GR_9-16_mt08601,_Geotechnical_Report.pdf

GEOTECHNICAL REPORT

Bozeman to Bridger Mountains Trail

MT DOT86(1)

Northeast of Bozeman, Montana IDIQ Contract No. DTFH70-10-D-00016

Task Order T-14-009 Project 14-3246G

Submitted by

2511 Holman Avenue P. O. Box 80190

Billings, Montana 59108-0910

Prepared for

Robert Peccia & Associates P. O. Box 5653

Helena, Montana 59604-5653

January 18, 2016 eric.lim Text Box WFLHD Geotechnical Report No. GR 9-16

January 18, 2016 Project 14-3246G

Mr. Brian Wacker, PE Robert Peccia & Associates P. O. Box 5653 Helena, Montana 59604-5653 Via Email: brian@rpa-hln.com

Dear Mr. Wacker:

Re: Geotechnical Report, 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

The geotechnical report for the above-referenced project has been completed. This work was performed in accordance with our Supplemental Agreement No. 2 to Task Order T-14-009 dated June 23, 2015.

Introduction

Project Description The anticipated project is to improve, connect, and construct a new bicycle/pedestrian trail from Story Mill Road to the "M" parking lot. The project begins at the intersection of Story Mill and Highway MT 86, Station 1500+00, with the trail on the south side of MT 86 heading to the east. The trail will basically travel through a relatively shallow roadside ditch up to about Station 1506+00, where an existing gravel surfaced trail is situated south of MT 86. The proposed trail will follow this existing gravel trail up to Station 1533+00, then extend along the south side of MT 86 up to about Station 1544+50. At this point, the proposed trail will cross MT 86 and follow an existing paved trail located on the north side of MT 86 up to Station 1557+00. From this point to the end of the project, the proposed trail will be situated on the north side of MT 86 adjacent to the existing rolling terrain and associated MT 86 hillside cuts needed to build the original highway. A new pedestrian bridge will likely be necessary to cross Bridger Creek near Station 1562+37. The project ends at the "M" trailhead parking lot at Station 1620+50. The project also includes a pedestrian underpass connecting the path on the north side of Highway 86 to a parking lot on the south side of Highway 86 at Station 1613+00.

Scope of Services and Background Robert Peccia & Associates (RPA) was selected by the Federal Highway Administration (FHWA) to assist in the development of this project. SK Geotechnical was added to the team to evaluate geotechnical components of the project.

A preliminary field reconnaissance by SK Geotechnical was performed on August 18, 2014. The initial fieldwork was limited to a visual geotechnical and geological assessment of the project area, but no subsurface investigation or testing was performed at that time. After completing the fieldwork, a Geotechnical Reconnaissance Memorandum dated November 19, 2014, was prepared and included preliminary recommendations for cut and fill slopes, the pedestrian bridge over Bridger Creek, the underpass beneath MT 86, an alternative pavement sections for the pedestrian trail.

2511 Holman Avenue P. O. Box 80190

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

Robert Peccia & Associates January 4, 2016 Project 14-3246G Page 2

A geotechnical drilling program was then outlined in a June 5, 2015, Revised Proposal for Geotechnical Work. The geotechnical work included soil borings, sampling, laboratory testing, and analysis. The drilling work proposed was14 borings along the project to depths ranging from 5 to 35 feet. The soil borings were performed along the alignment and at other critical areas along the project, including the pedestrian bridge over Bridger Creek, several cut and fill slopes, and the pedestrian underpass. Standard drilling and sampling was performed at each of the borings. Due to landowner access issues, the soil borings were performed in two separate trips. Those soil borings that could be performed without landowner permission were performed August 12 and 13, 2015, while those soil borings requiring landowner permission were performed on November 23 and 24, 2015. Due to these landowner permission issues, two of the proposed soil borings for a cut slope (ST-4 and ST-5) could not be performed, however, we recommend they be performed in the future once landowner permission is attained. After completing the drilling, laboratory testing was completed by SK Geotechnical and this geotechnical report was prepared, including pavement, cut slope, and bridge and underpass recommendations. This work is described in further detail below and represents refinement of the preliminary recommendations provided in the Geotechnical Reconnaissance Memorandum.

Review of Available Information and Reconnaissance

General Site Topography and Geology As can be seen on the attached Geologic Map, the proposed trail is situated northeast of Bozeman, Montana. The trail topography is primarily situated in the ancient alluvial flood plain of the Gallatin River and Bridger Creek from the beginning at Station 1500+00 up to about Station 1565+00. From this point to the end of the project, the site topography is primarily rolling terrain north of MT 86. MT 86 is a narrow paved highway, having a 24-foot wide driving surface and minimal shoulders. Narrow roadside ditches are present in cut and fill areas. Steep embankments were placed in fill areas, especially across drainages, creating the classic "barn roof" embankment. Due to the rolling terrain, numerous cuts are situated north of MT 86 with steep slopes. The cut and fill slopes are described in more detail later in this report.

A portion of the Preliminary Geologic Map of the Bozeman 30' x 60' Quadrangle Southwestern Montana, Susan M. Vuke, Jeffrey D. Lonn, Richard B. Berg, and Karl S. Kellogg, 2002, is attached. The map indicates three primary geologic deposits are situated along the alignment: Qat alluvium or alluvial terrace deposits, Qaf alluvial fan deposits, and QTaf older alluvial fan deposits. Based on our observations, the proposed trail alignment is situated in these alluvial deposits, in the valley up to Station 1565+00, then alluvial fan and terrace deposits to the end. Also shown is sedimentary bedrock (Tsuc), which is primarily situated above and east of the "M" parking lot.

Engineering Reconnaissance

Fieldwork. A geotechnical reconnaissance of the anticipated 2.3-mile alignment was performed on August 18, 2014, by Mr. Gregory T. Staffileno, PE, senior geotechnical engineer, and Mr. Brett M.

Warren, PE, geotechnical engineer. The alignment was closely observed, paying particular attention to geologic setting, existing cut slopes, existing fill slopes, and drainage features affecting the project.

Numerous photographs were taken of the alignment, some of which have been included with this report.

Robert Peccia & Associates January 18, 2016 Project 14-3246G Page 3

Existing Conditions. Table 1 below contains a summary of the existing conditions observed along the proposed trail alignment. The most significant geotechnical features mentioned in the table are discussed in more detail below the table.

Table 1. Existing Roadway Conditions and Preliminary Recommendations for Widening

Station General Description of Existing Conditions

Begin End

1500+00 1506+50 Trail located S. of MT 86. Roadside ditch 2 to 4 feet deep. Numerous buried utilities present.

1506+50 1533+50 Trail located S. of MT 86. Follows existing gravel surface trail, considered to be in fair condition.

Approx. 1 to 3 inches of gravel remaining. Geotextile fabric observed below existing gravel in isolated (most likely soft) areas.

1533+50 1545+00 Trail located S. of MT 86. Roadside ditch 1 to 3 feet deep with numerous trees.

1545+00 Trail crosses MT 86.

1545+00 1556+55 Trail located N. of MT 86. Follows existing paved trail. Paved trail 12 feet wide in good condition. Some longitudinal cracks 5 to 10 feet long.

1556+55 1562+37 Trail located N. of MT 86. Roadside ditch well below MT 86 pavement.

1562+37 1563+37 Trail located N. of MT 86. New Pedestrian Bridge likely needed to cross Bridger Creek.

1563+37 1576+00 Trail located N. of MT 86. Begin rolling terrain and existing cut slopes. Cut slopes up to 36°, upper native slopes approx. 22°. Appeared to be sufficient horizontal clearance (16 feet necessary) between ROW fence and catch point for trail placed above cut slope.

1576+00 1586+00 Trail located N. of MT 86. Insufficient clearance between ROW fence and catch point. VERY DIFFICULT LOCATION FOR TRAIL. Cut Slope = 38°.

1586+00 1588+00 Trail located N. of MT 86. Transition to drainage, where private dam constructed just N. of MT

86. MT 86 roadway fill 14 feet deep. Fill Slope = 30° to 33° (barn roof).

1588+00 1592+00 Trail located N. of MT 86. Appeared to be sufficient clearance for trail placed above cut slopes.

1592+00 1599+00 Trail located N. of MT 86. Insufficient clearance between ROW fence and catch point. VERY DIFFICULT LOCATION FOR TRAIL. Cut Slope = 33°.

1599+00 1611+00 Trail located N. of MT 86. Flatter cut slopes. Appeared to be sufficient clearance between ROW fence and catch point for trail placed above cut.

1611+00 1614+00 Trail located N. of MT 86. Drainage swale, desired location for Pedestrian Underpass beneath MT 86 from USFWS parking area. Fill Slope = 31° (barn roof).

1614+00 1620+00 Trail located N. of MT 86. Trail can be shifted away from catch point due to USFWS property extending north beyond ROW and up to "M" parking lot.

As the above table indicates, the existing roadside ditches and gravel surfaced/paved trails can be utilized for the proposed trail from Station 1500+00 up to about Station 1576+00. At this point heading east, the proposed alignment transverses through rolling terrain with significant steep existing cut slopes and fill slopes associated with the construction of MT 86, as described below.

Existing Cut Slopes. Numerous cut slopes are present along the anticipated trail alignment east of Station 1576+00. These cut slopes were created during construction of MT 86. The cut slopes range

Project 14-3246G Page 4 from about 33 to 38 degrees from horizontal. The horizontal clearance between the right-of-way (ROW) fence and the catch point at the top of the cut slope varies significantly depending on the height of the cut.

During our geotechnical reconnaissance, several cut slope sidewalls were logged and primarily appeared to consist of silty gravel. A recent boring above a cut slope encountered primarily lean clay with sand and gravel. It is our opinion the native clayey soils with sand and gravel have eroded along the sidewalls leaving a high percentage of surficial sand and gravel along the cut slope face, which are misleading. It is therefore important to perform borings to evaluate subsurface conditions, and the soils observed in the existing cut sidewalls do not appear representative.

Fill Slopes. The proposed alignment crosses several drainages associated with the hilly terrain, and embankments have been placed to construct MT 86 across these drainages. The fill slopes range from 32 to 33 degrees, which are relatively steep (barn roof embankment). Similar to the cut slopes, we observed the soils along the embankment sidewalls, but these results are likely not representative of the subsurface conditions.

Slope Observations. Cut and fill slopes ranging from 32 to 38 degrees were observed along the MT 86 in the proposed trail alignment. These are steep slopes and appear to be approaching the soil's angle of repose although signs of slope failures associated with landslides, slumps, or creeps were not observed.

Existing Dam. An existing property owner has built an earth dam impounding a pond just north of the trail alignment area from about Station 1588+00 to 1590+00. Extreme care will be needed for a trail alignment through this area to avoid impacting the existing dam.

Soil Boring Results

Drilling Procedures/Equipment/Sampling. The borings were performed on the date indicated on the boring logs with an ATV-mounted core and auger CME 1050 drill rig. The soil borings were performed to depths ranging from 5 to 35 feet deep. Penetration tests were performed at 2 1/2-foot intervals to a depth of 15 feet and at 5-foot intervals at depths greater than 15 feet. For those soil borings performed in the existing pavement, traffic control was performed while drilling and bag samples of the pavement subgrade and base course were collected. Additionally, bulk bag samples and thin-walled tube samples were taken for laboratory testing. The borings were extended with hollow-stem auger techniques and were extended to the proposed depth. Groundwater measurements (if encountered) were recorded. As previously indicated, Borings ST-4 and ST-5 were not performed due to landowner access issues.

Results.

General. Log of Boring sheets indicating the depth and identification of various pavement, soil strata, penetration resistances, laboratory test data, and water level information are included in Appendix 1.

Photographs of each boring location including the site topography are also included in Appendix 1. It should be noted, the depths shown as boundaries between the strata are only approximate. The actual changes vary between borings, especially when considering the complex geologic setting of the area.

A total of 12 borings were performed for the project. Table 2, following this page, displays the anticipated subgrade conditions at all 12 boring locations. The pavement section along MT 86 had an average thickness of 4.8 inches of asphalt pavement over and an average gravel base thickness of 13.2 inches.

R ob er t P ec ci a

A ss oc ia te s

Ja nu ar y

, 2

Pr oj ec t 1

4-

G

P ag e

T ab le

A n ti ci p at ed S u b gr ad e C on d it io n f or A li gn m en t B or in g S

T -1

S

-2

-3

-6

-7

-8

-9

-1

S

T -1

S

T -1

S

T -1

S

T -1

D at e

D ri ll ed

/2 4/

8/

/2

8/

/2

8/

/2

8/

/2

/2 3/

/2

8/

/2

/2 3/

/2 4/

/2

8/

/2

S ta ti on a nd

O ff se t

'R

5'

L

'R

'L

, 7 0'

, C L

5'

B or in g

P ur po se

A li gn m en t A li gn m en t A li gn m en t T oe o f C ut lo pe

F il l n ea r D am re st o f oe o f

E m ba nk m en t

U nd er pa ss ba nk m en t U nd er pa ss

A li gn m en t A li gn m en t B ri dg e A bu tm en t

B ri dg e

A bu tm en t

B or in g

G ro un d

S ur fa ce le va ti on el at iv e S ub gr ad e

E le va

M at ch in g E xi st in g

M at ch in g E xi st in g

3' -5

' F il l

'-3 0'

' F il l

' C

' C n/ a

4' F il l t o at ch in g E xi st in g

6' F il l

4' F il l

S u b gr ad e(1

D es cr ip la ye y S an d

F at

C la y S an dy

L ea n C la y

S an dy ea n C la y

(3

S n C la y

L ea n C la y w it h S an d

S n C la y

S an dy L ea n

C la y S an dy

L ea n C la y

S il ty G ra ve l w it h

S an d S n

C la y C la ye y S an d

A S

T M

C la ss

H

G

N -V al ue s 5, (3

4, 7, 8, 8, 7, , 5

(3

6, si st en cy oo of t

M ed iu st if f to s of t

M ed f to ve ry s f

V er y st if f

M ed ry s iu m s s of t

M ed iu m s en de ns e

M oi st ur e C on te nt

6, oi st ur e C on di r op ti um r ov er op er ow ne ar r to o ve r op ti ow to n ea r op ti r to a bo r op ti ab e op ti is k of ub gr ad e F ai lu re D ur in g T ot al ec on st ru ct io n

H ig h

M ed ub gr ad e S ub ex ca va d G eo sy nt he ti c

R ec om m en de d

N o

Y es

Y es o

N o

N o

N o

N o

N o

N o

N o

N o

(1 ) A nt ic ip at ed s ub gr ad e th at w ill b e pr es en t b en ea th th e gr av el s ur fa ci ng s ec tio n.

(2 ) N

-v al ue s m ea su re d in f ro ze n so il

, w hi ch o ve r es ti m at es c on si st en cy

(3 ) S ub gr ad e co nd it io n as su m ed u si ng

B or in gs

S T

-6 a nd S

-8

Project 14-3246G Page 6

General Soil Profile. As indicated in Table 2, the general soil profile along the alignment generally consisted of fine-grained alluvium or fine-grained alluvial fan deposits. These fine-grained deposits generally consisted of sandy lean clay, lean clay with sand, and fat clay. Occasional layers of coarse-grained alluvium or alluvial fan deposits were also encountered and generally consisted of poorly graded gravel with sand, clayey gravel with sand, and silty gravel with sand. It should be noted, these results were somewhat unexpected. We generally expected coarse-grained gravels to be present along the alignment. However, only one crest soil boring was performed in the area north of MT 86 (ST-8). We recommend additional deep soil borings be performed north of MT 86 to confirm the general soil profile.

The largest exceptions to the above general soil profile were Borings ST-13 and ST-14 performed near Bridger Creek. These soil borings generally encountered coarse-grained alluvium consisting of silty gravel, silty gravel with sand, silty sand, and silty sand with gravel.

As can be seen in Table 2, the subgrade along the majority of the alignment will consist of sandy lean clay and clayey sand. The sandy lean clay was generally medium stiff to stiff and the clayey sand was loose to medium dense. Soft, west fat clay was encountered in boring ST-2. Two areas of considerable existing fill were also encountered along the alignment at Borings ST-7 and ST-10 for the construction of Highway 86. The fill was also sandy lean clay , and was likely obtained from the nearby cuts, further supporting the lack of coarse-grained soils along the project.

Groundwater Observations. Groundwater was measured in four of the 12 soil borings at the time of drilling. Soil Borings ST-7 and ST-9 were performed in the upper alluvial fan deposits and encountered groundwater at depths ranging from 5.8 to 15.0 feet. Soil Borings ST-13 and ST-14 were performed near Bridger Creek and encountered groundwater depths ranging from 10 1/2 to 17 feet.

Laboratory Testing Program/Procedures After completion of the drilling and sampling, the samples were returned to our office for visual classification and laboratory testing. Laboratory tests were performed per AASHTO and ASTM standards. Representative samples were chosen for laboratory testing. Atterberg limits, soil classification, moisture content, sieve analysis, consolidation, and triaxial shear tests were performed on representative bulk subgrade, split-spoon, and thin-walled tube samples. The results of the moisture content and classification tests can be found on the Log of Boring sheets, and the results of the consolidation and triaxial shear tests can be found in Appendix 2. The test methods used are outlined in Table 3 below.

Table 3. Test Methods

Test Name Standard

Particle Size Analysis to 0.02 mm AASHTO T88

Plasticity Index (Atterberg Limits) AASHTO T89/T90

Soil Classification AASHTO M145

Sieve Analysis AASHTO T11/T27

Natural Moisture Content AASHTO T265

Triaxial Compression, CU with pore pressure measurements ASTM D 4767

Project 14-3246G Page 7

Analysis/Recommendations

Proposed Construction This project includes a 2.3-mile long paved shared-use trail with a bridge over Bridger Creek and a pedestrian underpass. The path will connect Story Mill Road to the trailhead to the "M." The trail will be constructed through a series of existing residential walking paths and through agricultural pastures. In these agricultural areas, large cuts and fills are required to construct the path, most of which will require the purchase of additional right-of-way. It is currently planned to use a mixture of 1:1.5 and 1:2 slopes to construct the path, but in many areas, 1:1.5 slopes are desired to reduce the amount of additional right-of-way required.

The path will also require a new pedestrian bridge over Bridger Creek. The proposed bridge will be constructed using pre-cast bulb tee beams and will have a span length of 95 feet. The pedestrian bridge will be supported on two end bents, each supported on shallow-spread footing foundations.

The project includes a pedestrian tunnel near the "M" trailhead to connect two parking lots used by hikers.

The pedestrian tunnel will be a 10-foot tall by 12-foot wide box culvert. In the same area near the tunnel, an existing round CSP culvert will be replaced.

Trail Pavement Section

Recommended Thicknesses. The pedestrian pavement thickness was determined using engineering judgement and past projects. For a pavement of this type, with very low structural demands, the surfacing and base course thicknesses are designed to support the anticipated relatively light construction equipment rather than the anticipated long-term structural demand. Therefore, we recommend the following two sections be considered for the trail.

Asphalt Pavement 2 inches Crushed Base Course 6 inches Total Thickness 8 inches

Portland Cement Concrete 4 inches Crushed Base Course 4 inches Total Thickness 8 inches

Consideration should be given to an overlay for the existing paved trail from about Station 1545+50 to 1557+00. Although this pavement is in good condition, an overlay will result in a matching surfacing.

We recommend a minimum overlay of 2 inches, along with crack sealing.

Unstable Subgrades. The anticipated subgrades at each of the borings were presented in previous Table 2 along with an evaluation of the risk of encountering unstable subgrades during construction. Unstable subgrades are those wet, soft clay subgrades that cannot be compacted to specification and generally will not support relatively light construction equipment without excessive deflection (pumping). Based on the borings, the following conditions are expected during construction.

Project 14-3246G Page 8

1 of 12 borings encountered had a high risk of becoming unstable during construction 4 of 12 borings encountered had a medium risk of becoming unstable during construction 7 of 12 borings encountered had a low risk of becoming unstable during construction

We therefore recommend providing a contingency in the project for shallow digouts if unstable subgrades are encountered, especially in the vicinity of Boring ST-2 from Station 1506+00 to 1535+00. Unstable subgrades can be identified by those areas that cannot be compacted to specification, or they deflect 1/2 inch or more under a loaded skidsteer. Once the extent has been identified, numerous options are available as indicated below.

Option 1. Let the wet, soft clays dry out sufficiently to be compacted to specification and deflect less than 1/2 inch.

Option 2. Discuss the unstable subgrade with the contractor, who may have a simple solution to the unstable subgrade.

Option 3. Dig out an additional 12 inches of subgrade, place a Class 1 woven Separation and Stabilization geotextile on the subgrade followed by 12 inches of additional base course to help bridge over the soft clays.

Pedestrian Underpass

Subgrade. The box culvert invert elevation on the north side of MT 86 is about 4915 and on the south side is about 4907. Boring ST-10 indicates the subgrade will be rather soft to medium stiff sandy lean clay fill underlain by stiff lean clay with organic soil. We anticipate these soils will be suitable to support the underpass, however, we recommend providing a 2-foot thick drainage layer beneath the base to 1) control potential seepage, and 2) provide a more stable working platform. These recommendations are discussed below and shown on the attached detail.

Seepage and Waterproofing. Directly beneath the box culvert, we recommend providing a 24-inch thick layer of drainage aggregate wrapped in geotextile and having perforated pipes to route water down and away from the culvert. We recommend incorporating a geogrid directly beneath the aggregate for additional strength. This seepage collection system will also help create a stable platform for construction of the tunnel. The extent and placement of these materials are shown on the attached detail and summarized below.

Drainage Aggregate: Open-graded aggregate meeting the requirements of Section 703.03(a).

Filter Fabric: Geotextile filter, Class 1 non-woven, Type A, per Section 714. Wrap completely around drainage aggregate.

Geogrid: Place on bottom only, over fabric, beneath drainage aggregate per Section 714. Prefer Tensar BX-1200 geogrid.

Drain Pipes: High strength 6-inch perforated drain pipe meeting Section 708.05 (PVC pipe).

Waterproofing: Waterproof the sides and top of the box culvert in accordance with Section 559.

Project 14-3246G Page 9

Backfill. As can be seen on the detail, we recommend using Select Borrow as backfill along the sides of the box culvert, and up to the top of the culvert. This material is recommended to promote seepage infiltrating down to the drainage layer, and is easier to place and compact in relatively small, confined spaces.

Above the top of the culvert, it is our opinion on-site lean clays from the box culvert excavation can be reused to provide a more uniform material. Approximately 7 to 10 feet of cover will be provided.

To reduce backfill settlement, we recommend the Select Borrow and clay material be placed in lifts not exceeding 8 inches uncompacted thickness, at a moisture content within 2 percent of optimum, and compacted to 95 percent per AASHTO T180 (modified Proctor). Full-time compaction testing is recommended during placement.

Settlement. Even though the box culvert essentially unloads the site, some settlement will occur after construction. We anticipate consolidation of the backfill will result in the majority of potential settlement, and anticipate up to 1 inch of total and differential settlement, provided the Select Borrow and clay have been compacted to specification. If they are not compacted to specification, several inches of settlement could occur. We recommend installing the culvert and backfilling, then waiting as long as possible prior to paving, if possible (i.e. one to two weeks).

Pavement Replacement. Assuming a cut and cover, or shoring approach is used, the pavement surface will have to be patched. The average existing section was about 5 inches of plant mix surfacing (PMS) over 13 inches of base course. It is our opinion this is relatively thin, and we recommend the following sections.

Material Option 1. Base Course

Section Option 2. Subbase

Section Asphalt Pavement Surface 5" 5"

Crushed Base Course, Type D 20" 8"

Subbase Course, Type A. --- 20"

Total Thickness 25" 33"

To reduce differential movement between the existing pavement and patched pavement, we recommend providing a 1:10 (V:H) transition from the bottom of the base/subbase courses.

Construction. Earthwork for the box culvert installation will need to be performed in accordance with OSHA guidelines. Because the excavation will be 20 feet or deeper, OSHA requires the excavation and/or shoring be designed by a licensed professional engineer. We agree with this requirement, especially when considering we do not have any idea what approach the contractor will use to install the culvert.

Bridge over Bridger Creek

Proposed Construction. As part of the project, a new 95-foot long pedestrian bridge is planned to be constructed over Bridger Creek. The preferred bridge construction will consist of two prestressed

Project 14-3246G Page 10 concrete bulb-T deck beams for an overall deck width of 15 feet and a span length of 95 feet. It is planned to support the two bridge abutments on spread footing foundations. We have estimated the load at each abutment will be about 200 kips.

Subsurface Conditions. Two soil borings were performed for the proposed bridge, one at each bridge abutment. The soil profile generally consisted of a layer of lean clay or sandy lean clay underlain by silty sand, silty sand with gravel, and silty gravel with sand. In Boring ST-13, a layer of very loose silty sand was encountered between the depths of 6 1/2 and 9 feet. This silty sand layer is moderately compressible and potentially liquefiable. Groundwater was encountered 10 to 15 feet below the ground surface at the time of our fieldwork.

Analysis and Recommendations.

Frost Depth. We recommend providing a minimum of 5 feet of earth cover over the bottoms of footings for frost protection on the outside of the abutments, and 2 feet of earth cover over the inside of the abutments. Additional embedment may be necessary to resist uplift loads.

Footing Subgrade. In order to create a stable working platform and reduce potential settlement, we recommend a 2-foot subexcavation be provided beneath both spread footings. The subexcavation should be backfilled with compacted Select Borrow backfill placed over a geogrid and separation fabric.

Geogrid should meet the requirements of Section 714. Separation fabric should consist of Class 1, Type A, and should extend up the sides of the subexcavation

Bearing Pressure. After the subexcavation has been provided, the footings can be designed for a net allowable bearing pressure of 2,000 pounds per square foot (psf). Net allowable bearing pressure is defined as that bearing pressure in excess of the final minimum overburden pressure. This bearing pressure includes a factor of safety of at least 3.0 against bearing capacity failure.

Settlement. Assuming up to 200 kips of load, we estimate up to 3/4 inch of total and differential settlement of footings supporting the pedestrian bridge. The structural engineer will need to evaluate if the bridge can tolerate this amount of movement. If it cannot tolerate this movement, then deeper borings and pile foundations will likely be necessary.

Liquefaction. Our calculations indicate up to 1 inch of additional liquefaction-induced settlement could occur during a seismic event. Again, the structural engineer will need to evaluate if this is suitable. If it is not suitable, then deeper borings and liquefaction mitigation will be required.

Backfill. We recommend using Select Borrow as backfill against the side and over the tops of spread footings supporting the bridge, but it can be capped with 1 foot of clay topsoil. We recommend it be compacted to 95 percent per AASHTO T180 (modified Proctor). The following lateral earth pressures can then be used against the sides of the footings.

Active earth pressure = 32 psf/ft At-rest pressure = 50 psf/ft Passive pressure = 500 psf Coefficient of friction = 0.5

Project 14-3246G Page 11

Uplift forces can be resisted using the weight of a wedge of soil extending upward and outward from the top edges of the abutment footing at an angle of 20 degrees from vertical. A moist unit weight of 135 pounds per cubic foot (pcf) can be used for the soil in this wedge.

Construction. Dewatering will likely be necessary during installation of the spread footings as well as during the subexcavation to install the geosynthetics and Select Borrow. Groundwater must be lowered prior to excavating, and to a minimum of 1 foot below the bottom of the excavation. The method of dewatering should be determined by the contractor based on their experience and available equipment, and in accordance with OSHA guidelines. We recommend assuming Type C soils for the footing excavations, less than 10 feet deep.

Slope Stability

Discussion. As indicated in our Geotechnical Reconnaissance Memorandum and the cross sections, multiple areas will require relatively large cuts and fills to construct the proposed trail. The slope stability of four cross sections was evaluated to determine appropriate cut and fill slopes for the project. These cross sections include:

Station 1586+00 Station 1588+00 Station 1606+00 Station 1614+50

Soil Conditions and Strength Parameters. At three of the four cross sections listed above the soil profile used for design was developed using nearby soil borings performed for the slope stability analysis.

However, due to the landowner access issues, no direct soils information is available at Station 1586+00.

The soil profile used for this cross section was developed using information from Borings ST-6 and ST-8.

Strength values for the soils at each cross section were evaluated using the SPT blow count and a triaxial shear test performed on a sample obtained from Boring ST-8.

The triaxial shear test was a consolidated-undrained (CU) test with pore water pressure measurements.

This test measures the total stress friction angle and cohesion and an estimated effective stress friction angle and cohesion. The results of the CU tests are shown below.

Total stress parameters: Friction Angle = 22.4°, Cohesion = 1,847 psf Effective stress parameters: Friction Angle = 25.9°, Cohesion = 2,061 psf

The above friction angles are within typical published values for soils of this type, however, the measured cohesion values are well above the typical published values. Without additional tests and soil borings to confirm their validity, it is our opinion the measured cohesion values are unconservative and should not be used for design. For our slope stability analysis, we used the tested friction angles, but used typical published cohesion values and results from the SPT tests.

Analysis and Recommendations. The slope stability analysis was performed using the computer program SVSlope® developed by SoilVision Systems Limited. The analysis was performed for the long-term case, using drained, effective stress parameters. The results of our slope stability analysis can be seen in the table below.

Project 14-3246G Page 12

Station Calculated Factor of Safety

1:1.5 Slope 1:2 Slope

1586+00 1.36 1.51

1588+75 1.63 2.11

1606+00 1.70 1.94

1614+00 1.43 1.60

As can be seen in the table above, the calculated factor of safety for 1:1.5 slopes range from 1.36 to 1.70.

The factor of safety calculated for 1:2 slopes range from 1.51 to 2.11.

Selection of the required factor of safety is critical to the design of the cut slopes on the project. The Federal Highways Project Development and Design Manual, Section 6.4.7.1, indicates long-term factors of safety should range between 1.3 and 1.5, depending on consequences of potential failure and uncertainty in how well the analysis model and its input parameters represent actual conditions.

Additionally, the Federal Highways Geotechnical Guidance Memorandum indicates the desired minimum factor of safety is typically between 1.3 and 1.5, but does not give any definitive guidelines.

The Montana Department of Transportation (MDT) Geotechnical Manual, Section 15.4.2, however, does give specific guidelines regarding the required factor of safety. For cut slopes into clay, MDT recommends a minimum factor of safety of 1.5. It is our opinion a factor of safety of 1.5 is reasonable given the relatively few borings performed through the slopes in question, as well as the atypical triaxial shear test result.

Therefore, we recommend 1:2 slopes be used along the project to achieve a factor of safety of 1.5.

However, constructing 1:2 slopes will require considerably more right-of-way than a 1:1.5 slope. If a 1:1.5 slope is required to reduce the amount of right-of-way necessary to construct the project, we recommend one or more of the following:

Additional soil borings and laboratory strength testing to better define the soil profile and strength parameters, Reduction of the required factor of safety through discussion with the owner and other project stakeholders, or

Additional slope stability analysis using different cross section profiles (such as use of a knee wall) that maintain the currently planned amount of right-of-way.

It is our opinion the best course of action would be to perform additional soil borings to better define the soil profile and strength parameters. A significant portion of the project, about 1/2 mile, has no representative soil borings. A better understanding of the soil profile may also aid in the selection of a lower required factor of safety.

If it is decided a factor of safety of 1.5 is required and additional right-of-way cannot be obtained, several options for constructing the trail may be available. These options could include installing various retaining walls above or below the pedestrian trail or the use of other slope reinforcement methods, such

Project 14-3246G Page 13 as soil nails or slope armoring. The retaining walls could be constructed a variety of ways including a concrete gravity block wall, a driven sheet pile wall, or a MSE well. A cross section sketch showing some of these alternative construction methods is included in Appendix 3. These construction options will need to be evaluated for stability, which was not included in our current scope of services.

Additional Geotechnical Work

It is critical that borings ST-4 and ST-5 be completed in the near future and incorporated into these geotechnical recommendations, after landowner access is given. Both of these borings are located along crests where cuts are anticipated, and are important to evaluate slope stability

Potential Material Sources

Three commercial borrow sources were identified within about 15 miles of the project. These sources are listed below.

Knife River 21730 I-90 Frontage Belgrade, Montana 59714 9 miles

TMC, Inc.

22540 Frontage Road Belgrade, Montana 59714 9 miles

Portable, Inc.

889 West Valley Center Road Bozeman, Montana 59718 11 miles

Additionally, the on-site soils from cut areas can be reused as compacted fill provided the on-site soils are properly moisture conditioned and compacted to 95 percent of their maximum Proctor dry density.

General Recommendations

Basis of Recommendations The analyses and recommendations submitted in this report are based upon the data obtained from the soil borings performed at the locations indicated. Often, variations occur between these borings, 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 construction costs, and it is suggested a contingency be provided for this purpose.

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

Project 14-3246G Page 14 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 borings at the times and under the conditions stated on the boring logs. These data were interpreted in the text of this report. The period of observation was relatively short, and fluctuation in the groundwater level may occur due to rainfall, flooding, irrigation, spring thaw, drainage, and other seasonal and annual factors not evident at the time the observations were made. Design drawings and specifications and construction planning should recognize the possibility of fluctuations.

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.

We appreciate the opportunity to provide these services for you. If we can be of further assistance, please contact us at your convenience.

Sincerely, Professional Certification I hereby certify this report was prepared by me and that I am a duly Licensed Professional Engineer under the laws of the State of Montana.

Brett M. Warren, PE License No. 17109

Gregory T. Staffileno, PE Reviewing Engineer

Appendix 1

N

G oo gle

G oo gle

G oo gle

Qat = Alluvium or Alluvial Terrace Deposit

Qaf = Alluvial Fan Deposits

QTaf = Alluvial Fan Deposit (Older) underlies Qaf

Tsuc = Sediment or Sedimentary Rock (coarser-grained conglomerate)

GEOLOGIC MAP

Bozeman to Bridger Mountains Trail

MT DOT86(1)

NE of Bozeman, Montana

Drawn by:

Google/SK

Geo Date 12-31-15

Project: 14-3246G

Scale: None FIGURE

Sheet 1 of 1 1

North

Begin Sta. 1500+00

End Sta. 1620+50

47454

W W

T L

P

T

N O

N U

M B

E R

W A R N I N G B U R I E D U T I L I T Y

S A

N S

E W

T

W A R N I N G B U R I E D U T I L I T Y

F

IB

E R

E M

B H

-1

B H

-2

W V

STORY MILL RD

B R

ID

G

E R

D R

STORY MILL RD

PI 117+31.92

POT 122+00.00

>=0°04'44"(LT)

E

S

E

S

W V

C I C

I

E x is ti n g g r o u n d

P r o f il e g r a d e

H e a d la n d s S u b d iv is io n

E l.

X

X X

.X X

E

X X

X .X

X

N

X X

X .X

X

M O

U N

T A

IN

S

T R

A

IL

B O

Z E

M A

N T

O B

R

ID

G E

R

B E

G I N

M T

D O

T

18" Pipe Culvert

1508+89

L in e t o b e c o n s tr u c te d

C P

M

C P

C P

N

B o z e m a n

M

T

C o m m e r c ia l D r

J e f f r e y

R

B r a n d n e r

B o z e m a n M

T

B r i d g e r D r

D a v id

W

L y n n H

N o y e s

B o z e m a n M

T

B r i d g e r D r

H a n n a h

I s a k

D i x

B o z e m a n M

T

H e a d la n d s D r

J e f f r e y

S

B e c k i C o o k

B o z e m a n M

T

H e a d la n d s D r

T h o m a s M

H il la r y P

C a r ls

B o z e m a n M

T

H e a d l a n d s S u b d i v i s i o n P a r k A r e a

B o z e m a n M

T

B r a n d i n g I r o n R d

L L

C

N

L L

C

:2

:2

P L

A N

A N

D P

R O

F

IL

E L

E G

E N

D

T y p ic a l in le t/ o u tl e t d it c h

C u lv e r t w it h i n le t/ o u tl e t d it c h

L in e t o b e c o n s tr u c te d

D

C U

Y D

E X

C

C U

Y D

E M

B

.2

A T

E P

R O

J E

C T

N U

M B

E R

S H

E

T

2:44 PM 28 July 2015] Int_ft2D [ F:\highways\FHWA\14500009_Bozeman_Trail\Design\Plan and Profile\mt08601fa2.dgn B. Wacker B. Thompson 4/2015 4/2015Checked by: Designed by:

4,734.00

1500+50

4,736.00

.9

V

C

K

S S

D

1501+10

4,735.15

.4

.0

V

C

K

1501+90

4,736.75

V

C

K

S S

D

1502+85

4,733.75

.1

V

C

K

1503+25

4,734.95

.0

V

C

K

S S

D

1503+75

4,735.25

.6

V

C

K

1504+25

4,737.05

.6

V

C

K

S S

D

1505+50

4,736.10

.7

%2 V

C

K

1506+00

4,738.00

.8

.5

V

C

K

S S

D

1508+00

4,741.00

V

C

K

1509+65

4,745.00

.4

.3

V

C

K

S S

D

1512+00

4,744.25

V

C

K

1513+50

4,746.00

.1

1513+75

4,746.25

.0

.4

Brett Boring Location

Brett

ST-1

04780

I R

A C

T

T V

T

E M

E x is ti n g g r o u n d

P r o f il e g r a d e

30" Pipe Arch Extension

1524+49

30" Pipe Arch Extension

1527+62

15" Pipe Culvert Extension

1533+51

N

B o z e m a n M

T

H e a d l a n d s S u b d i v i s i o n P a r k A r e a

B o z e m a n M

T

H e a d l a n d s S u b d i v i s i o n P a r k A r e a

B o z e m a n M

T

B r i d g e r D r

K a t h e r i n e R e n i e r

M it c h e ll

E S te c k m e s t

B o z e m a n M

T

B r id g e r D r

H o f f m a n

P a t r i c k

C a t h y

B o z e m a n M

T

S t i l l w a t e r C r e e k D r

V o g e l

G le n n W

O k a r c h e M

B o z e m a n M

T

B a b c o c k

S t

W a ll is M o r g e r

V a n K

B r y a n

B o z e m a n M

T

B r i d g e r D r

K a y

J

N e w m a n

B o z e m a n M

T

B r i d g e r D r

W e n d y B ia n c h in i

J o h n

M o r r i s o n

B o z e m a n M

T

B r i d g e r D r

S a n d r a J

A r c h e r

D a n ie l

D

A r c h e r

J r

B o z e m a n M

T

B r i d g e r D r

M ic h a e l

G

M a r y

D

E ll e r d

F o r t

C o ll in s

C O

S t o n e y

C r e e k

D r

L i v i n g T r u s t

C l a r a O

D i t t o n

C P

C

P

C P

C P

B o z e m a n M

T

B r i d g e r D r

C a m p b e ll

R o d n e y

D

K a t h r y n J

T h o r n e B a y A

K

P .O

B o x

Y o u d e r ia n

R o n a l d

F

M a r y

C b e c o n s tr u c te d

L in e t o

B o z e m a n M

T

P a r k

A r e a

C r e e k w o o d S u b d iv is io n

B o z e m a n M

T

C r e e k w o o d

D r

R i c h a r d s o n

R o b e r t

J e n n i f e r

C U

Y D

E X

C

C U

Y D

E M

B

.3

A T

E P

R O

J E

C T

N U

M B

E R

S H

E

T

1:01 PM 28 July 2015] Int_ft2D [ F:\highways\FHWA\14500009_Bozeman_Trail\Design\Plan and Profile\mt08601fb2.dgn B. Wacker B. Thompson 4/2015 4/2015Checked by: Designed by:

1521+00

4,756.50

.4

V

C

K

1522+60

4,761.50

.1

V

C

K

S S

D

1524+25

4,761.00

.3

V

C

K

1528+50

4,765.35 .0

1528+75

4,765.60

.0

.4

1534+50

4,773.75

.1

V

C

K

S S

D

1544+65

4,787.00 1544+85

4,787.00

.0

1537+50

4,777.25

V

C

K

1539+10

4,780.25

.8

V

C

K

1539+50

4,781.25

.4

1540+75

4,783.00

.8

V

C

K

S S

D

1543+00

4,781.00

.6

V

C

K

.5

Brett Boring Location

Brett

ST-2

0 4

5 4

0 4

5 4

0 4

5 4

0 4

5 4

0 4

5 4

0 4

5 4

0 4

5 4

0 4

5 4

0 4

47954

S M

A L L

T

T

T

T

T

E x is ti n g g r o u n d

P r o f il e g r a d e

L in e t o b e c o n s tr u c te d

24" Pipe Culvert

1569+47

18" Approach Culvert LT

1564+20

N

C P

C P

C P

C P

C P

A

X 3 A

C P

B o z e m a n M

T

P a r k

A r e a

C r e e k w o o d S u b d iv is io n

B o z e m a n

M

T

P .O

B o x

C a t t a n e o

A n t h o n y R

T a h n e e R

B o z e m a n M

T

C r e e k w o o d D r

H o m a n

J e f

J u s t i n a

M a n h a tt a n

M

T

P .O

B o x

E b b i g h a u s e n H o m e s I n c

B o z e m a n M

T

B o y la n R d

A n t o i n e t t e A n t h o n y

B o z e m a n M

T

B o y l a n R d

S i l l i t t i

S a m u e l

J

K a r i

A

M a n h a tt a n

M

T

P .O

B o x

E b b i g h a u s e n H o m e s I n c

B o z e m a n M

T

P a r k

A r e a

C r e e k w o o d S u b d iv is io n

B o z e m a n M

T

B o y l a n R d

C o r e y

F i s h

B o z e m a n M

T

P a r k

A r e a

C r e e k w o o d S u b d iv is io n

H o u s to n T

X

G le n w o o d D r

R u t h

D

D o d g e L i f e E s t a t e

D o n a ld

D D o d g e J r

L y m a n

C r e e k

L L

C

H o u s to n T

X

G le n w o o d D r

R u t h

D

D o d g e L i f e E s t a t e

D o n a ld

D D o d g e J r

L y m a n

C r e e k

L L

C

W e im a r

C A

P .O

B o x

L u k e n s T r u s t e e s

R i c h a r d

H

L o r n a J

B o z e m a n M

T

T a i l F e a t h e r L n A p t C

B e n t l e y

B r a n d o n L

J e s s i c a A

1562+36.92

1563+36.92S e e S h e e ts

G .X

G

.X C o n s tr u c t n e w p e d e s tr ia n b r id g e

B r id g e r C r e e k B r id g e

B ri d g e r

C re e k

C U

Y D

E X

C

C U

Y D

E M

B

.4

A T

E P

R O

J E

C T

N U

M B

E R

S H

E

T

1:12 PM 28 July 2015] Int_ft2D [ F:\highways\FHWA\14500009_Bozeman_Trail\Design\Plan and Profile\mt08601fc2.dgn B. Wacker B. Thompson 4/2015 4/2015Checked by: Designed by:

4,787.00

1545+65

4,784.25

.4

1556+55

4,794.50

.3

1562+37

4,802.50

1563+37

4,803.00

.5

1565+00

4,803.00

.0

V

C

K

1568+75

4,818.00

.0

.0

V

C

K

S S

D

1570+75

4,820.00

.8

V

C

K

Brett Boring Location

Brett Boring Location

Brett Boring Location

Brett Text Box

ST-14

Brett Text Box

ST-13

Brett Text Box

ST-3

Brett Text Box

ST-4

(not performed)

Brett Boring Location

48904895

0 4

E x is ti n g g r o u n d

P r o f il e g r a d e

L in e t o b e c o n s tr u c te d

24" Pipe Culvert

1575+37

24" Pipe Culvert

1579+14

24" Pipe Culvert Extension

1591+88

30" Pipe Culvert Extension

1587+85

24" Pipe Culvert

1593+41

18" Approach Pipe Culvert

1600+25 LT

36" Pipe Culvert Extension

1602+37

18" Pipe Culvert

1603+78

N

C P

F

C P

C P

E

C P

C P

D

C P

C

C P

C P

G

C P

Z

H o u s to n T

X

G le n w o o d D r

R u t h

D

D o d g e L i f e E s t a t e

D o n a ld

D D o d g e J r

L y m a n

C r e e k

L L

C

B o z e m a n M

T

E

M a in

S t.

S u it e

A

S a r a M

H a h n

B a r b e r to n O

H

N o la A v e

F P

R P r o p e r t i e s L

L C

B o z e m a n

M

T

P .O

B o x

S im m o n s

J a m e s C

J a n e t

D R

,2

.0

T

.3

L

.0

C U

Y D

E X

C

C U

Y D

E M

B

.5

A T

E P

R O

J E

C T

N U

M B

E R

S H

E

T

1:15 PM 28 July 2015] Int_ft2D [ F:\highways\FHWA\14500009_Bozeman_Trail\Design\Plan and Profile\mt08601fd2.dgn B. Wacker B. Thompson 4/2015 4/2015Checked by: Designed by:

1576+25

4,857.75

.8

.2

1579+75

4,862.00

.0

V

C

K

1585+00

4,883.50

.6

V

C

K

S S

D

1587+50

4,872.00

V

C

K

1590+00

4,882.50

.2

.5

V

C

K

S S

D

1593+75

4,895.75

V

C

K

1598+25

4,930.00

.6

-8 .7

V

C

K

S S

D

1600+25

4,912.50

V

C

K

1601+75

4,913.70

.8

.5

V

C

K

S S

D

1603+00

4,908.00

.8

V

C

K

Brett Boring Location

Brett Boring Location

Brett Text Box

ST-7

Brett Text Box

ST-6

Brett Text Box

ST-5

(not performed)

Brett Boring Location

IR

B O U N D A R Y

M A R K E R

E x is ti n g g r o u n d

P r o f il e g r a d e

M

P a rk in g

L o t

L in e t o b e c o n s tr u c te d

E l.

X

X X

.X X

E

X X

X .X

X

N

X X

X .X

X

18" Pipe Culvert

1612+88

18" Approach Pipe Culvert

1610+27 LT

Pedestrian underpass

12' span x 10' rise RCB

1613+00

N

B

C P

A

C P

C P

B o z e m a n

M

T

P .O

B o x

S im m o n s

J a m e s C

J a n e t

B o z e m a n M

T

B r i d g e r C a n y o n R d

C r a y t o n

R o b e r t F

C y n t h i a L

D e n v e r C

O

P .O

B o x

U .S

F is h

W il d li f e S e r v ic e

18" Pipe Culvert

1611+57

Extension

24" Pipe Culvert

1612+11

M O

U N

T A

IN

S

T R

A

IL

B O

Z E

M A

N T

O B

R

ID

G E

R

E N

D M

T D

O T

C U

Y D

E X

C

C U

Y D

E M

.6

A T

E P

R O

J E

C T

N U

M B

E R

S H

E

T

1:22 PM 28 July 2015] Int_ft2D [ F:\highways\FHWA\14500009_Bozeman_Trail\Design\Plan and Profile\mt08601fe2.dgn B. Wacker B. Thompson 4/2015 4/2015Checked by: Designed by:

1607+75

4,936.00

.8

.5

V

C

K

S S

D

1610+75

4,928.25

V

C

K

1611+25

4,928.75

.0

-9 .5

V

C

K

S S

D

1613+00

4,912.00

V

C

K

1616+50

4,940.00

.0

V

C

K

S S

D

1618+50

4,942.50

.2

.5

V

C

K

S S

D

4,941.40

Brett Boring Location

Brett Boring Location

Brett Boring Location

Brett Boring Location

Brett Boring Location

Brett Text Box

ST-12

Brett Text Box

ST-11

Brett Text Box

ST-10

Brett Text Box

ST-9

Brett

ST-8

12/06/12

Order of Descriptors

Criteria For Descriptors

- Angularity of coarse grained soils

Consistency of Fine Grained Soils

Very Stiff 16 - 30

Apparent Density of Coarse Grained Soils

Loose 4 - 10

Dense 31 - 50

Dry -Absence of moisture, dusty, dry to the touch.

Moist -Damp, but no visible water.

Angularity of Coarse-Grained Particles

Moisture Condition

- Other relevant notes

Medium Dense 11 - 30 plane sides with unpolished surfaces.

but have rounded edges.

well-rounded corners and edges.

Rounded -Particles have smoothly curved sides and no edges.

Definition of Particle Size Ranges

Boulder

Cobble

Gravel

Sand

Silt

Clay between silt and clay.

> 12 in (300 mm)

3 in (75 mm) - 12 in (300 mm)

No. 4 Sieve (4.75 mm) to 3 in (75 mm)

No. 200 (0.075 mm) to No. 4 Sieves (4.75 mm)

< No. 200 Sieve (0.075 mm)*

< No. 200 Sieve (0.075 mm)* grained soils only)

Consistency N-Value (uncorrected)

Soil Component Size Range

Subrounded-Particles have nearly plane sides, but have

Subangular -Particles are similar to angular description, Angular -Particles have sharp edges and relative

Very Loose < 4

Very Dense > 50

Very Soft < 2

Soft 2 - 4

Medium Stiff 5 - 8

Stiff 9 - 15

Hard > 30

Relative Density N-Value (uncorrected)

- Group Name

- Consistency or Relative Density

- Moisture Condition

- Color

- Particle size descriptor(s) (coarse

Wet -Visible free water.

Soil Classifications are Based on the Unified Soil

Classification System, ASTM D2487 and D2488.

Also included are the AASHTO group classifications (M145).

Descriptions are based on visual observation, except where they have been modified to reflect results of laboratory tests as deemed appropriate.

*Atterberg limits and chart below to differentiate

Example soil description: Sandy FAT CLAY (CH), soft, wet, brown. (A-7)

SPT (Standard Penetration Test-ASTM D1586):

The number of blows of a 140 lb (63.6 kg) hammer falling 2.5 ft (750 mm) used to drive a 2 in (50 mm)

O.D. Split Spoon sampler for a total of 1.5 ft (0.45 m) of penetration.

Written as follows:

first 0.5 ft (0.15 m) - second 0.5 ft (0.15 m) - third 0.5 ft (0.15 m)

(ex: 1-3-9)

Note: if the number of blows exceeds 50…