South Platte Raw Water Pipeline Tunnel Littleton, Colorado
The South Platte raw water pipeline allows the transfer of water from South
Platte Reservoir on the west side of the South Platte River to McLellan Reservoir
on the east side.
The photograph shows the steel pipe behind the 72-inch Akkerman
Tunnel Boring Machine.
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 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.
