Sinkholes are a common geohazard in karst areas that can threaten human life and causes significant damage to infrastructure. Approximately 18% of the United States falls into karst area where overburden soils are underlain by soluble carbonate rocks. In Florida, sinkhole-related insurance claims between 2006 and the third quarter of 2010 amounted to $1.4 billion according to the Florida Office of Insurance Regulation. Effective methods and tools for the sinkhole detection and characterization are necessary. Numerical analysis can play an important role in determining the stability of sinkholes and understanding the failure mechanism under varied subsurface geological conditions. In this study, the geomechanical behavior of sinkholes due to subsurface cavity and its expansion was numerically investigated by Plaxis 2D finite element (FE) software. The study investigated the effects of embedded clay layers on the failure mechanism of cover-collapse sinkholes. Selected sinkhole case histories (including Winter Park sinkhole) from different locations in Florida are also presented. Soil profiles and parameter values were determined using subsurface exploration data and published correlations in the geotechnical literature. Appropriate constitutive models were employed in the numerical simulations to reproduce the soil behavior that can account for small strain stiffness, soil nonlinearity, recent stress history effects, and large-strain asymptotic behavior. The constitutive models that were adopted in this study were elastoplastic models (Hardening Soil Small Strain model) and critical state models (hypoplasticity models) for sands and clays. Induced stress paths due to an evolving subsurface cavity were compared versus the yielding characteristics of different soil types. Induced ground settlements, distortions and influence zones due to an evolving subsurface cavity in the numerical environment were computed and compared versus the damage criteria of infrastructure in engineering practice. Based on a series of FE simulations, site-specific stability charts of selected sinkhole sites in Florida were developed using shear strength reduction techniques. The aim of this chart is to be used as a preliminary check of the sinkhole stability in the study domain, i.e. central Florida, at similar subsurface conditions.

Current seismic codes do not incorporate a well-established methodology for the selection of passive dampers type and their topological distribution and properties along the height of structures. Achieving the intended performance is made more complicated when structures are subject to extreme events and operate well within their inelastic range. This thesis utilizes a self-organizing genetic algorithm (soGA) with probabilistic gene-by-gene crossover and an adaptive active ground motion subset scheme to efficiently find optimal designs of low-rise steel frames subject to large number of extreme ground motions. Different types of passive dampers were considered, while the steel frames were modeled using the modified Ibarra-Medina-Krawinkler deterioration model with bilinear hysteretic response. Optimal design topologies were identified for different types of dampers that satisfied predefined performance levels in terms of story drift and floor acceleration demand parameters. With the capability to consider an active ground motion subset scheme, the computational effort was significantly reduced without prohibiting soGA to find optimal design solutions that satisfy the performance levels for the full ground motion set.

The objective of the thesis is to understand the factors affecting spatiotemporal ridehailing demand patterns as the COVID-19 pandemic has evolved. Specifically, the current study examines the key contributing factors of weekly ridehailing demand by employing Taxi and Transportation Network Companies (TNC) trip data from January 2019 through December 2020 for New York City. The ridehailing demand is partitioned across four time periods including Morning Peak, Morning Off Peak, Evening Peak and Evening Off Peak to accommodate for the time-of-day specific variations. Drawing on the high-resolution NYC data, the current study developed pooled spatial panel models to accommodate for the spatial and temporal heterogeneity. The thesis employs a recasting approach that enables the estimation of a parsimonious model specification across the four time periods. Two recasted spatial models: 1) Spatial Lag Model and 2) Spatial Error Model are estimated for ridehailing demand across the two services - Taxi and TNC - while considering a comprehensive list of factors including COVID-19 pandemic attributes, sociodemographic characteristics, land use and built environment attributes, transportation infrastructure and weather attributes. The model estimation results are further augmented with a robust policy analysis to predict potential ridehailing demand for future months. The policy exercise also illustrates how the proposed model can be employed by ridehailing companies and transportation agencies to examine ridehailing demand evolution as the pandemic continues.

Sinkholes are a significant geohazard in karst topography areas with life-threatening consequences and a need for timely detection and mitigation. However, sinkholes are challenging to characterize and a multi-disciplinary task. Currently, deterministic methods (e.g., analytical and numerical solutions) have been developed to provide a more robust analysis of sinkhole raveling in Central Florida but have limited applications for sinkholes throughout the state of Florida. Additionally, the mitigation methods after identification, such as grouting, need significant improvement based on currently available data. This study presents a four-step approach for improving sinkhole identification and mitigation: (1) build a substantial sinkhole geotechnical testing database for all areas of Florida; (2) use the expanded database to evaluate previously created sinkhole indices and raveling chart; (3) develop an effective method of monitoring susceptible sinkhole locations and (4) develop a sinkhole mitigation technique based on the existing site investigation data, specifically through grouting. These deliverables were developed through the collection of an extensive data set of geotechnical investigations performed in karst landscapes for sinkhole investigation and mitigation purposes throughout Florida. The methodology and conclusion of this research aim to provide safer and more cost-effective geotechnical evaluations and designs.

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The analysis of ground movements and nonlinear response of buildings induced by excavations in glacial clay deposits is conducted using finite element models built in PLAXIS2D and OpenSees. PLAXIS2D was used to simulate the performance of an urban cofferdam excavation braced with a concrete bracing system. Measured ground movements were compared with the computed response, and the influence of the temperature, installation, and curing effects on the concrete bracing is evaluated. Concrete time-dependent effects contributed to 32% of the maximum lateral wall movements. The numerical studies are expanded in a second finite element analysis to characterize the coupled fluid-solid response of fully saturated soils. Parametric analyses are conducted, and a design method aimed at determining the governing drainage characteristics, changes in excess pore water pressures, and ground movements induced by the excavation is presented. The method is validated with published case histories. The proposed method adequately described the pore water pressure buildup and excavation-induced ground deformations. A quasi-static framework for the modeling of fully saturated soils under partially drained or fully undrained conditions is presented. The implementation of a traction interface for the interaction between soil and foundation is also presented. Results confirmed the assumption that initial gravity forces acting on buildings can lead to more flexible responses, developing settlement profiles similar to those computed under free-field conditions. The nonlinear-inelastic building response to excavation-induced ground movements in glacial clay deposits is evaluated for the first time in the technical literature using OpenSees. Soil-structure interaction effects are parametrically studied, varying the proximity of the buildings to the excavation, the building aspect ratio, and stiffness and strength of beams and columns. Deep-seated movements caused beams to mobilize their flexural capacity and form plastic hinges. Curvature ductilities up to a maximum of five were computed for buildings designed for low LLD.

Soil-structure interaction (SSI) effects are relevant for the seismic analysis of tall buildings on shallow foundations since the dynamic behavior of structures is highly affected by the interaction between the superstructure and supporting soils. As part of earthquake-resistant designs of buildings, considering SSI effects in the analysis provides more realistic estimates of its performance during a seismic event, particularly when both the structure and soil undergo large demands that can compromise serviceability. Oversimplifications of structural or soil modeling in the analysis introduces variability and biases in the computed seismic response. The main goal of this dissertation is to investigate the interaction between archetype tall buildings and its supporting soils using numerical simulations. This dissertation develops the following objectives: i) to estimate the differences in the seismic performance of archetype tall building under different SSI approaches and compared to idealized fixed-base conditions; ii) to evaluate the seismic performance of tall building models by estimating intensity measures and engineering demand parameters (EDPs); iii) to assess the influence of SSI in the earthquake-induced losses of the structures; and iv) to evaluate the interaction of soil-structure systems using nonlinear constitutive models. To achieve these goals, numerical models of linear-elastic and nonlinear-inelastic tall buildings supported on mat foundation, combined with either fixed-base conditions at ground level or an explicit soil domain, are subjected to different earthquake time histories. The influence of SSI is quantified using structural and soil demands. It is concluded that the seismic response of tall buildings is largely affected by the inclusion of SSI effects when compared to conventional fixed-base structure models. SSI changed the computed seismic demands of the tall buildings in terms of inter-story drifts, peak horizontal accelerations, seismic-induced settlements, and losses compared to idealized buildings with fixed-base conditions. Nonlinear analyses show a significant decrease of EDPs when compared to those demands obtained with linear models. Energy distribution among both supporting soils and structure vary significantly as EDPs induce stresses and strains in the building beyond the onset of structural yielding. SSI impacts the structural and soil behavior and has practical implications in seismic resistant designs.

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Tätspont är en vanligt förekommande typ av stödkonstruktion och är i dagslägen den mest tids- och kostnadseffektiva på marknaden. Tätsponter består utav sammanfogade spontplankor i stål som ofta drivs med vibrationsutrustning. Ett antal studier har sedan början av 2000-talet undersökt vilka faktorer som påverkar drivbarheten av en planka. Men kunskapen kring förväntat produktionskapacitet, sett till ett helt projekt, är fortfarande bristfällig och det enda indikationerna för svår drivning som används idag är förekomsten av block och fast friktionsjord. Detta medför osäkerheter vid projektering som kan leda till förseningar och ökade kostnader. Målet med detta arbete är att möjliggöra för uppskattande av kapacitet vid spontdrivning i ett tidigt skede av projekt. Arbetet avser att besvara vilken kapacitet som kan förväntas vid spontdrivning och om det går att förutse denna utifrån de parametrar som kan utvärderas från en jord-bergsondering. För att uppfylla arbetets mål har nio spontprojekt utförda av Skanska Sverige AB studerats. Utifrån information från dagböcker och spontprotokoll, från dessa projekt, har kapaciteten för spontdrivning sammanställts. Sammanställd data för kapaciteten har sedan kopplats till utvärderat borrmotstånd från jord-bergsonderingar för att undersöka eventuellt samband. Det mest väsentliga resultatet av genomförd studie visar att inget samband mellan kapacitet och borrmotståndet vid jord-bergsondering tycks gå att påvisa. Denna avsaknad av samband kan användas som argument mellan parter för att påvisa att jord-bergsondering inte är lämplig för att beräkna förväntat kapacitet. Flera möjliga orsaker till resultatet finns och en är osäkerhet i information som inhämtats från projektens dagböcker. Ytterligare en förklaring kan vara att jord-bergsonderingen inte återspegla de parametrar i jorden som har störst betydelse vid drivning av spontplankor. / Sheet pile walls is a common type of retaining structure and is today the most time and cost effective solution on the market. Sheet pile walls consist of steel sheet piles which often are driven with vibratory equipment. A number of studies have since the beginning of the 21st century investigated which factors that influence the driveability of a sheet pile. But the knowledge about expected production capacity, for an entire project, is still limited and the only indication for difficulties when piling, that is used today, is the occurrence of blocks and firm friction soil. This leads to uncertainties in the planning phase of project which can lead to delays and increased costs. The goal of this work is to enable for estimation of the sheet piling capacity in an early state of projects. The work intends to answer what capacity can be expected when sheet piling and if it is possible to predict this from the parameters evaluated from the soil-rock sounding. To fulfill the goal of this work nine sheet piling project performed by Skanska Sverige AB have been studied. Based on information from diaries and sheet piling protocols, from these projects, the capacities of the sheet piling have been gathered. Gathered data for the capacity have then been connected to the penetration resistance evaluated from the soil-rock sounding to find a possible relationship. The most significant result of this study illustrates that no relationship between the capacity and penetration resistance from soil-rock sounding can be shown. This lack of relationship can be used as an argument between parties to show that soil-rock sounding is not suitable for calculating expected capacity. There are several possible reasons for this result and one is uncertainties in the information gathered from project diaries. Another explanation can be that soil-rock sounding does not reflect the parameters in the soil which has the greatest significance when sheet piling.