Hydraulic conductivity of a dense prehydrated geosynthetic clay liner

Dense prehydrated geosynthetic clay liners (DPH-GCLs) are a particular type of GCL which, unlike conventional GCLs manufactured with dry bentonite, contain bentonite prehydrated during manufacturing. DPH-GCLs are produced by a patented process that includes bentonite prehydration with a polymer solution and vacuum extrusion. This paper describes the results of permeability tests that were carried out using flexible-wall permeameters to investigate the hydraulic conductivity of a DPH GCL to water, natural seawater and a 12.5mmol/L CaCl2 solution. Moreover, the efficiency of the 0.1 m overlap seams between DPH-GCL panels has been investigated by means of a medium-scale permeameter able to accommodate specimens 0.305 m in diameter. Test results showed that the DPH GCL has very low hydraulic conductivity to water (1

Education policies in England: exploring the relationship between the focus on attainment/achievement in the school-environment and adolescents’ mental health

This study investigated the influence of the secondary school-environment on adolescent mental health (MH). Late adolescents (16-18-years-old) experience multiple contributors to their MH, particularly the pressure of high-stakes examinations engendering an emotionally charged, performance-based learning environment. These pressures. associated with transitioning and the greater responsibility for the future, reflect prevailing neoliberal values of competition, responsibilization and individualism. I studied the school-environment using a Critical Theory approach and ethnographic and participatory methods. Student-participants from a sixth-form college co-researched the study topic alongside teachers, parents and college-leaders. In this way, different ‘roles’ and lived experiences came together in a democratic platform to critically explore the relationship between education and MH. The study shows that late adolescents are grappling with introspection (e.g., self-esteem, self-doubt) and therefore managing different layers of recognition which include an ‘intimate estrangement’ that influence their well-being, their subjectivity, and MH. Subjectivity, and modes of subjectivation, helped explain a complex relationship with the self, revealing the influence of compulsory education environments on MH. Co-produced findings provided reflexive opportunities for participants to reconsider their status as service-users and stakeholders in school and mitigate a pervasive sense of ‘crisis’ through participatory action for change. The study’s findings can help policymakers to: (i) inform education policy for more precise definitions and inclusive approaches to define MH; (ii) monitor how schools and colleges engage with young people’s MH in the face of school environment and policy demands; (iii) assess through participatory consultations how students perceive MH related policy to adjust in implementation. The impact of educational policy on MH is critical as policy is often ideological and polyvalent and intersects with educational life during adolescents’ transition to adulthood. Policies constitute modalities of being (subjectivities) by imagining the ‘good life’ for all; they should thus also recognise students as stakeholders to be involved in their development, as people able to make authentic choices and hold critical views about educational success and failure

Policy ‘Meandering’: The Influence of Mental Health and Well-being in Educational Policies

This article contextualizes, and contests, the use of the terms mental health (MH) and well-being in ideologically driven educational policies and practices, market oriented, individualistic and measurable. Alongside an unprecedented worldwide trend to establish an educational ‘turn’, so called ‘therapeutic education’, it is argued that educational policies in the UK have arbitrarily merged, or ‘yoked’, the terms MH and well-being with ethical implication for policy implementation. Through ethnographic and participative methodologies, involving the main social actors to mobilize expert knowledge in two educational settings, the ‘yoking’ of MH with well-being becomes apparent and catalyst for further yoking. Hence, more policies and new concepts emerge as manipulations of school/colleges’ initiatives, such as achieving good results or promoting ‘character’ to engineer next generation citizenry. Juxtaposing the terms MH and well-being to education calls for clearer re-definitions of the aims of education. Every effort should be made by policy makers to keep the two terms independent from each other and well-articulated with performance indicators such as resilience that do not undermine the value of vulnerability. New definitions of MH and well-being should guide policy making and implementation in schools/colleges, to avoid lumping up together heterogeneous and multilayered terms that deserve distinct attention and application

Determination of consistency limits of clay by means of extrusion tests

The liquid limit of clay is commonly determined through the Casagrande test or the fall-cone test, while the plastic limit is determined through the hand rolling method. The greatest issue with some of these techniques is their low repeatability and operator dependency. In order to minimize those issues, an indirect-extrusion based technique was evaluated as an alternative method to determine both consistency limits. The experimental work was carried out on mixtures of kaolin and bentonite to cover a wide range of plasticity. The results suggested that there is a specific extrusion pressure linked to each consistency limit and that the results are repeatable. The liquid limit obtained through the extrusion method closely matches the results of the fall-cone test. Similarly, the plastic limit out of extrusion closely matches the results of the hand rolling method

Hydraulic conductivity of a dense prehydrated GCL: impact of free swell and swelling pressure

Exposure to liquids with high electrolyte concentrations or high cation valence present in landfill leachates can cause significant increases in hydraulic conductivity of clays due to a reduction in the thickness of the double layer. Methods to prevent compression of the interlayer are: prehydration of the bentonite, compression with increasing the solids content and addition of polymers. The aim of this study is to evaluate the performance of a dense prehydrated GCL (DPH GCL) compressed during manufacturing and pre-hydrated with a polymeric solution. A series of hydraulic conductivity tests with deionised water, sea water and a 0.01 M CaCl 2 solution were performed on single sheet and overlapped DPH GCL samples. Free swell and swelling pressure tests have also been performed with this solutions and with a series of KCI and CaCl 2 solutions with a concentration varying from 0.001 M to 1 M. The overlapped samples were analysed in large scale laboratory permeameters at different effective stresses. In addition, swelling pressure tests on single sheet samples were conducted to analyse the swelling behaviour of the factory prehydrated GCL. The concomitant effect of prehydration, addition of polymeric compounds and densification increased the hydraulic performance of GCLs under aggressive conditions. The use of bentonite paste to seal the overlap in presence of seawater was shown to be crucial. The swelling pressure test may be proposed as an alternative to the swell index test to characterize the swelling behaviour of polymer prehydrated GCLs

Hydraulic conductivity and swelling pressure of GCLs using polymer treated clays to high concentration CaCl(2) solutions

A Geosynthetic Clay Liner (GCL) is a frequently used h ydraulic barrier system designed to impede the flow of contaminated leachate into the environment. The main objective of this barrier system is to maintain a low hydraulic conductivity that is determined by the bentonite fraction. In this study, calcium bentonite, natural sodium bentonites, and sodium activated bentonite were treated with the HYPER clay technique. This involves the adsorption of an anionic polymer, Sodium CarboxyMethylCellulose (Na-CMC) onto the surface of the clay material. The purpose of this research was to show the beneficial effect of the HYPER clay treatment on the swelling and hydraulic performance, while the bentonite is permeated with high concentration CaCl2 solutions. The test results showed that swelling and hydraulic performance increased with Na-CMC treatment, regardless of the type of bentonite that was used. Additionally, a powdered Na CMC configuration provided higher swelling and hydraulic performance compared to a granular configuration