1,720,988 research outputs found
Numerical simulation of dynamic centrifuge tests on concrete faced rockfill dam
Get PDFThe design details of concrete faced rockfill dams (CFRDs) have depended extensively on empirical relations and experience. Empirical relations may become insufficient, however, as the height of the dam increases, or when geometric complexities are involved and coupled with complex loading conditions such as seismic loads. To make up for these limitations, numerical tools can give valuable insight into how CFRDs respond to both static and seismic loading conditions. This thesis utilizes numerical simulations using finite element method to study nonlinear dynamic responses of CFRDs.
The first part of the study reviews the current state of design details of CFRDs. The design details include properties of commonly used embankment zones, concrete faces, and plinths, including compaction methods of zones, particle sizes, thickness of layers during placement, slab and plinth dimensions, etc. In addition, the performance of some well-documented CFRDs are summarized.
The second part of the study evaluates the computed seismic response via numerical simulations representing prototype centrifuge experiments performed on a CFRD model. The effects of two factors on the computed response are investigated: (1) impact of un/reloading rules (hysteretic behavior), and (2) interface type between concrete face and rockfill (welded and friction contact) on the computed seismic response of the CFRDs. The numerical results are evaluated by comparing with measurements in terms of accelerations, bending moment increments of the concrete face, spectral accelerations and lateral deformations. The comparisons show that the proper representation of the hysteretic damping of the rockfill and the interface type have a key role in capturing the measured response of the dam. The analyses demonstrate the effectiveness of employed numerical tools in representing the seismic response of CFRD.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2018-09-27 without embargo termsThe student, Muhsin Acar, accepted the attached license on 2018-07-13 at 10:48.The student, Muhsin Acar, submitted this Thesis for approval on 2018-07-13 at 11:09.This Thesis was approved for publication on 2018-07-16 at 09:01.DSpace SAF Submission Ingestion Package generated from Vireo submission #12866 on 2018-09-27 at 10:48:27Made available in DSpace on 2018-09-27T16:17:52Z (GMT). No. of bitstreams: 2
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Previous issue date: 2018-07-1
Element-level behavior of dense coarse grained soils under multidirectional dynamic loading
Get PDFMade available in DSpace on 2019-02-08T18:39:52Z (GMT). No. of bitstreams: 3
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Previous issue date: 2018-12-03Embargo set by: Seth Robbins for item 109947
Lift date: 2021-02-08T18:40:00Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemIn 2011, the Tohoku earthquake generated a tsunami that led to the devastating Fukushima nuclear power plant (NPP) disaster in Japan. This accident prompted a global effort towards re-evaluation of the seismic safety criteria for NPPs. NPP structures, in absence of a rock stratum, may be founded on densified granular material to mitigate liquefaction related issues. Seismic deformations of these dense sands are generally considered to be within structure tolerable limits and are not incorporated in standard dynamic soil-structure interaction analyses of NPPs. However, research has shown that dense, compacted, or natural sands can experience considerable vibration-induced settlement when dry due to repeated loading cycles or reconsolidation settlement when saturated.
Present state-of-practice in seismic deformation analysis is primarily based on unidirectional tests, chiefly due to the lack of specialized devices that can apply complex multidirectional loading paths that occur during an earthquake. The limited studies that consider bi-directional shaking do not investigate volumetric strains in very dense sands or consider the effect of fines often present in natural sands. This work seeks to address these gaps in knowledge.
This dissertation describes and benchmarks the newly constructed Illinois multidirectional cyclic direct simple shear (I-mcDSS) device, which, for the first time, brings together the following capabilities: servo-hydraulic control than can apply stress- or strain-based monotonic, cyclic (e.g., sinusoidal, saw tooth, square), and high frequency broadband loads at the actual loading rate, improving over previous devices with pneumatic control; uni- and bidirectional loading; bender elements to measure shear wave velocity, to partly overcome small-strain (~10-2%) measurement limits of the device; a cell for applying different confinements (apart from K0), and back-pressure saturation; and a multi-directional load cell on the top of the specimen, to minimize the effect of compliance and friction of the device components on the load measurements. The effect of mechanical device compliance on the recorded response is explored with a comprehensice comparison to existing direct simple shear devices in literature. Recommendations are made for improving measurements at small shear strains in bidirectional devices.
A new unique database consisting of more than 650 drained and undrained multidirectional cyclic direct simple shear tests is developed to examine the effect of various material, state, and loading factors on volumetric response, i.e., drained volumetric strain and porewater pressure generation. The examined factors include loading frequency, duration, amplitude, path, multidirectionality, soil density, overburden, overconsolidation, prior shaking history, specimen preparation method, non-plastic and low-plasticity fines content, and gradation. The cyclic tests consisted of unidirectional, circular, figure-8 and broadband loading tests on medium dense to very dense clean, silty, and clayey sands at varying consolidation stresses. Different state factors that can be used for unifying clean sands and sands with fines were explored. It was observed that the coefficient of volume compressibility measured in Oedometer tests was most promising. Multidirectionality factors for drained and reconsolidation volumetric strain, and porewater pressure that can be readily used in engineering practice are evaluated with respect to each of the aforementioned factors and recommended.
Several demand and capacity parameters for estimating volumetric strain in medium to very dense sands with and without fines under multidirectional drained and undrained loading were examined including shear strain, cyclic shear stress, peak ground velocity, cumulative shear strain, dissipated energy (Ws), shear wave velocity, and coefficient of volume compressibility (mv). The relationship between (mv)(Ws) and volumetric strain appeared to be unique irrespective of soil type, soil density, number of loading directions, loading path, and loading duration. Thus, (mv)(Ws) is a promising parameter that potentially can be used to estimate volumetric strain for all soil types.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2020-12-01The student, Lopamudra Bhaumik, accepted the attached license on 2018-11-28 at 07:54.The student, Lopamudra Bhaumik, submitted this Dissertation for approval on 2018-11-28 at 08:31.This Dissertation was approved for publication on 2018-12-03 at 08:50.DSpace SAF Submission Ingestion Package generated from Vireo submission #13125 on 2019-02-08 at 11:39:14Embargo set by: Seth Robbins for item 109947
Lift date: 2021-02-08T18:42:23Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 109947
Lift date: 2021-02-08T18:43:54Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 109947
Lift date: 2021-02-08T18:44:50Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 109947 on 2021-02-09T10:15:34Z
Dynamic soil-structure interaction of underground structures adjacent to tall buildings
No full textSubmission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2023-12-01The student, Yuamar Basarah, accepted the attached license on 2021-12-01 at 06:09.The student, Yuamar Basarah, submitted this Dissertation for approval on 2021-12-01 at 06:11.This Dissertation was approved for publication on 2021-12-02 at 15:26.DSpace SAF Submission Ingestion Package generated from Vireo submission #17313 on 2022-04-06 at 17:17:18Made available in DSpace on 2022-04-29T21:46:06Z (GMT). No. of bitstreams: 3
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Previous issue date: 2021-12-02Embargo set by: Seth Robbins for item 123351
Lift date: 2024-04-29T21:46:25Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 123351
Lift date: 2024-04-29T21:47:53Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I OnlyUnderground structures are commonly constructed near existing or new tall buildings in dense urban areas. During earthquake shaking, tall buildings generate base shear that is carried by the building foundation and surrounding soils. This base shear may be transmitted to adjacent underground structures, increasing the seismic demand on the underground structure.
In the current practice of seismic design of underground structures, Engineers often rely on numerical models to evaluate the seismic response of a tunnel in dense urban area. However, these numerical models generally have not been validated against the field data because of the lack of experimental data. Therefore, the numerical model used in the analysis might be less reliable. Additionally, engineers often use simplified procedures in evaluating an underground structure under seismic loading that do not consider the soil-structure interaction among the superstructure, underground structure, and the surrounding soils in the system. These limitations in the seismic design of underground structures adjacent to tall buildings can lead to underestimation or overestimation of the seismic demands imposed on the underground structure. Therefore, the present study was conducted by combining the results from dynamic centrifuge tests and numerical simulations to evaluate the impact of highly idealized adjacent tall buildings on the seismic response of underground structures.
The study was started by developing calibrated numerical models by comparing the numerical simulations with the corresponding measurements from the centrifuge tests. The numerical model can reproduce the seismic behavior observed in the centrifuge including the additional loading demands imposed by adjacent building on underground structures. A large-scale parametric study using three-dimensional (3-D) nonlinear finite element analysis with more realistic soil-structure-underground structure (SSUS) representation was then performed to evaluate the impact of variability in the SSUS system on the seismic response of underground structures. The effects of different building heights, building foundations, underground structure configurations, and soil profiles are evaluated using a suite of ground motions. These configurations represent the range of conditions that are likely to be present in dense urban environments. The results show that (a) as the adjacent building became taller and hence the base shear increased, greater dynamic earth pressures were transmitted to the underground structure, (b) the dynamic earth pressures were reduced with increased building-to-underground-structure distance, and (c) the racking displacements of underground structures were strongly dependent on building foundation and underground structure configurations such as basement depth, pile length, and the depth of the underground structure. For design purposes, these interactions need to be considered by modeling a realistic building and underground structure representation in a SSUS system to evaluate the added demands that a given building will impose on underground structures including cut-and-cover boxes and bored tunnels
Integrated Tools for Predicting, Monitoring and Controlling Ground Movements due to Excavations
No full textOn the development of acoustic communication systems through unconventional media
Get PDFSubmission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2023-12-01The student, Sijung Yang, accepted the attached license on 2021-11-29 at 12:51.The student, Sijung Yang, submitted this Dissertation for approval on 2021-11-29 at 13:11.This Dissertation was approved for publication on 2021-11-30 at 13:09.DSpace SAF Submission Ingestion Package generated from Vireo submission #17287 on 2022-04-29 at 16:10:05Made available in DSpace on 2022-04-29T21:58:29Z (GMT). No. of bitstreams: 2
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Previous issue date: 2021-11-30Embargo set by: Seth Robbins for item 123449
Lift date: 2024-04-29T21:58:46Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemAuthor requested closed access (OA after 2yrs) in Vireo ETD systemLimited"One challenge of modern ""internet-of-things"" networks occurs because many of their installments are surrounded by unconventional media for communication like soils and water, where traditional radio-frequency (RF) signals cannot propagate for communication well. In some instances, acoustic communication can provide an alternative to RF signals in such environments, providing longer communication distances with less power consumption. In this thesis, we propose several approaches for the development of acoustic communication systems through unconventional media for a variety of potential applications. First, we focus on an ad-hoc implementation of an acoustic communication system for through-soil communication. Specifically, we propose a miniaturized through-soil acoustic modem, which can be implemented for practical underground applications including infrastructural monitoring, enabling reliable data transmission for tens of meter distances. The development of acoustic communication systems requires considerable field data to test and evaluate their performance in realistic environments, which can be extremely costly. In the second part of this thesis, we propose a practical method based on dithering techniques to enhance and maximize the reusability of such valuable field data when developing acoustic communication systems. In the last part of this thesis, we focus on algorithms for Doppler compensation in acoustic communications, one of the most common challenges in a variety of acoustic communications. In particular, we propose what we call hyperdimensional dynamic time warping to jointly estimate time varying Doppler and information symbols in multipath channels with non-uniform Doppler.
Nonlinear site amplification functions for Central and Eastern North America
Get PDFSite amplification functions are used to modify ground motions from a reference bedrock condition to a surface condition based on the geologic features of the site of interest. Site amplification has been extensively studied and evaluated empirically for seismic regions such as the Western United States where there are abundant ground motion recordings for many sites and earthquake events. In regions of relatively lower or infrequent seismicity, such as Central and Eastern North America (CENA), the lack of ground motion recordings and seismic site properties severely limits the empirical characterization of site amplification. This research uses site response simulations to develop site amplification functions for CENA.
The first part of this study is the development of 1,747,278 1-D linear elastic, equivalent linear, and nonlinear site response analyses. Simulations are designed to capture the variability in site conditions in CENA and the uncertainty in soil properties at individual sites. Site profiles are developed for 1,747,278 site response analyses, 582,426 each of linear elastic, equivalent linear and nonlinear 1-D analyses for 70,650 unique site profiles. The database of simulations is the largest of its kind. This study describes the process for generating VS profiles, soil and weathered rock material properties, and ground motions to represent the variability and uncertainty of site conditions in CENA.
The second part of this study is the modeling of the site response simulation data with linear and nonlinear site amplification functions for the response spectrum (RS) and Fourier amplitude spectrum (FAS) and a correction factor to convert site amplification from a 3000 m/s CENA hard rock condition to a 760 m/s condition. The modular RS amplification model includes terms for time averaged shear wave velocity in the top 30 m of a site (VS30), site natural period, soil depth, and site nonlinearity which can be coupled with empirically-developed linear empirical amplification models. Including site natural period into the amplification function is shown to greatly improve estimates of site response over models dependent only on VS30. The FAS site amplification model is the first model developed from simulations, and the first to include nonlinear amplification.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2019-05-01The student, Joseph Harmon, accepted the attached license on 2017-04-17 at 18:06.The student, Joseph Harmon, submitted this Dissertation for approval on 2017-04-17 at 18:18.This Dissertation was approved for publication on 2017-04-18 at 11:54.DSpace SAF Submission Ingestion Package generated from Vireo submission #10827 on 2017-08-10 at 15:05:54Made available in DSpace on 2017-08-10T20:33:01Z (GMT). No. of bitstreams: 3
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Previous issue date: 2017-04-18Embargo set by: Colleen Fallaw for item 102775
Lift date: 2019-08-10T21:27:21Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 102775 on 2019-08-11T09:15:32Z
Analysis of deep excavations in clay
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1992.Includes bibliographical references.by Youssef M.A. Hashash.Ph.D
Liquefaction probability mapping in greater Boston
No full textThesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1988.Includes bibliographical references.by Youssef M.A. Hashash.M.S
Learning of Soil Behavior from Measured Response of a Full Scale Test Wall in Sandy Soil
Get PDFIn urban deep excavations, instruments are placed to monitor deformations and to control construction and reduce the risk of excessive and potentially damaging deformations. The second author has introduced a new inverse analysis approach that utilizes measured excavation performance to extract the underlying soil behavior. The extracted soil behavior can be used in predicting the behavior of similar excavations. This paper provides a first implementation of this inverse analysis approach to a well instrumented full scale test wall in a sand deposit. A wall consisting of soldier beams with wood lagging was instrumented to study anchored (one and two level tie backs) wall behavior in sandy soil deposits at Texas A&M. Strain gauges, load cells, inclinometers, and settlement points were placed in two sections of the excavation to monitor the excavation behavior. The measured excavation response for the section with two-level tie-backs is used to extract the constitutive model through the inverse analyses approach. The extracted constitutive model is used in predicting the underlying soil behavior for the section with one tie-back level. The predicted behavior of the excavation and its agreement with measurements at the site are discussed in detail
Train-track discrete-element-method model for simulating ballasted track dynamics: coupling and validation
No full textSubmission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo termsThe student, Zhongyi Liu, accepted the attached license on 2024-07-08 at 17:27.The student, Zhongyi Liu, submitted this Dissertation for approval on 2024-07-08 at 17:41.This Dissertation was approved for publication on 2024-07-09 at 14:46.DSpace SAF Submission Ingestion Package generated from Vireo submission #20990 on 2025-02-04 at 21:04:30Railroad ballasted track is essential infrastructure for most railway mainlines supporting both passenger and freight trains. As the demands for growing traffic volumes and faster trains increase, understanding the dynamic interactions of train and track structures become critical to ensure railroad safety, sustainability and riding comfort. Measuring track dynamic behavior in the field while pausing normal traffic causes enormous economic costs. Furthermore, because of the particulate nature of the ballast layer, it is often challenging to track individual ballast particle movements in the field. Numerical modeling, as an economic solution, is commonly applied to simulate the structural dynamics of ballasted track. Among all widely used numerical models, train-track (TT) or train-track-bridge (TTB) models, also known as vehicle track interaction models, integrate major structural components together, whereas discrete-element-method (DEM) model when used for ballast layer modeling demonstrates a significant strength of replicating realistic ballast particle size and shape and tracking all ballast particle movements. In the TT models, ballast is simplified as one-degree-of-freedom mass blocks connected with a spring-damper in vertical direction, and the simplification neglects particle size and shape, as well as horizontal shear interactions within ballast layer. On the other hand, train and rail are difficult to be directly modeled within the DEM framework, so the rail seat loads applied on DEM crossties need to be assumed before simulations. To tackle the current limitations of the two models and combine their strengths, this doctoral research study develops a coupled train-track discrete-element-method (TT-DEM) model to realistically simulate the dynamic behavior of ballasted track in the field. This PhD dissertation presents the development, validation, and applications of coupled TT-DEM models, consisting of a single-crosstie DEM model and a 30-crosstie TT model. The coupled models were developed to simulate track responses at an open-track location. An iterative coupling method, achieving force equilibrium iteratively at each time step, was employed for the model coupling. After validation with field measurements of force, displacement and acceleration data, the TT-DEM model was applied to study the effect of crosstie spacings. Subsequently, a TTB-DEM model incorporating a single-crosstie DEM model was also established to simulate hanging crossties at bridge approaches. To enhance the coupling efficiency, a more robust proportional-integral-derivative (PID) -based coupling method was introduced to avoid the iterations during coupling. Similarly, the TTB-DEM model was validated with crosstie displacement and rail shear force field data. The two coupled models are limited to small-scale applications using only single-crosstie DEM models. To make large-scale simulations feasible, the PID-based coupling approach was extended to multi-crosstie coupling, and software optimizations were implemented for cross-software communications and data output. As a result, a TT-DEM model comprising a 30-crosstie DEM model was constructed and validated with field data. The large-scale TT-DEM model greatly enriched the predictions of ballast particle movements and the dynamic responses by eliminating the vertical boundaries present in the crib area of a single-crosstie DEM model. Furthermore, the effect of ballast degradation was investigated using single-crosstie DEM models and the newly developed large-scale TT-DEM models. The particle size and shape before and after degradation were replicated in clean and degraded ballast models, respectively. Crosstie-level and particle-level responses due to train passes were thoroughly investigated and compared. This PhD dissertation advances the field of ballasted track dynamics modeling through development and validation of an innovative modeling approach. By combining efficient coupling methods and software optimizations, this study enables large-scale simulations that were previously unattainable. The coupled TT-DEM model addressed limitations in the previous numerical models to provide a realistic digital laboratory for conducting a wide range of future numerical experiments, offering invaluable insights into ballasted track dynamics
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