GM 44-21 Walla Walla South ERFO 2020 Geotech Memo Rev1.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

TO: Matt Miller Project Manager

FROM: Eric Lim Sr. Geotechnical Engineer

Robert Kraig Geotechnical Engineer

DATE: April 26, 2022

SUBJECT: Geotechnical Memo 44-21 (Revision 1) Geotechnical Recommendations Walla-Walla South - Umatilla Repairs 2020, Phase 1

OR FS ERFO 2020(1)-14(1)

Umatilla National Forest, Oregon

INTRODUCTION

This memorandum provides geotechnical recommendations for the Walla-Wall South – Umatilla Repairs 2020 project.

PROJECT DESCRIPTION

The project is located in northeast Oregon in the Umatilla National Forest, with the beginning of the project located approximately 34 miles driving distance (approximately one hour) east from Pendleton, Oregon, near Bingham Springs. Project Location Map and Project Vicinity Map are provided as Figures 1 and 2, respectively. The area underwent a widespread storm event that occurred prior to May 2020. The event caused damage to many sites located along the South Fork Umatilla River and portions of the road adjacent to Thomas Creek, a tributary to the South Fork Umatilla River. For the sites located along the South Fork Umatilla River up to about MP 3.53, the primary damage was caused by intense river flows that resulted in severe erosion of the embankments, which in turn resulted in undermining of the road to a complete loss of road at some locations. For the sites located adjacent to Thomas Creek between approximately MP 4.0 to MP 6.0, the primary damage took the form of debris flows over the road that originated on the slope above. An additional site, FSR 3738 MP 8.35, is located near Phillips Creek approximately 4.6 miles (direct distance) to the southeast of the

April 26, 2022 Walla-Walla South - Umatilla Repairs 2020, Phase 1 last site on FSR 3200. Damage incurred at these sites qualified them for assistance under the Emergency Relief for Federally Owned (ERFO) program and Western Federal Land’s (WFL) involvement in the project. The project includes 14 sites. Detailed Damage Inspection Reports (DDIR) were prepared to facilitate the ERFO response. The Geotechnical information contained in this memorandum is largely based on published information, the DDIRs, site visits by others, and limited survey and developed cross sections. It is our understanding that completing the survey for the project was not possible due to widespread fire emergencies in the area during the survey effort.

Three additional damaged sites have qualified to be covered under the ERFO program. Those sites are located to the north in southeast Washington and are not covered under this project. We understand that those sites and may be covered under a future effort.

Figure 1: Project Location Map

Figure 2: Project Vicinity Map

GEOLOGY

The project is located in the Umatilla Basin bounded generally by the Blue Mountains to the south and east and the Columbia River to the north. The major stream draining the local area is the Umatilla River.

An excerpt from the geologic mapping is provided as Figure 3. According to the mapping, the damage sites located on FSR 3200 up to about MP 3.53 are shown to be located on deposits of alluvium (Qal) of the South Fork Umatilla River. At approximately MP 4.0, where Thomas Creek feeds into the South Fork Umatilla River, the river direction turns to the southwest. The sites adjacent to Thomas Creek and south of MP 4.0 on FSR 3200 may or may not be over alluvium as it is not mapped there. It is not known what geologic mapped conditions are at the site located on FSR 3738 at MP 8.35 as it is located beyond the limits of the map.

The predominant rock formation in the vicinity of the project is Grande Ronde Basalt. Grande Ronde Basalt is part of the Miocene Columbia River Basalt Group and is comprised of bluish-black aphyric to sparsely plagioclase phyric lava flows. Grande Ronde flows make up more than 85 percent by volume of the Columbia River Basal Group. This rock weathers to form steep slopes and generally weathers to orange-brown and angular blocks. Differential weathering results in distinctive bench topography, where flow tops and basal breccias are marked by bands of trees. Grass-covered benches mark more resistant flow interiors.

Project area

Figure 3: Excerpt from Oregon Department of Geology and Mineral Industries, Open-File Report O-07-15, 1:24,000

Grande Ronde Basalt is separated into three magnetostratigraphic units on the basis of magnetic polarity as measured in the field by a fluxgate magnetometer. Based on the mapping the unit present along the FSR 3200 project corridor is either the Tgn1 or Tgr2.

Brief descriptions of the three mapped units (Qal, Tgn1, and Tgr2) present within the project limits are described below. Given the widespread presence of Grande Ronde Basalt, it is thought likely that it is present in some form at the the FSR 3738 MP 8.35 site.

Qal: Alluvium (Holocene) — Sand, silt, and gravel deposited on the channels and on the floodplains of modern streams and rivers. Generally unconsolidated and ranging in thickness up to a few meters or tens of meters at most. This unit was mapped almost exclusively by using digital soils data from NRCS.

Tgn1: N1 magnetostratigraphic unit (middle Miocene) — Flow-on-flow sequence of aphyric to sparsely plagioclase phyric lava flows. Overlies the R1 magnetostratigraphic unit and is overlain by the R2 magnetostratigraphic unit. The age of the N1 unit is between 15.9 ± 0.2 Ma and approximately 16.1 Ma (Baksi, 1989).

Tgr2: R2 magnetostratigraphic unit (middle Miocene) — Flow-on-flow sequence of aphyric to sparsely plagioclase phyric lava flows. Overlies the N1 magnetostratigraphic unit and is overlain by the N2 magnetostratigraphic unit. The age of the R2 unit is between 15.7 ± 0.3 and 15.9 ± 0.2 Ma (Baksi, 1989).

SITE CONDITIONS

As discussed earlier the project sites are located along the South Fork Umatilla River and high flow event(s) and saturated conditions caused damage. The individual sites are described below based on the DDIRs. Included in the descriptions is the status of the survey. Damage site photos are provided as an attachment.

FSR 3200 MP 1.26 (Photo 1) Essentially a debris removal effort with little to no geotechnical input required. No cross sections were obtained at this location.

FSR 3200 MP 1.30-1.36 (Photo 2) Rock outcrops and with deposits of colluvium (possible talus). Rock outcrops are visible. Rock strength is unknown. The DDIR photos show bank erosion with the road being largely unaffected. The DDIR recommends embankment reconstruction and placement of riprap on the streambank to minimize future erosion. The cross sections show that the cut slopes range from approximately 2:1 (V:H) to 1:1.33 (V:H).

FSR 3200 MP 1.38-1.44 (Photo 3) The DDIR shows loss of the stream bank with erosion extending to several feet into the travel way with a recommendation for embankment reconstruction using riprap lining the stream channel. The cross sections show slope cuts that were measured at approximately 1:1 (V:H) to 1:1.43(V:H). A steep cut into an outcrop of bedrock is visible in at least one of the DDIR photos.

FSR 3200 MP 1.52-1.69 (Photo 4) DDIR calls for embankment reconstruction using riprap in the channel. Slope range is about near vertical 7:1 to 1:1.13 (V:H), with the majority being into steep rock cuts.

FSR 3200 MP 1.96-2.00 (Photo 5) DDIR calls for embankment reconstruction using riprap in the channel. Slope range is about near vertical 2:1 to 1:2 (V:H), with the majority being into rock cuts. Cuts experiencing pop outs with small piles of colluvium at road grade.

FSR 3200 MP 2.02-2.14 (Photos 6 & 7) Road washed out for 260 feet and embankment partially washed out for 305 feet. DDIR calls for embankment reconstruction using riprap in the channel. No cross sections were available.

FSR 3200 MP 2.54 (Photo 8) Scour of road for about 318 feet and deposition of debris. Remove debris and repair scoured area. Essentially flat to 1:2 (V:H).

FSR 3200 MP 3.08 (Photo 9) Deep washout of road for about 193 feet. Reconstruction required. Slopes standing at about 1.33:1 (V:H).

FSR 3200 MP 3.23 (Photo 10) Embankment and outside edge of road lost due to scour. Damage is about 130 feet. DDIR calls for embankment reconstruction using riprap in the channel. No cross sections were available.

FSR 3200 MP 3.53 (Photo 11) Road washed out for about 236 feet. Embankment reconstruction using riprap in the channel.

Slopes are standing at range of about 1:1.6 to 1:2 (V:H). Possible colluvium or talus.

FSR 3200 MP 4.87 (Photo 12) Debris washed down from slope above. Length of affected area along road is about 45 feet.

Essentially a debris removal effort. No cross sections were available.

FSR 3200 MP 5.58 (Photos 13 & 14) Debris washed down from slope above. Length of affected area along road is about 126 feet.

Essentially a debris removal effort. No cross sections were available.

FSR 3200 MP 6.0 (Photo 15) Debris washed down from slope above. Length of affected area along road is about 55 feet.

Essentially a debris removal effort. No cross sections were available.

FSR 3738 MP 8.35 (Photo 16) Possible saturated embankment and piping of materials combined with slumping at the outside edge. Deep patch to restore the roadway to original grade. Reported that the damage may have already been filled in by an unknown entity—possibly a logging contractor. No cross sections were available.

SUBSURFACE CONDITIONS

A subsurface investigation was not performed for this project.

ANALYSIS

No analyses were performed for this project.

DESIGN RECOMMENDATIONS

The majority of the design for the damage sites are primarily hydraulic designs, with the exception to the FSR 3738 MP 8.35 damage site. We understand that most of the repair areas scoured by the stream will be repaired with riprap at a 1V:1.5H face angle. We understand that the FSR 3200 MP 2.54 site will be repaired with a 12-foot diameter aquatic organism passage (AOP) structure, requiring approximately 7 feet of grade raise on the roadway.

The loss of ground at FSR 3738 MP 8.35 will be repaired with a full-width deep patch. The deep patch is a 5.5-foot thick geosynthetic reinforcement application with close vertical spacing. The deep patch is intended to bridge over the damaged ground and reduce additional piping and loss of ground in the roadway.

It is likely that the debris visible on the roads at the damage sites is suitable for use in embankment construction under the FP Section 204 and likely will meet the requirements of

704.03 for unclassified borrow.

Recommendations are based on the existing conditions as determined by the existing cuts.

Cuts in rock are interpreted to be standing in the range of 2:1 to 1:1 (V:H) and cuts in soil (colluvium) are interpreted to be standing in the range of 1:1.3 to 1:2 (V:H). Although not mapped, colluvium is interpreted based on the angular nature of the material appearing in many of the photos.

CONSTRUCTION CONSIDERATIONS

Outcroppings of bedrock were visible in the photographs at many of the site locations. Rock strength rating is unknown. Some excavation into rock may be required, which could require hoe-rams, hydraulic breakers, etc. to perform.

No laboratory tests were performed. It will be the responsibility of the contractor to prove suitability of reused on-site or borrow materials.

MATERIAL SOURCES

The U.S. Forest Service (USFS) has two potential material sources identified. Limited information on these sources is as follows and in the attachments:

Source Location Notes Ruckle Rock Pit

(ID 23725)

Road No. N32. NW¼ of NW¼ of Section 25, Township 2N, Range 37E

Excavated hole on flat ground. Collects water in spring. Good crushing and stockpile site. Diced basalt, LA Abrasion test result 15%, loose unit weight 109 pcf, rodded unit weight 121 pcf.

Shimmie Pit 4

(ID 23726)

Road No. N31. SW¼ of Section 36, Township 2N, Range 37E.

Pit run.

REFERENCES

Madin, I.P and Gietgey, R.P., 2007, Preliminary geologic map of the Umatilla Basin, Morrow and Umatilla Counties, Oregon, Oregon Department of Geology and Mineral Industries, Open- File Report O-07-15, 1:24,000.

CLOSING

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

CC: James Tran, Design Sven Leon, Hydraulics Steve Morrow, Environment Geotechnical File

Attachments: Site Photos Material Source Info mailto:eric.lim@dot.gov

Ruckle Rock Pit

ID: 23725

Ruckle Warming Shelter nearby

Legend

200 ft

N

N