Civil and Environmental Engineering

Permanent URI for this collectionhttps://uwspace.uwaterloo.ca/handle/10012/9906

This is the collection for the University of Waterloo's Department of Civil and Environmental Engineering.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

Waterloo faculty, students, and staff can contact us or visit the UWSpace guide to learn more about depositing their research.

Browse

Now showing 1 - 14 of 14

Advancements in bender-element testing - frequency effects
(University of Waterloo, 2019-09-24) Irfan, Muhammad; Cascante, Giovanni; Basu, Dipanjan
Modern building and bridge codes require seismic design of foundations and structures; for which, the evaluation of the soil’s response to dynamic loads is an important requirement in seismic design. The dynamic soil response is governed by its dynamic properties such as shear modulus (wave velocity) and damping ratio. These soil dynamic properties are typically measured in laboratory mostly using a bender element system (BE) or a resonant column (RC) device. However, the operating frequency range of BEs (e.g. 1 to 15 kHz) and the RC (e.g. 20 to 220 Hz) are not representative of typical earthquake loads (e.g. 0.1 to 10 Hz). In addition, there are significant limitations in BE and RC testing which reduce their reliability. Thus, current seismic designs could be either conservative or unsafe. A major limitation in BE testing is that there is no standard procedure; mostly because the soil-BE interaction is not well understood; and the characterization of BE inside a soil specimen was not possible. On the other hand in RC testing, the soil dynamic properties cannot be evaluated simultaneously as function of frequency and strain. In a typical narrow-band resonant column test (e.g. sine sweep, random noise), the induced shear strains are different at each frequency component. Therefore, the main objectives of this study are to understand better the soil-BE interaction; which will provide the basis for the development of reliable guidelines for BE testing; and to verify the BE test results using the standard RC device. The main objectives are achieved by testing the BE using a state-of-the-art laser vibrometer and a newly developed transparent soil to measure the actual response of the bender element transmitter (Tx) and receiver (Rx) inside different media such as air, liquids, and sand under different confinements. Then, the dynamic characteristics of the Tx are measured using advanced modal analysis techniques originally developed for structural applications (e.g. Blind Source Separation). The modal analysis is used to investigate if the different BE vibration modes correspond to a cantilever beam, as currently assumed or a cantilever plate. The Rx is also studied to assess the effects of compressional waves, the total damping of the BE system inside the medium on the actual evaluation of the shear wave velocity of the soil. In addition, the dependence of the output voltage from the Rx and the applied strain is investigated at different confining pressures. The thesis concludes with the dynamic characterization of a sensitive clay (Leda clay) that is present in large areas of Eastern Canada (Leda or Champlain sea clay) BE and RC tests are performed on unique undisturbed samples. All results presented in this study represent to the averages of multiple tests (more than 10 for RC and more than 500 for BEs). In all cases, the maximum coefficient of variance was 3 % which demonstrates the repeatability of the measurements. Contrary to a common assumption in BE testing, measurements on the transparent soil show that the Tx response inside the specimen is significantly different from the actual input voltage. In addition, BE measurements in soil and oil show that the time delay between input excitation and Tx response is not constant but it decreases with the increase in frequency. Results from the modal analysis of the Tx show a cantilever beam deformation (2D) only for the first mode of the Tx response in air and liquids; however, the response inside the soil specimen (no confinement) shows a cantilever plate behavior (3D). The excitation frequency in BE test should not be constant as commonly done; but it should be increased at each confinement level to match the increase in natural frequency and improve the signal-to-noise ratio. The overall damping ratio of the Tx increases up to 30% with confinement because of the soil-BE interaction, causing additional challenges in the evaluation of shear wave velocity and damping ratio from BE tests. The measured BE-system response shows a significant p-waves interference that affects the evaluation of the shear wave velocity. The p-wave interference must be carefully evaluated for the correct interpretation of the results. The p-wave interference is clearly observed when the Rx response is measured inside different liquids. This interference increases with the increase in the excitation frequencies. The Rx response in the transparent soil shows that participation of high frequencies and the interference of p-waves increases with increase in confinement. The p-wave arrivals mask the shear wave arrivals; which can lead to the overestimation of shear waves by more than 25 %. The results from the RC and BE tests on fused quartz and Leda clay specimens confirm the conclusion that high input frequencies enhance the generation of p-waves. The theoretical relationship between the maximum BE displacement and maximum input voltage for the Tx or the maximum output voltage for the Rx is verified for the first time for liquids and sands at no confining pressure. The peak displacements at the tip of the BE increased linearly with the input voltage because the maximum displacement in a piezo-electric transducer is proportional to the applied voltage. RC and BE tests performed on four Leda clay samples showed the effects of shear strain, confinement, and excitation frequency on shear modulus and damping ratio of the Leda clay. The effect of frequency is evaluated using a recently proposed methodology called the ‘carrier frequency’ (CF) method. The stiffest sample displayed the highest degradation with the increase in shear strain. There is a 15 % difference observed between the shear wave velocity estimates from RC and BE tests. The RC tests at frequencies below 100 Hz showed no effect of loading frequency on shear modulus and damping ratio; however, BE tests at frequencies centred at 12kHz did show a 15% change in wave velocity. This change could be attributed to the loading frequency or to the complex interaction of between p-waves and s-wave in BE testing. Loading frequency in BE tests does have a significant effect in the results, up to 40% error in the estimation of s-wave velocity, as the interaction between p-waves and s-waves increases with frequency.
Coupled Numerical Moelling Of Vacuum Consolidation With Nonuniform Pore Pressure Distribution
(University of Waterloo, 2021-09-27) Cai, Yi; Basu, Dipanjan
In this study, Biot’s type hydro-mechanical coupled numerical models are used to examine ground improvement of fine-grained soft soil deposits using prefabricated vertical drains (PVD) and vacuum assisted consolidation methods in combination with embankment preloading. Fully coupled numerical simulations are developed in the context of the traditional unit cell radial consolidation theory commonly applied to PVD and vacuum assisted consolidation. The theoretical justification of nonuniform stress and porewater pressure distribution under an embankment of finite dimension is examined, with reference to field observations from full-scale case studies of PVD/vacuum consolidation in the literature. The impact of nonuniform porewater pressure distribution on the traditional unit cell radial consolidation theory are examined through numerical modelling, and the theoretical compatibility of nonuniform porewater pressure distributions and unit cell radial consolidation theory is discussed. Through numerical modelling, it is observed that the traditional unit cell model of radial consolidation theory, which PVD and vacuum consolidation solutions were developed from, is functionally constrained to the assumption of uniform surcharge in the soil as the initial undrained condition. Deviations from the uniform surcharge assumption, such as nonuniform porewater pressure distribution in the soil that leads to variable porewater pressure gradients with respect to depth below the preloading embankment, or nonuniform applied vacuum pressure with depth, will effectively highlight the theoretical limitation of the traditional unit cell radial consolidation. To adequately address nonuniform stress and porewater pressure distribution in the soil, fundamental revisions to the traditional linear governing equations for PVD and vacuum consolidation are needed considering nonlinearity of the consolidation equation arising from evolving permeability and compressibility of the soil due to change in void ratio during consolidation; non-Darcian flow regime for low permeability soil; and large strain elasto-plastic behavior of the soil. In this study, considering the nonlinear soil stress-strain relationship are approximated using the Modified Cam-Clay model.
Evaluation of seismic activity and fault reactivation for Enhanced Geothermal Systems
(University of Waterloo, 2017-02-10) Valipoor Goodarzi, Faraz; Basu, Dipanjan
Growth in energy demand from developing nations necessitates the utilization of all available sources of energy. Primarily due to their environmental benefits, clean and renewable energy resources are of particular interest. Moreover, since renewable energy is gathered from naturally replenished sources, it is widely available around the world. Origins of renewable energy include sunlight, rain, wind, waves, and geothermal heat. Of these, geothermal heat is the area of focus in this research. The main goal of geothermal energy technology is to find a way to transfer the thermal energy to the surface where it can be used for heating and generating electricity. All geothermal technologies are based on this principle. The process of geothermal energy extraction can take place in both shallow and deep layers of crust. Among the commonly available energy extraction technologies, Enhanced Geothermal System (EGS) is of particular interest in this research. Through EGS, a cold fluid is injected into the ground and extracted heat energy is delivered through a process called “hydraulic stimulation”. The target of this research is to develop a model to investigate the geomechanical issues of a deep EGS set-up in addition to the influence of the “hydraulic stimulation” process on the geologic medium, particularly the problem of induced seismicity in a pre-existing fault which exists in the system. A 2D numerical finite element code is developed to iv analyze the behavior of porous subsurface in terms of displacement, stress, fluid pressure distribution, and temperature through a coupled thermo-hydro-mechanical (THM) approach using the corresponding mathematical governing equations. After modeling an EGS setup and stimulation program, an efficient approach is introduced along the concept of Mohr-Coulomb diagram which enables studying the seismic risk potential in an EGS using the final stress state of the geologic medium obtained from the THM approach.
Influence of Soil Parameters on Local Pier Scour Depth
(University of Waterloo, 2021-12-15) Budwal, Iqbal Singh; Basu, Dipanjan
Bridge scour is a phenomenon where erosion of the sediment bed surrounding bridge foundation occurs due to fluid forces arising from currents, waves, and turbulence. Scour around foundation components such as piers, piles and abutments may lead to structural instability and possible collapse. Scour has been documented as the leading cause of bridge failures; thus, the prediction, monitoring and mitigation of scour is paramount for safe and cost-efficient bridge design. The current methods of estimation of pier scour do not properly use information about soil parameters in the calculations. However, soil parameters among other factors play an important role in the scour process. Neglecting inputs of soil parameters leads to significant underestimation of pier scour depths and overtly expensive bridge foundation designs. To develop more accurate methods of scour prediction, parametric studies are required to systematically investigate the effects of soil parameters, such as grain size distribution, mineral composition, cohesion, angle of repose, and void ratio, and incorporate them in the scour prediction equations. Most published scour studies utilized scaled down laboratory experiments although there has been some limited research on scour using numerical simulations. Numerical studies on scour are less expensive and provide the opportunity to investigate a wide variety of scenarios through systematic parametric studies. In this thesis, a comprehensive review on the existing bridge scour theories and scour estimation methods are made. Subsequently, numerical simulations of pier scour are performed using the software SSIIM. Parametric studies are conducted using SSIIM to quantify the influence of sediment parameters on pier scour and to provide recommendations on the most appropriate scour prediction methods. The review performed in this thesis covers the existing literature on scour including the controlling mechanisms and the scour types that occur at bridges. Relevant soil, fluid, and structural factors and their influence on scour are examined. The most influential soil parameters on scour were found to be the grain size, angle of repose, and cohesion. However, the only soil parameters currently considered by empirical methods is the grain size or gradation. Also discussed in detail are the common empirical equations used for estimating equilibrium scour depths and scouring rates. The review covers laboratory-scale studies, numerical modeling, and soft computing techniques, such as artificial neural networks, used to investigate scour. A brief discussion is made on scour monitoring techniques and countermeasures to mitigate scour. Numerical simulations in this study were performed using the software SSIIM (Sediment Simulation in Intakes with Multiblock option). The ability of SSIIM to estimate pier scour was first investigated and the optimal modeling parameters required for accurate predictions of scour were determined. It was found that SSIIM was able to accurately model flow past piers with rigid beds and predict equilibrium scour depths with errors not exceeding 12.6% when compared to observed experimental scour depth. A parametric study was subsequently conducted using SSIIM investigating the effect of soil parameters on pier scour depths. To cover a range of structure sizes, numerical domains were created with pier diameters set as 0.1 m, 0.25 m, 0.5 m, and 0.8 m. Each of the four piers were simulated with two flow intensities of 0.5 and 0.75 for a total of eight flow scenarios. Each flow scenario was simulated with 16 different types of soils for a total of 128 cases. The soils tested were clean sands with control parameters of a 1 mm grain size, 30° angle of repose, and 0 Pa cohesion. While two soil parameters were kept constant, the third was varied to investigate the influence on scour depth. The scour depths for ten grain sizes were examined to evaluate the performance of 12 empirical methods for predicting pier scour. Of the empirical equations examined, the TAMU (Texas A&M University) method was found to be the best scour depth prediction equation. The angle of repose was modeled using stable slope angles between 20° and 40°. Variation of the stable slope angle was found to vary scour depths by -41.9% to +145.1%. Cohesive strength was added to the sediment to simulate the presence of fines and was found to significantly impact scour depths. A cohesion of 0.5 Pa was enough to reduce scour depths by about 90%. The significant variations in scour depth as functions of angle of repose and cohesion highlighted the need for their inclusion in scour prediction equations and methods. Discussions on the SSIIM’s numerical scour modeling established that the current numerical sediment models require improvement in their ability to capture soil behaviour based on the angle of repose and cohesion. Better sediment modeling and accurate numerical scour simulations are required for the development of accurate scour depth prediction models for safe and cost-efficient bridge designs.
Non-destructive Evaluation of Damage in Concrete with Applications in Shallow Foundations
(University of Waterloo, 2018-09-25) Fartosy, Sabah; Cascante, Giovanni; Basu, Dipanjan
The most widely used material for civil infrastructure is reinforced concrete. The concrete deteriorates over time because of several reasons, and therefore, inspection of concrete is necessary to ensure its compliance with the design requirements. Decision makers often have insufficient data to implement the appropriate corrective measures in the face of infrastructure failure. Better assessment methods are essential to obtain comprehensive and reliable information about the concrete elements. Although, different methods exist to inspect concrete members, there is no comprehensive technique available for condition assessment of concrete of shallow foundations. To ensure the integrity of shallow foundations during construction and during its service life, it is necessary to monitor their conditions periodically. To achieve this goal a new NDT methodology is developed to reliably evaluate the conditions of new shallow foundations without changing their future performances. Recently, there is a trend to overcome coupling issues between the transducers and the object under investigation, by installing sensor networks in concrete to assess its integrity. Although many NDT approaches are designed to evaluate the integrity of concrete structural elements, shallow foundations, which are concrete elements embedded in soil, have received less attention. The challenging aspect of characterizing shallow foundations is limited accessibility for in-service foundation inspections because of structural restrictions. Even when accessibility is possible, the NDT methods (ultrasonic pulse velocity, UPV) used may produce measurements with high uncertainties because of inconsistent coupling between the transducer and the surface of the material being tested. In the current research project, a new NDT procedure is developed based on design of new transducers embedded at the base of lab-scale concrete foundation models, and these transducers are waterproof and used as receivers. The transducers consist of radial-mode piezoceramics that can detect waves from different orientations. The developed methodology relies mainly on two methods to emit the transmission pulse; either using a direct contact method by gluing the transducer to the concrete surface or using a plastic tube partially embedded in concrete and filled with water. The first procedure is used when the accessibility to the top surface of the foundations is possible; otherwise, the second option is employed to reach the concrete surface of foundations. The new methodology can be used in different stages: during construction of foundations to monitor the uniformity and quality of the concrete, and during in-service life to periodically assess the condition of the foundations, specifically after an event that may cause severe damage in concrete such as earthquake and overloading. To verify the applicability of the methodology, unreinforced and reinforced shallow foundation lab-scale concretemodels were tested in the laboratory under uniaxial compression loads. In this work, all ultrasonic measurements are averaged 16 times to ensure the consistency of the results and to eliminate high frequency noise. The average coefficient of variance obtained is less than 3.5%; which is considered acceptable in this type of measurements (typical measurement error ~5%). Also, different tests were repeated more than three times by removing and putting back all the ultrasonic transducers to enhance the statistical significance of the results. The main contributions of the research presented in this thesis are:  Characterization of low and high frequency transducers using laser vibrometer to characterize their responses for better ultrasonic measurements.  Characterization of a single fracture growth in a homogenous material based on wave velocity and wave attenuation.  Characterization of cement-based materials using ultrasonic pulse velocity and laser vibrometer methods.  Evaluation of freeze/thaw damage and monitoring progressive damage in concrete specimens subjected to uniaxial compression load using ultrasonic pulse velocity and laser vibrometer methods.  Fabrication of thirty-six new radial ultrasonic transducers to embed in concrete models for quality control purposes and to monitor progressive damage using new transmission pulse methodology.
Performance of Soil Borehole Thermal Energy Storage System under Different Natural and Engineered Subsurface Conditions
(University of Waterloo, 2023-12-18) Pandey, Upasana; Basu, Dipanjan
Borehole thermal energy storage (BTES) system, a type of underground thermal energy storage (UTES) systems, is a promising technology for sustainable space heating. BTES stores thermal energy in subsurface media (rock or soil) using borehole heat exchangers (BHEs). BTES installed in soil are specifically known as soil borehole thermal energy storage (SBTES) system. In SBTES, a heat carrier fluid (HCF) collects thermal energy from various heat sources such as solar energy and industrial waste heat, circulating it through the BHEs. The heat from the BHEs is transferred to the surrounding soil and stored as thermal energy in the soil deposits, thereby increasing its temperature. Subsequently, the stored energy is extracted through BHEs for space heating applications. The ability to retain stored energy in soil deposits depends on subsurface thermal and hydraulic conditions. Previous studies have explored various subsurface conditions (saturated, unsaturated, and groundwater flow) to capture their influence on the thermal performance of SBTES system. While previous studies focused specifically on the role of soil thermal conductivity under saturated soil conditions, the influence of other soil properties, particularly under different SBTES design conditions, has not been systematically explored. In unsaturated subsurface conditions, studies have concentrated on assessing the thermal performance of SBTES systems under varying moisture content conditions, while considering different water retention parameters. However, the understanding of the role of soil porosity in the thermal performance of SBTES in unsaturated soil, particularly under long-term operation scenarios, is limited. Additionally, existing studies have predominantly examined homogeneous soil conditions and have not accounted for soil layering. Further, while some studies have explored the impact of seasonal climatic fluctuations, they have primarily focused on variations in seasonal surface temperatures alone. The effect of surface pressure variations induced by factors such as evapotranspiration, groundwater table fluctuations, and other climatic conditions has not been thoroughly investigated. Previous studies regarding groundwater flow consideration often assumed the groundwater table to be flush with the ground surface, with the BHEs completely submerged into the groundwater. However, when different groundwater table depths are considered, where the BHEs are partially submerged, these studies did not take into account the influence of flow velocity. Previous studies have established that the consideration of groundwater flow is important in the analysis and design of SBTES systems. However, there is no systematic study available that explores the SBTES performance for a wide range of flow velocities and for multiple groundwater table depths considered in conjunction. Additionally, in the presence of high velocity groundwater flow, it is commonly recommended to avoid installing SBTES at the location without proper engineering modifications. However, currently no strategies exist to effectively mitigate the adverse effects of groundwater flow on the thermal performance of SBTES systems. The aim of this study is to develop better understanding of the influence of different subsurface conditions on the thermal performance of SBTES system through rigorous numerical analysis. The analysis incorporates saturated, unsaturated, and groundwater flow conditions to capture their respective impacts. Initially, a simplified conduction-based model is used to investigate the influence of physical and thermal properties of soil under different BHE spacing and injection heat flux scenarios for saturated soil condition. Subsequently, for unsaturated soil conditions, a coupled heat and mass transfer based numerical model is used to investigate the thermal behavior of SBTES systems under various subsurface moisture conditions, encompassing fully dry, fully saturated, and varying moisture content scenarios with different depths of the saturated soil zone. Additionally, the study examines the impact of seasonal surface pressure variations on the thermal performance of the SBTES system in unsaturated soil. Further, the role of soil porosity under different soil stratifications and soil moisture conditions on the thermal performance of the SBTES system in unsaturated soil is investigated to augment the existing knowledge in this area. The effects of groundwater flow on the short- and long-term performances of SBTES systems under fixed- and variable-energy supply and demand conditions are studied for different groundwater velocities and different groundwater table depths. Numerical simulations of a SBTES system are performed for four groundwater table depths and with four groundwater velocities ranging from 0 m s−1 to 1 × 10−5 m s−1. The study aimed to highlight the importance of conducting long-term analyses and quantifies the adverse effects of groundwater flow on the thermal performance of SBTES. Finally, a design aid is proposed in the form of vertical barriers to be installed within the SBTES domain, aimed at mitigating thermal losses resulting from groundwater flow. A comprehensive study is conducted to provide recommendations regarding the suitable type of vertical barriers, their appropriate positioning with respect to SBTES domain, and the anticipated improvement in thermal performance of SBTES system upon integration with the vertical barrier as a design aid. A detailed analysis is conducted for small, medium, and large-scale SBTES domain to provide a suitable range of vertical barrier design components, refining the geometry of the vertical barrier to achieve optimal thermal performance.
Reliability-based Environmental Impact Assessment in Geotechnical Engineering
(University of Waterloo, 2023-11-30) Lee, Mina; Basu, Dipanjan
A sustainable design is achieved by balancing the four aspects, so called the four Es, of sustainability – environment, economy, equity, and engineering. Given that geotechnical constructions involve land transformations through earthworks and construction of large-scale concrete and/or steel structures (e.g., bridge abutments, retaining structures, and tunnels), geotechnical engineering can play a vital role in sustainable development by ensuring that the resources are consumed responsibly with minimal emissions to the environment. In this thesis, methodology frameworks, developed based on (i) environmental impact assessment, (ii) reliability-based design, and (iii) multi-objective optimization, are proposed to facilitate the process of sustainable design in geotechnical engineering. The frameworks are applied to common geotechnical structures such as drilled shaft foundation, pile group, and mechanically stabilized earth (MSE) wall. To quantify the environmental sustainability of geo-structures, life cycle assessment (LCA) is used. LCA utilizes inventory of energy and materials to calculate the emissions from the life cycle stages and characterize the emissions into environmental impacts. In this thesis, the procedures of LCA, which have been tailored to geotechnical applications, are demonstrated meticulously with detailed sample calculations to encourage the use of LCA in standard design practices and to demonstrate the usefulness of information obtained from LCA. In fact, for example, it was found, based on this research study, that the global warming impact and human toxicity of a typical drilled shaft are 39 and 486% of annual world impact per person, respectively. The use of reliability-based design (RBD) methods has been strongly promoted in the last two decades to better tackle the uncertainties involved in design and soil parameters; hence, the connection between important factors in RBD and environmental impacts is investigated in this thesis. A comprehensive analysis is conducted on the relationship between reliability and global warming impact of geotechnical designs (i.e., drilled shaft and MSE wall) considering uncertainties in soil properties, material properties, applied load, model, and design dimension. Parametric and sensitivity studies are systematically conducted using reliability analyses, like first-order reliability method (FORM) and Monte Carlo simulations, and LCA. To balance the multiple aspects of sustainability, a multi-objective optimization framework is proposed using which designers can determine design dimensions that aim for minimizations of cost and global warming impact and maximization of reliability of a geotechnical structure. The framework utilizes several methodologies including LCA, FORM, response surface methodology, and non-dominated sorting genetic algorithm (NSGA-II). To encourage sustainability considerations in geotechnical engineering design, charts are developed which are useful for determining (i) global warming impact of the geo-structures designed with working stress design (WSD) and RBD approaches and (ii) design dimensions optimized with respect to cost, engineering reliability, and environmental impact, without the use of and knowledge in the sophisticated methodologies incorporated in the proposed frameworks.
Resilience assessment in geotechnical engineering
(University of Waterloo, 2016-09-15) Lee, Mina; Basu, Dipanjan
Impacts of inevitable disasters and climate change have been major concerns for the safety and sustainability of communities in the recent past. In an effort to reduce these impacts, development of resilience in civil infrastructures is becoming crucial. Conceptually, resilience is the ability to absorb, recover from, and adapt to shocks or changing conditions. The current practice for infrastructure asset management needs to incorporate this concept of resilience in order to reduce or prevent the detrimental consequences not only to the physical infrastructure systems, but also to communities and other systems vital for fulfilling human needs. For example, consequences can include environmental impacts caused by an incident and rehabilitation construction activities, increased costs for the asset management, and degradation in the quality of life. Therefore, resilience thinking needs to be practiced for designing and managing civil infrastructure systems so that they are resilient to external stresses such as climate change and natural disasters. Despite the awareness that resilience can be a key to resolve the difficulties with extreme events and climate change and that geotechnical assets serve as crucial components in critical infrastructure systems, research in the resilience of geotechnical assets is lacking. To put resilience thinking into practical applications in geotechnical engineering, a quantitative-based framework suitable and applicable for geotechnical assets is necessary. A quantitative resilience assessment framework applicable for geotechnical assets is proposed in this thesis. Driver-Pressure-State-Impact-Response (DPSIR) framework is adopted in developing the framework. It quantifies the impacts of damaged geotechnical assets to the relevant civil infrastructure network subjected to hazard scenarios. It also evaluates which strategic planning for mitigation and rehabilitation against the hazards is the most effective way for improving the resilience of the geotechnical assets. Metrics which reflect robustness, rapidity, redundancy, and resourcefulness aspects of resilience are developed for the evaluation. Environmental, economic, and social impacts are also concurrently considered to understand the trade-offs between the response strategies and their implementation consequences. The proposed framework is demonstrated using a case study on road embankments in a transportation network connecting London and Toronto in the province of Ontario.
Semi-Analytical Framework for Thermo-Mechanical Analysis of Energy Piles in Elastic and Elastoplastic Soils
(University of Waterloo, 2024-10-29) Paul, Abhisek; Basu, Dipanjan
Energy piles or geothermal piles are used to reduce the energy demand of a building by helping in the heating/cooling of the building as required. The advantage of energy piles over other ground heat exchangers is that piles are an integrated part of the foundation of a building to carry the superstructure load. The same piles can be used to extract/inject heat from/to the ground and that heat can be used in the cooling/heating of the building. Thus, the energy demand of the building for heating/cooling is reduced. Energy piles are subjected to mechanical load that comes from the superstructure as well as thermal load (temperature change) caused by the heat exchange operation. The combined mechanical and thermal load changes the behavior of the pile foundation. Because the length of the pile is much higher compared to its diameter, the temperature change affects the axial behavior of the pile rather than its lateral response. The settlement of an energy pile is different than a conventional pile foundation as heating or cooling of the pile causes extension in some parts of the pile and compression in other parts of the pile. The axial response of an energy pile under mechanical and thermal loads in terms of vertical settlement, strain, and stress in the pile is calculated in the available literature where the pile-soil interaction has been considered by modeling the soil with equivalent linear and nonlinear soil springs. The representation of soil as springs does not take into account the effect of three-dimensional pile-structure interaction. Analysis of the energy pile considering the three-dimensional pile-structure interaction has been done in the literature using numerical methods which are computationally expensive. Apart from that, the thermo-mechanical behavior of soil needs to be considered in the energy pile analysis because of the temperature change of the pile and soil, and heat exchange between the pile and the soil. In this context, the thermo-mechanical soil constitutive model should satisfy the laws of thermodynamics. The analysis of the energy pile with a thermodynamically acceptable thermo-mechanical soil constitutive model is lacking in the available literature. In this thesis, a continuum-based semi-analytical framework for the analysis of the energy pile that takes into account the three-dimensional pile-structure interaction is proposed. First, the semi-analytical framework for an energy pile that is embedded in multi-layered soil and subjected to mechanical axial load and thermal load is developed using the variational principle of mechanics by minimizing the potential energy of the pile-soil continuum where both the pile material and soil are considered to behave as a linear elastic material. In the next part of the thesis, a semi-analytical framework for the same energy pile is developed where the soil is modeled as an elastoplastic material. The analysis framework for the energy pile in elastoplastic soil is developed from the laws of thermodynamics with the energy potential and dissipation function where the plastic behavior of soil is taken into account through the dissipation function. The derived analytical framework is used for elastoplastic soil response with the Drucker-Prager constitutive model. The results from the present analysis are verified with available results in the literature from experiments and numerical analysis. The Drucker-Prager constitutive model does not take into account the effect of temperature on the stress-strain response of the soil. So, this constitutive model is most suitable to model the thermo-mechanical behavior of sand as the effect of temperature on the thermo-mechanical response of sand is not significant. Therefore, energy piles in sand can be analyzed using the present framework with the Drucker-Prager constitutive model. Energy pile in clay needs to be represented with a soil constitutive model that can capture the effect of temperature on the thermo-mechanical response of clay. In the third part of the thesis, the present analytical framework for an energy pile in elastoplastic soil is used to analyze the pile in clay with a thermo-mechanical constitutive model that takes into account the change in the mechanical response of clay due to temperature change. The thermo-mechanical model used in the analysis was developed using the hyperplasticity formalism, which satisfies the laws of thermodynamics. The present framework in all cases predicts results with acceptable accuracy. The present analytical framework predicts the response of energy pile under different loads (mechanical and thermal) in terms of vertical displacement, stress (with <10% difference between the results from the present analysis and finite element analysis/field tests) with acceptable accuracy in less computational time. The run time for the present analysis is approximately 10 and 5 times faster than axisymmetric finite element analysis for elastic and elastoplastic cases, respectively. In the final part of the thesis, the stresses developed in an energy pile under mechanical and thermal loads are observed for different soil properties. A parametric study is conducted on the developed stresses in an energy pile in single and two-layer soils under multiple loading conditions. A correlation between the applied mechanical and thermal load is established, and under these loading conditions, the effects of soil layering and material properties on the developed stresses are observed. The development of the tensile zone and its range in an energy pile for certain conditions are concluded from the parametric study.
Soil-Structure Interaction Analysis of Monopile Foundations Supporting Offshore Wind Turbines
(University of Waterloo, 2018-08-07) Gupta, Bipin Kumar; Basu, Dipanjan
Monopile foundations supporting offshore wind turbines are hollow circular steel piles of diameter 4-6 m and a slenderness ratio (length/radius) of 10-12 driven into the seabed in an average water depth of 35 m. They are subjected to large lateral forces and overturning moments at the seabed level from wind, waves, and water currents acting on the wind turbine structure. Currently, they are designed using the p-y analysis method (p is the soil reaction force per unit length at any point along the pile shaft and y is the corresponding pile displacement at that point) which has a number of shortcomings. The p-y analysis was originally developed from a few full-scale field pile-load tests on small-diameter piles (less than 2 m in diameter) and their applicability to large-diameter monopiles is questionable. Besides, it is empirical, site-specific, and does not account for the three-dimensional pile-soil interaction important for large-diameter monopiles, thereby, resulting in a conservative design and an increase in the cost of the project. Three-dimensional finite element analysis can be used for the analysis and design of monopiles, but such analyses require significantly large computational time and effort besides, the specific expertise of finite element software that further limits its use in practice. The primary objective of this thesis is to develop a computationally efficient continuum-based mathematical model that takes the three-dimensional monopile-soil interaction into account. In the thesis, three tasks are performed towards the development of the mathematical model. First, a mathematical framework is developed to analyze laterally loaded monopiles following the Timoshenko beam theory in a multilayered elastic soil deposit subjected to static lateral loading. In the analysis, it is shown that successive simplification of the analysis can lead to monopiles modeled as a Euler-Bernoulli and rigid beam. The analysis is verified with finite element solutions and the suitability of the application each of the beam theories to obtain monopile response (head-displacement and rotation) is also investigated besides, a comparison of the computational time between the present analysis and finite element analysis is also shown. In the second task, the aforementioned framework is extended to analyze monopiles embedded in a multilayered linear viscoelastic soil deposit with frequency-independent hysteretic material damping subjected to harmonic dynamic lateral loading. It is shown that the analysis can be reduced to model monopiles following the Rayleigh, Euler-Bernoulli, and rigid beam theory. The analysis is verified with well-established solution techniques reported in the literature. Further, the results and the computational time obtained from this analysis are compared with those of the analysis in the first task for four different monopiles with varying slenderness ratio currently installed in the field. The purpose of the comparison is to investigate the applicability of the dynamic analysis for obtaining monopile response which is subjected to cyclic loadings of frequency less than 1.0 Hz. It is found that the static analysis following the Euler-Bernoulli beam theory is sufficient for obtaining monopile response. In the third task, the mathematical framework developed in the first task is extended to analyze laterally loaded monopiles modeled as a Euler-Bernoulli beam in a multilayered nonlinear elastic soil deposit and subjected to static loading. In the analysis, the nonlinear elastic relationships describing the variation of shear modulus with shear strain reported in the literature either applicable to undrained clays or sandy soil deposits are utilized. The mathematical accuracy of the analysis is verified by comparing results obtained from the analysis with the results of finite element analysis. A comparison of the computational time between the present and finite element analysis is also shown to demonstrate the computational efficiency of the present analysis. The results of the analysis are further validated with the results of several full-scale field pile-load tests and the p-y analysis procedure available in the literature. The accuracy of the results from this nonlinear elastic approach is further ensured by comparing monopile response with those of finite element simulations where the soil is modeled using an elastic-plastic constitutive model. A comparison of the monopile response is also shown in the p-y analysis to investigate the appropriateness of the currently used p-y curves to analyze and design monopiles. Finally, a preliminary step-by-step design procedure for monopile foundations embedded in nonlinear elastic soil deposit is developed following the recommendations outlined in current codes of practice for offshore wind turbines.
Stability Assessment of Salt Cavern Roof Beam for Compressed Air Energy Storage in South-Western Ontario
(University of Waterloo, 2017-10-24) Fazaeli, Mohammad Mahdi; Basu, Dipanjan; Dusseault, Maurice
Due to the intermittent nature of renewable energy sources, application of energy storage systems is an important part of the development in support of clean technologies. Compressed Air Energy Storage (CAES) plants can provide utility scale storage by compressing air into a reservoir during off-peak period and generating electricity by expanding the air when energy demand is high. CAES is a proven technology that offers various services to the power network and provides flexible load management; however, site selection is a critical step during the design process of a plant. Salt deposits are recognized as potentially suitable geological layers for a compressed air energy storage system. In south-western Ontario, salt beds of the Salina Group of the Michigan basin provide suitable salt deposits for the excavation of storage caverns. Only two salt beds of the Salina Group are thick enough for excavation of a cavern, these are known as the unit A2 and unit B salt beds. In the case of an underground storage system, stability and serviceability of the storage cavern must be investigated using geomechanical models. Geomechanical issues may cause serious damage to the cavern, which could stop the system from functioning. The stability of the cavern roof layer has been investigated using voussoir beam theory. This method has been widely used to model rock mass behavior around underground openings. The results of the analytical solution have been validated against an existing case and verified by using a Universal Distinct Element Code (UDEC). The stress distribution within roof beams is investigated and upper and lower limits of roof size have been determined. Based on the findings from numerical analyses, assumptions of the voussoir method iv oversimplify the problem and cause inaccurate results. Hence, the selected iterative solution has been modified using a nonlinear approach. The updated procedure significantly enhanced the consistency of the results obtained from analytical solution with numerical models. To demonstrate validity of the modifications, a systematic parametric study has been included by using a wide range of beam parameters. The impact of creep behavior of the roof beam was examined by adding the deformation due to steady state creep to the elastic response of the beam. Also, the effect of the pressure difference around the cavern roof has been examined to determine maximum and minimum pressure inside the cavern with respect to size of the roof layer.
A Stochastic Framework for Soil-Structure Interaction and Constitutive Modelling
(University of Waterloo, 2019-08-19) Chaperon, Julien; Basu, Dipanjan
A stochastic framework for soil-structure interaction and constitutive modelling is investigated in this thesis and developed to account for uncertainties in material properties and loading conditions. The development of a one-dimensional Stochastic Finite Element Method (SFEM) for foundation problems is used as a starting point to describe the statistical behaviour of shallow and deep foundations at a local scale, where spatial variability exists. The Winkler model is adopted, and three sets of loading and boundary conditions are analyzed. A 1-D Karhunen-Loeve (KL) expansion is used to propagate the uncertainties in the material properties or loading conditions of each case. An exponential covariance structure is assumed for its applications in geophysics and in earthquake engineering. A different series representation known as the Polynomial Chaos expansion (PCE) is used to represent the random response since the covariance structure of the response is not known a priori. The method is combined with the Finite Element method (FEM) and used to solve three foundation problems. The accuracy and computational efficiency of the methodology for different orders of expansion is then compared with the Monte Carlo method. Thereafter, a similar problem is tackled for random inputs with a 2-D random field. A 2-D Karhunen-Loeve expansion is used and incorporated in the analytical solution of a 2-parameter continuum pile. Because of the analytical nature of the solution, and due to the non-linearity that arises as a result of the spectral decomposition of the soil properties, the representation of the response using the PCE is dropped to give way to an iterative solution. The results of the mean response for two examples taken from Basu and Salgado, 2008 are presented and compared to the deterministic solution. The uncertainties in material properties and loading conditions are then propagated at the constitutive level. A new methodology, the Fokker-Plank-Kolmogorov equation (FPKE), is adopted. The FPKE transforms the stochastic continuity equation of non-linear constitutive laws to second order linear deterministic partial differential equations. The one-dimensional development of the FPKE is undertaken and validated for a linear elastic shear model and linear elastic-plastic Von Mises model. Finally, the FPKE is extended to a three-dimensional framework and validated for a 3-D linear elastic model.
Studies on Nonlinear and Dynamic Soil Structure Interaction
(University of Waterloo, 2023-07-21) Elhuni, Hesham; Basu, Dipanjan
High-speed trains, excessive loads in moving trucks, and vibrating machines on foundations on soft ground can generate significant vibration and deformation in the subgrade (soil). Better understanding and realistic analysis of the interaction between railway tracks, pavements, and foundations and the supporting soil under moving and dynamic loads is necessary. Experimental investigations are always associated with large costs when simulating the loading conditions. Modeling dynamic soil-structure interaction problems is often associated with a high level of complexity and a large computational effort. Analytical modeling of these problems that results in accurate and reliable prediction of these soil structure interaction problems with a low computational cost and ease of use is a distinct advantage that can supplement the numerical modeling and experimental investigations. In this research, a new computationally efficient but mathematically rigorous semianalytical continuum model is developed for dynamic analysis of beams resting on layered poroelastic nonlinear soil deposit and subjected to dynamic loads. The proposed model is developed in stages in terms of the complexity of simulating the soil behaviour. First, the soil is simulated as a discrete two-parameter foundation in which the soil body is represented by mechanical springs with shear interactions. Subsequently, the soil is simulated as a linear and nonlinear continuum. Finally, the soil is simulated as a linear and nonlinear poroelastic continuum, For the continuum-based analysis, a simplified continuum approach was adopted in which the soil displacement field is expressed as a product of separable variables. The principle of virtual work was applied to obtain the governing differential equations that were solved partly analytically and partly numerically. The semi-analytical approach was found to be significantly faster than the corresponding full blown finite element analysis. A significant contribution of this work is the simulation of the nonlinear and poroelastic response of soil in the semi-analytical framework, which otherwise require elaborate meshing by the users and high computational effort. A nonlinear hyperbolic stress-strain relationship is used to represent the soil nonlinearity. Biot’s poroelastic theory is used to represent the poroelastic behaviour of soil. The nonlinear dynamic, nonlinear consolidation, and nonlinear poroelastic dynamic responses of the beams under moving and oscillating loads are obtained. It is envisaged that the methods developed in this thesis will provide more insights into the dynamic soil structure interaction problem, and will help in developing design aids.
Technical and Economic Assessment of Ground Source Heat Pump Systems (GSHPs) in Ontario
(University of Waterloo, 2017-08-28) Al-Haq, Armughan; Nathwani, Jatin; Basu, Dipanjan
Ground Source Heat Pump Systems (GSHPs) are one of the most promising clean and low-carbon source of geothermal renewable energy technologies for heating, ventilation and cooling of homes. Geothermal heat pump (GHP) technologies, referred to as GeoExchange, comprise ground-source and/or water-source heat pumps that use the constant temperature of the earth as the exchange medium instead of the outside air temperature. This study is a technical and economic assessment of use of GSHPs to support the policy options for increasing the share of geothermal energy sources within the residential sector of Ontario. The study identifies the technical and economic barriers to the wide-spread adoption of ground source heat pumps in Ontario and is an assessment of the impacts of large-scale deployment of GSHPs on greenhouse gas (GHG) emissions. In this study, I have established the basis for evaluating the cost and environmental benefits of GSHPs in Ontario. The results provide a sound economic and technical foundation for supporting investment decisions in favour of implementing GSHPs as a viable alternative to traditional heating, ventilation, air-conditioning systems (HVACs), specifically, natural gas use for space heating and hot water usage in buildings. The study reveals that geothermal ground source heat pumps have a great potential to reduce GHG emissions for Ontario’s residential sector by a magnitude of 21.7 megatonnes (Mt) that will in turn reduce the overall emissions of Ontario by 13%. GSHPs are a cost-effective solution for implementation on a wide-scale. The economic analysis clearly indicates the horizontal ground source heat pump system (H.GSHPs) is a strong winner in multiple sensitivity analysis when considering different lifespans, discount factors, and base case scenario against comparative scenarios. The rankings of the twenty-seven (27) cities selected for this study identify that the GSHPs are more attractive compared to traditional HVACs from an investment point of view in cities of the southern and distinct region as compared to the northern regions because of low present value (PV) of costs. The PV compares the cash outflows based on the initial investment, operating costs, maintenance costs, and disposal costs in a project lifespan of 60 years that span life cycles of 20 – 30 years for GSHPs and 12 years for traditional HVAC applications. This study has conducted a comprehensive technical and economic assessment for twenty-seven (27) cities in Ontario to address the geographic variation of benefits. While there is a variation across regions of Ontario – and this is based on weather, soil condition and level of energy use – the overall conclusion is a compelling case for GSHPs as a viable alternative to the use of natural gas.

Browse

Browsing Civil and Environmental Engineering by Author "Basu, Dipanjan"