U.S. DEPARTMENT OF TRANSPORTATION
FEDERAL HIGHWAY ADMINISTRATION
ASSESSMENT REPORT
REPORT ON: US 36
Emergency Repair Sites 1 – 16
DIVISION:
CFLHD
DATE:
10/02/13
PROJECT NO.:
INSPECTION MADE BY:
See Below
Federal Highway Administration (FHWA), Central Federal Lands Highway Division
(CFLHD)
Mike Davies, Director, Project Delivery
Ed Hammontree, Project Management Branch Chief
Micah Leadford, Project Manager
Bob Bell, Survey Manager
Bart Bergendahl, Hydraulics Engineer
Matt DeMarco, Geotechnical Engineer
Julian Maskeroni, Project Engineer
Christine Black, Highway Design Manager
INTRODUCTION
During the week of September 9, 2013, a slow-moving cold front stalled over Colorado, clashing
with warm, humid monsoonal air from the south. This resulted in heavy rain and catastrophic
flooding along Colorado's Front Range. The situation intensified on September 11 and 12.
The area surrounding Estes Park, Colorado received significant amounts of rainfall over a five
day period. This rain caused rivers and stream to swell beyond their banks and impact adjacent
properties.
At the request of the Army National Guard, CFLHD Engineers visited US 36 between Lyons and
Estes Park on October 2, 2013 to inspect damage to the roadway. The following report provides
details on conditions observed during the inspection and provides recommendations for repair of
many of the sites.
SITE 1 - MP 18.6
Observations
The river encroached into the roadway ditch and caused approximately 190 feet of the roadway
to washout. There is a private residence adjacent to the site filled with debris.
Temporary repairs
The washed out section of roadway has been backfilled to match the grade of the inboard side of
the roadway.
Permanent repairs
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The existing ditch should be rehabilitated along the roadway to channel surface flows.
SITE 2 - MP 18.5
Observations
The river encroached into the roadway and caused approximately 105 feet of the roadway to
washout. It appears an existing culvert at this location also caused slope erosion at this site. The
existing material in the roadway prism includes a high percentage of fines. The river at this site
is located about 250 feet from the edge of the roadway.
Temporary repairs
The outboard slope should be rebuilt to match the grade of the inboard side of the roadway. Use
rocks from onsite to build slope approximately 10 feet tall x 10 feet wide.
Permanent repairs
Use a separation fabric to protect the fines in the roadway subgrade prism.
SITE 3 - MP 18.2
Observations
The river encroached into the roadway and caused approximately 470 feet of the roadway to
washout.
Temporary repairs
The roadway washout has been backfilled and graded to approximately match the grade of the
inboard side of the roadway. There is a high percentage of fines in the top lift, and few fines in
the lower lifts (embankment material in lower lifts appeared to be tabular quarry rock.)
Permanent repairs
The riprap rock placed during temporary repair work on the slope does not appear to need post
grouting for stability.
SITE 4 - MP 18.1
Observations
The outside bend of the river completely washed out the roadway for about 660 feet. There are
large quantities of depositional material in the river.
Temporary repairs
Access is provided using an old road grade to the northeast of the existing washed out roadway
(the ‘shoe fly’). Some cross culverts have been installed.
Permanent repairs
Consider adjusting the roadway horizontal alignment to more closely match the shoe fly
alignment. Large riprap should be placed to armor the roadway slope along the riverbend.
Above the riprap slope armor, the roadway slope can be laid back for about 15’ to tie into the
new roadway alignment. There is private property (Stone Mountain Lodge) on the east side of
the roadway adjacent to the temporary alignment, so right of way may be an issue.
FORM PR-33 (REV. 5-70)
EDITION OF 7-67 MAY BE USED
GPO 1977-778-944
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SITE 5 - MP 17.8
Observations
The roadway damage includes a 300-foot long undermined outboard shoulder. The river at this
site is wide and has a uniform slope.
Temporary repairs
The roadway should be backfilled with shouldering material, and riprap armor should be
installed on the slope.
Permanent repairs
N/A - Same as temporary repairs
SITE 6 - MP 17.6
Observations
The river encroached into the roadway and caused approximately 890 feet of the roadway to
washout to the centerline. The existing pavement on the inboard half of the roadway is still
intact. There is a box culvert that crosses under US 36 and outlets into the river. A survey
control point is on the north side of the road about midway through the site. Some existing cross
culverts remain intact. The river at this site includes a windrow of material in the middle of the
channel. There is a diversion structure in the river and penstock pipe downstream.
Temporary repairs
For sections of this site, the roadway has been backfilled to approximately match the existing
grade; temporary roadway bench is more than 24 feet wide. There is approximately 300 feet of
pavement edge failure at this site that has not yet been repaired; lower the grade of the roadway
as needed to allow for a 24-foot wide bench.
Permanent repairs
Remove the debris in the channel.
SITE 7 - MP 17.3
Observations
The river encroached into the roadway and caused approximately 1000 feet of the roadway to
washout to the inboard ditch in the widest point. There is a right-of-way marker on the north
side of the roadway.
Temporary repairs
The current elevation of the temporary repair is about 5 feet below the pre-disaster condition and
is relatively close to the elevation of the river. Riprap along the toe of the fill is tabular quarry
rock. There is approximately 200 feet of pavement edge failure at this site that has not yet been
repaired.
Permanent repairs
Additional slope armoring may be needed at this site. The inboard ditch has erosion damage and
localized areas of pavement edge drop off. There is a tall rock knob at this site that would likely
yield good embankment and riprap material. A section of inboard slope at this site has an
adversely jointed rock face, so cuts in this section are not recommended.
FORM PR-33 (REV. 5-70)
EDITION OF 7-67 MAY BE USED
GPO 1977-778-944
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SITE 8 - MP 16.8
Observations
This site is on the outside of a riverbend. Approximately 1000 feet of the roadway was washed
out at this site. Limited areas of the existing pavement remain intact. The channel narrows
through the riverbend. There is a utility riser pipe on the north side of the road.
Temporary repairs
The roadway has been backfilled with the toe of the new slope extending out into the river. The
grade of the temporary roadway is about 3 feet below the pre-disaster condition. After survey
data is available, the site will be analyzed to determine if the elevation is high enough for
hydraulic stability. A culvert should be installed to provide offsite drainage under US 36 near
the private residence on the north.
Permanent repairs
Some of the existing material in the river can be removed and used as roadway fill. Large riprap
should be installed to armor the slope around the riverbend. The rock knob on the north side of
the roadway could produce rock material and would improve the roadway geometry by
increasing sight distance.
SITE 9 – MP 16.5
Observations
Approximately 1435 feet of the roadway was washed out at this site. Both the channel and the
roadway bench are narrow through sections of this site.
Temporary repairs
The grade of the temporary roadway is about 3 feet below the pre-disaster condition. After
survey data is available, the site will be analyzed to determine if the elevation is high enough for
hydraulic stability.
Permanent repairs
The temporary repairs included cutting into an existing soft inboard slope. The depth of soil that
covers the rock slope is unknown; shallow soil depth may lead to the slope sloughing. If there’s
enough soil at this area, a soil nail wall may be needed.
SITE 10 – MP 16.3
Included in Site 9 above
SITE 11 – MP 16.2
Observations
Approximately 170 feet of roadway washed out to centerline, and backfill material near the
abutments of the existing bridge on County Road 80 was eroded away. During the storm event,
the river moved about 250 feet to the east, away from US 36 and towards private property.
Temporary repairs
Large riprap should be used to protect the wall and bridge abutments in the event the channel
returns to the pre-disaster location. Place larger rocks in front and smaller rocks behind. Grout
FORM PR-33 (REV. 5-70)
EDITION OF 7-67 MAY BE USED
GPO 1977-778-944
5 of 7
the rocks to fill voids. Approximate quantities: 900 cubic yards of riprap, 200 cubic yards of
flowable fill. The pavement washout should be sawcut and backfilled with embankment material
to match existing grade.
Permanent repairs
N/A - Same as temporary repairs
SITE 12 – MP 12.3
Observations
This Site was not assessed during this site visit. The pavement damage appeared to have been
repaired.
SITE 13 – MP 11.3
Observations
Approximately 1115 feet of roadway washed out to centerline. The channel is fairly wide
through this site. Bedrock was observed in the existing roadway prism at the riverbend, about 3
feet below existing grade. There is a large amount of rock debris in the channel.
Temporary repairs
Large riprap should be installed to armor the slope along the tangent and around the riverbend.
Based on preliminary observations, the toe of the temporary slope will be about where the
guardrail currently lies in the channel.
Another option would be to mine debris from the channel and use it for fill and to armor the
slope around the riverbend. The existing inboard guardrail could be removed, and the temporary
roadway alignment could be shifted to the inboard side. The roadway bench with this option
may not be wide enough for the full 24’ section, and alternate one-way traffic may be required.
Permanent repairs
The roadway could be shifted away from the river around the horizontal curve and extending to
the west. The horizontal shift would tie into the existing alignment prior to the existing bridge,
so no changes to the bridge are anticipated. Any material used to armor the roadway slope for
the temporary repair could be removed from the channel and used in the fill.
If further analysis shows the roadway horizontal alignment needs to remain at the existing
location, the slope armor would likely need to be grouted and pinned to bedrock.
SITE 14 – MP 11.2
Observations
Approximately 1380 feet of roadway washed out to the inboard ditch. Bedrock was observed in
the existing roadway prism and will likely dictate the elevation of the temporary roadway. There
is a right-of-way fence on the inboard side. The channel through this site is narrow and steep.
Temporary repairs
The roadway has been backfilled with the toe of the new slope extending out into the river.
After survey data is available, the site will be analyzed to determine if the temporary roadway
elevation is high enough for hydraulic stability. A culvert should be installed to provide offsite
drainage in the sags.
FORM PR-33 (REV. 5-70)
EDITION OF 7-67 MAY BE USED
GPO 1977-778-944
6 of 7
Permanent repairs
The roadway could be shifted away from the river. Riprap slope armor would likely need to be
grouted and pinned to bedrock.
SITE 15 – MP 11.1
Observations
Approximately 480 feet of roadway washed out to centerline. Bedrock was observed in the
existing roadway prism and will likely dictate the elevation of the temporary roadway. There is
a right-of-way fence on the inboard side. The channel through this site is narrow and steep.
Temporary repairs
The grade could be lowered to tie into the elevation of the temporary repairs in Site 16. After
survey data is available, the site will be analyzed to determine if the temporary roadway
elevation is high enough for hydraulic stability.
Permanent repairs
The roadway could be shifted away from the river using a flatter horizontal curve. This will
likely require blasting into the tall rock slope on the inboard side. The vertical alignment of the
permanent repair may be adjusted also, since it appears the roadway could be lowered. A wall or
grouted riprap on the outboard side may be needed to obtain bench width if the roadway
alignment is maintained at pre-disaster location.
SITE 16 – MP 10.9
Observations
Approximately 200 feet of roadway washed out to centerline. The rock cut slopes at this
location exhibit appear likely to yield angular rock backfill. There is risk that bedrock may be at
located at shallow depth in the roadway prism at this site. There is a knob across the channel
from the roadway that restricts the channel width.
Temporary repairs
Based on preliminary observations, the grade could be lowered about 5 feet. The temporary
roadway grade will be verified using survey data collected this week. If the roadway alignment
will be shifted for permanent repairs, it is recommended to complete cuts to match final grade as
much as practical during temporary repairs. The knob across the channel from the roadway does
not appear to need removal at this time.
Permanent repairs
The goal will be to maximize the channel width by using a steep slope from the river up to the
roadway bench. Grouted riprap pinned to bedrock could be installed to armor the slope. The
horizontal and vertical roadway alignment could be adjusted at this site to improve both
hydraulic capacity and roadway geometry.
APPROVED FOR DISTRIBUTION
FORM PR-33 (REV. 5-70)
EDITION OF 7-67 MAY BE USED
GPO 1977-778-944
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Micah Leadford
Project Manager
FORM PR-33 (REV. 5-70)
Date
EDITION OF 7-67 MAY BE USED
GPO 1977-778-944