Site-specific geotechnical ground response analyses (GRAs) are typically performed to evaluate stress and strain demands within soil profiles and/or to improve the estimation of site response relative to generic site terms from empirical prediction equations. Implementation of GRA results in probabilistic seismic hazard analysis (PSHA) requires knowledge of the mean and standard deviation of site amplification from GRA. We provide expressions for evaluating within-event standard deviations of ground motion given the parameterization of site amplification for a particular intensity measure into a nonlinear equation. A key component of those expressions is the standard deviation of site amplification, φlnY. We evaluate from the literature estimates of φlnY from ground response simulations using variable inputs and from interpretations of ground motion recordings. We find data-based studies to exhibit relatively consistent values of φlnY ≈ 0.3 over a wide range of oscillator periods, whereas simulation-based studies produce much higher values below the fundamental period of the analyzed soil column and lower values at longer periods. Values derived from the data-based studies are recommended for application.

We investigate the ability of 1-D ground response simulations to match observed levels of site amplification from California vertical arrays. Using 10 vertical arrays, we find simulations to best match data using a VS-based damping model from the literature. We find a higher percentage of California sites, as compared to KiK-net sites from Japan, to have a reasonable match of empirical and theoretical transfer function shapes. The empirical transfer functions also have a greater degree of event-to-event consistency than has been found previously in Japan. Cases with poor matches highlight that 1-D simulations can fail to accurately model site response.

Site-specific (non-ergodic) seismic hazard analysis is increasingly being employed as part of ground motion hazard characterization for critical projects. Non-ergodic site response can be evaluated from the interpretation of ground motions recorded at (or near) the site or from simu-lations. The simulation method that is most frequently employed is ground response analysis, which can capture impedance, resonance, and nonlinear effects for vertically propagating shear waves. Such effects are often large contributors to site response, but are not sole contributors, as other effects related to basin geometry can also be influential, particularly at long oscillator periods. We review procedures for conducting ground motion hazard analysis using non-ergodic site response models, including aleatory variability and epistemic uncertainty. We de-scribe preliminary new work related to spatial correlation of site response that is important for some applications. The challenges and benefits of applying these procedures are illustrated through case histories in California, Italy, and Japan.

Engineering assessments of ground failure potential commonly express seismic demands in the form of shear stresses or normalizations thereof. In soil materials underlying foundations, referred to as ‘foundation soils’, dynamic stresses result from wave propagation associated with site response in combination with demands associated with soil-structure interaction (SSI). Engineers presently lack a simplified procedure for analysis of SSI-related stress demands. To provide insight into the physics of the SSI-induced stresses, and to lay the ground work for an eventual simplified procedure, this paper presents preliminary solutions for the problem of a dynamic vertical point load on the surface of an elastic half-space (Lamb’s problem) and the resulting stresses within foundation soils. Results are presented in dimensionless graphical form and indicate the amplitude and phase of dynamic stresses.

Seismic response of levees is typically computed for short segments within which levee geometry, soil conditions, and seismic demands can be assumed to be essentially constant. However, from a flood protection perspective, the performance of the system as a whole is critical because any failure within the system can lead to inundation. An assessment of system risk requires knowledge of individual segment performance in combination with the spatial correlation of damage among segments. We present a correlation model for damage states among levee segments that can be used in combination with segment fragility models and correlated demand functions to assess levee system risk. We compute the autocorrelation of damage states as a function of separation distance for the Shinano River levee system in Japan, based on observational data from two shallow crustal earthquakes. Levee segment damage is found to be spatially correlated up to 4 km separation for small to moderate levels of damage but only to 1 km for severe damage.

The seismic analysis of bridge structures is often performed using the substructure method in which the foundation is replaced by an equivalent "spring" representing foundation impedance. Ground motions from seismic hazard analyses correspond to a free-field condition, and therefore should be modified to account for kinematic soil-structure interaction effects before being used as input to the springs. This paper presents closed-form analytical solutions for the response of an elastic pile subjected to harmonic seismic excitation in uniform elastic soil. We use these solutions to compute transfer functions relating foundation input motion to free-field ground motion and use the results to verify predictions from a beam-on-Winkler-foundation numerical model. The two approaches show good agreement, indicating that the numerical modeling method is appropriate for investigating more complex effects such as soil and pile nonlinearity. Ground motion deamplification due to kinematic SSI is demonstrated to be significant for stiff foundations in soft ground conditions. Numerical simulations using recorded ground motions demonstrates that transfer functions can be computed only from frequency bands for which the motions contain adequate energy.

Foundation damping incorporates the combined effects of energy loss due to waves propagating away from the vibrating foundation (radiation damping), as well as hysteretic action in the soil (material damping). Two closed-form solutions for foundation damping of a flexible-based single degree-of-freedom oscillator were derived from first principles where the inherent (structural) damping ratio, radiation damping and the soil hysteretic damping ratio appear as variables. Since both formulations are theoretically defensible, yet provide numerically distinct results, we look to case histories for validation. In addition to previously established case histories we evaluated data derived from forced vibration testing of a field test structure installed at two sites in California. Parametric system identification was employed to evaluate the fixed-base and flexible-base first mode period and damping ratio during tests performed across a wide frequency range and multiple load amplitudes. Foundation damping derived from these results is shown to favor one of the theoretical models over the other.

During earthquake ground shaking earth pressures on retaining structures can cyclically increase and decrease as a result of inertial forces applied to the walls and kinematic interactions between the stiff wall elements and surrounding soil. Limit equilibrium analysis imposes a pseudo-static inertial force to a soil wedge behind the wall (the mechanism behind the widely-used Mononobe-Okabe method), which is a poor analogy for either inertial or kinematic wall-soil interaction. Many basement walls and retaining structures are dominated by kinematic soil-structure interaction (SSI) effects arising from differences in displacement between the wall and the free-field soil. Kinematic SSI solutions are often formulated for uniform soil conditions, but the shear modulus of most soils is known to increase with mean effective stress, and therefore with depth. We examine the influence of vertical heterogeneity of shear modulus on kinematic SSI for rigid walls. An existing free-field displacement solution is presented first, followed by analysis of earth pressure increments using a Winkler assumption. Vertical heterogeneity is shown to reduce seismic earth pressures compared with a uniform soil case (for a given frequency and peak ground surface displacement) because free-field displacements are largest near the surface, where the soil is softest and Winkler stiffness is lowest. The proposed Winkler solution is then compared with an exact analytical solution for vertically heterogeneous soil over a rigid base and retained between two opposing rigid walls. The agreement is imperfect, but reasonable, with differences likely due to assumptions regarding the dynamic Winkler stiffness intensity.

Two large scale 9 m radius centrifuge tests were conducted at the NEES@UCDavis experimental facility to understand the interaction between soft peat and stiffer levee fills, to gain insight into the volume change behavior of organic soils under cyclic loading, and to study deformation potential of saturated sandy levees resting on peat due to liquefaction of the levee fill. This study has potential applicability to the Sacramento-San Joaquin Delta where unengineered levee fills rest atop soft compressible peat soils. This paper focuses on the interaction between a nonliquefiable clay levee resting atop soft peat during application of a sine sweep base excitation. Transfer functions derived from the data were compared with results of 1-D ground response analyses. The 1-D analyses capture reasonably well the first mode response of the levee-foundation system, but do not capture a prominent rocking mode. The rocking mode has not been previously observed experimentally for embankment systems and can impose substantial local demands on the levee fills and foundation peat near the edges of the levee.