28-Story Mixed-Use Building, 1620 Sansom Street, Philadelphia, Pennsylvania

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Overview: A proposed 28-story mixed-use high-rise building is planned at 1620 Sansom Street in Philadelphia, Pennsylvania. The building will host an underground parking garage, 306 residential units, and commercial space on the ground floor. GeoStructures was retained by Southern Land Company to provide demolition oversight of the pre-existing parking garage, environmental testing, geotechnical investigation, and foundation design for the project.

GeoStructures provided site inspection and oversight during demolition of the pre-existing parking garage at 1620 Sansom Street. To characterize the subsurface, 6 test borings were performed across the site. Geotechnical laboratory testing was then performed on the soil samples to determine the engineering properties of the load bearing materials for project analysis and design.

A 6-ft thick mat foundation covering the entire footprint was selected as the optimum foundation system. Adjacent structures (including the historic Liberti Church) thus required underpinning since their basements are located at a higher elevation than the mat bottom. GeoStructures was responsible for this design.

GeoStructures also performed soil clean fill testing, finding that select material is suitable as backfill for the basement wall, provided the moisture is at near optimum conditions at the time of the backfill operation. During a Phase II ESA, GeoStructures selected soil and groundwater samples to check contamination related to the historical use of the site as a filling station. Samples were subjected to laboratory analytical testing for PA short list of petroleum products including volatile organic carbons (VOCs), semi-volatile organic carbons (SVOCs), and priority pollutant metals. All of the tested constituents (with the exception of localized arsenic) were found to have concentrations lower than their respective PADEP Concentration Limits for Regulated Substances in Soils and Groundwater.

Lastly, GeoStructures also installed two geophones in adjacent structures to monitor construction vibration activity for the duration of the project.

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