May/June 2024 - 90

back analysis, a repair analysis can be
introduced. By using the same properties
identified in the back analysis, an
accurate representation of how the slope
will react to a stabilization solution can
be conducted.
Considering one lane of the Harlan
County Road took a joyride downslope,
the design would require an extensive
buildout for about 89 ft (27 m) of the
project. In less critical portions of the
failure, a more conventional buildout
method is utilized where the necessary
width is formed up and backfilled. To
replace the lost material under half the
road width, a 13 ft (4 m) tall geosynthetically
confined soil block wall was
designed. There needed to be enough of
a bench below the failure to have an
acceptable base to wall height ratio, a
weight check of the wall backfill and a
micropile design was needed for the
micropile cap (footing) located at the
bottom on the block wall. The micropile
cap was to support the weight of the
block wall to reduce any settlement and
to ensure no further movement of the
material behind the block wall. The
micropiles were rock dependent,
meaning they were required to be
drilled until they had an adequate rock
bond of 6 ft (1.8 m) in length.
The drainage system for the replaced
material was taken into consideration to
mitigate heavily saturated material. It is
crucial in the design process to remove
as much weight as possible from the top
of the slope and still achieve the
necessary goals. The opposite can be
said for the toe of the slope. Leaving the
material at the bottom of the slide helps
stabilize the remaining material above.
By having proper drainage throughout
the project, weight is reduced, and
erosion can be controlled. Drainage for
Harlan County was achieved by drilling
laser slotted PVC horizontal drains into
the lower portion of the slope. This
creates an easy passage for the water
behind the repair to take and removes
the unwanted weight in a controlled
fashion out the face of the wall.
90 * DEEP FOUNDATIONS * MAY/JUNE 2024
Repair analysis
The micropile cap was to
support the weight of the
block wall to reduce any
settlement and to ensure
no further movement of
the material behind the
block wall.
Construction
One of the most rewarding parts of
being on a design-build team is without
a doubt the construction of the
design. By having the engineers involved
in the operations side of a
project, an ease of communication is
created, and the constructability of a
design is considered a priority.
For the Harlan County project, a
crew was mobilized to the site to begin
construction within three days of the
initial site visit. This ability to respond
quickly is due to the design process
within the company and experience
in the area.
Safety being the number one
priority, stabilizing the remaining
roadway was assessed first. This was
accomplished by installing horizontal
soil nails into the exposed slope after
utility locations were confirmed. For
most projects, the nails are given a bond
strength that had been deduced during
the design phase and checked when
construction began by proof testing.
Open lines of communication between
the driller and engineer made actual
soil conditions easy to assess and any
design concerns could be modified
almost instantaneously. Once the soil
nail wall was completed to stabilize the
remaining roadway, the crew began
laying out the micropile locations on
the lower bench.
As is common with rural roads, the
Harlan County project was in a curve.
Rather than taking the time to form a
curved footing for the block wall, an
angle was strategically placed to keep
the necessary shoulder width. Micropiles
were drilled and formed around
with rebar reinforcement to create a
strong footing for the block placement.
Once the height of 13 ft (4 m) was
reached for the Harlan County project,
the top blocks were capped to prevent
any water from standing in the blocks.
The minor portions of the project
that could be repaired with a less
extensive buildout method were
formed at the correct buildout width.
This created a void between the
shotcrete wall and exposed slope that
was filled with lightweight backfill.
Positive drainage was ensured at the
base of the wall. The top of the wall was
constructed to be slightly lower than
May/June 2024

Table of Contents for the Digital Edition of May/June 2024
