Memo UT FLAP 218(1) Sheep Creek Road_FINAL.pdf

To: Braden Peters, Project Manager, CFLHD, Lakewood CO

From: Devin T. Dixon, Geotechnical Engineer, CFLHD, Lakewood CO

Through: Marilyn D. Dodson, Lead Geotechnical Engineer CFLHD, Lakewood CO

Subject: Evaluations and Recommendations for the Sheep Creek Geologic Loop, Ashley National Forest, Daggett County, Utah, UT FLAP 218(1)

1 PROJECT BACKGROUND INFORMATION

This geotechnical memorandum presents the results of the geotechnical engineering assessment and provides recommendations for the reconstruction and rehabilitation work to be performed on the 2.25-mile long section along Forest Road 10218 (Sheep Creek Geologic Loop). The project is located in the Ashley National Forest south of Manila, Utah. The geotechnical features that were examined during this visit, and will be addressed in this memo, included box culvert foundation material, existing rock cuts, the condition of existing gabion structures, and potential subexcavation areas.

The project begins at Station 10+00 at a cattle guard at the U.S. Forest Service (USFS) property line at an elevation of 6,540 feet, approximately 3.2 miles southwest of the northern intersection with Utah State Highway 44. The route continues north and east towards Utah State Highway 44, and terminates approximately 0.9 miles west of the intersection at a second cattle guard adjacent to an existing timber deck bridge at the USFS property line at an approximate elevation of 6,270 feet. The route is generally located within undeveloped scrubland adjacent to the Sheep Creek, and serves as the access road to recreational facilities and private residences. A site map is presented on Figure 1.

Recreational facilities accessed by this route include a picnic area, camping area, and cabins. In addition, the route itself is listed as a scenic byway interpretive site. The overall objective of this project is to rehabilitate the roadway conditions and to improve safety for the recreating public.

The existing route is characterized as a narrow two-lane thoroughfare with predominantly gentle grades and narrow roadway widths. The roadway traverses the bottom of a canyon with a live

Technical Memorandum

Date: October 17, 2019 stream adjacent to the roadway at various locations. Most of the existing roadway cuts are excavated in either colluvial/residual soils or Mesozoic sedimentary deposits. A combination of cut/fill and through embankment construction provides a 16- to 18-foot wide paved or gravel surfaced road with varying shoulder and traveled way widths. The existing road presents poor driving conditions and costly maintenance.

To improve the roadway surface conditions and improve safety for the traveling public, the roadway will be rehabilitated and paved with asphaltic cement concrete. The road will be widened to provide a consistent 20-foot paved width with no shoulders. Work will include rehabilitation and addition of roadway base followed by construction of a paved surface. Guardrail and cattle guards will be replaced as needed. Minor cut and fill is anticipated to provide a consistent roadway width. To minimize impacts to the adjacent stream, widening sections are anticipated to prioritize cut slopes over fill slopes.

Figure 1:- Project Location Map.

2 REGIONAL GEOLOGY

The project is located within the Uinta Mountain Range, in the Middle Rocky Mountains physiographic province. The project area is underlain by sedimentary deposits of Mesozoic Age (approximately 65 million to 250 million years old) and recent alluvial, colluvial, and talus deposits. The principal mapped surficial deposits are Quaternary alluvium, colluvium, alluvial fan, and talus deposits (Sprinkel, 2006). Limited portions of the western end of the alignment are mapped as underlain directly by Mesozoic sedimentary units including the Triassic Chinle Formation, Moenkopi Formation, and Dinwoody Formation; Pennsylvanian Park City and Phosporia Formations; and the Pennsylvania and Permian Weber Sandstone. Additional units mapped adjacent to the alignment include the Cretaceous and Jurassic Cedar Mountain and

Sheep Creek Geologic Loop

Morrison Formations; Jurassic Stump Formation, Entrada Sandstone, and Carmel Formation; and Jurassic and Triassic Nugget Sandstone. Published descriptions of these units are summarized in Table 1 and a regional geologic map can be found in Figure 2. In general, the Mesozoic strata consist of marine-deposited shale, claystone, siltstone, sandstone, and limestone. Much of the strata along the project alignment dips steeply towards the north (40° to 60°), causing transitions between units to occur over a relatively short horizontal distance and contribute to highly variable geological conditions. The Morrison Formation is noted to contain bentonite beds, while the Carmel and Moenkopi are noted to contain gypsum.

Table 1:- Mapped Geologic Units in the Project Vicinity

MAP

SYMBOL NAME AND DESCRIPTION

Qac MIXED ALLUVIUM AND COLLUVIUM (HOLOCENE AND PLEISTOCENE) - Unconsolidated, poorly to moderately sorted mud, silt, sand, and gravel along channels of Green River tributaries, smaller streams, and intermittent streams; on Mancos Shale, unit is mostly reworked mud; less than 10 m thick.

Qmt

TALUS DEPOSITS (HOLOCENE AND PLEISTOCENE) - Unconsolidated and unstratified angular rock fragments on and at the base of steep slopes and cliffs; many larger deposits include pro-talus ramparts and are likely Pleistocene in age; smaller deposits in which colluvium locally is significant are likely Holocene in age;

less than 5 m thick.

Qaf YOUNGEST ALLUVIAL FAN DEPOSITS (HOLOCENE) - Unconsolidated, poorly-sorted boulder, gravel, sand, and silt; less than 30 m thick.

KJcm

CEDAR MOUNTAIN FM (LOWER CRETACEOUS) – Purple, gray, and greenish-gray mudstone, siltstone, minor sandstone and limestone; contains calcrete beds that weather out as carbonate nodules; 0-60 m thick.

MORRISON FORMATION (UPPER JURASSIC) – Upper, Brushy Basin Member consists of soft, banded, variegated (light-gray, olive-gray, red, and light-purple) shale, claystone, siltstone, and minor cross-bedded sandstone, conglomerate, and bentonite; lower, Salt Wash Member consists of resistant, light-gray to white cross-bedded sandstone; Salt Wash Member may not be present in the Flaming Gorge area; dinosaur remains are preserved in Salt Wash Member at Dinosaur National Monument south of quadrangle; 90-287 m thick.

Jsc

STUMP FORMATION (UPPER JURASSIC) - Upper, Redwater Member is greenish-gray and light-green slope-forming shale with glauconitic, fossiliferous (belemnites and bivalves) sandstone and limestone; lower Curtis Member is resistant, light-gray to greenish-gray, cross-bedded, glauconitic sandstone; Curtis Member is thin or locally missing in this quadrangle because of erosion prior to deposition of Redwater Member along J-4 unconformity of Pipiringos and O’Sullivan (1978); palynomorph assemblage from base of Curtis Member indicates an Oxfordian age (Wilcox and Currie, 2006; Brian Currie, Miami University (Ohio), verbal communication, March 15, 2006); 40-82 m total thickness.

ENTRADA SANDSTONE (MIDDLE JURASSIC) - Upper part reddish-brown siltstone and fine-grained sandstone and lower part light-gray, pink, and light-brown sandstone; lower sandstone is resistant to erosion and forms cliffs and ridges; 30-75 m thick.

CARMEL FORMATION (MIDDLE JURASSIC) - Medium- to dark-red, green, and gray sandy shale, sandstone, siltstone, limestone and gypsum; upper part is mostly slope-forming red shale, siltstone, and sandstone underlain by a middle gypsiferous unit; lower part is mostly ledge-forming limestone, which is commonly oolitic and fossiliferous; may contain one or more biotite-rich ash layers; 30-144 m thick.

JTRn

NUGGET SANDSTONE (LOWER JURASSIC AND UPPER TRIASSIC) - Pink, light-gray, and light-brown, resistant, massive-weathering, large-scale cross-bedded sandstone; locally contains carbonate lenses (playa) and fluvial lenses (wadi) near top; forms cliffs and ridges; vertebrate tracks of Jurassic age preserved in a fluvial lens near the top of Nugget near Red Fleet Resevoir (Hamblin and others, 2000) and casts of vertebrate tracks of Late Triassic age are preserved on underside of base of Nugget south of quadrangle near Dinosaur National Monument (Lockley and others, 1992); 200-315 m thick.

TRc

CHINLE FORMATION (UPPER TRIASSIC) - Purplish-red, purple, light-gray, greenish-gray, light-green, ripple-marked siltstone, sandstone, claystone, shale, and conglomerate that locally contains abundant petrified wood; generally forms slopes; upper 26-36 m is light-reddish-brown planar laminated sandstone, cross-bedded sandstone, siltstone, and variegated mudstone that is correlated with Bell Springs Members of Nugget Sandstone by Jensen and Kowallis (2005); base is resistant conglomerate unit named the Gartra Member; 40-140 m thick.

MAP

SYMBOL NAME AND DESCRIPTION

TRm MOENKOPI FORMATION (LOWER TRIASSIC) - Medium- to dark-red, reddish-brown, green, and gray, ripple-marked siltstone, fine-grained sandstone, and shale with gypsum and limestone beds; mostly soft, slope-forming unit; 160-340 m thick.

TRd

DINWOODY FORMATION (LOWER TRIASSIC) - Light-gray, greenish-gray, light-brown, and brown, thin-bedded, ripple-marked shale, siltstone, and sandstone with minor amounts of limestone; mostly soft, slope-forming unit along south flank of Uinta Mountains in Ashley and Brush Creek drainages; Dinwoody Formation thins west of Ashley Creek drainage and is represented only by gypsum beds, and is not present in and west of Dry Creek drainage; 0-160+ m thick; tectonically thickened locally.

Pp

FRANSON MEMBER OF PARK CITY FORMATION - Gray, thick- to thin-bedded, cherty limestone and dolomite interbedded with brownish-gray sandstone and red to ochre shale; generally resistant and forms ledges and cliffs.

MEADE PEAK PHOSPHATIC SHALE MEMBER OF THE PHOSPHORIA FORMATION - Slope-forming, dark-gray phosphatic shale with interbeds of sandstone and limestone.

GRANDEUR MEMBER OF PARK CITY FORMATION - Light-gray to light-brownish-gray sandstone, dolomite, and limestone; generally resistant and forms ledges and cliffs.

PlPw WEBER SANDSTONE (LOWER PERMIAN TO MIDDLE PENNSYLVANIAN) - Light-gray to yellowish-gray, very thick bedded sandstone with interbeds of limestone in the lower part; highly cross-bedded sandstone in the upper part; forms steep cliffs and ridges; 186-472 m thick.

Figure 2:- Regional Geologic Map.

It should be noted that although much of the project is underlain by formational units, some of these materials are not classified as rock for engineering purposes. These units are relatively young and have been subject to minimum consolidation and cementation. These materials are typically considered stiff to very stiff or dense soils in terms of strength and engineering behavior.

No hazardous faults are mapped within 40 miles of the project area (U.S. Geological Survey, 2017). Non-seismic source faults are summarized on Table 2. These faults have a directional trend of NW-SE and have shaped the uplift and variability of the regional geological units as shown in Figure 2 above.

Sheep Creek Geologic Loop Project Area

Table 2:- Summary of Non-Seismic Quaternary Faults

FAULT NAME

DISTANCE TO

PROJECT

SLIP

RATE LENGTH AGE

(miles) (in/yr) (miles) (years) Faults on north flank of Phil Pico Mountain 7.52 < 0.008 2.49 < 130,000 Diamond Gulch Faults 23.67 < 0.008 12.43 < 1,600,000 Pot Creek Faults 28.58 < 0.008 8.08 < 1,600,000 Hogsback Fault, southern section 43.68 < 0.008 23.61 < 750,000

2.1 Seismic Design Parameters

The American Association of State Highway and Transportation Officials (AASHTO) criteria for Recommended seismic response parameters are based on AASHTO LRFD Bridge Design Specifications, 7th Edition, 2014, and represents horizontal peak ground acceleration (PGA) with 7 percent probability of exceedance in 75 years (approximate 1000-year return period). The 1000-year return period uniform hazard spectrum for NFSR 333 (35.21965º N latitude and -106.48096º W longitudes) was obtained in accordance with the AASHTO ground motion maps. The site was classified as “Class D” according to site class definitions specified in Table 3.10.3.1-1 of AASHTO based on assumed relatively soft (N < 50) sedimentary bedrock in the area. The recommended spectral acceleration coefficient values for probabilistic design are summarized in the following table.

Table 3:- Summary of Seismic Parameters Corrected for Site Class D

Peak Seismic Ground Acceleration Coefficient, (As) 0.158

Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDS) 0.320

Horizontal Response Spectral Acceleration at Period of 1.0 sec (SD1) 0.166

Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 1.6

Site Factor at Short-Period of Acceleration Spectrum, (Fa) 1.6

Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 2.4

Based on the long acceleration coefficient SD1 value of 0.166, the site is assigned to seismic hazard Zone 2 in accordance with Table 3.10.6-1 of AASHTO. Based on this classification, seismic loading may impact design of concrete structures (culverts).

2.2 Geologic Hazards

The Sheep Creek Geologic Loop is constructed in a narrow canyon on a sequence of steeply dipping sedimentary units including mudstone and claystone. Sedimentary units containing significant proportions of clay material, especially bentonite, are frequently subject to volume change (swell) upon wetting. Gypsum and gypsiferous deposits can be subject to solution weathering. Salt water (marine) sediments, and gypsum, may cause corrosion. Weathering rates and patterns of the sedimentary strata present at the site is highly variable.

This combination of natural conditions leads to the following potential geologic hazards: flash floods, debris flows, rockfall, erodible soils, swell/heave of soil/bedrock, and solution weathering and collapse. Evidence of swell/heave and solution weathering were not observed during the site reconnaissance. Hazards related to flash floods and debris flows may be mitigated by locating the roadway above the anticipated flood levels. Erodibility of soil should be considered in the size and layout of surface drainage features. Differential erosion of the sedimentary units contributes to the rockfall hazard along the project alignment, and can be temporarily mitigated by scaling of loose and unstable materials from slopes adjacent to the roadway. This concern can also be addressed by ensuring the roadside ditches have appropriate check dams to control water velocity and erosive capacity. Figure 3 below shows a typical roadway section of Sheep Creek Loop.

Figure 3:- Typical Roadway Section.

3 FIELD EVALUATION

A subsurface investigation targeting the proposed improvements was not performed for this scope of work. Observations of surficial conditions and reconnaissance mapping was performed in conjunction with the 30 percent design review field visit on June 25, 2019. The geotechnical features that were examined during this visit included box culvert foundation material, existing rock cuts, the condition of existing gabion structures, and potential subexcavation areas.

3.1 Box Culvert Station 28+98 (Lodgepole Creek)

Hydrologic and hydraulic analyses were conducted for the Sheep Creek Loop project using the 25-year flood for the design frequency and HY-8 for the hydraulic performance. The existing culverts along the project corridor will be replaced and outlet protection will be required. The major drainage crossing the route at STA 28+98 (Lodgepole Creek) is still pending final layout and design at the time of this writing. According to the CFLHD hydraulics engineer, the proposed culvert type and size will most likely be either two or three four-foot by eight-foot precast concrete box culverts with left and right headwalls. The foundation material, as seen during the 30 percent site visit, appears to be consistent with the regional geology and consists mainly of colluvial, alluvial, and talus deposits. More specifically, based on visual observations, the surficial and overburden materials are presumed to be fine to medium grained, medium dense to dense, silty or clayey sand with gravel, cobbles, and boulders observed to be up to 28 inches. Figure 4 below shows the conditions at the existing culvert outlet at STA 28+98.

Figure 4:- Outlet of Existing 2x 48-Inch CMP at STA 28+98 RT.

3.2 Existing Rock Cut Evaluation

[STA 19+00 to STA 24+00 LT] & [STA 67+50 to STA 71+00 LT]

Two locations along the proposed alignment of the Sheep Creek Geologic Loop were determined to have the potential for rockfall. These locations were between STA 19+00 to STA 24+00 LT and STA 67+50 to STA 71+00 LT. The slopes along these two areas are composed of sedimentary rock beds of varying resistance to erosion with highly resistant beds (generally sandstone or limestone) tending to form cliffs above slopes composed of weaker beds (generally shale and mudstone). The combination of these vulnerable geologic units with the steep gradient of the slopes and seasonal rainfall events increases the risk associated with rockfall hazards.

Rockfall was discussed with the Road Maintenance Supervisor of Daggett County, James Olsen, during the 30 percent site visit on June 25, 2019. From his experience related to the area between STA 19+00 to STA 24+00 LT he expressed that boulders of observed sizes between roughly 2 to 4 ½ feet in diameter have infrequently rolled down the lower, vegetated areas of these slopes during or after severe weather events. These fallen rocks, as he observed, mostly ended their trajectory in the roughly 3-foot ditch adjacent to the roadway. However, Mr. Olsen did mention that on rare occasions rocks have traveled to roughly the centerline of the roadway at this location. Similar observations were made at the rockfall area between STA 67+50 to STA 71+00 LT. Figures 5 and 6 below show the current condition of the two potential rockfall locations. As can be seen in these Figures, the shape of the rock tends to be more plate-like as opposed to rounded, which encourages sliding action along the alluvial surface as opposed to a tumbling movement generally associated with rounded rocks.

Figure 5:- Cliff Near STA 19+00 to STA 24+00 LT.

Figure 6:- Slope Near STA 67+50 to STA 71+00 LT.

3.3 Cut & Fill Slope Evaluation STA 67+51 LT & STA 71+17 LT

The roadway designer has indicated two locations where minor cuts into the existing slopes will be needed to accommodate the ditch width and back slope parameters related to two proposed culvert inlets. Both of these locations are within or near the second of the aforementioned rockfall hazard zones discussed in the previous section; however, the cut sections are minimal. Table 4 below shows the approximate dimensions of the proposed cut slopes as discussed with the designer. If weaker layers are encountered during excavation, however, then it may be necessary to consider rock embankments or rockeries as options at select locations.

Table 4:- Approximate Dimensions of Cuts for Culvert Inlets

STATION OFFSET

HEIGHT OF

DITCH

BACKSLOPE

(FT.)

CUTSLOPE

RATIO

HORIZONTAL DEPTH

INTO CUT FROM

EXISTING DITCH

LINE (FT.)

VERTICAL DITCH

LINE DEPTH

BELOW EXISTING

DITCH LINE (FT.)

67+51 LT 12.2 1:1 5.4 2.7

71+17 LT 9.6 1:1 7.8 3

3.4 Existing Gabions [STA 34+39 to STA 35+56 RT] & [STA 68+45 to STA 69+54 RT]

Two gabion walls exist to armor the embankment from stream erosion and provide lateral support at STA 34+39 to STA 35+56 RT and STA 68+45 to STA 69+54 RT. The exposed heights of these walls are estimated to be roughly 10 feet and 6 ½ feet at STA 34+39 RT and STA 68+45 RT, respectively, and it can be assumed that at least one row is partially or fully embedded below the toe of the wall. Bulging of the top row of the gabions and an inconsistent setback and batter angle were observed at both of the walls. However, the gabions appear to be performing satisfactorily and the roadway improvements are anticipated to avoid and not disturb these structures. According to the maintenance supervisor, the gabions are between 20 to 25 years old. Figures 7 and 8 below show the existing gabion walls. As can be shown in Figure 8, boulders were placed at the toe of the gabions to provide additional resistance against sliding and scour.

Figure 7:- Gabion Wall from STA 34+39 to STA 35+56 RT.

Figure 8:- Gabion Wall from STA 68+45 to STA 69+54 RT.

3.5 Subexcavation Areas

Select locations of subgrade spot repairs were originally discussed in a previous scoping report dated January 2017. During this scoping trip, areas of saturated subgrade and minor embankment distress were observed between STA 34+00 and 52+00. A combination of raising the grade, subexcavation, underdrain, and improving surface drainage were considered. However, during the 30 percent scoping trip in June 2019, the idea of simply specifying a deeper aggregate base section through the problematic areas was suggested by the pavements engineer. This topic will be covered in greater detail in the pavements report/memo. Figure 9 below shows one area of pavement distress likely caused by the saturated subgrade.

Figure 9:- Depression in Roadway Surface Near STA 65+00 (~2.4 inches in diameter).

3.6 Shrink/Swell Recommendations

It is estimated that these soils will have a 5-10% shrink percentage, corresponding to a shrink/swell factor of 0.95-0.90. The recommended shrink/swell factor is based on a combination of standard tabled values for common materials in the FLH Technical Guidance Manual (2006) and experience with other CFLHD projects in similar materials.

4 ANALYSIS & RECOMMENDATIONS

4.1 Box Culvert Bearing Capacity Calculations

A soil unit weight (γ) of 125 pounds per cubic foot, internal friction angle (φ) of 30, and cohesion intercept (c) of 0 are the estimated design values for the box culvert foundation. These properties were estimated based on typical design values shown in the NAVFAC Design Manual 7.01. This material is expected to be underlain by a sequence of sedimentary rocks including shale, mudstone, siltstone, sandstone, conglomerate, and limestone. Based on this knowledge of the geologic conditions near the structure site, the presumptive bearing resistance for this material type can be estimated to be between 4,000-8,000 psf with a recommended value of use of 5,000 psf according to Table C10.6.2.6.1-1 of AASHTO LRFD Bridge Design Specifications, 7th Edition, 2014. The bearing resistance values presented in this table are based on a maximum settlement of one inch and only apply at the service limit state (resistance factor of 1.0). For strength limit state, a resistance factor of 0.45 should be applied. It is recommended that the footing base be constructed below the depth of frost potential, which is estimated at approximately 30 inches according to the state average frost depth and local practices.

Active and at-rest lateral earth pressures of properly placed and compacted select granular backfill and unclassified borrow above the water table are presented in Table 5 below. The values are unfactored loads and assume that the surface of the soil slope behind the wingwalls is horizontal.

Unbalanced water behind a wall adds hydrostatic pressure and should be avoided by using structural backfill (FP-14, Section 704.04) against backfilled structures and assuring a free draining gravity outlet for captured water. Structural backfill should be used with the active zone, located within a 1V:1H plane projected from the back of the bottommost structural element.

Unclassified borrow (FP-14, Section 704.06) may be used in the retained zone beyond the active zone behind the wing walls. Below the mean stream level, the walls must also be designed for the full hydrostatic condition. Wing-wall design should consider surcharge loading due to traffic and construction equipment, and any sloping backfill.

Table 5:- Static Lateral Earth Pressures Concrete Box Culverts

Backfill Type Assumed Backfill Parameters

Rankine Earth Pressure Case

Unfactored Equivalent Fluid

Pressure (pcf)

Structural Backfill c = 0 psf

ᵠ = 34 deg.

γ = 125 pcf

Active 35

At-Rest 55

Unclassified Borrow c = 0 psf

ᵠ = 30 deg.

γ = 125 pcf

Active 42

At-Rest 63

Lateral loads imposed upon structures may be resisted by the development of friction between the base of the footings and the foundation soils. A nominal friction factor of 0.62 (based on assumed foundation friction angle of 30 degrees) may be used in design for cast-in-place footings established on silty or clayey sand and gravel. A resistance friction factor of 0.8 should be applied in the design for sliding.

Because the box culverts are located in a natural drainage channels, depending on the construction season, the surface and groundwater levels will vary but should be expected in the footing excavation and may requiring dewatering and/or water diversion. All foundation preparations should be in accordance with Section 209.

4.2 Cut & Fill Slope Recommendations

In general, non-saturated coarse-grained granular soil slopes can be constructed at a safe slope ratio of 1V:1.5H or flatter; non-saturated slopes composed of fine-grained, cohesive soils can be constructed at a safe slope ratio of 1V:2H; weathered bedrock slopes can be constructed at a slope ratio of 2V:1H or flatter depending on fracturing and degree of weathering; and combination soil and rock slopes can be cut at 1V:1H. Based on the observed conditions at the existing cut faces of the two sites discussed in Section 3.3, a slope ratio of 1V:1H can be used. Minor cuts into the opposite slope could be performed depending on the condition of the proposed cut slope to avoid sliver fills. Rockfall hazards need to be considered when performing these cuts and the geotechnical engineer should be contacted prior to excavation. Minor rock scaling, or slope reconditioning, should be incorporated with the construction of these two slopes. It should be noted, however, that scaling is a maintenance issue and not a long-term solution for rocks collecting in the ditches. Good maintenance practices are needed along the route and there will not be a reduced risk of rockfall as a results of this project work. Areas of observed springs and seeps encountered during construction may require flattening or additional support and should be evaluated by the CFLHD geotechnical engineer on a case by case basis.

The designer has not indicated significant fill slope sections along the route. Sliver fills, fills created on steep side slopes with narrow bench widths, should be avoided because they are prone to differential settlement with a significant horizontal component of movement (Rogers, 1992).

Continued raveling and destabilization is common with sliver fills which ultimately leads to failures.

4.3 Slope Reconditioning

Slope reconditioning is recommended to establish safe slopes for construction and to preserve the condition of the corridor. Significant cuts are not expected at either of these two locations, although mitigation measures are still advisable based on the reasons discussed earlier. Standard earthwork equipment, such as an excavator is anticipated to be used to round and shape hazardous slopes, remove protrusions and loose boulders, and improve areas with overhanging blocks for heights approximately 10- to 25-feet above the existing roadway elevation.

5 DISCLAIMERS/LIMITATIONS CLAUSE

Subsurface exploration was not performed as a part of this scope of work. Interpretation of surface and subsurface conditions is based on limited field reconnaissance and surface mapping of soil and rock outcrops. The Recommendations section of this report includes interpretations and recommendations developed by the Government in the process of preparing the design. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgement of the Contractor.

Attachments (1)

Bearing Resistance for Concrete Culverts

Prepared by:

______________________________________________ Date_________________

Devin T. Dixon, P.E.

Geotechnical Engineer, CFLHD

Reviewed by:

______________________________________________ Date_________________

James M. Arthurs, P.E., Ph.D.

Geotechnical Engineer, CFLHD

Approved by:

______________________________________________ Date_________________

Marilyn D. Dodson, P.E.

Lead Geotechnical Engineer, CFLHD

6 REFERENCES

American Association of State Highway and Transportation Officials (AASHTO). “AASHTO LRFD Bridge Design Specifications.” Seventh Edition, 2014.

Department of the Navy Facilities Engineering Command, (1986). NAVFAC, DM-7.02, “Foundations and Earth Structures,” Design Manual.

Federal Highway Administration (FHWA), 2007, Geotechnical Technical Guidance Manual, dated May.

Federal Highway Administration (FHWA), 2008, Federal Lands Highway Project Development and Design Manual (PDDM), dated March.

Federal Highway Administration (FHWA), 2017, Soil Description and Identification Guidelines, dated December.

Federal Highway Administration (FHWA), 2017, Rock Characterization Guidelines, dated December.

Rogers, David J. “Part 9: Ground Deformations Typical of Compacted Fill.” Lecture Notes, University of Missouri-Rolla (UMR).

Sprinkel, Douglas A. (2006). “Interim Geologic Map of the Dutch John 30’ x 60’ Quadrangle, Daggett and Uintah Counties Utah, Moffat County, Colorado, and Sweetwater County, Wyoming” 1:100,000. Utah Geologic Survey Open-File-Report 491DM.

U.S. Department of Transportation, Federal Highway Administration (FHWA). (2014). “Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP-14.”

Publication No. FHWA-FLH-14-001.

U.S. Geological Survey (2017). “Quaternary Fault and Fold Database of the United States.” USGS Earthquake Hazards Program, <http://earthquake.usgs.gov/hazards/qfaults/>

U.S. Geologic Survey (2017). “U.S. Seismic Design Maps.” USGS Earthquake Hazards Program, <https://earthquake.usgs.gov/hazards/designmaps/usdesign.php>

0 1 2 3 4 5 6 7 8 9 10

Be ar in g

Re si st an ce , R n (K

SF

Effective Foundation Width B' (FT)

EFFECTIVE WIDTH vs. BEARING RESISTANCE (LRFD) Box Culvert, STA 28+98 - Sheep Creek Road (UT FLAP 218(1))

B'

Q

Nominal (unfactored) strength and extreme event limit state -Strength limit state resistance factor = 0.45 -Extreme event limit states resistance factor = 1.0

Presumptive (factored) service limit state for 1-in settlement AASHTO LRFD Bridge Design SpecificationsTable C10.6.2.6.1-1

For cast-in-place concrete footing use sliding factor = 0.80 AASHTO LRFD Bridge Design SpecificationsTable 10.5.5.2.2-1