P-0037313_VOYA_Pavement_Preservation_Geotechnical_Report_0004.pdf

American Engineering Testing 550 Cleveland Avenue North St. Paul, MN 55114-1804 TeamAET.com • 800.972.6364

Geotechnical ● Materials Forensic ● Environmental

Building Technology Petrography/Chemistry

REPORT OF

GEOTECHNICAL AND PAVEMENT

EXPLORATION

Voyageurs National Park Pavement Preservation Rainy Lake and Ash River Visitor Center Areas International Falls, Minnesota

AET Project No. P-0037313

Date:

January 16, 2026

Prepared for:

CROFT & Associates 3380 Blue Springs Rd Kennesaw, GA 30144

550 Cleveland Avenue North | Saint Paul, MN 55114 Phone (651) 659-9001 | (800) 972-6364 | Fax (651) 659-1379 | TeamAET.com | AA/EEO

This document shall not be reproduced, except in full, without written approval from American Engineering Testing, Inc.

CROFT & Associates 3380 Blue Springs Rd Kennesaw, GA 30144

Attn: Chris Jung

RE: Report of Geotechnical and Pavement Exploration Voyageurs National Park Pavement Preservation

Rainy Lake and Ash River Visitor Center Areas International Falls, Minnesota AET Proposal No. P-0037313

Dear Mr. Jung:

American Engineering Testing, Inc. (AET) is pleased to present the results of our subsurface exploration program and geotechnical engineering review for the Voyageurs National Park Pavement Preservation in the Rainy Lake and Ash River areas. These services were performed according to our proposal to you.

We are submitting an electronic copy of the report to you.

Please contact us if you have any questions about the report. We can also be contacted to arrange construction observation and testing services during the construction phase.

Sincerely, American Engineering Testing, Inc.

Neil G. Lund, PE (MN) Principal Engineer nlund@teamAET.com 612-369-3163

Report of Geotechnical and Pavement Exploration Voyageurs National Park Pavement Preservation, International Falls, Minnesota

AET Report No. P-0037313

SIGNATURE PAGE

Prepared for: Prepared by:

CROFT & Associates American Engineering Testing, Inc.

3380 Blue Springs Rd 550 Cleveland Avenue North Kennesaw, GA 30144 St. Paul, Minnesota 55114

(651) 659-9001/www.TeamAET.com

Attn: Chris Jung

Authored by: Reviewed by:

Neil G. Lund, PE (MN) Jacob O. Michalowski, PE (MN) Principal Engineer Principal Engineer

I hereby certify that this plan, specification, or report was prepared by me or under my direct supervision and that I am a duly Licensed Professional Engineer under the laws of the State of Minnesota.

Name: Neil G. Lund, PE

Date: January 16, 2026 License #: 46212 nlund

MN PE 1 5/8

Page ii

TABLE OF CONTENTS

Page

TRANSMITTAL LETTER ...................................................................................................................... i TABLE OF CONTENTS ....................................................................................................................... ii

1.0 INTRODUCTION

2.0 SCOPE OF SERVICES

3.0 PROJECT INFORMATION

3.1 Pavement Condition Report

3.2 Site Visit and Scoping Document

3.3 Project Scope

3.4 Project Area

4.0 SUBSURFACE EXPLORATION AND TESTING

4.1 Field Exploration Program – Borings and Soundings

4.2 Field Exploration Program – Pavement Cores

4.3 Laboratory Testing

5.0 SITE CONDITIONS

5.1 Pavement Surface and Core Condition

5.2 Subsurface Soils/Geology

5.3 Groundwater

6.0 RECOMMENDATIONS

6.1 Discussion

6.2 Definitions

6.3 Removals and Excavation

6.4 Subgrade Preparation

6.5 Fill and Compaction

6.6 Subgrade Stability and Test Roll

6.7 Aggregate Base

6.8 Mill and Overlay

6.9 Bituminous Section Design

6.10 Bituminous Mixes

7.0 CONSTRUCTION CONSIDERATIONS

7.1 Potential Difficulties

7.2 Excavation Backsloping

7.3 Observation and Testing

8.0 TEST STANDARDS

9.0 LIMITATIONS

APPENDIX A - Geotechnical Field Exploration and Testing Boring Log Notes Unified Soil Classification System AASHTO Soil Classification System Boring and Core Location Sketches Core Photographs Subsurface Boring Logs

APPENDIX B - Geotechnical Report Limitations and Guidelines for Use

1.0 INTRODUCTION

We understand the National Park Service (NPS) is proposing rehabilitation of pavements within the Rainy Lake and Ash River areas of Voyageurs National Park (VOYA). To assist planning and design, CROFT & Associates (CROFT) authorized American Engineering Testing, Inc.

(AET) to conduct a subsurface exploration program at the sites, conduct soil laboratory testing, and perform a geotechnical and pavement engineering review for the project. This report presents the results of the above services and provides our engineering recommendations based on this data.

2.0 SCOPE OF SERVICES

AET's services were performed according to our proposal to CROFT. The authorized scope consisted of the following:

• Mobilization from AET Duluth office for staking and geotechnical drilling and from AET St. Paul office for pavement coring, project management or meetings, and site review

• Stake potential boring and core locations with GPS

• Arrange clearance of underground public utilities through the Gopher State One Call

(GSOC) System

• Extracting 33, 4-inch diameter pavement cores in various site locations in both areas.

• Performing 11 standard penetration test (SPT) borings at proposed depths ranging from

14 ½ to 24 ½ feet. We later added a 12th boring, (B-204A, 14 ½ feet deep) at RT-0912:

Paved Parking Lot Kabetogama Lake Overlook Trail to evaluate a special condition at that location

• Performing manual “soundings”/probes in the RT-0901: Paved Parking Lot Rainy Lake Visitor Center Launch Area to evaluate conditions near the toe of the slope

• Backfilling the cores and boreholes per Minnesota Department of Health (MDH) requirements and patching paved surfaces

• Logging the soil samples and cores including pertinent lab testing

• Preparing this report with a summary of our fieldwork, laboratory work, the results of our analyses, and discussion and recommendations for the project, which we describe in the sections below in greater detail

• Participating in an on-site project team meeting to discuss the results of this evaluation

These services were intended for geotechnical purposes only. The scope was not intended to explore for the presence or extent of environmental contamination in the soil or groundwater.

3.0 PROJECT INFORMATION

3.1 Pavement Condition Report

In September 2020, the Federal Lands Highway Road Inventory Program (RIP) published a road inventory and condition assessment of the paved routes within VOYA. The report generally described the pavements evaluated for this project as being in Good or Excellent surface condition, often due to recent overlays. NPS staff more recently observed that these conditions had since deteriorated, with increased frequency of transverse and random cracks, sinkhole-like “potholes,” and other distresses. Additionally, events including flooding appear to have affected the pavement conditions of some of the assets.

3.2 Site Visit and Scoping Document

As a result of the above, in May 2024, the current project team including personnel from NPS, CROFT and AET visited VOYA to observe conditions at Ash River and Rainy Lake. Work at this time included discussions with NPS staff regarding pavement distress, traffic flow, parking configuration, and other concerns, along with extensive photo documentation. Based on our observations, it appeared many of the pavements were in Fair condition, with some locations meeting Poor criteria. CROFT used the resulting information to create a scoping report (dated July 29, 2024) for the preservation project, which included the geotechnical scope described above in Section 2.0, as well as complete descriptions of the observed pavement distresses.

3.3 Project Scope

The pavements being evaluated for this project are summarized in Table 3.3.

Table 3.3 - VOYA Pavement Preservation Scope Area Asset ID and Route Name Paved Area (mi or sf)

Rainy Lake

RT-0010: Rainy Lake Visitor Center Road 1.64 mi RT-0900: Paved Parking Lot Rainy Lake Visitor

Center 57,788 sf

RT-0901: Paved Parking Lot Rainy Lake Visitor Center Launch Area 65,270 sf

RT-0902: Paved Parking Lot Rainy Lake Visitor Center Employee Area 3,254 sf

Ash River

RT-0100: Ash River Visitor Center Access Road 3.22 mi RT-0907: Paved Parking Lot Ash River Visitor

Center 39,489 sf

RT-0908: Paved Parking Lot Ash River Lower Overflow #1 30,833 sf

RT-0909: Paved Parking Lot Ash River Upper Overflow #2 30,833 sf

RT-0912: Paved Parking Lot Kabetogama Lake 11,454 sf

Area Asset ID and Route Name Paved Area (mi or sf)

Overlook Trail RT-0913: Paved Parking Lot Beaver Pond

Overlook 10,024 sf

Construction plans for the rehabilitation that took place in 2017 were available to review. This rehabilitation of the access roads including a full depth reclamation, 8 inches of cement stabilization and 3.5 inches of new asphalt surfacing.

The RIP report recommended preventive maintenance such as chip seal based on the pavement surface condition at that time. The NPS is now considering alternative treatments, including mill and overlay or reconstruction. The pavement and apparent soil conditions in some areas, such as the Rainy Lake Visitor Center Launch Area, may require other special treatments.

Additionally, there are areas where the NPS is proposing expansion of existing parking (Parking Lot at Rainy Lake Visitor Center) or new pull-offs (near the welcome sign on Rainy Lake Visitor Center Road).

The above stated information represents our understanding of the proposed construction. This information is an integral part of our engineering review. It is important that you contact us if there are changes to the project from our description so that we can evaluate whether modifications to our recommendations are appropriate.

3.4 Project Area

The existing parking lots and access drives are bituminous-paved and generally without perimeter curb and gutter. The terrain is mostly rolling.

Traffic counts were not available for most facilities. Rainy River Visitor Center Road, aka Koochiching County Road 96 or Park Road, has historical average counts that range from about 200 to 350 vehicles per day. There is limited heavy traffic apart from recreational and maintenance vehicles, and we estimate the pavements within VOYA will experience less than 100,000 equivalent single axle loads (ESALs) over a 20-year design period.

4.0 SUBSURFACE EXPLORATION AND TESTING

4.1 Field Exploration Program – Borings and Soundings

The subsurface exploration program conducted for the project consisted of SPT borings to depths of 14 ½ or 24 ½ feet as summarized in Table 4.1, performed in November 2024. The boring locations were chosen by AET and mutually agreed upon by the project team; in general, if there was a minimal desire for pavement reconstruction, we did not perform SPT borings for that asset.

Table 4.1 - SPT Boring Summary, VOYA Area Asset and Route Name Boring

Quantity Boring Depth

Rainy Lake

RT-0010: Rainy Lake Visitor Center Road (Entrance Pull-off) 2 14 1/2

RT-0900: Paved Parking Lot Rainy Lake Visitor Center (Parking Expansion) 2 14 1/2

RT-0901: Paved Parking Lot Rainy Lake Visitor Center Launch Area 2 24 1/2

Ash River

RT-0907: Paved Parking Lot Ash River Visitor Center 1 14 1/2

RT-0912: Paved Parking Lot Kabetogama Lake Overlook Trail 3 14 1/2

RT-0913: Paved Parking Lot Beaver Pond Overlook 2 14 1/2

Totals 12 194

In addition to the borings in Table 4.1, we performed two manual “soundings” near the apparent slope toe of the parking lot within Rainy Lake at the Visitor Center Launch Area.

Logs of the borings and details of the methods used appear in Appendix A. The logs contain information concerning soil layering, soil classification, geologic origins, and moisture condition.

A density description or consistency is also noted for the natural soils, which is based on the standard penetration resistance (N-value).

The boring locations are shown in Appendix A. The borings were marked in the field by AET personnel based on a preliminary location plan and adjusted to avoid utilities, parked vehicles and other obstructions. We backfilled the borings with cuttings in accordance with Minnesota Department of Health (MDH) requirements.

4.2 Field Exploration Program – Pavement Cores

We extracted 33, 4-inch diameter pavement cores during the same visit we marked proposed boring locations in October 2024. To some degree, we attempted to core in areas with different levels of distress, including directly over surface cracks, to help judge the variation in material condition across the project area. The cores were taken at the following locations and frequency (Table 4.2); we did not extract cores in locations where reconstruction of the pavement was the most likely repair method.

Table 4.2 - Pavement Cores, VOYA Area Asset and Route

Name Pavement Cores, Quantity

Rainy Lake

RT-0010: Rainy Lake Visitor Center Road 6

RT-0900: Paved Parking Lot Rainy Lake

Visitor Center

RT-0901: Paved Parking Lot Rainy Lake Visitor Center Launch

Area

Ash River

RT-0100: Ash River Visitor Center Access

Road

RT-0907: Paved Parking Lot Ash River

Visitor Center

RT-0908: Paved Parking Lot Ash River

Lower Overflow #1

RT-0909: Paved Parking Lot Ash River

Upper Overflow #2

Total 33

Following completion of the cores, we used a cold-mix bituminous patch material at the pavement surface.

4.3 Laboratory Testing

The laboratory test program included water contents tests and other tests on samples obtained from the borings. The test results to date appear in Appendix A on the individual boring logs adjacent to the samples upon which they were performed, or on the data sheets following the logs. The soils were visually and manually classified by the Unified Soil Classification System (USCS) with the American Association of State Highway and Transportation Officials (AASTHO) Classification designation noted in parentheses on the boring logs.

5.0 SITE CONDITIONS

5.1 Pavement Surface and Core Condition

Our observations of pavement surface condition in each location from our previous engineering site visit are described in the VOYA scoping report.

Table 5.1 summarizes pavement core thickness and our judgment of core material condition.

Table 5.1 – VOYA Pavement Core Thickness and Condition Summary Area Asset and

Route Name Core Thickness (in.) Core Condition BitA Stab. BaseB

Rainy Lake

RT-0010: Rainy Lake Visitor Center Road

C-101 4.0 10.1 Good

C-102 3.5 9.0 Good

C-103 3.8 10.0 Good

C-104 4.0 8.2 Good

C-105 4.0 8.6 Good

C-106 4.0 9.5 Good

RT-0900: Paved Parking Lot Rainy Lake

Visitor Center

C-107 5.4 -- Good

C-108 6.0 -- Good

C-109 5.1 -- Good

C-110 3.8 -- Good – taken from walking path RT-0901: Paved

Parking Lot Rainy Lake

Visitor Center Launch Area

C-111 4.8 -- Good

C-112 5.0 -- Good

C-113 5.2 -- Low-severity stripping from 1.5 to 3 inches

Ash River

RT-0100: Ash River Visitor

Center Access Road

C-201 3.5 9.9 Good

C-202 4.0 10.6 Good

C-203 3.8 9.6 Good

C-204 4.0 9.8 Good

C-205 4.0 9.6 Good

C-206 4.0 9.0 Good

C-207 3.8 8.8 Good

C-208 3.5 9.8 Good

C-209 4.0 10.3 Good

C-210 4.0 8.5 Good

RT-0909: Paved Parking Lot Ash

River Upper Overflow #2

C-211 5.5 -- Good

C-212 5.0 -- Debonded at 1.5 inches

C-213 5.0 -- Good

RT-0908: Paved Parking Lot Ash

River Lower Overflow #1

C-214 5.8 -- Good

C-215 5.2 -- Good

C-216 3.0 -- Good – taken from walking path

Area Asset and Route Name Core Thickness (in.) Core Condition BitA Stab. BaseB

C-217 5.2 -- Good

RT-0907: Paved Parking Lot Ash

River Visitor Center

C-218 5.8 -- Good

C-219 4.4 -- Good

C-220 6.3 -- Debonded at 2.0 inches A. Bituminous pavement B. Visually identified as cement stabilized base material. Debonded from overlying bituminous pavement wherever encountered.

The pavement cores were mostly in good condition; a single core (C-113) showed low severity stripping within an intermediate pavement lift. Two other cores (C-212, C-220) had debonding between pavement lifts.

On the access roads to both areas, the cores recovered a second layer of material that appeared to be a recycled aggregate base material stabilized with cement. The stabilized base averaged about 9 ½ inches thick and was debonded from the overlying pavement at each location where it was present.

A photo log of the cores is attached to the report in Appendix A.

5.2 Subsurface Soils/Geology

The near-surface geology of VOYA in both project areas is a complex intermingling of glacial and glacial lake sediment, peat deposits, and frequent bedrock outcroppings of biotite schist (Rainy Lake area) or granite and migmatite (Ash River area).

Across both areas, our soil borings generally encountered pavement or topsoil over mostly coarse fill over apparent bedrock, with hammer or auger refusal depth averaging about 5.7 feet and ranging from 2.5 to 12.5 feet. One exception was B-106 in the Rainy Lake launch area, which included fill over swamp deposits and fine alluvium to the 24 ½-foot boring termination depth.

The boring logs in Appendix A of this report provide additional details. Table 5.2 provides a general guide to the properties of the soils encountered on site, while the following sections provide detail for each asset.

5.2.1 RT-0010: Rainy Lake Visitor Center Road (Entrance Pull-off) The soils encountered in Boring B-101 and B-102 generally included lean clay fill over mixed clayey/sandy fill directly above an apparent bedrock layer at a depth of just under 5 feet. The upper layers in both borings had trace roots, with an apparent ½-foot topsoil layer consisting of silty sand in B-101. Both borings encountered difficult drilling, suggesting possible boulders or cobbles, between about 3 feet deep and the apparent point of refusal.

The sampled clayey soils mostly appeared to be above their likely optimum moisture contents (OMC) for compaction.

5.2.2 RT-0900: Paved Parking Lot Rainy Lake Visitor Center (Parking Expansion) Borings B-103 and B-104 were performed at the base of the former septic mound where NPS is proposing expansion of the parking area. The soils were similar in both locations, with an approximately ¼ to ½-foot topsoil layer overlying loose sandy fill. The borings met refusal on possible bedrock at varying depths of 4.9 and 9.1 feet.

5.2.3 RT-0901: Paved Parking Lot Rainy Lake Visitor Center Launch Area We performed Borings B-105 and B-106 near the south side of the Rainy Lake Launch Area lot to evaluate possible causes of continued slope movement in the area.

B-105 consisted of bituminous pavement over variable fill that included silty sand, sandy lean clay and gravelly sand. The soils became increasingly dense near the bottom before meeting refusal at about 7 feet.

B-106, performed to the east at a lower elevation than B-105, included about 4 ½ feet of pavement and fill before reaching swamp-deposited and lake-deposited fat clays. These soft to firm fat clays were present to a depth of about 18 feet before clayey sand and gravel with clay was encountered, which extended to boring termination.

Manual soundings near the apparent toe of the slope, within Rainy Lake, met refusal about 3 feet below the lake bottom.

5.2.4 RT-0907: Paved Parking Lot Ash River Visitor Center

Boring B-205 was performed near a “pothole” noted by NPS. In this location, our boring encountered bituminous pavement over mixed aggregate base-type fill to about 2 feet, which included pieces of recycled bituminous. The underlying fill was gravelly, possibly including cobbles and boulders, and continued to an auger refusal depth of 6.6 feet.

5.2.5 RT-0912: Paved Parking Lot Kabetogama Lake Overlook Trail We performed borings B-203 and B-204 within this parking area to evaluate it for possible reconstruction, as well as to explore the “pothole” distress at the surface. Additionally, we supplemented B-204A to the north away from the pavement to understand the local native soils.

Both B-203 and B-204 encountered a similar profile of bituminous pavement over increasingly dense fill, meeting refusal at 3.4 and 5.8 feet, respectively. B-204 was performed near the “pothole” and noted significant cobbles, possible voids and other irregularities within the fill soil.

Photo 5.2.5 shows a downhole view of the conditions, which appears to show the noted voids.

Photo 5.2.5 – B-204 Downhole Conditions

The supplementary Boring B-204A was performed in a low-lying area to the north of the paved lot, and first encountered about ½ foot of clayey topsoil over a mix of clayey and silty sand fill.

Below 4 ½ feet, a layer of soft, fat clay alluvium overlay similar lean clay deposits before penetrating sandy soils and meeting refusal at about 13.2 feet.

5.2.6 RT-0913: Paved Parking Lot Beaver Pond Overlook

B-201 and B-202 had similar profiles of bituminous pavement over mixed fill, which included pieces of recycled bituminous, below which was granular fill over bedrock refusal (2.5 and 4.2 feet, respectively).

5.3 Groundwater

Groundwater was encountered in Boring B-204A at an approximate depth of 12.5 feet. Based on the moisture contents and soil type present (sand), it appears this was a static groundwater condition.

At B-106 adjacent to Rainy Lake, the drill crew met saturated conditions that required a change to mud-rotary drilling techniques, which can obscure groundwater levels. Additionally, the soils penetrated were low permeability and there may not have been sufficient time for groundwater to rise to its true level. Groundwater elevations in this area will fluctuate closely with the levels of Rainy Lake.

Groundwater levels will fluctuate seasonally and annually due to natural variations in rainfall and snow melt. Additionally, groundwater levels can change due to construction events such as alterations in ground cover, surface water runoff control, and dewatering systems.

6.0 RECOMMENDATIONS

6.1 Discussion

6.1.1 New Pavements

The conditions found in the borings for the new parking areas generally included topsoil over variable fill over relatively shallow bedrock. The shallow fill soils will have variable compaction and should be thoroughly compacted or subcut and replaced with engineered fill material upon exposure. Assuming excavations will be relatively limited, and bedrock removal will not be required, these materials should be suitable for the support of new pavement sections.

Our recommendations for the new pavement areas are presented below. The recommendations are for preparation of the subgrade for the proposed pavement sections previously discussed.

An option for a sand subbase is also considered to improve long-term pavement performance.

6.1.2 Pavement Rehabilitation

Many of the VOYA site pavements are exhibiting distress and cracking that has worsened since the 2020 RIP report characterizing most site pavements as Good or Excellent. The following are the two major options to repair these pavements and restore their surface condition and ride. In our opinion, more substantial options that pulverize the complete pavement structure such as full-depth reclamation (FDR) are not justified based on the current surface conditions and project goals.

Pavement Preservation (Chip Seal) Chip seal is the preferred rehabilitation method for the evaluated pavements stated in the RIP report, which was based on the pavement conditions at that time. As noted throughout this report, conditions have worsened in several cases, making chip seal a less desirable and less effective alternative. In our opinion, a properly constructed chip seal can provide 5 to 7 years of additional life to pavements in Good condition or better; this service life will be reduced accordingly as pavement distress increases and does not address the underlying causes of other distresses including thermal cracks, “potholes,” and other observed problems. We understand that the project team is not likely to pursue chip seal for any of the project pavements.

Mill and Overlay (Partial and Full Depth) When selecting a pavement to rehabilitate by partial-depth mill and overlay, the following should be considered:

• Pavement surface condition – the amount of surface distress will have a proportional effect on mill and overlay service life. Cracks and other damage in the pavement below the milling will inevitably reflect to the new surface, which will require maintenance to limit water intrusion and excessive crack propagation. There are some ways to retard the onset reflective cracking, such as a pavement “underseal,” but it will eventually occur.

• Material condition – it is typically undesirable to leave highly stripped bituminous pavements as support for the new overlay. Stripped pavements will bond poorly to the overlay materials, reducing the effective pavement structure. Additionally, they can complicate construction and will result in an inconsistent finished product. The pavement materials at VOYA are in good condition overall.

• Pavement thickness – about 1 ½ inches of intact bituminous pavement should be left in place to support construction equipment and provide adequate structure for new pavements. In our opinion, a 2-inch mill depth can be applied throughout the site given the adequate thickness of bituminous pavement throughout.

Overall, we judge the pavements at VOYA will be suitable for mill and overlay based on the overall thickness, apparent material condition, and the current surface condition. Certain conditions may require additional milling and/or patching as part of the mill and overlay process.

The service life of a mill and overlay will usually vary between 8 and 15 years and is related to the degree of current distress, plus the diligence of the maintenance performed on subsequent reflected cracks. Please note, the existing thermal and shrinkage cracks that remain in the underlying asphalt after milling will reflect into the new surface within 1-3 years.

For roadways and parking areas, full-depth mill and overlay is another option that will result in a slightly improved service life (12-18 years, depending on underlying conditions). Where a stabilized aggregate base is present, there may be an opportunity to repair large shrinkage cracks, which appear to be influencing the condition of the bituminous surface in the entrance areas. In any case, crack patterns will be interrupted, which will reduce the required maintenance and limit costs over the short term. This cost reduction will need to be considered against the greater cost to place additional bituminous pavement, which we recommend be 4 inches thick for this approach.

At minimum, we recommend a “full-depth mill” for the walkway pavements where they will be replaced.

6.1.3 Pavement Reconstruction

Pavements being considered for reconstruction are exhibiting an increased frequency and severity of distresses at the pavement surface. Additionally, there are unique distresses, such as the “potholes” sporadically present across VOYA, that make reconstruction rather than continued patching a more attractive solution.

Overall, the soil borings do not suggest that the underlying materials are soft, weak or otherwise unable to properly support the pavement surfaces. However, we understand from discussions with NPS personnel that many of these parking areas were built on great depths of blasted bedrock, often of significant size such as cobbles and boulders. As illustrated in Photo 5.2.5, these foundation materials appear to contain voids into which the supported fill and aggregate base materials are eventually driven by water and gravity, resulting in the surficial “potholes” that we understand take significant volumes of material to repair without excavation.

Reconstruction of these small, paved areas will provide an opportunity to repair existing potholes, fill or repair those that may form, and reinforce the aggregate base materials to limit their future intrusion into any voids that remain. Our recommendations for these repairs are provided below.

6.1.4 Rainy Lake Visitor Center Launch Area

According to historic aerial photographs, it appears the Launch Area parking lot was originally a narrow causeway leading to the point that now contains the turnabout and shelter building.

Successive development widened the causeway into the surrounding lake and peatland until the current configuration appears to have been reached sometime between 2003 and 2008.

To construct a parking area in this way, there is the option to excavate as much of the compressible material as practical to reduce the potential for future instability and settlement of the embankment. The cost and effort associated with such an approach is high, and we suspect instead that, more typically, the fill was placed “in the wet” over the native lake deposits on both sides of the causeway until the proposed grades were reached. Our limited boring data, particularly Boring B-106, which shows fill over several feet of fat clay soil, appears to support this conclusion.

Even small amounts of fill can result in noticeable movement as soft soils consolidate and creep. This type of movement can slowly occur over many years, resulting in the observed slippage cracks near the lot perimeter, the small shoreline failures, and movement of site features such as trees and light poles. Wave/ice action and periodic flooding of the low areas exacerbate these issues, particularly the shoreline failures. That said, in general, we do not expect the rate of movement to increase unless it is further induced by additional loads, lowered water tables, or other external factors. The placement of large amounts of riprap at the shoreline to protect the slope may be one such factor that should be considered in balance with the need to protect the shoreline from ice, waves and other damaging effects of the marine environment.

Totally correcting the underlying causes of the observed distresses, which in part would require substantial excavations of the soft soils, does not appear practical. This may also preclude any wishes by the NPS to raise the grade of the parking lot above the likely flood elevation, which would very likely result in additional, unacceptable amounts of settlement and creep.

In our opinion, a reasonable course of action is to continue to maintain the pavements of the parking facility to prevent water intrusion and improve the driving surface. Periodic maintenance of light poles and other site features will likely be required, as will repair of shoreline damage. If shoreline damage becomes substantial or more frequent and affects the basic functionality of the parking facility, more comprehensive options for shoreline stabilization may be required.

6.2 Definitions

This report references the 2020 MnDOT Standard Specifications for Construction (MnDOT Spec.). The ensuing sections refer to the following words, which are defined below:

Grading grade is the bottom of the aggregate base layer.

Granular Material should meet the requirements of MnDOT Specification 3149, including Table 3149.2-1, which requires 0% to 20% for the ratio of the percent passing the No. 200 sieve/1-inch sieve.

Select Granular Material should meet the requirements of MnDOT Specification 3149, including Table 3149.2-1, which requires 0% and 12% for the ratio of the percent passing the No. 200 sieve/1-inch sieve.

Select Grading Material is mineral soil, excluding organic soils (>5% organic material by weight), silt (soil containing 80 percent or more silt-sized particles), and marl (soil consisting of clay and lime or unconsolidated sedimentary rock).

Top of Subgrade is the surface of material immediately beneath a granular material layer meeting MnDOT Spec. 3149, which is usually placed as a sand subbase layer. If there is no granular material layer, then the top of subgrade is the grading grade.

6.3 Removals and Excavation

We recommend removing surficial topsoil at new pavement sites. We also recommend removing the underlying unstable or organic materials if encountered in excavations. Based on our borings, the topsoil removal will require an excavation of up to about 2 feet below the existing ground surfaces; much of this excavation will already be necessary to accommodate the recommended pavement sections.

Short-term dewatering may be needed if excavations penetrate the apparent groundwater table.

Pumps can be used on a small scale but may cause unstable excavation bottoms in sandy soils if significant dewatering is required; in such cases, well points may need to be installed. We recommend soliciting a dewatering contractor for a plan if large-scale or long-term dewatering operations are necessary.

6.4 Subgrade Preparation

The soils exposed at the top of subgrade should be prepared per MnDOT Spec. 2112, Subgrade Preparation. This includes scarification, moisture conditioning, and compaction of the top 6 inches of the subgrade.

If subgrade preparation encounters unstable soils or soils which do not meet the requirements for Select Grading Material, we recommend removing these unsuitable materials and replacing them with Select Grading Material. Unstable soils typically have a water content exceeding the standard optimum water content as defined in ASTM D698 (Standard Proctor test). We caution that instability of soils presents beneath the soils being reworked and compacted may limit the ability to compact the upper soils; therefore, greater depths of subcutting and stability improvement may be needed.

For reconstruction areas with the potential to exhibit “potholes,” we recommend the following general procedure:

1. Remove pavements, including the bituminous surface and aggregate base

2. Regrade the underlying fill/coarse foundation materials

a. If voids are present as suggested by observation and borings, remove these areas or fill with a dense-graded aggregate base to achieve a tight surface

b. Test roll the graded surface and correct areas that yield under loading. Large compaction equipment can be used to potentially “seat” the coarse material in such a way that promotes a better matrix of the fill material with fewer voids, which may require additional material placement to re-achieve grades.

3. Place an appropriately sized biaxial or triaxial geogrid on the graded surface

4. Place the recommended amount of dense-graded aggregate base i.e. MnDOT Class 5 or

6 and compact

5. Place and compact bituminous pavement

The geogrid placed as support for new aggregate base layers will confine the material to prevent loss to underlying voids and will resist the formation of future potholes.

6.5 Fill and Compaction

All new fill and reworked soils for pavement support should be placed and compacted per MnDOT Spec. 2106, including the moisture content and compaction requirements shown in MnDOT Tables 2106.3-1 and 2106.3-4, respectively. In ASTM terms, this specification requires soils placed within 3 feet of grading grade be compacted to a minimum of 100% of the standard maximum dry unit weight defined in ASTM D 698 (Standard Proctor test). A reduced minimum compaction level of 95% of the standard maximum dry unit weight can be used below the critical subgrade zone (within 3 feet of top of subgrade elevation) for non-granular materials (those which do not meet MnDOT Spec 3149.2B).

Fill soils used to re-attain pavement subgrade may consist of on-site, non-organic, debris-free soils, and they should be moisture conditioned for compaction. If additional fill is needed, it should consist of soils substantially matching the existing soils in moisture content and composition.

6.6 Subgrade Stability and Test Roll

The final subgrade should have proper stability within the critical subgrade zone. Where clayey soils are exposed, stability should be evaluated using the test roll procedure. Where unstable soils are found using the test roll process, these soils should be improved by means of scarification, drying, and recompaction; or by subcutting and replacement. If highly variable conditions are present (either stability-wise or soil type), a compaction subcut should be performed to provide a more consistent subgrade condition. We recommend the final soils remaining in place be capable of passing a test roll prior to placing the aggregate base.

6.7 Aggregate Base

Aggregate base placed for pavement support should meet the gradation and quality requirements for Class 5 or 6 per MnDOT Spec. 3138. Aggregate base placement and compaction should be performed according to MnDOT Spec. 2211. All aggregate base material (including existing, imported, or reclaimed) should be tested for compaction using the Penetration Index Method per the requirements of MnDOT Table 2211.3-3.

6.8 Mill and Overlay

We recommend the following construction sequence for overlay and mill and overlay segments.

Mill and overlay should be performed in general accordance with MnDOT Specifications 2232 (Mill Pavement Surface) and 2360 (Plant Mixed Asphalt Pavement):

1. On mill and overlay segments, mill the pavement with appropriate self-propelled cold milling equipment to a depth of 2 inches. The mill depth may need to be adjusted or extended to remove damaged pavements.

2. Sweep or clean the surfaces until they are free of loose materials.

3. Review the milled bituminous pavements for areas of distress that may benefit from additional milling, removals, or patching.

4. Distribute a uniform tack coat on the clean surfaces and protect it from dirt and debris.

5. Place and compact the required thickness of bituminous pavement. We recommend a minimum of 2 inches of SPWEA340C.

6.9 Bituminous Section Design

We are presenting flexible pavement designs for “light-duty” traffic situations only. The light duty design refers to parking areas which are intended only for automobiles and passenger truck/ vans with low incidence of heavy traffic. We assumed 20-year bituminous equivalent single axle loads (BESALs) of 100,000. The traffic loading has a significant effect on the pavement section thickness design; please verify and contact us if actual traffic loadings are different than described.

The limiting subgrade soils encountered at the sites are the sandy lean clay soils. We estimate these soils exhibit an R-value of 20.

A summary of our recommended bituminous pavement thickness design is presented in Table 6.9.

Table 6.9 – Bituminous Pavement Thickness Designs

Pavement Course MnDOT Material Type (Spec.)

Thickness (in.)

Without Subbase With Subbase

Bituminous Wear Upper SPWEA340C (PG58H-34) 2.0" 2.0" Bituminous Wear Lower SPWEA340C (PG58H-34) 2.0" 2.0"

Aggregate Base Class 5 or 6 (3138) 8.0" 6.0" Subbase Select Granular (3149) -- 12.0”

Total Frost-Free Thickness 12.0" 22.0"

Please note that the pavement thicknesses recommended above are minimum, not average thicknesses. They should be noted as such on the project plans and specifications.

After the aggregate base has been placed, compacted, and tested, it is the contractor’s responsibility to maintain the base in a suitable condition for paving. If the subgrade or aggregate base materials become saturated or contaminated by clayey or silty soils, after testing, it may be rendered unsuitable for paving due to softness and pumping. This action would require remedial action before pavement can be placed.

6.10 Bituminous Mixes

The bituminous mixtures should meet the most current MnDOT Spec. 2360 (Plant-Mixed Asphalt Pavement) requirements. Compaction of all bituminous mixtures should be by the Maximum Density Method per MnDOT Spec. 2360.3D.1.

7.0 CONSTRUCTION CONSIDERATIONS

7.1 Potential Difficulties

7.1.1 Runoff Water in Excavations

Water can be expected to collect in the excavation bottom during times of inclement weather or snow melt. To allow observation of the excavation bottom, to reduce the potential for soil disturbance, and to facilitate filling operations, we recommend water be removed from within the excavation during construction. The exposed top of subgrade should be sloped to drain surface water away from the pavement areas.

7.1.2 Disturbance of Soils

The on-site soils can be disturbed under construction traffic, especially if the soils are wet. If soils become disturbed, they should be subcut to the underlying undisturbed soils. The subcut soils can then be dried and recompacted back into place, or they should be removed and replaced with drier imported fill.

7.1.3 Cobbles, Boulders, and Bedrock

The soils at this site can include cobbles and boulders. This may make excavating procedures somewhat more difficult than normal if they are encountered. We also encountered shallow bedrock throughout the site, which is likely to require blasting to remove it for grading.

7.2 Excavation Backsloping

If excavation faces are not retained, the excavations should maintain maximum allowable slopes in accordance with OSHA Regulations (Standards 29 CFR), Part 1926, Subpart P, “Excavations” (can be found on www.osha.gov). Even with the required OSHA sloping, water seepage or surface runoff can potentially induce sideslope erosion or sloughing which could require slope maintenance.

7.3 Observation and Testing

The recommendations in this report are based on the subsurface conditions found at our test borings and test pit locations. Since the soil conditions can be expected to vary away from the test locations, we recommend on-site observation by a geotechnical engineer/technician during construction to evaluate these potential changes. Soil density testing should also be performed on new fill placed to document that project specifications for compaction have been satisfied.

8.0 TEST STANDARDS

When we refer to an ASTM Standard in this report, we mean that our services were performed in general accordance with that standard. Compliance with any other standards referenced within the specified standard is neither inferred nor implied.

9.0 LIMITATIONS

Within the limitations of scope, budget, and schedule, we have endeavored to provide our services according to generally accepted geotechnical engineering practices at this time and location. Other than this, no warranty, express or implied, is intended.

Important information regarding risk management and proper use of this report is given in Appendix B entitled “Geotechnical Report Limitations and Guidelines for Use.”

Appendix A

Geotechnical Field Exploration and Testing Boring Log Notes

Unified Soil Classification System AASHTO Soil Classification System

Boring and Core Locations Core Photographs

Subsurface Boring Logs

01REP052C (12/23) AMERICAN ENGINEERING TESTING, INC.

BORING LOG NOTES

DRILLING AND SAMPLING SYMBOLS TEST SYMBOLS

Symbol Definition Symbol Definition

AR: Sample of material obtained from cuttings blown out the top of the borehole during air rotary procedure.

B, H, N: Size of flush-joint casing

CAS: Pipe casing, number indicates nominal diameter in inches

COT: Clean-out tube

DC: Drive casing; number indicates diameter in inches

DM: Drilling mud or bentonite slurry

DR: Driller (initials)

DS: Disturbed sample from auger flights

DP: Direct push drilling; a 2.125 inch OD outer casing with an inner 1½ inch ID plastic tube is driven continuously into the ground.

FA: Flight auger; number indicates outside diameter in inches

HA: Hand auger; number indicates outside diameter

HSA: Hollow stem auger; number indicates inside diameter in inches

LG: Field logger (initials)

MC: Column used to describe moisture condition of samples and for the ground water level symbols

N (BPF): Standard penetration resistance (N-value) in blows per foot (see notes)

NQ: NQ wireline core barrel

PQ: PQ wireline core barrel

RDA: Rotary drilling with compressed air and roller or drag bit.

RDF: Rotary drilling with drilling fluid and roller or drag bit

REC: In split-spoon (see notes), direct push and thin-walled tube sampling, the recovered length (in inches) of sample. In rock coring, the length of core recovered

(expressed as percent of the total core run). Zero indicates no sample recovered.

SS: Standard split-spoon sampler (steel; 1.5" is inside diameter; 2" outside diameter); unless indicated otherwise

SU Spin-up sample from hollow stem auger

TW: Thin-walled tube; number indicates inside diameter in inches

WASH: Sample of material obtained by screening returning rotary drilling fluid or by which has collected inside the borehole after “falling” through drilling fluid

WH: Sampler advanced by static weight of drill rod and hammer

WR: Sampler advanced by static weight of drill rod

94mm: 94 millimeter wireline core barrel

▼: Water level directly measured in boring

: Estimated water level based solely on sample appearance

CONS: One-dimensional consolidation test

DEN: Dry density, pcf

DST: Direct shear test

E: Pressuremeter Modulus, tsf

HYD: Hydrometer analysis

LL: Liquid Limit, %

LP: Pressuremeter Limit Pressure, tsf

OC: Organic Content, %

PERM: Coefficient of permeability (K) test; F - Field;

L - Laboratory

PL: Plastic Limit, % qp: Pocket Penetrometer strength, tsf (approximate) qc: Static cone bearing pressure, tsf qu: Unconfined compressive strength, psf

R: Electrical Resistivity, ohm-cms

RQD: Rock Quality Designation of Rock Core, in percent

(aggregate length of core pieces 4" or more in length as a percent of total core run)

SA: Sieve analysis

TRX: Triaxial compression test

VSR: Vane shear strength, remolded (field), psf

VSU: Vane shear strength, undisturbed (field), psf

WC: Water content, as percent of dry weight

%-200: Percent of material finer than #200 sieve

STANDARD PENETRATION TEST NOTES

The standard penetration test consists of driving a split-spoon sampler with a drop hammer counting the number of blows applied in each of three 6" increments of penetration. If the sampler is driven less than 18" (usually in highly resistant material), permitted in ASTM: D1586, the blows for each complete 6" increment and for each partial increment is on the boring log. For partial increments, the number of blows is shown to the nearest 0.1' below the slash.

The length of sample recovered, as shown on the “REC” column, may be greater than the distance indicated in the N column. The disparity is because the N-value is recorded below the initial 6" set (unless partial penetration defined in ASTM: D1586 is encountered) whereas the length of sample recovered is for the entire sampler drive (which may even extend more than 18").

01CLS021 (01/2022) AMERICAN ENGINEERING TESTING, INC.

UNIFIED SOIL CLASSIFICATION SYSTEM

ASTM Designations: D 2487, D2488

AMERICAN

ENGINEERING

TESTING, INC.

Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA

Soil Classification Notes ABased on the material passing the 3-in (75-mm) sieve.

BIf field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name.

CGravels with 5 to 12% fines require dual symbols:

GW-GM well-graded gravel with silt GW-GC well-graded gravel with clay

GP-GM poorly graded gravel with silt

GP-GC poorly graded gravel with clay DSands with 5 to 12% fines require dual symbols:

SW-SM well-graded sand with silt

SW-SC well-graded sand with clay

SP-SM poorly graded sand with silt SP-SC poorly graded sand with clay

(D30)

ECu = D60 /D10, Cc =

D10 x D60

FIf soil contains >15% sand, add “with sand” to group name.

GIf fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.

HIf fines are organic, add “with organic fines” to group name.

IIf soil contains >15% gravel, add “with gravel” to group name.

JIf Atterberg limits plot is hatched area, soil is a CL-ML silty clay.

KIf soil contains 15 to 29% plus No. 200 add “with sand” or “with gravel”, whichever is predominant.

LIf soil contains >30% plus No. 200, predominantly sand, add “sandy” to group name.

MIf soil contains >30% plus No. 200, predominantly gravel, add “gravelly” to group name.

NPl>4 and plots on or above “A” line.

OPl<4 or plots below “A” line.

PPl plots on or above “A” line.

QPl plots below “A” line.

RFiber Content description shown below.

Group

Symbol

Group NameB

Coarse-Grained

Soils More than 50% retained on

No. 200 sieve

Gravels More than 50% coarse fraction retained on No. 4 sieve

Clean Gravels

Less than 5% finesC

Cu>4 and 1<Cc<3E GW Well graded gravelF

Cu<4 and/or 1>Cc>3E GP Poorly graded gravelF

Gravels with

Fines more than 12% fines C

Fines classify as ML or MH GM Silty gravelF.G.H

Fines classify as CL or CH GC Clayey gravelF.G.H

Sands 50% or more of coarse fraction passes

No. 4 sieve

Clean Sands

Less than 5% finesD

Cu>6 and 1<Cc<3E SW Well-graded sandI

Cu<6 and/or 1>Cc>3E SP Poorly-graded sandI

Sands with

Fines more than 12% fines D

Fines classify as ML or MH SM Silty sandG.H.I

Fines classify as CL or CH SC Clayey sandG.H.I

Fine-Grained

Soils 50% or more passes the No. 200 sieve

(see Plasticity

Chart below)

Silts and Clays

Liquid limit less than 50 inorganic PI>7 and plots on or above

“A” lineJ

CL Lean clayK.L.M

PI<4 or plots below

“A” lineJ

ML SiltK.L.M organic Liquid limit–oven dried <0.75

Liquid limit – not dried

OL Organic clayK.L.M.N

Organic siltK.L.M.O

Silts and Clays

Liquid limit 50 or more inorganic PI plots on or above “A” line CH Fat clayK.L.M

PI plots below “A” line MH Elastic siltK.L.M organic Liquid limit–oven dried <0.75

Liquid limit – not dried

OH Organic clayK.L.M.P

Organic siltK.L.M.Q

Highly organic soil

Primarily organic matter, dark in color, and organic in odor

PT PeatR

3 2 ½ 1 ¾ 4 10 20 40 60 140 200

Sieve NumberScreen Opening (in.)

50 10 5 1.0 0.10.5

PARTICLE SIZE IN MILLIMETERS

SIEVE ANALYSIS

P E

R C

E N

T

P

A S

S

IN

G

P E

R C

E N

T

R

E T

A

IN

E D

D60 = 15mm

D30 = 2.5mm

D10 = 0.075mm

Cu = = = 200 D60

D10

0.075 Cc = = = 5.6

(D30)

D10 x D60

2.5

0.075 x 15

2 2

CL-ML

For classification of fine-grained soils and fine-grained fraction of coarse-grained soils.

Equation of "A"-line Horizontal at PI = 4 to LL = 25.5.

then PI = 0.73 (LL-20)

Equation of "U"-line Vertical at LL = 16 to PI = 7.

then PI = 0.9 (LL-8)

"A " L

IN

E

"U " L

IN

E

CL

OR O

L

CH OR O

H

10 20 30 40 50 60 70 80 90 100 110 0

P L A

S T

IC

IT

Y I N

D E

X

P I)

LIQUID LIMIT (LL)

Plasticity Chart

ADDITIONAL TERMINOLOGY NOTES USED BY AET FOR SOIL IDENTIFICATION AND DESCRIPTION

Grain Size Term Particle Size

Boulders Over 12"

Cobbles 3" to 12"

Gravel #4 sieve to 3"

Sand #200 to #4 sieve

Fines (silt & clay) Pass #200 sieve

Gravel Percentages

Term Percent

A Little Gravel 3% - 14%

With Gravel 15% - 29%

Gravelly 30% - 50%

Consistency of Plastic Soils Term N-Value, BPF

Very Soft less than 2

Soft 2 - 4

Firm 5 - 8

Stiff 9 - 15

Very Stiff 16 - 30

Hard Greater than 30

Relative Density of Non-Plastic Soils Term N-Value, BPF

Very Loose 0 - 4

Loose 5 - 10

Medium Dense 11 - 30

Dense 31 - 50

Very Dense Greater than 50

Moisture/Frost Condition (MC Column)

D (Dry): Absence of moisture, dusty, dry to touch.

M (Moist): Damp, although free water not visible. Soil may still have a high water content (over “optimum”).

W…