Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress-cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementation.Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history.

The behaviour of structures founded in liquefiable soils is an area that is often encountered in the offshore industry for facilities such as pipelines or shallow foundation elements acting either in compression or tension. Light immersed structures surrounded by liquefiable soils are vulnerable to liquefaction-induced hazards such as uplift and horizontal displacement demands. Large uplifts of immersed structures have been reported following strong earthquakes, and observed in the laboratory. The dynamic response of an immersed structure surrounded by liquefiable soil is complex and involves the simultaneous occurrence of phenomena such as pore pressure generation and dissipation, soil dilation and contraction, water flow, and soil structure interaction. Due to these complexities, liquefaction induced demands on immersed structures are generally poorly understood despite their potential catastrophic consequences. This limited understanding may adversely affect the ability to optimize design of new structures and assess the true vulnerabilities of existing structures. Indeed, current practice often uses simplistic approaches, with binary decision making related to whether liquefaction maybe triggered or not. However, tools and techniques are now available to better evaluate the consequences of liquefaction on buried structures. This paper presents a case history that illustrates the application of these techniques for a nearshore project.Extensive analytical and experimental work was performed to study the vulnerability to liquefaction-induced uplift and lateral displacements of an existing relatively light (i.e., relative to the surrounding soil) immersed tube tunnel in California. The studies were performed to guide decisions regarding the need for retrofit and subsequently to select optimal mitigation measures. The numerical evaluations were conducted with advanced soil constitutive models appropriately calibrated against laboratory cyclic simple shear and centrifuge model tests, and actual case histories. The experimental study involved the design and execution of two centrifuge tests modeling representative tube-soil cross sections. The favorable comparison between numerical results and experimental observations allowed the use of the numerical tools in vulnerability evaluations along the whole tunnel length. In contrast to the general belief that liquefaction-induced uplift is a force-controlled phenomenon governed by buoyancy forces on immersed structures, both analytical and experimental studies revealed that the prevalent uplift mechanism is kinematic in nature and is associated with the ability of the liquefied soil to move around the structure. This important finding resulted in retrofit decisions with significant associated cost savings for this project. Additional uplift contributions may occur from heaving of soft soils or by volumetric expansion due to water flow in response to a pressure gradient, which may be reversible. The results and findings of this study, are not restricted to the specific p...