PSI - Issue 78

Nadia Salvatore et al. / Procedia Structural Integrity 78 (2026) 81–88

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1. Introduction The evaluation of natural hazards' impact on critical structures like bridges and viaducts presents a complex challenge, requiring the expertise of engineers and geologists from various specializations. As noted in several studies (e.g., Kappes et al., 2012, Gill and Malamoud, 2014), the primary difficulty lies in understanding and quantifying the interactions between different natural hazards and their combined effects on these structures. In this context, Salvatore et al. (2025) introduced a geological-geotechnical index, GETI, which is currently focused on seismic risk and the combined effects of secondary hazards associated with earthquakes (ground shaking, liquefaction/lateral spreading, landslides). This index quantifies the vulnerability of a given linear structure based on its structural characteristics and the geological and geotechnical features of its location. In this study, the index was applied to the Cherry Hill Exchange, a viaduct located in Farmington, a few kilometers north of Salt Lake City (Utah, USA), an area with high seismic risk, close to the active Wasatch fault, in a deep tectonic basin filled with soft lacustrine/alluvial sediments. Following the procedure outlined by Salvatore et al. (2025), we conducted a two-step analysis, beginning with an extensive literature review, followed by a critical analysis of geological and geotechnical data to assess the area's susceptibility to earthquake effects. In the second step, we used this data to develop a reliable geological and geotechnical model of the subsoil, conducted a site seismic response analysis, and evaluated the soil liquefaction potential and its expected effects. Ultimately, the PGA value at the top of the piers and the expected lateral displacement due to liquefaction were used in fragility curves developed by Brandenberg et al. (2011) to calculate the probability of damage and the corresponding GETI values. The analysis considered the soil conditions at the time of the structure's construction and was repeated after soil reinforcement with gravel columns to test the index's sensitivity and effectiveness. 2. Geological framework and level 1 analysis To assess the probability of damage on the Cherry Hill Interchange area due to the occurrence of an earthquake, an extensive literature review was performed. The aim of this first step was to define the geological and geotechnical condition of the area, and the presence of known phenomena linked to the investigated hazard, such as historical landslides or soil liquefaction. From this point of view, we collected data from seismic microzonation studies, from the surveys conducted by the United States Department of Transportation (UDOT), and from the academic studies conducted before and during the construction of the U.S. Highway 89 and the Legacy Parkway (State Road 67). Cherry Hill Interchange is a viaduct that overpasses U.S. Highway 89. It is composed of two abutments and one central pile supported pier, which divided the eight lanes of the highway in four per direction. The viaduct has a length of 100 m, comprising two spans of 50 m each. The deck is designed as a continuous structure and is made up of 12 prefabricated steel IPE beams, joined together by lattice-type steel crossbeams. The pier is made of reinforced concrete, with a frame of four shafts connected at the height of the cap by arches. The abutments are of the through type, consisting of a visible bearing platform. Both the pier and abutments are founded on piles. Specifically, the foundation of the abutment 1 consists of a footing buried 2 m into natural ground, connecting piles 42 m long; the foundation of the east abutment consists of a footing buried 1 m into fill soil, connecting piles 36 m long; the foundation of the pier consists of a footing buried 4 m into natural ground, connecting piles 35 m long. The viaduct is located about 25 km North of Salt Lake City, between the Farmington Bay and the Wasatch mountain range (Fig.1). The Wasatch fault zone (WFZ) is a significant fault system located in northern Utah, delineates the stable Colorado Plateau and southern Rocky Mountains to the east from the Basin and Range area. (Parsons, 2006). The WFZ accommodates an east–west extension of 2–3 mm/yr (Chang et al., 2006) across 10 major structural segments that collectively span approximately 350 km. Paleoseismological observations reveal that 24 surface-rupturing earthquakes, believed to be of magnitude 6.5 or larger, have occurred over the past 7,000 years on the five central segments of the WFZ (Machette et al., 1991), establishing the WFZ as the largest contributor to seismic hazard in the region (Kleber et al., 2021). Recent studies (e.g., Pang et al., 2020) have highlighted the listric behavior of the WFZ, characterized by a steep dip plane (~70°) near the surface and a low angle dip at depth (~20° at >12 km).