Limited_Geotechnical_Site_Evaluation__USFWS_Mark-Up_Notes_0002.pdf

6420 S Macadam Avenue, Suite 100 Portland, OR 97239 503.620.7284

MEMORANDUM

DATE: December 3, 2020

TO: KPFF Consulting Engineers Attention: Danielle Pruett

FROM: Allison M. Pyrch, PE, GE

RE: Limited Geotechnical Site Evaluation Woodpecker Loop Trail Boardwalk Reconstruction William Finley National Wildlife Refuge Willamette Valley, Oregon 154-124-005

Hart Crowser, a division of Haley & Aldrich, is pleased to submit this memorandum to KPFF Consulting Engineers (KPFF) and U.S Fish & Wildlife Service (USFWS) presenting the results of our limited geotechnical site evaluation for reconstruction of the boardwalk along the Woodpecker Loop Trail at the William Finley National Wildlife Refuge (NWR) near Corvallis in Willamette Valley, Oregon.

We understand the improvements generally include repair and reconstruction of the existing boardwalks, a small bridge, and on-grade trail. However, the scope of our work included only portions of the improvements that are related to the boardwalk and bridge foundation design. The existing boardwalk will be partially demolished and removed and new boardwalk will be designed to carry 4-wheelers/all-terrain vehicles (ATVs). The boardwalk will be supported by helical piles constructed under a design-build contract.

Our specific scope of work was detailed in our Agreement for Geotechnical Services, dated October 8, 2020, and generally included performing geologic research, conducting a visual geomorphic reconnaissance of the site to observe the condition of the boardwalk and the surroundings, advancing five drive probes and two hand augers at locations along the boardwalk alignment and at bridge abutments, developing geotechnical parameters for the design of the foundation system, and preparing this memorandum.

The location of the site is shown on Figure 1. The locations of our explorations are shown on Figure 2.

zspruell Text Box Limited Geotechnical Evaluation provided for reference only. Foundation System Design is beyond the scope of this Supply Order Contract.

Woodpecker Loop Trail Boardwalk Reconstruction 154-124-005 December 3, 2020 Page 2

Site Conditions The project site is located at the east of Bellfountain Road and is accessible from Finley Refuge Road through Woodpecker Loop Road from the east end of the trail. The surface coverage of the site varies from heavily wooded wetlands with thick underbrush to native oak savannah habitat. Seasonal streams and wetlands, including Hull Creek that drains from highlands to the west of Bellfountain Road towards the east, exist at the site. Ground surface elevations in the project vicinity vary between approximately 461 feet above mean sea level (MSL) near Bellfountain Road and 295 feet MSL near Woodpecker Loop Road.

Geology and Soils Mapping The geology of the site is mapped in the Digital geologic map of the southern Willamette Valley, Benton, Lane, Linn, Marion, and Polk Counties, Oregon (McClaughry et al 2010) at 1:63,360 scale that maps the site as middle Eocene-age mixed source marine sedimentary rocks of the Spencer and Yamhill formations. These deposits are described as interbedded siliciclastic and volcaniclastic sandstone, siltstone and mudstone with minor conglomerate and claystone. While these deposits are classified as rock, they can be poorly lithified in the subsurface and heavily weathered to several tens of feet deep near the ground surface. A review of the local well logs indicates that up to 21 feet of fine-grained soils and soft sandstone overlie more competent sandstone and siltstone near the site (OWRD 2020).

The near surface soils at the site have been mapped in the U.S. Department of Agriculture (USDA) online web soil survey (USDA 2020), which incorporates soil mapping and descriptions from the Soil Survey of the Benton County, Oregon (Fillmore 2009). The report generated by the Web Soil Survey indicates that the near-surface soils at the site consist of Jory-Dupee complex, 2 to 12 percent slopes, and Santiam silt loam, 2 to 8 and 8 to 20 percent slopes. Jory-Dupee complex soils are described as “clayey colluvium and residuum derived from sandstone and siltstone” and are typically found in hilly areas. Santiam silt loam soils are described as “silty glaciolacustrine deposits over clayey alluvium” and are typically found on terraces at the edge of valleys. Both soil units are classified as hydrologic Soil Group C/D and have high water storage (greater than 10.0 inches) in each soil profile, however Jory-Dupee complex soils have a moderately high estimated hydraulic conductivity of 0.20 to 0.57 inches per hour while Santiam silt loam soils have a lower estimated hydraulic conductivity of 0.06 to 0.20 inches per hour.

Shrink-swell potential of soils are measured using Linear Extensibility, which refers to change in length of an unconfined clod between moist and dry soil conditions. Linear extensibility values less than 3 percent indicate low swell-shrink potential, moderate for values between 3 and 6 percent, high for values between 6 and 9 percent, and very high for values greater than 9 percent. Web Soil survey report indicated linear extensibility values ranging between 4.1 and 5.3 percent for this unit, indicating a moderate shrink-swell (frost action) potential.

December 3, 2020 Page 3

Subsurface Conditions We completed field explorations at the site by advancing five drive probe soundings (DP-1 through DP-5) and two hand-augered borings (HA-1/1A and HA-2). The locations of our explorations are shown on Figure 2. Summaries of our drive probe soundings and hand auger explorations are presented in Tables 1 and 2, respectively.

Drive Probes The drive probes extended to depths of approximately 8.8 to 16.5 feet below ground surface (bgs). The drive probe soundings were performed in general accordance with the guidelines of Williamson (1994) in order to evaluate in situ consistency/density of soils. The drive probe employs driving a 0.5-inch outer diameter pipe with a flat end drive plug using a 12-pound slide hammer. The “blows” required to advance each 6-inch increment are recorded and are correlated with standard penetration test (SPT) equivalent blows per foot based on Adams, Prellwitz, and Koler 2007. These values can be used to estimate relative soil density/consistency.

Table 1 – Drive Probe Exploration Summary

Depth (feet)

Range of Blows Required for 6-Inch Drive

Equivalent SPT Blow

Blows/Foota Comments Interpretation

Drive Probe #1 (DP – 1)

0 – 1.5 16 – 24 11 - 14 2-inches of topsoil with increasing blows with depth

Topsoil, fine-grained soil

1.5 – 5.5 22 – 34 14 – 18 Relatively consistent blow counts with increase at 5.5 feet bgs

Fine-grained soil

5.5 – 8.75 43 – 100 20 – 33

Blow counts increase continuously between approximately 5.5 to 8.5 feet bgs, refusal at approximately 8.75 feet bgs with 50 blows for 3-inch drive

Fine-grained soil

Drive Probe #2 (DP – 2)

0 – 2.5 7 - 16 7 - 9 Generally low blow counts. Topsoil, fine-grained soil

2.5 – 8.5 20 – 26 11 – 15 Relatively consistent blow counts Fine-grained soil

8.5 – 16.5 31 – 62 17 – 25

Blow counts increase continuously between approximately 8.5 and 16.0 feet bgs, rapid increase in blows at approximately 16.0 to 16.5 feet bgs

Fine-grained soil

December 3, 2020 Page 4

Depth (feet)

Range of Blows Required for 6-Inch Drive

Equivalent SPT Blow

Blows/Foota Comments Interpretation

Drive Probe #3 (DP – 3)

0.0 – 3.5 13 – 24 10 – 14 Lower blow counts at surface, then consistent blow counts

Topsoil, fine-grained soil

3.5 – 5.5 28 – 29 16 Consistent blow counts per foot Fine-grained soil

5.5 – 9.0 33 – 40 17 – 19 Increased blow counts, relatively consistent

Fine-grained soil

Drive Probe #4 (DP – 4)

0 – 2.5 3 – 15 4 – 11 Soft at the surface with increasing blow counts with depth

Topsoil, fine-grained soil

2.5 – 7.0 22 – 31 14 – 17 Increase in blows at approximately 2.5 feet bgs, then relatively consistent blow counts to approximately 7.0 feet bgs

Fine-grained soil

7.0 – 8.5 37 – 50 19 – 22 Increase in blows at approximately 7.5 feet bgs

Fine-grained soil

Drive Probe #5 (DP – 5)

0 – 2.0 4 – 18 5 – 12 Consistent increase in blow counts with depth

Topsoil, fine-grained soil

2.0 – 10.0 25 – 32 15 – 17 Relatively consistent blow counts Fine-grained soil

Notes: a. Adams, Prellwitz, and Koler 2007 “best fit” equation

Hand Auger In addition to the drive probes, we advanced two hand augers (HA-1/1A and HA-2) to approximately 3.5 and 4.0 feet bgs, respectively, in order to obtain soil samples at the site. Both hand augers refused at the final depths. Hand auger HA-1 refused at 1.5 feet bgs on roots and hand auger HA-1A was completed directly adjacent, similarly meeting refusal at 3.5 feet on roots. Hand auger HA-2 met refusal in very stiff fine-grained soils. Representative disturbed grab samples from the hand auger explorations were collected at depths shown in Table 2 below. The locations of the hand auger explorations are shown on Figure 2 at the end of this report.

In our hand auger explorations, we encountered approximately 2 to 3 inches of topsoil and root mat that were underlain by fine-grained soils to approximately 4.0 feet bgs. The fine-grained soils consisted of lean clay with variable amounts of sand. The equivalent SPT blow counts at the depths of the hand auger explorations varied between 7 and 17 blows per foot (bpf), indicating medium stiff to very stiff relative consistency, but we do note SPT blow counts increased with depth to as high as 30 bpf, potentially indicating hard relative consistency.

December 3, 2020 Page 5

In should be noted that due to the heavily vegetated nature of the site, we anticipate that topsoil thickness is variable across the site and anticipate it to be at least 3-inches thick. Larger tree roots were encountered to at least approximately 4.0 feet bgs, the full depth of our hand auger explorations.

At the time of our visit, we did not observe flowing water within any stream channels or wetlands.

However, due to the fine-grained nature of the near-surface soils and the presence of wetlands, we anticipate groundwater to perch near the surface and shallow soils to be saturated during the majority of the year.

Table 2 – Hand Auger Exploration Summary

Depth (feet) Samples Soil Type

Hand Auger #1/1A (HA - 1/HA - 1A)

0.0 – 0.2 Topsoil

0.2 – 1.5

HA-1/S-1

(1.0 – 1.5 feet bgs) LEAN CLAY (CL), (medium stiff to stiff), moist, mottled gray-brown, medium plasticity, iron oxide staining, scattered roots and rootlets. HA-1 refusal on tree root at 1.5 feet bgs.

1.5 – 3.5

HA-1A/S-1

(1.0 – 1.5 feet bgs)

HA-1A/S-2

(3.0 – 3.5 feet bgs)

SANDY LEAN CLAY (CL), (stiff), moist, mottled gray-brown, fine to coarse angular to subrounded sand, medium plasticity, iron oxide staining, scattered roots and rootlets.

3.5 HA-1A refusal on tree root at 3.5 feet bgs.

Hand Auger #2 (HA - 2) 0 – 0.3 Topsoil

0.3 – 2.0 S-1 (1.0 – 2.0 feet bgs) LEAN CLAY (CL), (medium stiff to stiff), moist, brown.

2.0 – 4.0 S-2 (2.0 – 3.0 feet bgs)

LEAN CLAY WITH SAND (CL), trace fine to coarse subangular gravel, (stiff to very stiff), moist, light brown to tan.

4.0 Refusal in very stiff soils

Foundation Support Recommendations The shallow soils at the site include topsoil and soft to medium stiff fine-grained soils. The soft soils are present near surface and generally extend to approximately 1 foot bgs. The topsoil and these soft soils are not suitable for supporting footings. In addition, roots were present up to approximately

3.5 feet bgs. The footings should bear directly on/through the medium stiff materials below the soft materials.

Based on our limited explorations and our experience with similar soils, it is our opinion that the soils at the site are suitable for supporting the design loads with spread footings, diamond piers, helical augers, or other similar foundation systems if the following recommendations are considered.

December 3, 2020 Page 6

We understand that KPFF is planning on using diamond piers or helical piles in order to support design footing loads of up to 15 kips and that these elements will be designed by the specialty contractor.

Table 3 below shows the recommended soil parameters for design of diamond pier or helical pile foundation systems for the boardwalk and bridge. We recommend a minimum target length/depth of 12 feet, or 10 feet below anticipated scour depth for intermediate foundation systems such as these.

Table 3 – Recommended Soil Parameters

Soil Type Depth Range (feet)

Undrained Friction Angle

(Degrees)

Undrained Shear Strength

(psf)

Drained Friction Angle

(Degrees)

Drained Shear Strength

(psf) Medium Stiff Fine-Grained

0-2 0 1,200 27 100

Stiff Fine-Grained Below 2 feet - 1,500 30 100

Based on the information provided by the diamond pier manufacturer, we anticipate that 4 to 6 diamond piers or 2 to 4 helical piers will be required for footings loads up to 15 kips.

Isolated spread footings should have a minimum width of 2 feet and should be embedded at least 2 feet bgs or below the anticipated scour depth if applicable. Soft soils and roots below footings should be removed prior to placing the footings. Footings constructed with these criteria can be designed using an allowable bearing capacity of 1,700 pounds per square foot (psf). This allowable bearing capacity can increase by 100 psf for each 1-foot increase in footing dimensions. The recommended allowable bearing pressure applies to the total of dead plus long-term live loads and may be increased by one-third for short-term loads, such as wind or seismic forces. We estimate that total post-construction settlements for footings constructed in accordance with the recommendations of this section should be less than approximately 1 inch.

Construction Considerations Conventional construction equipment in good working condition should be capable of excavating site soils and installing piers. The clayey soils present at the site are sensitive to moisture and will be susceptible to disturbance at all times. We recommend wet soil construction practices be implemented throughout construction. Wet soil construction practices include using equipment, such as smooth excavator buckets and tracked equipment, to limit subgrade disturbance.

December 3, 2020 Page 7

Construction Observations Satisfactory foundation and earthwork performance depend to a large degree on quality of construction. Sufficient monitoring of the construction is a key part of determining that the work is completed in accordance with the intents of this geotechnical memorandum. Subsurface conditions observed during construction should be compared with those encountered during subsurface explorations. Recognition of changed conditions often requires experience; therefore, Hart Crowser or their representative should visit the site with sufficient frequency to detect whether subsurface conditions change significantly from those anticipated.

We recommend that Hart Crowser be retained to monitor construction at the site to confirm that subsurface conditions are consistent with the site explorations and to confirm that the intent of project plans and specifications relating to earthwork and foundation construction are being met.

Limitations We have prepared this memorandum for the exclusive use of KPFF, USFWS, and their authorized agents for this specific site. Soil conditions interpreted from geologic maps and our explorations, in conjunction with soil properties inferred from field observations, formed the basis for the conclusions and recommendations provided in this memorandum. The subsurface information used for this study represents conditions at discrete locations across the project site and actual conditions in other areas could vary. Furthermore, the nature and extent of variations may not become evident until additional explorations are performed or until construction begins. If significant variations are observed at that time, we may need to modify our conclusions and recommendations accordingly to reflect actual site conditions. Our conclusions should not be construed as a warranty or guarantee of subsurface conditions or future site performance.

Within the limitations of scope, schedule, and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this memorandum was prepared. No warranty, express or implied, should be understood. Any electronic form, facsimile, or hard copy of the original document (email, text, table and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by Hart Crowser and will serve as the official document of record.

December 3, 2020 Page 8

References Adams, W.C., R.W. Prellwitz, and T.E. Koler 2007. Low-Technology Approach to Evaluating Slope Stability in Forested Uplands. In First North American Landslide Conference, Vail, CO (pp. 569-577).

Bowles, J.E. 2012. “Foundation Analysis and Design” 5th Edition. McGraw Hall, Inc., New York.

Diamond Pier Foundation System, https://www.diamondpiers.com/

McClaughry, J.D., Wiley, T.J., Ferns, M.L., Madin, I. and McConnell, V.S., 2010. Digital Geologic Map of the Southern Willamette Valley, Benton, Lane, Linn, Marion, and Polk Counties, Oregon. Oregon Department of Geology and Mineral Industries, Open-File Report O-10-03.

Oregon Water Resources Department (OWRD) 2020. Online Well Log Query. Accessed 10/16/2020 at http://apps.wrd.state.or.us/apps/gw/well_log/.

U.S. Department of Agriculture (USDA) 2020. Soil Survey Staff, Natural Resources Conservation Service, Web Soil Survey. Available online at the following link: http://websoilsurvey.sc.egov.usda.gov/.

Accessed October 16, 2020.

Williams, L.H., 1972. Soil Survey of Marion County Area, Oregon. US Soil Conservation Service.

Williamson, D.A. 1994. Geotechnical Exploration – Drive Probe Method, in D.E. Hall, M.T. Long, and M.D. Rembolt, ed., Slope Stability Guide for National Forests in the United States, U.S. Department of Agriculture Forest Service Washington Office Engineering Staff Publication EM 7170-13, pp. 317-321.

Attachments:

Figure 1 – Vicinity Map Figure 2 – Site Plan

F:\Notebooks\154124005_USFWS_Trails_Reconstruction\Deliverables\Memos\Woodpecker Loop Trail-GeotechncalEval_12-03- 20\Woodpecker-LimitedGeotechSiteEval.docx https://www.diamondpiers.com/ http://apps.wrd.state.or.us/apps/gw/well_log/

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Woodpecker Loop Trail Boardwalk Reconstruction Willamette Valley, Oregon

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Source: Aerial photograph provided by Hexagon Imagery Program Data.

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