Concave-up p-y behavior in liquefied sand has been observed by many researchers due to the dilatant tendency of sand that is dense of its critical state being suppressed in undrained loading. However, static analysis method often scale down the concave-down p-y curves that characterize drained loading, thereby missing the potentially important influence of concave-up behavior on pile response. For lateral spreading problems, large shear strains are typically assigned to the liquefied layer, which presupposes that the liquefied sand is soft and weak. This assumption is incompatible with the strengthening, stiffening concave-up p-y material. This paper presents a static lateral spreading analysis of a pile using concave-up p-y materials to demonstrate how this incompatibility can lead to unrealistic results.

Studies recently conducted by the authors and others have demonstrated that relatively simple equivalent-static analysis (ESA) procedures can adequately predict the response of bridge foundations to lateral spreading for design purposes assuming that the lateral spreading displacement demand is known or can be estimated. However, an important aspect of the analysis that remains to be addressed is how to account for the restraining force provided by foundations when the laterally spreading ground does not have a finite, measurable out-of-plane width. This study addresses this problem in the context of two parallel, adjacent bridges crossing the Colorado River in Mexico that were subjected to a broad field of laterally spreading ground during the 2010 Mw 7.2 El Mayor- Cucapah earthquake. Two-dimensional finite element analyses (FEA) are used to quantify the influence that the presence of each bridge had on the lateral spreading demand for the opposite bridge. The results show that the relatively stiff foundations of the first bridge provided a 'shielding' effect to the second bridge, significantly reducing the demand compared to the magnitude of the free-field lateral spreading observed at the site.

An ultrasonic p-wave reflection imaging system is used to non-invasively image submerged soil models with embedded anomalies and complex geometric layer contacts. The ultrasonic transducers emit compressive waves into water that subsequently transmit into the underlying soil, and measurements of the reflections are used to construct the images. Properties of the transducers and data acquisition hardware and software are explained. A soil model consisting of embedded high- and low-impedance anomalies, dipping soil layer contacts, and an undulating concrete base layer was imaged using 500 kHz transducers. The geometric features of the model are clearly visible in the images.