSTRACT)Comment: printed in A&

Conservation organizations need to consider adaptive capacity: why local input matters

Conservation organizations are increasingly applying adaptive capacity assessments in response to escalating climate change impacts. These assessments are essential to identify climate risks to ecosystems, prioritize management interventions, maximize the effectiveness of conservation actions, and ensure conservation resources are allocated appropriately. Despite an extensive literature on the topic, there is little agreement on the most relevant factors needed to support local scale initiatives, and additional guidance is needed to clarify how adaptive capacity should be assessed. This article discusses why adaptive capacity assessment represents a critical tool supporting conservation planning and management. It also evaluates key factors guiding conservation NGOs conducting these assessments in tropical island communities, and explores alternative priorities based on input from academic experts and key local stakeholders. Our results demonstrate that important differences exist between local stakeholders and nonlocal academic experts on key factors affecting adaptation and coping mechanisms. The exclusion of local community input affects the validity of adaptive capacity assessment findings, and has significant implications for the prioritization and effectiveness of conservation strategies and funding allocation

Analytic models of plausible gravitational lens potentials

Gravitational lenses on galaxy scales are plausibly modelled as having ellipsoidal symmetry and a universal dark matter density profile, with a Sersic profile to describe the distribution of baryonic matter. Predicting all lensing effects requires knowledge of the total lens potential: in this work we give analytic forms for that of the above hybrid model. Emphasising that complex lens potentials can be constructed from simpler components in linear combination, we provide a recipe for attaining elliptical symmetry in either projected mass or lens potential. We also provide analytic formulae for the lens potentials of Sersic profiles for integer and half-integer index. We then present formulae describing the gravitational lensing effects due to smoothly-truncated universal density profiles in cold dark matter model. For our isolated haloes the density profile falls off as radius to the minus fifth or seventh power beyond the tidal radius, functional forms that allow all orders of lens potential derivatives to be calculated analytically, while ensuring a non-divergent total mass. We show how the observables predicted by this profile differ from that of the original infinite-mass NFW profile. Expressions for the gravitational flexion are highlighted. We show how decreasing the tidal radius allows stripped haloes to be modelled, providing a framework for a fuller investigation of dark matter substructure in galaxies and clusters. Finally we remark on the need for finite mass halo profiles when doing cosmological ray-tracing simulations, and the need for readily-calculable higher order derivatives of the lens potential when studying catastrophes in strong lenses.Comment: 24 pages, 10 figures, matches published versio