Excavation and pilings are progressing at 242 East 71st Street, the site of a 22-story residential tower in the Lenox Hill section of Manhattan’s Upper East Side. Designed by Robert A. M. Stern Architects and developed by Avdoo, the 172,000-square-foot structure is slated to yield 50 condominium units, ground-floor retail space, and enclosed parking. The nearly 10,000-square-foot property is located at the southwest corner of Second Avenue and East 71st Street.