Observations from recent earthquakes show that all types of retaining structures with non-liquefiable backfills perform very well and there is limited evidence of damage or failures related to seismic earth pressures. Even retaining structures designed only for static loading have performed well during strong ground motions suggesting that special seismic design provisions may not be required in some cases. The objective of this study was to characterize the seismic interaction of backfill-wall systems using experimental and numerical models, with emphasis on cohesive soils, and to review the basic assumptions of current design methods. In the experimental phase of this research, two sets of centrifuge models were conducted at the Center for Geotechnical modeling in UC Davis. The first experiment consisted of a basement wall and a freestanding cantilever wall with level backfill, while the second one consists of a cantilever wall with sloping backfill. The soil used in the experiments was a compacted low plasticity clay. Numerical simulations were performed using FLAC2-D code, featuring non-linear constitutive relationships for the soil and interface elements. The non-linear hysteretic constitutive UBCHYST was used to model the level ground experiment and Mohr-Coulomb with hysteretic damping was used to model the sloping backfill experiment. The simulations captured the most important aspects of the seismic responses, including the ground motion propagation and the dynamic soil-structure interaction. Special attention was given to the treatment of boundary conditions and the selection of the model parameters. The results from the experimental and numerical analysis provide information to guide the designers in selecting seismic design loads on retaining structures with cohesive backfills. The experimental results show that the static and seismic earth pressures increase linearly with depth and that the resultant acts at 0.35H-0.4H, as opposed to 0.5-0.6H assumed in current engineering practice. In addition, the observed seismic loads are a function of the ground motion intensity, the wall type and backfill geometry. In general, the total seismic load can be expressed using Seed and Whitman's (1970) notation as: Pae=Pa+dPae, where Pa is the static load and dPae is the dynamic load increment. While the static load is a function of the backfill strength, previous stress history and compaction method, the dynamic load increment is a function of the free field PGA, the wall displacements, and is relatively independent of cohesion. In level ground, the dynamic load coefficient can be expressed as dKae=1/2gH2(0.68PGAff/g) for basement walls and dKae=1/2gH2(0.42PGAff/g) for cantilever walls; these results are consistent with similar experiments performed in cohesionless soils (Mikola & Sitar, 2013. In the sloping ground experiment the seismic coefficient came out to dKae=1/2gH2(0.7PGAff/g), which is consistent with Okabe's (1926) Coulomb wedge analysis of the problem. However, that slope was stable under gravity loads even without the presence of the retaining wall (FS=1.4). Measured slope displacements were very small and in reasonable good agreement with the predictions made with the Bray and Travasarou (2007) semi-empirical method. The experimental data was not sufficient to determine accurately the point of action of the seismic loads. However, the numerical simulations and Okabe's (1926) limit state theory suggest that the resultant acts between 0.37H-0.40H for typical values of cohesion. While the resultant acts at a point higher than 0.33H with increasing cohesion, the total seismic moment is reduced due to the significant reduction in the total load Pae, particularly for large ground accelerations. The results also show that typical retaining walls designed with a static factor of safety of 1.5 have enough strength capacity to resist ground accelerations up to 0.4g. This observation is consistent with the field performance of retaining walls as documented by Clough and Fragaszy (1977) and the experimental results by al Atik and Sitar (2010) and Geraili and Sitar (2013). The evaluation of earth pressures at the wall-backfill interface continues to be a technical challenge. Identified sources of error in the present study include the behavior of pressure sensors, the geometric and mass asymmetry of the model and the dynamic interaction between the model and the container. While these centrifuge experiments reproduced the basic response of prototype models, ultimately, instrumented full-scale structures are most essential to fully characterize the response of tall walls and deep basements with varieties of backfill.

Earth retaining structures have historically performed well under seismic loading, including cases in which the structures were designed for less intense ground motion or only considering static loading. The few reported failures are often attributable to waterfront structures retaining saturated backfill where the main factor was liquefaction. The remaining failures are rare and generally involve more complex conditions, such as sloping backfill, or poor construction or design. These observations suggest that seismic design provisions for engineered retaining structures may be too stringent, and in some cases may not be necessary. The objective of this study was to extend previous efforts to understand the seismic interaction of backfill-wall systems using experimental and numerical modeling, with an emphasis on deep, stiff basement walls in cohesionless soil and the current design methods thereof. The experimental phase of the study consisted of a dynamic centrifuge model of a deep, stiff basement structure with a dry, level, dense sand backfill. The results obtained in the centrifuge experiment were first used to develop and calibrate a two-dimensional, finite difference model using FLAC2-D. A non-linear, hysteretic constitutive model was used to model the cyclic behavior of the soil and linear elastic beam elements were used to model the structure. The numerical simulations captured the most important aspects of the centrifuge experiment, specifically the inertial response and dynamic soil-structure interaction. Special attention was given to the selection of model parameters, the boundary conditions, and the initialization process. The second part of the numerical modeling effort concentrated on analyzing the response of typical prototype basement structures of varying depth using the calibrated soil properties from the first phase of numerical modeling. As would be expected, the results from the experimental and numerical analyses show that the observed seismic load increments are a function of the ground motion, wall type and the depth of embedment. The dynamic earth pressure increment distribution for deep basement structures is highly non-linear in contrast with shorter retaining structures (

Observations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep excavation walls in earthquakes are rare even if the structures were not designed for the actual magnitude of the earthquake loading. Failures of retaining structures are most commonly confined to waterfront structures retaining saturated backfill with liquefaction being the critical factor in the failures. Failures of other types of retaining structures are relatively rare and usually involve a more complex set of conditions, such as sloping ground either above or below the retaining structure, or both. While some failures have been observed, there is no evidence of a systemic problem with traditional static retaining wall design even under quite severe loading conditions. No significant damage or failures of retaining structures occurred in the recent earthquakes such as Wenchuan earthquake in China (200) and, or subduction zone generated earthquakes in Chile (2010) and Japan (2011). Therefore, this experimental and analytical study was undertaken to develop a better understanding of the distribution and magnitude of seismic earth pressures on cantilever retaining structures. The experimental component of the study consists of two sets of dynamic centrifuge model experiments. In the first experiment two model structures representing basement type setting were used, while in the second test a U-shaped channel with cantilever sides and a simple cantilever wall were studied. All of these structures were chosen to be representative of typical designs. Dry medium-dense sand with relative density on the order of from 75% to 80% was used as backfill. Results obtained from the centrifuge experiments were subsequently used to develop and calibrate a two-dimensional, nonlinear, finite difference model built on the FLAC platform. The centrifuge data consistently shows that for the height of structures considered herein, i.e. in the range of 20-30 ft, the maximum dynamic earth pressure increases with depth and can be reasonably approximated by a triangular distribution This suggests that the point of application of the resultant force of the dynamic earth pressure increment is approximately 1/3H above the base of the wall as opposed to 0.5-0.6 H recommended by most current design procedures. In general, the magnitude of the observed seismic earth pressures depends on the magnitude and intensity of shaking, the density of the backfill soil, and the type of the retaining structures. The computed values of seismic earth pressure coefficient (delta Kae) back calculated from the centrifuge data at the time of maximum dynamic wall moment suggest that for free standing cantilever retaining structures seismic earth pressures can be neglected at accelerations below 0.4 g. While similar conclusions and recommendations were made by Seed and Whitman (1970), their approach assumed that a wall designed to a reasonable static factor of safety should be able to resist seismic loads up 0.3 g. In the present study, experimental data suggest that seismic loads up to 0.4 g could be resisted by cantilever walls designed to an adequate factor of safety. This observation is consistent with the observations and analyses performed by Clough and Fragaszy (1977) and Fragaszy and Clough (1980) and Al-Atik and Sitar (2010) who concluded that conventionally designed cantilever walls with granular backfill could be reasonably expected to resist seismic loads at accelerations up to 0.4 g. Finally, numerical models using FLAC finite difference code were quite successful and able to produce a reasonably good agreement with the results of the centrifuge experiments. However, while the finite difference models were able to capture the main aspects of the seismic response observed in the centrifuge experiments, the results of the analyses were highly sensitive to the selection of soil and interface parameters. Therefore, numerical models used for future designs should be carefully calibrated against experimental data in order to provide reliable results.

Structures placed on hillsides often present a number of challenges and a limited number of economical choices for site design. An option sometimes employed is to use the building frame as a retaining element, comprising a Rigidly Framed Earth Retaining Structure (RFERS). The relationship between temperature and earth pressure acting on RFERS, is explored in this monograph through a 4.5 year monitoring program of a heavily instrumented in service structure. The data indicated that the coefficient of earth pressure behind the monitored RFERS had a strong linear correlation with temperature. The study also revealed that thermal cycles, rather than lateral earth pressure, were the cause of failure in many structural elements. The book demonstrates that depending on the relative stiffness of the retained soil mass and that of the structural frame, the developed lateral earth pressure, during thermal expansion, can reach magnitudes several times larger than those determined using classical earth pressure theories. Additionally, a nearly perpetual lateral displacement away from the retained soil mass may occur at the free end of the RFERS leading to unacceptable serviceability problems. These results suggest that reinforced concrete structures designed for the flexural stresses imposed by the backfill soil will be inadequately reinforced to resist stresses produced during the expansion cycles. Parametric studies of single and multi-story RFERS with varying geometries and properties are also presented to investigate the effects of structural stiffness on the displacement of RFERS and the lateral earth pressure developed in the soil mass. These studies can aid the reader in selecting appropriate values of lateral earth pressure for the design of RFERS. Finally, simplified closed form equations that can be used to predict the lateral drift of RFERS are presented. KEY WORDS: Earth Pressure; Soil-Structure Interaction; Mechanics; Failure; Distress; Temperature; Thermal Effects; Concrete; Coefficient of Thermal Expansion; Segmental Bridges; Jointless Bridges; Integral Bridges; Geotechnical Instrumentation; Finite Element Modeling; FEM; Numerical Modeling.

This report explores analytical and design methods for the seismic design of retaining walls, buried structures, slopes, and embankments. The Final Report is organized into two volumes. NCHRP Report 611 is Volume 1 of this study. Volume 2, which is only available online, presents the proposed specifications, commentaries, and example problems for the retaining walls, slopes and embankments, and buried structures.

In this investigation, seismic response of retaining walls constructed with cohesive and cohesionless backfill materials was studied. Fully dynamic analysis based on finite difference method was used to evaluate the performance of retaining walls during the earthquake. The analysis response was verified by the experimental study conducted on a retaining wall system with cohesive backfill material in the literature. The effects of cohesion and free-field peak ground acceleration (PGA) on seismic earth thrust, the point of action of earth thrust, and maximum wall moment during the earthquake were compared with analytical and experimental solutions. The numerical results were compared with various analytical solutions. The motion characteristics of the retaining wall during the earthquake were also considered. The relative displacement of the walls with various backfill cohesions, under different ground motions, and free-field PGAs were investigated. Current analytical and empirical correlations developed based on Newmark sliding block method for estimating retaining wall movement during earthquakes were compared with the numerical approach. Consequently, fragility analyses were conducted to determine the probability of damage to the retaining walls. To evaluate the fragility of the studied models, specific failure criterion was chosen for retaining walls based on the suggested methods in practice. Using numerical approaches, the effects of soil-wall interaction and wall rigidity on the seismic response of retaining walls were also evaluated in earthquake conditions for both cohesive and cohesionless backfill materials. According to the findings, practical correlations were presented for conducting the seismic design of retaining walls.

Since the damage caused to retaining walls during past earthquakes are common, the behavior of such earth retaining structures has attracted the attention of researchers and practicing engineers. In this thesis, dynamic response of retaining walls is being studied using numerical method. The numerical analysis was undertaken using FLAC3D (Fast Lagrangian Analysis of Continua) along with FISH functions, which use a programming language embedded within FLAC3D. The FLAC family of programs have found wide use and acceptance among the geotechnical community because of its capability of modeling important aspects such as stress-dependent constitutive model, hysteretic nature non-linear stress-strain behavior and soil damping under dynamic loading, separation and slippage of soil at interface between soil an structure (i.e., interface elements), and incorporation of quiet lateral boundaries. More importantly, the FISH functions extend FLAC3D's usefulness since geotechnical applications often require reset and modification of stresses, strength and modulus properties during the execution of the program. Such requirements are needed to model failure, reset of initial condition prior to dynamic loading etc. As a baseline case, modeling of active and passive earth pressure were conducted and computed results were compared with those available from classical methods. The active and passive cases were modeled using a rigid wall under displacement control. The numerical model predictions for the passive and active pressures for various soil-wall friction angles were in good agreement with the available classical solutions. Retaining structures considered include a fixed end cantilever wall, flexible diaphragm wall and a gravity wall supporting a dry medium dense cohesionless soil. The fixed end cantilever wall allows for a closer inspection of the mechanism of interaction between the wall and backfill. The static analyses consisted of the stage-by-stage incremental construction of the wall using elastic-plastic backfill material modeled using stress-dependent incrementally elastic stiffness properties. Dynamic analysis followed the static analyses where the soil was modeled using non-linear stress-strain relationship along the Masing criteria for unloading and reloading. Particular attention has been devoted to physical modeling issues, use of appropriate soil constitutive relations and selection of ground excitations. Under sinusoidal motion, the dynamic characteristic behavior of the fixed cantilever wall and the gravity wall were clearly captured. The dynamic displacement of the fixed cantilever wall was found to always be outward from the backfill. The bending moments increased steadily. In the case of flexible walls, the residual bending moments at the end of excitation were substantially higher than the initial values. The effect of the flexibility of the wall and the effect of the integration of the Finn model for permanent volumetric strain in the constitutive model on the dynamic behavior of the cantilever wall were investigated. For the gravity wall, the movement of the wall was progressively away from the backfill and the gravity wall ends up with a permanent outward lateral movement and tilt. The results obtained with FLAC3D in terms of displacements and bending moments (in the case of flexible wall) were reported for different levels of excitation from four different past earthquakes of magnitude between 6.5 and 7.

This book gathers selected proceedings of the annual conference of the Indian Geotechnical Society, and covers various aspects of soil dynamics and earthquake geotechnical engineering. The book includes a wide range of studies on seismic response of dams, foundation-soil systems, natural and man-made slopes, reinforced-earth walls, base isolation systems and so on, especially focusing on the soil dynamics and case studies from the Indian subcontinent. The book also includes chapters addressing related issues such as landslide risk assessments, liquefaction mitigation, dynamic analysis of mechanized tunneling, and advanced seismic soil-structure-interaction analysis. Given its breadth of coverage, the book offers a useful guide for researchers and practicing civil engineers alike.

This book is a collection of papers presented at the International Workshop on Geotechnical Natural Hazards held July 12–15, 2014, in Kitakyushu, Japan. The workshop was the sixth in the series of Japan–Taiwan Joint Workshops on Geotechnical Hazards from Large Earthquakes and Heavy Rainfalls, held under the auspices of the Asian Technical Committee No. 3 on Geotechnology for Natural Hazards of the International Society for Soil Mechanics and Geotechnical Engineering. It was co-organized by the Japanese Geotechnical Society and the Taiwanese Geotechnical Society. The contents of this book focus on geotechnical and natural hazard-related issues in Asia such as earthquakes, tsunami, rainfall-induced debris flows, slope failures, and landslides. The book contains the latest information and mitigation technology on earthquake- and rainfall-induced geotechnical natural hazards. By dissemination of the latest state-of-the-art research in the area, the information contained in this book will help researchers, designers, consultants, government officials, and academicians involved in the mitigation of natural hazards. The findings and other information provided here is expected to contribute toward the development of a new chapter in disaster prevention and mitigation of geotechnical structures.

Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions contains invited, keynote and theme lectures and regular papers presented at the 7th International Conference on Earthquake Geotechnical Engineering (Rome, Italy, 17-20 June 2019. The contributions deal with recent developments and advancements as well as case histories, field monitoring, experimental characterization, physical and analytical modelling, and applications related to the variety of environmental phenomena induced by earthquakes in soils and their effects on engineered systems interacting with them. The book is divided in the sections below: Invited papers Keynote papers Theme lectures Special Session on Large Scale Testing Special Session on Liquefact Projects Special Session on Lessons learned from recent earthquakes Special Session on the Central Italy earthquake Regular papers Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions provides a significant up-to-date collection of recent experiences and developments, and aims at engineers, geologists and seismologists, consultants, public and private contractors, local national and international authorities, and to all those involved in research and practice related to Earthquake Geotechnical Engineering.