GM16-16_Final_Foundation_Recommendations.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

To: Janice Ritter, Project Manager In Reply Refer to: HFL-17 Geotechnical Memorandum GM16-16

From: Robert Kraig, Geotechnical Engineer

Date: May 10, 2016

Subject: Final Geotechnical Bridge Foundation Design & Construction Recommendations

Elk Lake Road Construction, Beaverhead County, MT

MT Beaverhead 273(1)

Background and Objective

The Elk Lake Road Construction Project (the project) is located in Southwestern Montana in Beaverhead County, approximately 36 miles driving distance westerly from the city of West Yellowstone, MT, about 110 miles driving distance northerly from Idaho Falls, ID, and roughly 125 miles southerly driving distance from Bozeman, MT.

(Refer to Figures 1 and 2 below.)

Figure 1: Project Location Map

Project

Figure 2: Project Vicinity Map

The proposed project will rehabilitate approximately 2.7 miles of the Elk Lake Road and includes removing an existing bridge at Red Rock Creek (44o 38’ 52.92” N, 111o 39’ 33.89” W), and replacing it with a new bridge crossing adjacent to the existing bridge alignment. The proposed project also involves removing two 5-foot culverts at Elk Springs Creek (44o 37’ 51.40” N, 111o 39’ 32.81” W), and replacing them with a new bridge.

Photos of the existing sites are shown in Figures 3 through 6. The average ADT on the project is 60 vehicles (off-season) and 85 (peak season), of which 2% are estimated to be trucks.

Western Federal Lands Highway Division (WFLHD) Geotechnical Report 08-16 was prepared for the project by Yeh and Associates and contains geologic and geotechnical information for the project. When substantive differences in content occur between the information appearing in the 08-16 report and this memorandum, the information appearing in this memorandum supersedes that appearing in the previous report.

The objective of this memorandum is to supplement Geotechnical Report 08-16 by providing final geotechnical information and construction recommendations for the construction of steel single-span bridges with precast concrete sill beams acting as footings to be constructed at the Red Rock Creek and Elk Springs Creek crossings.

Preliminary bridge foundation recommendations were provided by the WFLHD through Geotechnical Memorandum GM36-15. The recommendations were based on an RTI modular bridge (smaller than the currently proposed bridge) repurposed from the Lost Trail National Wildlife Refuge in Flathead County, MT, intended to be used at the Elk Springs Creek crossing. The memorandum included estimates for bearing capacity and settlement based on the assumed bridge type and size at the time, which are no longer valid. The memorandum also discussed seismically introduced liquefaction and lateral spreading.

West Yellowstone, MT

Approx. 36 mi.

Figure 3: Existing Red Rock Creek Bridge (Upstream side)

Figure 4: Existing Red Rock Creek Bridge (Downstream side)

Figure 5: Existing Culverts at Elk Springs Creek (Downstream side)

Figure 6: Existing Culverts at Elk Springs Creek (Upstream side)

Geologic Setting, Seismicity, Site Conditions & Climate

Geologic Setting

The project location is in the northern Rocky Mountains Geophysical Provence. Elk Lake Road lies in the Centennial Valley, the valley immediately to the north of, and adjacent to, the east/west trending Centennial Mountains. The Centennial Valley, a half graben, is actively subsiding and tilting into the fault zone at the base of the Centennial Mountains. Fault offset is estimated at approximately 32 feet over the last 15,000 years. This offset has resulted in about 25 feet of down faulting of the Centennial Valley. A large lake of approximately 65 feet deep occupied the valley in late Pleistocene time.

As shown in the geologic map and correlation of map units in Figures 7 and 8, Elk Lake Road lies upon three different mapped geologic formations. Holocene aged unconsolidated fluvial deposits of sand, silt and gravel (QaL-Alluvium), are found in the area of both Red Rock Creek and Elk Springs Creek. The borings at these locations confirmed the mapped geology.

Figure 7: Geologic Map (No scale)

Figure 8: Geologic Map Legend

The majority of the project is underlain by a Holocene aged low lobate deposit of unconsolidated moderately well sorted silt, sand, gravel, and cobbles (Qfy – Young Alluvial Fan Deposit). As the ancient lake subsided, this material was deposited onto the former lake bed by the surrounding streams that empty into the valley. The borings conducted in this deposit encountered silt, sand and gravel. No cobbles were found.

Seismicity

The project location is adjacent to the Centennial Fault, which is located at the southern boundary of the valley at the base of the Centennial Range. The Centennial Fault is grouped in the Idaho seismic zone or the Centennial tectonic belt, which extends from the Yellowstone area into central Idaho. This is the most seismically active area in the State of Montana and several large magnitude events have occurred here in the past 100 years. The largest of these was the Hebgen Lake earthquake, which was recorded at magnitude 7.5 and caused several deaths. The event also dammed the Madison River, creating Quake Lake.

The Centennial fault is classified as a Class A Quaternary fault by the Montana Bureau of Mines and Geology.

Class A is defined as, there being evidence that at least one large-magnitude earthquake has occurred on the fault during the Quaternary. The centennial Fault is divided into four sections. The project is located adjacent to the Red Rock Lakes section of the fault. Conflicting data exist on an estimate of the most recent historic deformation of the fault. Conflicting data exist on an estimate of the most recent historic deformation of the Red Rock Lakes section.

Site Conditions

Elk Lake Road is located in slightly sloping, ancient lakebed terrain of the Centennial Valley. The road descends slightly from an elevation of approximately 6665 feet at the intersection with South Valley Road to an elevation of approximately 6640 feet at the intersection with North Valley Road. Within the project limits, approximately

1.5 miles of Elk Lake Road is a tangent section running due north/south. Curved sections of approximately

0.6 miles each are found at either end of the tangent section, connecting Elk Lake Road to South Valley Road and North Valley Road.

Between South Valley Road and North Valley Road, Elk Lake Road crosses two major watercourses, Red Rock Creek and Elk Springs Creek. In addition to the creek crossings there are several low lying wetland areas where both surface water and high groundwater affect the roadway.

Climate

Climate data collected from the nearby Lima, Montana weather station is representative of the project location.

The average annual rainfall at the Lima weather station is 11.17 inches. The majority of the rainfall occurs between April and October. The average annual snowfall is 59 inches, the majority of which occurs between September and May. The annual average lowest temperature, which occurs in December, is 7.1 degrees Fahrenheit. The annual average highest temperature, which occurs in July, is 80.1 degrees.

Subsurface Conditions

Three subsurface borings, TH-9, TH-6, and TH-8, were drilled at the Red Rock Creek site and one, TH-2, was drilled at Elk Springs Creek. See Attachment 1 for Boring Location Maps, gINT logs, Laboratory Test Results, and Soil Lithology. Borings TH-8 and TH-9 were drilled in mid-to-late-September 2014. Borings TH-2 and TH-6 were drilled in mid-November 2014. Refer to WFLHD Report 08-16 for comprehensive information regarding the subsurface investigations. The subsurface conditions at each bridge site are summarized below. Unified Soil Classification System (USCS) classifications appear when laboratory tests were performed. Not all laboratory test information appears on the boring logs in Attachment 1, but all laboratory test reports are attached following the boring logs.

Red Rock Creek Bridge Site

Subsurface materials encountered in the Red Rock Creek Boring TH-6 consisted of loose to very dense silty sand and sandy silt. Loose silty sand was encountered above the 10 foot depth and medium dense to dense silty sand was encountered at 10 feet to 23 feet below ground surface (BGS), with very stiff non-plastic (NP) silt encountered from 23 to 32 feet. Beneath the silt, medium dense silty sand (SM) was encountered to the bottom of the boring at 41.5 feet. The soils have relatively high moisture contents ranging from about 12% to 31%.

Boring TH-8 encountered loose silty sand to about 7 feet BGS, followed by stratified loose to dense silty sand, sandy silt and clayey sand to 91.5 feet at boring termination. The soils were moist to wet. Only one sample taken at 40.0 feet underwent classification testing. The sample classified as non-plastic silty sand (SM) under the USCS.

Boring TH-9 encountered loose to medium dense silty sand and medium stiff clay to about 8 feet BGS. Stratified medium dense to very dense silty sand (SM), sandy silt (ML), and clayey sand was encountered from 8 to 58 feet. Stratified sandy clay and silt was encountered from 58 feet to the bottom of the boring at 90 feet.

Standard Penetration Test (SPT) field N values indicate that the clay soils have a consistency of very stiff and the relative density of the sand soils vary from medium-dense to very dense.

Groundwater measurements were observed in all of the borings at the time of drilling. Groundwater was measured at 3 to 3.5 feet BGS, representing the groundwater conditions at the time of drilling. Note that the measurements may not be indicative of other times, or at other locations; however, the sites are located within wetland areas. It is possible that the groundwater levels might fluctuate with varying seasonal and weather conditions; however, groundwater is expected to be high year-round given the local wetland environment.

Elk Springs Creek Site

One boring, TH-2, was drilled at Elk Springs Creek. Silty sand was encountered to a depth of 5.3 feet BGS, underlain by very loose to medium dense sandy silt (ML) to 12 feet, which contained a layer between 7 feet and

8.5 feet (possibly more) with a field N value of zero (sampler fell under its own weight). Beneath that, soft sandy clay (CL) was encountered to 20 feet, underlain by very loose to loose sandy silt (ML) from 20 to 22 feet. A layer of soft to firm sandy clay (CL) extended to 30.5 feet where a very thin layer of gravel was encountered, followed by stiff to hard silty clay (CL-ML) to the bottom of the boring at 36.5 feet. The sandy silt soils were shown to be non-plastic with P200 (material passing the No. 200 standard sieve) in excess of 70%. Natural moisture contents in the sandy silt ranged from about 30% to 40%. The sandy clay soils were shown to have low to medium plasticity and P200 of 65% to 91%. Moisture contents of the sandy and silty clay soil samples ranged from approximately 20 to 44%.

Artesian groundwater conditions were encountered in TH-2 at a depth of about 30 feet BGS in the thin gravel layer identified above. It was reported that the groundwater rose through the top of the hollow stem auger with flow estimated in excess of 15 gallons per minute. It is likely that the sandy clay layer above the gravel layer acts as an aquitard. Because of the artesian conditions, water table depth in the drill hole was not measured. Based on the moisture contents in the soil samples the water table was estimated to be at about 3 feet to 5 feet BGS at the time of drilling.

Bridge Foundation Design Discussions

Foundation Design

Foundation designs originally considered for the project included shallow cast-in-place spread footings, deep foundations (driven piles), and a geosynthetic reinforced soil integrated bridge system (GRS-IBS), but these were dropped from further consideration primarily due to issues concerning scour, expense, constructability, and ground disturbance.

Factors considered concerning foundation design included shallow groundwater conditions, seismic concerns and subsurface conditions susceptible to liquefaction, the depth of scour, and in the case of Elk Springs Creek, the artesian groundwater conditions located below the structure. Seismic hazards at this site were described in GM36-15 and Geotechnical Report No. 12-11. The seismic hazards include potential ground shaking, liquefaction, lateral spreading and lateral flow. Email letters in response to a November 6, 2015 meeting minutes addressed to WFLHD Project Manager Janice Ritter show that the owners accepted the risks pertaining to the consequences of liquefaction and the absence of satisfactory seismic design. The Email letters and meeting minutes appear in Attachment 2. Another factor that may have come into play is the fact that the project is located on a very low volume road, as discussed earlier.

With respect to the discussion above, the selected foundation type for both sites are precast concrete sill beams, 5 feet wide, by 2.5 feet thick, by 30 feet long. The sill beams will bear on a 2 foot thick seating course of open-graded backfill at Red Rock Creek, and on a 2 foot thick layer of seal concrete at Elk Springs Creek. The purpose of the seal concrete layer is to 1) increase the bearing capacity of the soils below by distributing the required loads and 2) to facilitate construction. Cofferdams consisting of sheet piling driven below the scour depth will protect the sill beams from scour and assist in supporting the foundation soils. The proposed designs call for construction of a three-sided cofferdam at Red Rock Creek and a four-sided cofferdam at Elk Springs Creek.

Geotechnical Design Parameters

Geotechnical design parameters were provided to the WFLHD Structures section for cofferdam design via email and are shown in Table 1.

Table 1: Geotechnical Design Parameters

Parameter Elk Springs Creek Red Rock Creek

(Applies to both abutments) (South Abutment) (North Abutment)

Depth Range (ft)

0 - 5 5 – 12 12 - 22 22 – 30.5

30.5 – 36.5

0 - 23 23 - 32 32 – 41.5

0 - 7 7 – 27.5 27.5 -

Phi (degrees)

28 22 14 14 22 30 22 30 29 30 28

Gamma (pcf)

120 100 110 110 100 118 110 118 115 125 122

Cohesion (psf)

0 0 300 550 1800 0 0 0 0 0 75

Ka 0.361 0.455 0.610 0.610 0.455 0.333 0.455 0.333 0.347 0.333 0.361

Kp 2.77 2.20 1.64 1.64 2.20 3.00 2.20 3.00 2.88 3.00 2.77

Bearing Capacity Estimate

Unfactored structural dead and live loads were provided by the WFLHD Structures Section as 209 kips dead load (includes leveling beam) and 194 kips live load, for a total unfactored load of 403 kips per abutment. (An additional dead load of 19.8 kips was added to account for the added seal concrete layer at the Elk Creek Springs site.)

Estimating the bearing capacity followed the procedures appearing in AASHTO LRFD Bridge Design Specifications. Bearing capacity was estimated based on footing dimensions of 11 feet wide by 36 feet long (footprint of the seal concrete layer) for Elk Springs Creek, and 5 feet wide by 30 feet long for the footprint of the sill beam at Red Rock Creek. Nominal bearing resistance, qn for the Service I Limit State, and factored bearing resistance, qR, for the Strength I Limit State, are shown in Table 2. Also shown is the factored bearing pressure, as based on the footing dimensions, and the capacity to demand ratio (CDR). A CDR ≥ 1.0 under AASHTO LRFD methodology shows that the factored bearing resistance of the soils under the Strength I Limit State is acceptable.

Table 2: Bearing Capacity & CDR

1.

Site Nominal Bearing Resistance, qn (ksf)

Resistance Factor, Φn

Factored Bearing Resistance, qR (ksf)

Factored Bearing Pressure, ksf

Capacity/Demand Ratio, CDR

Elk Springs Creek

4.26 0.45 1.92 1.58 1.23

Red Rock Creek

11.61 0.45 5.22 5.00 1.04

1. Bearing capacity estimated at bottom of seal concrete layer at approximate elevation 6625 feet for Elk Springs Creek and at the bottom of the sill beam at Red Rock Creek at about 6643 feet.

Settlement Estimate

Settlement at the Elk Springs Creek site may be significant and must be considered in the final design.

Settlement at the Red Rock Creek site is anticipated to be less significant, but should also be taken into consideration. It is our understanding that the owner agencies have accepted the risks associated with settlement in excess of 3 inches at each of the sites per the meeting minutes dated November 6, 2015.

Total settlement is the total of the elastic, primary consolidation and secondary consolidation. Settlement estimates relative to the amount of grade raise appear in Table 3.

Note that when clay soils were encountered in the borings they were assumed to be normally consolidated.

However, the low field N values recorded in some zones at Elk Springs Creek indicates that these soils are under-consolidated, thus the settlement estimates as discussed herein might be underestimated.

The plans call for a grade raise of about 4.5 feet at Elk Springs Creek that corresponds to predicted total settlement of about 7 inches, which includes estimated secondary consolidation of about 1 inch. Note that because only one boring is located at Elk Springs Creek, no differential estimate is possible; however, it is anticipated to be well within a 3-inch tolerance based on the assumption that subsurface conditions are essentially the same across the stream when project location and flat topography of the site are taken into consideration. A grade raise of 6 to 6.5 feet is anticipated at Red Rock Creek, which corresponds to predicted total settlement of about 3 inches. Due to the more favorable subsurface conditions at the Red Rock Creek site, only slight (insignificant) secondary consolidation is predicted and not shown in the table.

Table 3: Estimated Total Settlement (in)1,2 (St = Se + Sc + Ss)

Grade Raise, ft

Elk Creek Red Rock Creek (South side) (North side) Differ-ential, in.

Se+Sc, (in)

Ss, (in)

St= Se+Sc+Ss

(in)

Differ-ential, in.

Se+Sc, in.

in.

in.

Se+Sc, in.

in.

0 4.8 1.1 5.9

N o t p o ss ib le t o

D et er m in e

2.6 -- 2.6 2.5 -- 2.5 0.1

1 5.1 6.2 2.7 2.7 2.5 2.5 0.2

2 5.4 6.5 2.7 2.7 2.6 2.6 0.1

3 5.7 6.8 2.8 2.8 2.7 2.7 0.1

4 5.9 7.0 2.9 2.9 2.7 2.7 0.2

5 6.2 7.3 2.9 2.9 2.8 2.8 0.1

6 6.5 7.6 3.0 3.0 2.8 2.8 0.2

7 6.7 7.8 3.1 3.1 2.9 2.9 0.2

Table 3: Estimated Total Settlement Cont. (in)1,2 (St = Se + Sc + Ss)

Grade Raise, ft

Elk Creek Red Rock Creek (South side) (North side) Differ-ential, in.

Se+Sc, (in)

(in)

(in)

Differ-ential, in.

Se+Sc, in.

in.

Se+Sc, in.

in.

8 7.2 1.1 8.3 --- 3.2 --- 3.2 3.0 --- 3.0 0.2

9 7.4 8.5 3.2 3.2 3.1 3.1 0.1

10 7.4 8.5 3.2 3.2 3.1 3.1 0.1

1. Elastic (Se) and Primary Consolidation (Sc) were estimated based on procedures appearing in AASHTO 2014. A method appearing in the NAVFAC design manual was used to estimate Secondary Consolidation in cohesive soils.

2. Total settlement is the sum of Elastic (Se), Primary Consolidation (Sc), and Secondary Consolidation (Ss).

Seismic Design

The sites lie within Seismic Zone 4. Seismic design standards are not considered in the proposed design. As discussed earlier, it is our understanding that the owners have accepted the risks involved with a foundation design that does not meet AASHTO seismic design standards.

Liquefaction

Low plasticity silts and sands within the upper 75 feet of the soil strata are potentially liquefiable if corrected standard penetration test (SPT) blow counts (N1)60 are less than or equal to 25 blows per foot. Liquefaction and lateral spreading were discussed under WFLHD Geotechnical Memorandum GM36-15 dated October 22, 2015.

GM36-15 determined that due to the limited soil profile available at Elk Springs Creek (about 35 feet BGS), proper analysis of liquefaction induced settlement was not possible; nevertheless, a partial analysis was performed assuming the bottom of the observed soil profile extended indefinitely. That analysis showed that at least 3.4 inches (and up to 4 feet) of settlement might occur, and that the risk of lateral spreading existed at the site. The soil profile at the Red Rock Creek site was determined not to be susceptible to liquefaction. As discussed earlier it is our understanding that the owners have accepted the risks associated with design life issues related to liquefaction potential at the Elk Springs Creek site.

Frost Embedment Depth

The recommended embedment for frost protection is 4 feet.

Foundation Construction Considerations

Predominately sand and fine-grained soils containing gravel up to 1 inch were encountered in the project test borings, with the tested samples shown to contain up to 6 percent of coarse gravel (3/4” to 1”). This indicates favorable conditions for driving sheet piling; however, other aspects of foundation construction present challenges.

When constructing the cofferdams, the sheet piling must not be driven beyond 28 feet BGS (6601 feet elevation) at the Elk Springs Creek site due to the artesian groundwater conditions encountered at that site. There is no such restriction at the Red Rock Creek site.

The bridge locations are adjacent to wetlands. Groundwater was encountered at relatively shallow depths during the investigations. The four-sided cofferdam at Elk Springs Creek must be designed to overcome differential hydrostatic pressures during construction. Following installation of the cofferdam, and prior to dewatering inside the cofferdam, seal concrete must be in place and cured prior to placing the sill beam. It should be the contractor’s responsibility to develop a dewatering plan. Dewatering is not anticipated at Red Rock Creek where a three-sided cofferdam is proposed.

Do not over excavate below the planned bottom of excavation shown on the plans to avoid disturbing the low shear strength material below at the Elk Springs Creek site.

References:

WFL Geotechnical Report 08-16

WFL Geotechnical Memorandum 36-15

AASHTO LRFD Bridge Design Specifications, 7th Edition (2014), American Association of State Highway and Transportation Officials, Washington, D.C.

NAVFAC Soil Mechanics Design Manual 7.01, September 1986

U.S. Geological Survey, USGS Earthquake Hazards Program website, 2008 Interactive Deaggregations, http://geohazards.usgs.gov/deaggint/2008/, accessed May, 2016

Closing:

Please contact Robert Kraig at (360)619.7699 or robert.kraig@dot.gov with any questions regarding this memorandum.

Cc: Ben Oltman, Structures Section

Nathan Jenks, Geotechnical Team Lead

Dustin Woods, Geotechnical Engineer

Carolyn Sourek, Hydraulics Engineer

Curtis Jorgenson, Highway Design Manager

Geotechnical File

Attachments:

Attachment 1: Boring Locations, Soil Lithology, gINT logs & Laboratory Test Results

Attachment 2: November 6, 2015 Meeting Minutes & Owner’s Risk Approvals http://geohazards.usgs.gov/deaggint/2008/ mailto:robert.kraig@dot.gov

Attachment 1

Boring Location Maps

Soil Lithology gINT logs

Laboratory Test Results

Intentionally Blank

EL

K

C R

EE

K

S P

R

IN

G S

SH

O

W

IN

G B

O R

IN

G

L O

C A

TI

O

N

R

ED

R O

C K

C R

EE

K

S H

O W

IN

G

B O

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G L

O C

A

TI

O

S

Date:Project Number: 214-230

Project: Elk Lake Road

Legend for Symbols Used on Borehole Logs

Soil Lithology

Lab Test Abbreviations

Sample Types

YEH AND ASSOCIATES, INC.

GEOTECHNICAL ENGINEERING CONSULTANTS

Auger Cuttings Grab Sample Standard Penetration Test Split Spoon

Bedrock Lithology

USCS Low Plasticity Clay

USCS Poorly-graded Gravel USCS Silt USCS Clayey Sand

USCS Clayey Sand USCS Silty Sand

MC-Moisture Content DD-Dry Density #200-Percent Passing #200 Sieve LL-Liquid Limit PL-Plastic Limit PI-Plasticity Index S-Sulfate Content Chl-Chloride Content S/C-Swell/Consolidation UCCS-Unconfined Compressive Strength Re-Resistivity PtL-Point Load Test AASHTO-AASHTO Classification USCS-USCS Classification

* Indicates that gradation analysis was performed, Atterberg limits were not performed, but the USCS classification was applied assuming non plastic characteristics

NV

NV

NP

NP

NP

62.3

92.4

72.6

80.9

A-4 ( 0 )

ML

A-4 ( 0 )

ML

A-4 ( 0 )

ML

A-6 ( 11 )

CL

0.0 - 5.3 ft. silty SAND with angular gravel, brown, moist.

5.3 - 12.0 ft. sandy SILT, gray, wet, very soft to medium stiff.

Sampler fell under its own weight.

12.0 - 20.0 ft. sandy CLAY, gray, moist to wet, soft.

3-3-2

0-0

3-2-4

0-0-2

0-1-1

29.7

40.1

33.3

39.2

Logged By: W.Hoon

Final By: W. Hoon

Symbol Depth Date

Groundwater Levels:

Weather Notes: Cloudy/Cold

Inclination from Horiz.: Vertical

Boring Began: 11/20/2014

Boring Completed: 11/21/2014

Drilling Method(s):

Driller: Inberg-Miller

Drill Rig: CME 85

Hammer Type:

Artesian flow

Night Work:

Total Depth: 36.5 ft

Ground Elevation:

Coordinates: N: E:

Location:

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Li qu id Li m it

P la st ic ity In de x

Boring No.: TH-2

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

F in es C on te nt

PAGE

AASHTO

& USCS

Classifi-cations

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

/2

1/

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows per 6 in

M oi st ur e C on te nt

D ry

D en si ty

(p cf

NP

79.4

90.6

64.6

A-4 ( 0 )

ML

A-7-6 ( 19

CL

A-4 ( 2 )

CL-ML

20.0 - 22.0 ft. sandy SILT, gray, wet, very soft.

Sampler fell under its own weight.

22.0 - 30.5 ft. sandy CLAY, gray, wet, soft.

30.5 - 30.7 ft. GRAVEL, gray, wet, medium dense, fine, clean, washed, subrounded.

30.7 - 36.5 ft. silty CLAY with few fine sands, gray, moist, very stiff.

Bottom of Hole at 36.5 ft.

0-0

0-2-2

0-1-1

3-8-8

5-7-15

36.3

44.0

19.8

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Li qu id Li m it

P la st ic ity In de x

Boring No.: TH-2

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

F in es C on te nt

PAGE

AASHTO

& USCS

Classifi-cations

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

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T E

S T

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P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

/2

1/

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows per 6 in

M oi st ur e C on te nt

D ry

D en si ty

(p cf

A-1-b ( 0 )

SM

A-1-b ( 0 )

SM

NP

NP

NV

NV

16.2

15.6

11.7

0.0 - 23.0 ft. silty SAND few to little fine subangular gravels, SM, grayish brown, wet, loose to dense.

6-6-3

4-4-20

8-20-24

Logged By: W.Hoon

Final By: W. Hoon

Symbol Depth Date

Weather Notes: Clear/Cold

Inclination from Horiz.: Vertical

Boring Began: 11/19/2014

Boring Completed: 11/19/2014

Drilling Method(s):

Driller: Inberg-Miller Engineering

Drill Rig: CME 85

Hammer Type:

3.0 ft

11/19/14

Night Work:

Total Depth: 41.5 ft

Ground Elevation: 6649.0 ft

Coordinates: N: E:

Location:

Groundwater Levels:

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-6

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

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IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

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R A

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.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows per 6 in

A-4 ( 0 )

ML

A-4 ( 0 )

SM

A-1-b ( 0 )

SM

NP

NP

NP

NV

NV

NV

60.7

36.1

17.9

31.0

19.3

14.5

0.0 - 23.0 ft. silty SAND few to little fine subangular gravels, SM, grayish brown, wet, loose to dense.

23.0 - 32.0 ft. sandy SILT, ML, light brown, wet, stiff to very stiff.

32.0 - 41.5 ft. silty SAND, SM, black-brown-gray, wet, medium dense.

Bottom of Hole at 41.5 ft.

8-15-20

9-6-5

3-2-18

9-10-15

3-6-5

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-6

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

0.0 - 9.0 ft. silty SAND minor amount of subangular to angular fine gravel, gray, wet, very loose to dense.

9.0 - 14.0 ft. silty SAND minor amount of subangular to angular fine gravel, gray, wet, dense.

14.0 - 15.5 ft. sandy SILT, dark gray, wet, very loose.

15.5 - 20.0 ft. silty SAND minor amount of angular fine gravel, gray, wet, dense.

2-1-1

12-17-20

16-18-16

3-14-21

Logged By: W. Hoon

Final By: M. Boyd

Symbol Depth Date

Weather Notes: Sunny, breezy, 66 degrees

Inclination from Horiz.: Vertical

Boring Began: 9/21/2015

Boring Completed:

Drilling Method(s):

Driller: Inberg-Miller Engineering

Drill Rig: Mobile B-57

Hammer Type:

3.0 ft

9/21/15

Night Work:

Total Depth: 91.5 ft

Ground Elevation: 6647.0 ft

Coordinates: N: E:

Location: ~76 ft N of Rock Creek Bridge N Abutment

Groundwater Levels:

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-8

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

A-1-b (0)

SMNPNV18.616.7

20.0 - 25.8 ft. silty SAND trace subangular to angular fine gravel, dark gray, wet, very dense.

25.8 - 27.5 ft. sandy SILT, brown, wet, dense.

27.5 - 33.0 ft. clayey SAND some angular fine gravel, brown, wet, very dense.

33.0 - 37.0 ft. clayey SAND, gray - brown, moist, dense.

37.0 - 43.0 ft. clayey SAND some angular gravel, gray, wet, very dense.

43.0 - 52.0 ft. clayey SAND trace fine subangular gravel, brown, wet, medium dense to very dense.

7-22-29

7-15-22

6-30-36

9-14-19

18-19-24

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-8

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

39.919.2

50:5"

43.0 - 52.0 ft. clayey SAND trace fine subangular gravel, brown, wet, medium dense to very dense.

52.0 - 68.0 ft. clayey SAND some subangular to angular fine gravel, gray to brown, wet, very dense.

68.0 - 71.5 ft. SILT.

3-4-18

8-26-35

9-28-50:5"

36-33-41

12-32-44

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-8

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

50:3"

50:4"

68.0 - 71.5 ft. SILT.

71.5 - 90.0 ft. silty SAND few fine subangular gravels, gray, wet, very dense.

clayey SAND few subangular gravels, brownish gray, wet, dense.

Bottom of Hole at 91.5 ft.

18-28-50:3"

4-11-20

30-42-50:4"

9-18-30

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-8

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

A-1-b (0)

SMNPNV13.614.113

0.0 - 2.0 ft. silty SAND some gravel, cobbles, gray, dry.

2.0 - 3.5 ft. sandy CLAY, black, moist.

3.5 - 8.0 ft. silty SAND few subangular to angular fine gravels, dark gray, wet, medium dense.

8.0 - 23.0 ft. silty SAND few angular to subrounded fine gravels, dark gray, wet, dense.

3-7-6

10-20-18

4-12-16

Logged By: W. Hoon

Final By: M. Boyd

Symbol Depth Date

Weather Notes: Sunny, breezy, 70's

Inclination from Horiz.: Vertical

Boring Began: 9/23/2015

Boring Completed:

Drilling Method(s):

Driller: Inberg-Miller Engineering

Drill Rig: Mobile B-57

Hammer Type:

3.5 ft

9/23/15

Night Work:

Total Depth: 90.0 ft

Ground Elevation: 6649.0 ft

Coordinates: N: E:

Location: ~78 ft S of Rock Creek Bridge S Abutment, E side of road Groundwater Levels:

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-9

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

A-4 (0)

MLNPNV56.825.0

>50

8.0 - 23.0 ft. silty SAND few angular to subrounded fine gravels, dark gray, wet, dense.

23.0 - 28.0 ft. sandy VOID, brownish gray, wet, medium dense.

28.0 - 33.0 ft. clayey SAND some angular fine gravel, brownish gray, wet, very dense.

33.0 - 37.0 ft. sandy SILT, gray to light brown, wet, dense.

37.0 - 43.0 ft. silty SAND, dark gray, wet, very dense.

43.0 - 58.0 ft. silty SAND few fine angular gravel, brownish gray, wet, medium dense to very dense.

6-20-34

5-5-6

29-38->50

14-17-27

9-15-45

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-9

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

53.721.7

50:4"

50:4"

43.0 - 58.0 ft. silty SAND few fine angular gravel, brownish gray, wet, medium dense to very dense.

58.0 - 63.0 ft. sandy CLAY, light brown, moist, very stiff.

63.0 - 68.0 ft. clayey SAND few fine angular gravels, brownish gray, wet, medium dense to very dense.

68.0 - 73.0 ft. CLAY, gray, moist, very stiff.

9-34-36

2-15-18

20-45-50:4"

16-19-12

39-34-50:4"

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-9

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

A-4 (0)

MLNPNV

85.3

73.5

27.7

27.0

50:4"

68.0 - 73.0 ft. CLAY, gray, moist, very stiff.

73.0 - 79.0 ft. SILT, gray, wet, medium dense.

79.0 - 90.0 ft. clayey SAND, gray, moist to wet, very dense.

Bottom of Hole at 90.0 ft.

9-12-12

2-5-7

23-20-23

21-18-50:4"

Project Number: 214-230

Elk Lake Road

Atterberg Limits

Boring No.: TH-9

Field Notes and

Other Lab Tests

Yeh and Associates, Inc.

E le va tio n

(f ee t)

D ep th (f ee t)

S am pl e

T yp e/ A dv an ce m en t M et ho d

C o n s u l t i n g E n g i n e e r s & S c i e n t i s t s

Project Name:

PAGE

AASHTO

& USCS

Classifi-cations

P la st ic ity In de x

Li qu id Li m it

F in es C on te nt

B O

R

IN

G L

O G

E

LK

L

A K

E R

O A

D .G

P J

Y

E H

A S

S O

C

IA

T E

S T

E M

P

LA

T E

.G D

T

LI

B

R A

R Y

.G

LB

2/

8/

D ry

D en si ty

(p cf

M oi st ur e C on te nt

P en et ra tio n

R es is ta nc e

Li th ol o gy

Material Description

Soil Samples

Blows

P ro je c t N o

D a te

/1

/2

G ra d a ti o n A tt e rb e rg W a te r

S o lu b le

C h lo ri d e

T H

-2

S P

T

.7

.3 N

V N

P N

P

A -4

M

L

T H

-2

.4 S

P T

.1

N V

N P

N P

A

-4

M L

T H

-2

.0

S P

T

.3

N V

N P

N P

A

-4

M L

T H

-2

.5

C m b S

P T

.2

A -6

C L

T H

-2

.0

S P

T

.3

.9

.7

.4 N

V N

P N

P

A -4

M

L

T H

-2 .5 m b S

P T

.0

A -7

-6

C

L

T H

-2

.0

S P

T

.8

.8

.6

.6

A

-4

C L

-M L

T H

-6

S P

T

.6

.1

.9

N

V N

P N

P

A -1

-b

S M

T H

-6

C o m b

T

.7

.5

.3

.2

N V

N P

N P

A

-1 -b

S

M

T H

-6 m b S

P T

.0

.6

.7

.7

N V

N P

N P

A

-4

M L

T H

-6

.0

S P

T

.3

.6

.3

.1 N

V N

P N

P

A -4

S

M

T H

-6

.0

S P

T

.5

.1

.9 N

V N

P N

P

A -1

-b

S M

T H

-8

.0

S P

T

.7

.1

.3

.6

N V

N P

N P

A

-1 -b

O

S

M

T H

-8

.0

S P

T

.2

T H

-9

.0 S

P T

.1

.7

.7

.6

A -1

-B

S M

T H

-9

S

P T

.0

.9

.3

.8

N V

N P

N P

A

-4

M L

N a tu ra l

M o is tu re n te n t

U S

C S

A A

S H

T O

P I

W a te r

S o lu le u lf a te e s is ti v it y h m .c m

N a tu ra l ry n s

(p c f)

P L

Y E

H

A S

S O

C

IA

T E

S

IN

C

M T

B e a v e rh e a d

E lk

L a k e R o a d S tr u c tu re s

S u m m a ry o f

L a b o ra to ry T e s t R e s u lt s F ro m

W F

L H

D M a te ri a ls T e s ti n g L a b o ra to ry

C L

A S

S

IF

IC

A

T

IO

N

S a n d

F in e s

L L

S w e ll

C o n s li-ti o n p H

-2

P ro je c t N a m e

S a m p le L o c a ti o n

S a m p

T p e

B o ri g

D e p th ft

G ra v e l

R e v

/0

P a g e o f ro je c t N o

D a te

/1

/2

G ra d a ti o n A tt e rb e rg W a te r

S o lu b le

C h lo ri d e

T H

-9

S

P T

.7

.7

T H

-9

.0

S P

T

.7

.2

T H

-9

.0

S P

T

.0

N V

N P

N P

A

-4

M L

P L

P I

A A

S H

T O

U S

C S

R e s is ti v h m .c m

S w e ll

C o n s li-ti o n

C L

A S

S

IF

IC

A

T

IO

N

B o ri g

D e p th ft

S a m p

T p e

G ra v e l

S a

F in e s

L L

Y E

H

A S

S O

C

IA

T E

S

IN

C

S u m m a ry o f

L a b o ra to ry T e s t R e s u lt s F ro m

W F

L H

D M a te ri a ls T e s ti n g L a b o ra to ry

-2

P ro je c t N a m e

M T

B e a v e rh e a d

E lk

L a k e R o a d S tr u c tu re s

S a m p le L o c a ti o n N a tu ra l

M o is tu re n te n t

N a tu ra l ry n s

(p c f) p H

W a te r

S o lu u lf te e v

/0

P a g e o f

Attachment 2

November 6, 2015 Meeting Minutes & Owner’s Risk Approvals

MT Beaverhead 273(1) Elk Lake Road

Bridge Risk Meeting Minutes November 6, 2015

Attendees:

Conference Call:

Ritter, Janice (FHWA) Oltmann, Benjamin (FHWA) <Benjamin.Oltmann@dot.gov>; West, Bill <bill_west@fws.gov> (bill_west@fws.gov ); jcarpita@beaverheadcounty.org, David

Farmer

Goal of Meeting:

Understand the proposed design

Understand the risks (and ask questions)

Document concurrence of accepting the risks.

Proposed design:

Spanning Red Rocks Creek and Elks Springs Creek with modular bridges founded on shallow foundations.

The county wanted the bridge design to consider (dependent on estimated costs):

o The length of the bridge to be determined to be outside the effects of lateral scour based on stream velocity and volumes.

o Protect the abutment with riprap or masonry. Masonry may be a more reasonable option.

Avoiding impacts to stream.

Abutments would be constructed outside the creeks.

Existing drainage structures would be removed, and modular bridge would be placed.

Considerations to the design:

o Provide a stiff L\D for deflections (WFL checked AASHTO LRFD for deflection criteria, and typically L/800 is used for vehicular bridges without pedestrian traffic, L/1000 used when pedestrians are present on the bridge) o Provide for extra gravel on the bridge as a design load that could be added due to maintenance and grading operations in the future. This will ensure the bridge is designed for future anticipated loads.

Risks:

1. Settlement (Elk Springs Creek and Red Rocks Creek)

a. Red Rocks Creek has some potential for minor settlement, but the risk is less.

b. Elks Springs Creek drilling showed soft soils. Potentially adding extra embankment to Elk Springs Creek to allow extra settlement.

c. If Elks Springs Creek area was surcharged, the road could not be used until the surcharge was complete.

Additional investigational costs would be needed to calculate load and timing.

d. County recommended adding additional gravel fill to the design criteria for the bridge (allowing for future maintenance operations that may add depth to the gravel surface).. Embankment and structure load (dead and live) will need to be considered in the design of the abutments.

2. Scour protection (Elk Springs Creek and Red Rocks Creek)

a. The costs savings of not providing riprap and accepting the stream migration risk with the longer spanning bridge was explained, but the county and refuge did not want to accept this risk. If the lateral stream migration & abutment scour has a potential to expose the abutment the County/Refuge are willing to accept either: 1) reinforced soil foundation (no masonry block protecting the geotextile) with rip-rap protection in front of the abutment, or 2) Typical GRS foundation (with masonry blocks) founded below the design scour depth without any riprap protection.

b. The county said the costs of replacing the abutment or repairing the failed bridge was too much of a risk to accept.

c. Consider raising the bridge and increasing the free board if the anticipated settlement is greater than 3”.

The county does not usually take settlement into account for freeboard as it is normally minimal and within the range of the anticipated accuracy of debris sizing that would block the waterway.

3. Liquefaction (Elk Springs Creek)

a. Red Rocks Creek drilling to 90 feet showed no liquefaction mitigation was needed for Red Rocks Creek.

mailto:bill_west@fws.gov mailto:jcarpita@beaverheadcounty.org

From: Jim Carpita <jcarpita@beaverheadcounty.org>

Sent: Tuesday, November 10, 2015 8:22 AM

To: Ritter, Janice (FHWA); bill_west@fws.gov

Cc: David_M_Farmer@fws.gov; james_graves@fws.gov; dolson07@fs.fed.us

Subject:RE: Risk Approval for Elk Lake Road

Janice, Beaverhead County is in concurrence with both your e-mail below and the minutes attached thereto.

Thanks you for the opportunity to comment on and participate in the project design and implementation.

Sincerely, Jim

James B. Carpita, P.E.

Beaverhead County Engineer

2 South Pacific Street, Ste #12

Dillon, MT 59725

(406) 683-3724 jcarpita@beaverheadcounty.org

From: Janice.Ritter@dot.gov [mailto:Janice.Ritter@dot.gov]

Sent: Monday, November 09, 2015 5:20 PM

To: jcarpita@beaverheadcounty.org; bill_west@fws.gov

Subject: Risk Approval for Elk Lake Road

Please provide Approval or Comments to the risks summarized below and the Meeting Minutes discussing the risk evaluations for our records.

Proposed design:

* Spanning Red Rocks Creek and Elks Springs Creek with pre-fabricated modular bridges founded on shallow GRS (Geosynthetic Reinforced Soil) foundations to avoid impacts to the streams.

* Abutments would be constructed outside the creeks.

* Existing drainage structures would be removed, and modular bridge would be placed.

a. Red Rocks Creek has some potential for minor settlement, but the risk is less.

b. Taking in various design considerations, some settlement is allowed and anticipated at the Elk Springs Creek since the proposed roadway surface is aggregate. Potential settlement will be evaluated with recommendations.

2. Scour protection (Elk Springs Creek and Red Rocks Creek)

a. County and Refuge is not willing to accept the risk of stream migration. Either bridge length is design with lateral scour or provides protection for abutments.

3. Liquefaction (Elk Springs Creek)

a. Red Rocks Creek drilling to 90 feet showed no liquefaction mitigation was needed for

Red Rocks Creek.

b. Additional drilling for liquefaction assessment was removed from Elk Springs Creek with

County concurrence. County and USFWS provided concurrence to accept the seismic risk of Elk Springs Creek. The design proposed is a practical design that does not follow

AASHTO guidelines for seismic events.

c. Received email concurrence from County on October 27, 2015

d. Received verbal concurrence from Jim Graves (USFWS) on October 28, 2015.

4. Winter Construction

a. In case of bad weather, County and Refuge both agreed to provide snow removal to access construction site from Lakeview, MT to the project. If the County was not available, the Refuge said they would have resources to plow.

b. County and Refuge both agreed to extra construction costs for two seasons. Original costs were based on work being done in one season with grading done first due to environmental restrictions in the riparian areas.

c. Winter Construction is dependent on available funding. County’s recommended to do structures before roadway surfacing. Assume both structures can be completed between Thanksgiving and Christimas.

b. Additional drilling for liquefaction assessment was removed from Elk Springs Creek with County concurrence. County and USFWS provided concurrence to accept the seismic risk of Elk Springs Creek.

The design proposed is a practical design that does not follow AASHTO guidelines for seismic events.

c. Received email concurrence from County on October 27, 2105

d. Received verbal concurrence from Jim Graves (USFWS) on October 28, 2105.

4. Winter Construction

a. In case of bad weather, County and Refuge both agreed to provide snow removal to access construction site. If the County was not available, the Refuge said they would have resources to plow.

b. County and Refuge both agreed to extra construction costs for two seasons. Original costs were based on work being done in one season with grading done first due to environmental restrictions in the riparian areas.

c. Construction for both bridges could be done in three weeks beginning after Thanksgiving.

d. Refuge said there is usually a snowfall around Veterans Day. The weather is usually milder between

Thanksgiving and Christmas. There is usually more snowfall after Christmas.

e. County provides snow removal to Lakeview. It can extend its snow removal to the project if necessary.

Additional Information:

The county is providing similar bridges on the Big Sheep project that is a Reimbursable Agreement with Matt Joerin. Specifications have been submitted to Joerin. County said they would share the bid tabs when they open on Dec 16th. Country recommends leaving exact modular bridge configuration up to the manufacturer (typical steel girder, folded plate, or other options would be acceptable): provide depth of structure, span length and other general requirements but have the fabricator design the bridge and provide shop drawings during construction.

Document concurrence of accepting the risks:

Please review and comment on the minutes.

Please comment or approve the email noting risks for project records.

From: Jim Carpita <jcarpita@beaverheadcounty.org>

Sent: Tuesday, November 10, 2015 8:22 AM

To: Ritter, Janice (FHWA); bill_west@fws.gov

Subject:RE: Risk Approval for Elk Lake Road

Janice, Beaverhead County is in concurrence with both your e-mail below and the minutes attached thereto.

Thanks you for the opportunity to comment on and participate in the project design and implementation.

Sincerely, Jim

James B. Carpita, P.E.

Beaverhead County Engineer

2 South Pacific Street, Ste #12

Dillon, MT 59725

(406) 683-3724 jcarpita@beaverheadcounty.org

From: Janice.Ritter@dot.gov [mailto:Janice.Ritter@dot.gov]

Sent: Monday, November 09, 2015 5:20 PM

To: jcarpita@beaverheadcounty.org; bill_west@fws.gov

Subject: Risk Approval for Elk Lake Road

Please provide Approval or Comments to the risks summarized below and the Meeting Minutes discussing the risk evaluations for our records.

Proposed design:

* Spanning Red Rocks Creek and Elks Springs Creek with pre-fabricated modular bridges founded on shallow GRS (Geosynthetic Reinforced Soil) foundations to avoid impacts to the streams.

* Abutments would be constructed outside the creeks.

* Existing drainage structures would be removed, and modular bridge would be placed.

a. Red Rocks Creek has some potential for minor settlement, but the risk is less.

b. Taking in various design considerations, some settlement is allowed and anticipated at the Elk Springs Creek since the proposed roadway surface is aggregate. Potential settlement will be evaluated with recommendations.

2. Scour protection (Elk Springs Creek and Red Rocks Creek)

a. County and Refuge is not willing to accept the risk of stream migration. Either bridge length is design with lateral scour or provides protection for abutments.

3. Liquefaction (Elk Springs Creek)

a. Red Rocks Creek drilling to 90 feet showed no liquefaction mitigation was needed for

Red Rocks Creek.

b. Additional drilling for liquefaction assessment was removed from Elk Springs Creek with

County concurrence. County and USFWS provided concurrence to accept the seismic risk of Elk Springs Creek. The design proposed is a practical design that does not follow

AASHTO guidelines for seismic events.

c. Received email concurrence from County on October 27, 2015

d. Received verbal concurrence from Jim Graves (USFWS) on October 28, 2015.

4. Winter Construction

a. In case of bad weather, County and Refuge both agreed to provide snow removal to access construction site from Lakeview, MT to the project. If the County was not available, the Refuge said they would have resources to plow.

b. County and Refuge both agreed to extra construction costs for two seasons. Original costs were based on work being done in one season with grading done first due to environmental restrictions in the riparian areas.

c. Winter Construction is dependent on available funding. County’s recommended to do structures before roadway surfacing. Assume both structures can be completed between Thanksgiving and Christimas.