UTILITY TUNNELS STILL IN USE
PipelineExpress 2, no. 13 (July 13, 2001)
Saint Paul residents don't know it, but the sandstone under their
downtown streets are riddled with hand dug tunnels. Over 2.6 miles
of water tunnels, started by the private St. Paul Water Company
in 1856, have been constructed in downtown Saint Paul. The arching
walls, usually just bare sandstone, average four feet wide by six
feet tall. However, in faulted areas brick arches of concrete walls
supply additional support. Tunnel depths below ground elevation
range from 25 feet in the west to less than 10 feet near Cedar Street.
main entrance to the tunnels is through the courthouse, although
emergency and service access can be gain through numerous man-holes
scattered throughout the system. Security of the tunnel system is
of primary importance, and all possible points of access are carefully
secured to insure control and safety of the system.
1883, the City of Saint Paul was authorized to buy the water company
by the Minnesota State Legislature, and during the years following
this purchase, the tunnels were extended to a total length of over
upper geology of the downtown Saint Paul area consists of a limestone
layer covering a much softer layer of sandstone. This St. Peter
sandstone contains many fine particles where were "cemented"
together by the pressure of a great layer of overburden that has
since been eroded away.
sandstone, often referred to as sandrock, is still somewhat soft,
and can be easily removed using simple hand tools. Since the overlying
limestone is a much harder substance, tunnels were dug to carry
water distribution pipes instead of the more typical "open
tunneling was accomplished by hand laborers using shovels, picks,
and wheelbarrows. The pickmarks of these laborers' tools can still
be seen in the walls and ceiling of the tunnels today.
tunneling, though limited to very small service extensions called
"drifts," is still constructed using the same basic methods
of excavation, although air-powered tools have replaced the pick
for breaking away the sandrock.
tunnels contain pipes ranging in size from 4 to 20 inches in diameter,
The pipes convey water to over 50 domestic and residential services
in the downtown area. These customers consume nearly 10 million
gallons of water per month. In addition, these pipes supply water
for fire hydrants and auto-fire connections.
tunnels provide ready access to the pipes and fittings, making maintenance
and repair easy and fast. Continuous inspection and maintenance
of the numerous valves and fittings lessens the possibility of interrupted
service. Should a break or leak occur, any necessary repairs can
be made without disrupting city traffic.