
Construction has started on the tunnel boring machine launch pit for the WSDOT SR 99 Tunnel Project (Viaduct Replacement). The 420 foot long pit is being constructed using secant pile retaining walls, with 2 rows of 5 foot diameter piles, all around 90 feet deep. Based on the fantastic photos on WSDOT’s Flickr Page, it appears that Malcolm Drilling is performing the secant pile wall work. [Source: The Seattle Times via ASCE SmartBrief. Image: WSDOT Flickr]