Four Falls Corporate Center—A Case Study

Urban development in West Conshohocken, near Philadelphia, has been occurring at a fast pace over the past 10 years. The 300 Four Falls office complex was to be constructed in one of the few remaining undeveloped sites, near the original 100 Four Falls office building from the early 1980s. The site conditions were a major issue in the development. With an odd-shaped narrow lot, a creek across the site, and existing grade changes of nearly 18.3 m (60 ft), fitting a 26,942 m² (290,000 sf) building represented a major challenge. Exploration revealed further difficulties, including cuts of over 12.2 m (40 ft) into hard rock on one side of the site, and very-soft soil materials to depths of over 24.4 m (80 ft) on the other. Solutions included a combined foundations system consisting of spread footings on rock, micropiles, and 890 kN (100 ton) driven H-piles. To accommodate the deep excavations around three sides of the site and extensive filling on the fourth side, various earth support structures were built. These consisted of soldier piles and tiebacks, soil nails, rock bolts, and Mechanically Stabilized Earth (MSE) walls. This project was truly a study m geotechnical engineering challenges and solutions that met the needs of a difficult site. This paper describes the most relevant geotechnical aspects of the project, and the application of different geo-construction techniques to meet the demands of the site.