GM 09-18, OR FS ERFO 2016(1)-15(3), Umpqua Final Geotech Memo.pdf

158377846

M E M O R A N D U M Western Federal Lands Highway Division

610 E. Fifth Street Vancouver, WA 98661

DATE: April 4, 2018

TO: Helen Oppenheimer Project Manager

FROM: Eric Lim Geotechnical Engineer

SUBJECT: Geotechnical Memo 09-18 Geotechnical Recommendations Umpqua Repairs 2016 - 2017

OR FS ERFO 2016(1)-15(3)

Umpqua National Forest, Oregon

INTRODUCTION

In August 2017, the Western Federal Lands Highway Division (WFLHD) conducted a site reconnaissance to investigate damage that occurred at several locations within the Umpqua National Forest. These damaged sites were the result of large storm events in 2016 and 2017, which were subsequently reported to the Emergency Repair of Federally Owned (ERFO) Roads Program Manager for eligibility. At the request of the U.S. Forest Service, WFLHD provided technical assistance in preparation of the Damage Survey Reports (DSRs).

WFLHD will also design the repairs and administer the construction contract on behalf of the Forest Service.

The scope of work for these ERFO sites was limited to site visits and visual reconnaissance.

The site visits described in this memorandum were performed by Eric Lim (WFLHD Geotechnical Engineer), Helen Oppenheimer (WFLHD Project Manager), Sarah Belgard (WFLHD Highway Designer), and Dylan Hokanson (Forest Service Civil Engineer). Kent Steinhaus (WFLHD Hydraulics Engineer) visited several of the sites where hydraulics recommendations were needed. Additional information was added from follow-up site visit observations by Brian Collins (Sr. Geotechnical Engineer) and Nicholas Farny (Engineering Geologist) in March 2018. This memorandum contains our geotechnical observations and recommendations for design and construction.

PROJECT DESCRIPTION

The following sites were visited during the August 2017 site visit. A brief description of each site is provided in Table 1 – Site and Damage Descriptions. Approximate site locations are shown on Figure 1 – Vicinity Map.

Table 1 – Site and Damage Descriptions

Site Name Mile Post Damage Description Steamboat Creek Road 23.23 Slide debris on road interfered with drainage, causing substantial erosion of fill side of road.

Brownie Creek Road 0.17 High water eroded the fill on the sides of the 23-ft wide arch culvert. The culvert was pushed it off its foundation resulting in collapse of the culvert at its inlet, also compromising the embankment.

Junetta Creek Road 5.56 A plugged culvert caused water to overtop the road and erode the road and fill slope, causing a landslide of the road embankment.

Black Canyon Road 7.03 Landslide within embankment fill. Approximate 1 -ft settlement of fill slope and outside edge of traveled way, narrowing roadway.

Black Canyon Road 7.73 Landslide within embankment fill. Settlement and tension cracking of fill slope and outside edge of traveled way.

Black Canyon Road 8.62 Landslide within embankment fill Traveled way has settled about 4 ft.

Green Butte Road 7.27 Landslide encompassing entire fill embankment, removing about 40' length of the road for its entire width.

South Fork Cow Creek Road 6.37 Plugged culvert diverted stream down the road, causing a large fill-side erosion. Approx. 100' of road is narrowed, closing road to public.

Jonnie Springs Road 0.81 Deep seated slide, road has settled about 6 ft for a length of 50 ft. The road is within the limits of a larger scale landslide. This site has already had some repairs made by a timber company using the road.

Figure 1 – Vicinity Map

GEOLOGY

The National Geologic Map Database (USGS, 2018) was used to search for geologic mapping of the sites. The mapping of the sites are summarized in Table 2 – Geologic Mapping below.

Table 2 – Geologic Mapping

Site Name Mile Post Mapped Geology

Steamboat Creek Road

23.23 Tub, basaltic lava flows - Basaltic and basaltic andesite lava flows and breccia; grades laterally into rare bedded palgonitic tuff and breccia (Walker & MacLeod, 1991). Also adjacent to Tib, Basalt and andesite intrusions (Pliocene, Miocene, and Oligocene?) - Sills, plugs and dikes of basaltic andesite, basalt, and andesite. Mostly represents feeders, exposed by erosion, flor flows and flow breccias of units Tba and Trb (Walker & MacLeod, 1991)

Brownie Creek Road

0.17 Toeb, Basalt, basaltic andesite, and andesite flows (lower Oligocene to upper Eocene) (Murray & Kays, 2001)

Junetta Creek Road

5.56 Tub, basaltic lava flows - Basaltic and basaltic andesite lava flows and breccia; grades laterally into rare bedded palgonitic tuff and breccia (Walker & MacLeod, 1991)

Black Canyon Road

7.03 Tba, older basalt flows - black, coarse, textured basalts (Wilkinson, et al., 1941)

Black Canyon Road

7.73 Trh, Rhyolite - white to buff rhyolite flows, tuffs, and breccias (Wilkinson, et al., 1941)

Black Canyon Road

8.62 Trh, Rhyolite - white to buff rhyolite flows, tuffs, and breccias (Wilkinson, et al., 1941)

Green Butte Road

7.27 Ki, Silicic intrusive rocks (Cretaceous and Jurassic) (Murray & Kays, 2001)

South Fork Cow Creek Road

6.37 am, amphibolite (Jurassic or older) (Murray & Kays, 2001)

Jonnie Springs Road

0.81 Tba, older basalt flows - black, coarse, textured basalts (Wilkinson, et al., 1941)

SITE CONDITIONS

Table 3 summarizes the observations at each site during the reconnaissance. Site photographs are included in Appendix A.

Table 3 – Site Conditions

Post Observation Notes

Steamboat Creek Road

23.23 A shallow surficial skin slide appeared to occur in the slope above the road, removing all vegetation. Loose soils appear to be collecting at the bottom of the slope blocking the ditch and redirecting water to the eroded area across the road. The cut-side slope measured approximately 60 feet in height and varied from approximately 51 degrees from horizontal near the bottom 7 feet, to 42 degrees from 7 to 32 feet above the road, to 56 degrees from 32 to 60 feet as measured with a laser range finder. The majority of the slope consisted of a brown moist silty sand with gravel. At a height of approximately 32 feet above the roadway, there appeared to be a finer-grained layer several feet in thickness.

The downslope side of the roadway embankment appears to have been eroded away by the water from the blocked ditch. This washout exposed a silty sand with gravel soil. The sides of the channel formed by the washout consist of loose silty sand soils with some vegetation and roots. A vertical headscarp on the order of 5 feet remains, and soil was bermed above it to apparently prevent cars from driving off the edge. The slope below the headscarp was approximately 36 degrees from horizontal to approximately 15 feet below the roadway, flattening out to approximately 27 degrees below.

Excavation for the MSE wall will likely encounter loose grading to dense silty sand with gravel soils and possibly reach bedrock back into the cut.

Across the roadway, the bedrock appears to be a tan to light gray, weathered tuff, which could likely be excavated several feet before refusal.

Just to the south of the washout, there is an existing MSE wall that was reportedly constructed to repair a similar damage event sometime in the past. The wall is an approximately 18-foot high galvanized wire faced wall, likely with welded wire reinforcement (Hilfiker tag on facing) at 2 feet vertical spacing. The reinforcement length was not noted on the tag.

Post Observation Notes

Brownie Creek Road

0.17 This site is a partially failed corrugated metal arch culvert approximately 23 feet in diameter. Approximately half of the length of the culvert along with all the backfill and roadway fill had been removed. The soils were reported to have been washed out of the sides of the culvert due to high flows. The concrete foundation is placed on top of strong basalt or andesite rock that comprises the channel bottom and was not undermined. The metal appears to have been corroding due to poor quality backfill (i.e., high fines content and/or organics) in direct contact with the steel. Nearly all of the backfill was removed to close the roadway to traffic.

Junetta Creek Road

5.56 This erosion and landslide appears to have been caused by a plugged culvert allowing water to overtop the roadway and washout the downslope embankment soils in two major channels, leaving a small spine of soil in between. The exposed soils appeared to be a silty sand with gravel, in a loose to medium dense condition. Bedrock was not directly observed, although the washout appears to have been stopped from eroding further back into the slope by encountering boulders or bedrock in the slope.

Below the near vertical headscarp, the failed slope is on approximately 45 degrees from horizontal and facing southwest. The slope above the roadway appears to consist of very loose to loose silty sand with gravel at an angle of 40 degrees and is moderately vegetated with slightly pistol-butted trees.

Black Canyon Road

7.03 The shoulder settled on the order of 1 foot due to a landslide. There was no apparent overflowing of the cut side ditch; the cause was likely oversaturation of loose embankment soils. Narrow tension cracks were observed at the time of our visit.

Black Canyon Road

7.73 A series of tension cracks on the order of 6 to 12 inches in width were observed in the shoulder embankment soils due to landsliding of the road embankment. No signs of a ditch overtopping were apparent during our visit; the cause was likely oversaturation of loose embankment soils.

Black Canyon Road

8.62 Landslide of the embankment fill resulted in settlement up to approximately 4 feet, creating a vertical scarp along the edge of the roadway. Tension cracks were observed within the slide mass, but the soil did not wash away. There was no apparent overflowing of the cut side ditch; the landslide was likely caused by oversaturation of loose embankment soils.

We performed a drive probe test using a Forest Service drive probe. Data is in Appendix B. The downslope angle is approximately 42 degrees and the upslope angle is approximately 2V:1H. The soil type appears to be a silty sand with gravel.

Post Observation Notes

Green Butte Road

7.27 The entire roadway failed here in an arcuate flow slide. The material appears to behave similar to decomposed granitics, which behave like a strong cemented sand until saturated. Once saturated, the cementation is lost and the material mobilizes. The Forest Service has previously performed drive probe testing here and determined that the depth of disturbed material is approximately 19 feet below the road surface.

South Fork Cow Creek Road

6.37 The slide at this site appears to have been caused by a plugged culvert and water overflowing from the cut side ditch. The water crossed the road and created a large wash out the downslope side of the embankment. The soils eroded consisted of silty sand with gravel, but appeared to stop when the water encountered a closely jointed and highly fractured metamorphic rock, interpreted to be amphibolite based on the geologic mapping.

The outer 2 to 3 feet of rock appears to be excavatable, rippable or breakable using large excavators with rock teeth and/or hoe-rams or bulldozers with ripping shanks due to the close fracturing to create limited width benches. The rock also dips back into the slope providing some stability.

Jonnie Springs Road

0.81 Upon arrival, the roadway had been re-graded by a local timber company to restore their access. The landslide here was documented by Forest Service geotechnical engineers with test pit explorations and site reconnaissance (see Appendix C). The landslide appears to be a localized failure within a larger ancient landslide that extends several hundred feet both upslope and downslope of the road. The FS recommended additional explorations down the slide system to better characterize the depth and mechanism of the slide.

Two borings were drilled by WFLHD in December 2017 to depths of approximately 50 to 55 feet. Inclinometers and vibrating wire piezometers were installed to monitor the slide for movement and water levels.

Multiple springs in the cut slope above the landslide were observed during a follow-up site visit in March 2018.

JONNIE SPRINGS BORINGS

The two borings were advanced at the Jonnie Springs Road site to determine the depth(s) of the slide plane(s), rate of movement, and groundwater levels. Borings JSR17-01 was installed approximately 90 feet downslope of the edge of the roadway, and boring JSR17-02 was installed near the eastern edge of the roadway in the approximate locations shown on Figure D-1, Boring Locations Map.

Both borings were completed with 2.75-inch diameter inclinometer casing, with a Slope Indicator vibrating wire (VW) piezometer strapped to the outside of the casing. Slope Indicator

VW Miniloggers were attached to the VW piezometers for data recording. The borings were advanced by hollow-stem auger using a track-mounted drill rig and logged by a geotechnical engineer from DJ&A/Terracon under contract to WFLHD. Samples were obtained at 2.5-foot intervals in the upper 20 feet, then 5 feet thereafter. HQ rock coring was performed once rock was encountered. Samples were transported to WFLHD for additional visual identification.

Boring logs are included in Appendix E.

The borings generally encountered firm to very stiff clays of various plasticity, dense clayey sand, and very dense poorly graded sand in the upper 35 and 20 feet in borings JSR17-01 and JSR17-02, respectively. These sediments were interpreted to be residuum, or bedrock materials that have weathered completely to soil. Below the residuum, the borings encountered what we interpret to be tuff bedrock with fair to excellent Rock Quality Designation (RQD).

The soil and rock samples and boring data did not readily identify the shear zones at Jonnie Springs Road. It is likely that the slide plane is within the upper 10 to 20 feet based on the increasing blow count and RQD values with depth. Determination of the actual slide plane depths will depend on the inclinometer data performed on a quarterly basis.

DESIGN RECOMMENDATIONS

The repairs for the above-described damage will range from simple regrading/realignment of the roadway to construction of Special Rock Embankments (SRE) and Mechanically Stabilized Earth (MSE) walls. The intent of the ERFO program is to replace the roadway in-kind, without substantial betterments unless a cost-benefit can justify a structure or improvement to the pre-disaster conditions. One such justifiable betterment is the construction of a SRE or MSE walls over steep terrain where regular embankment slopes would not catch until very far down the slope. Access to the lower reaches of the slope and the large volumes of fill could be reduced with special rock embankment material that could be steepened up to 1V:1.25H or near-vertical MSE walls. Table 4 provides the repair recommendations for each site.

Table 4 – Repair Recommendations

Site Name Mile Post Recommended Repair

Steamboat Creek Road

23.23 MSE retaining wall on fill slope side due to steep existing slopes and failure area. Match adjacent wire-facing wall type for consistent aesthetics. Place gabion baskets against excavated cut slope to buttress over-steepened toe and reduce surficial slides that block the ditch.

Brownie Creek Road

0.17 Replace failed culvert with 23-ft wide structural plate arch with aquatic organism passage design. Design foundations for direct support on strong basalt/andesite rock. A factored bearing resistance of 10 ksf may be assumed for support directly on the rock. Install inlet protection to keep water from eroding the face of the culvert and infiltrating along the slides and weakening fill.

Junetta Creek Road

5.56 Reconstruct roadway with special rock embankment to limit soil embankment volumes. Replace culvert and add a downspout to reduce future erosion of the embankment.

Black Canyon Road

7.03 Realign the road, shift into hillside and change grade (as practical) to improve drainage. Replace 18" CMP culvert.

Black Canyon Road

7.73 Determined ineligible for ERFO funding.

Black Canyon Road

8.62 Excavate to a suitable foundation estimated at 10 feet below the roadway and construct keyed riprap 2 feet below the shear plane.

Construct keyway 2 feet below the shear plane in stable soils.

Green Butte Road

7.27 Excavate to a suitable foundation estimated at 19 feet below the roadway and construct keyed riprap 2 feet below the shear plane.

Install groundwater interceptor drain system with gravity flow discharge.

South Fork Cow Creek Road

6.37 Excavate to limited width benches into the slope and construct special rock embankment to reconstruct roadway. Repair the scour in the roadway and replace existing 24" culvert with a 36" culvert to accommodate natural stream debris.

Jonnie Springs Road

0.81 Install a 5- to 7-foot deep underdrain along the inside of the cut-side ditch through this area to capture spring water and keep it out of the roadway embankment and landslide area below the road. Discharge the underdrain in the low area below the road about 100 feet past the landslide.

CONSTRUCTION CONSIDERATIONS

The requirements of the Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (FP-14) will apply to these projects. FP-14 should be amended with Special Contract Requirements (SCR) using the following SCR from the Library of Specifications (LOS) for geotechnical considerations:

• 201 – Clearing and Grubbing

• 204 – Excavation and Embankment

• 253 – Gabion and Revet Mattresses

• 255 – Mechanically-Stabilized Earth Walls

• 257 – Contractor-Designed Retaining Walls

• 703 – Aggregate

• 705 – Rock

The fill-side retaining wall on Steamboat Creek Road will be contractor-designed. The contractor should follow the requirements of both sections 255 and 257 listed above. The following soil parameters may be assumed for design:

Table 5 – MSE Wall Soil Parameters

Material Friction Angle Cohesion Unit Weight Foundation Soils 32 0 120 Retained Soils 32 0 120 Reinforced Fill 34 0 125

For global stability, the minimum grid length should be at least 75 percent of the wall total wall height, including embedment, from face to back of grid. The minimum embedment should be 4-feet due to the steepness of the ground in front of the wall. Alternatively, the wall embedment could be reduced to 2 feet if the base of the wall is setback at least 4 feet horizontally from the slope face. A uniform traffic surcharge of 250 psf should be added as a live load. Seismic design is not necessary.

Explorations were not performed at these sites, except for Jonnie Springs Road. Bedrock was observed at South Fork Cow Creek in the eroded failed slope areas and will be encountered during excavation for the benches for the SRE. Unweathered rock was exposed in the stream bed surface at Brownie Creek. Bedrock and/or boulders are likely to be encountered at the other sites based on the outcrops across the roads and limited depth of failures. The contractor should be prepared to use large excavators with rock teeth, bulldozers with ripping shanks, and/or hydraulic breakers (e.g., hoe-rams) to excavate into the rock as required by design and specifications. It is our understanding that blasting will not be permitted for these construction projects.

Temporary slope cuts will be the responsibility of the contractor and depend on the soil and rock conditions encountered. Shoring is not expected to be necessary, but will be the responsibility of the contractor to determine the need for shoring and supply as necessary per subsection 255.03.

The contractor should also control surface water to prevent directing runoff into the construction site and the failed areas. The use of temporary diversion berms and/or trenches, erosion control best management practices (BMPs), and staged construction methods could be utilized as needed and determined by the contractor.

Material Sources

The following quarries were noted during our site visits. Determination of the eligibility of these sources for these projects should be coordinated with the Forest Service:

Table 6 – Potential Material Sources

Site Name Lat./Long. Recommended Repair Quarry Near Cow Creek

42.766890 -122.927804

Basalt exposed in the eastern cut of the pit. Area mapped as Toeb, basalt, basaltic andesite, and andesite flows, lower Oligocene to upper Eocene (Murray and Kays, 2001)

Quarry Near Green Butte

42.886725 -122.970811

Rock type not identified. Area mapped as Qd, quartz diorite, intrusive masses, dikes and related rock (Wilkinson, et al., 1941)

No testing was performed on these sources. However, they appeared to be potential close proximity sources for special rock embankment materials, rip rap, aggregate, and various soil borrow.

CLOSING

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

CC: Mark Martini, Highway Designer Brian Collins, Sr. Geotechnical Engineer Geotechnical File

Attachments: Appendix A: Site Photographs A-1 to A-44 Appendix B: Black Canyon Road MP 8.62 Drive Point Data Appendix C: Forest Service Field Visit Memo for Jonnie Springs Road

Appendix D: Boring Locations Map Appendix E: Field Classifications for Soil and Rock Unified Soil Classification System Soil Descriptive Terminology Rock Descriptive Terminology Boring Log Legend Boring Logs JSR17-01 to JSR17-02

REFERENCES

Murray, R.B., and Kays, M.A., 2001, Geologic map of the Richter Mountain quadrangle, Douglas and Jackson Counties, Oregon, Oregon Department of Geology and Mineral Industries Geological Map Series GMS-103, scale 1:24,000.

Walker, G.W., and MacLeod, N.S., 1991, Geologic map of Oregon, U.S. Geological Survey, Map Scale: 1:500,000

Wilkinson, W.D., Allen, J.E., Lowell, W., Lowry, W., Hutchinson, M., Harper, H., Littleton, R., Mead, R., and Jones, S., 1941, Reconnaissance geologic map of the Butte Falls quadrangle, Oregon, Department of Geology and Mineral Industries Quadrangle Map 2, scale 1:96,000.

USGS, 2018, National Geologic Map Database, https://ngmdb.usgs.gov/mapview/, website accessed March 14, 2018.

Federal Lands Highway, FP-14, Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, U.S. Department of Transportation, Federal Highway Administration mailto:Eric.Lim@dot.gov https://ngmdb.usgs.gov/mapview/

APPENDIX A

Site Photographs

Photo A-2, Steamboat Creek Road, uphill slope.

Photo A-1 Steamboat Creek Road site, view facing north.

Photo A-4, Steamboat Creek Road, slide scarp facing north.

Photo A-3, Steamboat Creek Road, view of slide area facing down to the west.

Photo A-6, Steamboat Creek Road, boulders used to block off the edge of the MSE wall.

Photo A-5 Steamboat Creek Road, nearby wire faced MSE wall.

Photo A-8, Closeup of rock outcrop north of Steamboat Creek Road Failure.

Photo A-7, Outcrop of rocks north of the Steamboat Creek Road failure area.

Photo A-10, Brownie Creek Road, culvert foundation is set directly on basalt/andesite rock.

Photo A-9, Brownie Creek Road, damaged culvert facing north.

Photo A-12, Junetta Creek Road, failure area facing west.

Photo A-11, Junetta Creek Road, failure area facing northwest.

Photo A-14, Black Canyon Road MP 7.03, failed shoulder/embankment facing southwest.

Photo A-13, Black Canyon Road MP 7.03, facing south.

Photo A-16, Black Canyon Road MP 7.03, facing north.

Photo A-15, Black Canyon Road MP 7.03, narrow tension crack.

Photo A-18, Black Canyon Road MP 7.73, middle crack facing northwest.

Photo A-17, Black Canyon Road MP 7.73, southern crack facing northwest.

Photo A-20, Black Canyon Road MP 7.73, rock outcrop on uphill side of road.

Photo A-19, Black Canyon Road MP 7.73, northern crack facing northwest.

Photo A-22, Black Canyon Road MP 8.62, steep slope below embankment.

Photo A-21, Black Canyon Road MP 8.62, facing south.

Photo A-24, Green Butte Road, facing south.

Photo A-23, Black Canyon Road MP 8.62, drive probe testing.

Photo A-26, Green Butte Road, facing west.

Photo A-25, Green Butte Road, facing southwest.

Photo A-28, Green Butte Road, facing east.

Photo A-27, Green Butte Road, road subgrade closeup.

Photo A-30, Green Butte Road, facing north.

Photo A-29, Green Butte Road, facing northwest.

Photo A-32, South Fork Cow Creek, facing west.

Photo A-31, South Fork Cow Creek, facing west.

Photo A-34, South Fork Cow Creek, facing down to the north.

Photo A-33, South Fork Cow Creek, facing down to the northwest.

Photo A-36, South Fork Cow Creek, facing down to the east.

Photo A-35, South Fork Cow Creek, facing east.

Photo A-38, South Fork Cow Creek, closeup of fractured closely jointed rock.

Photo A-37, South Fork Cow Creek, facing south up the slide. Note erosion stopped by rock.

Photo A-40, South Fork Cow Creek, closeup of rock.

Photo A-39, South Fork Cow Creek, closeup of rock.

Photo A-42, Jonnie Springs Road, view of upslope area, facing west.

Photo A-41, Jonnie Springs Road, temporarily repaired road.

Photo A-44, Jonnie Springs Road, view of rock buttress.

Photo A-43, Jonnie Springs Road, view of downslope area facing east. Note sidescarp between two logs on the right.

APPENDIX B

Black Canyon Road MP8.62 Drive Point Data

CONSTRUCT ABLITY

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APPENDIX C

Forest Service Field Visit Memo for Jonnie Springs Road

FIELD VISIT MEMO

USDA - Forest Service, Region 6 & 10 Engineering, Geotechnical & Dams Services Edith Green Wendell Wyatt Federal Building, Portland, Oregon

DATE: May2, 2017

TO: Umpqua NF Engineering- Steve Marchi, Forest Engineering Staff Officer

FROM: Jonathan Berry, P.E., Geotechnical Project Engineer

SUBJECT: DRAFT Preliminary Geotechnical Site Assessment of Landslide on FS road 1810

A request was made by the forest engineering staff to the R6 Geotechnical group to provide geotechnical assistance and perform an initial site visit to evaluating a slide at MP 0.9 on the FS 1810 road near Tiller, OR. This is a preliminary site assessment of the landslide that occurred during the ERFO event the winter of 2016/17. Jonathan Berry, R6 Geotechnical Project Engineer, met Steve Marchi Forest Engineering Staff Officer, Mike Karr, Supervisory Engineering Equipment Operator, Amber Nelson, Archeologist, and Amy Rusk, Tiller Ranger District Hydrologist. Equipment on-site was a Case CX225 excavator.

Introduction

The Umpqua National Forest is located in southern Oregon’s Cascade Range. The area near the landslide is located near Tiller, between Crater Lake and Roseburg OR. The site is located at Latitude 42.989370° N, Longitude -122.861920°W.

Annual average precipitation in the area is typically around 40 in/year. The closest Snotel site found was the Toketee Airstrip Snotel site area which indicated that the area received approximately146% above the average, and 152% above the median value (figure 1, NRCS, 2017) between October, 2016 and April, 2017, contributing to the observed displacement on the slide at MP 0.9.

R6 & 10 Geotechnical & Dams Services, April 27, 2017 Draft Umpqua NF ERFO Draft Site Visit Report Road 1810 Landslide

Figure 1 Snotel site showing precipitation accumulation vs the average accumulation since October, 2016

The geology is diverse, with multiple contacts within the general vicinity of the landslide, but predominately includes volcanic deposits originating from Mount Mazama and western cascade volcanic rocks (USGS, 1982). There were also many signs of instability within the general vicinity of the most recent displacement. Signs of instability included multiple areas of jack strawed trees (photo 1), and hummocky terrain near the area of instability. This larger area of instability manifested in the form of creep are not the focus of this report and are moving at what appear to be relatively slow rates, but is significant in understanding the overall stability and consequences of remedial action on the landscape. Providing proper drainage for the road and maintaining the drainage features including ditches and culverts appears to be the most cost effective management approach for these areas, although continued potential for movement is high. Significantly changing drainage patterns could adversely affect the stability in other locations. The area of potential instability is outlined in the google earth image, based on professional judgement and review of google earth images (figure 2). If LiDAR data is available for the area, the area should be re-evaluated with better topographic data to outline the area of potential instability.

Both overhead electrical lines, and buried phone line providing utilities to homes beyond the slide were present. The overhead electrical line did not appear to be compromised, but does pose a hazard for construction equipment and construction activities. The buried electrical line was compromised at one point, and further landslide movement could damage the line further if still in use.

Figure 2. Aerial view with large area of instability outlined. Location of localized landslide is identified with the marker.

Site Specific discussion

Specific to the slide at MP 0.9, water was ponding on the surface at multiple locations upslope of the road (photo 2). Two investigation holes were dug with the excavator upslope of the road on relatively gentle terrain. Both holes, dug perpendicular and across the lateral scarp, showed what appeared to be landslide deposits overlying what appeared to be an intact weathered tuff deposit.

Ponded water was visible near the location of test pit 1 & 2 (figure 3). Test pit 1 & 2 identified fully saturated predominately organic silty soil matrix with some sand and gravel containing basalt clasts that were cobble to boulder sized, up to 18” in diameter. There was very little shear capacity of the predominately silty material. As the test pit was dug, the excavator sunk approximately 2’, and the side walls of the hole produced significant amount of flowing water (estimated at approximately 5 gallons per minute) and the side walls caved in shortly after initial excavation.

Figure 3 Drawing showing approximate location of drainage features, ponded water and slide. Drawing not to scale.

Potential to capture water here to remove water from slide area

Significant amount of water running down ditch to HDPE

Test Pit 3

Test Pit 1

Test Pit 2

Overland Flow

Approximately 5-6 ft below the ground surface was a thin ash layer (approximately 3” thick), with saturated red clay material below the ash layer. The red clay was approximately 2’ thick.

Directly below the red clay layer was silicic ash flow tuff layer (Figure 4. Figure 4 does not show the 3”ash layer). The bottom of this deposit was not located, and is of variable thickness in mapping done by Smith and others (USGS, 1982). The deposit was moist to dry to the touch, indicating that the saturated red clay was acting as an aquitard, or a layer that is impermeable.

It appeared that the slip plane was near the 2’ thick red clay deposit in the area above the road. A third test pit was dug in the road prism as well. In this hole, the 3” layer of ash was identified, but the lower ash deposit was not located. It appears that there is more vertical displacement within the road template, which may be an indication that there was more vertical movement relative to the location of holes 1 and 2, and that the slip plane is lower in this area than what was assumed based on visual inspection of holes 1 and 2.

Figure 4 Log of test pit 1 and 2 within slide. The 3” ash layer was not well defined in the slide mass. See photo 6 for cross section outside the active slide.

Figure 3 Geologic map showing contacts in the vicinity of the landslide

Figure 5. Topographic map showing approximate location of 24" culvert and slide

Approximate location of slide

Location of 24”

CMP

Potential location to divert overland flow

Short Term Stabilization alternatives.

The predominant driver of this slide is groundwater, coupled with low friction angle material with very little cohesion in the saturated condition. Figure 3 shows a large overland flow area above Forest Service Road 2810-105, with a 24” CMP concentrating water into the area of the slide. The culvert was flowing nearly ½ full on April 20. This water continues to saturate the slide mass, contributing to the instability. As seen during the investigation, trenching and installing drainage will be difficult since the slide mass is acting more like a fluid than a soil. To mitigate this, the water coming out of the 24” CMP could be captured and diverted to a location below the road (Figure 5). An ideal location to divert the water was not identified since there were signs of instability across much of the landscape, but diverting water to the drainage to the east of the slide appeared make the most sense short term. This would likely reduce the water content in the slide area significantly, allowing for installation of underdrains to capture the water before it enters the slide mass.

If water is removed from the site by capturing the water in the culvert and diverting it to a relatively stable location below the road prism, the forest could rebuild the road template for summer access, likely between June and September, but dependent on precipitation) but the slide will likely continue to move in the winter months once precipitation increases and it becomes saturated again. The road will likely require the reinstallation of culverts sheared when the landslide moved, and will require frequent monitoring and blading. More permanent installation of drainage, and a structural solution to stabilize the road prism is likely needed as a long term solution.

There was also a significant amount of water coming out of the cutbank to the east of the slide that was draining back to an HDPE pipe and into the slide. If the source of the water is mitigated by diverting the water in the 24” pipe on road 2810-105, this area likely will dry in the short term, but re-grading the road and ditch to divert the water away from the active slide may be needed for short term stability. For long term stability, diverting this water away from the active slide should be part of the overall site grading plan, keeping in mind the potential to destabilize another area.

Long Term Stabilization Needs.

Long term solutions likely need to include permanent drainage of the site as well as a structural component. Installing a French drain system above the slide and diverting that water to a relatively stable channel to lower the groundwater table in the slide mass appears to be a good long term mitigation for the slide, but the slip plane within and below the road prism is unknown.

For this reason, the site should be drilled within and below the road prism to determine where the slip plane exists. The overall landscape and instability seen in the area is a concern, and it appears that there may be a larger area of instability included in a historic slide.

There is likely a relatively shallow slip plane, likely within 30 ft of the ground surface, but there may also be a deeper seated slip plane that could be up to 100 ft deep and may be sliding on another geologic contact. Both piezometers and inclinometer tubes should be included in the investigation to identify the slip plane. For the shallower movement, drilling should be to a depth of 40 ft. To better understand the potential for larger sale movement, ideally a hole up to 100 ft, would be ideal. Continued movement of the slide may not occur immediately, therefore it may take another wet season before the slip plane depth is determined.

Once the location of the slip plane is determined, possible mitigation may include installing a keyed trench using angular riprap that would be installed within the road prism and intersect the slip plane.

Understanding where the slip plane is critical to determining a viable long term solution and to perform proper stability analysis of the site. The displacement on the surface suggest that it is a relatively shallow slide, but if the slip plane is not intersected, a key riprap trench could surcharge rather than stabilize the slide.

Other possible mitigations include micropiles, but micropiles depend on soil arching, and based on the saturated conditions and the lack of shear capacity of the soil, this is not a recommended fix for this site.

Over-excavating the entire slide mass, placing a drain, and reinstalling the soil, reinforcing it with geogrids may also be a viable alternative to stabilize the current movement. Stabilizing the larger land mass that appears to be moving is not financially viable.

References

Google Earth Image, April, 2017

Oregon Department of Geology and Mineral Industries (DOGOMI) http://www.oregongeology.org/geologicmap/ April, 2017.

USGS, 1982. Smith, et al, Preliminary geologic map of the Medford 1 degree by two degrees quadrangle, Oregon and California http://pubs.er.usgs.gov/publication/ofr82955

NRCS, 2017 https://www.wcc.nrcs.usda.gov/snow/snow_map_beta.html Station 1044 http://www.oregongeology.org/geologicmap/ http://pubs.er.usgs.gov/publication/ofr82955 https://www.wcc.nrcs.usda.gov/snow/snow_map_beta.html

Appendix A Photos:

photo 1 View of jack strawed trees in the vicinity of the active landslide

Photo 2 View of overturned tree and saturated conditions below root ball

Photo 3 View of right lateral scarp looking south, or downslope

Photo 4. View of groundwater table within landslide deposit

Photo 5 View of hole 1. Note saturated soil conditions above the red clay layer.

Photo 6View of hole 2 with material slumping in at the bottom of the hole

Photo 7. View of soil profile in hole 1

Photo 8 View of road showing vertical displacement

Photo 9 View of road template showing vertical and horizontal displacement.

Photo 10 View of water in ditch flowing back to active slide area and HDPE pipe

APPENDIX D

Boring Locations Map

Western Federal Lands Highway Division 610 East Fifth Street Vancouver, WA 98661

Project No. BORING LOCATIONS MAP FigureOR FS ERFO 2016(1)-15(3) Scale

JONNIE SPRINGS ROAD

UMPQUA REPAIRS 2016-2017

UMPQUA NATIONAL FOREST, OREGON

B-1

NONE

File Name:

FIG B-1, BORING LOC MAP

Date:

MAR 2018

N

BH17-01

BH17-02

MAP DATA: GOOGLE MAPS, 2018

APPENDIX E

Field Classifications for Soil and Rock Unified Soil Classification System

Soil Descriptive Terminology Rock Descriptive Terminology

Boring Log Legend Boring Logs JSR17-01 to JSR17-02

SOIL DESCRIPTIVE TERMINOLOGY

CONSISTENCY OF COHESIVE SOILS

SPT N-Value (blows/ft) Consistency Field Identification

0 - 1 Very Soft Easily penetrated several inches by first

2 - 4 Soft Easily penetrated several inches by thumb

5 - 8 Firm Moderate effort required to penetrate several inches by thumb

9 - 15 Stiff Readily indented by thumb but penetrated only with great effort

16 - 30 Very Stiff Readily indented by thumbnail

> 30 Hard Indented with difficulty by thumbnail

RELATIVE DENSITY OF

COHESIONLESS SOILS

SPT N-Value (blows/ft) Relative Density

0 - 4 Very Loose

5 - 10 Loose

11 - 30 Medium Dense

31 - 50 Dense

> 50 Very Dense

PARTICLE SIZE

Term Sieve Size Boulder > 12” (>300mm)

Cobble 3” - 12” (75mm - 300mm)

Gravel – coarse ¾” - 3” (19mm - 75mm)

Gravel – fine #4 - ¾” (4.75mm - 19mm)

Sand – coarse #10 - #4 (2.00mm - 4.75mm)

Sand – medium #40 - #10 (0.425mm - 2.00mm)

Sand – fine #200 - #40 (0.075mm - 0.425mm)

Silt & Clay < #200 (<0.075mm)

MOISTURE CONTENT

Dry Dusty, dry to the touch

Moist Damp, but no visible free water

Wet Visible free water, saturated, over optimum

ROCK DESCRIPTIVE TERMS

ROCK WEATHERING

Field Identification Term Crystals are bright. Discontinuities may show some minor surface staining.

No discoloration in rock fabric. Fresh

Rock mass is generally fresh. Discontinuities are stained and may contain clay. Some discoloration in rock fabric.

Slightly Weathered

Significant portions of rock show discoloration and weathering effects.

Crystals are dull and show visible chemical alteration. Discontinuities are stained and may contain secondary mineral deposits.

Moderately Weathered

Rock can be excavated with geologist’s pick. All discontinuities exhibit secondary mineralization. Complete discoloration of rock fabric. Surface of core is friable and usually pitted due to washing out of highly altered minerals by drilling water.

Highly Weathered

Rock mass is completely decomposed. Original rock “fabric” may be evident. May be reduced to soil with hand pressure. Decomposed

DISCONTINUITY SPACING ROCK QUALITY DESIGNATION (RQD)

Spacing (in) Spacing Term RQD % Designation < 2.5 Very Close 0 - 25 Very poor

2.5 – 8 Close 25 - 50 Poor 8 – 24 Moderately close 50 - 75 Fair 24 – 80 Wide 75 - 90 Good

> 80 Very Wide 90 - 100 Excellent (RQD is the percent of a core run with intact lengths greater than 4 inches excluding breaks caused by drilling.)

INTACT ROCK STRENGTH

Field Identification UCS (psi) Hardness Term Indented by thumbnail. 35 - 150 Extremely Weak (R0) Crumbles under firm blows with point of geological hammer, can be peeled by a pocket knife. 150 - 725 Very Weak (R1)

Can be peeled by a pocket knife with difficulty, shallow indentations made by firm blow with geological hammer.

725 – 3,500 Weak (R2)

Cannot be scraped or peeled with a pocket knife, specimen can be fractured with a single blow of geological hammer.

3,500 – 7,000 Medium Strong (R3)

Specimen requires more than one blow of geological hammer to fracture it. 7,000 – 15,000 Strong (R4)

Specimen requires many blows of geological hammer to fracture it. 15,000 – 36,000 Very Strong (R5)

Specimen can only be chipped with geological hammer. > 36,000 Extremely Strong (R6) (UCS – Unconfined Compressive Strength)

1-1-1 (0" = 0%)

2-3-4 (6" = 33%)

2-2-7 (8" = 44%)

2-6-7 (10" = 56%)

4-8-11 (12" = 67%)

5-16-22 (10" = 56%)

3-20-28 (15" = 83%)

10-47-44 (15" = 83%)

12-50/4" (8" = 80%)

6-32-50/4" (12" = 75%)

9-48-50/4" (12" = 75%)

S-1

S-2

S-3

S-4

S-5

S-6

S-7

S-8

S-9

S-10

S-11

PP = 1.0 tsf

PP = 2.5 tsf

PP = 2.5 tsf

SILT (ML), soft, brown, moist, rapid dilatancy, (FILL).

El. 1478.5 ft 2.5 ft Lean CLAY with sand (CL), firm, light brown with mottled orange, moist, fine sand, slow dilatancy, medium plasticity, homogenous, (RESIDUUM).

El. 1473.5 ft 7.5 ft Fat CLAY with sand (CH), stiff, light brown, moist, slow dilatancy, medium to high plasticity, homogenous, (RESIDUUM).

El. 1471 ft 10 ft

Lean CLAY with sand (CL), very stiff, tan, moist, slow dilatancy, medium plasticity, homogenous, (RESIDUUM).

El.

1468.5 ft 12.5 ft

Clayey SAND (SC), dense, light tan with mottled gray, moist, fine sand, homogenous, (RESIDUUM).

El.

1463.5 ft 17.5 ft

Poorly graded SAND (SP), very dense, tan to brown, moist, fine sand, homogenous, weak cementation, (RESIDUUM).

El. 1446 ft 35 ft

Groundwater Depth:

While Drilling: --- At Completion: --- After Drilling: --- Water not encountered

Notes:

VWPs ( ) installed at 55 ft depth.

Inclinometer casing to 55 feet.

Elevations estimated from Google Earth Pro.

Surface Elevation: 1481 ft Datum: MSL Latitude: 42.989236° Longitude: -122.86139° Datum: WGS84

Weather: Cold, clear skies

Date Started: 11/30/17 Date Completed: 12/1/17 Driller/Company: Terracon - Chad Nix Hammer Type: Automatic

Drill: Diedrich D-50 Turbo

Logger/Company: J. Encarnacion/Terracon

JSR17-01BORING LOG

Sheet: 1 of 2

Project Location: Umpqua National Forest

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Medford District Road Repairs

E le va tio n (f t)

D ep th ft)

D ril lin g

M et ho d

Field Blow Count (Recovery)

Core Rec., RQD, and Frac. Freq.

No. Test Results

T yp e

SAMPLE

MATERIAL DESCRIPTION

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

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7( 1)

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G P

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20 40 60 80

Recovery

RQD

G ra ph ic

L og

50/5" (2" = 40%)

Rec = 87%

RQD = 62%

Rec = 90%

RQD = 77%

Rec = 100%

RQD = 90%

Rec = 100%

RQD = 100%

S-12

R-1

R-2

R-3

R-4

TUFF, light brownish grey, fresh to slightly weathered, strong rock (R4). Discontinuities are very closely spaced to widely spaced and in fair condition, joint/fractures Dip direction: 30 degrees.

El. 1426 ft 55 ft Bottom of borehole at 55 ft.

JSR17-01BORING LOG

Sheet: 2 of 2

Project Location: Umpqua National Forest

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Medford District Road Repairs

E le va tio n (f t)

D ep th ft)

D ril lin g

M et ho d

Field Blow Count (Recovery)

Core Rec., RQD, and Frac. Freq.

No. Test Results

T yp e

SAMPLE

MATERIAL DESCRIPTION

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

B O

R

IN

G L

O G

F

H W

A _D

A T

A T

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P

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20 40 60 80

Recovery

RQD

G ra ph ic

4-6-3 (6" = 33%)

3-3-4 (6" = 33%)

5-5-8 (8" = 44%)

7-10-13 (8" = 44%)

4-14-18 (12" = 67%)

4-13-15 (12" = 67%)

9-17-22 (12" = 67%)

7-16-23 (12" = 67%)

4-28-50/5" (12" = 71%)

40-50/3" (2" = 22%)

Rec = 100%

RQD = 53%

S-1

S-2

S-3

S-4

S-5

S-6

S-7

S-8

S-9

S-10

R-1

PP = 2.0 tsf

PP = 2.0 tsf

Gravelly SILT with sand (ML), medium dense, brown, moist, coarse gravel, angular, no dry strength, rapid dilatancy, low plasticity, (FILL).

El. 1471 ft 1 ft Lean CLAY with sand (CL), stiff, brown, moist, medium plasticity, homogenous, (RESIDUUM).

El. 1464.5 ft 7.5 ft Fat CLAY with sand (CH), stiff, light tan, moist, high plasticity, homogenous, (RESIDUUM).

Very stiff.

El.

1459.5 ft 12.5 ft

Clayey SAND (CL), dense, brown with mottled orange, moist, fine sand, stratified, weak cementation, (RESIDUUM).

El. 1447 ft 25 ft Poorly graded SAND (SP), very dense, light tan, moist, fine sand, weak cementation, (RESIDUUM).

El. 1442 ft 30 ft TUFF, light greenish grey, slightly weathered to moderately weathered, medium strong rock (R3).

Discontinuities are moderately spaced to closely spaced and in good condition, joint/fractures Dip direction: 20 degrees.

Groundwater Depth:

While Drilling: --- At Completion: --- After Drilling: --- Water not encountered

Notes:

VWPs ( ) installed at 50 ft depth.

Inclinometer casing to 50 feet.

Elevations estimated from Google Earth Pro.

Surface Elevation: 1472 ft Datum: MSL Latitude: 42.989275° Longitude: -122.8617° Datum: WGS84

Weather: Cold, clear skies

Date Started: 12/2/17 Date Completed: 12/4/17 Driller/Company: Terracon - Chad Nix Hammer Type: Automatic

Drill: Diedrich D-50 Turbo

Logger/Company: J. Encarnacion/Terracon

JSR17-02BORING LOG

Sheet: 1 of 2

Project Location: Umpqua National Forest

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Medford District Road Repairs

E le va tio n (f t)

D ep th ft)

D ril lin g

M et ho d

Field Blow Count (Recovery)

Core Rec., RQD, and Frac. Freq.

No. Test Results

T yp e

SAMPLE

MATERIAL DESCRIPTION

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

B O

R

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G L

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G P

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20 40 60 80

Recovery

RQD

G ra ph ic

Rec = 100%

RQD = 98%

Rec = 100%

RQD = 100%

Rec = 100%

RQD = 75%

R-2

R-3

R-4

TUFF, light greenish grey, slightly weathered to moderately weathered, medium strong rock (R3).

Discontinuities are moderately spaced to closely spaced and in good condition, joint/fractures Dip direction: 20 degrees. (continued)

El. 1422 ft 50 ft Bottom of borehole at 50 ft.

JSR17-02BORING LOG

Sheet: 2 of 2

Project Location: Umpqua National Forest

25 50 75 100

PL LLWC

N VALUE

10 20 30 40

Project Name: Medford District Road Repairs

E le va tio n (f t)

D ep th ft)

D ril lin g

M et ho d

Field Blow Count (Recovery)

Core Rec., RQD, and Frac. Freq.

No. Test Results

T yp e

SAMPLE

MATERIAL DESCRIPTION

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

B O

R

IN

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RQD

G ra ph ic

END MEMO