Faculty - Research - Soil Nailed Walls in Moscow, ME
One phase of the construction of the wall in July 1997.
The Moscow Soil Nailed Wall Project started in the
spring of 1997.
Dr. Thomas Sandford and
Dr. Dana Humphrey are working with funding from the
Maine Department of Transportation (MDOT) to investigate
the use of this relatively new technology in Maine's harsh
climate. The project will monitor the frost penetration and water
seepage around the wall for at least two winters.
The site conditions, which include a very steep
slope, variable rock elevation, and combinations of soil and rock,
make this an excellent location for this type of wall. Therefore,
the MDOT decided to use soil nails for this project because it
would be much more cost effective than a conventional retaining
wall. The University of Maine Department of Civil & Environmental
Engineering suggested that the wall be insulated to prevent frost
penetration into the susceptible glacial till that is present
behind the wall. The wall height ranges from 5m to 10m high and it
runs along State Route 201 for approximately 580m.
Four UMaine undergraduates working under the
direction of graduate student Don Kingsbury and professors
Sandford and Humphrey, installed some 450 instruments to monitor
the wall's performance in Maine's harsh winter climate. According
to Humphrey, "Instrumentation includes strain gages, load cells,
total earth pressure cells, piezometers, tilt meters,
thermocouples and thermistors. Everything is hooked up to a data
acquisition system that allows the data to be downloaded by
telephone. The students (Kingsbury, Adam White, Karen Gross, Aaron
Smart, and Josh Coombs) completed all the wiring and programmed
the data acquisition system. It was, and still is, a great
learning experience for everyone."
A load cell and other instrumentation can be seen behind a
green anchor plate on the end of a soil nail. The drilling
equipment viewed from the top of the slope. Wyman Lake can be seen
in the background.
The construction process started at the top of the
slope. A bench of 4 to 5 feet (0.6 to 0.7m) in height was cut into
the hillside. Then, a five inch (nominal depth) layer of concrete
was sprayed over a layer of plastic mesh to stabilize the cut
area. Next, holes were drilled into the hillside and the nails
were installed. Instrumentation was installed, the nails were
grouted, and then the ends of the nails were covered with anchor
plates (as pictured above, left). This process was repeated until
the bottom of the slope was reached.
The design of the Moscow wall required a ten inch
facing of reinforced concrete to protect the soil nails. Four
inches of blue board insulation was installed over this. The
finished face of the wall is tongue and groove timber.
This is the second soil nailed wall to be
constructed in Maine. The first was built in Brunswick with
instrumentation to monitor frost penetration. Master's degree
candidate Sandi Duchesne is currently writing her thesis about the
Brunswick project and the performance of the wall during its first
winter of service.
Photos and information contributed by Dana Humphrey, Tom
Sandford, Aaron Smart, and Don Kingsbury.
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