Enhancing the understanding of lime stabilisation processes

Lime stabilisation is a ground improvement technique used to improve the engineering properties of cohesive fill materials. During earthworks operations, specialist plant is used to rotovate the clay fill material and intermix lime binder around clay clods. After completion of the lime treatment, the layer is compacted in the usual way. Immediately after mixing, the lime instigate a series of physico-chemical reactions within the clay soil. Where the chemical reactions are favourable and with time after compaction (curing) the material becomes progressively stronger and durable to environmental influences, e.g. inundation by surface or ground water. However, where sulphate is present within the soil, the reactions may change and the ingress of water into the layer can result in the expansive growth of deleterious minerals e.g. ettringite. While sulphate swell issues are relatively rare, when they do occur the degree of expansion can be very high. A high profile sulphate swell failure developed during the construction of the M40, Oxford, UK in 1989. Over the winter period after the lime stabilisation works, a 250mm deep lime treated layer heaved by up to 150mm - destroying the overlying road construction. Since the M40 failure, a substantial amount of effort has been undertaken to better understand the sulphate swell reactions and in this regard the state of scientific knowledge is relatively strong. A fundamental issue for field applications of lime stabilisation is that the vast majority of research has been undertaken on laboratory specimens prepared using methods which do not reflect site practice. Laboratory studies often use oven dried and finely crushed clay, whereas site operations will treat much larger clay clods to result in a more heterogeneous distribution of lime through the compacted soil body. With large clay clods, the chemical reactants must migrate through clods and this may cause the sequence of chemical reactions to change. A further challenge is that laboratory studies are typically undertaken with cure temperatures of 20°C, whereas a typical near surface temperature in the UK is <10°C. This is of particular relevance to sulphate swell failures which are reported to coincide with a reduction in ambient temperature over winter periods. Thus, the direct relevance of laboratory studies to site application was unclear. A series of laboratory experiments using a preparation method which reflects field applications of lime stabilisation was used to investigate the influence of large clay clods on the durability of lime stabilised clay soil. This method was applied to both low and high sulphate clay soils. A fundamental discovery from work on low sulphate clay is that the addition of lime binder to the surface of the clay clods causes a physico-chemical boundary to form. This boundary develops due to the rapid increase to the plastic limit of the clay preventing adjacent clods from joining together during compaction. This causes the engineering properties of each individual clod to develop independent to its neighbours and for each clay clod to be separated by an inter-clod pore space. The strength of each individual clay clod will increase with curing as the added lime dissociates into Ca2+ and OH- and migrates to form C-S-H deep within the clods. Where the material is compacted wet of the optimum water content, this condition improves ion migration and enables development of diffuse cementation deep within clods. The inter-clod porosity remains as a weakness throughout curing especially during specimen soaking, where the pore channels comprise a pathway, accelerating the ingress of soaking water. With low sulphate soil, the soaking water softens the treated material, however, with high TPS soil substantial sulphate swelling may develop. Thus, efforts to minimise this porosity during preparation is important and the use of quicklime with longer mellowing periods can cause the clay clods to develop high strength before compaction. The high strength clods resist compaction and the degree of inter-clod porosity in the compacted mass increases, worsening specimen durability to water ingress. The investigations into high sulphate clays included the development of a Novel Swell Test (NST) to assess volume change. A unique aspect of the NST was that the sulphate swell response of the lime treated material was investigated at site realistic temperatures of 8°C. It was identified that, when compared with standard laboratory test temperatures of 20°C the rate of sulphate swell is substantially higher at the low temperature. The mineralogical testing has permitted the hypothesis that, at 8°C the growth of crystalline ettringite becomes slower and the ettringite precursor, which has a high affinity to imbibe water, remains in this state for much longer. Thus, laboratory swell tests at 20°C may substantially underestimate the degree of swell that may develop in the field. As a pressing need, it is recommended that the industry adapt sulphate swell test methods to appraise the degree of swell at field realistic temperatures i.e. < 10°C. The work also identifies that the primary defence against sulphate swell is to condition the fill so that the risk of post compaction water ingress, via inter-clod porosity, is minimised. The use of GGBS and water addition during extended mellowing periods also reduces the degree of sulphate swell in natural clay soils. This work concludes that working methods for lime stabilisation of medium high plasticity soils of a potentially high sulphate content, should be adapted to encourage diffuse cementation and minimise the degree of (post compaction) inter-clod porosity. Practically this involves the use of hydrated lime and the addition of mixing water throughout extended mellowing periods. Fundamentally, the study recommends that where construction programmes allow, the long term durability of a fill material should be the priority over immediate strength

The "Reducing the Impact of Sexual Exploitation" (RISE) Project: An Implementation evaluation

This project reports on the implementation evaluation of a two year pilot "Reducing the Impact of Sexual Exploitation (RISE)", that ran in Aberdeen and Dundee. The project was designed to address the Scottish Government’s National Action Plan to Prevent and Tackle Child Sexual Exploitation (2014, 2016), through the deployment of CSE advisors. The overall aim of RISE is to identify, protect and support children and young people who are vulnerable or at risk of CSE, and those who have been identified as victims, and to prevent CSE by disrupting patterns of perpetration. The work of the CSE Advisors has three major strands: training and consultation; direct work with children and families; and improving intelligence sharing. Evaluation Aims: The aim of this research was to evaluate the implementation of RISE, and to identify early indications of potential impact. Four main research objectives underpin this principle aim: i) To examine the processes and structures which have been put in place to implement the project ii) To assess the effectiveness of these processes and structures across the two pilot sites iii) To provide an indication of the overall impact of the project – by gaining insights into the impact the project has on the intended outcomes of the pilot iv) To identify the key lessons learned in implementation of the project and identify potential challenges and opportunities for the future delivery and sustainability of the project Method The implementation evaluation takes a mixed method approach to examine the impact of the RISE project on the service landscape in the two pilot sites. Focus groups were conducted with 31 professionals from policing, social care, education, health and the voluntary sector in each site. Individual interviews were conducted with the CSE Advisors. In addition, the research team examined routinely collected service data, including anonymised and aggregated outcomes data for children and young people, and self-assessment questionnaires for participants on CSE training programmes. Qualitative data was analysed thematically (Braun and Clarke 2006) and quantitative data was analysed descriptively and using a repeated measures ANOVA. Data was then mapped against an implementation framework using a matrix based analysis, to explore service and implementation outcomes. Findings The CSE Advisor role was highly valued in both pilot sites, and was viewed as an effective way to support an improved and more appropriate response to children and young people who are at risk of or have experienced CSE. The introduction of the CSE Advisor role was seen as an effective way to improve professional responses to CSE, to provide targeted support for children, young people and carers, to enhance professional knowledge and skills. CSE Advisors have played a vital role in improving multiagency collaboration and information sharing, and multiagency and police partners indicated that the implementation of the CSE Advisor role has resulted in more trauma-aware practice, and trauma sensitive systems. Stakeholder professionals also indicated that there was evidence that the role had supported more effective disruption of perpetration

Model Skill and Sensitivity for Simulating Wave Processes on Coral Reefs Using a Shock-Capturing Green-Naghdi Solver

International audienceWave flume data from published benchmark experiments were used to extensively evaluate numerical model skill and sensitivity for applying a shock-capturing Green-Naghdi (GN) model to simulate nonlinear wave transformation processes on complex coral reefs. Boussinesq-type models that utilise nonlinear shallow water equations (NSWEs) to represent wave breaking and dissipation hold significant potential for understanding coastal hazards associated with global environmental change and sea-level rise. These fully nonlinear phase-resolving models typically require a threshold condition to switch from dispersive equations to shock-capturing NSWEs in areas of active wave breaking. However, limited information exits regarding how this splitting approach influences the behaviour of different surf-zone processes that contribute to wave runup and inundation on coral reefs. This paper presents a comprehensive analysis of model sensitivity to explore how input parameters that control wave breaking and dissipation influence the behaviour of sea-swell (SS) waves, infragravity (IG) waves, wave setup, runup and solitary waves on coral reefs. Results show that each wave process exhibits unique sensitivity to the free-surface slope threshold (B) that is used to represent areas of active wave breaking by locally switching from the weakly-dispersive GN equations to the shock-capturing NSWEs. However, accurate representation of all wave processes can be achieved if the wave-face steepens to at least 35 degrees (B ≥ 0.7) before breaking is initiated. Results from this research support and encourage the use of nonlinear phase-resolving wave models as tools for academic research, coastal management, coastal engineering and hazard forecasting on atoll and fringing reef environments

Child trafficking in Scotland

First paragraph: The Scottish Government Trafficking and Exploitation Strategy (2017) identified the need for Scotland-wide research to explore experiences of child trafficking in Scotland. This study, commissioned by the Scottish Government, aimed to provide an overview of how many children and young people had been identified as victims of human trafficking, to establish their geographic and demographic routes into Scotland and their experiences of professional responses. The research employed case file analysis and interviews with young people and professionals to illuminate these issues. For the index time-period for the research, no UK nationals were identified for the case file analysis. Consequently, the focus of the research was on children and young people who came to the UK across international borders

Exposure to the Law: Accountability and its impact on Street Level Bureaucracy

This article has been accepted for publication and will appear in a revised form, subsequent to peer review and/or editorial input by Cambridge University Press, in Social Policy and Society published by Cambridge University Press. Copyright.Little research has been conducted exploring the relationship between public sector accountability and the law. This is a significant oversight given the potential for this relationship to cause unintended consequences around issues of liability, especially in the context of a growing litigation culture. The purpose of the current research is to explore this relationship, using qualitative studies of public sector professionals in England. The findings of the study suggest that increasing emphasis on accountability has led to a growing magnification of legal risk in the public sector, with consequences for the ways in public sector professionals perceive their relations with the public

Child Trafficking in Scotland

First paragraph: The Scottish Government Trafficking and Exploitation Strategy (2017) identified the need for Scotland-wide research to explore experiences of child trafficking in Scotland. This study, commissioned by the Scottish Government, aimed to provide an overview of how many children and young people had been identified as victims of human trafficking, to establish their geographic and demographic routes into Scotland and their experiences of professional responses. The research employed case file analysis and interviews with young people and professionals to illuminate these issues. For the index time-period for the research, no UK nationals were identified for the case file analysis. Consequently, the focus of the research was on children and young people who came to the UK across international borders

Lime stabilisation for earthworks: a UK perspective

Lime stabilisation is a versatile technique applied during earthworks operations. Modern soil recycling units are much more efficient at pulverising fill material and intermixing the added binder/water than machinery available 20 years ago. While supplier innovation adds flexibility to the site working method, specifications have not been sufficiently updated to permit optimal application. This review paper details the physico-chemical changes instigated through the lime-clay soil reaction, updating previous reviews. It aims to assist scientific debate, current practitioners and future specification changes. For example, the application of the minimum 24 h mellowing periods (mandatory to UK specifications) with high reactivity, quicklime powders is concluded to cause increased air voids in the compacted fill. Increased air voids are associated with reduced long-term strength and potential volume change from water ingress, which is of particular concern for sulfate swelling. Shorter mellowing periods and/or use of hydrated lime may lesson this issue; however, a 'one size fits all' approach is discouraged in preference to site-specific methodologies refined to suit the fill material and project requirements. The discussion also summarises working methods which may lower the risk of sulfate swell and defines areas requiring further practical research

Fossil Java Sea corals record Laurentide ice sheet disappearance

The Laurentide ice sheet was the largest late Pleistocene ice mass and the largest contributor to Holocene pre-industrial sea-level rise. While glaciological dates suggest final ice sheet melting between 8 and 6 ka, inversion of sea-level data indicates deglaciation at ca. 7 ka. Here, we present new chronostratigraphic constraints on Laurentide ice sheet disappearance based on Holocene relative sea-level observations from the tectonically stable north coast of Java, Indonesia. Age-elevation data from the flat upper surfaces of 13 fossil intertidal corals (i.e., microatolls) indicate that the Java Sea experienced a relative sea level of 1.3 ± 0.7 m above present between 6.9 and 5.3 ka. To determine uncaptured relative sea-level trends within the observational uncertainties of this apparently constant highstand, we analyzed the internal structure of three sliced microatolls from the same site to produce a high-resolution data set. These data were used to statistically model relative sea-level rates and trends. Employing the data with the model provided evidence for a short-lived rise of relative sea level from 1.0 ± 0.3 m above present at 6.7 ± 0.1 ka to 1.9 ± 0.3 m above present at 6.4 ± 0.1 ka. The end of this rise likely represents the last input of meltwater from the vast Laurentide ice sheet, which, consequently, collapsed at least 400 yr later than assumed by some widely used models of glacial isostatic adjustment. Incorporating these new results into such predictive models will help to better understand the geographical variability of future sea-level rise as a result of global warming

The Sydney playground project- levelling the playing field: a cluster trial of a primary school-based intervention aiming to promote manageable risk-taking in children with disability

BackgroundProviding children and adults with opportunities to engage in manageable risk taking may be a stepping stone toward closing the gap in life conditions currently experienced by young people with disabilities. We aim to demonstrate the effectiveness of a simple, innovative program for 1) changing the way parents and teachers view manageable risk-taking for children with disabilities and 2) increasing the level of responsibility that children take for their own actions, as seen on the school playground.Methods/DesignWe will employ a cluster repeated measures trial with six Sydney-area primary-school-based programs for children with disabilities. The intervention comprises two arms. 1) Risk-reframing- teachers and parents will participate together in small group intervention sessions focusing on the benefits of manageable risk-taking; 2) Introduction of play materials- materials without a defined purpose and facilitative of social cooperation will be introduced to the school playground for children to use at all break times. A control period will be undertaken first for two school terms, followed by two terms of the intervention period. Outcome measures will include playground observations, The Coping Inventory, qualitative field notes, and The Tolerance of Risk in Play Scale.DiscussionNew national programs, such as Australia’s National Disability Insurance Scheme, will place increasing demands on young people with disabilities to assume responsibility for difficult decisions regarding procuring services. Innovative approaches, commencing early in life, are required to prepare young people and their carers for this level of responsibility. This research offers innovative intervention strategies for promoting autonomy in children with disabilities and their carers.Trial RegistrationAustralian and New Zealand Clinical Trials Registration Number ACTRN12614000549628 (registered 22/5/2014)