2114/2116 14th St. NW Standing 34 ft (10 m) in height, this twostory brick building required the preservation of all exterior brick walls, the second-floor concrete slabs and concrete columns. The scope of work consisted of underpinning the existing brick facade at the east and the exterior west wall to provide vertical support as well as to provide temporary support for the excavation (for lateral soil retention). The existing brick building required shoring to allow for the demolition of the foundation, the slab on grade and concrete roof while enabling the construction of the new structure. Challenges: The vertical concentrated loads were too high for a fullbearing shoring and underpinning system given the soft and wet grounds at subgrade elevation. Therefore, the shoring and underpinning systems needed to incorporate deep foundations (micropiles). More than half of the total number of micropiles needed (60 in total) were to be installed from within the existing building. The second-floor slab (to remain), and the 4.5 ft (1.3 m) deep concrete beams supporting this slab, created considerable headroom limitations. There was a substantial amount of existing and proposed columns at the north and south walls that made the needle shoring of these existing walls and columns complex and meticulous. Contaminated soils were encountered during the excavation process, which could have substantially impacted the schedule if careful and considerate coordination had not occurred. Solutions: The underpinning system provided was designed to resist the vertical loads by using resistance forces from a combination of the piers' allowable bearing capacity and the geotechnical capacity of the micropiles. The idea behind this combined system was to use the micropiles to limit the vertical loads transferred into the concrete piers, thus reducing the bearing pressure under the piers to acceptable levels. Micropiles - The micropiles were pressure-injected grouted elements 7 in (180 mm) in diameter, made of grade 80 steel casing reinforced with 52/26 Titan IBO bars. The maximum load acting on the micropiles was 90 kip (400 kN). 98 * DEEP FOUNDATIONS * JULY/AUG 2023 2114/2116 14th St. NW