Abstract:
The geology of Washington, DC as part of the overall United States (US) Northeast Atlantic coast is very old, having bedrock formed more than a billion years ago and surface geology that is very complex and variable. Today, Washington, DC is densely populated and home to critical facilities, infrastructure, and national treasures with high monetary, cultural, and security value. The urban design principle of low-rise only buildings allows for broad, sunlit streets and stunning views of the Capitol. Below ground, the city is full of deep basements and excavations in challenging, dense urban spaces and unique geologic conditions. The city has many tales to tell since Pierre L’ Enfant first envisioned the National Mall as the nation’ s “ Grand Avenue, ” more than two centuries ago, when the land was used for a multitude of purposes, including military training facilities and railroads, with many canals and animal farms that have now been filled. This presentation will share some of these tales as they relate to site and foundation evolution, and discuss associated risks from rare but known hazards, such as moderate earthquakes, and newly imposed challenges resulting from climate change. Risk will be examined through the conventional lens of damage and loss, but also using the newly developed concept of NIST-FEMA (2021) of functional recovery time. This parameter may be even more detrimental for densely built urban centers that rely heavily on their infrastructure to function.