Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography

In situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposi

Application of wavelet analysis in tool wear evaluation using image processing method

Tool wear plays a significant role for proper planning and control of machining parameters to maintain the product quality. However, existing tool wear monitoring methods using sensor signals still have limitations. Since the cutting tool operates directly on the work-piece during machining process, the machined surface provides valuable information about the cutting tool condition. Therefore, the objective of present study is to evaluate the tool wear based on the workpiece profile signature by using wavelet analysis. The effect of wavelet families, scale of wavelet and statistical features of the continuous wavelet coefficient on the tool wear is studied. The surface profile of workpiece was captured using a DSLR camera. Invariant moment method was applied to extract the surface profile up to sub-pixel accuracy. The extracted surface profile was analyzed by using continuous wavelet transform (CWT) written in MATLAB. The re-sults showed that average, RMS and peak to valley of CWT coefficients at all scale increased with tool wear. Peak to valley at higher scale is more sensitive to tool wear. Haar was found to be more effective and significant to correlate with tool wear with highest R2 which is 0.9301

Analysis of piezocone penetration under different drainage conditions with the two-phase Material Point Method

The piezocone penetration test (CPTU) is commonly used to identify the soil profile and to estimate material properties. Depending on the soil type, ranging from clay to sand, undrained, partially drained or drained conditions may occur during cone penetration. In silt and sand-clay mixtures the CPTU penetration is characterized by partially drained conditions, which are often neglected in data interpretation. The effect of drainage on CPTU measurements has been mainly studied experimentally. Numerical analyses are rare because taking into account large soil deformations, soil-water and soil-structure interactions, as well as non-linear soil behaviour is still a challenging task. This paper presents and discusses numerical simulations of CPTU in saturated soils with the two-phase Material Point Method. Soil behaviour is described with the Modified Cam Clay model. This study investigates the effects of pore pressure dissipation during penetration, cone roughness and horizontal stress state, comparing the results with experimental data. The paper discusses the effect of neglecting partial drainage in deriving the shear strength parameters for silty soils and suggests a procedure to estimate the consolidation coefficient performing CPTU at different penetration rates

Numerical techniques for fast generation of large discrete-element models

In recent years, civil engineers have started to use discrete-element modelling to simulate large-scale soil volumes thanks to technological improvements in both hardware and software. However, existing procedures to prepare ‘representative elementary volumes’ are unsatisfactory in terms of computational cost and sample homogeneity. In this work, a simple but efficient procedure to initialise large-scale discrete-element models is presented. Periodic cells are first generated with a sufficient number of particles (enough to consider the cell a representative elementary volume) matching the desired particle size distribution and equilibrated at the desired stress state, porosity and coordination number. When the cell is in equilibrium, it is replicated in space to fill the problem domain. And when the model is filled, only a small number of mechanical cycles is needed to equilibrate a large domain. The result is an equilibrated homogeneous sample at the desired initial state in a large volume

Pile penetration in crushable soils:Insights from micromechanical modelling

A 3D discrete element model (DEM) was used to simulate calibration chamber experiments of a cone shaped tip pile penetrating into crushable granular media. Both monotonic and cyclic jacking are considered. Particle crushing is simulated by employing a rigorous breakage criterion applied to elasto-brittle spheres. Particle scaling is used to limit the number of particles considered and it is shown that, above a threshold limit, the penetration curves become scale independent, provided a scalable crushing model is used. The particle crushing model parameters were calibrated by matching triaxial and one-dimensional compression tests. The DEM model could capture the stress measurements made around a model pile during and after its penetration into sand relatively well. The particle-scale mechanics that underlie the observed macroscopic responses are analysed, placing emphasis on the distribution of crushing events around the pile tip and distributions of particle stresses and forces around the shaft. Comparing simulations made with crushable and uncrushable grains, and analysing the particle displacement fields, provides insights into one of the mechanisms proposed for the well-known, yet not fully understood, marked shaft capacity increases developed over time by piles driven in sands.RÉSUMÉ:Un modèle 3D d'éléments discrets (DEM) est utilisé pour prédire les expériences en chambre d'étalonnage de la pénétration de cônes et de pieux dans des supports pouvant être écrasés, à la fois par fonçage monotone et cyclique. Un modèle de broyage de particules basé sur un critère de rupture rigoureux pour les sphères élasto-fragiles est utilisé. Une mise à l'échelle des particules est réalisée pour limiter le nombre total de particules. Il est montré qu'au-delà d’un nombre minimum de particules, les courbes de pénétration deviennent indépendantes de leur taille, à condition qu'un modèle de broyage évolutif soit utilisé. Le modèle, calibré en faisant correspondre les tests de compression triaxiale et unidimensionnelle, fournit de bonnes prévisions pour les mesures de contrainte effectuées lors d’essais de pieux, pendant et après les phases de pénétration. Les caractéristiques micromécaniques expliquant les réponses macroscopiques observées sont analysées. Il s’agit notamment d’identifier la répartition de l’intensité de broyage autour de la pointe du pieu et d’analyser en détail les contraintes exercées par les particules et les chaînes de force autour du fût du pieu. La comparaison de simulations réalisées avec ou sans grains broyables, ainsi que l'analyse des champs de déplacement de particules, offrent une explication possible de l'impact bien connu, mais pas encore bien compris, du vieillissement sur la capacité du fût de pieux battus dans le sable

Newmark sliding block model for pile-reinforced slopes under earthquake loading

Recent studies have demonstrated that the use of a discretely-spaced row of piles can be effective in reducing the deformations of slopes in earthquakes. In this paper, an approximate strain-dependant Newmark sliding-block procedure for pile-reinforced slopes has been developed, for use in analysis and design of the piling scheme, and the model is validated against centrifuge test data. The interaction of the pile within the slipping soil was idealised using a non-linear elasto-plastic (P-y) model, while the interaction within the underlying stable soil was modelled using an elastic response model in which (degraded) soil stiffness is selected for an appropriate amount of shear strain. This combined soil-pile interaction model was incorporated into the improved Newmark methodology for unreinforced slopes presented by Al-defae et al. [1], so that the final method additionally incorporates strain-dependent geometric hardening (slope re-grading). When combined with the strain-dependent pile resistance, the method is therefore applicable to analysis of both the mainshock and subsequent aftershocks acting on the deformed slope. It was observed that the single pile resistance is mobilised rapidly at the start of a strong earthquake and that this and the permanent slope deformation are therefore strongly influenced by pile stiffness properties, pile spacing and the depth of the slip surface. The model shows good agreement with the centrifuge test data in terms of the prediction of permanent deformation at the crest of the slope (important in design for selecting an appropriate pile layout/spacing i.e. S/B) and in terms of the maximum permanent bending moments induced in the piles (important for appropriate structural detailing of the piles), so long as the slip surface depth can be accurately predicted. A method for doing this, based on limit analysis, is also presented and validated

An integrated approach for evaluating the effectiveness of landslide risk reduction in unplanned communities in the Caribbean

Despite the recognition of the need for mitigation approaches to landslide risk in developing countries, the delivery of ‘on-the-ground’ measures is rarely undertaken. With respect to other ‘natural’ hazards it is widely reported that mitigation can pay. However, the lack of such an evidence-base in relation to landslides in developing countries hinders advocacy amongst decision makers for expenditure on ex-ante measures. This research addresses these limitations directly by developing and applying an integrated risk assessment and cost-benefit analysis of physical landslide mitigation measures implemented in an unplanned community in the Eastern Caribbean. In order to quantify the level of landslide risk reduction achieved, landslide hazard and vulnerability were modelled (before and after the intervention) and project costs, direct and indirect benefits were monetised. It is shown that the probability of landslide occurrence has been substantially reduced by implementing surface-water drainage measures, and that the benefits of the project outweigh the costs by a ratio of 2.7 to 1. This paper adds to the evidence base that ‘mitigation pays’ with respect to landslide risk in the most vulnerable communities – thus strengthening the argument for ex-ante measures. This integrated project evaluation methodology should be suitable for adoption as part of the community-based landslide mitigation project cycle, and it is hoped that this resource, and the results of this study, will stimulate further such programmes.Landslide modelling, Risk assessment, Cost Benefit Analysis, Developing countries, Community