New York City Harbor — Remediation of Seawalls on the Historic Liberty and Ellis Islands

Located in the Upper New York Bay, the historic Ellis and Liberty Islands attract a combined total of almost 4 million visitors each year. The seawalls that surround the Islands were constructed in the early 1900s and now show varying degrees of deterioration, especially at Ellis Island. This is indicated by erosion of mortar joints, dislodged granite blocks along the wall face, decay of wood cribbing, washout from behind the seawall, and local wall displacements compromising its stability at some locations. During a recent study, a detailed survey of the conditions of the seawalls was performed that included visual inspection and geophysical techniques to assess the condition of the almost 10,000 ft of seawall on the two Islands. A remediation plan was developed that includes a large number of restoration and retrofit techniques ranging from simple repointing of stone blocks, to significant structural underpinning and lateral support of the seawall using modern geo-technologies such as micropiles and grouting. This paper summarizes the history and construction of these national monuments and describes the intended application of various technologies for the repair of the seawalls.