GR_3-18,_mt08601_Geotechnical_Report_Addendum_1.pdf

December 21, 2017 Project 14-3246G

Mr. Brad Thompson, PE Robert Peccia & Associates P. O. Box 5653 Helena, Montana 59604-5653 Via Email: bthompson@rpa-hln.com

Dear Mr. Thompson:

Re: Geotechnical Report Addendum 1, Gilliland Parcel Slope Stability, Bozeman to Bridger

Mountains Trail, MT DOT86(1), Northeast of Bozeman, Montana, IDIQ Contract No. DTFH70- 10-D-00016, Task Order No. T-14-009

Addendum 1 to the geotechnical report for the above-referenced project has been completed. This work was performed in accordance with our Supplement Agreement #3 to Task Order T-14-009, dated June 23, 2015.

Introduction

Project Description. The purpose of the project is to improve, connect, and construct a new bicycle/pedestrian trail from Story Mill Road to the "M" parking lot. This addendum addresses the global stability of steep slopes and retaining walls required between Stations 1566+00 to 1587+75 as the trail passes south of the Gilliland Parcel. In this area, additional right-of-way could not be purchased and the trail will need to be constructed within the existing highway right-of-way, requiring the use of retaining walls along the existing steep cut slopes.

While performing the original fieldwork for this project, soil borings between Station 1566+00 to Station 1587+75 could not be performed due to landowner access. Therefore, we proposed to perform test pits in lieu of soil borings to evaluate the soils along this parcel.

Scope of Services. The scope of services for this addendum is included in Supplement Agreement #3 dated September 19, 2017. The scope of services included performing four test pits within the existing highway right-of-way, laboratory testing of samples obtained from the test pits (including triaxial shear tests) and performing global slope stability analysis of proposed retaining walls along the steep slopes as well as reinforced slopes.

Test Pit Results

Test Pit Procedures and Equipment. The test pits were performed on October 11, 2017. The Log of Test Pit sheets are attached to this report and the locations are shown on the attached plan and profile sheet. The test pits were excavated using a Caterpillar 316E excavator. The test pits were performed by extending the excavator bucket as high up the slope as possible and excavating down into the slope until the excavator's lower limit was reached. In Test Pits TP-3 and TP-4, where the existing cut slopes was taller, a small equipment pad was constructed to raise the excavator's height approximately 3 to 4 feet.

This allowed the test pit excavation to start 3 to 4 feet higher up the slope.

2511 Holman Avenue P. O. Box 80190

Billings, Montana 59108-0190 p: 406.652.3930; f: 406.652.3944 www.skgeotechnical.com eric.lim Text Box WFLHD Geotechnical Report No. GR 3-18

Robert Peccia & Associates December 21, 2017 Project 14-3246G Page 2

As the test pit excavation advanced, the soils within the test pit sidewalls were visually classified and logged in the field in accordance with American Society for Testing and Materials (ASTM) Method of Test D 2488, "Standard Practice for Description and Identification of Soils (Visual – Manual Procedures)." The soils were classified and logged from inside the test pit while it was safe to do so and were then classified and logged from the ground surface after the excavation reached an unsafe depth.

Bulk bag samples and thin-walled tube samples were taken for laboratory testing. The thin-walled tube samples were taken by slowly pushing the thin-walled tube into the ground using the excavator bucket, then digging them out.

We also performed dynamic cone penetrometer tests on the excavation bottom (as the excavation advanced) to evaluate strength. The dynamic cone penetrometer developed by our firm 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.

The ground surface elevation at the top of the test pit was estimated using the ground surface elevations shown on the preliminary conceptual cross sections provided by RPA, and dated March 24, 2017.

After completing a test pit, the test pit was then backfilled and compacted using the excavator bucket.

The drainage ditch at the slope toe was then regraded to allow for proper drainage. After the test pits were backfilled and compacted, the disturbed ground surface and drainage ditch bottom were then covered with a biodegradable erosion control fabric and reseeded.

Soils. Log of Test Pit sheets indicating the depth and identification of the various soil strata, penetration resistances, laboratory testing, and water level information are attached to this report. Photographs of each test pit location are also included. It should be noted, the depths shown as boundaries between the strata are only approximate. The actual changes vary between test pits, especially when considering the complex geologic setting of the area.

As can be seen on the attached logs, the general soil profile consists of fine-grained alluvial soils consisting of lean clay, sandy lean clay, and fat clay underlain by coarse-grained alluvial soils consisting of poorly graded gravel with sand, silty gravel with sand, and clayey gravel with sand. The exception to this general soil profile is Test Pit TP-1, which did not encounter fine-grained alluvial soils, rather, poorly graded gravel alluvium was logged.

The fine-grained alluvial soils were generally medium to very stiff while the coarse-grained alluvial soils ranged from medium dense to dense.

Groundwater was not encountered in the test pits. Seepage was also not observed in the test pit sidewalls.

Laboratory Testing. After the test pits were performed, the samples were returned to our office for laboratory testing. These tests included Atterberg limits, percent-finer-than-a-200-sieve, moisture content, sieve analysis, and triaxial shear tests. The results of the moisture content and classification tests can be found on the attached Log of Test Pits sheets and the results of the triaxial shear tests can be seen in Table 1 below, and are attached to this Addendum. The triaxial shear tests were performed on intact, relatively undisturbed, thin-walled tube samples. Laboratory test results from previous Boring ST-8 are included in the table, as well.

Project 14-3246G Page 3

Table 1. Triaxial Shear Test Results

Location Depth (feet)

ASTM

Class

Total Stress Effective Stress

Friction Angle (deg)

Cohesion (psf)

Friction Angle (deg)

Cohesion (psf)

TP-3 13 to 14 CL 25.2 660 28.9 633

TP-4 7 to 8 CL 21.1 158 22.6 155

ST-8 10½ to 11½ CL 22.4 1,847 25.9 2,061

Analysis and Recommendations

Discussion. The preliminary Gilliland Parcel cross sections show slopes steeper than 1:1.5 (V:H) would be required to construct the proposed trail between the edge of the existing pavement and the existing right-of-way. The required slopes shown on the preliminary cross sections are summarized below:

Table 2. Summary of Preliminary Required Slopes

Station Required Trail Side Slope

1566+00 to 1573+75 1:2 Fill Slope

1573+75 to 1579+75 1:1.5 Fill Slope

1579+75 to 1581+75 1:1.25 Fill Slope

1581+75 to 1583+25 1:1.5 Fill Slope

1583+25 to 1584+00 1:1.25 Fill Slope

1584+00 to 1587+25 Retaining Wall

1587+25 to 1588+25 1:1.5 Cut Slope

1588+25 to 1589+75 1:1.5 Fill Slope

During initial discussions with the design team, it was decided the use of soil nails or other tied-back elements would not be feasible because the nails/tiebacks would extend past the existing right-of-way, and obtaining temporary construction easements did not appear possible. This makes construction of any type of up-hill, cut slope retaining wall practically not possible due to the very steep temporary slope that would be required to stay within the existing right-of-way. Even the use of down-hill, fill slope retaining walls will require a steep temporary excavation.

Therefore, our analysis of the retaining wall cross sections centered on using a down-hill, fill slope wall.

We analyzed a mechanically stabilized earth (MSE) wall, a gravity block wall, and a soldier pile and lagging wall. The global factors of safety (FOS) for each of these walls are shown in Table 4. We also analyzed cross sections for 1:1.5 and 1:1.25 fill slopes, and a 1:1.5 cut slope. The results of these analyses are discussed later in this report.

Project 14-3246G Page 4

Soil Conditions and Strength Parameters. As discussed above, the general soil profile consists of medium to low plasticity lean clay underlain by poorly graded gravel with sand. Two triaxial shear tests were performed on the sandy lean clay from Test Pits TP-3 and TP-4, along with the triaxial shear test performed on a sample from previous Boring ST-8.

As can be seen in Table 1 above, the friction angles measured in the clay alluvium ranged from 21.1 to

25.2 degrees and the total stress cohesion ranged from 158 to 1,847 pounds per square foot (psf). As discussed in our final geotechnical report, the cohesion obtained from the test at Boring ST-8 is considerably outside typically published values for soils of this type. The triaxial shear test for the soil sample obtained from Test Pit TP-4 very nearly matched the soil parameters we assumed for the clay in our final geotechnical report. However, based on the results of the test pits, dynamic cone penetrometers, pocket penetrometers, and triaxial shear test result from Test Pit TP-3, it is our opinion a slightly higher value for cohesion and friction angle can be justified for design.

In our analysis, we used the soil strength parameters shown in Tables 3 and 4 below.

Table 3. Summary of Drained Soil Strengths Used for Design

Soil Type Moist Unit Weight

(psf) Cohesion

(psf) Friction Angle

(deg)

Lean Clay (above road) 115 200 25

Sandy Lean Clay (below road) 105 150 25

Native Gravel 135 0 34

Retained Soil 135 0 34

Imported Structural Gravel 135 0 38

Table 4. Summary of Undrained Soil Strengths Used for Design

Soil Type Moist Unit Weight

(psf) Cohesion

(psf) Friction Angle

(deg)

Lean Clay (above road) 115 600 0

Sandy Lean Clay (below road) 105 400 0

Native Gravel 135 0 34

Retained Soil 135 0 34

Structural Gravel 135 0 38

Analysis. The slope stability analysis was performed using the computer program SVSlope® developed by SoilVision Systems Ltd. The analysis was performed for the long-term case using drained effective stress parameters. For the analysis for seismic conditions and the construction cross section, we used short-term drained total stress parameters. The results of our slope stability analyses are attached and summarized in Table 5 below.

Project 14-3246G Page 5

Table 5. Summary of Slope Stability Analyses

Case Station

Calculated Factor of Safety

Long-Term Drained

Short-Term Undrained-

Seismic

Mechanically Stabilized Earth Wall 1586+00 1.40 1.15

Gravity Block Wall 1586+00 1.38 1.15

Soldier Pile and Lagging Wall 1586+00 2.85 2.00

Wall Construction Slope 1586+00 1.29 n/a

1:1.5 Unreinforced Fill Slope 1578+00 1.19 n/a

1:1.5 Reinforced Fill Slope 1578+25 1.46 1.13

1:1.25 Reinforced Fill Slope 1581+25 1.54 1.17

1:1.5 Cut Slope 1587+50 1.46 1.30

Factor of Safety Selection. Selection of the required FOS is critical to the design of the retaining wall.

The Montana Department of Transportation (MDT) Geotechnical Manual, Section 17.3.5, Figure 17.3-C, shows the global FOS for cut and fill retaining walls should be 1.5 or greater. Section 15.4.2 indicates cut slopes in clay should have a minimum FOS of 1.5, and all other slopes should have a long-term FOS of 1.3, and FOS of 1.1 for seismic conditions.

The Federal Highways Project Development and Design Manual, Section 6.4.4, indicates global stability analysis should be performed for earth retention systems, but gives no specific FOS for circular global stability analyses. 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. Generally speaking, a resistance factor of 0.75 is equal to a FOS of 1.3.

MSE and Gravity Block Retaining Walls. As shown in Table 4 above, the MSE wall and gravity block wall options have very similar FOS of approximately 1.4. The MSE wall has a base-to-height ratio of about 1, while the gravity block wall has a ratio of about 0.7. MSE and gravity block walls with larger base-to-height ratios would likely result in a higher long-term FOS greater than 1.5. However, these wider walls cannot be constructed without cutting further into the hillside, and our analysis indicates the construction FOS is already less than 1.3.

It is our opinion these two options are generally equivalent, and if a 1.4 FOS is deemed acceptable, the less expensive of these two options should be selected. A gravity block wall will likely be the least expensive option given the space and time constraints of the site. We recommend the walls be designed by the contractor by including a performance based specification.

An important component of the MSE wall and gravity block wall is the elevation of the bottom of the wall. If the trail and wall is constructed relatively high on the slope, then clay soils left beneath the wall could fail. Our analysis indicates the base of the wall needs to be supported in the coarse-grained gravel alluvium, which will require the wall and trail generally be moved down the face of the slope. The

Project 14-3246G Page 6 approximate elevation of the top of the gravel has been plotted on the attached profile portion of the plan and profile sheet.

Additionally, relatively steep construction slopes will be required for both the retaining walls and reinforced slopes. We recommend the horizontal extent of slope excavation be limited to that amount which can be constructed and backfilled in a period of three days, or less. This is a critical component to help avoid the risk of adverse impacts to the Gilliland Parcel and highway.

Soldier Pile and Lagging Retaining Wall. If a FOS of 1.5 is required for the retaining wall, our analysis indicates a soldier pile and lagging wall will be able to provide a FOS of at least 1.5. The soldier pile and lagging wall will need to be designed by a structural engineer. However, we did perform preliminary shoring design calculation to determine if a soldier pile and lagging wall can be constructed using reasonable pile types and spacings. These calculations indicate a soldier pile and lagging wall consisting of HP 12x53 pile spaced on 6-foot centers will be possible.

1:1.5 to 1:1.25 Embankments. We performed additional slope stability for 1:1.5 and 1:1.25 slopes constructed of imported gravel soils. As can be seen in Table 5 above, constructing the trail with a 1:1.5 slope results in a FOS of 1.19, which is below the recommended minimum of 1.3. Due to the geometry constrictions of the area, flattening the slope will not be possible. Therefore, we recommend all fill slopes steeper than 1:1.5 be constructed as geosynthetic reinforced slopes. Our analysis indicates geosynthetic reinforced slopes will have a FOS greater than 1.3.

Our analysis indicates that for 1:1.5 fill slopes, three layers of biaxial geogrid (Tensar BX 1200 or exact equivalent) placed on 1.5-foot vertical intervals will be required to provide a FOS greater than 1.3. For 1:1.25 slopes, our analysis indicates the entire fill slope will need to be reinforced with biaxial geogrid placed on 2-foot vertical intervals.

Seismic Stability. Each cross section was also analyzed under undrained seismic conditions. The 2009 AASHTO Guide Specifications for LRFD Seismic Bridge Design manual indicates a peak ground acceleration (PGA) of 0.285g for Site Class D. This corresponds to a return period of 1,000 years. As shown in Table 5, all alternatives analyzed have a FOS in excess of the recommended minimum of 1.1.

Conclusions. Based on the results of our analyses, we recommend the following design guidelines shown in Table 6 for slope and wall configurations.

Table 6. Summary of Recommended Slope Guidelines

Slope Recommendation

1:1.5 Geogrid reinforcement, place minimum 3 layers of 12-foot wide geogrid at 18" vertical spacing, corresponding depths of 18", 36", and 54" below trail surface.

1:1.25 Geogrid reinforcement full height of fill slope, using 10-foot wide geogrid, at 24-inch vertical spacing.

Steeper than 1:1.25

Use Retaining Wall

MSE or block wall if FOS of 1.3 acceptable.

Soldier pile and lagging wall if FOS is 1.5 is required.

Project 14-3246G Page 7

General Recommendations

Basis of Recommendations. The analyses and recommendations submitted in this report are based upon the data obtained from the test pits performed at the locations indicated. Often, variations occur between these test pits, the nature and extent of which do not become evident until additional exploration or construction is conducted. A reevaluation of the recommendations in this report should be made after performing on-site observations during construction to note the characteristics of any variations. The variations may result in additional foundation costs, and it is suggested a contingency be provided for this purpose.

It is recommended we be retained to perform the observation and testing program for the site preparation phase of this project. This will allow correlation of the soil conditions encountered during construction to the soil borings, and will provide continuity of professional responsibility.

Review of Design. This report is based on the design of the proposed roadways and structures as related to us for preparation of this report. It is recommended we be retained to review the geotechnical 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.

Groundwater Fluctuations. We made water level observations in the test pits at the times and under the conditions stated on the 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.

Use of Report. This report is for the exclusive use of Robert Peccia & Associates and the FHWA to use to design the proposed roadways and structures 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.

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.

0.5

18.0

4847.5

4830.0

50-6" 50-4"

Elevation Reference:

Contour lines on plans and cross sections.

Max cobbles size 6" to 8", Typical Cobbles Size 3" to 5"

MC=7.8%

ORGANIC LEAN CLAY, low plasticity, with roots, black, moist. (Topsoil and Root Zone) POORLY GRADED GRAVEL with SILT and SAND, fine- to coarse-grained, trace cobbles, brown, moist, medium dense to dense. (Alluvium)

BOTTOM OF TEST PIT

Water not observed in test pit.

OL

GP

GM

4848.0

LOGGED BY: B. Warren

TEST PIT:

WLB

PROJECT:

Depth

TP-1

10/11/17 1" = 4'

RemarksSymbol

14-3246G

DATE: SCALE:

LOG OF TEST PIT

qpElev.

See attached sketch.

14-3246G

GEOTECHNICAL EVALUATION

Bozeman to Bridger Mountains Trail

MT DOT 86(1)

NE of Bozeman, Montana

METHOD: Backhoe

0.0

LOCATION:

TP-1 page 1 of 1

Description of Materials

2511 Holman Avenue P. O. Box 80190

Billings, MT 59108-0190 Phone: 406.652.3930

Fax: 406.652.3944

T E

S T

P

IT

B W

L Q

P

6-

T P

.G P

J L

A G

N N

N

.G D

T

1/

/1

1.0

5.0

6.0

10.0

11.0

16.0

20.0

22.0

4859.0

4855.0

4854.0

4850.0

4849.0

4844.0

4840.0

4838.0

4+

4+

3½

4+

3½

50-5"

LL=38, PL=19, PI=19

P200=87.8%

MC=13.4%

MC=16.9%

MC=8.7%

MC=22.4%

LL=32, PL=16, PI=16

P200=39.7%

MC=9.5%

*qp=pocket penetrometer estimate of unconfined compressive strength, tons per square foot.

ORGANIC LEAN CLAY, low plasticity, with roots, trace cobbles, dark brown, moist. (Topsoil and Root Zone) SANDY LEAN CLAY, medium plasticity, with salts, trace pinholes, light brown, rather dry.

(Alluvium)

LEAN CLAY with SAND, trace large cobbles, brown, moist. (Alluvium) SANDY LEAN CLAY with GRAVEL, low plasticity, trace salt, rust, and cobbles, light brown to reddish brown, rather dry to moist, very stiff to hard.

(Alluvium)

POORLY GRADED GRAVEL with SAND, fine-to coarse-grained, possible coal, dark brown to black, rather dry. (Alluvium) SILTY GRAVEL with SAND, fine- to coarse-grained, light brown, rather dry to moist, medium dense to dense. (Alluvium)

LEAN CLAY, low to medium plasticity, trace rust, light brown, moist to wet. (Alluvium)

CLAYEY GRAVEL with SAND, fine- to coarse-grained, brown, moist to wet. (Alluvium)

BOTTOM OF TEST PIT

Water not observed in test pit.

OL

CL

CL

CL

GP

GM

CL

GC

PROJECT:

Depth

TP-2

10/11/17 1" = 4'

RemarksSymbol

14-3246G

DATE: SCALE:

LOG OF TEST PIT

Elev.

See attached sketch.

14-3246G

GEOTECHNICAL EVALUATION

Bozeman to Bridger Mountains Trail

MT DOT 86(1)

NE of Bozeman, Montana

METHOD: Backhoe

0.0

LOCATION:

TP-2 page 1 of 1

Description of Materials 4860.0

LOGGED BY: B. Warren

TEST PIT:

WLB qp*

2511 Holman Avenue P. O. Box 80190

Billings, MT 59108-0190 Phone: 406.652.3930

Fax: 406.652.3944

T E

S T

P

IT

B W

L Q

P

-T

P .G

P J

L A

G N

N N

.G

D T

1/

2.0

11.0

14.0

16.0

28.0

4880.0

4871.0

4868.0

4866.0

4854.0

4+

2½

TW

50-4"

LL=39, PL=18, PI=21

P200=76.6%

MC=26.3%

See triaxial shear test.

LL=38, PL=23, PI=15

P200=90.0%

MC=34.2%

MC=33.7%

MC=16.8%

Likely on cobble.

LL=28, PL=20, PI=8

P200=40.8%

MC=13.4%

5" topsoil and root zone over FAT CLAY, high plasticity, trace roots, brown, rather dry. (Alluvium)

LEAN CLAY, low to medium plasticity, trace salts and boulders, light brown, rather dry to moist.

(Alluvium)

-trace gravel lenses

CLAYEY GRAVEL with SAND, fine- to coarse-grained, low plasticity, trace boulders, brown, rather dry to moist. (Alluvium)

SILTY CLAY, low plasticity, light brown to white, moist. (Alluvium)

CLAYEY GRAVEL with SAND, fine- to coarse-grained, trace cobbles and boulders, brown, moist, medium dense. (Alluvium)

BOTTOM OF TEST PIT

Water not observed in test pit.

CH

CL

GC

CL

ML

GC

4882.0

LOGGED BY: B. Warren

TEST PIT:

WLB

PROJECT:

Depth

TP-3

10/11/17 1" = 4'

RemarksSymbol

14-3246G

DATE: SCALE:

LOG OF TEST PIT

qpElev.

See attached sketch.

14-3246G

GEOTECHNICAL EVALUATION

Bozeman to Bridger Mountains Trail

MT DOT 86(1)

NE of Bozeman, Montana

METHOD: Backhoe

0.0

LOCATION:

TP-3 page 1 of 1

Description of Materials

2511 Holman Avenue P. O. Box 80190

Billings, MT 59108-0190 Phone: 406.652.3930

Fax: 406.652.3944

T E

S T

P

IT

B W

L Q

P

6-

T P

.G P

J L

A G

N N

N

.G D

T

1/

14.0

28.0

4874.0

4860.0

4+

TW

50-6"

See triaxial shear test.

LL=41, PL=18, PI=23

P200=87.7%

MC=24.3%

MC=31.3%

MC=6.1%

LEAN CLAY, low to medium plasticity, trace salt, light brown, rather dry to moist, medium to very stiff. (Alluvium)

-trace gravel

POORLY GRADED GRAVEL with SAND, fine-to coarse-grained, trace cobbles and boulders, brown, moist, dense to very dense. (Alluvium)

BOTTOM OF TEST PIT

Water not observed in test pit.

CL

GP

4888.0

LOGGED BY: B. Warren

TEST PIT:

WLB

PROJECT:

Depth

TP-4

10/11/17 1" = 4'

RemarksSymbol

14-3246G

DATE: SCALE:

LOG OF TEST PIT

qpElev.

See attached sketch.

14-3246G

GEOTECHNICAL EVALUATION

Bozeman to Bridger Mountains Trail

MT DOT 86(1)

NE of Bozeman, Montana

METHOD: Backhoe

0.0

LOCATION:

TP-4 page 1 of 1

Description of Materials

2511 Holman Avenue P. O. Box 80190

Billings, MT 59108-0190 Phone: 406.652.3930

Fax: 406.652.3944

T E

S T

P

IT

B W

L Q

P

6-

T P

.G P

J L

A G

N N

N

.G D

T

1/

Test Pit TP-1, Exterior Test Pit TP-1, Interior

Test Pit TP-2, Exterior Test Pit TP-2, Interior

Test Pit TP-3, Exterior Test Pit TP-3, Interior

Test Pit TP-4, Exterior Test Pit TP-4, Interior

Test Pit TP-1, Covered and Seeded Test Pit TP-2, Covered and Seeded

Test Pit TP-3, Covered and Seeded Test Pit TP-4, Covered and Seeded

Total: φ = 25.2°, C = 0.660 ksf Effective: φ' = 28.9°, C' = 0.633 ksf

Sample Number 1 2 3

Water Content, % 34.2 34.2 34.2

Dry Density, pcf 81.8 81.8 81.8

Saturation, % 90.5 90.5 90.5

Void Ratio 0.982 0.982 0.982

Diameter, in. 2.860 2.860 2.860

Height, in. 4.888 4.888 4.888

Water Content, % 37.5 37.2 36.7

Dry Density, pcf 82.2 82.5 83.1

Saturation, % 100.0 100.0 100.0

Void Ratio 0.975 0.967 0.953

Diameter, in. 2.849 2.838 2.818

Height, in. 4.870 4.851 4.817

Strain Rate, in/min 0.004 0.004 0.004

Back Pressure, psi 0.50 1.00 2.00

Cell Pressure, psi 10.50 21.00 42.00

Pore Pressure @ Fail, ksf 0.32 0.58 1.30

Deviator Stress, ksf 4.24 6.38 10.57 σ'1 Effective Failure, ksf 5.36 8.69 15.04 σ'3 Effective Failure, ksf 1.12 2.30 4.46

TRIAXIAL COMPRESSION Client: Robert Peccia & Associates

ASTM D4767, CU with Pore Pressures Project: Bozeman to Bridger Mtns Trail, MT DOT86(1)

Description: Geotechnical Evaluation

Project: 14-3246G Laboratory Testing Sample: TP-3 Depth: 14-15 '

Bozeman to Bridger Mtns Trail Received: 10/13/17 by: JD/SK

Bozeman, Montana Type: Shelby Thinwall

Description:

P. O. Box 80190

Billings, MT 59108-0190

Phone: 406.652.3930 Remarks:

Fax: 406.652.3944 Figure ______

A t

Te st

In it ia l

Silty Clay, low plasticity, light brown to white, moist.

0 2 4 6 8 10 12 14 16 18 20

Sh ea r St re ss ks f

Total Normal Stress, ksf ________ Effective Normal Stress, ksf _ _ _ _ _

0 2 4 6 8 10

D ev ia to r St re ss ks f

Axial Strain, % mm

Total: α = 23.1°, a = 0.598 ksf Effective: α' = 25.8°, a' = 0.554 ksf Skempton's Af = 0.08

TRIAXIAL COMPRESSION Client: Robert Peccia & Associates

ASTM D4767, CU with Pore Pressures Project: Bozeman to Bridger Mtns Trail, MT DOT86(1)

Description: Geotechnical Evaluation

Project: 14-3246G Laboratory Testing Sample: TP-3 Depth: 14-15 '

Bozeman to Bridger Mtns Trail Sampled: 10/13/17 by: JD/SK

Bozeman, Montana Type: Shelby Thinwall

Description:

P. O. Box 80190

Billings, MT 59108-0190

Phone: 406.652.3930 Remarks:

Fax: 406.652.3944 Figure ______

Silty Clay, low plasticity, light brown to white, moist.

0 2 4 6 8 10

To ta l P o re P re ss u re

, k sf

D ev ia to r

St re ss ks f

0 2 4 6 8 10

Axial Strain, %

0 2 4 6 8 10

Axial Strain, %

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 q , k sf p, ksf Stress Paths: Total ________ Effective _ _ _ _ _

Total: φ = 21.1°, C = 0.158 ksf Effective: φ' = 22.6°, C' = 0.155 ksf

Sample Number 1 2 3

Water Content, % 32.4 32.4 32.4

Dry Density, pcf 84.2 84.2 84.2

Saturation, % 90.9 90.9 90.9

Void Ratio 0.927 0.927 0.927

Diameter, in. 2.861 2.861 2.861

Height, in. 5.563 5.563 5.563

Water Content, % 30.5 32.9 33.3

Dry Density, pcf 90.5 87.5 86.9

Saturation, % 100.0 100.0 100.0

Void Ratio 0.794 0.855 0.867

Diameter, in. 2.664 2.755 2.772

Height, in. 5.179 5.357 5.390

Strain Rate, in/min 0.004 0.004 0.004

Back Pressure, psi 0.50 1.00 2.00

Cell Pressure, psi 10.50 21.00 42.00

Pore Pressure @ Fail, ksf 0.14 0.29 0.58

Deviator Stress, ksf 2.15 3.72 6.85 σ'1 Effective Failure, ksf 3.44 6.31 12.04 σ'3 Effective Failure, ksf 1.30 2.59 5.18

TRIAXIAL COMPRESSION Client: Robert Peccia & Associates

ASTM D4767, CU with Pore Pressures Project: Bozeman to Bridger Mtns Trail, MT DOT86(1)

Description: Geotechnical Evaluation

Project: 14-3246G Laboratory Testing Sample: TP-4 Depth: 7' -8'

Bozeman to Bridger Mtns Trail Received: 10/13/17 by: JD/SK

Bozeman, Montana Type: Shelby Thinwall

Description:

P. O. Box 80190

Billings, MT 59108-0190

Phone: 406.652.3930 Remarks:

Fax: 406.652.3944 Figure ______

A t

Te st

In it ia l

Lean Clay, low to medium plasticity, trace salt, light brown, rather dry to moist.

0 2 4 6 8 10 12 14 16 18 20

Sh ea r St re ss ks f

Total Normal Stress, ksf ________ Effective Normal Stress, ksf _ _ _ _ _

0 2 4 6 8 10

D ev ia to r St re ss ks f mm

Total: α = 19.8°, a = 0.147 ksf Effective: α' = 21.0°, a' = 0.143 ksf Skempton's Af = 0.04

TRIAXIAL COMPRESSION Client: Robert Peccia & Associates

ASTM D4767, CU with Pore Pressures Project: Bozeman to Bridger Mtns Trail, MT DOT86(1)

Description: Geotechnical Evaluation

Project: 14-3246G Laboratory Testing Sample: TP-4 Depth: 7' -8'

Bozeman to Bridger Mtns Trail Sampled: 10/13/17 by: JD/SK

Bozeman, Montana Type: Shelby Thinwall

Description:

P. O. Box 80190

Billings, MT 59108-0190

Phone: 406.652.3930 Remarks:

Fax: 406.652.3944 Figure ______

Lean Clay, low to medium plasticity, trace salt, light brown, rather dry to moist.

0 2 4 6 8 10

To ta l P o re P re ss u re

, k sf

D ev ia to r

St re ss ks f

0 2 4 6 8 10

Axial Strain, %

0 2 4 6 8 10

Axial Strain, %

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 q , k sf p, ksf Stress Paths: Total ________ Effective _ _ _ _ _

Brett Callout Existing R/W