libi01002_LittleBighornParkRoad_FinalGeotechAddendum GM40-23.pdf

PDF 2 MB Posted Sep 19, 2024

Attached to: MT NP LIBI 10 (2), Little Bighorn Battlefield National Monument
Solicitation number: 69056723B000002
Issued by: Department of Transportation Federal Highway Administration

About this file

Written by GovTribe AI · Sep 19, 2024

This document is a revised geotechnical addendum for the MT PRA LIBI 10(2) project at the Little Bighorn Battlefield National Monument. The addendum provides recommendations for reinforced soil slope (RSS) design to address right-of-way limitations and steeper slopes needed for the project. The analysis is based on previous boring information and presents two RSS systems - one for slopes up to 1:1.4 and another for slopes between 1:1.5 and 1:1.9. The recommended RSS systems use 13-foot long primary geogrid reinforcement placed at 1-foot vertical intervals to achieve minimum factors of safety of 1.5. The document also includes foundation recommendations, internal stability analysis results, and a conceptual detail drawing of the RSS system. This addendum is related to Federal Contract Opportunity ID 7a8d9b0f8a0947c4ba244700c212054f, Solicitation Number 69056723B000002 for the MT NP LIBI 10(2) project at the Little Bighorn Battlefield National Monument.

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August 10, 2023 Project 19-3836G

Mr. Brad Thompson, PE Robert Peccia and Associates PO Box 5653 Helena, Montana 59604 Via Email: BThompson@rpa-hln.com

Dear Mr. Thompson:

Re: Revised Addendum #1, Reinforced Slope Recommendations, Geotechnical and Pavement Geotechnical Report, MT PRA LIBI 10(2), Little Bighorn Battlefield National Monument, IDIQ Contract No. 69056721 D000008, Task Order No. 69056722F000041

Background

We are providing this revised addendum addressing reinforced slope recommendations for the above project. In our original Geotechnical and Pavement Report dated February 13, 2020, we recommended fill slopes be constructed no steeper than 1(V):2(H). However, it is our understanding that due to right-of-way limitations, steeper slopes are needed for the project. This report has been revised to address design comments and includes internal and global slope stability results.

A total of 15 locations are anticipated for slope improvement at this time. The slope improvements are 20 to 310 feet long, and based on available cross-sections, heights range from about 4 to 10 feet.

Scope of Work

The desired scope of services and project approach was discussed in telephone, and conference calls with the Federal Highway Administration and Robert Peccia and Associates (RPA). We submitted a field exploration plan dated August 24, 2022. The scope of services outlined in that exploration plan is briefly described below:

• Coordinate field work with RPA, Federal Highway Administration and National Park Services.

• Perform twenty hand auger borings at eleven locations, accompanied by an archeologist from the National Park Service (NPS).

2511 Holman Avenue P. O. Box 80190

Billings, Montana 59108-0190 p: 406.652.3930; f: 406.652.3944 www.skgeotechnical.com

WFL GM40-23

Robert Peccia and Associates August 10, 2023 Project 19-3836G Page 2

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

• Performing global stability analysis at each of the eleven locations to analyze reinforced soil slopes for the entire project.

• Discussing the project with Mr. Brad Thompson of RPA.

• Submitting a draft geotechnical evaluation report containing logs of the hand auger borings, our analysis of the field and laboratory tests, a summary of our global stability analysis, and recommendations for reinforced soil slope design.

• Finalizing the report after receiving review comments.

However, due to a longer than normal winter and frozen subgrades making hand augers impossible, as well as deadline pressures, it was decided not to perform the field and laboratory work initially proposed.

Therefore, the analysis and recommendations provided in this addendum are based on previously available shallow boring information obtained along the project. It is important that the project team recognize the limitations of this approach, which are highlighted below.

• The PDDM referenced in the Scope of Work indicates that soil borings should be performed along the crest and toe of the slope to a depth of two-times the fill height. Borings of this type are generally performed with a drill rig to depths ranging from 15 to 20 feet with standard penetration test and thin-wall samples to evaluate soil strength in the field and laboratory. To use the available hand auger information, this requirement for drilling will need to be relaxed.

• Available subsurface information includes 15 shallow hand auger borings performed for the Geotechnical and Pavement report dated February 13, 2020, as well as 15 subgrade borings performed by Western Federal Lands Highway Division presented in a memorandum dated, January 22, 2001. All of these shallow borings were generally performed at the existing pavement surface elevation and did not necessarily extend through the fill or into the foundation soils.

• The lack of deep geotechnical borings will require us to make assumptions on the consistency and strength of the foundation and retained soils for the reinforced soil slope (RSS) locations.

Relatively conservative assumptions were made.

Global Slope Stability Analysis

General. We performed global slope stability analyses for two general RSS systems. The first RSS system will be designed for 1:1.25 slopes, and this design should be applied to all slopes up to 1:1.4. The second RSS system was designed for 1:1.5 slopes, and should be applied all slopes between 1:1.5 and 1:1.9. The initial analysis included an unreinforced gravel slope to confirm the need for a reinforced soil slope. A series of analyses were then performed, starting with primary biaxial geogrid reinforcement 13

Project 19-3836G Page 3 feet long (a full roll width), and placed every 1 vertical foot. Based on the results of these analyses, the length of the reinforcement was adjusted until a factor of safety (FOS) of at least 1.50 was realized. The trial analyses were performed for both long-term and short-term conditions using drained strength parameters and undrained strength parameters, respectively. Seismic stability was not analyzed since the project is in an area of low seismic activity. An applied load simulating traffic was applied to the short-term condition analysis.

Soil Conditions and Strength Parameters. The global slope stability analysis was performed using the computer program SVSlope® developed by SoilVision Systems Ltd and now owned by Bentley Systems.

The analysis was performed using both drained and undrained soil strength parameters to evaluate both long-term and short-term conditions, respectively.

In our analysis, we used the soil parameters shown in Table 1 below. These soil parameters were developed using a combination of engineering judgment and our familiarity with overburden soils in eastern Montana, as well as dynamic cone penetrometer results and hand auger borings results previously obtained for the pavement report. As previously mentioned, no additional field, laboratory, or shear strength data was obtained for the RSS analysis.

Table 1. Summary of Soil Strength Parameters

Soil Type Moist Unit

Weight (psf)

Long-Term Conditions (Drained Strength

Parameters)

Short-term Conditions (Undrained Strength

Parameters) Friction Angle

(deg) Cohesion

(psf) Friction

Angle (deg) Cohesion

(psf) Native Lean Clay 110 26 0 0 600

Select Gravel 130 34 0 34 0 Topsoil 95 20 200 20 200

The primary reinforcement geogrid analyzed conformed to the requirements found in Table 714-4 of FHWA FP-14 for biaxial geogrid. We recommend that the RSS structure be constructed using compacted Select Borrow, meeting the requirements of FHWA FP-14 section 704.07. This material is a 3-inch minus sandy gravel which is common in Montana and used for roadway and utility projects. Materials meeting Select Borrow requirements are available in the Billings, Montana area and may be available in the Hardin, Montana area, as well.

Global Slope Stability Results. The results of the slope stability analyses are summarized in Table 2 below. A conceptual detail drawing showing the configuration of the recommended RSS slope is also attached to this report. The results of the slope stability analysis are discussed in more detail below.

Project 19-3836G Page 4

Table 2. Summary of Slope Stability Analysis Primary Reinforcement Calculated Factor of Safety

Slope Length Vertical Spacing Long-Term Short-Term 1:1.25 -- -- 1.14 1.21 1:1.25 13’ 1’ 1.52 2.24 1:1.5 -- -- 1.31 1.31 1:1.5 13’ 1’ 1.62 2.22

Reinforced Slope Recommendations.

Factor of Safety Selection. Selection of the required FOS is critical to the design of the RSS structure.

The Federal Highways Project Development and Design Manual, Section 6.4.6.5, indicates global stability analysis should be performed for embankments, with short-term FOS between 1.1 and 1.2, and long-term FOS ranging from 1.3 to 1.5. The overall stability of conventional retaining walls is addressed in the AASHTO LRFD Bridge Design Manual, Section 11.6.2.3, and indicates a resistance factor of 0.75 should be used when the geotechnical parameters are well known, and 0.65 where geotechnical parameters are based on limited information or where the slope contains a structural element. A resistance factor of 0.75 is approximately equivalent to a FOS of 1.3, and 0.65 is equivalent to a FOS of 1.5.

It is our opinion that a final FOS of 1.5 is required for RSS structures on this project due to the relative lack of subsurface information.

RSS Structures Between 1:1.25 to 1:1.4. Our analysis of the steeper RSS structures show that an unreinforced gravel soil slope has a FOS of 1.14, which is less than the required FOS of 1.3 for an unreinforced slope. We then analyzed the length and spacing of the primary geogrid reinforcement. The initial analysis consisted of a primary reinforcement layer placed at 1-foot vertical intervals. The length of the reinforcing was varied until a FOS greater than 1.5 was obtained. Our calculations indicate a 13-foot-long reinforcement length will be required. This design should be applied to all slopes steeper than 1:1.5, as shown in the attached sketch.

RSS Structures Between 1:1.5 and 1:1.9. The evaluation of the 1:1.5 RSS structures was performed in a similar manner to the 1:1.25 structures. Our first analysis consisting of an unreinforced gravel slope and resulted in a calculated FOS of 1.31, just marginally meets the required FOS of 1.3 for unreinforced slopes. However, due to the relatively unknown nature of the on-site soils, it is our opinion that installing an RSS structure is justified for slopes between 1:1.5 and 1:1.9.

The initial analysis consisted of a 13-foot-long primary reinforcement layer placed every one vertical foot, which resulted in a FOS of 1.62. To reduce overall gravel quantity, and to ease construction staging, we also analyzed 10-foot long reinforcement layers, but this analysis did not provide the required FOS of 1.5.

Project 19-3836G Page 5

Secondary Reinforcement and Slope Vegetation. Secondary reinforcement is not required because the primary reinforcement is placed on one-foot intervals.

The face of the RSS structure will also require some manner of erosion control to promote vegetation.

RSS structure facing options are addressed in FHWA-NHI-00-03, Table 13 and facing options show wrapped faces when slopes are 1:1.4 or steeper, while unwrapped faces are used for slopes flatter than 1:1.5. These requirements are based on Select Borrow or similar well-graded gravel used as fill for the reinforced slope.

We wish to point out, however, that considerable advances have been made in turf reinforcement mat (TRM) materials and installation. Wrapping the faces with the secondary reinforcement takes more time to install, which results in higher costs. As an alternative to wrapping the face of the steeper RSS structures, we recommend using a robust TRM to reduce installation costs and protect the slope face. We have assumed that the installation details and selection of the exact TRM will be determined by RPA.

Foundation Recommendations. For both RSS structures, we recommend vegetation, topsoil, and rootzone be removed from beneath the proposed RSS extent. We recommend a minimum of 6 inches of Select Borrow be placed and compacted before placing the first layer of geogrid reinforcement. We recommend the subgrade surface below the RSS be graded to drain any water to the faces of the slope, if possible. It is our opinion that a drainage layer is not warranted below or behind the RSS structure due to the relatively well-drained site topography and semi-arid environment.

Internal Stability. The internal stability of the RSS slopes were checked using ReSSA+ software created by ADAMA Engineering. The software can check multiple conditions including global and internal stability. The internal stability checks include sliding and wedge failure. The RSS slopes were modeled with a wrapped face, because a TRM is not an analysis option. The internal stability results for both the 1:1.25 and 1:1.5 slopes are attached. The results of these analyses show that both slope designs have factors of safety for sliding and wedge failure greater than the 1.5.

General We appreciate the opportunity to present these services. Please refer to our original Geotechnical and Pavement Report dated February 13, 2020, for more information related to our fieldwork and general limitations of our reports. If you have any questions regarding this addendum, please contact Greg Staffileno at (406) 652-3930.

Project 19-3836G Page 6

Sincerely, Brett M. Warren, PE Senior Geotechnical Engineer

I hereby certify that this report was prepared under my direct Supervision and that I am a duly Licensed Professional Engineer under the laws of the State of Montana.

Gregory T. Staffileno, PE President, Senior Engineer License Number 10798PE August 10, 2023

Attachments:

Slope Stability Analysis (4 sheets) ReSSA+ Internal Stability Analysis 1:1.5 Slope (8 sheets) 1:1.25 Slopes (8 sheets) RSS System Conceptual Detail Drawing

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 48.0

X (ft)

360.0

365.0

370.0

375.0

380.0

385.0

390.0

395.0

Y (ft)

F=500 F=0

FOS=1.62

1.2 1.4 1.6 1.8 2.2 2.4 2.6 2.8

FOS Calculation Method: GLE Search Method: Slope Search

FOS: 1.62

Total Weight: 2.045E+004 (lbf) Total Volume: 1.641E+002 (ft^3) Total Activating Moment: 1.630E+005 (lbfft) Total Resisting Moment: 2.647E+005 (lbfft) Total Activating Force: 5.816E+003 (lbf) Total Resisting Force: 9.442E+003 (lbf) Rotation Center: 16.422, 390.475 (ft) Radius: 25.827 (ft) Slip Surface Entry Point: 37.912, 376.150 (ft) Slip Surface Exit Point: 6.112, 366.796 (ft)

Slope Information NameNameNameName Strength TypeStrength TypeStrength TypeStrength Type Unit WeightUnit WeightUnit WeightUnit Weight

(lbf/ft^3)(lbf/ft^3)(lbf/ft^3)(lbf/ft^3) CohesionCohesionCohesionCohesion (psf)(psf)(psf)(psf)

PhiPhiPhiPhi (deg)(deg)(deg)(deg)

Select Gravel Mohr Coulomb 130.000 0 34 Lean Clay Mohr Coulomb 110.000 0 26 Topsoil Mohr Coulomb 95.000 200 20

Materials

TITLE

Typical 1V:1.5H RSS, 13' Excavation, Long Term Condition

PROJECT

Little Bighorn Battlefield Road

PROJECT No. 19-3836g File No. 1

Author

Date 3/28/2023 FIGURE 1

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 48.0

360.0

365.0

370.0

375.0

380.0

385.0

390.0

395.0

Y (ft)

F=500 F=0

250 lbf/ft² 250 lbf/ft²

FOS=2.22

1.2 1.4 1.6 1.8 2.2 2.4 2.6 2.8

FOS Calculation Method: GLE Search Method: Slope Search

FOS: 2.22

Total Weight: 1.473E+004 (lbf) Total Volume: 1.143E+002 (ft^3) Total Activating Moment: 1.563E+005 (lbfft) Total Resisting Moment: 3.469E+005 (lbfft) Total Activating Force: 5.488E+003 (lbf) Total Resisting Force: 1.218E+004 (lbf) Rotation Center: 17.922, 393.677 (ft) Radius: 26.682 (ft) Slip Surface Entry Point: 38.040, 376.150 (ft) Slip Surface Exit Point: 12.949, 367.463 (ft)

Slope Information NameNameNameName Strength TypeStrength TypeStrength TypeStrength Type Unit WeightUnit WeightUnit WeightUnit Weight

(lbf/ft^3)(lbf/ft^3)(lbf/ft^3)(lbf/ft^3) CohesionCohesionCohesionCohesion (psf)(psf)(psf)(psf)

PhiPhiPhiPhi (deg)(deg)(deg)(deg)

Select Gravel Mohr Coulomb 130.000 0 34 Lean Clay Mohr Coulomb 110.000 600 0 Topsoil Mohr Coulomb 95.000 200 20

Materials

TITLE

Typical 1V:1.5H RSS, 13' Excavation, Short Term Condition

PROJECT

Little Bighorn Battlefield Road

PROJECT No. 19-3836g File No. 1

Date 3/28/2023 FIGURE 2

4.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 48.0

360.0

365.0

370.0

375.0

380.0

385.0

390.0

395.0

Y (ft)

F=500 F=0

FOS=1.52

1.2 1.4 1.6 1.8 2.2 2.4 2.6 2.8

FOS Calculation Method: GLE Search Method: Slope Search

FOS: 1.52

Total Weight: 2.261E+004 (lbf) Total Volume: 1.845E+002 (ft^3) Total Activating Moment: 2.087E+005 (lbfft) Total Resisting Moment: 3.164E+005 (lbfft) Total Activating Force: 6.664E+003 (lbf) Total Resisting Force: 1.010E+004 (lbf) Rotation Center: 14.439, 392.069 (ft) Radius: 28.559 (ft) Slip Surface Entry Point: 38.150, 376.150 (ft) Slip Surface Exit Point: 3.508, 365.685 (ft)

Slope Information NameNameNameName Strength TypeStrength TypeStrength TypeStrength Type Unit WeightUnit WeightUnit WeightUnit Weight

(lbf/ft^3)(lbf/ft^3)(lbf/ft^3)(lbf/ft^3) CohesionCohesionCohesionCohesion (psf)(psf)(psf)(psf)

PhiPhiPhiPhi (deg)(deg)(deg)(deg)

Select Gravel Mohr Coulomb 130.000 0 34 Lean Clay Mohr Coulomb 110.000 0 26 Topsoil Mohr Coulomb 95.000 200 20

Materials

TITLE

Typical 1V:1.25H RSS, 13' Excavation, Long Term Condition

PROJECT

Little Bighorn Battlefield Road

PROJECT No. 19-3836g File No. 1

Date 3/28/2023 FIGURE 3

4.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 48.0

360.0

365.0

370.0

375.0

380.0

385.0

390.0

395.0

Y (ft)

F=500 F=0

250 lbf/ft² 250 lbf/ft²

FOS=2.24

1.2 1.4 1.6 1.8 2.2 2.4 2.6 2.8

FOS Calculation Method: GLE Search Method: Slope Search

FOS: 2.24

Total Weight: 1.595E+004 (lbf) Total Volume: 1.252E+002 (ft^3) Total Activating Moment: 1.021E+005 (lbfft) Total Resisting Moment: 2.288E+005 (lbfft) Total Activating Force: 5.999E+003 (lbf) Total Resisting Force: 1.344E+004 (lbf) Rotation Center: 20.717, 381.822 (ft) Radius: 16.093 (ft) Slip Surface Entry Point: 35.778, 376.150 (ft) Slip Surface Exit Point: 14.029, 367.185 (ft)

Slope Information NameNameNameName Strength TypeStrength TypeStrength TypeStrength Type Unit WeightUnit WeightUnit WeightUnit Weight

(lbf/ft^3)(lbf/ft^3)(lbf/ft^3)(lbf/ft^3) CohesionCohesionCohesionCohesion (psf)(psf)(psf)(psf)

PhiPhiPhiPhi (deg)(deg)(deg)(deg)

Select Gravel Mohr Coulomb 130.000 0 34 Lean Clay Mohr Coulomb 110.000 600 0 Topsoil Mohr Coulomb 95.000 200 20

Materials

TITLE

Typical 1V:1.25H RSS, 13' Excavation, Short Term Condition

PROJECT

Little Bighorn Battlefield Road

PROJECT No. 19-3836g File No. 1

Date 3/28/2023 FIGURE 4

ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+ ReSSA+

ReSSA+ Stability Analysis of Geosynthetic Reinforced Soil Structures Little Bighorn Battlefield, 1:1.5 Slope Present Date/Time: Wed Aug 02 16:16:08 2023 Z:\PROJECTS\2019\3836G Little Big Horn Park Road\Analysis\ReSSA\1.5-1 simplified.MSEp

Little Bighorn Battlefield, 1:1.5 Slope ReSSA+: Update #0.179

PROJECT IDENTIFICATION

Title: Little Bighorn Battlefield, 1:1.5 Slope Project Number: - Client:

Designer: B. Warren

Description:

Company's information:

Name: SK Geotechnical Street: 2511 Holman Ave

Billings, MT 59101 Telephone #:

Fax #:

E-Mail:

File path and name: Z:\PROJECT ..... orn Park Road\Analysis\ReSSA\1.5-1 simplified.MSEp Original date and time of creating this file: Tue Aug 01 16:41:51 2023

PROGRAM MODE: Analysis of a Simplified Slope using GEOSYNTHETIC as reinforcing material.

INPUT DATA (EXCLUDING REINFORCEMENT LAYOUT)

SOIL DATA

=========== Soil Layer #: =========== Unit weight, [lb/ft ³]

Internal angle of friction, [deg.] Cohesion, c

[lb/ft ²]

REINFORCED SOIL

RETAINED SOIL

FOUNDATION SOIL

130.0

110.0

34.0

26.0

0.0

REINFORCEMENT

R e i n f o r c e m e n t

Type # Geosynthetic Designated Name

Ultimate Strength, Tult

Reduction Factor for Installation Damage, RFid

Reduction Factor for Durability, RFd

Reduction Factor for Creep, RFc

Additional Reduction Factor, RFa

Coverage Ratio, Rc

[lb/ft]

1 Geosynthetic type #1 1970.00 1.11 1.10 4.20 1.00 1.00

I n t e r a c t i o n P a r a m e t e r s Type # Geosynthetic

Designated Name

== Direct Sliding == ==== Pullout ==== Cds-phi Cds-c Ci Alpha

1 Geosynthetic type #1 0.80 0.00 0.80 0.80

Relative Orientation of Reinforcement Force, ROR = 0.00. Assigned Factor of Safety to resist pullout, Fs-po = 1.50 Design method for Global Stability: Comprehensive Bishop.

WATER

Water is not present

SEISMICITY

Not Applicable

Little Bighorn Battlefield, 1:1.5 Slope

DRAWING OF SPECIFIED GEOMETRY - SIMPLE

GEOMETRY

.......................................................................Height of slope, H 10.00 [ft] .......................................................................Slope angle, i 33.70 [deg.] .......................................................................Horizontal crest length, A 5.00 [ft] .......................................................................Horizontal crest length, B 0.00 [ft] .......................................................................Backslope angle, 0.00 [deg.] .......................................................................Sloping angle, 0.00 [deg.]

UNIFORM SURCHARGE

.......................................................................Surcharge load over A, Q1 0.00 [lb/ft²] .......................................................................Surcharge load over backslope B, Q2 0.00 [lb/ft²] .......................................................................Surcharge load away from backslope, Q3 0.00 [lb/ft²]

SCALE:

0 5 10 15 20 25 30 [ft]

Little Bighorn Battlefield, 1:1.5 Slope

DISTRIBUTION OF AVAILABLE STRENGTH ALONG EACH REINFORCEMENT LAYER

A = Front-end of reinforcement (at face of slope) B = Rear-end of reinforcement AB = L1 + L2 + L3 = Embedded length of reinforcement

Tavailable = Long-term strength of reinforcement Tfe = Available front-end strength (e.g., connection to facing) Tr-o = Pullout resistance at rear-end

L1 = Front-end 'pullout' length L2 = Rear-end pullout length Tavailable prevails along L3

Factor of safety on resistance to pullout on either end of reinforcement, Fs-po = 1.50

Reinforcement Layer #

Designated Name

Height Relative to Toe [ft]

L [ft]

L1 [ft]

L2 [ft]

L3 [ft]

Tfe [lb/ft]

Tr-o [lb/ft]

Tavailable [lb/ft]

1 Geosynthetic type #1 0.50 13.00 0.00 0.62 12.38 384.15 0.00 384.15 2 Geosynthetic type #1 1.50 13.00 0.00 0.62 12.38 384.15 0.00 384.15 3 Geosynthetic type #1 2.50 13.00 0.00 0.69 12.31 384.15 0.00 384.15 4 Geosynthetic type #1 3.50 13.00 0.00 0.82 12.18 384.15 0.00 384.15 5 Geosynthetic type #1 4.50 13.00 0.00 0.95 12.05 384.15 0.00 384.15 6 Geosynthetic type #1 5.50 13.00 0.00 1.15 11.85 384.15 0.00 384.15 7 Geosynthetic type #1 6.50 13.00 0.00 1.48 11.52 384.15 0.00 384.15 8 Geosynthetic type #1 7.50 13.00 0.00 2.07 10.93 384.15 0.00 384.15 9 Geosynthetic type #1 8.50 13.00 0.00 3.44 9.56 384.15 0.00 384.15

10 Geosynthetic type #1 9.50 13.00 0.00 10.27 2.73 384.15 0.00 384.15

Little Bighorn Battlefield, 1:1.5 Slope

RESULTS OF TRANSLATIONAL ANALYSIS

Results in the table below represent critical two-part wedges identified between specified starting (X1) and ending (X2) search points. Wedges along all reinforcement layers and at elevation zero are reported. The critical two-part wedge, one for each predetermined elevation, is defined by Xa, Xb and Xc where Xa is the front end of the passive wedge (slope face), Xb is where the passive wedge ends and the active one starts, and Xc is the X-ordinate at which the active wedge starts.

Critical two-part wedge along each interface:

Interface Height Relative to Toe [ft]

( Xa, Ya ) [ft]

( Xb, Yb ) [ft]

( Xc, Yc ) [ft]

Fs STATUS

. .At toe elevation 0.00 0.00 0.00 12.80 0.00 29.44 10.00 1.68 Minimum on Edge

Reinf. Layer #1 0.50 0.75 0.50 13.50 0.50 29.95 10.00 1.87 Minimum on Edge Reinf. Layer #2 1.50 2.25 1.50 15.00 1.50 29.72 10.00 2.08 Minimum on Edge Reinf. Layer #3 2.50 3.75 2.50 16.50 2.50 29.49 10.00 2.36 Minimum on Edge Reinf. Layer #4 3.50 5.25 3.50 18.00 3.50 29.26 10.00 2.70 Minimum on Edge Reinf. Layer #5 4.50 6.75 4.50 11.94 4.50 17.84 10.00 2.98 OK Reinf. Layer #6 5.50 8.25 5.50 13.44 5.50 17.79 10.00 3.30 OK Reinf. Layer #7 6.50 9.75 6.50 14.94 6.50 20.76 10.00 3.94 OK Reinf. Layer #8 7.50 11.25 7.50 13.92 7.50 17.12 10.00 4.89 OK Reinf. Layer #9 8.50 12.75 8.50 15.42 8.50 17.21 10.00 7.86 OK Reinf. Layer #10 9.50 0.00 0.00 0.00 0.00 0.00 0.00 N/A No convergence

Note: In the 'Status' column, OK means the critical two part-wedge was identified within the specified search domain. 'Minimum on Edge' means the critical result corresponds to a minimum on the edge of the search domain; i.e., either on X1 or X2 or the internally preset limits on Xc.

Little Bighorn Battlefield, 1:1.5 Slope

RESULTS OF 3-PART WEDGE ANALYSIS

Results in the table below represent the critical slip surface composed of a three-part wedge and identified by the specified points (X-left, Y-left) and (X-right, Y-right) and angles Zeta(L) and Zeta(R). ReSSA finds the (X,Y) coordinates, as well as the angles Zeta, based on user-specified search domain.

The trace of the critical three-part wedge is fully defined by four points: (X1, Y1), (X-left, Y-left), (X-right, Y-right), (X2, Y2).

Critical 3-part wedge (Automatic search):

(X2, Y2) [ft]

Zeta(L) [degrees]

( X-left, Y-left ) [ft]

( X-right, Y-right ) [ft]

Zeta(R) [degrees]

( X1, Y1 ) [ft]

(-10.99, 0.00) 20.00 (0.00, -4.00) (8.75, -3.50) 35.00 (28.03, 10.00) 1.539

Little Bighorn Battlefield, 1:1.5 Slope

SAFETY MAP: SPENCER TRANSLATIONAL, 2-PART WEDGE

Little Bighorn Battlefield, 1:1.5 Slope

SAFETY MAP: SPENCER TRANSLATIONAL, 3-PART WEDGE

Little Bighorn Battlefield, 1:1.5 Slope

ReSSA+ Stability Analysis of Geosynthetic Reinforced Soil Structures Little Bighorn Battlefield,1:1.25 Slope Present Date/Time: Wed Aug 02 16:10:34 2023 Z:\PROJECTS\2019\3836G Little Big Horn Park Road\Analysis\ReSSA\1.25-1 simplified.MSEp

Little Bighorn Battlefield,1:1.25 Slope ReSSA+: Update #0.179

PROJECT IDENTIFICATION

Title: Little Bighorn Battlefield,1:1.25 Slope Project Number: 19-3836G - Client: RPA Designer: B. Warren

Description:

Company's information:

Name: SK Geotechnical Street: 2511 Holman Ave

Billings, MT 59101 Telephone #:

Fax #:

E-Mail:

File path and name: Z:\PROJECT ..... rn Park Road\Analysis\ReSSA\1.25-1 simplified.MSEp Original date and time of creating this file: Tue Aug 01 11:45:51 2023

PROGRAM MODE: Analysis of a Simplified Slope using GEOSYNTHETIC as reinforcing material.

Little Bighorn Battlefield,1:1.25 Slope

INPUT DATA (EXCLUDING REINFORCEMENT LAYOUT)

SOIL DATA

=========== Soil Layer #: =========== Unit weight, [lb/ft ³]

Internal angle of friction, [deg.] Cohesion, c

[lb/ft ²]

REINFORCED SOIL

RETAINED SOIL

FOUNDATION SOIL

130.0

110.0

34.0

26.0

0.0

REINFORCEMENT

R e i n f o r c e m e n t

Type # Geosynthetic Designated Name

Ultimate Strength, Tult

Reduction Factor for Installation Damage, RFid

Reduction Factor for Durability, RFd

Reduction Factor for Creep, RFc

Additional Reduction Factor, RFa

Coverage Ratio, Rc

[lb/ft]

1 Geosynthetic type #1 1970.00 1.11 1.10 4.20 1.00 1.00

I n t e r a c t i o n P a r a m e t e r s Type # Geosynthetic

Designated Name

== Direct Sliding == ==== Pullout ==== Cds-phi Cds-c Ci Alpha

1 Geosynthetic type #1 0.80 0.00 0.80 0.80

Relative Orientation of Reinforcement Force, ROR = 0.00. Assigned Factor of Safety to resist pullout, Fs-po = 1.50 Design method for Global Stability: Comprehensive Bishop.

WATER

Water is not present

SEISMICITY

Not Applicable

Little Bighorn Battlefield,1:1.25 Slope

DRAWING OF SPECIFIED GEOMETRY - SIMPLE

GEOMETRY

.......................................................................Height of slope, H 10.00 [ft] .......................................................................Slope angle, i 38.70 [deg.] .......................................................................Horizontal crest length, A 0.00 [ft] .......................................................................Horizontal crest length, B 0.00 [ft] .......................................................................Backslope angle, 0.00 [deg.] .......................................................................Sloping angle, 0.00 [deg.]

UNIFORM SURCHARGE

SCALE:

0 5 10 15 20 25 30 [ft]

Little Bighorn Battlefield,1:1.25 Slope

DISTRIBUTION OF AVAILABLE STRENGTH ALONG EACH REINFORCEMENT LAYER

A = Front-end of reinforcement (at face of slope) B = Rear-end of reinforcement AB = L1 + L2 + L3 = Embedded length of reinforcement

Tavailable = Long-term strength of reinforcement Tfe = Available front-end strength (e.g., connection to facing) Tr-o = Pullout resistance at rear-end

L1 = Front-end 'pullout' length L2 = Rear-end pullout length Tavailable prevails along L3

Factor of safety on resistance to pullout on either end of reinforcement, Fs-po = 1.50

Reinforcement Layer #

Designated Name

Height Relative to Toe [ft]

L [ft]

L1 [ft]

L2 [ft]

L3 [ft]

Tfe [lb/ft]

Tr-o [lb/ft]

Tavailable [lb/ft]

1 Geosynthetic type #1 0.50 13.00 0.00 0.56 12.44 384.15 0.00 384.15 2 Geosynthetic type #1 1.50 13.00 0.00 0.62 12.38 384.15 0.00 384.15 3 Geosynthetic type #1 2.50 13.00 0.00 0.69 12.31 384.15 0.00 384.15 4 Geosynthetic type #1 3.50 13.00 0.00 0.82 12.18 384.15 0.00 384.15 5 Geosynthetic type #1 4.50 13.00 0.00 0.95 12.05 384.15 0.00 384.15 6 Geosynthetic type #1 5.50 13.00 0.00 1.15 11.85 384.15 0.00 384.15 7 Geosynthetic type #1 6.50 13.00 0.00 1.48 11.52 384.15 0.00 384.15 8 Geosynthetic type #1 7.50 13.00 0.00 2.07 10.93 384.15 0.00 384.15 9 Geosynthetic type #1 8.50 13.00 0.00 3.44 9.56 384.15 0.00 384.15

10 Geosynthetic type #1 9.50 13.00 0.00 10.27 2.73 384.15 0.00 384.15

Little Bighorn Battlefield,1:1.25 Slope

RESULTS OF TRANSLATIONAL ANALYSIS

Critical two-part wedge along each interface:

Interface Height Relative to Toe [ft]

( Xa, Ya ) [ft]

( Xb, Yb ) [ft]

( Xc, Yc ) [ft]

Fs STATUS

. .At toe elevation 0.00 0.00 0.00 12.80 0.00 28.80 10.00 1.73 Minimum on Edge

Reinf. Layer #1 0.50 0.62 0.50 13.40 0.50 27.48 10.00 1.97 Minimum on Edge Reinf. Layer #2 1.50 1.87 1.50 14.70 1.50 26.84 10.00 2.18 Minimum on Edge Reinf. Layer #3 2.50 3.12 2.50 8.34 2.50 17.60 10.00 2.42 OK Reinf. Layer #4 3.50 4.37 3.50 9.64 3.50 17.67 10.00 2.51 OK Reinf. Layer #5 4.50 5.62 4.50 10.84 4.50 16.95 10.00 2.84 OK Reinf. Layer #6 5.50 6.87 5.50 12.14 5.50 16.49 10.00 3.25 OK Reinf. Layer #7 6.50 8.11 6.50 10.82 6.50 16.01 10.00 3.78 OK Reinf. Layer #8 7.50 9.36 7.50 12.12 7.50 14.90 10.00 4.63 OK Reinf. Layer #9 8.50 10.61 8.50 13.32 8.50 15.17 10.00 7.95 OK Reinf. Layer #10 9.50 0.00 0.00 0.00 0.00 0.00 0.00 N/A No convergence

Little Bighorn Battlefield,1:1.25 Slope

RESULTS OF 3-PART WEDGE ANALYSIS

The trace of the critical three-part wedge is fully defined by four points: (X1, Y1), (X-left, Y-left), (X-right, Y-right), (X2, Y2).

Critical 3-part wedge (Automatic search):

(X2, Y2) [ft]

Zeta(L) [degrees]

( X-left, Y-left ) [ft]

( X-right, Y-right ) [ft]

Zeta(R) [degrees]

( X1, Y1 ) [ft]

(-10.99, 0.00) 20.00 (0.00, -4.00) (8.75, -3.50) 35.00 (28.03, 10.00) 1.535

Little Bighorn Battlefield,1:1.25 Slope

SAFETY MAP: SPENCER TRANSLATIONAL, 2-PART WEDGE

Little Bighorn Battlefield,1:1.25 Slope

SAFETY MAP: SPENCER TRANSLATIONAL, 3-PART WEDGE

Little Bighorn Battlefield,1:1.25 Slope

RSS Structure, Conceptual Detail Drawing Revised Addendum #1

Geotechnical and Pavement Reconnaissance Little Bighorn Park Road

MT PRA LIBI 10(2)

Drawn by: Google/SK Geo Dat e 07/11/23

Project: 19-3836G

Scale: See Photo FIGURE

Sheet 1 of 4 3

Global Slope Stability Analysis

Reinforced Slope Recommendations.

Revised Analysis Attachments.pdf

1.5 long term

1.5 short term

1.25 long term

1.25 short term

1.5-1 simplified long term

1.25-1 simplified long term

File details come from the government source that posted it. Updated Sep 19, 2024.