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.

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.

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.

Chap. 1 sets forth the general require. for applying the analysis & design provisions contained in Chap. 2 through 12 of the Nat. Earthquake Hazards Reduction Prog. Recommended Provisions for Seismic Reg's. for New Bldgs. & Other Structures. It is similar to what might be incorporated in a code as administrative regulations. Also includes info. on: quality assurance; ground motion; structural design criteria; architectural, mechanical, & electrical components; seismically isolated structures; & design require. for foundation, steel structure, concrete structure, composite steel & concrete structure, masonry structure, wood structure, & non-building structures. Illustrated.

Includes the institute's report, 1953-