Application of endochronic densification law for designing vibroflotation soil improvement technique

The densification phenomenon in dry or completely drained sands is mainly due to the application of dynamic loading, like an earthquake or other kind of vibrations. This fact causes a reduction of voids volume and in a consequence the compaction of the soil. A finite element model, including the generalized endochronic densification law, formulated in cylindrical coordinates, has been developed for simulating the vibroflotation soil improvement technique the numerical model. Punctual dynamic loadings, like those occurring in vibroflotation treatment, are reproduced in the code. There are several other vibration-compacting soil improvement techniques which could be modelled like an axi-symmetric problem with this new approach, which includes absorbent boundary conditions (silent boundaries)

Numerical Simulations of the Monotonic and Cyclic Behaviour of Offshore Wind Turbine Monopile Foundations in Clayey Soils

Most of the reported centrifuge tests available in the existing literature on offshore wind turbine foundations are focused on the behaviour of monopiles in sands, but very few studies on clayey soils can be found, due to the very long saturation and consolidation periods required to properly conduct experiments in such materials. Moreover, most of the reported numerical simulations using finite element analyses have been validated with monotonic centrifuge tests only. In this research, both monotonic and cyclic performance of offshore wind turbines in clay are validated and justified. The relationship between the monopile rotation in clays and the geometry and strength of the soil has been found and quantified. A prediction of the rotation for a high number of cycles of loading, based on the one experienced by the pile during the first cycle, can be obtained using the correlation derived in the paper. For those cases in which the rotation does not reach a steady value after a high number of cycles, the cumulative rate has been found significantly larger than the prediction conducted with standard analytical methods. A new design methodology for the design of offshore monopile foundations in clay is presented

Meshfree numerical schemes applied to seepage problems through earth dams

Modelling seepage along with the mechanical responses of deformable Earth Dams under transient conditions is a challenging task, since both coupling between different phases, and computation of free-surface variables are involved. In the present work, we take on the meshfree numerical schemes to establish a framework for solving coupled, transient problems for unconfined seepage through Earth Dams. The equations of Biot are formulated in displacement (or u − w formulation) assuming an elastic solid skeleton. Shape functions based on the principle of Maximum Entropy are implemented for the meshfree framework. The free surface location and its evolution in time, is obtained by interpolation of pore water pressures through the domain. Applications to benchmark problems are compared with available results in the literature. The preliminary simulations for steady flow conditions show promising results

Effect of Class F Fly Ash on Fine Sand Compaction through Soil Stabilization

This paper presents the results of an experimental investigation carried out to evaluate the effect of fly ash (FA) on fine sand compaction and its suitability as a material for embankments. The literature review demonstrates the lack of research on stabilization of sandy material using FA. The study is concerned with the role of FA content in stabilized soil physical characteristics. The main aim of this paper is to determine the optimum quantity of FA content for stabilization of this type of soil. This is achieved through particle size distribution and compaction (standard proctor) tests. The sand was stabilized with three proportions of FA (5%, 10% and 15%) and constant cement content of 3% was used as an activator. For better comparison, the sand was also stabilized by 3% cement only so that the effect of FA could be observed more clearly. The results were in line with the literature for other types of soil, i.e. as the % of FA increases, reduction in maximum dry density and higher optimum moisture content were observed

Dynamic consolidation problems in saturated soils solved through u-w formulation in a LME meshfree framework

A meshfree numerical model, based on the principle of Local Maximum Entropy (LME), including a B-bar algorithm to avoid instabilities, is applied to solve axisymmetric consolidation problems in elastic saturated soils. This numerical scheme has been previously validated for purely elastic problems without water (mono phase), as well as for steady seepage in elastic porous media. Hereinafter, an implementation of the novel numerical method in the axisymmetric configuration is proposed, and the model is validated for well known theoretical problems of consolidation in saturated soils, under both static and dynamic conditions with available analytical solutions. The solutions obtained with the new methodology are compared with a finite element commercial software for a set of examples. After validated, solutions for dynamic radial consolidation and sinks, which have not been found elsewhere in the literature, are presented as a novelty. This new numerical approach is demonstrated to be feasible for this kind of problems in porous media, particularly for high frequency, dynamic problems, for which very few results have been found in the literature in spite of their high practical importance

Experimental evaluation of kaolin stabilised with class F fly ash

This study aims to investigate the effectiveness of fly ash (FA) in stabilising a kaolin soil through laboratory tests. Kaolin is an example of moderate plasticity clays that require stabilisation methods for construction purposes. The influence of FA on the improvement of kaolin is studied by varying its dosages in the mixtures (0%, 10% to 20%) as well as the cement content, used as an activator in different percentages (5 and 7%). The influence of the dry unit weight and the curing time of the soil mixture is also analysed through unconfined compressive strength and indirect tensile strength tests. The experimental results show that the strength increases linearly with both FA and cement contents. Moreover, higher initial dry unit weights also yield higher final strengths. To further assess the improvement, the application of the porosity over the volumetric cement content ratio, as the main variable, succeeded in attaining a relationship with the strength and the stiffness of the studied soil. Results for the combined effect of the porosity and the volumetric cement on the secant modulus were also determined. Furthermore, a unique relationship was obtained combining porosity, volumetric cement and FA content

Simplified numerical models to simulate hollow monopile wind turbine foundations

The majority of wind turbine foundations consist of hollow monopiles inserted in the soil, requiring high computational effort to be numerically simulated. Alternative simplified models are very often employed instead. Three-dimensional solid models, in which the hollow structure and pile are substituted by solid cylinders with equivalent properties, are the most extended simplifications. Very few 2D models can be found in the literature due to the challenge of finding suitable equivalent properties and loads to fully represent the 3D nature of the problem. So far, very limited attention has been devoted to the accuracy of both 3D and 2D simplified models under dynamic and even static actions. Thus, in this paper, simplified 3D and 2D solid models are proposed and justified. An elasto-plastic constitutive model with accumulative degradation is used to simulate the soil behaviour, and frictional contact elements are implemented between the soil and pile to model their interaction. These simplified approaches are compared with the full 3D hollow model, under static and cyclic loads. The results demonstrate that the proposed simplified approaches are a reasonable alternative to the 3D hollow model, which allows researchers and designers to drastically reduce the computational effort in the simulations under long term conditions

Exploring the Effect of Different Team Compositions on Team Motivation, Student Satisfaction and Performance in Team Practical Activities

The main source of diversity in engineering education usually is the distinct level of motivation, which sometimes causes lack of engagement. Working in motivated teams is likely to enhance the overall performance of the whole group. The aim of this paper is to find the best composition of teams in practical activities proposed in the classroom for engineering students to enhance team motivation. The experience with a group of Civil Engineering students at the University of West London is presented as a case study. This group was very diverse in the level of individual motivation. In this experiment, the whole group was split in two subgroups, and each one divided in teams of 3 people. For one of the subgroups, the distribution in teams was forced by the lecturer, while for the second one the students were allowed to freely distribute themselves. All teams were requested to solve a practical activity, consisting of the classification of several soils according to three different systems, based on experimental data equally provided to all the students. The different results obtained for both configurations of teams show an overall better performance for the “forced” composition, with a higher level of student satisfaction on the activity and on their achieved learning

Effect of polymer emulsion of the bearing capacity of Aeolian sand under extreme confinement conditions

An experimental investigation, aimed at evaluating the improvement of Aeolian sand (from Saudi Arabia) when treated with low dosages of a vinyl acrylic (a polymer emulsion), is reported in this paper. Special attention is devoted to the influence of the lateral confinement, particularly in terms of compaction and bearing capacity (represented by CBR), for which a modification of the standard test has been developed trying to simulate extreme confinement conditions. Experimental results demonstrate that this kind of chemical stabilizers can be considered as a suitable alternative for these materials. The main modifications induced in the sand by this additive are highlighted and quantified by means of the modification achieved for different geotechnical properties as well as Scanning Electron Microscope (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) analyses