Learn how "Redi-Rock’s large unit size and weight combined with its interface shear capacity made the construction of the Burt Lake Road Wall a viable solution," in Cheboygan, Michigan.

1. Case Study
L I M I T E D S ET B A C K C H A L L E N G E
Project Name: Mullett-Burt Lake Road
Reconstruction Project
Project Location: Cheboygan, MI
Project Size: 4,225 Square Feet
Application: Redi-Rock Slope Armor
Contractor: MDC Contracting
Charlevoix, MI
Engineers: Northwest Design
Group Petoskey, MI
Part 1
Overview of Burt Lake
Reconstruction Project
Cheboygan, Michigan
In the spring of 2004, the
State of Michigan and
the Federal Highway
Commission decided to Limited Setback
fund road improvements The right-of-way in Michigan allows the road
for a stretch of road in the commission 66 total feet of width or 33’ from the
center line to private property on either side. While this is
Cheboygan county area. plenty of room in most cases, in hilly terrains
This particular section retaining walls are needed. In the Burt Lake Road case, the
of road had a steep project needed to widen the roadway and reduce the
grade of a very steep slope while staying within the 66’
grade that resulted in
right-of-way. The adjacent properties were wooded and
many traffic accidents the landowners wanted to save the trees. A retaining
in winter conditions. wall up to 18 feet high was required to retain the slope.
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2. Potential solutions included
Part 2
sheet piling, poured in place
concrete and geo-grid reinforced
Design Criteria and the
segmental retaining walls. Redi-Rock Solution
However, these solutions were not The modular block wall, can be
desirable due to problems such analyzed as a rigid body as suggested by
as excessive cost, inabliity to be AASHTO* (section 5.9) The net overturning
constructed within the right-of-way, moment for the site specific conditions is
and were not aesthetically pleasing. into the slope. Therefore, the wall behaves
more like slope armor or cladding than a
retaining wall. From an overturning
Redi-Rock Solution perspective, the soil is actually supporting
MDC Contracting proposed using the wall.
Redi-Rock, a 2,500 pound modular 1) Sliding Resistance
block with a 9” setback to create Interface shear between the
a wall with a batter angle at 2V:1H modular units is a significant design
requiring no geo-grid. The wall point. The shear loads are transferred
needed to be buried up to between Redi-Rock units by a 10”
6 feet at the tallest part to shear knob-shear groove joint. This joint
provide global stability and base has been non-destructively tested to
sliding resistance. Redi-Rock’s to 9,000 pounds per foot. Theoretical
large unit size and weight shear strength is significantly higher.
combined with its interface shear
capacity made the construction 2) Base Sliding between the wall and the soil
of the Burt Lake Road Wall a viable Sliding resistance is frequently
solution. Redi-Rock provided the the controlling criteria for tall
following significant advantages. non-reinforced walls. Appropriately
First, it provided a wall solution sized site specific foundations are
within the limited space constraints. required to provide sliding resistance.
Second, it is a cost effective These foundations may incorporate
solution, fast and efficient to install, soil anchors or be buried sufficiently
and required no easements. Third, deep enough to provide sliding resistance.
Redi-Rock is a durable wet cast
concrete unit that 3) Global Stability
performs Stability of the soil
well in the behind the wall must
freeze-thaw also be checked for
environment tall non-reinforced
of northern walls. Increasing the
Michigan. wall bury depth or
Lastly, the foundation size are
superior common methods
aesthetic employed to address
appearance global stability.
of Redi-
Rock. For more information on
Redi-Rock Retaining Wall
systems, please contact us at
866-222-8400 or on the web
at www.redi-rock.com.
* American Association of State Highway and Transportation Officials, Standard Specifications for Highway Bridges, 17th edition, Section 5.9