Earthquake induced ground strains in the presence of strong lateral soil heterogeneities

Abstract

Transient ground strains are recognized to govern the response of buried elongated structures, such as pipelines and tunnels, under seismic wave propagation. Since a direct measure of ground strains is not generally available, simplified formulas relating peak ground strain to peak ground velocity, and based on 1D wave propagation theory in homogeneous media, are typically used for seismic design. Although they are adopted by most of the available technical guidelines, the use of these formulas may be questionable in complex realistic situations as either in the presence of strong lateral discontinuities, or in the epicentral area of large earthquakes, or in sites where relevant site amplification effects and spatial incoherency of ground motion are expected. \ud To provide a contribution to overcome the previous limitations, a simplified formula relating peak ground longitudinal strain to peak ground velocity is proposed in this paper, as a function of the geometrical and dynamic parameters which have the major influence on strain evaluation. The formula has been obtained under small-strain assumptions, so that it can reasonably be applied under linear or moderately non-linear soil behaviour. The adequacy of this formula in the most common case of vertically propagating S-waves has been checked against 2D numerical solutions by Spectral Elements (SE) for representative geological cross-sections in Parkway Valley (New Zealand) and in the cities of Catania (Italy) and Thessaloniki (Greece). \ud The shear strain and the longitudinal strain variability with depth is also investigated, through some qualitative examples and comparisons with analytical formulas

A critical review on the vulnerability assessment of natural gas pipelines subjected to seismic wave propagation. Part 1: Fragility relations and implemented seismic intensity measures

“…Actually, in such conditions the seismic vulnerability of pipelines is expected to increase significantly (e.g. Trifunac and Todorovska, 1997;Takada et al, 2002;Scandella and Paolucci, 2006;Psyrras and Sextos, 2018), while a worse correlation between the εg and PGV is commonly observed (Paolucci and Pitilakis, 2007). Several approaches have been proposed in the literature to account for the effects of irregular topography on the ground strain in a simplified fashion.…”

“…Several approaches have been proposed in the literature to account for the effects of irregular topography on the ground strain in a simplified fashion. Indicatively, O'Rourke M.J. and Liu (1999) presented a simplified procedure for the computation of the ground strain in cases of soil deposits with inclined soil-bedrock interface, while Scandella and Paolucci (2006) proposed an analytical relationship for the εg-PGV correlation near the boundaries of basins with simplified geometries. Numerous studies that examine the effects of topography and soil heterogeneous soil condition on the soil straining ph c f l = response may be found in the literature.…”

A critical review on the vulnerability assessment of natural gas pipelines subjected to seismic wave propagation. Part 2: Pipe analysis aspects

“…hills, canyons, valleys etc) may cause local site effects, which may amplify significantly the ground seismic motion (e.g. Scandella and Paolucci, 2010;Gelagoti et al, 2010;Riga et al, 2018), resulting in high ground deformations on the pipelines. The critical effect of inhomogeneous soil sites on the pipeline seismic response has been reported by numerical, analytical and experimental studies (e.g.…”

Can a buried gas pipeline experience local buckling during earthquake ground shaking?

“…Local site response is caused by gradients in soil properties (material inhomogeneity), surface topography (e.g., hills, ridges and canyons) and special geologic conditions, such as a soft surficial layer surrounded by stiff rock (valley-type) and cavities. Under optimally directed seismic excitation, the presence of any of the above in the vicinity of a buried pipeline can amplify the ground motion locally, alter its frequency characteristics and spatial profiles, prolong its duration and induce pronounced ground strains and curvatures (e.g., [5][6][7][8][9]) mainly close to the interface of different soil formations, which in turn can induce local pipeline deformation. As an example, a pipeline crossing the interface between soil strata that exhibit a sharp lateral change in stiffness will suffer principally from alternating axial compression-extension under direct seismic wave action, due to the different vibrational characteristics of the said strata, even if the pipeline fully conforms to the ground motion (i.e., no interaction).…”