Development of Innovative, Adaptable Video Learning Modules for the Civil Engineering Classroom

As engineering and technology continue to evolve, so should the use of such innovations in engineering pedagogy. Standard course learning modules have not often utilized technology to assist in learning of engineering principles and concepts; that is, until the COVID-19 pandemic required teachers and students to use technology more frequently in a virtual teaching/learning environment. Therefore, it is even more critical now that engineering pedagogy be adapted to incorporate technology in the classroom to enhance student learning of complex engineering concepts. In this study, a team of Civil Engineering professors has set out to incorporate technology into their classrooms to help students gain a stronger understanding of the fundamental building blocks of Civil Engineering. A series of comprehensive educational video and simulation-based learning modules were created for the Civil Engineering subdisciplines of environmental, geotechnical, transportation, and structural engineering. The development and implementation of such technology-based learning modules offer new opportunities to teach students the complex concepts of Civil Engineering through visual means. The efficacy of the learning modules were evaluated through student assessment surveys for: (1) the appropriateness of the module in aiding the introduction of course content, (2) the effectiveness of the module in enhancing student understanding of course content, and (3) the overall perception of students of the module. Implementation of the modules into the classroom has shown that students responded positively to the modules, referencing the modules as both engaging and comprehensive in aiding their understanding of course content

What causes large submarine landslides on low gradient (

Submarine landslides can cause damaging tsunamis, the height of which scales up with the volume of the displaced mass. The largest underwater landslides are far bigger than any landslides on land, and these submarine mega-slides tend to occur on open continental slopes with remarkably low gradients of less than 2°. For geohazard assessments it is essential to understand what preconditions and triggers slope failure on such low gradients. Previous work has suggested that generation of high excess pore pressure due to rapid sediment deposition plays a key role in such failures. However, submarine slope failure also occurs where sedimentation rates are low (<0.15 m/ky), such as off north-west Africa. We use a fully coupled stress and fluid flow finite element model to test whether such low sedimentation rates can generate sufficient excess pore pressures to cause failure of a 2° slope. The sensitivity of overpressure generation and slope stability is assessed with respect to different sedimentation rates and patterns, sediment consolidation properties and stratigraphic layer configurations. The simulations show that in general it is difficult to generate significant excess pore pressure if sediment accumulation is slow and the only pressure source. However, we identify a sediment compression behavior that can lead to submarine landslides in locations worldwide. Our results imply that compressibility is an important factor for the stability of low gradient continental slopes

Chemico-mechanical improvement of bentonite barriers for pollutant containment.

Pollution control represents one of the main problems of public interest in all industrialised countries. Since the 1970s, when the engineering of waste containment began, the overall objective of Environmental Geotechnics was to limit contaminant discharge to groundwater and subsoil. Since the 1990s design engineers and environmental agencies have shown a growing interest in the use of geosynthetic clay liners (GCLs) as an alternative to compacted clays in cover systems or in bottom lining of waste containment facilities because they have very low hydraulic conductivity to water and relatively low cost. GCLs contain a thin layer of sodium bentonite with a dry thickness between 5 and 10 mm, sandwiched between two geotextiles or glued to a geomembrane, GM. The excellent hydraulic performances of GCLs have to be attributed to bentonite characteristics and, since these last are greatly influenced by the chemical composition of the environment surrounding the barrier and by the state parameters, the performances of GCLs can be altered, and then worsened, by a simple variation of the chemical or physical boundary conditions. Aimed at solving this last issue, clay liners and GCLs have undergone great change during the last two decades, with new material being introduced (i.e. polymers) and new design methods being adopted (i.e. membrane behaviour investigation, contaminant diffusion estimation). The research project developed during the Ph.D. has been focused on bentonite barriers. The term “bentonite barriers” includes bentonite or bentonite-based barriers which find application both in urban waste landfill, hazardous or radioactive wastes final disposal and in hydrocarbon containment. The developed theoretical and experimental study has had the aim of evaluating the possible improvement of containment performance of the bentonite barriers, towards standard and non standard liquids, acting on their state parameters, chemical composition, and boundary conditions at installation. The contents of the thesis are reported below: Chapter 1 – Bentonite barriers. This chapter is an introduction to the topic of the research activity: the improvement of contaminant containment performances of the bentonite barrier. Chapter 1 gives a phenomenological and physical description of the mineralogical, chemical and physical properties of sodium and calcium bentonite. Moreover, the main features and issues concerning Geosynthetic Clay Liners, and bentonite barriers in general, are introduced. Chapter 2 – Containment performances of natural and polymer-modified bentonite barriers subjected to physical pre-treatments. The role of physical pre-treatments, such as pre-hydration, pre-consolidation and salt removal, applied to sodium and polymer modified bentonites, has been analyzed in the Paper reported in chapter 2, titled: “THE ROLE OF PHYSICAL PRETREATMENTS ON THE HYDRAULIC CONDUCTIVITY OF NATURAL AND POLYMER MODIFIED SODIUM BENTONITES”. Moreover, the effect of the presence or absence of needling across the bentonite layer has been studied. All these variables have been shown to influence the hydraulic performances of bentonite through hydraulic conductivity change in both short and long term conditions. Physical pre-treatments and polymer addiction, in fact, influence the swelling behaviour of bentonite and its response to the cation exchange phenomenon. Chapter 3 – Osmotic and swelling properties of bentonite barriers. In the Paper included in this chapter, titled “COUPLED CHEMICAL-HYDRAULIC-MECHANICAL BEHAVIOUR OF BENTONITES”, a theoretical approach has been proposed in order to derive constitutive equations which describe the coupled chemical-hydraulic-mechanical behaviour of bentonite barriers, with the aim to assess their long term performance. The phenomenological parameters that govern the transport of electrolyte solutions through bentonites, i.e. the hydraulic conductivity, the reflection coefficient, which is also called the chemico-osmotic efficiency coefficient, and the osmotic effective diffusion coefficient, have been measured through laboratory tests on a natural sodium bentonite The obtained results have been interpreted by assuming that the microscopic deviations of the pore solution state variables from their average values are negligible. In this way, it is possible to interpret the macroscopic behaviour on the basis of the physical and chemical properties of the bentonite mineralogical components. At the end of the chapter two further chemico-osmotic tests are described aimed at analysing (1) the osmotic behaviour of calcium bentonite and (2) the effects induced on osmotic behaviour by stress-strain properties. Moreover, the osmotic results are confronted with data from literature. Finally, the design of a new osmotic apparatus to measure both the swelling pressure and the reflection coefficient is proposed. Chapter 4 – Hydrocarbon containment performances of natural and polymer-modified bentonite barriers. Background information on hydrocarbon behaviour in soils is reported in the first part of this chapter. In particular, the effects of capillary forces on the distribution of immiscible fluids in porous media and the theoretical aspects, regarding the formation of tactoids induced by the low dielectric constant that characterizes the most of hydrocarbon species, are studied. An experimental study is presented in the Paper titled “HYDRAULIC PERFORMANCE OF GCLS WITH DIESEL OIL AND POLYMER TREATMENT PROPOSAL”, which is aimed at evaluating the hydraulic performance of a needle-punched GCL using both standard liquids (i.e. de-ionized water) and diesel oil in order to estimate the change in hydraulic conductivity and swelling ability upon contact or permeation with hydrocarbons. Moreover, the hydraulic conductivity to diesel oil of GCL samples saturated at different initial gravimetric water contents was investigated with the aim to analyse the effect of initial water saturation on hydrocarbon containment performances. Finally, the swelling and hydraulic performances to diesel oil of an innovative material, obtained by mixing sodium bentonite with a polymer, were measured. Chapter 5 – Containment performances of a bentonite-based barrier constituted of municipal solid waste bottom ashes. The research described in the Paper included in this chapter, titled “REUSE OF MSWI BOTTOM ASH MIXED WITH NATURAL SODIUM BENTONITE AS LANDFILL COVER MATERIAL” has the aim of evaluating the reuse of incinerator slag, mixed with sodium bentonite, for landfill capping system components. A chemical, hydraulic and mechanical characterization was performed on pure bottom ash (BA) samples from an incinerator in the North of Italy and on the BA-bentonite mixture. This study qualifies the BA-bentonite mixture as a suitable material for landfill cover in Italy. Moreover, owing to the low release of toxic compounds from BA, the proposed cover system does not affect the leachate quality in the landfill. Chapter 6 – Finite difference modelling of diffusive flux of Calcium through a bentonite barrier in in-situ conditions. The evidence of the strong degradation induced in the hydraulic performances of sodium bentonite barriers by the cation exchange phenomenon has been highlighted in the previous chapters. This experimental result underlines the need to study the transitional development of the cation exchange phenomenon with the aim to compare that to the period in which landfill barrier performances have to be guaranteed in in-situ conditions. The mathematical study developed in this chapter is focused on the evaluation of the role of the diffusive component of Calcium flux in the cation exchange phenomenon which can develop in a sodium bentonite barrier, placed in an environment inexorably rich in chemical compounds containing soluble Calcium (i.e. the natural soil, the aquifer, the drainage layer saturated with waste leachate or raining water)

Numerical analysis to quantify the influence of smear zone characteristics on preloading design in soft clay

In this paper, the effects of uncertainties of smear zone characteristics induced by installation of prefabricated vertical drains on the preloading design are numerically investigated. FLAC 2D finite difference software with additional developed subroutines has been employed to conduct the numerical simulations. The finite difference analyses have been verified using a case study. Furthermore, a comprehensive parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Results of this study indicate that the assumptive properties for smear zone characteristics may result in inaccurate predictions of ground deformations and pore water pressures. This may lead to early removal of the surcharge in the construction process causing excessive post construction settlement. It is recommended to practising engineers to use results of trial preloading to back calculate the required smear zone characteristics in the early stages of embankment construction to optimize the design

Simulation and evaluation of improvement effects by vertical drains/vacuum consolidation on peat ground under embankment loading based on a macro-element method with water absorption and discharge functions

AbstractThe authors previously extended the macro-element method proposed by Sekiguchi to include water absorption and discharge functions and incorporated this into a soil–water coupled finite deformation analysis code capable of accounting for inertial forces. The primary objective of this study is to validate the ability of the proposed method to simulate actual ground behavior by comparing the simulation results with the actual measurements of the embankment loading of a soft peat ground improved with vertical drains and vacuum consolidation. It was found that the proposed method is capable of comprehensively and closely simulating not only the magnitude of settlement, but also various ground behaviors, including the deformation of the surrounding ground and pore water pressure distributions. Furthermore, additional simulations were performed to elucidate the effect of a continuous middle sand layer found to exist and to span the entire improved area at an actual embankment site.The next objective of this study is to investigate the impact of ground improvement, using vertical drains and vacuum consolidation with embankment loading on a soft ground, placing a particular focus on the effect of drain spacing. In this case, an ultra-soft ground with alternating peat and clay layers was modeled to represent a typical ground to which vacuum consolidation would be applied. Based on a series of simulations, it was found that, although the use of vacuum consolidation in combination with vertical drains is effective in cases where it is necessary to limit the deformation of the surrounding ground, the same reduction in residual settlement can be achieved using vertical drains alone, provided that the drains are deployed at a sufficient frequency

Large Motion Assessment in Soils Under Dynamic Loading

This paper presents the mathematical formulation of the nonlinear multiphase dynamic model meant for porous media, obtained by applying the finite transformation assumption. This assumption is appropriate when large motions take place either during mass wasting processes, such as large slumps and earthflows, or during earthquake events when site liquefaction occurs and results for instance in large irrecoverable settlements or lateral spreads. The weak formulation and numerical implementation of the dynamic model uses the mesh-free h-p clouds method, which is based on the more general Partition of Unity Method. The mesh-free numerical methods seem indeed to be more appropriate for large transformation problems, where geometry may change in an important manner during simulation, as usual mesh constraints no longer exist. The numerical simulations of observed liquefaction-induced lateral spreads, performed with the proposed model are not presented in this paper

Investigation of the Permeability of Soil-rock Mixtures Using Lattice Boltzmann Simulations

Based on the discrete element method and the proposed virtual slicing technique for three-dimensional discrete element model, random pore-structural models of soil-rock mixtures are constructed and voxelized. Then, the three-dimensional lattice Boltzmann method is introduced to simulate the seepage flow in soil-rock mixtures on the pore scale. Finally, the influences of rock content, rock size, rock shape and rock orientation on the simulated permeability of soil-rock mixtures are comprehensively investigated. The results show that the permeability of soil-rock mixtures remarkably decreases with the increase of rock content. When the other conditions remain unchanged, the permeability of soil-rock mixtures increases with the increase of rock size. The permeability of soil-rock mixtures with bar-shaped rocks is smaller than that of soil-rock mixtures with block-shaped rocks, but larger than that of soil-rock mixtures with slab-shaped rocks. The rock orientation has a certain influence on the permeability of SRMs, and the amount of variation changes with the rock shape: when the rocks are bar-shaped, the permeability is slightly decreased as the major axes of these rocks change from parallel to perpendicular with respect to the direction of main flow; when the rocks are slab-shaped, the permeability decreases more significantly as the slab planes of these rocks change from parallel to perpendicular with respect to the direction of main flow

Medición de la conductividad hidráulica bajo trayectorias horizontales en suelos granulares

In geotechnical structures, the permeability-dependent stability analysis is generally evaluated under vertical trajectories, because most permeameters are configured so that the water passes through the porous medium in this way. However, it is clear from the physical point of view that water can flow along different paths, including preferential ways that can include horizontal trajectories, parallel to the deposit of the stratum. The foregoing implies that both the vertical and horizontal component of the hydraulic conductivity or permeability coefficient must be estimated for a given stratum. The current research aims to explore possibilities for measuring the coefficient of permeability in horizontal trajectories, on granular soils, under a constant condition of relative density. For this purpose, a special chamber attached to a constant head permeameter was designed and constructed, which allows to measure the permeability in conditions of horizontal flow parallel to the soil layers. The proposed camera also admits the estimation of the permeability coefficient by combining stratifications of different granular soils, where the trajectories are not perfectly horizontal, but have diagonal paths. The results are compared with data obtained by conventional vertical flow permeameters, in order to check the difference in the measurements considering both situations in the samples. As a conclusion, it is important to report that there is evidently a difference in the permeability coefficients measured under different trajectories,En las estructuras geotécnicas generalmente el análisis de estabilidad dependiente de la permeabilidad, es evaluado bajo trayectorias verticales, debido a que la mayoría de permeámetros están configurados para que el agua atraviese de esta manera el medio poroso. No obstante, es claro desde el punto de vista físico que el agua puede fluir siguiendo diferentes caminos, entre ellos recorridos preferenciales que pueden incluir trayectorias horizontales paralelas a la depositación del estrato. Lo anterior implica que se debe estimar para un estrato, tanto la componente vertical, como horizontal de la conductividad hidráulica o coeficiente de permeabilidad. En la investigación actual se pretende explorar posibilidades de medición del coeficiente de permeabilidad en trayectorias horizontales, en suelos granulares, bajo una condición constante de densidad relativa. Para ello se diseñó y construyó una cámara especial adosada a un permeámetro de cabeza constante, que permite medir la permeabilidad en condiciones de flujo horizontal paralelo a los estratos. La cámara propuesta admite también, la estimación del coeficiente de permeabilidad combinando estratificaciones de diferentes suelos granulares, donde las trayectorias no son perfectamente horizontales, sino presentan recorridos diagonales. Los resultados son comparados con datos obtenidos mediante permeámetros convencionales de flujo vertical, con el fin de comprobar la diferencie en las mediciones considerando ambas situaciones en las muestras. Como conclusión generar es importante reportar que evidentemente existe una diferencia en los coeficientes de permeabilidad medidos bajo diferentes trayectorias

Three-dimensional finite element analysis of spatially variable PVD improved ground

A stochastic approach that investigates the effects of soil spatial variability on stabilisation of soft clay via prefabricated vertical drains (PVDs) is presented and discussed. The approach integrates the local average subdivision of random field theory with the Monte Carlo finite element (FE) technique. A special feature of the current study is the investigation of impact of spatial variability of soil permeability and volume compressibility in the smear zone as compared to that of the undisturbed zone, in conjunction with uncoupled three-dimensional FE analysis. A sensitivity analysis is also performed to identify the random variable that has the major contribution to the uncertainty of the degree of consolidation achieved via PVDs. The results of this study indicate that the spatial variability of soil properties has a significant impact on soil consolidation by PVDs; however, the spatial variability of soil properties in the smear zone has a dominating impact on soil consolidation by PVDs over that of the undisturbed zone. It is also found that soil volume compressibility has insignificant contribution to the degree of consolidation estimated by uncoupled stochastic analysis