AK FWS KNA 1192(1) Skilak Lake - Final AOP Foundation and Geotechnical Recommendations 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: October 14, 2022

TO: Reuben Johnson Project Manager

FROM: Hayden Gluck Geotechnical Engineer

SUBJECT: Geotechnical Memo 16-22 Final AOP Foundation and Geotechnical Recommendations Skilak Lake Road AOP Improvements

AK FWS KNA 1192(1)

Kenai National Wildlife Refuge, Alaska

INTRODUCTION

This memorandum summarizes subsurface investigation results and provides final aquatic organism passage (AOP) foundation recommendations and geotechnical recommendations for the Skilak Lake Road AOP Improvements project. The subsurface investigation was performed July 14, 2022 with WFLHD Geotechnical personnel present. The coordinates and orthometric elevations referenced in this report are based on the Alaska State Plan Zone 4 NAD83 2011 coordinate system and the NAVD88 vertical datum unless stated otherwise. The recommendations presented herein are based on the 30-percent plan set. A site photography log may be found in Attachment A, site maps may be found in Attachment B, and laboratory test results may be found in Attachment C.

PROJECT DESCRIPTION

This project includes three sites along Skilak Lake Road and Upper Skilak Lake Road in the Kenai National Wildlife Refuge in Alaska. Both roads are two-lane, low-volume, gravel-surfaced access roads utilized primarily for nearby recreation. AOP site 1 is located on Jean Creek approximately ¼ mile south of the Skilak Lake Road and Sterling Highway intersection at milepost (MP) 58.0. AOP site 2 is located on Lower Ohmer Creek along Upper Skilak Lake Road approximately ¼ mile south of the Skilak Lake Road and Upper Skilak Lake Road intersection. AOP site 3 is located on an unnamed creek along Upper Skilak Lake Road at approximate MP 1.6. Refer to Figure B-1 for a project location map and Figure B-2 for a vicinity map.

Project Scope

The project will improve passage of aquatic organisms at each of the three existing culvert locations. AOP design and construction may also require raising the roadway grade at site locations. Subsurface investigation results presented herein support development of geotechnical strength parameters for soils in the areas of the proposed AOP locations. Refer to Figure B-3 for the test pit exploration location.

GEOLOGY

The project area is located in the Chugach mountain range of the Kenai Peninsula on the north side of Skilak Lake. As shown in below, Geologic Map of the Cook Inlet Region, Alaska, Including parts of the Talkeetna, Talkeetna Mountains, Tyonek, Anchorage, Lake Clark, Kenai, Seward, Iliamna, Seldovia, Mount Katmai, and Afognak 1:250,000-scale Quadrangles (Wilson,

et. al., 2012), the project area is located within the vicinity of upper Pleistocene-aged major moraine and kame deposits (Qm) and Cretaceous to Mississippian-aged McHugh and Uyak Complexes (KMm). Major moraine and kame deposits are described as variable glacial deposits ranging from peat to well- to poorly-bedded sands and gravels. Some Kame deposits may contain cores of diamicton and areas may include areas of bedrock covered by thin or discontinuous glacial deposits. McHugh and Uyak Complexes consist of lithologically distinct but structurally juxtaposed packages, most predominantly composed of gray, gray-green, and dark-green metamorphosed siltstone, graywacke, arkose, and conglomerate sandstone.

Figure 1. Excerpt of the Geologic Map of the Cook Inlet Region, Alaska, Including parts of the Talkeetna, Talkeetna Mountains, Tyonek, Anchorage, Lake Clark, Kenai, Seward, Iliamna, Seldovia, Mount Katmai, and Afognak 1:250,000-scale Quadrangles (Wilson, et. al., 2012)

SITE CONDITIONS

Initial site reconnaissance was conducted July 12, 2022 with a follow-up visit later in the week on July 14 to conduct a test pit excavation with the USFWS. Please refer to Attachment A for photographs of site conditions.

AOP Site 1 – Jean Creek

Surface observations within the vicinity of the AOP site indicate there are two corrugated metal pipe (CMP) culverts approximately 40 linear feet apart. The first existing culvert, located at the proposed AOP location, is 72 inches in diameter and located at approximate stationing STA 212+65 on Skilak Lake Road. The second existing culvert is 60 inches in diameter and located at approximate stationing STA 213+06 on Skilak Lake Road. The road is 24 feet wide and aggregate-surfaced at this location. According to field notes from a site visit conducted by the WFLHD Hydraulics Group, a beaver dam was observed upstream of the existing 60-inch diameter culvert. However, this places the beaver dam 40 feet away from the proposed AOP site. Plant species in proximity to the AOP site were generally hydrophytic. Bearing probe analysis of surface soils using a ½-inch diameter pin indicate approximately 18 to 20 inches of muck underlain by subrounded to rounded poorly-graded gravel with sand. Test pits were not advanced due to the steep drop off and mucky soil making it too risky for the backhoe operator.

Jean Creek AOP

Unnamed Creek AOP

Lower Ohmer Creek AOP

AOP Site 2 – Lower Ohmer Creek

Surface observations within the vicinity of the AOP site indicate there is an existing 36-inch diameter CMP culvert beneath Upper Skilak Lake Road. The road is 27 feet wide and aggregate-surfaced at this location. On the downstream portion of the site, surface gravels were subrounded to rounded in shape and at particle sizes varying from ½ to 8 inches in diameter.

On the upstream portion of the site, surface vegetation consisted of hydrophytic plant types and shallow soil conditions were marshy. Test pits were not advanced at this proposed AOP location due to shallow surface water and anticipated gravelly soil conditions.

AOP Site 3 – Unnamed Creek

Surface observations within the vicinity of the AOP site indicate there is an existing 72-inch wide and 60-inch tall oblong-shaped CMP culvert beneath Upper Skilak Lake Road. The road is 24 feet wide and aggregate-surfaced at this location. At the upstream portion of the existing culvert, boulders of up to 5 feet in diameter were observed to line the creek as it entered the inlet. A bedrock outcrop was observed near the existing culvert outlet. Excavation observations of this test pit are summarized below in Subsurface Conditions.

SUBSURFACE CONDITIONS

The subsurface investigation for this project consisted of one test pit (TP22-01). The test pit was excavated to a maximum depth of 8.5 feet bgs, where exploration was terminated due to maximum reach of the excavator. Material sampling methods included bulk grab samples. Table 1 summarizes subsurface investigation activity performed for this project and Figure B-3 of Attachment B – Site Maps shows the excavation location. A tabulated test pit log may be found in AOP Site 1 – Unnamed Creek.

Table 1. Test Pit Excavation

Designation Location Groundwater

Depth (feet bgs)

Maximum Depth (feet bgs)

Coordinates 1 (Decimal Degrees)

Latitude Longitude

TP22-01

~20 feet SW of Existing Culvert at Unnamed Creek

Slight sidewall seeps at 7 – 8½ 8½ 60.724771° -150.678113°

1. Coordinates were obtained using a hand-held GPS device and locations are not surveyed.

AOP Site 1 – Unnamed Creek

Test pit TP22-01 was advanced southwest of and adjacent to the existing culvert and proposed AOP location at Unnamed Creek. Subsurface materials may generally be grouped into two categories: roadway prism fill and glacial moraine and kame deposits.

Table 2. TP22-01 Test Pit Log

Depth (feet bgs) Material Description Sample No.

0 – 4½

Light brown to brownish gray, dry to moist silty SAND with gravel (fill).

Sand is fine to coarse and gravels are subrounded to angular.

Nonplastic.

4½ – 7 Dark blue to gray, moist to wet lean CLAY with sand, silt, and cobbles, stiff to very stiff. Medium plasticity.

S-1

7 – 8½ Dark gray to blue, wet, clayey GRAVEL with sand and silt, very dense. Fines have medium plasticity.

S-2

Materials interpreted to be roadway prism fill consisted of medium dense, light brown to brownish gray, dry to moist silty SAND with gravel and extended from the ground surface to 4½ feet bgs. Particle size in fill soils ranged from fine to coarse and angularity from subrounded to angular. Roadway prism fill material may be described as nonplastic.

Materials interpreted to be glacial moraine and kame soils consisted of stiff to very stiff, dark blue to gray, moist to wet lean CLAY with sand, silt, and cobbles between 4½ and 7 feet bgs.

Lean clay soils were underlain by wet, very dense, dark gray to blue, clayey GRAVEL with sand and silt between 7 and 8½ feet bgs.

Slight groundwater seeps were observed at 7 feet bgs and below during the time of excavation, likely to match surface water elevation in Unnamed Creek.

Lab testing results may be found in Attachment C – Laboratory Test Results.

DESIGN RECOMMENDATIONS AND CONSTRUCTION CONSIDERATIONS

AOP Site 1 – Jean Creek

The existing 72-inch diameter CMP culvert at this location will be replaced by a new 156-inch diameter AOP pipe culvert with riprap and headwalls. The existing 60-inch diameter CMP culvert at this location will be replaced by a new 60-inch diameter pipe culvert. No subsurface investigation was performed at this site; however, the geologic map shows the site to be on moraine and kame deposits, Qm. Moraine and kame deposits are described as glacial deposits ranging from peat to well- to poorly-bedded sands and gravels. Based on surface observations conducted during the site visit on July 12, 2022 and review of field notes and site photographs from a site visit in 2019 by WFLHD Hydraulics Group, the shallow subsurface is anticipated to be muck, consisting of soft silt with fine sand and organics, underlain by gravelly glacial soils.

Review of the 30 percent plan sheets indicates the AOP base will be approximately 15 feet below existing grade, which may be beneath any surficial muck layers and into granular material.

AOP Site 2 – Lower Ohmer Creek

The existing 36-inch diameter CMP culvert at this location will be replaced by a 120-inch diameter AOP pipe culvert with riprap and headwalls. No subsurface investigation was performed at this site; however, the geologic map shows the site to be on moraine and kame deposits, Qm. Moraine and kame deposits are described as glacial deposits ranging from peat to well- to poorly-bedded sands and gravels. Based on surface observations conducted during the site visit on July 12, 2022 and review of field notes and site photographs from a site visit in 2019 by WFLHD Hydraulics Group, gravelly and cobbly soil conditions are anticipated in the shallow subsurface. Review of the 30 percent plan sheets indicates the AOP base will be approximately 12 feet below existing grade which may be into bedrock. The contractor should be prepared with appropriate equipment for rock excavation or blasting, if rock or large boulders are encountered.

AOP Site 3 – Unnamed Creek

The existing 72-inch diameter CMP culvert at this location will be replaced by a 108-inch diameter AOP pipe culvert with riprap and headwalls. Subsurface investigation indicates shallow subsurface soils are consistent with mapped kame and moraine deposits mentioned in the Geology section of this report. Given the presence of boulders of up to 5 feet in diameter and the presence of a bedrock outcrop near the site, the contractor should be prepared with appropriate equipment for boulder excavation and rock removal, if encountered.

Foundations

Shallow or deep foundations are not anticipated given the proposed AOP culverts are pipes and not open-bottom. Based on correspondence with the WFL Hydraulics Group and the 30-percent plan set, AOP pipe culverts will bear on 6-inch bedding course underlain by unyielding native material or compacted backfill. If spread footings are utilized, the nominal bearing resistance on native dense, granular materials, such as gravels, and rock is 4 ksf with resistance factors of

0.45 and 0.85 for bearing and sliding, respectively. If soft fine-grained or loose sand materials are encountered, the soft or loose materials should be removed down to suitable bearing materials described above. Additional depth to suitable bearing elevations due to scour may be recommended by the Hydraulics Engineer. Overexcavated materials should not be replaced with foundation fill due to scour potential; footings should rest directly on dense gravel or rock, or be replaced with structural concrete up to the design footing elevation. Foundation settlements at each of the AOP sites are expected to be less than an inch provided the recommendations described herein are followed.

Lateral Earth Pressures

The following recommendations for lateral earth pressures apply to each of the three AOP sites.

Lateral earth pressures of backfill material acting on AOP pipe culverts are based on the Structural Backfill specification (FP-14 Subsection 704.04) and do not include load or resistance factors. It is assumed that compacted backfill creates at-rest lateral earth pressures behind pipe culverts.

Table 3. Recommended Lateral Earth Pressure Parameters

Parameter Design Value

Backfill Moist Unit Weight 130 pcf

Backfill Angle of Internal Friction 34 degrees

Backfill Interface Friction Angle, δ 26 degrees

Active Earth Pressure Coefficient, Ka 0.28

Active Equivalent Fluid Pressure 36 psf/ft

At-Rest Earth Pressure Coefficient, K0 0.44

At-Rest Equivalent Fluid Pressure 57 psf/ft

Passive Earth Pressure Coefficient, Kp 3.54

Passive Equivalent Fluid Pressure 460 psf/ft

Base Soil Moist Unit Weight 125 pcf

Base Soil Angle of Internal Friction 35 degrees

Coefficient of Sliding Along the Base2, tan δ 0.65

Equivalent Height of Soil for Vehicle Loading of Abutment End Walls3, heq 3.5 ft

Equivalent Height of Soil for Vehicle Loading of Abutment Wing Walls4, heq 2.0 ft

Notes:

1 Design values based on a drained condition behind the wall.

2 A resistance factor of 1.0 is recommended for sliding resistance of semigravity walls at the strength limit state (AASHTO Table 11.5.7-1)

3 Interpolated from Table 3.11.6.4-1 in AASHTO LRFD Bridge Design Specifications.

4 From Table 3.11.6.4-2 in AASHTO LRFD Bridge Design Specifications.

Dewatering

Dewatering recommendations described herein apply to each of the three AOP sites. Culvert construction will require excavations extending below the stream beds. Groundwater levels are expected to fluctuate seasonally and match surface water levels. However, during the dry summer months, we anticipate most of the stream channels will be dry. Therefore, the need for dewatering will depend on construction timing and the specific site conditions. If required, bypass pumping or piping may be necessary to transport surface water through the work zone.

During periods of sustained rain or snowfall, groundwater may infiltrate into the excavations and dewatering may be necessary. Excavations should be protected from surface water.

REFERENCES

American Association of State Highway and Transportation Officials (2020), AASHTO LRFD Bridge Design Specifications, 9th Edition, Washington, D.C.

Chen, Michael (2022), Aggregate Pavement Design Memo, Federal Highway Administration – Western Federal Lands Highway Division, Vancouver, Washington.

Wilson, Frederic H., Hults, Chad P., Schmoll, Henry R., Haeussler, Peter J., Schmidt, Jeanine M., Yehle, Lynn A., and Labay, Keith A. (2012), Geologic Map of the Cook Inlet Region, Alaska, Including parts of the Talkeetna, Talkeetna Mountains, Tyonek, Anchorage, Lake Clark, Kenai, Seward, Iliamna, Seldovia, Mount Katmai, and Afognak 1:250,000-scale Quadrangles, United States Geological Survey.

CLOSING

Please contact Hayden Gluck at (360) 619-7591 or hayden.gluck@dot.gov with any questions regarding this memorandum.

CC: James Neighorn – Hydraulics Engineer Benn Oltmann – Structural Team Lead Thomas Parker – Environmental Protection Specialist

Mike Baron – Construction Operations Engineer Kevin Parker – Highway Design Engineer Justin Bowling – Geomatics Vera Anderson – Right-of-Way/Utilities Engineer

Doug Anderson – Geotechnical Team Lead Geotechnical File

Attachments:

Attachment A – Site Photographs Attachment B – Vicinity Map, Project Map, Exploration Location Maps Attachment C – Laboratory Test Results

ATTACHMENT A – SITE PHOTOGRAPHS

A-1. Bearing Probe Analysis of Jean Creek Surface Muck Conditions Adjacent to

Existing Culvert, 18 to 20 inches of Penetration A-2. Lower Ohmer Creek Surface Soil Conditions Adjacent to Existing Culvert A-3. Boulders Observed at Unnamed Creek AOP Site A-4. Backhoe Used for Test Pit at Unnamed Creek AOP Site A-5. Test Pit Profile at Unnamed Creek AOP Site A-6. Close-Up of Clay Soils Between 4 ½ and 7 feet bgs at Unnamed Creek AOP Site A-7. Backfilled Test Pit at Unnamed Creek

Photo A-1. Bearing Probe Analysis of Jean Creek Surface Muck Conditions Adjacent to Existing Culvert, 18 to 20 inches of Penetration

Photo A-2. Lower Ohmer Creek Surface Soil Conditions Adjacent to Existing Culvert

Photo A-3. Boulders Observed at Unnamed Creek AOP Site

Photo A-4. Backhoe Used for Test Pit at Unnamed Creek AOP Site

Photo A-5. Test Pit Profile at Unnamed Creek AOP Site

Photo A-6. Close-Up of Clay Soils Between 4 ½ and 7 feet bgs at Unnamed Creek AOP Site

Photo A-7. Backfilled Test Pit at Unnamed Creek

ATTACHMENT B – SITE MAPS

Figure B-1: Project Location Map Figure B-2: Project Vicinity Map Figure B-3: Test Pit Exploration Map

610 East Fifth Street

Vancouver, WA 98661

Project No. Project Location Map FigureAK FWS KNA 1192(1) Scale

Skilak Lake Road AOP Improvements Kenai Peninsula, Alaska B-1

See Scale File Name:

Figure B-1.pptx Date:

September 21, 2022

Project Location

Vancouver, WA 98661

Project No. Vicinity Map FigureAK FWS KNA 1192(1) Scale

Skilak Lake Road AOP Improvements Kenai Peninsula, Alaska B-2

See Scale File Name:

Figure B-2.pptx Date:

September 21, 2022

Lower Ohmer Creek AOP

Unnamed Creek AOP Jean Creek AOP

Vancouver, WA 98661

Project No. Test Pit Location Map – Unnamed Creek FigureAK FWS KNA 1192(1) Scale

Skilak Lake Road AOP Improvements Kenai Peninsula, Alaska B-3

See Scale File Name:

Figure B-3.pptx Date:

September 21, 2022

R iv er si de R oa d

TP22-01

ATTACHMENT C – LABORATORY TEST RESULTS

Station:

Western Federal Lands

Project No.: AK FWS KNA 1192(1) Sample ID: W-22-0790-GS

Materials Laboratory

ISO/IEC 17025:2017 Accredited

Material Description: SO-COM

MilePost:

Offset:

Intended Use:

Remarks:

Source Name:

Source Location:

Sample Location: Other

Submitted By: Hayden Gluck

Quantity Represented:

Item No.:

Field Sample No.: S-1

Lot No.:

Date Sampled: 7/14/2022

Depth: 6.0'-6.25' Hole No.: TP22-01

Project Name: SKILAK LAKE ROAD AOP

IMPROVEMENTS

Unit of MeasureResult

Specific Gravity @ 20°C 2.765

Methods: T 100 - AASHTO Test Date: 9/9/2022 Tested By: Don Rowe

Comments:

Test Validated By: Don Rowe Validated Date: 9/9/2022

Version 1

All reported results apply to the sample as received.

Page 1 of 1Sample ID: W-22-0790-GS

Con tro lle d C op y

Unit of MeasureResult

Liquid Limit From T 89 31

Plastic Limit from T 90 18

Plasticity Index 13

Methods: T 89 & T 90 - AASHTO Atterberg Limit Test Date: 8/2/2022 Tested By: Don Rowe

Comments:

Test Validated By: Don Rowe Validated Date: 8/4/2022

Version 1

All reported results apply to the sample as received.

Page 1 of 1Sample ID: W-22-0790-GS

Con tro lle d C

Classification A-6 (7)

Gravel (2.00-mm and larger) 12.7 %

Coarse sand (2.0 to 0.42-mm) 5.5 %

Fine Sand (0.42 to 0.074-mm) 8.9 %

Silt-clay (0.002 and smaller) 72.9 %

Methods: M 145 - AASHTO (AASHTO M 145 is not an AAP accredited test) Test Date:

Tested By:

Comments:

Test Validated By: Don Rowe Validated Date: 9/9/2022

Version 1

All reported results apply to the sample as received.

Page 1 of 1Sample ID: W-22-0790-GS

Con tro lle d C

See Attached Report Document

Methods: AASHTO T 88 - Interim Test Date: 9/8/2022 Tested By: Don Rowe

Comments:

Test Validated By: Don Rowe Validated Date: 9/9/2022

Version 1

All reported results apply to the sample as received.

Page 1 of 1Sample ID: W-22-0790-GS

Con tro lle d C

AASHTO T 88

Particle Size Analysis of Soils Laboratory ID #

➖➖➖ Results ➖➖➖

6" sieve ( 152.4 mm) % Passing - %

5" sieve ( 127 mm) % Passing - %

4" sieve ( 101.6 mm) % Passing - %

3.5" sieve ( 88.9 mm) % Passing - %

3" sieve sieve ( 76 mm) % Passing - %

2.5" sieve ( 63.5 mm) % Passing - %

2" sieve (50.0 mm) % Passing - %

1.5" sieve (37.5 mm) % Passing 100.0 %

1" sieve (25.0 mm) % Passing 97.6 %

3/4" sieve (19.0 mm) % Passing 97.6 %

1/2" sieve (12.5 mm) % Passing 96.1 %

3/8" sieve (9.5 mm) % Passing 94.5 %

No. 4 sieve (4.75 mm) % Passing 90.8 %

No. 10 sieve (2.0mm) % Passing 87.3 %

No. 40 Sieve (0.425mm) % Passing 81.8 %

No. 200 Sieve (0.075mm) % Passing 72.9 % interpolated .020 mm % Passing 60.7 % interpolated .010 mm % Passing 52.6 % interpolated .005 mm % Passing 44.0 % interpolated .002 mm % Passing 29.7 % interpolated .001 mm % Passing - %

W-21-0790-GS

Attachment - Page 1 of 1

Drying Temperature 140 ° F

% Moisture 18.31 %

Methods: T 265 - AASHTO Test Date: 9/27/2022 Tested By: Chuck Miller

Comments:

Test Validated By: Don Rowe Validated Date: 9/9/2022

Version 1

All reported results apply to the sample as received.

Page 1 of 1Sample ID: W-22-0790-GS

Con tro lle d C