WorldWide Drilling Resource

34 APRIL 2019 WorldWide Drilling Resource ® Breaking Ground on Block 9 Compiled by Caleb Whitaker, Associate Editor WorldWide Drilling Resource ® The architecture firm Skidmore, Owings & Merrill has broken ground on Block 9, an 18-story mixed use tower in the heart of downtown Fargo, North Dakota. Inspired by the prairies, the development was designed to reflect the scale of the city and surrounding buildings. The project includes an expansive public plaza with retail, office, hotel, and residential space, and will make use of timber and local stone. Developed by Block 9 Partners, a partnership of Kilbourne Group, and R.D. Offutt Company, Block 9 will create a slender tower profile on the Fargo skyline. At its base, the podium will embrace the street and adjacent public plaza. A wood-framed public arcade will open out to the street and function as the building’s main entrance. On the fifth floor of the tower, a wide outdoor terrace and glass-enclosed multifunction ballroom and conference space will overlook the public plaza. Block 9 will have to resist stronger wind forces because of its greater surface area and the strength of the wind higher up. The tower is designed to sway less than an inch in wind gusts of 115 miles per hour. To achieve the necessary rigidity, the tower will be built with a hollow concrete shaft at its core, with 14-inch-thick walls. This stiff spine will house the stairwells and elevators. The outer skin of the high-rise will be a concrete cage, where the windows are installed. The space between the cage and the spine will be spanned by concrete floor slabs. When the wind blows, each window will transfer the force to the slab above and below it, and the slabs will transfer the force to the spine. Upon its completion in 2020, the tower will be the tallest building in the city and second tallest in the state. However, con- struction is going to start by drilling deep into the subsurface. For practical purposes, the clay soil at the surface can only bear the weight of buildings four to five stories tall. To bear the high-rise's 25,000 tons, the foundation has to reach 110 feet down to hard, compressed clay. Fargo was once the bottom of a lake which formed at the end of the last ice age. The waterlogged clay can compress a lot under a tall building, leading to substantial settling. Beneath the lake bottom is a mix of clay and gravel brought by glaciers during past ice ages. The glaciers compacted these layers, with the deepest layers being the most compact. Workers will drill 280 holes spread across Block 9's footprint, each deep enough to reach the compacted layers. Concrete will then be poured into the holes. These long columns (pilings) will transfer the high-rise's weight to the compact clay below, as well as to the clay clinging to the sides of the pilings through friction. Each piling will have a maximum capacity of 200 tons, which will be plenty to spare for the building's weight and everything held within its walls. Illustration of Block 9 courtesy of Skidmore, Owings & Merrill. C&G