UT.FLAP.73(1).LaSal_Mtn_Loop.Geotech.2016.pdf

La Sal Mountain Loop Road Manti-La Sal National Forest

Grand County San Juan County

UT FLAP 73(1)

Final Geotechnical Design Report

Report # UT-FX-0073-16-01

Prepared by Federal Highway Administration

Central Federal Lands Highway Division

Geotechnical Services Branch

June 2016

La Sal Mountain Loop Road UT FLAP 73(1) i June 2016

Table of Contents

SECTION ONE--INTRODUCTION

1.1 OBJECTIVE AND SCOPE

1.2 PROPOSED CONSTRUCTION

1.3 SITE CONDITIONS

SECTION TWO--GEOLOGY AND SEISMICITY

2.1 REGIONAL GEOLOGY

2.2 SITE GEOLOGY

2.2.1 Segment 1

2.2.2 Segment 2

2.3 GEOLOGIC HAZARDS

2.4 SEISMICITY

2.5 SEISMIC DESIGN PARAMETERS

SECTION THREE—FIELD EXPLORATION

FIELD EXPLORATION AND LABORATORY TESTING PROGRAM ............... 6 3.1

SECTION FOUR--ANALYSIS AND RECOMMENDATIONS

MSE WALL ............................................................................................................ 7 4.1

4.1.1 MSE Wall Geotechnical Profile

4.1.2 Preliminary External Design

EMBANKMENTS ................................................................................................ 11 4.2 CUT SLOPES ........................................................................................................ 12 4.3 CORROSION POTENTIAL ................................................................................. 15 4.4 CONSTRUCTION CONSIDERATIONS ............................................................. 16 4.5 SPECIFICATIONS ............................................................................................... 16 4.6 LIMITATIONS ..................................................................................................... 16 4.7

SECTION FIVE -- REFERENCES

La Sal Mountain Loop Road UT FLAP 73(1) ii June 2016

TABLES

TABLE 1:- Summary of Seismic Parameters Corrected for Class C Soil TABLE 2:- Minimum Acceptance Criteria for MSE Walls TABLE 3:- Estimated Subsurface Material Properties for MSE Design TABLE 4:- Summary of MSE Wall Fill Design Parameters TABLE 5:- Summary of MSE Stability Analyses TABLE 6:- Summary of Cut Slope Recommendations

FIGURES

FIGURE 1 – Vicinity Map FIGURE 2 – Site Map FIGURE 3a – Geologic Map FIGURE 3b – Geologic Map Units FIGURE 4a – Boring Locations, B1, B2, B3 & B4 FIGURE 4b – Boring Locations, B5 & B6 FIGURE 5 – Rock Embankment Typical Section

APPENDICES

APPENDIX A - Field Exploration Program APPENDIX B - Laboratory Test Results APPENDIX C - Photographs APPENDIX D - MSE Analysis

La Sal Mountain Loop Road UT FLAP 73(1) 1 June 2016

SECTION ONE--INTRODUCTION

This report presents the results of the geotechnical engineering study conducted for the La Sal Mountain Loop Road, UT 73-(1), project. The project involves improvements to select locations of Forest Highway 73 (UT FH 73), referred to as La Sal Mountain Loop Road and County Route 1704 (CR-1704). La Sal Mountain Loop Road is 36.4 miles long from the intersection of Highway 191 and Old Airport Road to the intersection of Highway 128 and Mountain Loop Road/Castleton Road, as shown on Figure 1, Vicinity Map. The route is characterized as a narrow two-lane road with switch-backs and steep grades that navigates mountainous terrain from an elevation of 4,080 feet to 8,320 feet.

Two segments along the route, totaling 10.86 miles have been selected for improvements.

Segment 1 begins at the Mill Creek Bridge (Station 11+50), near the intersection of Wilson Mesa Road, and extends to where UT PFH 46-1(2) Miner’s Basin project started (Station 413+71).

Segment 2 begins where UT PFH 46-1(2) project left off (Station 490+71), and ends at the intersection of La Sal Mountain Loop Road and Castleton Road (Station 660+47). The project alignment is shown on Figure 2, Site Map. The rehabilitation and reconstruction of the roadway segments are designed to improve roadway geometry, replace deficient structures, improve roadway safety, and improve drainage issues.

1.1 OBJECTIVE AND SCOPE

The objectives of this investigation are to develop recommendations concerning foundations, retaining structures, embankments, cut slopes, subsurface drainage, corrosion potential, geologic hazards, material shrink/swell, and construction considerations. In accomplishing these objectives, the scope of work included field exploration, laboratory testing, correlation of available data, and engineering analysis. The field exploration included subsurface exploration and site reconnaissance.

1.2 PROPOSED CONSTRUCTION

Central Federal Lands Highway Division (CFLHD) cross-functional team and partnering agencies on the project (Grand County, San Juan County, and the Manti-La Sal National Forest) determined that rehabilitation of the roadway will include roadway widening to a consistent 22 feet, improve roadway geometry, improve roadway safety, improve drainage issues, and provide a new pavement surface. Rehabilitation will require the expansion of existing embankments, cut slopes, ditch reconditioning, shoulder stabilization, and an Mechanically Stabilized Earth (MSE) walls to limit environmental impacts.

La Sal Mountain Loop Road UT FLAP 73(1) 2 June 2016

1.3 SITE CONDITIONS

The regional topography slopes to the southwest from an elevation of 12,721 feet at Mount Peale to the City of Moab, on the Colorado Plateau at an elevation of 4,025 feet. The region containing gullies, canyons, cliffs, debris fans, landslides, and areas of relatively steep terrain.

The La Sal Mountain Loop Road consists of a winding two-lane roadway with sharp curves and variable widths climbing steeply from the desert environment to an alpine mountain environment. Arid climatic conditions are present in the lower elevations and seasonally wet areas typical of mountainous regions are present in the higher elevations.

The project is generally located in undeveloped forested terrain between the elevations of about 6,500 feet and 8,350 feet within the La Sal Mountain Range. Climatic conditions are closely related to semi-arid to arid mountainous conditions with seasonal precipitation. Forested portions of the alignment generally consist of a mixture of Gambel Oak, Douglas Fir, Juniper, and Aspen trees. Minor amounts of Willow, Red Osier, Dogwood, Rush, Wood’s Rose, and Boxelder are also present.

The existing roadway varies in width from 17 feet to 22 feet and was constructed utilizing steep cut and fill shoulder treatments with limited ditch width, consistent with side-cast construction techniques. Existing cut slopes extend to a height of approximately 35 feet and show evidence of continuous raveling and are typically not vegetated. Cut slopes in soil vary between 25 and 50 degrees and cut slopes in weathered bedrock range from 55 to 65 degrees while naturally occurring slopes are typically found between 25 and 35 degrees. Near vertical slopes exist where resistant sandstone bedrock is exposed. Fill slopes are typically less than 35 feet in height and embanked at angles of about 25 to 40 degrees. The pavement surface is severely deteriorated and maintenance of the roadway requires constant attention.

La Sal Mountain Loop Road UT FLAP 73(1) 3 June 2016

SECTION TWO--GEOLOGY AND SEISMICITY

2.1 REGIONAL GEOLOGY

The La Sal Mountain Loop Road lies within the Colorado Plateau geologic province. The Colorado Plateau is primarily characterized by sedimentary rocks forming iron-stained plateaus, canyons and rivers and extends throughout most of the land between AZ, NM, CO, UT (four corners region). The province is named after the Colorado River and its main tributaries drain most of the region.

The La Sal Mountains are a cluster of Tertiary intrusions of igneous rocks within the Colorado Plateau, about 35 million years old. These clusters are referred to as laccoliths which have domed the older sedimentary rocks of the Permian, Triassic, Jurassic, and Cretaceous time periods. The sedimentary rocks were pushed upward by the rising masses of magma creating an uplift mountain building event. Increased erosion rates from the uplift have now eroded away the majority of the sedimentary units from the upper reaches of the La Sal Mountains, but they still remain on the lower flanks and in irregular rings around the intrusions. The exposed igneous formations generally consist of gray, coarsely crystallized diorite and rhyolite.

Segment 1 is generally underlain by the sedimentary Morrison Formation and boarder’s Quaternary colluvium and slide deposits. Segment 2 is generally underlain by exposed igneous bedrock of diorite and much younger Quaternary colluvium and alluvial fan deposits. Geologic units are discussed in more detail in Section 2.2, Site Geology. Illustrated geology according to the “Geology, Structure, and Uranium Deposits of the Moab Quadrangle, Colorado and Utah” compiled by Paul L.Williams in 1964. are displayed on Figure 3a, Geologic Map, with brief formation descriptions displayed on Figure 3b, Geologic Map Units.

2.2 SITE GEOLOGY

2.2.1 Segment 1

Bedrock underlying Segment 1 belongs to the “Upper Jurassic-age (~161.2 to 145.5 million years old) Morrison Formation” according to the “Geologic Map of the La Sal 30’ x 60’ Quadrangles, San Juan, Wayne, and Garfield Counties, Utah, and Montrose and San Miguel Counties, Colorado” compiled by Hellmut H. Doelling in 2004. Quaternary age (11,500 years old to present) slumps and slides are mapped as overlying the Morrison Formation on the slopes above the roadway.

The Morison Formation in the project area is comprised of two members; the Saltwash and Tidwell Members. The Saltwash Member is comprised of interbedded lenses of light-brown, white, yellow-gray, and very-pale-orange sandstone and medium red-brown and green-gray

La Sal Mountain Loop Road UT FLAP 73(1) 4 June 2016 siltstone and mudstone. Local minor gray limestone and conglomeritic sandstone are present, (Doelling, 2004). Underlying the Saltwash member is the Tidwell Member. The Tidwell Member is 10 to 50 feet thick and, as described by Doelling, 2004, as a red-brown, fine grained calcareous silty sandstone with light-gray mottling in undulating thin beds.

Limestone is present with accompanying red and white chert.

Slumps and landslides mapped above the roadway are described by Deolling, 2004, as irregular hummock deposits of rotated and slumped material made up of small to large blocks of sandstone cobbles and boulders within a matrix of clayey and silty material.

2.2.2 Segment 2

Bedrock beneath Segment 2 is mapped as “Middle Tertiary-age (28 to 25 million years old) La Sal Mountains Intrusive Rocks,” as shown on “Geologic Map of the Moab and Eastern Part of the San Rafael Desert 30’ x 60’ Quadrangles, Grand and Emerys Counties, Utah, and Mesa County, Colorado” compiled by Hellmut H. Doelling in 2002. The La Sal Mountain intrusive rocks are overlain by surficial deposits of Late Quaternary-age (11,500 years old to present) talus and colluviums, as well as alluvial fan deposits. The La Sal Mountain intrusive rocks are generally comprised of Hornblende-plagioclase trachyte, quartz-plagioclase trachyte, peralkaline trachyte, and peralkaline rhyolite, all porphyritic with fine-grained ground mass.

The talus and colluvium originated from the La Sal Mountain intrusive rocks as a product of weathering and are generally comprised of rockfall blocks, smaller angular gravel, sand and silt with an estimated average thickness of 20 feet. Alluvial fan deposits, with an estimated average thickness of 50 feet in depth, overlie La Sal Mountain intrusive rocks in the broad valleys. These alluvial fan deposits are poorly sorted, angular to subrounded gravels, containing cobbles and sparse boulders.

2.3 GEOLOGIC HAZARDS

Geologic hazards exist from both the natural environment of the project sites and from existing and proposed construction of the roadway. Geologic hazards that exist in the vicinity of the project areas are rock fall, avalanches, highly erodible granular soils, debris flows, slope instability at cut and fill slope locations, and seismic events. Variability of the geologic profile and groundwater conditions found at the sites increase the risk of failure of cut and fill slopes.

Cut slope failures and rock fall, in particular, may occur during construction. Debris flows are possible in many of the cross drainages in Segment 2 during periods of high precipitation. The risk is particularly high during the summer monsoon season and in the wet winter and early spring months.

La Sal Mountain Loop Road UT FLAP 73(1) 5 June 2016

2.4 SEISMICITY

There are no known active or potentially active major faults that cross the project area. An unnamed fault is mapped immediately west of the end of Segment 1, as shown on Figure 3. The major fault zones within a 40-mile range to the project location are the Castle Valley faults, Fisher Valley faults; Granite Creek fault zone, Little Dolores River fault, Moab fault and deformation zones, Ryan Creek fault zone, Salt and Cache Valleys faults, Sand Flat graben faults, Sinbad Valley graben, and Ten Mile graben faults. These faults have a slip-rate of less than 0.2 millimeters per year and vary in length from 7.5 miles, as seen in the Castle Valley faults, to 42 miles in the Moab fault and deformation zones. The overall trend of the faults within 40 miles of the project location is Northwest by Southeast.

2.5 SEISMIC DESIGN PARAMETERS

Recommended seismic response parameters for the project site are based on the (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, near the proposed MSE wall location of 38.5463 N latitude and -109.2956 W longitude, was obtained in accordance with the AASHTO ground motion maps and corrected for the site class. Based on shallow bedrock and dense soils observed throughout the site, the site is classified as Class C according to site class definitions specified in Table 3.10.3.1-1 of AASHTO. The recommended spectral acceleration coefficient values for probabilistic design are summarized in Table 1.

TABLE 1:- Summary of Seismic Parameters Corrected for Class C Soil

Horizontal Peak Ground Acceleration, (As) 0.073g Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDs) 0.161g Horizontal Response Spectral Acceleration at Period of 1.0 sec, (SD1) 0.066g

Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 1.20 Site Factor at Short-Period Range of Acceleration Spectrum, (Fa) 1.20 Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 1.70

Based on the long acceleration coefficient SD1 value of 0.066, the site is assigned to seismic hazard Zone 1 in accordance with Table 3.10.6-1 of AASHTO. While the soil class, seismic parameters and hazard zone was developed for the MSE wall, these values are conservative for the entire project.

La Sal Mountain Loop Road UT FLAP 73(1) 6 June 2016

SECTION THREE—FIELD EXPLORATION

FIELD EXPLORATION and LABORATORY TESTING PROGRAM 3.1

CFL geotechnical personnel conducted a subsurface investigation on June 16 and 17, 2015, to characterize subsurface materials. The subsurface exploration program consisted of drilling a total of 6 borings, 2 borings at proposed embankment locations and 4 borings at the proposed MSE wall location. Boring locations are shown on Figures 5a and 5b, Boring Locations.

Subsurface conditions were logged and representative samples were collected and transported to the CFLHD Materials Laboratory in Lakewood, CO, for physical property testing. More detailed descriptions of the work performed, borings logs, and laboratory test data are contained in Appendices A and B, respectively. Subsurface exploration site photos are contained in Appendix C.

La Sal Mountain Loop Road UT FLAP 73(1) 7 June 2016

SECTION FOUR--ANALYSIS AND RECOMMENDATIONS

This section provides analysis and recommendations for the proposed MSE wall, embankments, shoulder stabilization, and cut slopes required for roadway rehabilitation. Discussions with respect to corrosion potential, construction considerations, specifications, and limitations are also included.

MSE WALL 4.1

A retaining wall is required to widen the roadway from Station 391+50 to Station 405+34.

Various retaining wall types, including Mechanically Stabilized Earth (MSE), modular gabion gravity walls, and concrete cantilever walls were evaluated as potential solutions. Reinforced slopes, rock embankments, or realignment of the roadway into the cutslope was not considered for design because of the excavation volume required and the significant environmental impacts and site disturbance anticipated.

The analysis indicated that an MSE wall system is the preferred alternative and is recommended to gain the required roadway width. MSE walls tolerate larger differential settlement than other wall alternatives and were selected as the most economical due to subsurface materials and steep slopes found on-site. Concrete cantilever walls would require foundation improvement to limit deflection to within tolerable standards and to satisfy global stability requirements.

4.1.1 MSE Wall Geotechnical Profile

A geotechnical profile was developed for the design of the proposed MSE wall from the data collected during the subsurface investigation. Borings B-2 through B-5 were drilled in Segment 1 at the MSE wall site to determine subsurface conditions for design of the proposed MSE wall. The borings revealed a pavement section of about 0.4 feet of asphalt pavement overlying silty Sand with gravel (SM) to silty Gravel with sand (GM) overburden material extending to Siltstone bedrock at depths between 14.5 feet to more than the maximum depth explored of 50.5 feet.

The silty SAND with gravel (SM) was the predominate overburden material found in Borings B-2 through B-5 and contains cobble and boulder size rock fragments. Boulders greater than 3 feet in diameter were observed on the surface in nearby slopes and appeared angular. Uncorrected representative N-values from SPT’s ranged from 3 to 56 blows per 12 inches with an average of Navg = 22 indicating medium dense consistency. Soil moisture conditions were generally moist to dry with no correlation with depth. Fines content of tested samples ranged from 12 to 25 percent and are generally described as non-plastic to low plasticity. Silty GRAVEL with sand (GM) was also encountered in the borings; however, to be conservative, the material property values for silty SAND with gravel should be used in design.

La Sal Mountain Loop Road UT FLAP 73(1) 8 June 2016

Siltstone bedrock was encountered in borings B-3 at 24.5 feet in depth and B-4 at 14.5 feet in depth. Exposed bedrock in the areas generally consists of interbedded reddish-brown to yellow-brown Siltstone and reddish-brown Sandstone. The Siltstone is described as highly to moderately weathered with a relative hardness of very weak (R1) to medium strong (R3).

Exposed sandstone observed is described as moderately to slightly weathered with a relative hardness of medium strong (R3) to strong (R4). Considering the proposed MSE structure, and the high variability of depths that bedrock was encountered, bedrock should not be assumed in design of MSE walls but may be encountered during construction.

Groundwater was not detected in the borings at the time of drilling in June 2015. However, springs and seeps in the cut slopes and roadway inboard ditch have been observed and correspond to areas of embankment and pavement distress. Groundwater conditions can vary significantly within short distances and the volume of groundwater flow may fluctuate between seasons. The wall system should include a drainage system and groundwater should be anticipated and controlled during construction, especially during periods of high precipitation. Increased groundwater and soil moisture is expected during the wet winter and spring snow melt months.

4.1.2 Preliminary External Design

Preliminary external design including global stability, bearing resistance, overturning, sliding, and eccentricity was performed to evaluate the proposed wall geometry. The final MSE wall bearing pressures and internal stability will be designed and submitted by the contractor. Design walls in general accordance with AASHTO “LRFD Bridge Design Specifications” (7th edition), and FHWA Publication NHI-10-024 and NHI-10-025, Volumes 1 and 2, respectively, entitled “Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes” dated November 2009. Acceptance criteria used for preliminary design are shown in Table 2.

TABLE 2:- Minimum Acceptance Criteria for MSE Walls

Stability Mode Minimum Acceptance Criteria

Global Stability

Static FS = 1.25* Seismic FS = 1.1

Bearing Resistance CDR = 1.0 Sliding CDR = 1.0

Limiting Eccentricity emax = L/4 Notes: FS = Factor of Safety

CDR = Capacity to Demand Ratio Eccentricity (emax) for soil foundations

* Acceptable FS for Rural Highways

La Sal Mountain Loop Road UT FLAP 73(1) 9 June 2016

The capacity to demand ratios (CDR) for bearing resistance and sliding are used to quantify the ratio of the factored resistance to the factored load. Resistance factors used in the preliminary external design for bearing and sliding are 0.65 and 1.0, respectively. Load factors for bearing, sliding, and the eccentricity check are shown in Tables 4-1 and 4-2 of

FHWA (2009).

Material properties were estimated for foundation design based on observations during the field investigation, results of laboratory testing, and known empirical strength characteristics of like materials. In addition, slope stability was conducted to calibrate estimated material values of the overburden. The selected design values for soil unit weight (γ), internal friction angle (φ), and cohesion intercept (c) are shown in Table 3.

TABLE 3:- Estimated Subsurface Material Properties for MSE Design

Material Unit

Weight γ (pcf)

Cohesion c (psf)

Friction Angle φ (deg)

Silty SAND with Gravel, Cobbles and

Boulders (SM) 125 100 38

The reinforced and retained portions of the wall system are backfilled with select granular backfill and backfill material in accordance with the requirements in Section 704 of the FP-

14. Based on laboratory testing results, on-site, existing fill and native soils will generally not meet the requirements for select granular backfill. In addition, local rock found on-site within the vicinity of the wall will generally not meet the requirements of wall facing fill.

Alternatively, the proposed wall may be designed and constructed in accordance with Draft FHWA Publication FHWA-CFL/TD-15-XXX, entitled “Mechanically Stabilized Earth (MSE) Wall Fills, A Framework for Use of Local Available Sustainable Resources (LASR)” dated April 2016. A copy of the is document will be provided upon request. MSE-LASR Fill in accordance with the requirements of SCR Section 704.09 are to be designed with a maximum internal friction angle (φ) of 32 degrees. MSE-LASR Fills are anticipated to originate from the excavation of the proposed MSE wall and processed to meet the requirements of Section 704.09. The fill material parameters assumed for preliminary designs are listed in Table 4.

La Sal Mountain Loop Road UT FLAP 73(1) 10 June 2016

Table 4:- Summary of MSE Wall Fill Design Parameters

Description Total Unit

Weight, γ pcf.

Friction Angle, φ (deg)

Cohesion Intercept, c psf

Backfill Material (704.03 (a)) 125 32 0

Select Granular Backfill (704.08) 125 34 0

MSE-LASR Fill

(SCR 704.09) 125 32 0

The proposed MSE walls were preliminarily evaluated for feasibility based on the existing site conditions and available subsurface information using the program Mechanically Stabilized Earth Walls (MSEW 3.0) developed by ADAMA Engineering. The design methodology used by MSEW is consistent with current AASHTO and FHWA guidelines for assessment of the internal and external stability of MSE walls. Global stability analysis was performed using Slide, Version 6.0, a two dimensional, limit equilibrium computer program from RocScience. The Bishop method of slices was used with isotropic soil parameters estimated from site observations and experience with similar soils.

Cross sections were evaluated where the wall height was at its maximum and/or where the slope in front of the fill wall was the steepest. A traffic surcharge of 250 psf was modeled in the analyses. The seismic coefficient used in design, representing the 7 percent in 75-year hazard level, was determined from equation C11.6.5-1 in AASHTO assuming 2.0 inches of tolerable lateral displacement. Groundwater was not detected in the borings; therefore, a water table was not included in the analyses. The wall system will include interior drainage and is considered drained.

Based on the results of the analyses, the proposed MSE wall system will meet the required acceptance criteria shown in Table 2, Minimum Acceptance Criteria for MSE Walls, provided that the wall system be constructed with a minimum horizontal setback from the slope at the wall toe of 6 feet and a minimum reinforcement length equal to 70 percent of the wall height (0.7H) or 8 feet, whichever is greater. Summary results of the most critical cross section cases from Slide, Version 6.0 and estimated static factored bearing resistances assuming a Resistance Factor (φ) of 0.65 (AASHTO, Table 11.5.6-1) and an acceptable maximum settlement of 1 inch. Analysis of the most critical design sections are presented in Appendix D.

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Table 5: - Summary of Stability Analyses

Station Description

Estimated Factored Bearing

Resistance

Global Stability

Cross Section Case

Required F.S.

Calculated F.S.

396+75

MSE Critical Surface for H=13ft, 40 deg. Slope

3,600 psf

Existing -- 1.36 Static 1.25 1.28

Seismic (7% in 75) 1.1 1.26

398+25

MSE Critical Surface for H=17ft, 37 deg. Slope

4,200 psf

Existing -- 1.45 Static 1.25 1.31

Seismic (7% in 75) 1.1 1.29

398+75

MSE Critical Surface for H=15ft, 38 deg. Slope

4,050 psf

Existing -- 1.44 Static 1.25 1.27

Seismic (7% in 75) 1.1 1.27

EMBANKMENTS 4.2

Roadway reconstruction requires embankments associated with roadway realignment, widening, side-road approaches, and culvert replacement. It is recommended that proposed embankments be constructed at 1V:2H slopes or flatter to maintain slope stability and facilitate vegetation growth. Due to the granular nature of the on-site soils and limited heights anticipated, settlements of the embankments are expected to be negligible with the majority of the settlement occurring during construction.

As an alternative, embankments can be steepened when mitigation treatments such as reinforced soil slopes (RSS) or rock embankment that acts as a buttress. At the time of this report, no RSS locations were identified and are not included in this report, if soil slopes over 1V:2H are required, an RSS design can be provided. Suitable rock embankment typical section for heights less than 8 feet is provided on Figure 5.

Groundwater may be encountered within embankment and culvert foundations. Dewatering and stabilization methods will depend on conditions encountered. Based on on-site observations, it is not likely that a significant depth of top soil will be present on the project sites. For estimation purposes, it should be assumed that limited topsoil will be stripped and stockpiled for re-use on the project. Topsoil is anticipated to be imported for this project.

No sub-excavation or underdrain locations were specifically identified during design, partially due to the severely deteriorated pavement condition and the likelihood that the new pavement section and surface drainage improvements are sufficient repairs. However, 500 cubic yards of

La Sal Mountain Loop Road UT FLAP 73(1) 12 June 2016 sub-excvation and 500 linear feet of underdrain are recommended to be included in the contract for when saturated or poor subgrade conditions are encountered during construction.

CUT SLOPES 4.3

Expansion of existing cut slopes are proposed to accommodate the roadway design width. Cut slope recommendations provided avoid deep seated instability of the slope. However, steeper slopes decrease the likelihood of re-vegetation and increase the likelihood and frequency of slumping, raveling, and rock fall events; flatter slopes should be utilized where possible.

Shrink/Swell

Materials shrink/swell percentage represents the difference in volume between undisturbed bank materials and then compacted embanked volume. A material that occupies a larger volume as fill from the excavation volume (e.g. rock) is considered to swell and represented as a positive (+). A material that occupies a smaller volume as fill from the bank excavation volume (e.g.

soil) is considered to shrink and represented as a negative (-).

Shrink/Swell values are dependent on subsurface conditions estimated from the borings and observations of materials found in existing cut slopes. On-site soils encountered along Segment 1 generally consist of red-brown sandy clay and clayey sand with cobble to boulder size rock (sandstone) fragments with larger boulders up to 5 feet present in existing cutslopes near the beginning and end of the segment. Without the cobble and boulder size rock fragments, the material classifies as a CL to SC material and is not anticipated to be used as embankment.

However, for design estimating purposes, it is anticipated that these soils will have a shrink percentage ranging from -5 to -10 percent.

On-site materials encountered along Segment 2 generally consist of (1) colluvium, which is a brown to yellow brown sandy clay with volcanic gravels to boulders, and (2) fractured volcanic rhylolite bedrock exhibiting varying degrees of weathering. For design estimating purposes, it is anticipated that colluvial soils will have a shrink percentage of approximately -10 percent and volcanic bedrock will exhibit a swell percentage of +10 to +15 percent.

The recommended shrink/swell factors are 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. Estimated shrink/swell values within a station range were weighted to represent the area of anticipated excavation; therefore, they are intended to be an average for station ranges shown. Shrink/Swell values are shown in Table 6. Values were rounded to the nearest 0.05 due to variability and uncertainty within subsurface materials.

Structural Stability

Recommended slope ratios are based on observed conditions at the existing cut face, investigation data, and anticipated slope height. In general, non-saturated course grained

La Sal Mountain Loop Road UT FLAP 73(1) 13 June 2016 granular soil slopes can be cut at 1V:1.5H, non-saturated fine grained residual soil or colluvial slopes can be cut at 1V:2H, weathered bedrock slopes can be cut at 2V:1H to 4H:1V depending on litology and degree of weathering, and combination soil and rock slopes can be cut at 1:1. Cut slopes should not exceed slope ratios presented in Table 6. Areas of observed springs and seeps encountered during construction may require flattening and should be evaluated by the geotechnical engineer.

Table 6: - Summary of Cut Slope Recommendations

Station to Station Maximum

Slope Ratio (V:H)

Shrink (-) /Swell (+)

Shrink/ Swell

Factor Description

10+00 to 38+50 1:1 0% 1.00

Ditch Reconditioning: 1:1 in Soil slopes less than 10 feet in height and 1:0.5 for cuts in bedrock.

Brown red silty sand and rock fragments

38+50 to 84+50 1:2 -10% 0.90

Gray, green, & brown bentonitic Sandy CLAY with gravel. Cut slopes less than 10 foot height, 1:1.5 may be used.

84+50 to 125+00 1:1.5 -10% 0.90 Brown Sandy CLAY with gravel 125+00 to 355+00 1:2 -10% 0.90 Brown Sandy CLAY with gravel 355+00 to 390+25 1:1.5 -5% 0.95 Brown Silty SAND with gravel

390+25 to 407+50 1:1 0% 1.00

Ditch Reconditioning: 1:1 in Soil slopes less than 10 feet in height Brown red silty sand and rock fragments. 1:1.5 Slope where possible

407+50 to 410+00 1:1.5 0% 1.00 Brown red silty sand and rock fragments.

410+00 to 413+50 1:2 -5% 0.95 Brown Silty SAND with gravel

490+00 492+50 2:1 +10% 1.10 Lt brown yellow to tan Rhyolite, highly weathered

492+50 to 499+00 4:1 +15% 1.15 Lt brown yellow to tan Rhyolite, mod. weathered

499+00 to 504+00 2:1 +10% 1.10 Lt brown yellow to tan Rhyolite, highly weathered

504+00 to 507+50 2:1 +15% 1.15 Lt brown yellow to tan Rhyolite, mod. weathered

507+50 to 512+00 1:1 +0% 1.00 Lt brown yellow to tan Rhyolite, highly weathered

512+00 to 520+00 1:1.5 -5% 0.95 Lt brown yellow silty sand and (50%) rock fragments

520+00 to 523+00 1:2 0% 1.00 Loose Scree: Lt brown yellow silty sand and (75%) rock fragments

La Sal Mountain Loop Road UT FLAP 73(1) 14 June 2016

Station to Station Maximum

Slope Ratio (V:H)

Shrink (-) /Swell (+)

Shrink/ Swell

Factor Description

523+00 to 532+00 1:1.5 -5% 0.95 Lt brown yellow silty sand and (50%) rock fragments

532+00 to 542+00 1:1.5 -10% 0.90 Lt brown yellow silty sand and (25%) rock fragments

552+50 to 555+00 No Cut 0 1.00 Talus: Do not Cut

555+00 to 571+00 1:2 -10% 0.90 Lt brown yellow silty sand and (25%) rock fragments

571+00 to 588+00 1:1.5 0 1.00 Lt brown yellow silty sand and (75%) rock fragments. 1:1 OK from 571+50 to 575+50

588+00 to 590+00 1:1.5 -10% 0.90 Brown red silty sand and (25%) rock fragments

590+00 to 594+00 1:1.5 -5% 0.95 Lt brown yellow silty sand and (50%) rock fragments

594+00 to 600+00 1:1.5 0 1.00 Lt brown yellow silty sand and (75%) rock fragments

600+00 to 606+00 1:1.5 -5% 0.95 Tan silt/sand and (50%) rock fragments

606+00 to 608+00 1:1.5 -5% 0.95 Brown red welded tuff/red brown soil mix

608+00 to 612+00 1:1.5 -10% 0.90 Brown red silty sand and (25%) rock fragments

612+00 to 621+00 1:1.5 -5% 0.95 Lt brown yellow silty sand and (50%) rock fragments

621+00 to 623+00 1:1.5 0 1.00 Lt brown yellow silty sand and (75%) rock fragments

Rockfall Catchment Area

A rockfall catchment area is defined as the area between the roadway edge of shoulder and the base of a cut slope used to restrict high percentage of rockfalls from reaching the roadway. The use of catchment areas to contain and restrict rockfall from reaching the roadway is one of the best and most effective rockfall protective measures. The Oregon Department of Transportation (ODOT) Rockfall Catchment Area Design (RCAD) design charts were used to evaluate various slope cut ratios and slope heights. A standard catchment area using a 6-foot wide area sloping at 14 degrees (1V:4H) with a 1 to 2-foot shoulder is recommended for an estimated 75% rockfall containment. Routine ditch cleaning should be included in the county’s maintenance plan to avoid decreased rockfall retention.

Scaling

Scaling and crest rounding of existing cut slopes is recommended in locations not mitigated by proposed permanent cut slopes. Scaling is conducted to reduce the amount and frequency of rock

La Sal Mountain Loop Road UT FLAP 73(1) 15 June 2016 fall debris on the roadway by removal of loose and unstable material from existing slopes.

Scaling is anticipated to be achieved by hand and light tools. Approximately 32 crew hours are recommended to be included in the contact documents. Half of these crew hours are anticipated for brow scaling from Station 10+00 to Station 12+75 and from Station 32+50 to Station 34+50.

The remaining half should be held in reserve for locations to be determined during construction.

Scaling is only considered a temporary or short term rock fall mitigation technique to remove any loose material that could potentially dislodge. Routine scaling should be included in the county’s maintenance plan.

CORROSION POTENTIAL 4.4

Analytical tests were conducted on selected samples collected to determine if soils may have detrimental effects on concrete and buried metals. A combined soil sample from Borings B-2, B-3, and B-5 from various depths was tested for resistivity and pH chemical characteristics. The minimum resistivity measured was 5,570 ohm-cm, and the pH was 7.9. Resistivity and pH results indicate a mildly corrosive soil environment; therefore, sulfates and chlorides were not tested.

Acceptable ranges of soil aggressiveness for anticipated culverts, MSE walls, and concrete structures vary with respect to the proposed structure. For culverts, the electrical resistivity measurements indicate values above 1,500 ohm-centimeters and pH tests indicate values between 5.0 and 9.0. These test results indicate no corrosive restrictions will be necessary for the proposed type of pipe culverts used on the project. In addition, special sulfate resistant cement will not be required for concrete exposed to the on-site soils. Type II cement with a maximum water to cement ratio by weight of 0.44 is recommended for concrete structures in contact with onsite soils.

Processed local material originating from the excavation of the proposed MSE wall is anticipated for MSE-LASR Fill in the MSE wall reinforcement zone and is required to meet the following corrosion related requirements according to SCR Section 704, Soil, which is based on recommendations from FHWA-NHI-10-024 (2009):

• Resistivity, AASHTO T 288 3,000 ohm-cm minimum

• pH, AASHTO T 289 5.0 to 10.0

• Sulfate content, AASHTO T 290 200 ppm maximum

• Chloride content, AASHTO T 291 100 ppm maximum

MSE backfill material that meets the above criteria will be considered non-corrosive to the metallic soil reinforcement. Analytical geochemical tests should be performed on wall fills during construction to determine suitability.

La Sal Mountain Loop Road UT FLAP 73(1) 16 June 2016

CONSTRUCTION CONSIDERATIONS 4.5

Roadway cuts are proposed at steep slopes and are anticipated to encounter colluvium and weak to strong bedrock with large boulders (3-feet in diameter or larger) requiring carefully planned and uniquely adapted excavation approaches. Evidence of blasting is apparent in the existing bedrock cut slopes; however, hoe-rams may be sufficient to achieve proposed excavations. The contractor will be required to make the final determination on the rippability characteristics of encountered material based on review of site conditions and equipment capabilities. Due to the weathered and jointed nature of the rock mass anticipated, special attention must be paid to minimize over-break to the final cut face. Scaling will be a critical element in arriving at stable cut slopes along the roadway.

Depending on the time of year, surface water and groundwater seeps might be present during excavation and construction of cut slopes and embankments. In addition, roadway excavations conducted in Segment 1 are anticipated to encounter moisture sensitive fine-grained cohesive soils. Control of groundwater and surface water flows are imperative to maintaining stable working conditions. Temporary diversion, dewatering and stabilization methods for foundation construction will depend on conditions encountered.

SPECIFICATIONS 4.6

Special provisions were developed to be consistent with geotechnical recommendations stated above and should be incorporated into the special contract requirements (SCR) to amend the FHWA Standard Specification for Construction of Roads and Bridges on Federal Highway Projects; known as FP-14. SCR sections provided are Section 204 – Excavation and Embankment, Section 207- Earthwork Geosynthetics, Section 255- Mechanically Stabilized Earth Walls, Section 623- General Labor, Section 704- Soil, and Section 705- Rock.

LIMITATIONS 4.7

The recommendations in this report are based on the data obtained from exploratory borings, field review, and the laboratory test results. The results of these explorations and tests represent conditions at the specific locations indicated. Subsurface variations across the site are likely and may not become evident until excavation is performed. The Analysis and Recommendations sections in this report include 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 judgment of the Contractor.

La Sal Mountain Loop Road UT FLAP 73(1) 17 June 2016

SECTION FIVE -- REFERENCES

ACI, 2005, “Building Code Requirements for Structural Concrete (ACI 318-05) and

Commentary (318R-05)”.

ADAMA Engineering, Inc, Computer Program, MSEW, Version 3.0, Copyright 2006.

American Association of State Highway and Transportation Officials (AASHTO), 2014, LFRD

BRIDGE DESIGN SPECIFICATIONS, 7th Edition

Central Federal Lands Highway Division (CFLHD), 2015, “Plans for Proposed UT FLAP 73(1)

La Sal Mountain Loop Road,” Preliminary 70% October 2015, by Central Federal Lands Highway Division, dated October 22, 2015.

CFLHD, 2015, “La Sal Mountain Loop Road, UT FLAP 73(1), 70% Design Technical

Memorandum,” by Federal Highway Administration, Central Federal Lands Highway Division, dated October, 2015.

Federal Highway Administration (FHWA), 2007, LRFD for Highway Bridge Substructures and

Earth Retaining Structures, Publication FHWA-NHI-05-094, dated January.

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

March.

FHWA, 2009, Design of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes, Publication FHWA-NHI-10-024, dated November.

FHWA, Draft 2015, “Mechanically Stabilized Earth (MSE) Wall Fills, A Framework for Use of

Local Available Sustainable Resources (LASR), Publication FHWA-CFL/TD-15-xxx, Draft dated April 2015.

Federal Lands Highway (FLH), 2006, “Technical Guidance Manual (TGM)”, A geotechnical supplement to the FLH Project Development and Design Manual.

Federal Lands Highway (FLH), 2014, “Standard Specifications for Construction of roads and

Bridges on Federal Highway Projects, FP-14.”

Hellmut, Doelling H. 2002 Geologic Map of the Moab and Eastern Part of the San Rafael Desert

30’ x 60’ Quadrangles, Grand and Emerys Counties, Utah, and Mesa County, Colorado, Utah Geological Survey, Map 205.

Hunt, Charles B., “Structural and Igneous Geology of the La Sal Mountains, Utah,” U.S.

Department of the Interior, Geological Survey Professional Paper 294-I, Dated 1958.

La Sal Mountain Loop Road UT FLAP 73(1) 18 June 2016

Oregon Department of Transportation Highway Division. 1987. “Soil and Rock Classification Manual.”

Pearthree, P.A., compiler, 1995, Quaternary fault and fold database of the United States: U.S.

Geological Survey website, http://earthquakes.usgs.gov/regional/qfaults.

Pierson, L.A., C.F. Gullixson, and R.G. Chassie, 2001, “Rockfall Catchment Area Design Guide, Final Report,” Oregon Dept. of Transportation Research Group pub. No. SPR-3(032), November 2001.

RocScience Geotechnical Software, Computer Program, SLIDE with SLIDE INTERPRET

Version 6.033, Copyright 2015

Utah Geological Survey, 2000, “Digital Geologic Map Of Utah”, website:

http://geology.utah.gov/maps/geomap/statemap/pdf/digitalgeoutah.pdf.

United States Geological Survey (USGS), 2008, “National Seismic Hazard Map”, website:

http://earthquake.usgs.gov/research/hazmap

Wayne, and Garfield Counties, Utah, and Montrose and San Miguel Counties, Colorado, Utah

Geological Survey, Map 180.

Williams, Paul L., “Geology, Structure, and Uranium Deposits of the Moab Quadrangle, Colorado and Utah,” Department of the Interior, United States Geological Survey, Map I 360, Dated 1964.

http://earthquakes.usgs.gov/regional/qfaults http://geology.utah.gov/maps/geomap/statemap/pdf/digitalgeoutah.pdf http://earthquake.usgs.gov/research/hazmap

FIGURES

FIGURE 1 – Vicinity Map FIGURE 2 – Site Map FIGURE 3a – Geologic Map FIGURE 3b – Geologic Map Units FIGURE 4a – Boring Locations, B1, B2, B3 & B4 FIGURE 4b – Boring Locations, B5 & B6 FIGURE 5 – Rock Embankment Typical Section

Dominic.Monarco Typewritten Text

FIGURE

Dominic.Monarco Typewritten Text

Dominic.Monarco Text Box

FIGURE

Rectangle

Rectangle

B2 392+60 3' RT 8024 34.5

B3 396+68 1' LT 7997 29.6

B4 398+73 CL 7985 24.5

GEOTECHNICAL BORINGS

Investigation Location

Station Offset From Centerline

Elevation (ft)

Depth (ft)

B1 31+35 8' LT 7837 17.0

GEOTECHNICAL BORINGS

Depth (ft)

Elevation (ft)

Offset From Centerline

Station Investigation Location

B5 402+23 1' LT 7962 50.5

GEOTECHNICAL BORINGS

Investigation Location

Station Offset From Centerline

Elevation (ft)

Depth (ft)

B6 570+18 4' LT 7129 15.5

GEOTECHNICAL BORINGS

Investigation Location

Station Offset From Centerline

Elevation (ft)

Depth (ft)

NO SCALE 252-A

1:4

6' min.

2%

S lo p e Fa ce (1 :1

Mechanically Placed

Special Rock Embankment

Final Grade

Existing Ground

NOTE:

1.

1' min.

8' max.

Level the top layer of the Rock Embankment with Class 1 Riprap

Type C, Non-woven Geotextile, Class 1, G4

TYPICAL SECTION

ROCK EMBANKMENT

pay item.

for payment. Payment is included in special rock embankment

Earthwork geotextile, class 1 riprap, and excavation will not be measured

ROCK EMBANKMENT

STATE PROJECT

P

M N U

T R o a d w a y C

A D

D S h e e ts G s p A .d g n

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

FEDERAL HIGHWAY ADMINISTRATION

U.S. DEPARTMENT OF TRANSPORTATION

SPECIAL

U.S. CUSTOMARY SPECIAL

U s e r l e s li e .d e w it t_

NUMBER

SHEET

UT

La Sal Mountain Loop Road

UT FLAP 73(1)

APPENDIX A

Field Exploration Program

UT FLAP 73 (1) La Sal Mountain Loop Road Appendix A Page A-1

APPENDIX A

FIELD EXPLORATION PROGRAM

A.1 INTRODUCTION

The Central Federal Lands Highway Division (CFLHD) Geotechnical Section completed a field exploration program for UT FLAP 73, La Sal Mountain Loop Road, on June 16 and 17, 2015.

The scope of work for the geotechnical field exploration program included a total of six borings.

The field exploration program was coordinated and observed by an Engineering Geologist from CFLHD. Individual boring logs are attached. These logs represent a compilation of field and laboratory data and description of the soil samples by CFLHD Geotechnical personnel. The methods used to conduct the field exploration program are described below. Photos of drilling equipment and field exploration activities are included in Appendix C. Representative soil samples collected during the field exploration program were transported to the CFLHD Materials Laboratory in Lakewood, Colorado for testing. A summary of the laboratory testing program is provided in Appendix B.

A.2 EXPLORATIONS

Borings

Vine Laboratories, Inc. of Denver, Colorado provided the drilling services for all of the borings.

Borings were completed using a CME 55 truck mounted drill rig.

Six borings were completed to depths ranging from 15.5 to 50.5 feet below the existing road.

The borings were drilled using 4-inch I.D. hollow stem augers and were terminated at refusal or at approximately 50 feet. Standard Penetration Test (SPT) was performed in accordance with

AASHTO T-206.

The location and elevation of individual borings were estimated relative to features shown on the plan set. Boring locations are listed on individual boring logs and are shown below in Table A-1.

Following drilling activities, field personnel backfilled the borings in accordance with applicable local, state, and federal regulations.

UT FLAP 73 (1) La Sal Mountain Loop Road Appendix A Page A-2

TABLE A1 – Field Exploration Locations

Approx.

Station(1)

Offset From Centerline(1)

Exploration Type

Exploration Designation

Approx.

Depth (ft)

Approx.

Depth to Bedrock

(ft)

Exploration Purpose

31+35 8 ft LT Geotech Boring B-1 17.0 11.0 Embankment

392+60 3 ft RT Geotech Boring B-2 34.5 -- Wall

396+68 1 ft LT Geotech Boring B-3 29.6 24.5 Wall

398+73 0 ft Geotech Boring B-4 24.5 14.5 Wall

402+23 1 ft LT Geotech Boring B-5 50.5 -- Wall

570+18 4 ft LT Geotech Boring B-6 15.5 -- Embankment

Notes: (1) Stationing and Offsets based on 70% Design Alignment

A.3 SOIL SAMPLING

Disturbed samples were obtained from the borings in accordance with the SPT procedures of which are detailed in AASHTO T-206. The SPT involves driving a 2-inch outside diameter, 1.375-inch inside diameter split spoon sampler a depth of 18 inches with a 140-pound hammer falling a distance of 30 inches. The number of blows required to advance the split-spoon sampler through each of the 6-inch increments was recorded. The SPT resistance, or N-value, is defined as the number of blows required to drive the sampler over the second and third 6-inch increments. The N-value provides a means for evaluating the relative density or compactness of cohesionless (granular) soils and consistency or stiffness of cohesive (fine-grained) soils. Energy corrected N-value, N60, is used to standardize the energy levels of the hammer system in the SPT to 60% efficiency. Recent energy measurements of the automatic hammer system employed for the SPTs on this project indicate an efficiency of 80%. Because high penetration resistance prevented driving the total length of the sampler at times, the penetration resistance for the partial penetration was recorded where applicable.

Representative portions of the split-spoon sample obtained in conjunction with the SPT were placed in plastic bags and transported to the CFLHD Materials Laboratory for testing. A summary of the laboratory testing program is provided in Appendix B.

UT FLAP 73 (1) La Sal Mountain Loop Road Appendix A Page A-3

A.4 SOIL CLASSIFICATION SYSTEM

During the completion of borings, CFLHD Geotechnical personnel collected soil samples and prepared field logs of the borings. Soil identification and descriptions, as shown on the boring logs, are based on ASTM D 2488, a systematic process for identifying and describing individual soil samples by visual and manual means. When sufficient laboratory testing was completed, select samples from borings were classified using the Unified Soil Classification System (USCS) and American Association of State Highway and Transportation Officials (AASHTO) soil classification system. Both the visual soil identification system and the referenced soil classification systems are summarized in the attached Soil Classification Field Reference.

UT FLAP 73 (1) La Sal Mountain Loop Road Appendix A Page A-4

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UT FLAP 73 (1) La Sal Mountain Loop Road Appendix A Page A-6

UT FLAP 73 (1) La Sal Mountain Loop Road Appendix A Page A-7

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