a b s t r a c tThe response of an equivalent 26 m-thick deposit of dry, medium-dense, Nevada Sand with a relative density of 60% is measured in the centrifuge under six 1-D, horizontal earthquake motions applied to the base of the centrifuge container. Several 1-D site response analysis techniques are employed to simulate the experiments, including (a) equivalent linear analyses, (b) nonlinear analyses using a multi-degree-offreedom, lumped mass model, and (c) finite element analyses of a soil column using a pressuredependent, multi-yield, plasticity soil model. An average V s profile was estimated using empirical correlations. Soil dynamic properties included published generic modulus reduction and damping curves with implied strength correction as well as recommended plasticity model parameters based on soil index properties. Computed and measured lateral displacements, accelerations, shear strains, spectral accelerations, and Arias Intensities are presented and their differences are quantified in terms of mean residuals and variance. The comparisons demonstrate that 1-D seismic site response analyses using the available strength corrected, generic, pressure-dependent modulus reduction and damping curves for medium-dense dry sand can reliably compute soil response under 1-D wave propagation using any of the three methods, with an absolute mean residual of less than 0.5.

Settlement of soil layers during and after earthquake shaking is a major cause of damage to buildings and geotechnical structures. The available empirical design methods to consider seismically induced settlement focus on sands in dry or water-saturated conditions, and there is currently a gap in the basic understanding of the mechanisms of seismically induced settlements of partially saturated sands. An effective stress-based empirical methodology is proposed to estimate the seismically induced settlement of a free-field layer of sand in partially saturated conditions. This approach estimates the settlement by separately considering the volumetric strains caused by compression of void space during strong shaking (seismic compression) and dissipation of excess pore water pressures generated during earthquake shaking (postcyclic reconsolidation). A parametric evaluation of the methodology indicates that the small strain shear modulus, the parameters of the modulus reduction curve, the approach to estimate the upper bound on volumetric strain during liquefaction, and the pore water pressure generation parameter can have significant impacts on the predicted settlement. The model predictions were validated using results from a newly developed centrifuge physical modeling system that involved the use of steady-state infiltration to maintain a uniform degree of saturation with depth in the sand layer. Both the model and experimental results show a nonlinear trend in surface settlement with degree of saturation, with a minimum value obtained for sand at a degree of saturation between 0.3 and 0.6.

A broad diversity of biological organisms and systems interact with soil in ways that facilitate their growth and survival. These interactions are made possible by strategies that enable organisms to accomplish functions that can be analogous to those required in geotechnical engineering systems. Examples include anchorage in soft and weak ground, penetration into hard and stiff subsurface materials and movement in loose sand. Since the biological strategies have been ‘vetted’ by the process of natural selection, and the functions they accomplish are governed by the same physical laws in both the natural and engineered environments, they represent a unique source of principles and design ideas for addressing geotechnical challenges. Prior to implementation as engineering solutions, however, the differences in spatial and temporal scales and material properties between the biological environment and engineered system must be addressed. Current bio-inspired geotechnics research is addressing topics such as soil excavation and penetration, soil–structure interface shearing, load transfer between foundation and anchorage elements and soils, and mass and thermal transport, having gained inspiration from organisms such as worms, clams, ants, termites, fish, snakes and plant roots. This work highlights the potential benefits to both geotechnical engineering through new or improved solutions and biology through understanding of mechanisms as a result of cross-disciplinary interactions and collaborations.

The available simplified analytical methods for the seismic design of underground 5 structures either assume yielding or rigid-unyielding conditions. Underground reservoir 6 structures do not fall into either of these categories. In this paper, we present the results of three 7 centrifuge experiments that investigate the seismic response of stiff-unyielding buried structures 8 in medium dense, dry sand and the influence of structure stiffness and earthquake motion 9properties on their performance. The structure to far-field spectral ratios were observed to 10 amplify with increased structural flexibility and decreased soil confining pressure at the 11 predominant frequency of the base motion. Lateral earth pressures and racking displacements for 12 a range of structural stiffnesses were compared with procedures commonly used in design. Pre-13 earthquake measured lateral earth pressures compared well with expected at-rest pressures. 14 However, none of the commonly used procedures adequately captured the structural loading and 15 deformations across the range of stiffness and ground motions for which these reservoirs must be 16 designed. Further, it is unclear if the current methods of analysis provide conservative or 17 unconservative results for engineering design purposes. This identifies a critical need for 18 improved methodologies to analyze and design underground reservoir structures. ManuscriptClick here to download Manuscript Journal paper manuscript_vf.docx 4 of these structures are not fully captured by simplified seismic design procedures. Soil-structure-5 interaction (SSI) for these buried structures is complex and depends on foundation fixity, 6 properties of the surrounding soil, flexibility of the structure relative to soil, and the 7 characteristics of the earthquake motion. There is an increasing need in engineering practice to 8 obtain a better understanding of the seismic performance of these underground structures. For 9 example, the Los Angeles Department of Water and Power (LADWP) is replacing some of its 10 open water reservoirs with buried, reinforced-concrete reservoirs to meet water quality 11 regulations. Understanding the seismic performance of these restrained underground structures 12 will improve the structural and geotechnical seismic design of these type of projects. 13 Traditionally, underground structures are categorized either as yielding or rigid-unyielding, 14 and are designed differently based on the categorization. A yielding wall is one that displaces 15 sufficiently to develop an active earth pressure state. The current state of practice for assessing 16 seismic earth pressures on yielding structures relies heavily on the Mononobe-Okabe (Okabe 17 1926; Mononobe and Matsua 1929) and Seed-Whitman (Seed and Whitman 1970) methods. For 18 rigid-unyielding walls that don't undergo any deformation, the method of choice is often the 19 simplified solution proposed by Wood (1973), which assumes a completely rigid wall (with no 20 flexure). Underground reservoir structures fall in ...