I-84 Snake River Twin Bridges

RLW installed 5’ diameter drilled shafts at various locations in the Snake River. The waterway was 950’ feet wide and ranged from 3-15 feet deep depending on the location of time of year. The design proposed to install sheet pile coffer dams around each bent location for the installation of the drilled shafts. However, with the wide waterway, access was difficult as the waterway was a flowing river, and difficult to install the cofferdams. RLW developed a dewatering plan that was more cost-effective and easily accessible.

RLW constructed a temporary bridge across the waterway, this allowed access to each hole RLW installed 10 Casing at each drilled shaft location using a vibratory hammer. This casing was driven into the subsurface of the waterway approximately 10’ or until refusal. RLW installed this 10’ Casing by vibrating the temporary (10’ diameter casing) casing using a 4450 vibratory hammer approximately 10’ below the existing ground elevation. The sub-surface contained enough fine-grained cohesive material that 10’ of overburden cut the water flow from the bottom. Once the excavation was dewatered RLW installed the permanent 66” diameter casing using a 4450 vibratory hammer to get the casing to the desired elevation tip. In most areas, this method completely stopped the water inflow. However, in some of the shallow areas we poured concrete seal slabs to add weight and plug the water inflow. This provided a clean dry workspace for the installation of the permanent drilled shafts.