libi01002_FinalGeotech_PavementReport GR56-20.pdf

GEOTECHNICAL AND PAVEMENT REPORT

Little Bighorn Park Road IDIQ DTFH70-15D00007 Task Order 69056719F000062

Little Bighorn Battlefield National Monument Crow Agency, Montana

Project 19-3836G

Submitted by

2511 Holman Avenue P. O. Box 80190

Billings, Montana 59108-0910

Prepared for

Robert Peccia & Associates P.O. Box 5653

Helena, Montana 59604

February 13, 2020

Table of Contents Description Page

A. Introduction A.1. Little Bighorn Park Road Description A.2. Scope of Services A.3. Available Information A.4. General Site Topography and Geology

B. Engineering Reconnaissance B.1. Fieldwork B.2. Little Bighorn Park Road Pavement Conditions B.3. Little Bighorn Park Road Geotechnical Features

C. Results C.1. Hand Auger Borings C.2. Dynamic Cone Penetrometer Tests C.3. Pocket Penetrometer Tests C.4. Alignment Borings C.5. Culvert Borings

D. Laboratory Tests D.1. Moisture Content D.2. Index Property Tests D.3. Consolidation Test

E. Preliminary Geotechnical Analysis and Recommendations E.1. Fill Slopes E.2. Station 156+00 to 157+00 Deep Patch E.3. Cut Slopes E.4. Box Culverts E.5. Pavement E.6. Digout Pavement Section E.7. Constructability

F. General F.1. Basis of Recommendations F.2. Review of Design F.3. Groundwater Fluctuations F.4. Use of Report F.5. Level of Care

Professional Certification

Attachments Geology Map Boring Location Sketch (6 pages) Photographs (11 pages) Logs of Hand Auger Borings (15 pages) Laboratory Tests Pavement Distress Rating Table and Parking Area Digout Sketches Conceptual Deep Patch Sketch

A. Introduction

A.1. Little Bighorn Park Road Description Little Bighorn Park Road is located within the Little Bighorn Battlefield National Monument near Crow

Agency, Montana. The project starts at the park entrance station located at approximately 45°34'17.3"N

107°25'59.8"W. The project ends at the Reno-Benteen parking area located at approximately

45°31'18.5"N 107°22'38.8"W. The project area contains those areas within the park boundaries and the tour road connecting the Visitor Center and Reno-Benteen parking area.

The project primarily includes improvements to the 5.2-mile long Tour Road. Tour Road and adjacent pullouts will be rehabilitated and widened. Rehabilitation and reconfiguration improvements are also planned for the Visitor Center, Reno-Benteen and Stone House parking lots. The project also includes repair and extensions to the large box culverts at Deep Coulee and Medicine Tail Coulee.

A.2. Scope of Services To evaluate the pavement rehabilitation and widening for the project, SK Geotechnical performed pavement and geotechnical work along the alignment. Our scope of services is briefly described below:

Reconnaissance of the site by a geotechnical engineer to observe pavement conditions and geotechnical features.

Painting the proposed hand auger boring locations on the pavement.

Coordinating the location of underground utilities near the hand auger boring locations.

Conducting a total of 15 hand auger borings along Tour Road: 11 borings just off the edge of the pavement and 4 borings at the box culvert extension areas. An archaeologist from the National

Park Service was present during the hand auger borings to observe cuttings.

Visually classifying soils encountered by the hand auger boring and preparing boring logs.

Collecting bag samples and California tube samples of soils for various laboratory tests conducted by WFLHD.

Discussing the project with Mr. Brad Thompson of Robert Peccia & Associates.

Providing geotechnical recommendations related to roadway widening, pavement digouts, cut slopes, fill slopes, and culvert extensions.

Robert Peccia & Associates February 17, 2020 Project 19-3836G Page 4

A.3. Available Information The following documents were provided for our use:

August 2000 FHWA Geotechnical Memorandum

January 2007 FHWA Geotechnical Memorandum

2001 Pavement Structure Recommendations

November 2004 Pavement Memo

August 2010 Environmental Commitment Summary

2019 Plan and Profile Drawings

August 2019 Statement of Work

A.4. General Site Topography and Geology The Boring Location Sketch shows the 5.2-mile Little Bighorn Park Road alignment and is attached. As this sketch indicates, the roadway is located in hilly terrain and crosses several drainages and coulees. A portion of the Geologic Map of the Hardin 30' x 60' Quadrangle, Montana, Susan M. Vuke, Edith M.

Wilde, and Robert N. Bergantino, Revised 2007, is also attached. The map indicates that the first portion of the roadway, from about Station 0+00 to 140+00, alternates between the Judith River Formation (Kjr) and the Bearpaw Shale Formation (Kb), as well as alluvial deposits (Qal). From about Station 140+00 to

288+00 the roadway is in the Bearpaw Shale Formation. Both formations are thick and consist of beds of both shale and sandstone.

B. Engineering Reconnaissance

B.1. Fieldwork Robert Peccia and Associates, Inc. (RPA), was selected by FHWA to assist in the development of this project. SK Geotechnical will also assist the development of the geotechnical and some pavement features of the project. FHWA is performing the pavement thickness design. A reconnaissance of the alignment was performed by Mr. Gregory T. Staffileno, PE, Senior Geotechnical Engineer, and Mr. Eddie

K. Coldwell, an Engineer Intern with our firm on November 15 and 18, 2019. The 5.2-mile Little

Bighorn Park Road alignment and the three parking areas were observed, paying particular attention to the existing pavement surface defects and drainage, as well as geotechnical features. Numerous photographs of these roadways were taken, some of which have been included as attachments to this report. More photographs are available upon request. Note that the 2019 Plan and Profile Drawings were referenced for stationing used throughout this report.

B.2. Little Bighorn Park Road Pavement Conditions

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The Tour Road was originally constructed in 1935. Minor maintenance was completed from then until the late 1960's, and the road was 16 feet wide. During the late 1960's, the road was overlaid and widened to 18 feet. In 2003, it is our understanding a 3-inch thick cold-in-place recycle and 3-inch thick overlay were used on the existing section consisting of 4 1/2-inch pavement over 6-inch base course. Therefore, we believe the current existing pavement section is as follows:

Chip Seal Yes Asphalt Pavement (2003) 3" Asphalt Cold-In-Place Recycle (2003) 3" Old Asphalt Pavement (Existing) 1½" Old Base Course (Existing) 6"

Total Thickness 13½"

It is our opinion that the Tour Road from Station 0+00 to 120+00 is in fair condition, then the roadway surfacing is in poor to fair condition from Station 120+00 to 288+00. The Reno-Benteen parking area is in fair to good condition, the Visitor Center parking area is in poor to fair condition, and Calhoun Loop was in fair condition. The Stone House parking lot and Cemetery Rd were generally in poor to fair condition. The entrance to the Stone House Parking Lot and the area that has been resurfaced for a utility cut are in good condition, but areas of moderate to severe pavement distress were noted, covering nearly half of the Stone House Parking Lot.

Numerous areas of pavement distress as well as pavement failures were observed along the roadway and are described below. We have also attached a Pavement Distress Rating table identifying the type and severity of pavement distress observed along the roadway and in the parking lots.

Moderate to severe rutting (especially down the centerline) was observed throughout Tour Road, but in particular beyond Station 120+00. Rutting occurred in all three tire tracks and was up to three inches deep. Some locations in which rutting was observed included alligator cracking, standing water, and in one area, exposed base course.

Alligator cracking and patches indicative of fatigue cracking were observed in separate locations along the roadway and are indicated in the attached Pavement Distress Rating table. Several of these areas are also shown in the attached photographs.

Longitudinal cracking was also observed along the roadway, mostly down the center line but also in the driving lanes near the pavement edges. About half of these cracks had been previously sealed. Roadway specific crack mapping or counting were not performed.

B.3. Little Bighorn Park Road Geotechnical Features

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Fill Slopes. Numerous fill slopes exist along the roadway typically ranging from 5 to 20 feet deep and having relatively steep slopes of about 1:2 (vertical: horizontal) or slightly steeper. Embankment consolidation and subsequent settlement at the pavement surface was also observed at the following fill slopes:

Station 155+70 to 157+20

Station 213+00 to 215+70

Station 220+00 to 221+60

Station 224+90 to 226+10

At these locations, the pavement surface in the westbound lane was almost even with the adjacent grades, indicating several inches of settlement. Photographs of the pavement in some of these areas are attached.

Fill Slope Slump. A fairly significant tension crack in the pavement surface was observed at the Station

155+70 to 157+20 fill slope. Some differential movement also occurred across the crack, indicating a possible slump in the westbound (uphill) lane. A photo of this fill slope is attached and repair (deep patch) is discussed in more detail later in this report.

Steep Natural Coulee Slopes. The current alignment is relatively close to the existing native slopes breaking down into the Little Bighorn River. These slopes were generally observed to have a 1:2 slope and exceed a height of 100 feet near portions of the alignment. A representative photo at Station 205+00 is attached.

Were instructed by the National Park Service to not get more than 20 feet from the edge of the pavement, so it was not possible to perform a detailed reconnaissance of the slopes. However, we did not see any obvious signs of slope movement or failures.

Steep Cut Slopes. Several steep 1:2 cut slopes were observed along the current alignment. Some of these slopes were eroded, as shown in the attached photograph at Station 225+50. The erosion has led to a loss of vegetation, which increases further erosion. However, we did not see any slope failures in the existing cut slopes.

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C. Results

C.1. Hand Auger Borings Hand auger borings (HAB's) were performed to reduce the risk of disturbance and because the entire alignment is considered a cultural site. Eleven hand auger borings were performed along the Tour Road shoulders, approximately every 1/2-mile to depths ranging from 3 to 5 feet. Four borings were performed at two box culverts extensions (one on each side) to depths up to 8 feet. The borings were performed to these depths unless auger refusal was encountered shallower. One of the four box culvert extension borings was terminated at a shallow depth by the archaeologist because an object of potential cultural significance was found. The HAB's were generally performed with a 2 1/2-inch diameter hand auger.

The soils collected in the barrel of the hand auger were visually classified and logged in the field in accordance with ASTM Method of Test D2488, "Standard Practice for Description and Identification of

Soils (Visual-Manual Procedures)."

C.2. Dynamic Cone Penetrometer Tests We performed dynamic cone penetrometer tests next to hand auger borings to evaluate soil strength. The dynamic cone penetrometer (DCP) used was developed by SK Geotechnical and consisted of a 1.2-inch diameter cone mounted on a 3/4-inch diameter rod. A 10-pound weight falling 24 inches was used to drive the cone into the soil. The blows required to drive the cone each 6-inch increment of advance, or the depth driven with 50 blows, are noted on the attached logs. Our engineers have been using this DCP for over 20 years, and we are therefore more comfortable interpreting the results. In particular, the DCP blow per six inches are basically correlated to the blows per foot obtained in a standard penetration test, i.e., equivalent to N-values.

C.3. Pocket Penetrometer Tests Clay samples collected in the auger barrel were also tested with a pocket penetrometer to estimate their unconfined compressive strengths. A pocket penetrometer consists of a ¼-inch diameter rod that is pushed ¼-inch into the clay soil by a spring. Compression of the spring has been correlated to the unconfined compressive strength of the clay soils by the manufacturer. The results of the pocket penetrometer tests are presented on the attached Boring Logs.

C.4. Alignment Borings A total of 11 alignment hand auger borings were performed for the project. Borings HA-1 through

HA-11 were advanced to depths ranging from 3 to 5 feet. The general profile encountered by the borings was topsoil and/or fill over alluvium and decomposed shale. Topsoil thicknesses ranged from

3 to 8inches, with an average thickness of 6 inches. The fill soils encountered were lean clays, lean clays

Project 19-3836G Page 8 with sand, sandy lean clays, and clayey gravels, while the natural soils were lean clays, lean clays with sand and sandy lean clays. The clays ranged from low to bordering on high plasticity.

DCP results in the predominant lean clays and sandy lean clays ranged from 8 to 47 blows for 6 inches of penetration, but primarily ranged from 11 to 30 blows for 6 inches of penetration. Pocket penetrometer estimates of the unconfined compressive strength primarily ranged from ½ to 1 ¾ tons per square foot

(tsf). These values indicated the clays were firm to hard, but primarily stiff to very stiff.

C.5. Culvert Borings A total of four culvert hand auger borings were performed for the project. Borings HA-12 through HA-15 were advanced to depths ranging from 4 to 8 feet, except for HA-13, which encountered an object of potential cultural significance identified by the archaeologist at 0.7 feet. The general profile encountered at Deep Coulee was thick sandy lean clay over thin layers of clayey sand and lean clay with sand, while the general profile encountered at the Medicine Tail Coulee was thin layers of slopewash consisting of clayey gravel, lean clay with gravel, lean clay with sand, sandy lean clay, silty clayey sand and silty sand with gravel. The clays ranged from low to medium plasticity.

DCP results in the clays primarily ranged from 9 to 34 blows for 6 inches of penetration and pocket penetrometer results ranged from ½ to 2 ½ tsf. These values indicated the clays were stiff to hard. DCP results in the sands were 19 to 34 blows for 6 inches of penetration indicating they were medium dense to dense.

D. Laboratory Tests

D.1. Moisture Content Moisture content tests were recorded for the hand auger cuttings and California tube samples at each boring location. Moisture contents throughout the soil strata are presented on the attached Boring Logs.

The moisture content in the clay layers ranged from 13 to 32 percent. This indicated that the clays encountered ranged from moist to wet. The moisture content in the coarse-grained soils ranged from

7 to 23 percent. Coarse-grained soils encountered, therefore, also ranged from moist to wet.

D.2. Index Property Tests Several samples were selected for laboratory index property testing. The results are summarized in Table

1 below and are attached to this report.

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Table 1. Summary of Laboratory Index Property Tests

Sample Atterberg Limits

P200 (%) ASTM Symbol

LL PL PI

HA-1, 3.0'-3.5' 33 17 16 59.6 CL

HA-2, 0.9'-1.3' 49 19 30 61.5 CL

HA-4, 2.5'-3.0' 49 18 31 71.1 CL

HA-6, 3.0'-3.5' 46 17 29 89.0 CL

HA-7, 0.5'-1.0' 40 17 23 84.5 CL

HA-8, 0.2'-0.6' 33 18 15 13.8 SC

HA-9, 1.0'-1.5' 32 18 14 72.2 CL

HA-12, 7.0'-7.5' 32 18 14 18.2 SC

HA-15, 2.3'-2.7' 35 17 18 41.9 SC

D.3. Consolidation Test The results of the consolidation test performed on the California tube sample from Boring HA-15 are shown on the attached graph. The clayey sand sample swelled about 0.3 percent when it was inundated under a load of 50 psf, which is considered a negligible amount. The sample consolidated about 4 percent, excluding the swell, under a load increase of about 2,000 psf, which is considered a moderate amount.

E. Preliminary Geotechnical Analysis and Recommendations

E.1. Fill Slopes The 1:2 (1 vertical:2 horizontal) fill slopes are relatively steep, especially assuming the embankments were constructed with on-site lean clays. With the exception at Station 155+70 to 157+20 embankment, the fill slopes appeared relatively stable.

Widening of the roadway on both sides or just one side will likely be used for the improvements. We recommend using the following criteria for fill slopes.

1:2 fill slope widening can be used provided fill materials consist of relatively clean Select

Borrow or similar gravel soils having ASTM classifications of GP or GW.

1:2.5 fill slope widening can be used for all other inorganic soils used as fill.

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E.2. Station 156+00 to 157+00 Deep Patch An existing 15-foot high embankment is located from about Station 155+70 to 157+20. We observed a possible slump in the fill slope, as well as embankment settlement. We recommend a 5-foot deep patch from Station 156+00 to 157+00 in the westbound lane. A conceptual sketch of the deep patch is attached.

E.3. Cut Slopes Relatively steep cut slopes, including some slopes with fairly significant erosion, were observed along the alignment, as previously described. Besides the shallow erosion, however, the existing cut slopes appeared to be relatively stable. Due to erosion, it is desirable for cut slopes to be as flat as possible, although it may not be practical when considering right-of-way limitations. Therefore, we recommend cut slopes no steeper than 1:2 slope angle, or flatter where possible. We also recommend establishing vegetation on the cut slopes (existing and proposed) to reduce erosion.

E.4. Box Culverts Two box culvert extensions are planned for the project. One at Deep Coulee (HA-12 and HA-13) and the other at the Medicine Tail Coulee (HA-14 and HA-15). The general profile encountered at Deep Coulee was topsoil over a thick sandy lean clay layer. Only one boring could be completed to depth at Deep

Coulee because HA-13 encountered an object of potential cultural significance. The general profile encountered at the Medicine Tail Coulee was topsoil over lean clay and sand layers.

A settlement analysis has been performed assuming a 1:2.5 fill slopes for both culverts and resulted in similar estimates. We estimate about 1/2-inch of foundation material consolidation under the widened embankments. Even with good compaction, fill will also compress over time and we anticipate

3/4- to 1 inch of settlement at the pavement elevation. In our opinion, this amount of settlement is acceptable and standard bedding, as specified in the plan and cross section drawings for the culverts, should be used. The estimated time to achieve 90 percent consolidation is 26 days for Deep Coulee and

15 days for the Medicine Tail Coulee box culvert extension. We therefore anticipate at least half of the settlement will occur prior to paving.

E.5. Pavement The significant rutting, transverse, and longitudinal cracking of the pavement is a concern for the roadway. The specific cause of pavement distress is unknown and beyond the scope of this report.

FHWA is performing the pavement design for the project, and is considering a phased recycling approach with geogrid stabilization. In our opinion, an initial step in pavement rehabilitation is to repair the distressed areas indicated in the attached Pavement Distress Rating table. These areas represent distressed pavement associated with alligator cracking, rutting, potholes, longitudinal cracks, settlement, deformations and patches.

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E.6. Digout Pavement Section The Pavement Distress Rating table attached to this report contains the extent of low to severe distressed pavement areas along the roadway, which should be repaired by installing the digout pavement section indicated below.

Plant Mix Surfacing 3 inches 3 inches

1 1/2-inch minus crushed base course 18 inches 4 inches

Select Borrow None 14 inches

Geogrid, Stabilization Yes Yes

Separation-stabilization nonwoven geotextile, Class 1, Type C Yes Yes

E.7. Constructability The DCP tests performed along the roadway shoulders indicate that the subgrade for widened areas will primarily consist of firm to very stiff lean clays, except for Boring HA-11 at the southwest corner of the

Reno-Benteen parking area. We therefore anticipate the shoulder subgrade soils will be relatively stable during rehabilitation and can predominantly be scarified, moisture conditioned, and recompacted to specification beneath the specified pavement section.

Boring HA-11 at the southwest corner of the Reno-Benteen parking area encountered groundwater at about 1 foot and soft clay subgrades. We anticipate that this groundwater is trapped surface water perched on the clay subgrade, although the actual source is unknown. We are therefore recommending the digout pavement section for the west portion of the parking area as shown by the hatched area on the attached sketch.

Other isolated areas of excessively soft, wet clay subgrades likely occur along the shoulders due to poor drainage. When considering the poor pavement condition observed along the majority of the existing roadway, it is our opinion soft, wet clay subgrades are likely present beneath the existing pavement.

When identified during rehabilitation, the thicker digout pavement section with geogrid stabilization at the bottom will bridge over most soft clays.

As previously discussed, consideration should be given to performing additional borings through the existing pavement to further evaluate the existing pavement thickness and subgrade conditions as well as to collect representative samples for testing. Having worked at the Little Bighorn Park, we certainly understand and appreciate the cultural sensitivity of the park, and recognize additional investigation may not be possible.

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F. General

F.1. Basis of Recommendations The analyses and recommendations submitted in this report are based up our visual observations performed along the roadway. Often, variations occur along roadway and embankment areas, the nature and extent of which do not become evident until additional exploration (as recommended) or construction is performed.

F.2. Review of Design This report is based on the design of the proposed alignment as related to us for preparation of this report.

It is recommended we be retained to review the geotechnical and pavement aspects of the designs and specifications. With the review, we will evaluate whether any changes in design have affected the validity of the recommendations, and whether our recommendations have been correctly interpreted and implemented in the design and specifications.

F.3. Groundwater Fluctuations We made water level observations in the borings at the times and under the conditions stated on the boring logs. These data were interpreted in the text of this report. The period of observation was relatively short, and fluctuation in the groundwater level may occur due to rainfall, flooding, irrigation, spring thaw, drainage, and other seasonal and annual factors not evident at the time the observations were made. Design drawings and specifications and construction planning should recognize the possibility of fluctuations.

F.4. Use of Report This report is for the exclusive use of Robert Peccia & Associates and the Federal Highway

Administration (FHWA) to use to design the proposed improvements and prepare construction documents. In the absence of our written approval, we make no representation and assume no responsibility to other parties regarding this report. The data, analyses, and recommendations may not be appropriate for other structures or purposes. We recommend parties contemplating other structures or purposes contact us.

F.5. Level of Care Services performed by SK Geotechnical Corporation personnel for this project have been conducted with that level of care and skill ordinarily exercised by members of the profession currently practicing in this area under similar budget and time restraints. No warranty, expressed or implied, is made.

We have appreciated the opportunity to provide services on this project. If we can be of further assistance, please contact us at your convenience.