SR 4 Update

Soil Mixing for Very Large Shafts in Dune Sands

State Route 4 Interchange Improvement Project near San Francisco is currently under construction and will improve traffic flow through Contra Costa County’s major transportation corridor. Malcolm, under contract with RGW is currently helping the Contra Costa Transportation Authority (CCTA) in their freeway widening effort by installing a series of 8 and 13 foot diameter drilled shafts over 110 feet deep for the foundation of three new fly-over structures. A few of the foundation shafts are precariously close to active traffic requiring complex project coordination with the CCTA. Before shaft drilling could commence, Malcolm installed CMP casings to depth of 60 feet; an impressive sight for commuters. The location of all three bridge foundations involves working with very dry and loose overburden material and the implementation of a uniquely designed 15 feet in diameter support ring to stabilize the 13 foot diameter drilled foundation shafts. In addition, single point soil mixing to a depth of 40 feet was used to stabilize dune sand material and minimize the potential for catastrophic ground failure close to active traffic.

“The SR4 widening project is not a typical project and requires complex solutions in respect to safety and ground control,” commented David Walker, Malcolm’s Project Manager.

For more information about the project contact Malcolm’s Project Manager at