A deep seated landslide covering over 250 acres threatened
Hwy 80 near Fairfield , CA. CALTRANS contracted with Condon-Johnson
and Associates (CJA) to install a large diameter shaft which
would house horizontal drains to drain the slide plane of
the moving soil mass.
The shaft and drains together are known as a “Rainey
Drain”. CJA excavated the shaft at a diameter of 6 meters
to allow access in the shaft for the horizontal drain drilling
equipment. The shaft was excavated in sandstone, melange and
basalt formations by excavation and/or drill and blast methods
to a depth of 91 meters and secured with a shotcrete lining
as it was advanced.
204 horizontal drains were installed at three levels in the
shaft. The resulting drainage, which moves up to 80 gallons
of water per minute, is successfully relieving the pressure
on the slide plane.
The $ 8.8 million contract was performed in
a thirty-month period.