Attachment9_SchematicDesign_1Dec21_0003.pdf

Bureau of Land Management Nome Creek Road Repair Nome Creek Road, Alaska

Schematic Design

For:

222 University Avenue Fairbanks, Alaska 99709

December 1, 2021

Nome Creek Road Repair Nome Creek Road, Alaska

Schematic Design

Table of Contents Narrative Cost Estimate (To be provided separately) Specification Index Draft Geotechnical Report Appendix

By:

Design Alaska, Inc.

601 College Road Fairbanks, Alaska 99701

December 1, 2021

BUREAU OF LAND MANAGEMENT

NOME CREEK ROAD REPAIR

NOME CREEK ROAD, ALASKA

SCHEMATIC DESIGN

CIVIL NARRATIVE

Design Alaska, Inc. Page 1 of 11

GENERAL

The general scope of this project involves improvements to the drainage structures and driving surface of Nome Creek Road. This project is located within the White Mountains Recreation area, and is accessible via US Creek Road, located at milepost 57 of the Steese Highway. The project involves 18 miles of dirt road between Mt. Prindle Campground to the east and Ophir Creek Campground to the west. The project begins at the Nome Creek bridge and generally runs parallel to, and along the north side of Nome Creek.

Nome Creek Road provides access to several hiking and motorized recreational trails, campgrounds, gold panning and camping opportunities. It is a critical access point for the White Mountains Recreation Area.

The road is primarily used by the recreating public during the summer months. During winter, both campgrounds are closed and maintenance and snow removal is suspended for the season. The road is still utilized for recreation access by snowmachine, ski, and dog sled.

Design Alaska conducted several site visits during the summer of 2021. Site visits were performed just after spring breakup, during summer, and immediately before heavy snow accumulation in the fall. During site visits, Design Alaska performed an inventory of 124 existing culverts along the Mt. Prindle alignment to the east of the bridge, and the Ophir Creek alignment to the west of the bridge. The general condition of the road and campgrounds was also noted and specific problem areas were identified and discussed with the maintenance personnel present at the site. The condition of the gabions and stream channel migration at Nome Creek bridge was also observed, photographed and discussed.

Design Alaska performed a topographic survey of the entire Nome Creek corridor including photogrammetric and aerial mapping flights. The areal mapping data was correlated with ground survey data to produce a detailed survey of the existing grade along the entire extent of the project.

Shannon and Wilson performed geotechnical borings along the road to determine in place material and subsurface conditions along the road corridor, especially at areas of significant settlement and embankment failure. Exploratory drilling was also performed for the purpose of determining material availability and suitability at several sites near the project area.

DESIGN CRITERIA – GOVERNING CODES AND REGULATIONS

Authority Having Jurisdiction BUREAU OF LAND MANAGEMENT

USACE, CWA 404 Permit Regulations

ADEC, CWA 401 Water Quality Certification

State of Alaska – AS 16.05.841 – Fishway Required, 2020

AKDOT&PF, Standard Specifications for Highway Construction, 2020

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Design Alaska, Inc. Page 2 of 11

Manual on Uniform Traffic Control Devices, 2009

Alaska Highway Preconstruction Manual, 2020

American Association of State Highway and Transportation Officials, 2020

Occupational Safety and Health Administration

EXISTING CONDITIONS

Nome Creek Road was constructed as a DOT project approximately 30 years ago. Several major repairs have been performed since the initial construction, including significant embankment buildup and culvert upgrades at both Twin Creek crossings and at Moose Creek. Extensive maintenance is performed each spring in preparation for opening to the public. Several areas have experienced recurring washout and embankment failure and have been specifically identified as needing additional analysis and strategic repairs. Several specific areas of interest are discussed below.

Some portions of Nome Creek Road experience buildup of aufeis during winter months. Aufeis is a condition unique to arctic climates which can present significant design challenges for roadways.

Aufeis is commonly encountered along roads and trails in arctic and sub‐arctic climates. Subsurface water flow occurs year‐round within the un‐frozen soils between the permafrost layer and the seasonally frozen active layer. The freezing front of the active layer advances more quickly and penetrates more deeply in soils with greater thermal conductivity such as gravel roadways. Roadways also alter the thermal regime of the soils by removal of the insulating organic layers. Snow removal or compaction by trail users throughout the winter months also effectively eliminates the insulating properties of the accumulated snowpack. The combined effect of more thermally conductive soils and decreased insulation relative to adjacent soils ensure that the seasonal frost line is significantly deeper along roadways than in the adjacent, undisturbed soils. Seasonal frost depths of 4 feet‐6‐feet are common in undisturbed soils at this project site. In disturbed areas, the frost will commonly reach depths of 12 feet‐16 feet. The transition between relatively shallow frost depths in undisturbed areas and deeper frost depths along roads or trails can be very abrupt, even near vertical. As roads and trails are typically constructed parallel to slope contours for ease of travel, and water flows perpendicular to slope contours, the confinement caused by an impermeable, deeply frozen roadbed confines subsurface flow much like a dam, and forces water to the surface where it freezes. Aufeis will accumulate initially in stream channels and swales, especially at culverts and other improvements intended to capture and convey runoff during summer months. In the springtime, the large accumulation of aufeis at some culverts and stream crossings is slow to melt as solid sheets of ice, often greater than 10 feet thick, thaw more slowly than the surrounding, loose snowpack.

As runoff from melting snow seeks the path of least resistance, it is impeded in the areas where the accumulated aufeis has formed a dam in some stream channels and culverts. The flowing meltwater will frequently overtop the road embankment causing washouts and significant erosion damage. The location and extent of aufeis accumulation is not consistent year to year, as it is highly dependent upon specific

NOME CREEK ROAD, ALASKA

Design Alaska, Inc. Page 3 of 11 temperature and subsurface flow conditions. Though this makes predicting and mitigating potential damage very challenging, some consistency can be anticipated and controls put in place to protect areas of frequent recurrence.

Road Surface and Ditches

Since construction, the road has been maintained by general blading and repair of specific damaged areas.

Frequent blading, hydraulic segregation, and fugitive dust caused by vehicle traffic has significantly deteriorated the surface course of the existing road in many areas. Much of the fines from the original road surface have accumulated in the ditches, along with other soils from suspended sediment and blading repairs. In addition to the decreased capacity of the existing ditches caused by accumulated sediment, many of the culvert inlets have also become partially obstructed by sediment, further decreasing the effectiveness of the designed drainage system along the road corridor. The originally constructed crown of the road has also been largely eliminated. Re‐establishing and maintaining the crown has become increasingly challenging for maintenance crews as the surface course has become very thin or completely absent over years of use and maintenance. In some areas, large cobbles are visible in the traveled way where the subbase has become exposed. These large, exposed cobbles are an impediment to travel and user safety. The decreased drainage potential of the road has resulted in frequent saturation of portions of the embankment, causing failure and blowout of many areas.

Existing Culverts

During initial site investigation, an inventory of the existing culverts was performed. Approximately 30 of the 124 culverts inventoried are in need of repair or replacement. Many of the culverts have been obstructed by accumulated sediment in the ditches and by settlement of the road embankment.

The Nome Creek valley is underlain by permafrost at varying depths along its entire length. In many areas the altered thermal regime of the soils and the poorly performing drainage structures has accelerated permafrost degradation along the road corridor. As permafrost thaws under the road embankment, the soils consolidate and differential settlement occurs relative to the adjacent undisturbed soils. This differential settlement causes a belly shape in the culverts, which can greatly reduce their effectiveness at conveying water under the embankment. In some cases, the belly can be severe enough to cause separation of the culvert allowing runoff water to be injected directly into the roadbed.

Informational Signs

Many of the existing signs along Nome Creek Road are in need of replacement. Existing signs include traffic signs, information signs, parking signs, campground signs and mileage markers. An inventory of the existing signs is included in the drawings for this project.

NOME CREEK ROAD, ALASKA

SCHEMATIC DESIGN

CIVIL NARRATIVE

Design Alaska, Inc. Page 4 of 11

Dickie’s Hole

Dickie’s Hole is a developing problem site that has experienced significant sedimentation buildup, washout, and settlement in recent years. The upstream permafrost appears to be rapidly degrading and settling into a more pronounced drainage channel. As the drainage channel expands, it collects additional runoff and develops more aufeis each year, which accelerates embankment failure downstream. The degrading permafrost is also changing the erosion regime and significant sedimentation has accumulated where the developing stream encounters Nome Creek Road. During high seasonal or stormwater flow, the existing culverts are inadequate to convey the runoff. Water builds up on the upstream side and sediment falls out of suspension, further reducing ditch volume and clogging the existing culverts. At the time of the most recent site visit, deposited sediment had accumulated against the road embankment to a depth of at least 8 feet.

Another arctic phenomenon is also believed to be causing damage to the existing culverts in this location.

Aufeis, built up at the culvert inlet over the winter, maintains adfreeze grip on the culvert inlet. As liquid water levels rise within the flowline of the ditch, buoyancy forces acting on the remaining aufeis clinging to the drainage structure impart powerful uplift forces, causing buckling and failure of the culvert inlet.

This damage will, at best, reduce the effectiveness of the culvert, but often damages the culvert within the embankment, allowing flow to escape within the embankment and cause massive erosion. Saturation of the embankment can further lead to loss of soil strength and blowout of the roadway. The failed ditches and culverts have led to overtopping of the road embankment, washout, and further erosion.

Moose Creek

The Moose Creek crossing was the subject of a major repair project in 2006 to correct damages similar to what is presently being observed at Dickie’s Hole. In the recent past, the corrections and improvements to the Moose Creek crossing have begun to degrade, settle, and show signs of inadequacy.

Mt. Prindle Campground

Mt. Prindle Campground has experienced seasonal flooding in recent years which has degraded the existing roads and camp sites. The embankment height of the campground roads and campsites are relatively low, making them susceptible to flooding. Vegetation around the campground is a mix of low willow, alder, and some small black spruce. The low vegetation provides great access to the surrounding viewshed but provides limited erosion protection.

Nome Creek has experienced significant aufeis buildup near the campground in recent winters. This aufeis occasionally forms a complete blockage of the stream channel. With the regular channel blocked, accumulated spring runoff is diverted to the next available path. In the area of Mt. Prindle Campground, the next available path is directly through the campground, causing widespread erosion and washout of campground drives and campsites.

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Vehicle circulation at the Mt. Prindle campground is generally in the form of an elongated loop drive with campsites arranged around the outside of the loop. Well and outhouse structures are located on the inside of the loop to provide the shortest access to the most campsites. Maintenance and repair have generally been focused on the access drive loop, and the inner, foot trail connecting the drive loops to the well is in need of reconstruction. The existing well located near the center of the campground is a hand operated pitcher pump on a 4‐inch concrete slab. During a recent flooding event, which washed out the foot trail leading to the well, the concrete slab was severely undercut and eroded, causing uneven settlement and instability of the slab.

Ophir Campground

Ophir Creek Campground also experiences significant spring flooding and washout for the same reason as Mt. Prindle campground. However, where Mt. Prindle Campground experiences widespread, general overtopping and washout, Ophir Creek Campground experiences channelized and concentrated washout at specific locations. This is partially because the road and campsite embankment height are greater at Ophir Creek than at Mt. Prindle. Ophir Creek Campground is also surrounded by larger, mature trees including spruce, birch and aspen. The trees and root mass protect the surrounding area from erosion by trapping ice and slowing runoff velocity. Ophir Creek Campground has several historic minor channels running through the campground. These channels are generally dry throughout the summer months, but during spring melt, they are major conduits for diverted and flooded stream flow. This concentrated channelization reduces widespread erosion but causes severe damage where the channels encounter campground drives and campsites. Existing culverts at these locations adequately handle peak flows during spring runoff and major repairs are typically required each spring before the campground can be reopened.

In general, the road and campsite surface at Mt. Prindle Campground is in good condition. Major reshaping throughout the campground is not anticipated. Flood control and road embankment repair will be limited to areas of recurring washout damage.

Nome Creek Administrative Runway

BLM operates a small, gravel runway near the maintenance yard along the Ophir Line. The runway has experienced settlement and ponding which makes use by aircraft unsafe.

This project will not evaluate the safety or code compliance of the runway for aircraft use. Consideration of any aircraft or runway code is outside the scope of work performed herein. Repairs will be limited to addressing drainage and grading failures. For this work, the runway will be considered the same as a section of gravel road.

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Nome Creek Bridge and Gabion Revetment

Nome Creek Bridge is a vehicle bridge crossing Nome Creek and was installed as part of the original road construction. The bridge is 24 feet wide with metal guard rails, and spans 30 feet between abutments.

The bridge deck is a voided, reinforced concrete slab with a 3 percent cross slope. The bridge abutments are a pile supported timber wall with a concrete cap supporting the bridge decking. The initial construction of the Nome Creek Bridge included installation of a network of interlocking, 3‐foot by 3‐foot, galvanized chain‐link gabion baskets to control erosion upstream and downstream of the bridge.

As part of the bridge construction, the stream channel was altered to concentrate flows at a location more suitable for bridge construction. Since construction, the stream has been slowly eroding and migrating back to the original channel path. The channel migration has caused undercutting of the upstream and downstream erosion protection gabions.

DEMOLITION

Demolition for this project is limited to removal of several of the failed culverts along the alignment and damaged gabions at the Nome Creek Bridge. Demolition will be limited to the extent needed for replacement work.

RENOVATED OR NEW WORK

Repairs to the existing road will include reconditioning and resurfacing of the entire length of road. The road prism will be re‐shaped and graded where needed to improve surface runoff. The ditches will be cleaned and reconditioned as needed to improve roadside drainage. In areas where embankment settlement has reduced the ditch depth or other areas where ditch depth is inadequate, ditches will be enhanced by adding additional height to the embankment. Past repairs and improvements have demonstrated that in areas where the vegetated mat is disturbed by excavation, the regrowth and revegetation can take as long as 10 years. During that time improvements and disturbed soils are subject to substantial erosion. In order to avoid erosion damage, the existing vegetative mat will be maintained as much as possible and all ditch improvements will be made by raising the grade of the embankment.

Road Surface

The existing ditches will be cleaned of accumulated sediment and vegetation as much as possible without disturbing the native vegetation nearby. Some portions of the embankment will require reshaping and revisions to the vertical grading. This effort will be performed where needed to add ditch depth, improve flow, and generally move runoff away from the embankment more quickly.

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Once changes to the road structure, ditch lines and culverts have been completed, the driving surface of the road will be improved by adding a maximum of 4 inches of additional crushed aggregate surface course to the entire length.

Culverts

The inventory of the existing culvert conditions and signs of past performance were evaluated. Many of the culverts are in need of minor inlet repairs, erosion protection at the outlets and clearing of grown‐up vegetation within the ditches. A few of the culverts have failed or been damaged beyond simple repair and will require replacement. The culverts were ranked by priority for replacement. High priority culverts are shown in the attached appendix. Some culverts will require lengthening where road embankment buildup and alterations will widen the road assembly beyond the extent of the existing culverts. Culverts repaired or replaced by this project will include steel cable installation for spring thawing and carsonite marker posts with placards for culvert identification. New culverts will be galvanized, corrugated, welded seam metal pipe.

Informational Signs

This project will replace all roadside signs and signposts including, but not limited to, parking signs, creek signs, campground signs, and road milage marker signs within the project area. All existing signs shall be salvaged for future reuse. The contractor will deconstruct and store all existing signs in a designated salvage location identified on site for owner collection. New and replaced roadside signs will comply with DOT standard drawing S05.02 for rural roads. Campground and information signs will meet BLM sign standards and be similar to other BLM campgrounds in interior Alaska.

Dickie’s Hole

The primary cause of the sediment accumulation and damage at Dickie’s Hole is believed to be deterioration of the permafrost and expansion of the drainage channel upstream of the road. Addressing this cause is not within the scope of this project, but this project will instead focus on mitigating the effects. Specifically, this project will address the following items: sediment accumulation; standing, confined water against the road embankment; runoff overtopping of the road embankment; and recurring damage to the drainage structures. Quantifying the design flood intensity and recurrence interval is a unique exercise for this situation, as the worst case flooding event is not caused by precipitation, but by snowpack melt. Also, catchment area, time of concentration, and drainage paths vary year to year as aufeis blockages are not consistent. Volume of water contained in a measured snowpack is highly variable, and dependent upon wind conditions, relative humidity and air temperatures throughout the winter months.

Initial repairs will, at a minimum, include removal of accumulated sediment against the road embankment and restoration of the stream channel for at least 50 feet upstream of Nome Creek Road.

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Standing water against the embankment and sediment accumulation at the inlet end of drainage structures are believed to be caused by the same overall problem. Specifically, inadequate capacity of the culverts prevents free passage of runoff under the road embankment. While the culverts may be adequately sized to convey the design storm event in summer months, the culverts are partially or completely obstructed by accumulated ice during spring melt. A 144‐inch diameter, multiplate culvert installed at the flow line of the drainage will provide more space for ice accumulation and bypass flow.

The multiplate culvert will be constructed with a cross slope of at least 4 percent to ensure that flow velocity does not fall low enough to allow suspended sediment to precipitate and accumulate at the inlet or within the culvert. A series of 36‐inch overflow culverts will be installed above the large multiplate culvert. When the stream channel, including the multiplate culvert, becomes completely obstructed by accumulated aufeis, any runoff flow will be conveyed through the embankment by the overflow culverts.

The recurring damage to drainage structures is believed to be caused in part by buoyancy forces, acting through the adfreeze strength of accumulated aufeis, bending the culvert inlet upward. To mitigate this mechanism of damage, we propose a concrete headwall with concrete wingwalls and bottom plate. The headwall will protect the culvert by providing ballast to resist the buoyancy forces acting on the inlet.

Concrete will also provide a smooth surface, which will reduce adfreeze strength compared to an open pipe end. The thermal mass of the concrete may also accelerate melt as heat from spring sunshine warms the concrete, allowing more rapid melt along the face of the headwall than in areas not in contact with the concrete. The concrete bottom plate will reduce erosion at the inlet and enable more convenient cleaning of any sediment that may accumulate in the future.

The multiplate culvert with concrete headwall described above, in combination with the overflow culverts installed at higher elevations, will ensure that there is a drainage path for spring runoff in this location even when the drainage channel is completely blocked by accumulated ice. This will eliminate the opportunity for overtopping, reducing annual maintenance and reconstruction in this location.

The degrading permafrost and settlement of the surrounding terrain in this area will affect the performance of this repair, especially in the short term as the altered thermal regime returns to some equilibrium or homogeneous, ongoing deterioration. In order to mitigate short term and long term failure, the embankment will be reconstructed with a core of less permeable soils. Side slopes will be constructed at a maximum slope of 3 horizontal to 1 vertical to homogenize differential settlement. Slopes on the upstream and downstream sides of the embankment will be armored for erosion protection.

Moose Creek

A condition report prepared in 2018 rated the 15‐foot diameter culvert at Moose Creek Crossing as “satisfactory condition overall”. Some undermining was noted in the concrete apron at the right side of the inlet. Additionally, overflow barrels were in need of inlet and outlet armoring and reconstruction.

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This project will address the issues described in the 2018 report. Specifically, scour damage at the inlet and outlet of the 15‐foot diameter major culvert will be repaired and regraded. Undermining of the concrete apron on the inlet side will be repaired by grout injection. A layer of 6‐inch through 8‐inch angular rip rap will be installed to a depth of at least 12 inches on the inlet and outlet sides of the headwall to mitigate further erosion and undermining. Concrete wing walls and a concrete apron will be installed at the inlet of the culvert to reduce ice erosion damage. The existing thaw pipe and thaw wire will be removed and replaced with a single thaw wire suspended from the top of the culvert barrel and supported at an interval of 4 feet.

The overflow culverts were also identified by the report as needing erosion correction. The overflow culverts are numbered in the direction of alignment stationing from 1 to 5 consecutively.

Overflow Barrel 1: Remove and replace sagging pipe with same size corrugated metal pipe culvert. Install rip rap at inlet and outlet end to protect from scour and erosion damage. Install thaw wire and suspend from the crown of the barrel at 4‐foot intervals.

Overflow Barrel 2: Repair scour and undermining at inlet (5‐foot‐8‐inch scour) and outlet (4‐foot‐9‐inch undermining) end and replace scoured material. Install riprap at inlet and outlet ends to prevent future damage by erosion and scour. Install thaw wire and suspend from the crown of the barrel at 4‐foot intervals.

Overflow Barrel 3: Repair scour and undermining at inlet (6‐foot scour) and outlet (11‐foot undermining) end and replace scoured material. Install riprap at inlet and outlet ends to prevent future damage by erosion and scour. Install thaw wire and suspend from the crown of the barrel at 4‐foot intervals.

Overflow Barrel 4: Repair minor scour and undermining at inlet and outlet ends and replace scoured material. Install riprap at inlet and outlet ends to prevent future damage by erosion and scour. Remove thaw pipe and install thaw wire and suspend from the crown of the barrel at 4‐foot intervals.

Overflow Barrel 5: Repair minor scour and undermining at inlet and outlet ends and replace scoured material. Install riprap at inlet and outlet ends to prevent future damage by erosion and scour. Install thaw wire and suspend from the crown of the barrel at 4‐foot intervals.

Mt. Prindle Campground

The road and camp sites at Mt. Prindle Campground will be reshaped to add additional height relative to adjacent grade. The added height will reduce overtopping and provide flow paths against the embankment. Additional culverts may be needed at strategic locations to convey the concentrated runoff through the drives. The road and campsites will be resurfaced similar to Nome Creek Road. All campground road, directional, and information signs will be replaced as described in the sign replacement portion of this design narrative.

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A foot trail will be constructed connecting both sides of the loop drive to the center well. The well head hand pump, and concrete slab will be removed and replaced.

A diversion structure, including 500‐foot long, by 48‐inch deep drainage ditch with 12‐foot bottom width will be constructed upstream of the campground to provide a drainage path for flooding meltwater.

Excavated materials from the ditch construction will be piled on the downstream side of the ditch and sculpted to form a levee of at least 48 inches vertical height with at least 3:1 side‐slopes.

Ophir Campground

Repairs at Ophir Creek Campground will be limited to locations damaged by recurring flooding and general resurfacing of the roadway.

Two locations within the Mt. Prindle campground will require major reconstruction and reshaping of the road prism. Alterations to grade leading to and from the affected areas will also require reshaping. At the locations depicted in the design drawings, a series of drainage and overflow culverts will be installed similar to previous control measures installed at station 4+70. At each of the two flood channel damaged locations, a single, 36‐inch culvert will be installed at the flow line and two, 24‐inch, overflow culverts will be installed above. Erosion control riprap will be installed at the inlet and outlet end of the crossing.

Nome Creek Administrative Runway

Repair work at Nome Creek Administrative Runway will be limited to regrading settled areas and providing a culvert to convey runoff across the runway. The regrading will fill the washout portion and ensure a minimum embankment height of at least 12 inches above adjacent existing grade at the shoulders of the runway. The runway will be center crowned along its entire length with a 3 percent cross slope. Shoulders will slope at 3H:1V to grade. At the low point, where seasonal ponding has been occurring, a 24‐inch culvert will be installed to convey runoff from the uphill side, under the runway. Culvert pipe will be installed at a minimum cross‐slope of 4 percent to ensure that the pipe is self‐cleaning. Minor ditching will be constructed along the uphill side of the runway to collect runoff from the hillside and concentrate it at the culvert inlet. A small basin will be installed at the inlet of the culvert to ensure adequate burial depth. The basin will be constructed in such a way that slopes to the flowline will not exceed 5 percent for at least 20 feet up‐station, down‐station, and perpendicular to the runway embankment. Beyond 20 feet, side slopes will be installed at 3H to 1 V max.

There is evidence that Nome Creek has flooded onto or near the runway embankment. To mitigate this mechanism of damage, a 30‐inch tall by 150‐foot long levee will be constructed. The levee will begin 75 feet upstream of the closest point of flooding to the runway and will be aligned parallel to the runway alignment.

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MATERIAL SITE DEVELOPMENT

Additional work by Shannon and Wilson involved an assessment of possible material source sites. Initial findings suggest two locations may have suitable aggregate quality, at the area above and below Nome Creek Bridge and at the BLM 56 mile Steese Highway material site that is near ADOT Material Site 670‐ 101‐2. Findings near Nome Creek Bridge were determined to not be viable sources for the quantity of aggregate needed for this project. However, preliminary review of the BLM material site along the Chatanika River indicated that the quantity of alluvial gravel may be sufficient for use as aggregate on this project. Initial estimates suggest that over 100,000 cubic yards of aggregate are available for use.

Additional exploration will help outline the quality and quantity of aggregate and determine the allowable mining area.

POINTS OF DISCUSSION

1. Material stockpile phasing.

2. Closing the access road in stages for road and campground repairs.

3. Budget constraints and modification of overall scope to fit within proposed budget.

Specification Index

NOME CREEK ROAD, ALASKA

SPECIFICATION INDEX

Design Alaska, Inc. Index‐ 1

DIVISION 01 GENERAL REQUIREMENTS

01 10 00 Summary of Work 01 31 00 Project Management and Coordination 01 32 00 Construction Progress Documentation 01 32 20 Photographic Documentation 01 33 00 Submittal Procedures 01 40 00 Quality Requirements 01 42 00 References 01 50 00 Temporary Facilities and Controls 01 52 40 Construction Waste Management 01 56 39 Temporary Tree and Plant Protection 01 60 00 Product Requirements 01 70 00 Execution Requirements 01 71 23 Field Engineering 01 77 00 Closeout Procedures 01 78 10 Project Record Documents

DIVISION 02 EXISTING CONDITIONS

02 41 19 Selective Demolition

DIVISION 03 CONCRETE

03 33 00 Cast in Place Concrete

DIVISION 31 EARTHWORK

31 10 00 Site Clearing 31 20 00 Earth Moving

DIVISION 32 EXTERIOR IMPROVEMENTS

32 92 19 Seeding

DIVISION 33 UTILITIES

33 42 13 Stormwater Culverts

Draft Geotechnical Report

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SUBMITTED TO:

Design Alaska Inc.

601 College Road Fairbanks, AK 99701

BY:

Shannon & Wilson 2355 Hill Road Fairbanks, AK 99709

907-479-0600 www.shannonwilson.com

GEOTECHNICAL RECOMMENDATIONS REPORT

White Mountains Recreation Area Access Improvements

NOME CREEK ROAD

November 30, 2021 Shannon & Wilson No: 107285-001

White Mountains Recreation Area Access Improvements DRAFT Geotechnical Recommendations Report

107285-001 November 30, 2021

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107285-001 November 30, 2021 11/30/2021-107285-T.docx i

Submitted To: Design Alaska Inc.

601 College Road Fairbanks, AK 99701 Attn: Contact Name

Subject: DRAFT GEOTECHNICAL RECOMMENDATIONS REPORT, WHITE

MOUNTAINS RECREATION AREA ACCESS IMPROVEMENTS, NOME

CREEK ROAD

Shannon & Wilson prepared this report and participated in this project as a subconsultant to Design Alaska, Inc. Our scope of services was specified in Subconsultant Letter of Agreement dated September 11, 2021. This report presents our findings and draft recommendations and was prepared by the undersigned.

We appreciate the opportunity to be of service to you on this project. If you have questions concerning this report, or we may be of further service, please contact us.

Sincerely, SHANNON & WILSON

Wendy Presler, P.E. Christopher Helland, P.E.

Associate / Geotechnical Engineer Senior Hydraulic EngineerDRAFT

S R REPORTEPO , WH

MPROVEMENTSMPROVE , NO

ed in this project as a subconsultant toed in this project as a subc cified in Subconsultant Letter of cified in Subconsultant Letter of ort presents ort pres our findings and drafaft t undersigned.unders f service to you on this project. If you ho you on this be of further service, please contact us. ice, ple

Wendy Presler, P.E., P.E.

Associate / GeotechnicaAssociate / Geotech

Wendy Presler

Digitally signed by Wendy Presler Date: 2021.11.30 10:22:50 -09'00'

107285-001 November 30, 2021 ii

EXECUTIVE SUMMARY

This project will make improvements to the 18-mile length of Nome Creek Road, including drainage, possible culvert replacement, and stockpiling of material for future maintenance.

We explored several locations along the existing alignment, and potential material sources in the Nome Creek Valley. We reviewed existing culvert survey data and a culvert condition assessment conducted by Design Alaska.

Our explorations in the Nome Creek Valley did not yield promising results with regard to material availability for the road surfacing or for stockpile development. The Owner provided information regarding a potential material source at the 56-mile Steese Highway pit that is shared between the Alaska Department of Transportation & Public Facilities, and the Bureau of Land Management. We recommend explorations for the 56-mile Steese Highway site.

Additionally, approximately 30 existing or potential culvert locations have been identified for further analyses.

DRAFT

r futurer futur d potential material d potent vey data and a culvert convey data and a t yield promising results with regard tot yield promising results with reg r stockpile development. The Owner r stockpile development. The Owner material source at the 56-material source at the mile Steese HiHi partment of Transportation & Public Fament of Transporta recommend explorations for the 56d exploratio -mi y 30 existing or potentixisting or potential culvert locationrt locat

107285-001 November 30, 2021 iii

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CONTENTS

1 Introduction

1.1 Project Understanding

1.2 Scope of Services

2 Field and Laboratory Studies

2.1 Field Exploration and Methods

2.1.1 Geotechnical Soil Borings

2.2 Laboratory Testing

3 Site Conditions

3.1 Surface Conditions

3.2 Subsurface Conditions

3.2.1 Road Alignment

3.2.2 Material Source Sites

3.2.2.1 Area above and below Nome Creek Bridge, permitted

F91438 site

3.2.2.2 BLM 56 Mile Steese Highway Material site near ADOT

Material Site 670-101-2

4 Site Geological Setting

4.1 Geological Setting

5 Hydrology

6 Geotechnical Discussion

6.1 Road Embankment Recommendations

6.2 Road Surface Course Recommendations

6.3 Culvert Installation

6.4 Soft Subgrade Soils

7 Materials

7.1 Backfill

7.2 Surface Course

7.3 Common Fill

7.4 Bedding

7.5 Nonwoven Geotextile Fabric

8 Closure

DRAFT

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Sites ...........................................................Sites a above and below Nbove and belo ome Creek BridgeCreek Br 91438 site...................................................site

2.2 BLM 56 Mile Steese Highway MaterMile Steese Highway Mate

Material Site 670-101-2 .................Material Site 670-101-2 ogical Settingogical Setting

Geological SettingGeological Setting

Hydrologydrology

Geotechnical Discussion....................hnical Discussion

6.1 6.1 Road Embankment RecomRoad Embank

6.2 Road Surface Course Road Surface Cou

6.3 Culvert Installatiolvert Installatio

6.4 Soft SubgradSub

7 Materials ........7 Materials

7.1 7.1 BackBack

7.2 7.2

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9 References

Exhibits Exhibit 2-1: Material observed at MS07 Exhibit 2-2: Collecting sample at MS08 Exhibit 2-3: Collecting sample at MS09 Exhibit 2-1: Wax Density Test Results Exhibit 2-2: Aggregate Quality Test Results Exhibit 3-1: Narrow embankment near 21-08 Exhibit 3-2: Potholes near culvert crossing Exhibit 3-3: Silt accumulation at Dickie's Hole Exhibit 5-1: Culverts needing maintenance, repair or upsizing Exhibit 7-1: Backfill Gradation Exhibit 7-2: Surface Course Gradation Exhibit 8-3: Bedding Material Gradation Limits

Figures Figure 1: Vicinity Map Figure 2: Material Site Locations

Appendices Appendix A: Soil Classification Appendix B: Laboratory Test Results Appendix C: Project Photos Appendix D: Exploration Plan Important Information

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.................................................................1 or upsizing ................................................or upsizing

Limits .........................................................ts e Locations ions il il ClassificationClassificatio Laboratory Test ResultsLaboratory Test R

C: Project PhotosC: Project Photos dix D: Exploration Planx D: Exploration Plan ortant Informationnformation

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ACRONYMS

AASHTO American Association of State Highway and Transportation Officials ASTM ASTM International ATM Alaska test method bgs below ground surface BLM Bureau of Land Management DOT&PF Alaska Department of Transportation &Public Facilities GeoTek GeoTek Alaska, Inc.

H&H hydraulics and hydrology MS material site RFP request for proposal

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1 INTRODUCTION

This geotechnical recommendations report was prepared for the proposed improvements to the Nome Creek Road in the White Mountains Recreation Area. This report presents our findings from the site exploration, laboratory test results, geotechnical analyses, preliminary hydrology review, discussion and recommendations. The following introductory sections summarize our scope of services and project understanding.

1.1 Project Understanding

We understand the 18-mile length of the Nome Creek Road will be upgraded to reduce maintenance cost and effort. The project may include repairs to existing ditches, improvements at Dickie's Hole, improvements at the Moose Creek culvert crossing, minor grade changes and addition of four inches of crushed aggregate surfacing, and construction of two 10,000 cubic yard stockpiles for future maintenance.

The request for proposal (RFP) mentions maintenance and infrastructure degradation concerns including road settlement distress, grade changes, ditching and drainage, loss of aggregate surfacing, inadequate culvert performance at several drainage crossings, maintenance and road stability at Dickie's Hole, and lack of crushed surfacing material for future maintenance.

Our services included geotechnical exploration, laboratory testing, geotechnical, and hydraulics and hydrology (H&H) analyses, and development of geotechnical and H&H recommendations for the design and construction of the improvements. Based on meetings with the Bureau of Land Management (BLM) and Design Alaska we understand the focus of our studies should be limited to the items discussed above, though additional potential scope items were mentioned in the RFP.

Our scope includes geotechnical exploration to develop an understanding of subsurface conditions at multiplate culvert replacement locations, significant road dip/settlement areas, and at possible borrow site locations.

1.2 Scope of Services

The BLM scope of work outlines several tasks that require geotechnical and/or H&H input.

The tasks were listed in order of priority; the first five priorities are interpreted to include the following scope of work:

report prepor nical analyses, nical an owing inowing introductory se g.g.

Creek Road will be upgraded to reduceCreek Road will be upgraded to reduc ayy includeinclu repairs to existing ditches, rs to ex ments at the Moose Creek culvert crosss at the Moose Cr nches of crushed aggregate surfacing, anshed aggreg s for future maintenance. s for future maintenance.

P) mentions mentions maintenance and infrastrumaintenance and infrast settlement distress, grade changes, ditct distress, grade changes, ditc nadequate culvert performance at sevevert performance at seve road stability at Dickie's Hole, and lack road stability at Dickie's Hol ance.ance.

ices included geotechnical exploration, ices included geotechnical exploration aulics and hydrology (s and hydrology (H&HH&H) ) analyses, aanalyses, a commendations for the design and contions for the design and con with the with the Bureau of Land ManagementBureau of Land our studies should be limited toour studies should be limit th scope items were mentioned inwere mentioned i

Our scope includes geotedes conditions at multiplaconditions at multip and at possible borand at possible bo pe ofpe of

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Ditch Repair: Provide typical ditch and backslope geometry, recommendations and concepts for stabilization of sloughing backslopes. Provide surface hydrology study to provide input on ditch sizing and design.

Dickies Hole: Provide subsurface exploration to assess subsurface soil conditions for the installation of a large multiplate culvert and improve road embankment grade.

Moose Creek Culvert Crossing Repair: Consider the adequacy and shortfalls of the Moose Creek Crossing and provide geotechnical and H&H recommendations for repair or upgrade to bring this crossing into better long-term, low-maintenance sustainability.

Road Grade Corrections and Resurfacing: Conduct subsurface explorations to develop an understanding of possible causes of the settlement.

Gravel Source and Stockpiles: Explore or assess potential material sites to evaluate the possible quantity and quality of aggregate available in select areas of the Nome Creek valley.

The following tasks were identified in the RFP but have not been prioritized, studied in detail, or included in this report:

Mt. Prindle and Ophir Campground Repairs;

Informational Sign Replacement;

Mt. Prindle Campground Diversion;

Nome Creek Administrative Runway Repair

Nome Creek Bridge Gabion Repair.

2 FIELD AND LABORATORY STUDIES

The field explorations for this project consisted of 16 borings along the road. We additionally advanced six borings in the proposed material site areas, collecting grab samples and observing the depth of gravel. The proposed boring locations were identified in our exploration plan, presented in Appendix D.

Borings 21-01 through 21-16 were drilled along the current road alignment including two at "Dickie's Hole". The boring locations were identified as locations of increased settlement or erosion, moist soils at the road surface from poor drainage, and poor road surface conditions including wash-boarding, potholing, and/or road distress. The boreholes were advanced between October 13th and October 16th, 2021. We collected representative soil samples from the field explorations for index testing in our Fairbanks soil laboratory.

Six potential material site (MS) borings, designated 21-17 through 21-22, were identified in the exploration plan. Three additional sites were identified after mobilization. A sample was

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menmen ndnd shortfal sho recommendations frecomm w-maintenance sustainabw-maintenan ubsurface explorations to developubsurface exploration ent. ent.

ss potential material sites to evaluate thss potential material sites to evaluat available in select areas of the Navailable in select a ome Cme C n the RFP but have not been ut have not prioritized, mpground Repairsground Repairs;

eplacementnt; ;

pground Diversionion; ;

AdminAdministrative Runway Repair istrative Runway Re reek Bridge Gabion Repairreek Bridge Gabion .

ELD AND AND LABORATORYLABORATORY

The fieldThe field explorations for this projec explorations for additionally advanced additionally advanced sixsix boringbo samples and observing the deobserving the de in our exploration planon p , pr

BoringsBorin 21-01 througthrou DickDickie's Hie's Hole"ole". T. T ion, ion, moistmoist onsons

107285-001 November 30, 2021 collected from MS07. MS07 was identified as a berm south of Nome Creek Road, north of Nome Creek. The berm of material is assumed to be a windrow of material pushed up out of the valley bottom during dredging. We used a pickaxe and shovel to collect the sample (Exhibit 2-1).

Exhibit 2-1: Material observed at MS07

We used the drill rig to explore MS08 near the base of a ridge south of Nome Creek and west of U.S. Creek Road, which was accessed by a trail. The auger was used to disturb the surface and probe for depth of gravel. Gravel extended approximately three feet from the surface at this location. DRExhibit Exhibit 2-12-1: : Material observedMaterial observe at MS07

We used the drill rig to explore e drill rig to explor west of U.S. Creek Road, reek R whwh surface and probe for depsurface and probe fo surface at this locationsurface at this locati

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Exhibit 2-2: Collecting sample at MS08

We visited the site of the 56-mile Steese Highway pit (MS09) to collect a sample of near-surface soils using the drill rig auger. We observed silty gravel from the surface to five feet below ground surface (bgs) at this location.

DRAecting ecting sample at MS08sample at M d the site of the 56-d the site of the 56-mile Steese Highwamile Steese Highw ce soils using the drill rig auger. We obls using the drill rig auger. We ob elow ground surface (d surface (bgsb ) at this locatioti

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Exhibit 2-3: Collecting sample at MS09

Figure 1 shows the project location on a Vicinity Map. Figure 2 presents the approximate location of MS07, MS08 and MS09.

The purpose of our borings along was to collect subsurface data and samples for laboratory index testing and selected engineering property testing. The data collected in the borings was used to supplement our understanding of subsurface conditions in the project area, especially regarding:

Subgrade soil type and stratigraphy;

Depth to bedrock;

Frost-susceptibility and compressibility of subgrade soils;

Presence or absence of permafrost within the exploration depth;

Moisture content of unsaturated and frozen soils; and

Aggregate quality and estimated quantity of potential material sources.

DRAecting sampleecting sample at MS09at M shows the project location on a Vicinityshows the project location on a Vicinit on of MS07, MS08 and MS09. MS07, MS08 and MS09.

The purpose of our borings along was The purpose of our bori index testing and selected engineerindex testing and selected e was used to supplement our uno supplement our u especially regarding:arding

Subgrade soil type aoil ty

Depth to bedrocDepth to bedro

FrostFrost-suscep-suscep sencsenc

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The data collected along the current road alignment and at the material sites is the basis for our discussion and geotechnical engineering analyses.

2.1 Field Exploration and Methods

We subcontracted GeoTek Alaska (GeoTek) of Anchorage, Alaska to advance the soil borings. GeoTek advanced the borings using a CME 75 truck-mounted drill rig equipped with a continuous-flight hollow-stem augers.

2.1.1 Geotechnical Soil Borings

We advanced Borings 21-17 through 21-22 on October 12th, 2021. The borings were advanced to depths ranging from 9.5 feet bgs to 14.5 feet bgs. We advanced Borings 21-01 through 21-16 in the current road alignment between October 13th and October 16th, 2021.

The borings were advanced to depths ranging from 9.5 feet bgs to 22.0 feet bgs.

Approximate locations of the borings are presented in Appendix D.

We collected samples from three additional material sites on October 16, 2021. We used the drill rig auger, pickaxe, and shovel to collect these samples for laboratory testing.

Approximate sample locations are presented in Figure 2.

Nathan Adamczak, an experienced geotechnical staff member with our firm, observed the drilling operations, created a boring log for each boring, and collected the soil samples for index testing in our laboratory. Soil samples were photographed, recorded, and placed in air-tight containers for transport to our Fairbanks, Alaska laboratory. The boring were backfilled with soil cuttings from drilling.

Shannon & Wilson uses a soil identification system modified from the Unified Soil Classification System. Soil descriptions are based on visual-manual procedures consistent with ASTM International (ASTM) D2488 and laboratory testing procedures consistent with

ASTM D2487.

Soil and drilling observations are included in the boring logs presented in Appendix A. Our observations are specific to the locations, depths, and dates noted on the logs, and may not be applicable to all areas of the site. Photographs of drilling operations and select soil samples are presented in Appendix C.

2.2 Laboratory…