SD TIG BIA 10(1) Lower Brule - V2 tech memo-FINAL.pdf

Subject: Addendum to BIA Geotechnical Report SD TIG BIA 10(1) Lower Brule Road

From: Mike Voth, Team Lead, Pavement & Materials, CFLHD Marilyn Dodson, Team Lead, Geotech, CFLHD

To: Justin Henwood, Project Manager, CFLHD Darin Lockhart, Highway Design Engineer, CFLHD

INTRODUCTION

CFLHD was asked to review and repackage a 95% set of plans developed by the BIA for the Lower Brule Road located in the Lower Brule Reservation about 50 miles southeast of Pierre, SD. It was determined that there were insufficient funds available (from the fixed TIGER grant) to build the project as designed by the BIA. The CFLHD project team reviewed numerous design scenarios and procurement concepts to optimize the design. One of the key concepts in the repackaged project is a fixed-price variable-scope (FPVS) procurement method. The repackaged project has three distinct segments/scopes that are discussed in the following sections. CFLHD believes this approach will allow the entire 13.5-mile project to be resurfaced, reconstructed and/or rehabilitated.

Because of the optimization process, there were some changes made to the pavement structural section and upper subgrade design details as included in the BIA’s Geotechnical Report and plan set. This memorandum provides the final design recommendations for the pavement structural section and upper subgrade. Where conflicts exist, this memorandum supersedes the attached Geotechnical Report developed for the BIA by Core Engineering and Consulting, Inc.

It should be noted that CFLHD did not complete additional pavement and subgrade exploration and relied heavily on the boring data provided Core Engineering and Consulting, Inc.

EXISTING CONDITIONS AND VARIABLE SCOPE

A field review of Lower Brule Road was completed from December 4-6, 2019. The existing pavement is in very poor condition. The two predominant distresses are roughness due to the expansive clay and shale in the subgrade, and thermal and block cracking from the age-hardening (embrittlement) of the asphalt. The route has very low traffic from the start of the project at milepost 0 to milepost 11.5 (start of village area). As a result, the typical rutting and fatigue related distress from heavy truck traffic was not observed. The village area from

Technical Memorandum

Date: August 14, 2020 milepost 11.5 to the end of the project does have more traffic, but still quite low with estimates of 200 to 300 ADT provided by the BIA.

From a roughness and heaving perspective, the project can be broken into two distinct segments.

From milepost 0 to milepost 7.2 (near Medicine Creek Bridge) the road is generally straight and flat. In this segment, the road has a continuous roughness chatter but no large bumps from heaving soils or fault traces were observed. From milepost 7.2 to the end of the project, the road climbs and falls through more hilly terrain and is more curvilinear. It is evident from cuts and slopes that expansive clays and shale is more prevalent in this segment. Several car-jolting bumps were observed/felt in this segment.

From a roadway design perspective, the project is split into three distinct scopes:

• 4R (widening and reconstruction),

• 3R (undercut with no widening), and

• Full-depth reclamation (FDR - recycling existing pavement and base in place and overlaying with asphalt pavement)

The goal of using the FPVS procurement method is to maximize the amount of 4R work that is completed while still being able to resurface the entire 13.5-mile project. The tribe’s priorities for the project include the reconstruction of the approximate 2-mile segment in the village area at the east end of the project (from the gas station to the Lower Brule Administration Building), and some mitigation for the severe bumps along the route. The plans dictate where the FDR application occurs (milepost 0 to 7.2), but allow bidding competition to maximize the 4R scope built starting from the east end and progressing west (milepost 13.8 to 7.5). The logic for this approach is that the highest priority segments based on function, use, safety, and subgrade heaving are on the east end of the project.

DESIGN RECOMMENDATIONS

Much of the information gathered and described below originates from a geotechnical report prepared by Core Engineering and Consulting Inc. dated October 15, 2019. Although not all the recommendations from the report have been incorporated into the project, the boring logs, soil testing, and analysis was used to support final design recommendations. The full report is included as an attachment to this memorandum.

TRAFFIC:

Annualized average daily traffic (AADT) data with classifications were not provided for the route. The SDDOT indicated that the route has little to no commercial truck traffic. The ADT listed on the BIA’s plan set from the year 2006 was 303 with 5% trucks and an annual growth rate of 2%. This data was used to estimate ESALs for pavement design. The following is a summary of assumptions and calculations used to develop the ESAL estimate:

• 2006 ADT = 303

• 2022 ADT = 416 (2% growth rate)

• Percent trucks = 5% o 1% Class 4 o 2% Class 5 o 1.5% Class 8 o 0.5% Class 9

• Directional factor = 50% (per recommendation from SDDOT)

• Estimated/assumed truck factors o 1.5 for Class 4 o 0.5 for Class 5 o 1.5 for Class 8 o 2.0 for Class 9

• Design Lane ESAL’s = 107,000

The 20-year 18-kip equivalent single axle load (ESAL) used for design for the 4R and 3R segments was 107,000. For the FDR segment, the minimum ESAL value of 50,000 was used as the likely AADT in this segment is less than 100.

PAVEMENT DESIGN CRITERIA:

In developing the pavement structural and rehabilitation recommendations the following criteria was used:

Design Criteria Initial Serviceability 4.2 Terminal Serviceability 2.5 Design Reliability Level 75% Overall Standard Deviation 0.49 Soil Resilient Modulus (CBR = 1 to 2) 3000 psi Performance Period (3R) 20 years Calculated Structural Number (SN) 3.11 (4R & 3R) Calculated Structural Number (SN) 2.74 (FDR)

Summary tables of the existing pavement and base depths are included below. For more precise and detailed results, refer to boring logs in the attached report.

FDR Segment (Milepost 0 to 7.2): Summary of Pavement and Base Depths

Average Pavement

Depth

Range of Pavement

Depth

Average Base Depth

Range of Base Depth Comments

5.0 inches 3 to 7 inches 10.6 inches 2 to 18 inches Discernment of base depths was difficult or not recorded in some borings.

Associated inaccuracies may exist.

4R and 3R Segment (Milepost 7.5 to 13.8): Summary of Pavement and Base Depths

Average Pavement

Depth

Range of Pavement

Depth

Average Base Depth

Range of Base Depth Comments

6.6 inches 3.5 to 13 inches 7.1 inches 2,5 to 18 inches

Discernment of base depths was difficult or not recorded in some borings.

Associated inaccuracies may exist.

RECOMMENDED PAVEMENT STRUCTURAL SECTIONS:

FDR Segment (start of project to ~milepost 7.2) Layer Thickness

Asphalt Concrete Pavement 4 inches (two lifts) Full-Depth Reclamation (FDR) 8 inches Existing Subbase (remains in place) 4 inches

SN = 2.94

4R and 3R Segments (~milepost 7.2 to end of project) Layer Thickness

Asphalt Concrete Pavement 4 inches (two lifts) Aggregate Base 10 inches Undercut (no structural value assigned;

moisture reconditioning of subgrade only) 3 feet

SN = 3.16

The use of continuous undercut to moisture condition the subgrade material is a standard practice for the SDDOT as an inexpensive approach to temporarily mitigate expansive soils. CFL does not have experience with this type of undercut approach, but the CFT adopted its use based on recommendations from SDDOT geotechnical staff.

The 4R and 3R segments are recommended for the east side of the project where average daily traffic is higher and a wider typical section is warranted. The most extensive pavement heaving and largest bumps are also on the east side of the project.

The first 7.2 miles of the project do not exhibit the heaving and faulting noted in other project segments. Extensive undercut in this area does not appear needed, and could create more risk by exposing currently stable soils to moisture. The undercut would also increase production time and earthwork with little to no benefit. The pavement distress in this area is related primarily to the aging and oxidation of the pavement. The FDR treatment appears to be the most optimal approach while also being relatively inexpensive. The use of the FDR treatment on the west end will allow for more miles of 4R reconstruction to occur on the east end, without sacrificing performance.

MITIGATION OF EXPANSIVE SOILS AND SHALE FAULTS:

It must be noted that the recommendations for mitigating the expansive soils and shale fault lines are temporary and will not prevent future fault movements or completely prevent future roughness from developing due to subgrade expansion. The required improvements to fully address and solve these issues are cost prohibitive for this project and class of road.

The geotechnical report highlights three areas of particular concern for shale faults and expansive soils. These locations are as follows:

• East of Medicine Creek to Iron Nation Recreation Area (STA 398 to 467)

• Iceberg Hill (STA 545 to 595)

• Red Cloud Circle to Tribal Administration Building (STA 668 to 725)

In the above three segments, it is recommended to place a stabilization geogrid on the top of subgrade and just below the aggregate base for the full width of the pavement according to Section 207 and 714 of the FP. In addition to providing stabilization for vertical loads, it is expected that the geogrid will distribute upward stresses from swelling/heaving soils and reduce the severity of future roughness. The use of geogrids continuously throughout the project, as recommended in the geotechnical report, was considered excessive because structural failures are not prevalent along the route. Targeting the use of geogrids to critical spot locations is more cost effective.

Based on the review of the route video and boring logs, fault trace treatments using the design approach of the SDDOT (detail drawing attached) are recommended at the following locations:

• STA 425+00, STA 444+00, STA 466+00, STA 509+00, and STA 552+00.

These locations are based on the best information available (severe bumps from video and known near surface shale in the area) but exact locations will need to be field verified by the project engineer. Include a note on the plans indicating that the CO may adjust locations based on field conditions encountered.

The use of edge drains is not recommended due to the expected lack of future maintenance to address drain pipe and outlet cleaning to assure a free-flowing system. Plugged edge drains would worsen the retainage of water in the subgrade over the long term and lead to lower performance than if they had not been installed. SDDOT geotechnical staff confirmed that for similar reasons they also do not use edge drains.

The use of a wicking geosynthetic to mitigate moisture progression into the expansive subgrade is also not recommended. While wicking geosynthetics is a cost effective technical solution in areas of high rainfall or poor roadway drainage, these conditions are not pervasive on this route.

Wicking geosynthetics are relatively expensive and were considered cost prohibitive for the low volume nature of this route. The SDDOT does not use wicking geosynthetics on their state highway system.

SPECIAL CONTRACT REQUIREMENTS & CONSTRUCTION CONSIDERATIONS

• The asphalt binder grade should be PG 58-34. This generally aligns with recommendations from LTPPBind and it matches the grade commonly used on SDDOT projects.

• Specify Type III-B for pavement roughness (3 chances to improve smoothness and speeds are greater than 35 mph). This is a similar standard that SDDOT would use on this project.

• For the 4R and 3R segments, an SCR has been developed for optional use of salvaged asphalt millings as recycled aggregate base.

• Per SDDOT, corrosive soils are known to exist along the route. All concrete structures including culvert pipe should use Type V cement. CMP’s, if used, should be polymer coated and have increased gauge thickness.

• For temporary surfacing, a cutback asphalt (MC-70) placed on the aggregate base followed by robust blotting should be used. Maintenance of the primed surface will be the responsibility of the contractor until the asphalt surfacing is placed. An SCR has been developed.

• Include a nominal amount of subexcavation (~1000 cu yd) to be used at discretion of CO.

• Recommend the following bid items:

Item Number Item Description Unit 20402-0000 Subexcavation CUYD 20703-2000 Stabilization Geogrid SQYD 30203-2000 Roadway aggregate, Method 2 SQYD 30401-5500 Full depth reclamation, Method 2, 8-inch MILE

40101-0500 Asphalt concrete pavement, Gyratory mix, ½ inch NMA, < 0.3 ESALs TON

40105-3000 Antistrip additive type 3 TON 41102-0000* Prime coat (MC-70) SQYD 41105-0000 Blotter TON 41201-0000 Tack Coat TON

• The typical approach for SDDOT projects involving a significant amount of excavation and embankment is to have the “dirt work” completed in season one, then allow for settlement and equilibrium of embankment over the winter, and pave the route in season two. This approach is also recommended for the Lower Brule Road project.

• To promote drainage, the aggregate base and undercut should be daylighted to the fore slopes. During construction of the subgrade and undercut, the subgrade material should always be shaped to promote surface water drainage. Ponding of water on the subgrade will not be allowed. Soft spots that develop from construction or public traffic will be the responsibility of the contractor to repair.

• Based on discussions with the SDDOT and a review of their standards, the QA and quality requirements for their asphalt mix and aggregate have many similarities to CFL.

Gyratory based asphalt mixes with lime, incentives/disincentives, and roughness control are used frequently. The use of an MTV is also typically required by the SDDOT. The SDDOT Q2 mix appear to be a good match for the Lower Brule Project. This is a ½ inch nominal maximum aggregate size, 50-gyration mix. The CFL standard 401 specification and SCR, while not a perfect match with the SDDOT Q2 specification, provides enough similarities to allow for local availability and production. A project specific SCR was developed to align some of the SDDOT and CFL standards.

• The typical paving season for the SDDOT is from May 1 to October 15. Many plants shut down outside this season. This should be considered when evaluating construction schedules.

• There is one asphalt supplier in Pierre, SD, but the SDDOT expects bids from multiple contractors on this project. There are at least two aggregate sources within 75 miles of the project.

Attachments:

Pavement Design Calculations SDDOT fault trace detail Geotechnical Report – Core Engineering & Consulting, Inc.

AASHTO FLEXIBLE PAVEMENT DESIGN

Layer Thickness Determination Using Layered Analysis Approach

1 Enter applicable information in cells C15 through F22

2 For the first layer, use the E of the next lower layer as the MR in the Inputs Box below this table and enter the resulting layer SN.

3 The minimum layer thickness is calculated in column H. Enter the "practical" layer thickness in column I.

4 Repeat steps 2 and 3 for each layer, always using the E of the next lower layer as the MR in the Inputs Box spreadsheet below this table.

5 Check to ensure resulting SN meets or exceeds required SN

6 Note that this procedure is not valid if any layer beneath layer 1 has an E greater than 40,000 psi.

SN Using E of next Min. Layer Practical Layer

Layer Drainage Elastic lower layer in Thickness, D, Thickness, D, Associated

Layer No. Description Coefficient, ai Coefficient, mi Modulus, psi inputs box below inches inches SN

(topmost) Layer 1 AC Layer 0.44 1.00 400,000 1.14 2.59 4.00 1.76 Layer 2 Aggregate Base 0.14 1.00 35,000 3.11 9.64 10.00 1.40 Layer 3 Undercut 0.00 0.90 3,000 3.11 0.00 36.00 0.00 Layer 4 0.00 0.00 0.00 Layer 5 0.00 0.00 0.00 Layer 6 0.00 0.00 0.00 Layer 7 0.00 0.00 0.00

(bottommost) Layer 8 0.00 0.00 0.00 Subgrade Subgrade N/A N/A 3,000 N/A N/A N/A N/A

AC Layer 401 = 0.44 Total Pavement 3.16 Calculated SN 403 = 0.40 Thickness, inches, 12.23 50.00 3.11 SN to Match

CAB 301 = 0.14 Design is sufficient

Subbase/Minor agg 302 = 0.12

FDR 304 = 0.12

Select borrow 204 = 0.06 to 0.08

(Refer to Exhibit 11.2-C in Chapter 11 of PDDM for additional guidance on coefficients)

Inputs Box

W18 = 107,000 ESALs Applications Over Design Period Typ. Range 50k to 10 million R = 75 % Reliability Typ. Range 75 to 95% So = 0.49 Standard Deviation AASHTO Standard MR = 3,000 psi Subgrade Resilient Modulus Typ. Range 3000 to 15000 psi Pi = 4.2 Initial Serviceability Typ. Range 4.2 to 4.4 Pt = 2.5 Terminal Serviceability Typ. Range 2.0 to 3.0

SN on top of layer = 3.11

3R and 4R Design

AASHTO FLEXIBLE PAVEMENT DESIGN

Layer Thickness Determination Using Layered Analysis Approach

1 Enter applicable information in cells C15 through F22 2 For the first layer, use the E of the next lower layer as the MR in the Inputs Box below this table and enter the resulting layer SN.

3 The minimum layer thickness is calculated in column H. Enter the "practical" layer thickness in column I.

4 Repeat steps 2 and 3 for each layer, always using the E of the next lower layer as the MR in the Inputs Box spreadsheet below this table.

5 Check to ensure resulting SN meets or exceeds required SN 6 Note that this procedure is not valid if any layer beneath layer 1 has an E greater than 40,000 psi.

SN Using E of next Min. Layer Practical Layer Layer Drainage Elastic lower layer in Thickness, D, Thickness, D, Associated

Layer No. Description Coefficient, ai Coefficient, mi Modulus, psi inputs box below inches inches SN (topmost) Layer 1 AC Layer 0.44 1.00 400,000 1.00 2.27 4.00 1.76

Layer 2 FDR Layer 0.12 1.00 35,000 1.27 -4.08 8.00 0.96 Layer 3 Existing Subbase 0.06 0.90 20,000 2.74 0.37 4.00 0.22 Layer 4 0.00 0.00 0.00 Layer 5 0.00 0.00 0.00 Layer 6 0.00 0.00 0.00 Layer 7 0.00 0.00 0.00

(bottommost) Layer 8 0.00 0.00 0.00 Subgrade Subgrade N/A N/A 3,000 N/A N/A N/A N/A AC Layer 401 = 0.44 Total Pavement 2.94 Calculated SN

403 = 0.40 Thickness, inches, -1.44 16.00 2.74 SN to Match CAB 301 = 0.14 Design is sufficient Subbase/Minor agg 302 = 0.12

FDR 304 = 0.12

Select borrow 204 = 0.06 to 0.08 (Refer to Exhibit 11.2-C in Chapter 11 of PDDM for additional guidance on coefficients)

Inputs Box W18 = 50,000 ESALs Applications Over Design Period Typ. Range 50k to 10 million R = 75 % Reliability Typ. Range 75 to 95% So = 0.49 Standard Deviation AASHTO Standard MR = 3,000 psi Subgrade Resilient Modulus Typ. Range 3000 to 15000 psi Pi = 4.2 Initial Serviceability Typ. Range 4.2 to 4.4 Pt = 2.5 Terminal Serviceability Typ. Range 2.0 to 3.0

SN on top of layer = 2.74

FDR segment design

ADT 416 Annual Growth R0.02 Design Years 20

Directional Distribution

0.5

Lane Distribution

Classification Percent Truck Factor

Growth Factor ADT Yr 1 Design Lane ESALs ADT at N

Autos 83.0% 0.0006 345 0 513 Values Pickups, Vans 12.0% 0.004 24.29737 50 885 74

416 (calculated) Class 4 buses 1.0% 1.5 24.29737 4 27670 6 303 Class 5 trucks/RVs 2.0% 0.5 24.29737 8 18447 12

2006 Class 6 0.0% 1 24.29737 0 0 0 2022 Class 8 1.5% 1.5 24.29737 6 41505 9

2 Class 9 0.5% 2 24.29737 2 18447 3 100.00% 106953 618

(refer to Exhibit 11.2-A in the PDDM for additional guidance on truck factors)

GR = Growth Rate (%)

Future ADT Calculation ADTf = ADTi (1 + GR)(F-I)

ADTf = Average daily traffic for future year ADTi = Average daily traffic for initial year

I = Initial year for ADT F = Future year for ADT

Traffic Data for Pavement Design

STATE

OF

SHEET

NO.

TOTAL

SHEETS

PROJECT

SOUTH

DAKOTA

P l o t t e d

F r o m

TYPICAL UNDERDRAIN SECTIONS

A A’

CL

TYPICAL FAULT TRACE UNDERDRAIN

SECTION A - A’

Fault Trace

Underdrain Trench

Fault Heave

Fault TracePorous Backfill

4" Slotted Corrugated

Polyethylene Tubing

Subgrade Surface

2’

4’

50’

50’

Existing Surfacing to be Removed

3’ Undercut / Re-establish

Subgrade Profile

Limits of 3’ Undercut

P 0065(16)164 39 61

FAULT TRACE UNDERDRAIN PLAN VIEW - MRM 165.00 + 0.200, 167.00 + 0.200 and 172.00 +0.900

SDDOT typical fault trace detail

Michael.Voth Highlight www.coresd.com

Geotechnical Engineering • Environmental Services • Materials Testing

115 West Beebe Avenue

Chamberlain, South Dakota 57325 ph: (605) 234-2673 fx: (605) 234-2674

1603 Locust Street

Yankton, South Dakota 57078 ph: (605) 260-4908 fx: (605) 260-4908

October 15, 2018

Kul Wicasa Oyate Road Maintenance Program 187 Oyate Circle Lower Brule, SD 57548

Attn: Mr. Ivan Umberger

RE: Geotechnical Exploration and Review Proposed BIA Route 10 Roadway Reconstruction

SD Highway 273 to Lower Brule Tribal Administration Building Kul Wicasa Lakota Nation

CEC No. 01-18-034

Dear Mr. Umberger, This report presents the results of a subsurface exploration program and geotechnical engineering review for the BIA Route 10 roadway reconstruction project spanning from SD Highway 273 to the Lower Brule Tribal Administration Building on the Kul Wicasa Lakota Nation. This work was conducted in accordance with the contract between the Kul Wicasa Oyate and Core Engineering & Consulting, Inc. (CEC) dated April 23rd, 2018. We are submitting a copy of the report to you electronically and one (1) additional hard copy with the appropriate engineers’ seals affixed.

The opinions expressed in this report are based on information provided by you and the data obtained from our subsurface exploration. Should there be any changes as the project develops, we request that we be notified so that these new conditions can be reviewed and, if necessary, we can modify our recommendations.

The soil samples remaining after the laboratory testing is completed will be retained for a period of one month, at which time they will be discarded. Please advise us in writing if you wish to have us retain them for a longer period of time.

CEC appreciates the opportunity to provide these services to you. As your project proceeds, we would be interested in providing additional geotechnical and construction materials engineering services. If you have any questions about this report, or if you require additional information, feel free to contact us.

Sincerely, Core Engineering & Consulting, Inc.

Victoria D. Job, PE Geotechnical Engineer victoria@coresd.com

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REPORT OF GEOTECHNICAL EXPLORATION

AND ENGINEERING REVIEW

Proposed BIA Route 10 Roadway Reconstruction SD Highway 273 to Lower Brule Tribal Administration Building

Lyman County, South Dakota Kul Wicasa Lakota Nation

CEC Job No.: 01-18-034

Report Date: Monday, October 15, 2018

Prepared For: Kul Wicasa Oyate

187 Oyate Circle Lower Brule, South Dakota

CEC Job No. 01-18-034

PROJECT SUMMARY

Core Engineering & Consulting, Inc. (CEC), under contract with the Kul Wicasa Oyate, mobilized to the site on the Kul Wicasa Lakota Nation on July 2nd, 2018 to perform a subsurface exploration program and subsequent engineering review. The purpose of the work performed at this site is to provide you and your project team the necessary subsurface soil information to adequately plan, design and construct the project.

The proposed project consists of providing recommendations for reconstruction of the existing roadway. At the time of our exploration, the existing roadway consisted of a two-lane, asphalt concrete paved secondary road with narrow shoulders and typical ditch sections.

The field exploration consisted of sixty-seven (67) Standard Penetration Test (SPT) borings, each within the existing pavement section, drilled and sampled to a depth of 6’ below existing surface grade each. The existing pavements were found to have a thickness ranging from approximately 3” to 13” of asphalt concrete pavement. The soils encountered for borings below the existing pavement are summarized below:

Boring Number Generalized Soil Profile

B24,31,32,34,37,40-42,44,52,54,60 Fill

B1,2,5-9,12,22,23,25-29,43,45,46, 49-51,55-59,61-67

¾’-5½’ of Fill over Alluvial Soil

B4,15,30 4¾’-5½’ of Fill over Topsoil

B3,11,13,14 1¼’-3¼’ of Fill over ¾’-3’ of Topsoil over Alluvial Soil

B53 ~1¼’ of Fill over ~¾’ Eolian over Alluvial Soil

B10,18,47 1’-3’ of Fill over 1’ Alluvial Soil over Pierre Formation

B16,17,19,20,21,33,35,36,38,39,48 1’-4’ of Fill over Pierre Formation

Groundwater measurements were not taken as part of this exploration.

The fill soils encountered at the site were found to consist primarily of aggregate base course overlying silty/sandy fat clay, silty lean clay and high-plasticity silt. The SPT N-values indicate the soils range from soft to stiff or medium dense with N-values generally increasing with depth. In our opinion, the existing site soils are weak, unstable and at least mildly expansive under varying moisture conditions. Based on these findings, we make the following recommendations.

Roadway:

• Prior to fill placement, all existing pavements should be milled and stockpiled, leaving no particles larger than 2” nominal diameter on the exposed subgrade surface

• The existing pavement base materials are generally not acceptable for re-use as aggregate base course as their integrity has been compromised, rather they should be incorporated into the milled asphalt and re-used as pavement sub-base soils instead

• Prior to fill placement, the exposed subgrade soils should be scarified to a minimum depth of 12”, moisture-conditioned to be within a range of -2% to +3% of their respective optimum moisture contents and re-compacted to be within a range of 96% to 100% of their respective Standard Proctor maximum dry densities

• Prior to subbase and/or base course placement, the final subgrade surface should be shaped to provide positive drainage of the entire subgrade surface; drainage should be directed to the roadway shoulders

• Through several particularly difficult areas where localized heaves have been pervasive, we recommend installing a wicking geotextile product, such as Tensar® RD-5 or equivalent, immediately above the prepared subgrade to improve moisture management and maintain a consistent subgrade moisture content where changes in moisture are known to be particularly problematic; these areas are as follows o Medicine Creek Bridge to Iron Nation Recreation Area entrance o Steep grade adjacent to the buffalo pasture o Red Cloud Circle to the Tribal Administration Building

• Following the scarify/re-compact process, pavement grade should be re-attained using a Federal Highway Administration aggregate sub-base or base course material, or the recycled asphalt materials salvaged from the existing roadway, reinforced using a biaxial or triaxial geogrid product

• As added protection against subgrade softening and localized heaving, we recommend installing edge-drains throughout the project; the edge drains will help to maintain positive drainage of the subbase and base course layers throughout the design life of the pavements

• Aggregate sub-base and base course materials should be compacted to a minimum of 98% of the Standard Proctor maximum dry density, at or near optimum moisture content

• Based on these subgrade preparation recommendations, pavement sections can consist of the following:

Base Section Min. Surfacing

Thickness Min. Base Course

Thickness

Min. Subbase Course

Thickness

Unreinforced AC Pavement Section over Reinforced Base Course

5” 10” 8”

Reinforced AC Pavement Section using BX1200

Bi-axial Geogrid over Reinforced Base Course 5” 6” 8”

Reinforced AC Pavement Section using TX140

Tri-axial Geogrid over Reinforced Base Course 4” 6.5” 8”

* Geogrids are referenced as Tensar® product numbers for ease of reference; equivalent products from other suppliers are also acceptable.

These recommendations are summarized for your convenience; please read the entire report for additional details.

TABLE OF CONTENTS

INTRODUCTION

BACKGROUND INFORMATION

PROPOSED CONSTRUCTION

AUTHORIZED SCOPE OF SERVICES

METHODOLOGIES

FIELD TESTING & OBSERVATIONS

Drilling

Sampling

Split-Spoon Samples (SS)

Bulk Samples

Sampling Limitations

Soil Classification

Water Level Measurements

LABORATORY TESTING

Natural Moisture Content (ASTM:D2216)

Atterberg Limits (ASTM:D4318)

Particle Size Analyses (ASTM:D422)

Standard Proctor Moisture/Density Relationship (ASTM:D698)

California Bearing Ratio (ASTM:D1883)

FINDINGS

SURFACE OBSERVATIONS

SUBSURFACE CONDITIONS

Pavement

Site Geology

Subsurface Soils

Table 1: Boring Log Soil Classification/Depth Summary

Topsoil

Coarse-Grained Fill

Table 2: Summary of Particle Size Analysis Test Results

Fine-Grained Fill

Eolian

Alluvium

Pierre Formation

Bulk Samples

Groundwater

RECOMMENDATIONS

APPROACH DISCUSSION

GRADING

Asphalt Milling

Subgrade Preparation

Subgrade Drainage

Problem Areas

Geogrid Subbase/Base Layer Reinforcing

TABLE OF CONTENTS

Base Course Placement

PAVEMENT SECTIONS

Table 3: Pavement Section Summary

OBSERVATION & TESTING

LIMITATIONS

SIGNATURES

APPENDIX A – FIELD TESTING

FIGURE 1 – SITE LOCATION MAP

FIGURE 2 - BORING LAYOUT MAP

SUBSURFACE BORING LOG (67)

BORING LOG NOTES

UNIFIED SOIL CLASSIFICATION SYSTEM

APPENDIX B – LABORATORY TESTING

ATTERBERG LIMITS TEST RESULTS (ASTM:D4318) (4)

PARTICLE SIZE ANALYSES (ASTM:D422) (6)

MOISTURE/DENSITY RELATIONSHIP OF SOILS (ASTM:D698) (14)

CALIFORNIA BEARING RATIO (ASTM:D1883) (5)

REPORT OF GEOTECHNICAL EXPLORATION

AND ENGINEERING REVIEW

PROPOSED BIA ROUTE 10 ROADWAY RECONSTRUCTION

SD HIGHWAY 273 TO LOWER BRULE ADMIN. BUILDING

LYMAN COUNTY, SOUTH DAKOTA

KUL WICASA LAKOTA NATION

CEC NO. 01-18-034

INTRODUCTION

This report presents the results of a subsurface exploration program and geotechnical engineering review for the proposed BIA Route 10 roadway reconstruction project located on the Kul Wicasa

Lakota Nation. To protect you, Core Engineering & Consulting, Inc. (CEC), and the public, we authorize use of the opinions and recommendations in this report only by you and your project team for this specific project. Contact us if other uses are intended.

Prior to releasing plans and specifications for bidding and/or construction, we request the opportunity to review said documents to verify our recommendations have been correctly interpreted. Even though this report is not intended to provide sufficient information to accurately determine quantities and locations of particular materials, we recommend that your potential contractors be advised of the report availability.

BACKGROUND INFORMATION

Proposed Construction

Based on the information provided, we understand that the project consists of full-depth reconstruction of the existing roadway pavements. We assume the reconstruction of the roadway will include complete removal and replacement of the existing pavement section and reuse of the existing pavement and granular material as subbase. New pavements are anticipated to be asphalt concrete pavements. Changes in site grades are expected to be minimal.

The above project 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 from that described so that we can evaluate whether changes in our recommendations are appropriate.

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Authorized Scope of Services

CEC’s services for this project were performed in accordance with the contract between Kul

Wicasa Oyate and Core Engineering & Consulting, Inc. (CEC) dated April 23rd, 2018. The authorized scope of services for this project consists of the following:

• Drill sixty-nine (69) Standard Penetration Test (SPT) borings to a depth of 6’ below existing surface grade within the existing roadway

• Perform laboratory analyses on select soil samples to aid in classification and engineering review

• Perform a geotechnical engineering analysis based on the above and prepare this report

Due to historic soils data being available through portions of the project, the total number of soil borings was reduced from 69 to 67.

The contracted scope of services is intended for geotechnical purposes only and is not intended to explore for the presence or extent of environmental contamination at the site or provide opinions regarding the status of the site relative to “wetland” definitions.

METHODOLOGIES

Field Testing & Observations

The subsurface exploration program consisted of sixty-seven (67) standard penetration test borings. The field testing was performed on July 2nd through 31st, 2018.

The approximate soil boring locations are shown on attached Figure 2. Boring locations were spotted in the field based on existing site features. Surface elevations were not taken at the boring locations with the assumption that grades would not change significantly as part of the new construction.

Drilling

The standard penetration test borings were drilled using 3¼” I.D. hollow-stem augers. The boreholes were backfilled in compliance with Tribal and/or Federal regulations.

Sampling

Split-Spoon Samples (SS)

Soil sampling was performed according to the procedures described by ASTM:D1586. Using this procedure, a two-inch O.D., split-barrel sampler is driven into the soil by a 140-pound weight

Proposed BIA Route 10 Roadway Reconstruction Page 3 of 16 falling 30 inches. After an initial set of six inches, the number of blows required to drive the sampler an additional 12 inches is known as the penetration resistance, or N-value. The N-value is an index of the relative density of cohesionless soils and the consistency of cohesive soils.

Bulk Samples

Bulk samples taken for laboratory testing were obtained from drill cuttings which are brought to the ground surface. The depth of the sample is estimated based on the auger depth, the soil appearance and the action of the drill tooling. Due to the sampling method, some mixing of the soils can be expected as the cuttings are brought to the surface and subsequently shoveled into the sample container.

Sampling Limitations

Unless actually observed in a sample, contacts between soil layers are estimated based on the spacing of samples and the action of drilling tools. Cobbles, boulders and other large objects generally cannot be recovered from test borings. They may still be present in the ground even if they are not noted on the boring logs.

Soil Classification

Included are the Subsurface Boring Logs, indicating the depth and identification of the various strata, the N-value, the laboratory test data, water level information and pertinent information regarding the method of maintaining and advancing the borehole. Soil classifications shown on the boring logs are based on the Unified Soil Classification (USC) system. The USC system is described in ASTM:D2487 and D2488. Where laboratory classification tests (i.e. particle size analyses and Atterberg Limits) have been performed, classifications per ASTM:D2487 are possible. We have attached charts illustrating the USC system, the descriptive terminology and the symbols used on the boring logs.

As the samples were obtained in the field, they were visually and manually classified by a registered geotechnical engineer or a qualified field geologist in accordance with ASTM:D2488.

Representative portions of all samples were then sealed and returned to the laboratory for further examination and for verification of the field classification. The boring logs also include judgments of the geological depositional origin. This judgment is primarily based on observation of the soil samples, which can be limited. Observations of the surrounding topography, vegetation and development can sometimes aid this judgment.

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Water Level Measurements

The ground water measurements are shown at the bottom of the boring log. The following information appears under “Water Level Measurements” on the log:

• Date and Time of measurement

• Sampled Depth: lowest depth of soil sampling at the time of measurement

• Casing Depth: depth to bottom of casing or hollow-stem auger at time of measurement

• Cave-in Depth: depth at which measuring tape stops in the borehole

• Water Level: depth in the borehole where free water is encountered

• Drilling Fluid Level: same as Water Level, except the liquid in the borehole is drilling fluid, if used

The true location of the water table at the boring location may be different than the water level measured in the borehole. This is possible because there are several factors which can affect the water level measurements in the borehole. Some of these factors include permeability of each soil layer in the profile, presence of perched water, amount of time between water level readings, presence of drilling fluid, weather conditions and the use of borehole casing.

Laboratory Testing

Representative samples of the soils encountered were selected for laboratory testing to determine index properties. The tests included the determination of the natural moisture content, Atterberg

Limits, particle size distribution, Standard Proctor moisture/density relationship and California

Bearing Ratio. The test results can be found on the Subsurface Boring Log sheets opposite the samples upon which they were performed and/or on the respective test reports included in

Appendix B.

Natural Moisture Content (ASTM:D2216)

The natural moisture content was determined for soils recovered from each boring location, at various depths below ground surface. The natural moisture content is determined by drying a representative sample of the soil to a constant weight in an oven at approximately 230°F. By weighing the soil before and after drying the total moisture loss can be compared against the total weight of soil solids to determine the percent moisture content.

Atterberg Limits (ASTM:D4318)

The Atterberg Limits were determined for soils recovered from each boring location, excluding the Boring #51 through #55 locations, and composite bulk samples of soils recovered from the approximately 1’ to 3’ below surface grade, excluding Boring #55. The Atterberg Limits are those

Proposed BIA Route 10 Roadway Reconstruction Page 5 of 16 moisture contents at which a soil changes phases from a solid material to a plastic material (plastic limit) and from a plastic material to a liquid material (liquid limit). The plastic limit is determined by rolling a moist soil sample into a thread until it will no longer hold together at a diameter less than ⅛”. The liquid limit is determined by adjusting the moisture content of a soil sample until dropping a brass cup against a solid surface a distance of ½” 25 times causes a standard groove cut through the soil sample to close upon itself. The Atterberg Limits can be used to evaluate the shrink/swell potential of soils and their relative stability under varying moisture conditions.

Particle Size Analyses (ASTM:D422)

The particle size distribution was determined for soils recovered from each boring location and composite bulk samples of soils recovered from the approximately 1’ to 3’ below surface grade, excluding Boring #55 location. The particle size distribution for the coarse fraction (gravel/sand) is determined by mechanical sieve analysis where the soil particles are agitated over a series of sieves and the weight retained on each recorded as a percent of the total. The particle size distribution for the fine fraction (silt/clay) is determined by colloidal analysis where the soil particles are forced into suspension and the rate of sedimentation is monitored by measuring the change in specific gravity of the solution through the use of a calibrated hydrometer. The particle size distribution is plotted on a logarithmic scale as a function of “percent finer by weight” and

“effective particle size”.

Standard Proctor Moisture/Density Relationship (ASTM:D698)

The Standard Proctor moisture/density relationship was determined for the composite bulk samples of soils recovered from approximately 1’ to 3’ below surface grade at each boring location, excluding Boring #55 location. The moisture/density relationship of soils is determined by compacting multiple samples of similar soil materials into a standardized mold using a 5.5 lb hammer dropped from a height of 12”. For methods “A” and “B”, the mold used is 4” in diameter and the soil is compacted in three equal lifts by dropping the hammer 25 times per lift. For method “C”, the mold used is 6” in diameter and the soil is compacted in three equal lifts by dropping the hammer 56 times per lift.

For each compacted sample, the moisture content and density are determined. Each moisture/density value is then plotted and a best-fit curve is constructed. The equation of the curve is then used to calculate a maximum dry density and optimum moisture content.

California Bearing Ratio (ASTM:D1883)

The California Bearing Ratio (CBR) was determined for the composite bulk samples of soils recovered from the approximately 1’ to 3’ below surface grade at each boring location, excluding

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Boring #55 location. The CBR is determined by compacting a specimen to a specified compaction level in a 6” diameter mold. The sample is inundated for a period of 96 hours prior to being subjected to a penetrating load. Stress and strain are logged during the penetration process and values are compared against standardized bearing values to obtain a bearing ratio to be used in pavement computations.

FINDINGS

Surface Observations

The site is located along BIA Route 10 between SD Highway 273 and the Lower Brule Tribal

Administration Building in rural Lyman County, South Dakota on the Kul Wicasa Lakota Nation.

The existing roadway consists of a two-lane, asphalt concrete (AC) paved secondary road with narrow shoulders and typical ditch sections.

The existing pavements are in varying degrees of distress, including localized heaves, both transverse & longitudinal cracking and a number of patches. Of particular note are three problem areas, the first from the Medicine Creek Bridge to the Iron Nation Recreation Area entrance, the second on the steep grade adjacent to the buffalo/elk pasture and the third from Red Cloud Circle to the Tribal Administration Building. These area have exhibited substantial heaving and as such have required extensive maintenance over the life of the roadway.

Subsurface Conditions

Logs of the test borings are included in Appendix A. The logs contain information concerning soil layering, soil classification, geologic description and moisture. Relative density or consistency is also noted, which is based on the standard penetration resistance (N-value). Please note the boring logs only indicate the subsurface conditions at the sampled locations. Variations often occur between and beyond borings.

Pavement

The existing pavement section was measured at each boring location. Pavement thickness measurements resulted in 3” to 13” of asphalt concrete pavements with the average pavement section thickness found to consist of 5.8” of asphalt over. The underlying base course layer was found to range in thickness from 0” to 18” with the average base layer consisting of 8.6” of aggregate base course.

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Site Geology

The primary geologic origin of the soils encountered at this site consists of fill soils placed during the construction of the roadway & culverts; eolian soils, referring to soils transported and deposited by wind action; alluvial soils, referring to soils transported and deposited by water action; and Pierre Formation shale bedrock.

The Pierre Formation in its undisturbed state consists primarily of waxy, dark gray to olive colored shale deposited in a marine environment during the Cretaceous period. The exception to this is the Crow Creek member which is primarily light brown to buff in color. The Crow Creek Member is one of several marl units recognized within the Upper Cretaceous Pierre Shale Formation of eastern South Dakota and northeastern Nebraska. The formation contains interbedded layers of bentonite, which can vary from less than 1” to several feet in thickness. Laminations and lenses of silty claystone concretions up to several inches thick can be predominant in the formation.

When weathered, the Pierre Formation reverts back to the constituent clays that form the shale structure.

The shale-derived clays resulting from weathering of the Pierre Formation typically classify as fat clay, silty fat clay or high-plasticity silt. The shale-derived clays are known to be problematic with regards to structural support due to their high swell potential. Slope instability is common in the

Pierre Formation as the shale is weak, poorly-drained bedrock prone to shear failure under load.

Subsurface Soils

Based on our interpretation of the soil boring results, it is our judgment the generalized profile of existing roadway embankment consists of asphalt concrete pavements ranging in thickness from approximately 3” to 13” overlying varying depths of fill, topsoil, eolian, alluvial and/or Pierre

Formation deposits. The soils encountered for borings below the existing pavement are summarized below:

Table 1: Boring Log Soil Classification/Depth Summary

Boring Number Generalized Soil Profile

B24,31,32,34,37,40-42,44,52,54,60 Fill

B1,2,5-9,12,22,23,25-29,43,45,46, 49-51,55-59,61-67 ¾’-5½’ of Fill over Alluvial Soil

B4,15,30 4¾’-5½’ of Fill over Topsoil

B3,11,13,14 1¼’-3¼’ of Fill over ¾’-3’ of Topsoil over Alluvial Soil

B53 ~1¼’ of Fill over ~¾’ Eolian over Alluvial Soil

B10,18,47 1’-3’ of Fill over 1’ Alluvial Soil over Pierre Formation

B16,17,19,20,21,33,35,36,38,39,48 1’-4’ of Fill over Pierre Formation

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The following are detailed descriptions of the different soil layers encountered.

Topsoil

The topsoil encountered at the site consists primarily of fat clay, silty fat clay and clayey silt.

These soils are slow draining and are judged to be highly frost susceptible. The topsoil at this site has a moderate potential for shrink/swell under varying moisture conditions; however, is considered compressible under the fill and/or pavement loads.

No laboratory tests were performed on the recovered topsoil.

Coarse-Grained Fill

The upper fill soils were found to be comprised primarily of 0” to 18” of road base. We assume these soils were placed under controlled density conditions as part of the roadway construction and therefore are considered adequate to support the existing/new pavements. The coarse-grained fill soils encountered are moderate to fast draining and are judged to be at least moderately frost susceptible though not significantly expansive.

Laboratory tests performed on the recovered samples of the fill soils include the determination of the natural moisture content, Atterberg Limits determination and particle size distribution.

The natural moisture content tests indicate the fill soils are existing at moisture contents ranging from 1% to 24%, likely well below to well above the Standard Proctor optimum moisture content for these soil types.

The results of the Atterberg Limits tests indicate the fill soils have liquid limits (LL) ranging from

25% to 33%, plastic limits (PL) from 17% to 28% and resultant plasticity indices (PI) ranging from 3% to 14%. The results indicate the soils have USC classification of lean clay (CL), silt (ML) and silty lean clay (CL-ML).

The results of the particle size analyses performed are summarized below, as compared to the

Aggregate Base Course specifications from the FP-14. The following table summarizes the test results; for complete results see the attached test reports.

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Table 2: Summary of Particle Size Analysis Test Results

Boring

Percent Passing

1”

(25 mm)

¾”

(19 mm)

#4

(4.75 mm)

#40

(425 µm)

# 200

(75 µm)

Spec. 100 97-100 41-71 12-28 9.0-16.0

1-5 97 97 72 21 13.0

6-10 100 99 69 24 13.9

11-15 100 100 71 24 13.2

16-20 100 100 68 19 11.3

21-25 100 100 65 21 11.8

26-30 100 100 68 15 9.5

31-35 100 100 70 15 8.7

36-40 100 100 75 19 10.2

41-45 100 100 71 17 10.6

46-50 100 100 74 22 12.3

51-54 100 100 77 25 16.4

56-60 100 100 74 26 9.3

61-64 100 100 81 31 16.7

65-67 100 100 71 24 13.4

Average 100 100 72 22 12.2

Fine-Grained Fill

The lower fill soils were found to be comprised primarily of fat clay with topsoil, fat clay, silty fat clay, lean clay, silty lean clay, sandy lean clay, clayey high-plasticity silt, high-plasticity silt, clayey silt, gravelly sand and millings. Again, we assume these soils were placed under controlled density conditions as part of the existing construction and therefore have limited compressibility potential under the fill and/or pavement loads. The fine-grained fill soils encountered are typically very slow draining and are judged to be highly frost susceptible and moderately to highly expansive.

Laboratory testing performed for the fine-grained fill soils consist of the determination of the natural moisture content. The test results indicate these soils at this site occur naturally at moisture contents ranging from 13% to 42%, values well below to well above the Standard

Proctor optimum moisture content for these soil types.

Eolian

The eolian deposits encountered were found to be comprised primarily of clayey silt. These soils are considered low-strength materials and are considered potentially collapsible if allowed to

Proposed BIA Route 10 Roadway Reconstruction Page 10 of 16 become saturated under load. The eolian soils encountered are very slow draining and are judged to be highly frost susceptible though not…