Search

Cyanobacteria blooms represent a global problem with human health and economic and ecosystem nuisance effects. Until now, we have used arbitrary and sometimes confusing criteria to decide whether we are in the presence of a Cyanobacteria bloom. Through scientometric analysis of studies published between 1953 and 2022, I aimed to identify a threshold value that can be used to quantify Cyanobacteria blooms numerically. I considered several methodological approaches (field, field-experimental, and satellite data) and kinds of environments (coastal, marine, and continental ecosystems). The analysis revealed that 48% of the papers used "cyanobacteria bloom" or similar terms qualitatively without providing or employing a quantitative definition. These papers were focused on other topics related to the ecology of Cyanobacteria (78%), while some others (21%) defined blooms by using visual criteria (scum visualization or water discoloration). Of the other half (52%), a few were mathematical models or review papers (5%), while the rest (65%) defined blooms quantitatively. Of these, most reports (approximately 80%) were from eutrophic inland waters and reported mean values for blooms between 80 000 and 249 000 cells mL−1 or 41 and 69 µg L−1 of chlorophyll-a. Calculations were also carried out for oligotrophic to mesotrophic inland waters and marine-coastal waters, which had fewer reports available in the literature. This is a first attempt to identify a consensual definition based on values reported as blooms in nature, a threshold that can undoubtedly be useful in the future to make possible comparisons among several environments and temporal scales. [ABSTRACT FROM AUTHOR]

During the fall season in cold regions when the air temperature drops below freezing levels, it removes heat from the water surface and creates a supercooled surface layer. In weak turbulent flows, the supercooled surface layer initiates the formation of ice particles on the water surface, which could evolve into various types of surface ice runs. In this paper a mathematical model of the formation and evolution of surface ice is presented. A heat balance model at the water surface is applied to calculate the heat loss from the water. The turbulent kinetic energy and the energy dissipation rates are modelled to find the eddy viscosity that affects the mixing rate. The mathematical model is then calibrated and verified using experimental data collected at the Hydraulics Research and Testing Laboratory at the University of Manitoba. The model simulates the supercooling process reasonably well for all surface ice conditions. [ABSTRACT FROM AUTHOR]

According to the Canada infrastructure report 2016, 62.6% of roads in Canada are in a good condition, nevertheless, with current investment rates, significant road networks will suffer a decline in their condition and will be vulnerable to sudden failure. Accordingly, this paper tackles the pavement resilience from an asset management perspective and aims at developing a resilience-based asset management framework for pavement networks. This was carried out through the development of five components: (i) a central database of asset inventory, (ii) a pavement condition and level of service assessment models, (iii) a regression of the effect of freeze–thaw on pavement network, (iv) a financial and temporal models, and (v) an optimization model to formulate the mathematical denotation for the proposed resilience assessment approach and integrate the above components. The model results were promising in terms of maintaining pavement resiliency by selecting a near optimal intervention plan that meets the municipality limitations. [ABSTRACT FROM AUTHOR]

The daily production planning of sawmills is a critical task in pursuing the optimal exploitation of forest resources. Production planning determines which logs are to be processed, taking into account their characteristics with the aim of satisfying the demand for final products. Logs are turned into lumber when they are cut according to a set of available cutting patterns (CPs). The development of efficient production planning is a key factor in improving the productivity of sawmills, and mathematical modeling is a suitable technique to achieve this objective. In this paper, a mixed integer linear programming (MILP) model for optimal daily production planning in sawmills is proposed. The model involves a set of CPs for each type of log, which is obtained through an exhaustive algorithm, attaining all possible feasible CPs. The proposed approach determines the optimal number of logs of each type to be cut, the selected CPs to be used, material inventory, demand fulfillment, and other industrial and commercial issues with the objective of maximizing the firm's benefit, in reasonable computational time, considering the size of the problem. [ABSTRACT FROM AUTHOR]

The photosynthetic light-response (PLR) curve is a mathematical description of a single biochemical process that has been widely applied in many ecophysiological models. For trees, the heterogeneity of PLR curves within the crown is significant but rarely modeled by mathematical techniques. This paper establishes a modified model for estimating crown PLR curves based on PLR functions by linking the parameters of the PLR functions to leaf nitrogen (N), specific leaf area (SLA), and relative depth into the crown (RDINC). The modified models were assessed by considering the goodness of fit (adjusted coefficient of determination, --> R a 2 --> ; root mean square error, RMSE; and Akaike information criterion, AIC) and model structure. Significant correlations were observed between the parameters of PLR functions and N, SLA, and RDINC. The optimal modified PLR model, by linking RDINC into a modified Mitscherlich function, fit well due to its simple and easily understood structure. Therefore, it is feasible to simultaneously estimate the multilayered and varied PLR curves of the tree crown. [ABSTRACT FROM AUTHOR]

Canadian hard rock mines continue to reach deeper deposits, which poses greater challenges to mine safety including rock burst control. Destress blasting techniques have been successfully employed in such underground mines with the aim of preconditioning highly stressed rock mass to mitigate the risk for rock burst occurrence in deep mines. In the present study, the efficiency of destress blasting is examined through a comparison between traditional and alternative numerical modelling approaches. The traditional modelling approach assumes a uniformly distributed blast-induced damage zone extending over the entire drift face, whilst the alternative modelling approach, presented herein, simulates the damage zone for each individual blast hole. In the first part of this paper, a three-dimensional numerical model of a single blast hole is constructed, whereby the extent of blast-induced damage zone is delineated. The latter part of this paper uses the single-hole model results to examine the efficiency of destress blasting as practiced in drift development in deep mines. It is demonstrated through comparison of FLAC3D numerical simulation results that the traditional modelling approach may lead to an overly optimistic indication of destress blasting efficiency when compared with the alternative modelling approach, in which a more precise simulation of the damage zones is applied. [ABSTRACT FROM AUTHOR]

Knowledge about soil behaviour in the near surface is fundamental to a broad range of military strategic research efforts. The prevailing mathematical representations of near-surface shear strength do not necessarily reflect the observed shear strengths. This paper presents an experimental procedure for testing self-supported, unconfined-drained specimens to investigate the shear strength of a poorly graded sand with the inferred unsaturated behaviour from typical effective stress expressions. The impact of soil suction is quantified from the soil–water characteristic curve obtained from a modified, unsaturated, one-dimensional oedometer device: Fredlund's device. Seventy-seven unconfined tests illustrate that while individual or discrete states can be explained by effective stress relationships, those expressions do not accurately quantify the observed shear strength from one state to the next. Saturation failure is observed when the degree of saturation is between 70.5% and 76.5%, well below the assumed threshold. The results show that the dry shear resistance is a function of the initial density state, but as the degree of saturation increases, the shear resistance becomes independent of the initial density, and converges to the saturation failure. These findings expose the limitations of effective stress expressions and suggest a revised nonlinear, three-dimensional, unconfined Mohr failure envelope based on an applied external stress. [ABSTRACT FROM AUTHOR]

The design of manholes dates back more than 100 years. However, there have been developments such as the use of new materials for the manufacture of manholes, and advances in inspection and maintenance technologies, allowing improvements to the shape of manholes. This paper presents an innovative design for manholes, created to overcome the challenges associated with the installation of separate sewer systems in narrow streets, common to both UK and EU cities. The traditional separate sewer system has two separate manholes. The proposed manhole combines these two manholes into one structure, with two separate chambers, to allow storm flow and foul flow to pass through the same manhole without mixing. The structural performance of the new design has been tested using mathematical modelling validated by experimental tests. The results are compared with the structural performance of traditional manholes. The new design shows an improved resistance to high live loads. [ABSTRACT FROM AUTHOR]

One of the advanced methods of modeling activity duration is the multiple discrete-continuous extreme value (MDCEV) model. The translating satiation parameter of the model is intended to capture the constant marginal utility effect, but model testing shows that it does not do so. In this paper, the structure of the translating satiation parameter was modified to incorporate an additional parameter that enables the model to capture this effect. Two datasets from cities in Saudi Arabia and Germany were used to test the applicability of the modified model for any dataset. The results showed that the proposed model structure increased the accuracy of activity duration prediction by up to 74%. The modified model represents an improvement to the conventional MDCEV model in terms of accuracy and flexibility, and as such should be a valuable tool in transportation planning and management. [ABSTRACT FROM AUTHOR]

Currently, there is a lack of direct design provisions in structural codes and literature that address design temperatures in tunnel structures and thus it is common practice for designers to resort to bridge codes. The main focus of this paper is the study of the temperature distribution in concrete road tunnels due to ambient temperature. In this context, the temperature distributions of the Airport Trail Tunnel in Calgary, Alberta is studied using numerical modelling and long-term temperature monitoring data collected from the tunnel. The overall aim is to evaluate findings from the numerical analysis and sensor data with current Canadian structural code provisions considered in tunnel design in regards to temperature loads. From the investigation, it is determined that the design temperature range was within CSA S6, however CSA S6 underestimates the temperature gradient effect in the walls and slabs of the tunnel under study. [ABSTRACT FROM AUTHOR]

Finding a relationship on how a three-dimensional protein folds from its linear amino acid chain gets more complex with increasing chain length, so working on a smaller peptide conformational problem can provide initial ideas on what are the main molecular forces and how these influence the folding process. Following the study of conformations of amino acid units entering the proteins to understand the secondary structure of small peptides, this paper proposes mathematical models for the several two-rotor cross-sections of the five-dimensional N-acetyl-glycyl-glycine-N′-methylamide potential energy hypersurface (PEHS). These cross-sections are extracted along the first glycine subunit, with its coordinates fixed at the five energy minima of the glycine diamide. The resulting mathematical models yield an average RMSE of 1.36 kJ mol−1 and an average R2 of 0.9923 with respect to energy values obtained from DFT calculations. The minima geometries obtained from these models are also in good agreement with DFT-optimized energy minima conformers. An important aspect of this study also tackles the relationship between the PEHS of the glycyl-glycine diamide and its glycine subunits. It has been observed that there are deviations up to 28.35 kJ mol−1 and 29.52 kJ mol−1 between the PEHS cross-sections along γL and γD conformations, respectively, in the first glycine subunit. This may suggest that there are significant backbone–backbone intermolecular forces acting on the dipeptide. The abovementioned findings can help in developing more complex mathematical models for polypeptide folding from amino acid subunits. [ABSTRACT FROM AUTHOR]

Quantifying the age characteristics of a forest can provide valuable information about the forest’s impact on the environment. For instance, the age of a forest can affect the ecosystem’s carbon exchange, soil enzyme activity, and biodiversity. In this paper, we investigate the use of different sampling methods to estimate the age characteristics of three simulated ponderosa pine (Pinus ponderosa Dougl. ex P. Lawson & C. Lawson) forests having different spatial and age patterns. This includes estimating the mean tree age and the age-class distribution of the trees in the forest. The trees in the sample are selected using k-tree sampling, fixed-radius plot sampling, or variable-radius plot sampling, and we compare the properties of the resulting estimators via design-based and model-based approaches. Analyses of the different sampling methods applied to the three forests suggest that the estimator associated with k-tree sampling, with the addition of a few extra trees per plot, is feasible for forests having a spatially mosaic or random spatial pattern. The estimator associated with fixed-radius plot sampling performed well for the forest having a clustered spatial pattern. [ABSTRACT FROM AUTHOR]

This paper presents an analytical solution for drained expansion in both spherical and cylindrical cavities with a unified state parameter model for clay and sand (CASM). The solution developed here provides the stress and strain fields during the expansion of a cavity from an initial to an arbitrary final radius. Small strains are assumed for the elastic region and large strains are applied to soil in the plastic region by using logarithmic strain definitions. Since its development, the unified CASM model has been demonstrated by many researchers to be able to capture the overall soil behaviour for both clay and sand under both drained and undrained loading conditions. In this study, the CASM model is used to model soil behaviour whilst a drained cavity expansion solution is developed with the aid of an auxiliary variable. This is an extension of the undrained solution presented by the authors in 2017. The parametric study investigates the effects of various model constants including the stress-state coefficient and the spacing ratio on soil stress paths and cavity expansion curves. Both London clay and Ticino sand are modelled under various initial stress conditions and initial state parameters. The newly developed analytical solution highlights the potential applications in geotechnical practice (e.g., for the interpretation of cone penetration test data) and also provides useful benchmarks for numerical simulations of cavity expansion problems in critical state soils. [ABSTRACT FROM AUTHOR]

The goal of this paper is to establish a pedestrian model that is capable of simulating pedestrian movement at the microscopic level under normal conditions. Such a model would be useful in studying pedestrian-related transportation issues that require predicting accurate trajectories of pedestrians. The model utilizes the agent based modeling approach in which a continuous space was used to represent the pedestrian environment. This paper presents the first step of the model development: details of a unidirectional micro-simulation pedestrian model along with its calibration and validation. The model was validated by comparing simulated trajectories with real trajectories extracted from video footage by means of computer vision techniques. Results show that the average location difference between simulated and actual trajectories was 20 cm in the X direction and 40 cm in the Y direction. Results also show that the model is capable of predicting pedestrian speed with relative error of 12.8%. [ABSTRACT FROM AUTHOR]

Topological indices are numerical parameters of a graph that characterize its topology and are usually graph invariant. In a QSAR/QSPR study, physicochemical properties and topological indices such as Randić, atom-bond connectivity (ABC), and geometric-arithmetic (GA) indices are used to predict the bioactivity of chemical compounds. Graph theory has found a considerable use in this area of research. In this paper, we study different interconnection networks and derive analytical closed results of the general Randić index ( Rα( G)) for α = 1, , -1, only, for dominating oxide network (DOX), dominating silicate network (DSL), and regular triangulene oxide network (RTOX). All of the studied interconnection networks in this paper are motivated by the molecular structure of a chemical compound, SiO4. We also compute the general first Zagreb, ABC, GA, ABC4, and GA5 indices and give closed formulae of these indices for these interconnection networks. [ABSTRACT FROM AUTHOR]

Using survey data and an equilibrium displacement model, we estimate the market and economic impacts of the American Forest and Paper Association's Sustainable Forestry Initiative (SFI) on stumpage markets in the US South. We examine four timber product markets: softwood pulpwood, softwood sawtimber, hardwood pulpwood, and hardwood sawtimber. In each market we calculate changes in producer and consumer welfare using the equilibrium displacement model that accounts for reductions in timber inventories caused by SFI compliance. We find that SFI compliance costs the US South's economy about $36 million annually. SFI-compliant stumpage producers lose more than $33 million each year in producer surplus as a result of SFI compliance, and consumers lose about $12 million annually in consumer surplus due to higher product prices. These costs are offset partially by benefits to nonindustrial private forest producers, non-SFI-compliant industry producers, and public forest producers, who collectively gain about $10 million in producer surplus annually as a result of higher stumpage prices. [ABSTRACT FROM AUTHOR]

With the rapid growth of the helical piling industry for oil and gas projects and transmission lines, reliable installation torque estimates and measurements become crucial. This paper presents a theoretical model developed to estimate the torsional resistance of cohesionless soils to helical pile installation. The theoretical torque model was verified using installation records collected from different sites. The paper also highlights factors that affect helical pile installation, including soil properties, fluctuation in groundwater levels, shape of pile shaft, pile geometry, and method of helical pile installation. The proposed torsional resistance model was then used to establish the traditional torque factors to proportionally correlate the axial capacity of helical pile and the installation torque. The results of the study indicated that the torque factor is a function of the load path (i.e., tension or compression). Therefore, torque factors in compression and tension, Kc and Kt, respectively, were formulated and presented in the paper. [ABSTRACT FROM AUTHOR]

This paper presents the development of a dual porosity numerical model of multiphase, multicomponent chemical-gas transport using a coupled thermal, hydraulic, chemical, and mechanical formulation. Appropriate relationships are used to describe the transport properties of nonideal, reactive gas mixtures at high pressure, enabling the study of geoenergy applications such as geological carbon sequestration. Theoretical descriptions of the key transport processes are based on a dual porosity approach considering the fracture network and porous matrix as distinct continua over the domain. Flow between the pore regions is handled using mass exchange terms and the model includes equilibrium and kinetically controlled chemical reactions. A numerical solution is obtained with a finite element and finite difference approach and verification of the model is pursued to build confidence in the accuracy of the implementation of the dual porosity governing equations. In the course of these tests, the time-splitting approach used to couple the transport, mass exchange, and chemical reaction modules is shown to have been successfully applied. It is claimed that the modelling platform developed provides an advanced tool for the study of high-pressure gas transport, storage, and displacement for geoenergy applications involving multiphase, multicomponent chemical-gas transport in dual porosity media, such as geological carbon sequestration. [ABSTRACT FROM AUTHOR]

Multichannel analysis of surface waves (MASW) is a fast, low-cost, and environmentally friendly technique to estimate shear wave velocity profiles of soil sites. This paper introduces a new open-source software, MASWaves, for processing and analysing multichannel surface wave records using the MASW method. The software consists of two main parts: a dispersion analysis tool (MASWaves Dispersion) and an inversion analysis tool (MASWaves Inversion). The performance of the dispersion analysis tool is validated by comparison with results obtained by the Geopsy software package. Verification of the inversion analysis tool is carried out by comparison with results obtained by the software WinSASW and theoretical dispersion curves presented in the literature. Results of MASW field tests conducted at three sites in south Iceland are presented to demonstrate the performance and robustness of the new software. The soils at the three test sites ranged from loose sand to cemented silty sand. In addition, at one site, the results of existing spectral analysis of surface waves (SASW) measurements were compared with the results obtained by MASWaves. [ABSTRACT FROM AUTHOR]

Core overtopping in embankment dams is an important phenomenon that may lead to contact erosion along the core-filter interface. This paper presents new experimental results regarding erosion mechanisms at the core-filter interface during core overtopping. The experimental results were obtained using a reduced-scale model with a variable upstream water level. Digital image correlation (DIC), microcomputed tomography (μCT), and sediment collection at the outlet were used to quantify erosion. Four experimental runs were conducted with a till core and different filters. Only one of the four filters satisfied the filter criteria that were applied. No contact erosion occurred during this test. For filters that did not respect the filter criteria, piping occurred within the core along the downstream slope when the water level reached the top of the core. As a result of the self-healing process within the core material, the erosion rate decayed with time as the hydraulic gradient increased. Results for DIC mainly reflected settlements within the filter due to erosion and a soil arching effect. The magnitude of the displacement vector obtained with DIC is directly proportional to the volume of till eroded. μCT showed that contact erosion occurred continuously. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear solution of a radial subgrade reaction-displacement ( pk- ur) curve for circular tunnel lining design in undrained clay. With the concept of soil shear strength nonlinearly mobilized with shear strain, an analytical solution of pk is obtained using the mobilized strength design method. Two typical deformation modes are considered, namely oval and uniform. A total of 197 orthogonally designed cases are used to calibrate the proposed nonlinear solution of pk using the finite element method with the hardening soil model. The calibration results are summarized using a correction factor, η, which is defined as the ratio of pk_FEM to pk_MSD. It is shown that η is correlated to some input parameters. If this correlation is removed by a regression equation, f, the modified solution f( pk_MSD) agrees very well with pk_FEM. Although in reality the mobilized soil strength varies with principal stress direction, it is found that a simple average of plane strain compression and extension results is sufficient to produce the above agreement. The proposed nonlinear pk- ur curve is applied to an actual tunnel lining design example. The predicted tunnel deformations agree very well with the measured data. In contrast, a linear pk model would produce an underestimation of tunnel convergence and internal forces by 2-4 times due to the overestimation of pk at a large strain level. [ABSTRACT FROM AUTHOR]

The factor of safety of a slope ( Fs) is invariably assessed using methods underpinned by moment, force, and (or) shear strength equilibrium concerning slip surfaces. Each method inherently embeds some form of limitations, despite being popularly adopted in practice. In this paper, a new Fs is devised using the ratio of ultimate energy ( eu, upon sliding) over accumulated 'elastic' energy. The Fs is then reduced to a simple expression of the power to shear stress and shear strength, by taking soil as an elastic-plastic material obeying the Mohr-Coulomb failure criterion. This expression empowers significant efficacy in gaining the factor of safety (without involving energy or directions of shear stresses). The Fs values were calculated for three typical slopes concerning various mechanical properties (dilation, Poisson's ratio, and shear modulus) and effective computational strategies. All of the Fs values (to a congruous accuracy of available methods) were obtained in less than 1% the time of conventional numerical analyses. The proposed Fs, equally applicable to limit equilibrium methods, may be utilized in practice to expedite slope design. [ABSTRACT FROM AUTHOR]

Integration of repetitive and non-repetitive scheduling methods utilizes the merits and unique features of those methods. This paper presents a new scheduling method for repetitive projects that integrates linear scheduling (LSM) and critical chain project management (CCPM) methods. The proposed method introduces a framework for scheduling of repetitive projects; accounting for constraints of resources continuity and uncertainties associated with activity durations. It introduces a new buffer, named resource conflict buffer (RCB) to account for delays that may occur due to conflict in controlling resources among successor and predecessor activities. The developed method provides a systematic procedure for identifying several critical chains to replace the visual identification method that is currently used in linear scheduling. The features of the proposed method are illustrated in a case example for scheduling of repetitive projects using an integration of LSM and CCPM scheduling techniques. A discussion of results is performed and conclusions are drawn to highlight the features and capabilities of the proposed method. [ABSTRACT FROM AUTHOR]

Water main systems are aging and becoming a growing concern for maintenance. The structural deterioration of water mains is affected by different factors, such as pipe age, pipe material, soil condition, and pipe size, among others. Various methods of modeling have been used to predict the failure of water mains. Since pipe networks are underground and obtaining data on pipe conditions is very costly, statistical modeling has been widely used for pipe condition assessment. An emerging statistical method known as copula modeling is used here for pipe data analysis. The copula method is very useful in cases where marginals belong to different families of distributions. It is also useful for generating a large number of data points when it is difficult to obtain a data set, as is the case for pipe condition assessment, and where data sets have random variables belonging to non-Gaussian family distributions. Different copula families are applied here to model the dependency between the pipe age and repair age of pipes. The paper uses a Bayesian framework to estimate the parameter values in the copula model. This approach offers an additional option for estimating copula parameters for pipe data. [ABSTRACT FROM AUTHOR]

The full potential of pile optimization has not been realized as the interactions between superstructures and foundations, and the relationships between material usage and foundation performance are rarely investigated. This paper introduces an analysis and optimization approach for pile group and piled raft foundations, which allows coupling of superstructure stiffness with the foundation model, through a condensed matrix representing the flexural characteristics of the superstructure. This coupled approach is implemented within a multi-objective optimization algorithm, capable of providing a series of optimized pile configurations at various amounts of material. The approach is illustrated through two case studies. The first case involves evaluation of the coupled superstructure-foundation analyses against field measurements of a piled raft-supported building in London, UK. The potential benefits of pile optimization are also demonstrated through re-analyses of the foundation by the proposed optimization approach. In the second case, the effects of a soft storey on the superstructure-foundation interactions are investigated. These cases demonstrate the importance of properly considering the superstructure effects, especially when the building consists of stiff components such as concrete shear walls. The proposed approach also allows engineers to make informed decisions on the foundation design, depending on the specific project finances and performance requirements. [ABSTRACT FROM AUTHOR]

This paper describes an ontology-driven framework for developing distributed simulation modeling of construction processes. The research described in the paper is motivated by the necessity of knowledge sharing between distributed simulation modeling collaborators, and reuse and portability challenges in construction simulation models. Our approach addresses these challenges through ontological modeling and linking of construction simulation modeling components including ( i) ontology of construction process, ( ii) ontology of simulation world view, and ( iii) ontology of distributed simulation modeling application tool. Within the paper, ontology driven approach and mapping of ontologies for information transference between simulation components has been described. Another discussed application of ontologies is structuring of simulation modeling development through use of reusable elements. A large-scale distributed simulation model of industrial construction processes has been outlined to illustrate the application of the approach. [ABSTRACT FROM AUTHOR]

The consolidation process could be slow in an upstream tailings dam; therefore, the stability can reduce due to an increase in excess pore pressures when the dam is raised. The safety of the dam can be enhanced by constructing rockfill berms on the downstream side. This paper presents a case study on the strengthening of an upstream tailings dam with rockfill berms. The finite element analyses were performed for modelling the staged construction of the dam and for optimizing the volume of the rockfill berms. The dam was raised in 11 stages; each stage consisting of a raising phase and a consolidation phase. The study shows that the slope stability of the dam reduced due to an increase of excess pore pressures during the raising phase. The stability of the dam was successfully improved by utilizing rockfill berms as supports on the downstream side. A technique has been presented to minimize the volume of the rockfill berms so that the required stability can be achieved at minimum cost. This paper shows that the finite element method can be a useful tool for modelling the consolidation behaviour of an upstream tailings dam and minimizing the volume of the rockfill berms that may be needed to maintain the stability of the dam during staged construction. [ABSTRACT FROM AUTHOR]

The thermal conductivity of bitumen concrete is a key parameter in the thermal analysis of pavements submitted to widely varying climate conditions. This paper presents the experimental results of thermal conductivity of bitumen concrete typically used in the Province of Quebec. The results show that the thermal conductivity of bitumen concrete is dependent on the aggregate's mineral origin and on the amount of air voids. It is also shown that the presence of bitumen increases thermal conductivity compared to unbound aggregates. The paper demonstrates that the effect of bitumen creates thermal bridges between aggregate particles similarly to other types of binders such as Portland cement and natural binders found in sedimentary rocks. Based on these observations and on the analyses of over 80 data sets from the literature, an existing model is used to develop a simplified thermal conductivity equation to estimate this parameter for bitumen concrete. [ABSTRACT FROM AUTHOR]

Based on the excessive deformations and support failure encountered during tunnel construction at the Driskos Twin Tunnel site in Northern Greece, this paper provides insight on how tunnels designed in such weak rock environments can be realistically analyzed with a view of determining better analytical tools to predict deformations and improving current design methods. Specific factors that were assessed include rock strength based on the geological strength index (GSI), tunnel deformation, numerical analysis techniques employed, three-dimensional model type, support considerations, dilation, sequencing of tunnel excavation, influence of single bore construction on twin bore, and homogenization of tunnel faces. This work involves the use of nominally identical two- and three-dimensional numerical models of tunnel sequencing for analytical simulation of weak material behaviour and sequential tunnel deformation response with the goal of investigating the strength and deformation of such weak rock masses. These have been used in combination with monitoring data that were obtained in the field during the Driskos Twin Tunnel construction. A discussion of the geological conditions, material property determination, monitoring data, and model calibration strategy is given. This paper provides insight into these issues and poses many more fundamental questions regarding the analysis of tunnel excavation within weak rock masses requiring further investigation. [ABSTRACT FROM AUTHOR]

Different empirical formulas have been proposed to describe the water retention curve (WRC) and relative permeability ( kr) of soils. This paper presents a Bayesian framework that evaluates not only the most probable empirical fitting constants, but also their joint probability density function. A dataset containing two soil classes - sand and silty loam - compiled from the UNSODA database is used for illustration. First, model constants of the van Genuchten's WRC formula are calibrated and subsequently used to predict kr of the studied soils using two existing formulas based on Mualem's and Burdine's models. The best estimated kr in both formulas is found to skew towards the lower side of the measurement. Then, a new three-parameter empirical formula is proposed to describe kr with suction while the model constants are calibrated from the permeability data. Using the proposed framework, the statistical distribution of kr and subsequently the unsaturated permeability ( kunsat), as a function of suction, can be obtained. The results are then applied to a hypothetical two-layer capillary barrier composed of soils of the compiled dataset to determine the breakthrough suction ( ψBT) of the barrier. The proposed Bayesian approach gives a probabilistic distribution of ψBT instead of a single value in the traditional deterministic method. [ABSTRACT FROM AUTHOR]

This study describes a new modified prediction method of surface settlement (SS) for Xi'an Metro. The estimation method of SS and its characteristic parameters, volume loss (VL), maximal SS, and settlement trough width (STW) are reviewed and discussed in this paper. The gap parameter (GP) is applied to estimate VL; however, the calculation method of GP and its influence factors have not been clarified entirely. In this study, six influence factors are introduced into the new GP model, and the detailed solutions are presented. This estimation method is able to take into account the support pressure of the shield head at the tunnel face, the lining support pressure around the tunnel opening, the filling effect of tail grouting, yawing, and pitching of the shielding machine, and the long-term deformation of the remoulded surrounding soil. Based on Xi'an Metro line 2, the soil behaviors and measured SS characteristics are deeply investigated. The upper and lower bounds of the total GP of the 15 cases are predicted. Comparison of the predicted SS troughs with field observations can show reasonable agreement. It is suggested that the new estimation method can be used effectively in estimating the SS induced by the shield tunneling method. [ABSTRACT FROM AUTHOR]

An increasing number of catastrophic progressive collapses of deep excavations have occurred throughout the world. However, the research on progressive collapse mechanisms is limited. In this paper, two categories of model tests were conducted to investigate the mechanism of partial collapse (sudden failures of certain retaining piles) and progressive collapse. The model test results show that partial collapse can cause a sudden increase in the bending moments of adjacent piles via an arching effect. The load-transfer coefficients are defined to be equal to the peak increase ratios of the maximum bending moments in adjacent piles (peak moments caused by collapse over the values before the collapse). When the maximum load-transfer coefficient is larger than the bearing capacity safety factor of the piles, the partial failure will lead to progressive collapse. The influential factors of the progressive collapse mechanism, such as the partial collapse extent, excavation depth, and capping beam, were also investigated. During progressive collapse, the previous failed pile could cause new stress arching; simultaneously, the soil behind certain nearest intact piles could become loosened and destroy the arch springing of the stress arching, causing the progressive collapse to cease gradually. [ABSTRACT FROM AUTHOR]

In this paper, we have considered spatially homogeneous and anisotropic Bianchi type-III space-time filled with matter and anisotropic modified holographic Ricci dark energy in general relativity. We have solved Einstein's field equations using the following possibilities: ( i) hybrid expansion law proposed by Akarsu et al. (JCAP, 01, 022 (2014)); ( ii) a varying deceleration parameter considered by Mishra et al. (Int. J. Theor. Phys. 52, 2546 (2013)); and ( iii) a linearly varying deceleration parameter given by Akarsu and Dereli (Int. J. Theor. Phys. 51, 612 (2012)). We have presented the cosmological models in each of the preceding cases and studied their evolutions. We have also discussed physical and kinematical properties of the models. [ABSTRACT FROM AUTHOR]

The simplified procedures for evaluation of the earthquake-induced displacement in earth and rockfill dams are widely used in practice. These methods are simple, inexpensive, and substantially less time consuming as compared to the complicated stress-deformation approaches. They are especially recommended to be used as a screening tool, to identify embankments with marginal factor of safety, assuming that these methods always give conservative estimates of settlements. However, recent studies show that application of these methods may not be conservative in some cases, especially when the tuning ratio of a dam is within a certain range. In this paper, the fundamental theory behind the simplified methods is critically reviewed. A case in which the results of the simplified methods are reportedly nonconservative is investigated in detail and possible reasons are discussed. The reliability of the simplified methods is examined here based on the existing thresholds proposed in the literature and accounting for the embankment geometry and type, and for the seismic activity characterization, and a practical framework is proposed accordingly. The effectiveness of this framework is evaluated in the study of seismic behaviour of a rockfill dam where all simplified procedures failed to predict the order of deformation experienced by the dam under a recent earthquake event. [ABSTRACT FROM AUTHOR]

This paper proposes an updated vehicle-tire contact force model to simulate vehicle-bridge interaction, considering the tire contact area and the thickness of the bridge wearing surface. In contrast to the traditional methods of using a single-point tire contact force with a moving average filter, the proposed model uses multiple-point contact forces to account for the tire contact area. Results show that both the longitudinal and transverse distribution of tire contact force have a significant effect. [ABSTRACT FROM AUTHOR]

Helical piles are used increasingly to support new and existing foundations. This paper presents a field study on the axial monotonic and cyclic behaviour of steel fibre-reinforced helical pulldown micropiles. Test piles consisted of a round corner square helical pile with three helices attached to it, and a steel fibre-reinforced grout shaft. To assess the grout shaft contribution, one helical pile without a grout shaft was tested. Piles were instrumented with strain gauges to evaluate the load-transfer mechanism. This paper discusses the load-displacement response of this pile system, and load-sharing mechanism between the grout shaft and lead section. The study shows that the grout shaft significantly improves the helical pile axial performance. It was found that the load-transfer mechanism within the lead section is through individual bearing of each helix. Also, the findings demonstrate that the behaviour of this pile system is satisfactory under one-way cyclic loading conditions. The results suggest that the reinforced helical pulldown micropile is a viable deep foundation option for axial monotonic and one-way cyclic loading applications. [ABSTRACT FROM AUTHOR]

The paper presents a methodology to evaluate flow slide susceptibility in potentially liquefiable sandy slopes. The proposed approach accounts for both contractive and dilative volumetric behaviour during shearing using the MIT-S1 constitutive model. As a result, it is possible to distinguish among different types of undrained response induced by a rapid shear perturbation. The first part of the paper describes the general methodology for infinite slopes, providing an index of stability for incipient static liquefaction in shallow deposits. The methodology accounts for the anisotropy due to the initial stress state and uses simple shear simulations to assess instability conditions as a function of slope angle, stress state, and density of the soil. The resulting stability charts define the margin of safety against static liquefaction and the depths likely to be affected by the propagation of an instability. The second part of the paper applies the methodology to the well-known series of flow failures in a berm at the Nerlerk site. The MIT-S1 model is calibrated using published data on Nerlerk sands and in situ cone penetration test (CPT) data. The analyses show that in situ slope angles α = 10°-13° are less than the critical slope angle needed for incipient instability. Liquefaction and flow failures were therefore promoted by small perturbations in shear stresses that could be generated by rapid deposition of hydraulic fill. [ABSTRACT FROM AUTHOR]

Drift and internal forces due to lateral forces on multi-storey concrete buildings composed of flat plates, columns, and shear walls are considered. For analysis, the structure should be idealized by a model composed of all monolithic components: shear walls, slabs, and columns. All components affecting the structure's stiffness should be considered in design; this is required by codes. However, for seismic design, codes allow, as alternative, a lateral force-resisting system composed of the shear walls only, but require that the design for the moment and the shearing force, transferred between the column and the slab, be based on the calculated drift. The study in this paper shows that this alternative can greatly overestimate the drift, the unbalanced moments transferred between the columns and the slabs and the bending moments on the shear walls. The design forces depend upon the natural period of vibration, whose value would be overestimated by ignoring the contribution of the slabs and columns to the stiffness of the structure. This paper recommends that the design be based on the analysis of a structural model composed of the shear walls, the slabs, and the columns; the paper also gives guidance on the design of flexural and punching shear reinforcements in the slabs. [ABSTRACT FROM AUTHOR]

This paper presents an integrated bearing capacity-settlement approach to the design of shallow foundations on heavily overconsolidated clays by alterations of the 'modified Cam clay' (MCC) model. The bearing capacity of soils and their settlements from loads imposed on shallow footings have been studied extensively. Yet, there is no consensus on a method that provides both reliable load-bearing capacity and settlement predictions. Current methods treat the soil under shallow footings as different ideal materials for the purpose of calculating the bearing capacity and settlement. The method proposed in this paper treats the soil as a single ideal material for both bearing capacity and settlement. The MCC model is tailored by adding Hvorslev's findings on overconsolidated clays and delineating stress states that bring the soil to tensile failure from those that cause it to yield or behave elastically or to show discontinuous response. A limiting stress surface is established as defining a limiting bearing capacity. A heavily overconsolidated clay is assumed to behave elastically if its stress state is below the limiting stress surface. Predictions from the method proposed in this paper compare favorably with model tests and field test results. Examples are provided illustrating how to use the proposed method. [ABSTRACT FROM AUTHOR]

The application of electro-osmosis (EO) for stabilizing soft clays is receiving more attention in geotechnical engineering. When the application of traditional ground improvement techniques, such as surcharge, pre-loading, wick drains, and vacuum pre-loading, is not appropriate for a particular situation, innovative techniques such as electro-osmosis need to be considered. Although the effectiveness of electro-osmosis has been widely demonstrated in many field applications, geotechnical engineers are still hesitant to apply electro-osmosis due to unknown effects such as electro-chemical changes, which could not be accounted for in the design. This paper presents a design of an electro-osmotic triaxial testing apparatus suitable for electro-osmotic treatment of soft clays and for measuring electro-osmotic permeability and generated pore-water pressure, as well as a testing procedure that accounts for the contribution of electro-chemical changes in the improvement of soil properties. A series of electro-osmotic triaxial tests with various initial stresses and boundary conditions were conducted and the results are presented in the paper. [ABSTRACT FROM AUTHOR]

In general, clayey soils exhibit more or less both creep and swelling. In this paper, 'creep' means viscous compression under a constant load condition in an oedometer test, while 'swelling' means viscous expansion under a constant load condition in an oedometer test and is a reverse behaviour to creep for all saturated soils. Clayey soils containing the clay mineral montmorillonite show strong creep and swelling characteristics. Both creep and swelling characteristics have a significant influence on the deformation and failure of geotechnical structures. This paper presents main data from tests on a mixture of bentonite-silica sand in one-dimensional (1D) straining. Tests include ( i) multistaged loading tests with unloading-reloading and enough time for creep and swelling in 1D straining and ( ii) step-changed constant rate of strain (CRSN) compression tests with unloading-reloading in 1D straining as well. From the test data, the creep, swelling, and strain rate effects are observed and discussed. Based on the test data and a 1D elastic viscoplastic (1D EVP) model developed by Yin and Graham (1989, 1994), the authors propose a new 1D elastic viscoplastic model considering both creep and swelling (called 1D EVPS). The data from the multistage oedometer tests are used to calibrate the new model. After this, the new model is used to simulate the step-changed CRSN compression tests and make a comparison. In this way, the new model is verified. The new 1D EVPS is then used to simulate CRSN tests with a single strain rate, relaxation in the creep or swelling region, and constant rate of stressing tests. It is found that the new model can simulate well the strain (or stress) rate effects, loops in unloading-reloading, and stress relaxation in the creep region or stress increase in the swelling region, which are all caused by both creep and swelling of the soil. [ABSTRACT FROM AUTHOR]

Dam safety has drawn increasing attention from the public. To ensure dam safety, it is essential to diagnose any dam distresses and their causes properly. The main objective of this paper is to develop a robust probability-based tool using Bayesian networks for the diagnosis of embankment dam distresses at the global level based on past dam distress data. A database of 993 distressed in-service embankment dams in China has been compiled, including general information on the dams, distresses, and causes. Based on the database, general characteristics of embankment dam distresses are studied using Bayesian networks, which can tackle not only the multiplicity of dam distresses and causes, but also the complex interrelations among them. Common patterns and causes of distresses are identified. The interrelations among the dam distresses and their causes are quantified using conditional probabilities determined based on the historical frequencies from the dam distress database. A sensitivity analysis is also conducted to identify and rank the most important factors that cause the distresses. With the prior information of common characteristics extracted from the database, Bayesian networks are further used to diagnose a specific distressed dam at the local level by combining global-level performance records and project-specific evidence in a systematic structure, which is presented in a companion paper. [ABSTRACT FROM AUTHOR]

Based on prior information on common characteristics of dam distresses extracted from the dam distress database described in a companion paper, this paper attempts to extend the technique of Bayesian networks to the diagnosis of a specific distressed dam. The diagnosis is conducted by combining two sources of information, i.e., global-level knowledge from the database and project-specific evidence. Based on results of the diagnosis, key distress factors for a specific dam can be identified and suitable remedial measures can be suggested. Further, the Bayesian network analysis is conducted to evaluate the effectiveness of the adopted remedial measures. A case study on the diagnosis of a distressed embankment dam, Chenbihe Dam, with seepage problems is presented to illustrate the methodology. In this case study, the observed leakage rates, seepage exit locations, and boundary conditions of the embankment are used as project-specific evidence. [ABSTRACT FROM AUTHOR]

Unlined pressure tunnels were first driven by the Norwegians into hard granitic rock, which is the ideal material for this type of structure. However, the increase in demand for electric power has propelled the industry to develop projects at sites all over the world with less favourable geological conditions. The paper places emphasis on the preliminary design phase when no field measurements are available. A recent study by Rancourt (published in 2010) has investigated the spatial distribution of the minimum stress that is required to control hydraulic jacking around unlined pressure tunnels. Various surface topographic profiles including slopes, hills, and valleys; the rock cover to tunnel diameter ratio; as well as the presence of geological features such as shear zones and dykes were investigated with numerical modelling. Effective rock cover predictions are compared to those given by the well-known Norwegian design criterion, and a correction factor called cover alteration ratio (CAR) has been introduced. In this paper, a design methodology is proposed for use of CAR at the preliminary design stage in the form of a factor of safety against hydraulic jacking to be used in conjunction with the Norwegian criterion. Limitations on the use of the Norwegian criterion are highlighted. [ABSTRACT FROM AUTHOR]

This paper investigates the ultimate limit state load and resistance factor design (LRFD) of deep foundations founded within purely cohesive soils. The geotechnical resistance factors required to produce deep foundation designs having a maximum acceptable failure probability are estimated as a function of site understanding and failure consequence. The probability theory developed in this paper, used to determine the resistance factors, is verified by a two-dimensional random field Monte Carlo simulation of a spatially variable cohesive soil. The agreement between theory and simulation is found to be very good, and the theory is then used to derive the required geotechnical resistance factors. The results presented in this paper can be used to complement current ultimate limit state design code calibration efforts for deep foundations in cohesive soils. [ABSTRACT FROM AUTHOR]

The US Army Corps of Engineers (USACE) completed a liquefaction potential analysis as part of the seismic evaluation of Milford Dam in 1986. This paper uses data from the 1986 study to compare fines content data from in situ frozen and standard penetration test (SPT) samples that suggest fines content can be overestimated by 1-10% by SPT samples in stratified sand deposits. This result may have implications for liquefaction assessments because split-spoon samples may overestimate the actual fines content, resulting in a liquefiable deposit being classified as nonliquefiable. In addition, the paper evaluates the effectiveness of ground freezing on maintaining in situ soil structure and aging of the foundation sands at Milford Dam. [ABSTRACT FROM AUTHOR]

Concrete manholes are widely used in sanitary sewer and storm water systems in Canada. However, technical information regarding their structural aspects is limited. The main objective of this paper is to evaluate the effect of main parameters that impact the design of precast concrete manholes. A three-dimensional finite element model for circular precast concrete manholes was developed using Plaxis 3D and was calibrated against the experimental results presented in an earlier paper by the authors. The calibrated numerical model was used to analyze different configurations of concrete manholes and to conduct a parametric study on the parameters that govern its design including: type of native soil around the manhole; trench width ( Tw); water table elevation ( Wt); effect of manhole stage installation; and effect of soil compaction. The critical conditions were identified based on the change in the pressure underneath the centre of the manhole base and the bending moments within the manhole base. It was found that the trench width, stage installation of manhole, and filling soil compaction had marginal effects on the total vertical pressure beneath the centre of the manhole base. The presence of the water table at the top of the manhole resulted in the most critical contact pressure at the manhole base. [ABSTRACT FROM AUTHOR]

This paper uses finite element upper and lower bound limit analysis to produce chart solutions for three-dimensional (3D) natural slopes for both short- and long-term stability. The presented chart solutions are convenient tools that can be used for preliminary design purposes. The rigorous limit analysis results in this paper were found to bracket the true factor of safety within ±10% or better, which can be used as a benchmark for the solutions from other methods. The depth of the slip surfaces is observed to be generally shallow for most analyzed cases, particularly for the long-term slope stability problem. In addition, it was found that using a two-dimensional (2D) analysis may lead to significant differences in estimating safety factors, which can differ by 2%-60% depending on the slope geometry and soil properties. Therefore, great care and judgement are required when applying 2D analyses to 3D slope problems. [ABSTRACT FROM AUTHOR]

In this paper, we discuss issues in verification, validation, and uncertainty prediction in computational fluid dynamics (CFD). Mesh adaptation is used to perform the systematic grid refinement studies required for code and simulation verification. We demonstrate the method of manufactured solutions (MMS) for code verification. Examples of successful and failed validation show that reliable prediction can only occur with an appropriate mathematical model of physics along with accurate numerical solution of the differential equations. The paper emphasizes good CFD practices to achieve systematic verification and put validation studies on solid grounds. Finally, the sensitivity equation method (SEM) is used to cascade input data uncertainty through the CFD code for estimating the uncertainty of the flow response. On discute des enjeux de vérification, validation et de prédiction d'incertitudes en CFD (« computational fluid dynamics »). On utilise des maillages adaptatifs lors des études systématiques de raffinement de maillages requises pour la vérification de code et de simulation. On présente la méthodes des solutions manufacturées pour la vérification de code. Des exemples de verification réussie et échouée démontrent que des prédictions fiables s'obtiennent uniquement avec un modèle mathématique approprié et des solutions numériques précises des équations différentielles. L'article met l'accent sur les bonnes pratiques en CFD pour assurer une vérification systématique et la rigueur de la validation. Finalement, on utilise la méthode de l'équation des sensibilités pour obtenir des estimés des incertitudes des prédictions induites par celles des inputs. [ABSTRACT FROM AUTHOR]

The paper describes a series of tests performed in a drum centrifuge on instrumented model displacement piles in normally consolidated sand. These tests examined the influence of the pile installation method, the stress level, and the pile aspect ratio on the increase in lateral effective stress on the pile shaft during static load testing to failure. A parallel series of constant normal load and constant normal stiffness (CNS) laboratory interface shear experiments was performed to assist interpretation of the centrifuge tests. It is shown that although the cycling associated with pile installation results in a progressive reduction in the stationary horizontal effective stress acting on a pile shaft and densification of the sand in a shear band close to the pile shaft, this sand dilates strongly during subsequent shearing to failure in a static load test. The dilation (the amount of which depends on the cyclic history) is constrained by the surrounding soil and therefore leads to large increases in lateral effective stresses and hence to large increases in mobilized shaft friction. The increase in lateral stress is shown to be related to the radial stiffness of the soil mass constraining dilation of the shear band and to be consistent with measurements made in appropriate CNS interface shear tests. The paper's findings assist in the extrapolation of model-scale pile test results to full-scale conditions. [ABSTRACT FROM AUTHOR]