Seismic Performance of Steel Helical Piles

Recent earthquakes have highlighted the need for safe and efficient construction of earthquake resilient structures. Meanwhile, helical piles are gaining popularity as a foundation for new structures and retrofitting solution for existing deficient foundations due to their immense advantages over conventional driven pile alternatives. In addition, helical pile foundations performed well in recent earthquakes, proving they can be a suitable foundation option in seismic regions. The objective of this thesis is to evaluate the seismic performance of helical piles by conducting full-scale shaking table tests and nonlinear three-dimensional numerical modeling using the computer program ABAQUS/Standard. The experimental setup involved installing ten steel piles with different configurations and pile head masses in dry sand enclosed in a laminar shear box mounted on the NEES/UCSD Large High Performance Outdoor Shake Table. The loading scheme consisted of white noise and two earthquake time histories with varying intensity and frequency content. The performance of different moment curve fitting techniques used for reduction of shake table experimental data are compared. The experimental results are presented in terms of natural frequency and response of the test piles. The effects of the loading intensity and frequency and the pile’s geometrical configuration and installation method were evaluated. The dynamic numerical model constructed accounted properly for the test boundary conditions, employing tied vertical boundaries. In addition, the nonlinear behavior of the soil during the strong ground motion was simulated by considering a strain-dependent shear modulus and applying Masing’s loading-unloading rules by the overlay method to account for the soil non linearity more realistically. The numerical model was verified employing the full-scale experimental results, then was used to conduct a limited parametric study that investigated the effect of pile stiffness and the location of helix on its lateral response. The experimental results show that the natural frequency of the driven pile was slightly higher than that of the helical piles. However, the response of the helical pile was close to that of the driven pile, which illustrates the ability of helical piles to perform as good as conventional piles under seismic loading

Large-scale Finite Element Simulation of Seismic Soil-Pile foundation-Structure Interaction

Ph.DDOCTOR OF PHILOSOPH

Performance of Inelastic Structures on Mitigated and Unmitigated Liquefiable Soils: Evaluation of Numerical Simulations with Centrifuge Tests

A series of dynamic centrifuge experiments involving soil-foundation-mitigation-structure (SFMS) interaction on liquefiable soils are used to evaluate the ability of state-of-the-art numerical modeling in reliably predicting system performance (e.g., in terms of foundation settlement, rotation, roof accelerations, and column strains). This research comprises of two major components: (1) calibration and validation of two soil constitutive models with a series of fully drained and undrained, monotonic and cyclic, triaxial tests as well as a free-field centrifuge test on a layered, liquefiable soil deposit (without a building or a mitigation technique); and (2) numerical simulation of centrifuge tests that include multi-degree-of-freedom, shallow-founded, inelastic structures on mitigated and unmitigated liquefiable soil profiles, investigating the strengths and shortcomings of the available continuum numerical tools in capturing the key engineering demand parameters of interest.Solid-fluid, fully-coupled, nonlinear, effective stress, 3D, finite element analyses are performed in parallel OpenSEES finite element platform with two different soil constitutive models. Overall, the numerical predictions agreed well with the experimental measurements in terms of acceleration, pore pressure, and settlement under structure in the presence of a relatively thin liquefiable layer or a mitigation strategy (when the extent of soil softening and volumetric strains due to sedimentation was reduced). However, these numerical simulations (and a continuum framework in general) could not capture volumetric strains due to sedimentation. This shortcoming became critical in thicker, unmitigated liquefiable layers and in the far-field, leading to a notable underestimation of total settlements. The cumulative foundation rotation or tilt was also generally underestimated numerically, regardless of the constitutive model. Improvements are needed to better capture numerically the accumulation of localized shear and volumetric strains below the foundation’s edges. The dynamic response of the soil-foundation-structure system and the required analysis time were highly sensitive to the choice of small-strain soil damping, soil constitutive model, and element type. They were also sensitive to the characteristics of the soil-foundation interface, but to a lesser extent. The results presented in this dissertation aim to guide future numerical modelers in simulating the seismic response of highly nonlinear SFMS systems and in better understanding the modeling sensitivities and uncertainties

Coastal Geohazard and Offshore Geotechnics

With rapid developments being made in the exploration of marine resources, coastal geohazard and offshore geotechnics have attracted a great deal of attention from coastal geotechnical engineers, with significant progress being made in recent years. Due to the complicated nature of marine environmnets, there are numerous natural marine geohazard preset throughout the world’s marine areas, e.g., the South China Sea. In addition, damage to offshore infrastructure (e.g., monopiles, bridge piers, etc.) and their supporting installations (pipelines, power transmission cables, etc.) has occurred in the last decades. A better understanding of the fundamental mechanisms and soil behavior of the seabed in marine environments will help engineers in the design and planning processes of coastal geotechnical engineering projects. The purpose of this book is to present the recent advances made in the field of coastal geohazards and offshore geotechnics. The book will provide researchers with information reagrding the recent developments in the field, and possible future developments. The book is composed of eighteen papers, covering three main themes: (1) the mechanisms of fluid–seabed interactions and the instability associated with seabeds when they are under dynamic loading (papers 1–5); (2) evaluation of the stability of marine infrastructure, including pipelines (papers 6–8), piled foundation and bridge piers (papers 9–12), submarine tunnels (paper 13), and other supported foundations (paper 14); and (3) coastal geohazards, including submarine landslides and slope stability (papers 15–16) and other geohazard issues (papers 17–18). The editors hope that this book will functoin as a guide for researchers, scientists, and scholars, as well as practitioners of coastal and offshore engineering

Vibration induced damage due to construction work – Effect of vibrations on slope stability

A landslide-triggered tsunami caused extensive material damage at Statland, Norway in 2014. Other landslides in Sweden and US have also been triggered by man-made vibrations. To understand better how vibrations from vibratory compaction affect slope stability a numerical tool has been extended to account for realistic non-linear soil behaviour. The tool is validated by comparison field experiments of vibratory compaction. The nonlinear analysis is believed to have captured the essential behaviour of the vibratory compaction and the response of the slope. The peak response at the frequency is close to the one stated by the operator of the vibratory roller and the manufacturer's data sheet. The numerical analysis and evaluations strongly indicate vibratory compaction can have contributed to triggering the slide at Statland. To perform compaction in the vicinity of slopes with low stability near the shoreline with vibration susceptible soils we suggest: • Using lighter equipment and/or higher loading frequencies or performing compaction without vibration. Avoiding excessive jumping of the vibratory roller drum is imperative. • Applying thinner layers and more time between compaction passes. Allowing for more time between placing of layers reduces the number of load cycle sensed by the soil and allows for drainage of potential built up pore pressures. • Monitor slope horizontal and vertical displacements at some critical points. • Monitor pore pressures at critical points if possible. Further work with and possible extension of the numerical tool is needed to capture better, theNorges Forskningsråd The Research Council of Norwa

Lattice Element Method and its application to Multiphysics

In this thesis, a Lattice element modelling method is developed and is applied to model the loose and cemented, natural and artificial, granular matters subject to thermo-hydro-mechanical coupled loading conditions. In lattice element method, the lattice nodes which can be considered as the centres of the unit cells, are connected by cohesive links, such as spring beams that can carry normal and shear forces, bending and torsion moment. For the heat transfer due to conduction, the cohesive links are also used to carry heat as 1D pipes, and the physical properties of these rods are computed based on the Hertz contact model. The hydro part is included with the pore network modelling scheme. The voids are inscribed with the pore nodes and connected with throats, and then the meso level flow equation is solved. The Euler-Bernoulli and Timoshenko beams are chosen as the cohesive links or the lattice elements, while the latter should be used when beam elements are short and deep. This property becomes interesting in modelling auxetic materials. The model is applied to study benchmarks in geotechnical engineering. For heat transfer in the dry and full range of saturation, and fractures in the cemented granular media.How through porous media failure behaviours of rocks at high temperature and pressure and granular composites subjected to coupled Thermo hydro Mechanical loads. The model is further extended to capture the wave motion in the heterogeneous granular matter, and a few case studies for the wavefield modification with existing cracks are presented. The developed method is capable of capturing the complex interaction of crack wave interaction with relative ease and at a substantially less computational cost

Cone Penetration Testing 2022

This volume contains the proceedings of the 5th International Symposium on Cone Penetration Testing (CPT’22), held in Bologna, Italy, 8-10 June 2022. More than 500 authors - academics, researchers, practitioners and manufacturers – contributed to the peer-reviewed papers included in this book, which includes three keynote lectures, four invited lectures and 169 technical papers. The contributions provide a full picture of the current knowledge and major trends in CPT research and development, with respect to innovations in instrumentation, latest advances in data interpretation, and emerging fields of CPT application. The paper topics encompass three well-established topic categories typically addressed in CPT events: - Equipment and Procedures - Data Interpretation - Applications. Emphasis is placed on the use of statistical approaches and innovative numerical strategies for CPT data interpretation, liquefaction studies, application of CPT to offshore engineering, comparative studies between CPT and other in-situ tests. Cone Penetration Testing 2022 contains a wealth of information that could be useful for researchers, practitioners and all those working in the broad and dynamic field of cone penetration testing

New Advances in Marine Engineering Geology

The ocean is the cradle of life and is rich in natural resources. With the worldwide boom in exploration and application of ocean resources, a dramatically increasing amount of coastal engineering and offshore engineering facilities have been constructed in the last few decades. The rapid development of human economic activities and the global climate change have significant impacts on the marine environment, resulting in frequent geological disasters. Under this circumstance, there is an urgent demand for a platform for scientists and engineers to share their state-of-art research outcomes in the field of Marine Engineering Geology. This book is a collection of a series of articles from the 2nd International Symposium of Marine Engineering Geology (ISMEG 2019), presenting some of the recent efforts made towards marine engineering geology and geotechnics, including theoretical advances, laboratory and field testing, design methods, and the potential for further development of these disciplines