Centrifuge modelling of active slide–pipeline loading in soft clay

Submarine slides are a significant hazard to the safe operation of pipelines in the proximity of continental slopes. This paper describes the results of a centrifuge testing programme aimed at studying the impact forces exerted by a submarine slide on an offshore pipeline. This was achieved by dragging a model pipe at varying velocities through fine-grained soil at various degrees of consolidation, hence exhibiting properties spanning from the fluid to the geotechnical domains, relevant to the state of submarine slide material. To simulate the high strain rates experienced by the soil while flowing around a pipe in the path of a submarine slide, tests were conducted at pipe–soil velocities of up to 4.2 m/s. The changing density and shear strength of the samples were back-calculated from T-bar penetrometer test results. A hybrid approach combining geotechnical and fluid-mechanics-based components of horizontal drag resistance was developed. This approach provides an improved method to link the density and strength of the slide material to the force applied on the pipe. Besides fitting the present observations, the method provides an improved reinterpretation of similar data from the literature

Laboratory development of a vertically oriented penetrometer for shallow seabed characterization

Current site investigation practice for offshore pipeline design relies on soil parameters gathered from boreholes or in-situ test soundings to depths of 1-2 m below the mudline. At these depths, the fine-grained seabed is very soft and possesses low undrained strength, which can be difficult to measure. This paper describes a centrifuge test programme undertaken to evaluate the feasibility and performance of a novel penetrometer designed to assess the shallow strength of soft seabed over continuous horizontal profiles. This device is termed the vertically oriented penetrometer (VOP). Tests were performed on a normally consolidated kaolin sample, with the VOP translated horizontally at velocities ranging from 1 – 30 mm/s, after embedding the VOP at 30 mm and 45 mm depths. All tests involved many cycles of VOP forward and backward movement to assess its potential to derive the ratio of intact to fully remoulded strength. Strength determination is achieved by dragging the VOP at a specified embedment depth along the soil surface, and deriving the soil strength from the measured resistance as if the VOP were a laterally loaded pile. The VOP is shown to yield comparable strength measurements to that of a T-bar penetrometer. The VOP is a potentially valuable addition to the range of tools used to characterize soil strength, both in small scale centrifuge models and, following practical development, potentially also in the field

Engaging with issues of emotionality in mathematics teacher education for social justice

This article focuses on the relationship between social justice, emotionality and mathematics teaching in the context of the education of prospective teachers of mathematics. A relational approach to social justice calls for giving attention to enacting socially-just relationships in mathematics classrooms. Emotionality and social justice in teaching mathematics variously intersect, interrelate or interweave. An intervention, usng creative action methods, with a cohort of prospective teachers addressing these issues is described to illustrate the connection between emotionality and social justice in the context of mathematics teacher education. Creative action methods involve a variety of dramatic, interactive and experiential tools that can promote personal and group engagement and embodied reflection. The intervention aimed to engage the prospective teachers with some key issues for social justice in mathematics education through dialogue about the emotionality of teaching and learning mathematics. Some of the possibilities and limits of using such methods are considered

Pass a Law, Any Law, Fast! State Legislative Responses to the Kelo Backlash

The Supreme Court in Kelo v. City of New London left protection of property against takings for economic development to the states. Since Kelo, thirty-seven states have enacted legislation to update their eminent domain laws. This paper is the first to theoretically and empirically analyze the factors that influence whether, in what manner, and how quickly states change their laws through new legislation. Fourteen of the thirty-seven new laws offer only weak protections against development takings. The legislative response to Kelo was responsive to measures of the backlash but only in the binary decision whether to pass any new law. The decision to enact a meaningful restriction was more a function of relevant political economy measures. States with more economic freedom, greater value of new housing construction, and less racial and income inequality are more likely to have enacted stronger restrictions, and sooner. Of the thirteen states that have not updated, Arkansas, Oklahoma and Mississippi are highly likely to do so in the future. Hawaii, Massachusetts and New York are unlikely to update ever if at all

Poly-lactic acid nanoparticles (PLA-NP) promote physiological modifications in lung epithelial cells and are internalized by clathrin-coated pits and lipid rafts

BackgroundPoly-lactic acid nanoparticles (PLA-NP) are a type of polymeric NP, frequently used as nanomedicines, which have advantages over metallic NP such as the ability to maintain therapeutic drug levels for sustained periods of time. Despite PLA-NP being considered biocompatible, data concerning alterations in cellular physiology are scarce.MethodsWe conducted an extensive evaluation of PLA-NP biocompatibility in human lung epithelial A549 cells using high throughput screening and more complex methodologies. These included measurements of cytotoxicity, cell viability, immunomodulatory potential, and effects upon the cells’ proteome. We used non- and green-fluorescent PLA-NP with 63 and 66 nm diameters, respectively. Cells were exposed with concentrations of 2, 20, 100 and 200 µg/mL, for 24, 48 and 72 h, in most experiments. Moreover, possible endocytic mechanisms of internalization of PLA-NP were investigated, such as those involving caveolae, lipid rafts, macropinocytosis and clathrin-coated pits.ResultsCell viability and proliferation were not altered in response to PLA-NP. Multiplex analysis of secreted mediators revealed a low-level reduction of IL-12p70 and vascular epidermal growth factor (VEGF) in response to PLA-NP, while all other mediators assessed were unaffected. However, changes to the cells’ proteome were observed in response to PLA-NP, and, additionally, the cellular stress marker miR155 was found to reduce. In dual exposures of staurosporine (STS) with PLA-NP, PLA-NP enhanced susceptibility to STS-induced cell death. Finally, PLA-NP were rapidly internalized in association with clathrin-coated pits, and, to a lesser extent, with lipid rafts.ConclusionsThese data demonstrate that PLA-NP are internalized and, in general, tolerated by A549 cells, with no cytotoxicity and no secretion of pro-inflammatory mediators. However, PLA-NP exposure may induce modification of biological functions of A549 cells, which should be considered when designing drug delivery systems. Moreover, the pathways of PLA-NP internalization we detected could contribute to the improvement of selective uptake strategies

An investigation of two peat slope failures in the Wicklow mountains

Although peat slope failures have occurred in Ireland for many thousands of years their causal factors and the triggering mechanisms involved are poorly understood. A particular barrier to quantitative assessment of the risk of failures is the lack of knowledge of the geotechnical properties of peat and its role in failures. In order to advance the understanding of these issues case history data is invaluable. This paper describes a case study from the Wicklow mountains where a desk and remote sensing based study was used to identify peat slope failures. Subsequently detailed field studies were carried out at two failure locations. It was found that although the full causal factors at the time of failure are unknown, a common factor was that the failure took place in a zone of highly decomposed and relatively low fibre content peat. A revision of the standard test method for fibre content for use in peat soils is proposed.Not applicabl

Informed mine closure by multi-dimensional modelling of tailings deposition and consolidation

This paper introduces an advanced geotechnical numerical modelling approach, which can be used to simulate the gradual deposition and large-strain consolidation of tailings in a multi-dimensional space. The findings from the modelling can be used not only to inform planning and design at mine closure but also help the management of tailings impoundments. For example, the results can be used to determine the settlement of tailings with time and thus inform backfilling planning; or inform on the tailings settlement and thereby assist with the design of an effective drainage network to divert surface water. Following a state-of-practice review of tailings consolidation modelling, the recently developed multi-dimensional modelling technique (the Norwegian Geotechnical Institute [NGI] model) is described in the paper, with validations against available analytical solutions and comparisons with commonly used predictions presented by Townsend & McVay (1990). An example of the application of the NGI model is presented to demonstrate its capability and performance in modelling a full-scale scenario. The NGI modelling approach is built on commercially available specialised geotechnical modelling software, FLAC (and FLAC3D), through its embedded programming language, FISH. The NGI model extends FLAC’s existing capability of large-strain consolidation calculation to simulate the gradual deposition process of the tailings. The deposition of the tailings slurry is divided into many discontinuous layers, and these layers are activated one after another from the bottom up. Activation of each new layer (on top of the existing tailings surface) is followed by a large-strain consolidation stage, with the consolidation time being determined as a function according to the volume of the layer and discharge history. Rock backfilling can be modelled in a similar fashion or can be customised. A user-defined constitutive model (as part of the NGI model) has been developed to reproduce the key characteristics of the tailings during consolidation, including the variation of compressibility and permeability with reducing voids ratio. The consolidation of the tailings is modelled in a large-strain mode (i.e. the coordinates of the grid are updated frequently) in order to capture its effect on the consolidation behaviour and the deformation occurred prior to addition of a new layer. The NGI model is also capable of performing complex three-dimensional problems accounting for varying consolidation boundary conditions, non-uniformity of the tailings material, and irregular pit geometries. As illustrated by the example application, this approach can be used to predict the development of tailing consolidation settlement with time, the amount of water expressed during consolidation, the capacity of the pit for tailings storage and the required amount of rock for backfilling. Further development is ongoing in order to expand its modelling capability, such as prediction of increase in tailings strength with consolidation, modelling drying and consolidation of tailings, simulation of tailings dam construction process to improve prediction of tailings dam stability, and so forth.publishedVersio

Development of a direct simple shear apparatus for peat

This paper discusses the design and development of a new direct simple shear (DSS) apparatus for testing peat soils. The apparatus has been designed to test peat at low effective stresses, representative of its in-situ condition and allow the deformation of the specimen to be monitored. This device uses Particle Image Velocimetry (PIV) image analysis techniques to monitor the side of the peat specimen and provide an insight into the behaviour of peat during shearing. A set of comparative tests on remoulded clay have been conducted with another widely used DSS apparatus and has shown both to yield similar undrained strength ratios (su/σ'vc) for a range of stress levels. Application of the apparatus to peat soils is demonstrated by a set of tests on a high water content blanket bog peat. Analysis of these tests using the PIV technique reveals the complex shear strain and volumetric strain behaviour of peat undergoing shearing. Identification of partial slippage of a specimen is also demonstrated through these analyses.Not applicabl

Peat slope failure in Ireland

Recent peat failures in Ireland in the autumn of 2003 at Pollatomish, County Mayo and Derrybrien, County Galway have focused attention on such events. However, peat failures are not a recent phenomenon with possible evidence of peat failures in Ireland having been identified as far back as the Early Bronze Age. This paper summarises the issues surrounding peat failures in Ireland that would be of interest to an engineer\engineering geologist assessing this geohazard. The distribution of peat throughout Ireland, its formation, and its typical characteristic properties are discussed. A review of historical failures shows that there is a relationship between run out distance and failure volume and that the majority of the failures are clustered at slope angles between 4º and 8º. It seems that the risk of fatalities from peat slides is relatively low. The likely casual factors attributed to peat failures are presented using examples of failure, including the recent failures at Pollatomish and Derrybrien both of which have been investigated by the authors. Particular attention is paid to shear strength properties of peat and the applicability of traditional soil mechanics. Given the uncertainties which exist about peat strength, a cautious approach to slope stability assessment is advocated together with identification of potential causal factors to mitigate against this geohazard.Not applicabl