Trip Report 2024-07-30 WY NP GRTE 13(1) North Park Rd.pdf

158377846

TRIP REPORT

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661

REPORT DATE: September 23, 2024

TRIP DATE:

TO:

July 30, 2024

Kevin Gray, Project Manager

FROM:

Eric Lim, Geotechnical Engineer Michael Heck, Engineering Geologist

SUBJECT: Trip Report and Temporary Repair Recommendations WY NP GRTE 13(1) Repair North Park Road at Milepost 15.8 Grand Teton National Park, Wyoming

INTRODUCTION

This trip report presents notes of our observations during the field scoping trip in July 30-31, 2024. As requested, we have also included recommendations for temporary repairs.

PROJECT DESCRIPTION

A series of landslides have damaged the north-south aligned North Park Road in the vicinity of mileposts 16.5, 15.8, and 15.6. Based on review of available light detection and ranging (lidar) imagery of the vicinity, the landslide types appear to be rotational to earthflow in nature.

We understand the most active landslide is at milepost 15.8, where an approximately 200-foot long section is patched approximately once a year due to settlement and movement. We understand that several improvements to the slides have been made over the last 20 or so years, including drainage improvements, subexcavations, and pavement patching.

OBSERVATIONS

We visited the site the afternoon of July 30, 2024. We walked the project area from the turnout near MP 16.8 southward to the Jackson Lake Overlook turnout near MP 15.3. Some observation comments were based on verbal communication with Park maintenance staff and WFLHD construction staff present during the site visit. Our field notes are summarized in Table 1 below.

Table 1 - Scoping Trip Observations Summary

Estimated Milepost

Photo No.

Observations

16.67 1 Pavement damage reportedly within the last 2 years. Cause unknown.

16.64 2 Possible frost heave area.

16.56 3 Road damage and possible settlement from previous culvert repair.

This is at the north lateral margin of the MP 16.5 earthflow landslide based on lidar images.

16.53 4 Possible frost heave area.

16.49 5 Transverse crack and possible frost heave area.

16.47 6 Shift of edge of pavement and settlement shows past landslide movement. Approximate rate of movement is 1 ft per 10 years based on WFL Construction’s memory of last repair of culvert here.

16.45 7 Sandstone outcrop on east side of the road. This area is outside the apparent earthflow landslide based on lidar images.

16.31 8 Several steel horizontal drain pipes observed on east side of roadway. One pipe had a flow of approx. 1 gallon per minute.

Further east up the slope we observed a landslide headscarp.

WFLHD Construction reported 1000 ft of underdrain was constructed here. This area of the roadway has not been problematic for the Park since then.

16.31 9 Landslide headscarp observed ~100 yards east of roadway. A shoefly was reported to the west of the road (still visible in the lidar), when past landslide activity caused a re-route.

16.11 10 Transverse crack in pavement.

16.07 11 Transverse crack in pavement.

16.04 12 Transverse crack in pavement.

16.03 13 Longitudinal crack in northbound lane. Probable frost heave.

16.00 14 Transverse crack in pavement.

15.91 15, 16 North end of ~200-ft long asphalt patch. Note the lateral shift of the road to the west in Photo 14.

15.89 17 Middle of the most active landslide area. Note numerous asphalt patch layers on the embankment that have shifted laterally to the west.

15.82 18 South end of proposed temporary deep patch repair based on damage and movement observed in the road. Recommended temporary repair area length is approximately 500 ft in length.

15.82- 15.70 n/a Adjacent to the riprap buttress, the road appears to be in relatively good condition.

15.69 19 Thick pavement edge being undermined by erosion on the slope.

Estimated Milepost

Photo No.

Observations

15.68 20 Inclinometer casing from Geotech Report 12-04, dated 2004

15.61 21 Third major mapped landslide area appears relatively less active based on relative roadway smoothness.

Notes: Milepost locations were visually estimated from the NPS RIP website.

Photo 1 – Pavement damage near MP 16.67.

Photo 2 – Possible frost heave at MP 16.64.

Photo 3 – Road damage and possible settlement of previous culvert repair at MP 16.56.

Photo 4 – Possible frost heave at MP 16.53.

Photo 5 – Crack and possible frost heave at MP 16.49.

Photo 6 – Lateral shift of pavement at MP 16.47 at southern edge of MP16.5 Landslide.

Photo 7 – Sandstone outcrop on east side of road at MP 16.45.

Photo 8 – Old horizontal drains at MP 16.31.

Photo 9 – Landslide headscarp partially obstructed by trees at MP 16.31.

Photo 10 – Transverse crack at MP 16.11.

Photo 11 – Transverse crack at MP 16.07.

Photo 12 – Transverse crack at MP 16.04.

Photo 13 – Longitudinal crack at MP 16.03 facing south.

Photo 14 – Transverse crack at MP 16.00.

Photo 15 – Active slide area starting MP 15.91 facing south. Note lateral shift of road to west.

Photo 16 – Closeup of most active landslide area starting near MP 15.91 facing south.

Photo 17 – View of most active landslide area starting near MP 15.89 facing north.

Photo 18 – South end of active slide area standing at MP 15.82 facing N.

Photo 19 –Thick edge of pavement being undermined by erosion at MP 15.69 facing SE.

Photo 20 – Inclinometer casing from 2004 geotech report at MP 15.68 facing SE.

Photo 21 – Potential boring B-13 location at MP 15.61 facing N. Note relatively smooth road.

TEMPORARY RECOMMENDATIONS

We understand that construction is not planned until the year 2028. Based on the information provided, it appears likely that the most active portion of the landslide at MP 15.8 will continue to move causing vehicle damage and potential accidents. To mitigate the movement until the landslides can be studied in more depth and a preferred solution is selected, designed, and constructed, we offer the following recommendations for temporary repairs.

Temporary Operational Measures

Based on our observations during our limited site visits, the bumps created by the landslide movements can currently be safely driven over at lower speeds. Currently, there are “Road Damage Ahead”, “Bump” and “Rough Road” ahead signs, as well as signs indicating a slower 25 miles per hour speed limit. However, we observed many vehicles going approximately 45 mph or higher through this area, despite the signage.

During our scoping visit meeting with the Park on July 30, a suggestion was made that temporary rumble strips could help reduce speeds coming into this area. However, Park staff said that rumble strips were not preferred due to the loud noise and resulting disturbance to wildlife. We recommend contacting a Highway Safety Engineer for additional options for encouraging vehicles to slow down through the landslide areas.

Temporary Repairs

To help reduce the effect of differential settlement and/or lateral movement caused by the landslide, a deep patch could be used to smooth out the bumps in the more active landslide areas. A deep patch is a geosynthetic reinforced subexcavation that is typically 2 to 5 feet in depth below the pavement section. In our opinion, a 3-foot thick deep patch should be sufficient to bridge over the faster moving portions of the landslide and reduce maintenance needs in this location for several years. A design life of approximately 5 years is typical for deep patches.

The 3-foot thick deep patch should consist of a 3-foot deep subexcavation below the pavement section (hot mix asphalt surfacing plus aggregate base course). The subexcavation should be backfilled with Select Borrow with 4 layers of stabilization geogrid with a vertical spacing of 9 inches. A separation geotextile fabric should be placed along the base and side slopes of the subexcavation prior to backfilling. Also, an underdrain is recommended to promote drainage from the deep patch. An illustration of a deep patch cross section is shown in Figure 1 below. Additional details and specifications can be provided if requested.

Figure 1 - Full width deep patch cross-section.

CLOSING

Please contact Eric Lim at (360) 619-7826 or eric.lim@dot.gov with any questions regarding this memorandum.

CC: Katherine Alexander, Design Cyrus Bullock, Environment Geotechnical File