Compaction behaviour of clay

This paper presents an experimental study of the compaction behaviour of non-active clay. One-dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using Trento high-capacity tensiometers. At lower water contents, a transistor psychrometer was used to measure post-compaction suction. Samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses. Three water content regions were identified in the compaction plane depending on whether post-compaction suction increased, decreased or remained constant as the degree of saturation was increased at constant water content. Hydraulic paths of specimens subjected to loading-unloading cycles at constant water content have clearly shown that post-compaction suction may increase as the degree of saturation increases. This non-intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour. To this end, a coupled mechanical water retention model was formulated. Irreversible one-dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress, modified suction and void ratio. Irreversible hydraulic 'wetting' paths were modelled by a boundary surface in the space suction, degree of saturation, and void ratio. This study was completed by investigating the pore size distribution of compacted samples through MIP tests

Effects of high temperatures on soil properties : lessons to share from smouldering remediation experience

Aggressive, high-temperature contaminant remediation processes such as smouldering remediation are growing in popularity as technical knowledge of their capabilities becomes more widespread. Smouldering remediation is most aggressive of these processes and exposes soils to temperatures across the range of 500-1000 oC for hours to days, displacing water and destroying in excess of 99.9% of contaminant mass. The high temperatures and aggressive chemical reactions result in significant changes to the soil properties, particularly at the particle surface. Shifts in soil geochemistry, mineralogy, and structure are observed. Micro computed tomography shows that grain surfaces become significantly smoother after remediation. The changes are more extensive than initial mineralogy testing had suggested. Increased smoothness affects grain-grain and grain-water interactions and may explain some of the dynamic changes in infiltration, permeability, cohesiveness, and strength that have been observed in soils after smouldering remediation. Understanding these effects is essential to link micro-scale changes to macro-scale behaviour and develop a holistic approach to contaminated soil remediation and reuse. Important analogies can be drawn to the effects of fires on soil properties

Unsaturated soils : compacted versus reconstituted states

The paper presents a comparison between compacted and reconstituted soils in terms of microstructure, and hydraulic and mechanical response. It is commonly assumed that reconstituted and compacted soils exhibit a fundamentally different behaviour due to different microstructures. However, the variety of pore size distributions observed in both compacted and reconstituted/natural soils suggests that the boundary between compacted and reconstituted states is more blurred. In the paper, an attempt is made to recognize similarities and differences between compacted and reconstitutes states based on a number of recent experimental studies where the microstructure and the hydraulic and mechanical behaviour of unsaturated soils in compacted and reconstituted states have been investigated. This exercise will also offer the opportunity to gain a better insight into the microstructure of compacted soils

Numerical analysis of temperature stratification in the CIRCE pool facility

In the framework of Heavy Liquid Metal (HLM) GEN IV Nuclear reactor development, the focus is in the combination of security and performance. Numerical simulations with Computational Fluid Dynamics (CFD) or system codes are useful tools to predict the main steady-state phenomena and how transitional accidents could unfold in GEN IV reactors. In this paper, to support the validation of CFD as a valid tool for the design, the capability of ANSYS CFX v15.0 to simulate and reproduce mixed natural convection and thermal stratification phenomena inside a pool is investigated. The 3D numerical model is based on the CIRCE facility, located in C.R. ENEA Brasimone. It is a pool facility, structured with all the components necessary to simulate the behavior of an HLM reactor, where LBE flows into the primary circuit. For the analysis, the LBE physical properties are implemented in CFX by using recent NEA equations [2]. Previously published RELAP5-3D© results [1] are employed to derive accurate boundary conditions for the simulation of the steady-state conditions in the pool and for CFX validation. The analysis focuses on the pool natural circulation with the presence of thermal structures in contact with LBE, considered as constant temperature sources. The development of thermal stratification in the pool is observed and evaluated with a mesh sensitivity analysis

Creep response in shear of clayey geo-materials under saturated and unsaturated conditions

Translational slides in clays are often characterized by long-lasting intermittent movements associated with the fluctuations of pore-water pressure. Physically-based models designed to support hazard analysis of landslide movements and early warning systems require the integration of time-dependent (viscous) constitutive models for the shear displacements because landslide movements are typically controlled by the viscous behaviour of the clay geo-material. This paper presents an investigation of the viscous response of a clay geo-material under saturated and unsaturated conditions. Creep and relaxation tests have been first carried out on saturated clay samples by means of direct shear box. To gain a conceptual understanding of the viscous response of the clay in shear, mechanical analogues were considered based on combinations of springs and dashpots. Preliminary tests on unsaturated samples were finally carried out to gain a first insight into the viscous response of the clay under unsaturated conditions

MEMS sensor-based monitoring system for engineered geological disposal facilities

The design of a novel MEMS (Micro-Electro-Mechanical System) sensor-based monitoring system is presented in this article for the in-situ monitoring of the conditions (temperature, relative humidity) of an engineered bentonite barrier for the underground disposal of radioactive waste in a geological disposal facility (GDF). A first prototype of the monitoring system incorporating multiple state-of-the-art MEMS sensors has been developed on a PCB-based (Printed Circuit Board) structure, in order to measure the variation of temperature and relative humidity inside a cylindrical bentonite block during the hydration process. The monitoring system comprises of separate sensor boards, the microcontroller-equipped interface board, and the software user interface in Labview environment. One of the main design priorities is to reduce the size of the embedded sensors in order to minimize their influence on the hydro-mechanical response of the bentonite block. The sensor boards are encapsulated in different manners to protect them from moisture, chemical corrosion and mechanical shocks. The sensor system has been tested and calibrated in the temperature range between -20°C and 120°C, and at different relative humidity levels implemented by saturated salt solutions in enclosed containers. Test results demonstrate that the sensors have shown good functionality and robustness in harsh test environments such as high temperature and high humidity. Both temperature and relative humidity sensors have shown satisfactory precision level and temporal stability, which are in good accordance with the design specification of these devices

Instability of flood embankments due to pore water pressure build-up at the toe : lesson learned from the Adige river case study

A case study is presented of the Adige River embankment, a segment of which experienced instability of the landside slope due to the development of uplift pressures. Soil profile and hydromechanical properties of the embankment and foundation materials have been assessed via site investigation, laboratory testing, and field monitoring for two cross sections, within and outside the failure segment. The hydromechanical model developed thereof was first validated against its ability to reproduce the probability of failure for the two sections with a first-order, second-moment (FOSM)-based approach. Comparison of water flow regimes between the two sections was then used to highlight the importance of the hydraulic properties of the material on the landside for the development of uplift pressures at the toe of the embankment. The lesson learnt from this case study is that the hydraulic response of the ground on the landside may play a critical role on the stability of flood embankments and its characterization should therefore not be overlooked when planning site investigation

The Relationship between Perceived Emotional Intelligence, Work Engagement, Job Satisfaction, and Burnout in Italian School Teachers: An Exploratory Study

The study investigates the relationship between perceived emotional intelligence, burnout, work engagement, and job satisfaction in 238 Italian school teachers. The mean age was 50 years, ranged from 26 to 66 (SD = 9.16). The research protocol included a demographics data sheet, the Wong and Law Emotional Intelligence Scale (WLEIS; Wong & Law, 2002), the Copenhagen Burnout Inventory (CBI; Kristensen, Borritz, Villadsen, & Christensen, 2005), the Utrecht Work Engagement Scale (UWES; Schaufeli, Bakker, & Salanova, 2006), and the Organizational Satisfaction Scale (QSO; Cortese, 2001). Several international studies already demonstrated an association among these variables. Our results showed that perceived emotional intelligence positively correlates with work engagement and job satisfaction, and negatively correlates with burnout. Hierarchical regression analyses also point out that, among all the perceived emotional intelligence subdimensions, the use of emotion is the best predictor of the study variables, even when controlling for gender differences. These results suggest that emotional intelligence may have a protective role in preventing negative working experiences of teachers

Recent developments in the techniques of controlling and measuring suction in unsaturated soils

The difficulty of measuring and controlling suction in unsaturated soils is one of the reasons why the development of the mechanics of unsaturated soils has not been as advanced as that of saturated soils. However, significant developments have been carried out in the last decade in this regard. In this paper, a re-view of some developments carried out in the techniques of controlling suction by using the axis translation, the osmotic method and the vapour control technique is presented. The paper also deals with some recent de-velopments in the direct measurement of suction by using high capacity tensiometers and in the measurement of high suction by using high range psychrometers. The recent progresses made in these techniques have been significant and will certainly help further experimental investigation of the hydromechanical behaviour of un-saturated soils.Comment: First International Conference on Unsaturated Soils, Durham : Royaume-Uni (2008