The pipeline was a conventional cut and cover project with the exception of a 530-foot long tunnel under Santa Fe Drive (Highway 85) and two sets of high traffic railroad tracks. The tunnel consisted of a 72-inch steel casing pipe with a 48-inch ductile iron carrier pipe.
The photograph shows the steel pipe behind the 72-inch Akkerman Tunnel Boring Machine.
The tunnel was driven with a 72-inch Akkerman open face tunnel boring machine with removable sand shelves. Intermediate jacking stations were installed periodically within the steel jacking pipe. Upon completion of the drive, the annular space between the ground and casing pipe was grouted and the carrier pipe was jacked in on skids.
The tunnel encountered three geologic units. The uppermost was a soft to medium stiff silty clay. Below it was a very clean, coarse sand with local cobble zones. Within the coarse sand, stiff to hard clay zones (mud lenses) were encountered. Cover ranged from 12 to 22 feet and the tunnel remained above the groundwater table. The tunnel encountered full faces of all three geologic units, as well as mixed conditions.
Deere & Ault’s staff performed the geotechnical investigation, designed the tunnel, and provided full time construction engineering services during tunneling.
Client: Centennial Water and Sanitation District
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