Drilled shafts have been installed by Malcolm Drilling to form the secant pile retaining walls to support the 400 ft x 80 ft x 80 ft launch pit for the SR 99 tunnel boring machine on the Alaskan Way Viaduct Tunnel Replacement Project in Seattle. Excavation has commenced on the pit in preparation for the launch of a world record 57.5-ft diameter TBM (until Russia launches a planned 63-ft TBM). The Seattle Times article indicates there are a total of 1400 drilled shafts in the pit walls and nearby, but a press release by WSDOT indicates the walls are comprised of approximately 200 drilled shafts. [Source: Seattle Times via ASCE SmartBrief. Image: WSDOT Flickr]
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FHWA NHI Manual: Drilled Shafts Construction Procedures and LRFD Design Methods
The FHWA has released for download a comprehensive update to the 1999 O’Neil and Reese manual “Drilled Shafts: Construction Procedures and Design Methods”, lovingly referred to in the industry as the “Brown Book” or the “Drilled Shaft Bible”. This 2010 manual from the National Highway Institute (NHI) of the FHWA is entitled “Drilled Shafts: Construction Procedures Procedures and LRFD Design Methods” and was authored by Dan A. Brown, Ph.D, P.E. of Dan Brown and Associates, John P. Turner, Ph.D, P.E. of the University of Wyoming, and Raymond J. Castelli, P.E. From an FHWA Memo on the manual:
Distributed with this memorandum is the publication entitled "Drilled Shafts: Construction Procedures and LRFD Design Methods" (FHWA-NHI-10-016). This manual is the reference text used for the National Highway Institute (NHI) course numbered 132014 on Drilled Shafts. The publication will become the tenth in the series of geotechnical engineering guidelines called "Geotechnical Engineering Circulars." Geotechnical Engineering Circular (GEC) No. 10 is prepared as a significant revision and update to "Drilled Shafts: Construction Procedures and Design Methods" (FHWA IF-99-025), and reflects the standard of practice for the design, construction and inspection of these features. The guidance is developed following Load and Resistance Factor Design (LRFD) procedures and will enable engineers to identify and evaluate technical feasibility and potential applications. The text is developed with a sufficiently broad scope to be of value to a wide range of transportation specialists responsible for assisting with selection, design, development of materials specifications, construction monitoring, and contracting methods for Drilled Shafts.
Click through for the download link and some preliminary comments on what has been updated in this significant new publication in the drilled shaft construction industry as well as the geotechnical engineering profession.
Voids Open as a Result of Tunneling Under Seattle’s Beacon Hill
The Seattle Times (hat tip to ASCE SmartBrief) has reported that seven voids have been discovered above the Beacon Hill Tunnel with one opening up at the ground surface. The tunnel is being constructed by Sound Transit, the area’s transportation agency as part of a roughly $2.6 billion (yep, billion) light-rail project connecting downtown Seattle with the University of Washington and SEA-TAC airport. The voids were a result of running sand pockets in the otherwise stable clay units that were encountered by the tunnel boring machine or TBM. These voids migrated up like a chimney with one reaching the surface, almost 160-ft above the tunnel. This void was apparently 21-ft deep and opened up in a resident’s front yard and could have easily swallowed her up as she noticed it while gardening. The other voids were discovered at a depth of 20- to 65-ft below the ground surface. More after the break. (Illustration from Seattle Times)