NLR_Final_Geotechnical_Report.pdf

Geotechnical Design Report Navajo Lake Road

Dixie National Forest Kane County, Utah

August 27, 2015

Submitted To:

CH2M

322 E. Front Street Suite 200

Boise, ID 83702

By:

Shannon & Wilson, Inc.

1321 Bannock Street, Ste. 200 Denver, CO 80204

23-1-01373-107

23-1-01373-107-R3/wp/kdd 23-1-01373-107 i

TABLE OF CONTENTS

Page

1.0 INTRODUCTION

2.0 SCOPE OF WORK

3.0 SITE AND PROJECT DESCRIPTION

4.0 FIELD EXPLORATIONS AND LABORATORY TESTING

5.0 REGIONAL GEOLOGY AND SUBSURFACE CONDITIONS

5.1 Regional Geology

5.2 Geographic Setting

5.3 Roadway Surfacing

5.4 Soil and Rock

5.5 Rock Outcrops

5.6 Groundwater

6.0 GEOLOGIC HAZARDS

6.1 Unstable Slopes

6.2 Groundwater Seepage

6.3 Corrosive Soil and Bedrock

6.4 Seismic Hazards and Ground Motion Design Parameters

7.0 GEOTECHNICAL RECOMMENDATIONS

7.1 Cut and Fill Slope Analysis

7.2 Rockery Walls

7.3 Culverts

7.4 Underdrains

7.5 Shrink and Swell Factors

8.0 CONSTRUCTION CONSIDERATIONS

8.1 Site Preparation

8.2 Earthwork and Grading

8.2.1 Excavation

8.2.2 Subgrade Preparation and Proof Rolling

8.2.3 Fill Placement and Compaction

8.3 Riprap

9.0 CONSTRUCTION OBSERVATION

10.0 LIMITATIONS

TABLE OF CONTENTS (cont.)

ii

11.0 REFERENCES

TABLES

1 Corrosivity Ratings Based on Soil Resistivity

2 Sulfate Exposure

3 Seismic Design Ground Motion Parameters

4 Summary of Recommended Underdrain Locations

5 Shrink/Swell Factors for Commons Materials

FIGURES

1 Vicinity Map

2 Site and Exploration Plan (6 Sheets)

APPENDICES

A Subsurface Explorations

B Laboratory Test Results

C Exploration Photographs

D Global Stability Calculations

E Important Information About Your Geotechnical Report

GEOTECHNICAL DESIGN REPORT

NAVAJO LAKE ROAD DESIGN

DIXIE NATIONAL FOREST

KANE COUNTY, UTAH

1.0 INTRODUCTION

This report presents the results of our subsurface exploration program and provides geotechnical engineering recommendations for the Navajo Lake Road Design, UT FLAP 30053 (1) at Navajo

Lake in Kane County, Utah. The project consists of paving 5.7 miles of Navajo Lake Road and replacing several culverts along this stretch. This report summarizes our subsurface explorations, laboratory testing and geotechnical engineering studies, and presents conclusions and recommendations for design and construction of the roadway features based on 95 percent design plans provided by CH2M and dated August 13, 2015. This report supersedes our Draft

Geotechnical Report dated July 6, 2015. Pavement recommendations are presented in our

Pavement Design Report, dated August 28, 2015.

2.0 SCOPE OF WORK

Our services were conducted in general accordance with our Purchase Order No. 10006-7-

102209 with CH2M, dated April 16, 2015 and the Central Federal Lands Highway Division

(CFLHD) Scope of Work for Task Order Number DTFH6814D00012/0018, dated April 3, 2015.

We completed the following geotechnical tasks for the project.

Coordinated subcontractors for drilling borings

Observed, logged, and collected soil and rock samples from 14 auger borings

Completed laboratory testing on selected soil and rock samples from the borings

Evaluated geotechnical data and completed geotechnical engineering analyses to develop conclusions and recommendations for design of the project

Evaluated subsurface conditions relative to construction of the project

Prepared this report

3.0 SITE AND PROJECT DESCRIPTION

Navajo Lake is located approximately 26 miles east of Cedar City, Utah (Figure 1). The only route to Navajo Lake from Cedar City is along State Highway (SH) 14 through Cedar Canyon.

The topography at Navajo Lake consists of rolling hills and steep cut and fill slopes along the current road alignment from approximately Stations 70+00 to 220+00. The cut slopes along the alignment generally lack vegetation and are topped with loose to moderately cemented colluvium with areas of highly fractured rock outcropping. The cut slope inclinations in this section of the alignment are typically 1.5H:1V (horizontal to vertical) to 2H:1V with a maximum height of about 20 feet. Between SH 14 and Station 70+00 and between about Station 220+00 and the end of the alignment, the roadway has minor slope heights or no slope on either side. The road is unpaved with an aggregate base surface.

We understand the improvements to Navajo Lake Road will include a newly paved surface from

SH 14 to Forest Service Road 31762 providing two 11 foot travel lanes, 4 foot shoulders, and paving at five existing pullout locations. Improvements will generally follow the existing road with minor realignments to improve safety and minimize impacts. Widening the road will be accomplished by enlarging current fill slopes on the north side of the road and cutting into select locations along the south side of the road. New or modified cut and fill slopes are proposed to have an inclination of 2H:1V or flatter. The maximum inclination of 2H:1V was established by

CFLHD based on the observed performance of steeper slopes. Where a 2H:1V cut slope does not catch the existing slope until beyond the project limits, rockery walls have been proposed.

The walls vary from less than 4 feet to about 8 feet high and range in length from 20 feet to almost 1,000 feet. We understand that the project also consists of replacing about 30 culverts.

The road will also be signed and striped to meet local Kane County and Forest Service requirements.

4.0 FIELD EXPLORATIONS AND LABORATORY TESTING

Shannon & Wilson conducted a reconnaissance walk with the CH2M and CFLHD Team on June

3, 2015 and again on July 15, 2015. During the site walks, existing unstable slopes, seeps and springs, and drilling locations were observed. Slope stability and groundwater from seeps and springs are discussed in Section 6.0 and 7.2.

Additionally, Shannon & Wilson conducted a subsurface exploration program on June 9 and 10, 2015. The subsurface exploration program consisted of drilling and sampling 14 borings, designated SW-P-1 through SW-P-8 and SW-B-1 through SW-B-6. The locations of the borings are shown on Figure 2. Appendix A presents a discussion of the drilling and sampling procedures used to complete the borings. Appendix A also presents the individual boring logs and an explanation of the symbols and terminology used on the logs.

Geotechnical laboratory tests were completed on select samples retrieved from the borings to estimate soil and rock index and engineering properties. Tests included natural water content, grain size distribution, Atterberg limits, moisture-density relationship, Hveem Stabilometer (R-value), and corrosion. Laboratory test methods and results are provided in Appendix B. The natural water content, fines content, and Atterberg limits are also shown on the individual boring logs included in Appendix A.

Photographs of the drill rig setup at each boring location are included in Appendix C.

5.0 REGIONAL GEOLOGY AND SUBSURFACE CONDITIONS

We based our understanding of the geology and subsurface conditions at the project site on a review of regional geologic maps and the results of our field exploration program. In general, the subsurface materials consist of fill, colluvium, alluvium, and Claron Formation.

5.1 Regional Geology

The project area is situated within the transition zone between the Colorado Plateau (east) and the Basin and Range Province (west). The area is characterized by north-northwest oriented ranges and high plateaus transitioning eastward to low-lying plateaus and elongate basins.

Navajo Lake lies within an elongated, east-west depression on the south margin of the

Markagunt Plateau and the north side of the Pink Cliffs. The plateau is capped by extensive

Tertiary and Quaternary basalt flows and volcanic deposits. The Pink Cliffs are formed by limestone beds of the Tertiary-age Claron Formation. Navajo Lake is bordered on the north and south by the Claron Formation. Quaternary basalt outcrops at the east end of the lake and arkosic sandstone of the Cretaceous-age Kaiparowits Formation is present on the east end of the lake. Bedrock dips gently to the northeast. The Claron Formation includes a white limestone and chalky clay unit near the top, and a dominant pink limestone with lesser sandstone, conglomerate, siltstone and dolomite throughout the majority of the formation. The Kaiparowits

Formation is composed primarily of yellowish-gray, arkosic sandstone with salt-and-pepper appearance, gray clay and mudstone beds, and minor lenses of iron concretions and limestone-clast conglomerate. (Doelling et. al., 1989)

5.2 Geographic Setting

The Markagunt Plateau is part of the Dixie National Forest where Navajo Lake resides. It covers approximately 800 square miles and the highest point within the plateau is Brian Head Peak at

11,307 feet located about 13 miles northwest from Navajo Lake. The region receives an average annual precipitation of about 30 inches as reported at Blowhard Mountain (Average Annual

Precipitation for Utah, 2015). The frost depth is reported to range from about 20 inches up to 30 inches (U.S. Frost Depth Map, 2015).

5.3 Roadway Surfacing

All of the geotechnical borings drilled within the roadway were drilled through a roadway surfacing of aggregate base course (boring SW-B-01 was drilled off the roadway). At these locations, base course thicknesses varied from 3.5 to 9 inches, with an average value of 5.5 inches. The roadway surfacing was measured after individual borings were completed and the auger was pulled out of the hole. A screw driver was used to probe the soil for density variations and a tape measure was used to measure the base course thickness. Actual aggregate base course thicknesses may vary from measured thicknesses. Visual observations of the roadway surfacing indicated that the material generally consisted of a poorly graded sand with silt and gravel.

Overall, the base course was similar across the site.

5.4 Soil and Rock

The soils encountered during this exploration program generally consisted of loose to dense, clayey sand with gravel; clayey gravel with sand; and soft to stiff, sandy lean clay with gravel.

Borings SW-P-1, SW-B-1, SW-P-2, and SW-B-2 were located near basalt flows and some gravel fragments consisted of pumice and basalt rock clasts.

Bedrock was only encountered in boring SW-B-3. It was inferred to be encountered at roughly

12 feet. A drive sample was taken at 14 feet and consisted of red-brown highly weathered shale and was consistent with published descriptions of the Claron Formation (Doelling et al., 1989).

5.5 Rock Outcrops

Rock outcrops were observed in the existing slopes along the alignment. The rock types observed were dark gray basalt, pink-gray limestone, and red-brown sandstone. Rock ranged from intensely fractured to moderately fractured and slightly to moderately weathered. Basalt will likely be encountered on either side of the roadway from Stations 10+00 to 30+00.

Limestone will likely be encountered from approximately Stations 30+00 to 220+00 with basalt likely on the north side of the road until approximately Station 70+00. Sandstone was observed in outcrops from approximately Station 220+00 to 308+63.17.

5.6 Groundwater

Groundwater was not observed in the borings at the time of our exploration program; however, we understand there are intermittent groundwater seeps that occur along the alignment and the locations typically move annually.

6.0 GEOLOGIC HAZARDS

Based on our geotechnical reconnaissance and subsurface explorations, and our knowledge of the geology of the area, there are geologic hazards along the corridor. The hazards that could pose an impact to the roadway are described below.

6.1 Unstable Slopes

Several of the existing cut and fill slopes along the project alignment appear to have been excavated near 1.5H:1V and may have a factor of safety (FS) for global stability that is below typical values for engineered cuts and fills (FS=1.3 to 1.5). At approximately Station 163+00, we observed a slope failure in an oversteepened cut slope adjacent to the road. A rockery wall has been constructed to buttress the slope and there does not appear to be recent movement of the rockery or roadway. The date of construction of the rockery is unknown. Groundwater seepage has been observed on the slope above and behind the rockery.

6.2 Groundwater Seepage

Groundwater seepage was observed at several locations on the existing cut slopes. Based on conversations with Forest Service personnel, we understand the location and duration of groundwater seepage regularly changes and these are typically intermittent features. During our site reconnaissance groundwater seepage was observed in cut slopes near approximately Station

163+00 and Station 214+00.

6.3 Corrosive Soil and Bedrock

Clays can be aggressive and especially corrosive when in contact with steel pipes. To assist in estimating the corrosion potential at the site, two samples were tested for pH, resistivity, water soluble sulfates, and chlorides. The samples tested were SW-B-2, S-2 and SW-B-5, S-2 and the results are presented in Table B-1 in Appendix B.

The resistivity measured in the sample SW-B-2 was 2,900 ohm-cm and in sample SW-B-5 was

1,250 ohm-cm. Roberge (1999) provides corrosivity ratings based on soil resistivity (Table 1).

The resistivity value measured in the sample indicates highly corrosive subsurface conditions.

TABLE 1

CORROSIVITY RATINGS BASED ON SOIL RESISTIVITY

ROBERGE (1999)

Soil Resistivity (ohm-cm) Corrosivity Rating

> 20,000 Essentially noncorrosive

10,000 – 20,000 Mildly corrosive

5,000 – 10,000 Moderately corrosive

3,000 – 5,000 Corrosive

1,000 – 3,000 Highly corrosive

< 1,000 Extremely corrosive

The concentration of water soluble sulfates measured in samples SW-B-2 and SW-B-5 was 0.01 percent by weight. Based on classifications as defined by ACI-318-11 (ACI, 2011) (Table 2), this suggests a negligible exposure of sulfate attack on concrete exposed to site soils (exposure class S0).

TABLE 2

SULFATE EXPOSURE ACI (2011)

Water Soluble Sulfate in Soil

(Percent by Weight) Sulfate Exposure

< 0.10 Negligible (S0)

0.10 – < 0.20 Moderate (S1)

0.20 – 2.00 Severe (S2)

> 2.00 Very Severe (S3)

We recommend that a specialist in corrosion-resistance design review the results included in

Table B-1 to determine actual construction materials and methods based on the test results.

6.4 Seismic Hazards and Ground Motion Design Parameters

Navajo Lake is located in a transition zone between the Colorado Plateau and Basin and Range province in southwestern Utah. It is an area of moderate to high potential for damaging earthquakes. There are several active faults in the general area. The Hurricane Fault is the most active and potentially dangerous fault located about 18 miles west of Navajo Lake and last active in the Quaternary (<15 ka) (Black et al., 2004). The Hurricane fault is generally north-south oriented (northeast-southwest near Cedar City) with Quaternary normal displacement up to 450 meters (~1476 feet) (Black et al., 2004).

Although, saturated cohensionless sands were not encountered during our drilling program, it is possible that they exist deeper in the subsurface. If so, liquefaction may occur when subjected to earthquake ground shaking. Based on the subsurface conditions encountered at the project site and ground motion parameters, it is our opinion that the liquefaction potential is low.

Using the American Association of State Highway and Transportation Officials (AASHTO)

Load and Resistance Factor Design (LRFD) Bridge Design Specifications (AASHTO, 2014) criteria, and based on subsurface conditions encountered in borings SW-B-1 through SW-B-6

(assuming that similar conditions are present from the maximum depth of our boring to a depth of 100 feet), Site Class E is recommended for the Navajo Lake Road improvements.

Ground motion parameters were determined for the project site using the United States

Geological Survey (USGS) U.S. Seismic Design Maps Web Application (USGS, 2014) and the

2009 AASHTO LRFD Manual (the design parameters have not changed in the current 2014 manual). Table 3 below presents recommended seismic design ground motion parameters at

Navajo Lake.

TABLE 3

SEISMIC DESIGN GROUND MOTION PARAMETERS

Ground Motion Parameters Value

Peak Ground Acceleration1 (PGAB) 0.165g

Site Class E

Short-period Spectral Acceleration, SS 0.399 g

Long-period Spectral Acceleration, S1 0.127 g

Site Factor, Fpga 2.0

Site Factor, Fa 2.023

Site Factor, Fv 3.419

Peak Design Spectral Acceleration, AS 0.327 g

Short-period Design Spectral Acceleration, SDS 0.807 g

Long-period Design Spectral Acceleration, SD1 0.434 g

T0 0.108 sec.

TS 0.538 sec.

NOTES:

1. PGAB = peak ground acceleration for a site underlain by Site Class B soil (soft rock).

2. g = gravity

7.0 GEOTECHNICAL RECOMMENDATIONS

7.1 Cut and Fill Slope Analysis

A generalized slope stability evaluation was performed for the proposed new cut and fill slopes along the alignment. Borings were not completed within the slopes and our reconnaissance was limited to surficial observations that were supplemented by the general geologic conditions along the alignment. Our analyses were based on proposed cut and fill slope inclinations of 2H:1V and assumed properties based on the materials observed in the borings.

Per the Geotechnical Technical Guidance Manual (FLH, 2007), cut and fill slopes are evaluated for a static loading condition and pseudostatic (seismic) loading condition. The desired FS for static loading is 1.3 to 1.5 depending on the risk tolerance for the feature and the uncertainty in the analysis parameters. For evaluation under seismic loading, the pseudostatic FS was considered based on a minimum value of 1.1 for the proposed slopes. For our analysis, a static

FS of 1.3 was selected due to the generalized nature of the global stability model. The analyses indicate that for static and pseudostatic conditions, the FS meets or exceeds recommended FS values. The analysis output is provided in Appendix D.

We recommend hand scaling of loose rock or colluvial boulders and seeding the slopes along the south side of the roadway. To mitigate future slope instability hazards, existing cut slopes with erosion features or historical slumping features should be regraded to a 2H:1V slope and have rip rap lining the ditch where active water flow is observed.

7.2 Rockery Walls

We understand that 10 rockery walls are proposed along the alignment presented in the 95 percent plans. Rockery wall locations were selected based on topographic modeling that indicated that a 2H:1V cut slope would not intersect the existing slope within the approved project limits. The proposed rockery heights vary from less than 4 feet to up to 8 feet tall and from about 20 feet to nearly 1,000 feet in length.

Global stability was evaluated for a typical section of a maximum rockery wall height of 8 feet and meeting the same FS criteria as required for the cut and fill slopes. The analyses indicate that for static and pseudostatic conditions, the FS for this section is above the guideline values, provided the soil strength parameters are above the values used in the model. The analysis output is provided in Appendix D.

At approximate Station 163+00, a rockery wall was previously constructed to stabilize a landslide that originated in an over-steepened cut slope. At the time of our site reconnaissance, a seep was present in the slope above the wall and discharge water was flowing in the ditch at the base of the slope. Based on discussions with CFLHD and CH2M representatives during our June

2015 reconnaissance, we recommend extending the existing rockery approximately 46 feet east to provide an additional buttress area. The extension should be tied into the existing rockery but include drainage features as detailed in the plan set. Additionally, the ditch should be lined with riprap to prevent erosion at the road edge.

7.3 Culverts

We understand nearly 30 culverts will be removed and replaced along the Navajo Lake Road alignment, with a new maximum size of 36 inches. Corrosion testing was performed at two locations proposed for the maximum sized culvert. The corrosion testing performed at location

SW-B-2 (approximately Station 86+00) will have a 36-inch culvert and at SW-B-5

(approximately Station 229+00) will have two 36-inch culverts. Both of these locations will replace existing culverts.

Design details were provided in the 95 percent plan set provided by CH2M. The plans include the inlet/outlet elevation and end section treatment (i.e., rip rap class). Based on the boring information collected along the alignment, the foundation materials are suitable for removing and replacing the culverts. If soft and/or loose soils are encountered at subgrade elevation during construction, they should be removed and replaced as discussed in Section 8.2.3.

Four culverts will have headwalls with wing walls constructed to accommodate double and triple culvert installations for culverts of 30- to 36-inches in diameter (approximate stations: 140+39, 188+81, 228+99, and 261+59). Bearing capacity for the headwalls was evaluated at these locations. The estimated nominal bearing capacity for 0.5-inch of settlement was 2.3 kips per square foot (ksf). For an estimated settlement value of 1-inch, the nominal bearing capacity was

4.6 ksf.

7.4 Underdrains

Underdrains are recommended at locations where surface drainage results in ponded water between culvert inlets as well as locations where seepage is actively occurring. Based on our site reconnaissance, we recommend 4 feet deep edge drains constructed between the stations listed in

Table 4. Additionally, we recommend installation of slope drains and underdrains at locations where groundwater discharge is encountered in new slope excavations during construction.

TABLE 4

SUMMARY OF RECOMMENDED UNDERDRAIN LOCATIONS

Approximate Station Range

62+00 70+00

161+00 165+00

204+80 215+00

7.5 Shrink and Swell Factors

The soil and rock at the site can be grouped into six material types for the purpose of earthwork planning. These materials are expected to be encountered during slope excavation and beneath the existing roadway along the alignment. Where encountered below overburden materials and within cut slopes, basalt will likely be encountered from Stations 10+00 to 30+00 and limestone will likely be encountered from approximately Stations 30+00 to 220+00. Sandstone will likely be encountered from Stations 220+00 to 308+63.17 (end of alignment).

Soils encountered within the borings varied along the alignment. Sand with silt was encountered at the surface and in the upper 0.5 feet in all but boring SW-B-1; sandy lean clay was observed in

SW-B-1. Soil underlying the base course varied between clayey gravel, clayey sand, and sandy lean clay. Coarse grained soils (gravel or sand) were encountered generally between the start of the alignment and approximately Station 60+00, between approximately Stations 150+00 and

165+00, at approximately Station 200+00, and at approximately Station 238+00. Clayey soils were encountered at other boring locations not encompassed in the station ranges above.

Table 5 presents shrink and swell factors for the soil and rock types expected to be encountered on the project. These values are based on criteria provided in the FHWA Geotechnical Technical

Guidance Manual (U.S. DOT and FHWA, 2007).

TABLE 5

SHRINK/SWELL FACTORS FOR COMMON MATERIALS (FHWA, 2007)

Material Loose – % Swell1

Embankment –

% Swell or Shrink1

Gravel

Dry

Wet

-8

-2

Sand

Wet

-11

-11

Clay

Damp

-10

-10

Basalt 64 36

Limestone 63 36

Sandstone 61 34 Note: 1. A negative value indicates shrinkage.

8.0 CONSTRUCTION CONSIDERATIONS

The applicability of the design recommendations provided in this report is contingent on good construction practice and adherence to the project specifications. Poor construction techniques may alter conditions from those on which our recommendations are based and result in poor performance. Our analyses assume that this project will be constructed according to FP-14 U.S.

Customary Units (USDOT and FHWA, 2014) standards. The following sections provide additional construction considerations for this project.

8.1 Site Preparation

We recommend that brush and other vegetation be cleared, and roots and stumps be removed from all areas to be graded. All surface and subsurface structures associated with current development of the site, including utility poles, fence poles, underground utilities and other deleterious material, should also be removed. Any existing surficial topsoil and soil containing organics should be stripped and removed from areas proposed for new fill. The depth of this removal is anticipated to vary, but generally be less than 6 inches. Topsoil and organic-rich soils are not considered suitable for reuse as fill and should be removed from the site or stockpiled for reuse in landscaping areas.

8.2 Earthwork and Grading

Earthwork, including placement of fill and subgrade preparation, should conform to the requirements provided in the FP-14 and the recommendations provided in the following sections.

8.2.1 Excavation

The soil materials can likely be excavated using conventional excavating equipment, such as a rubber-tired backhoe or tracked hydraulic excavator. In some slope areas, shallow limestone, shale, and/or basalt bedrock may be encountered. We do not anticipate blasting will be required for rock excavation where this bedrock is encountered. However, excavation in fresh rock could be slow at times and require the use of hydraulic excavators and dozers with ripper attachments.

8.2.2 Subgrade Preparation and Proof Rolling

Proper subgrade preparation is required for culvert and pavement performance.

Foundation subgrade excavations should be cleaned of all undocumented fill, debris, or loose/soft material prior to concrete placement. After the subgrade is excavated to the required depth, the subgrade should be probed to determine its suitability.

The compacted surface should be proof-rolled with a fully-loaded, tandem-axle, 10-yard dump truck or equivalent. Areas that are identified as being loose, soft, or yielding during proof-rolling should be compacted in place, removed and reconditioned, or replaced with fill material as discussed in Section 8.4.3. Care should be taken during proof-rolling and subgrade preparation to avoid disturbing subgrade soils and supporting soils that will remain in place, as they can rut and pump under repeated construction traffic. The final subgrade surface should be sloped to promote positive drainage and kept free of water at all times. Leaving the subgrade elevation high until final grading begins is a means to reduce the potential for disturbance to the final subgrade materials. Additionally, subgrades should be protected from drying or wetting in excess of what is required to achieve the specified compaction requirements.

Additional recommendations related to pavement preparation are presented in our

Pavement Design Report (2015).

8.2.3 Fill Placement and Compaction

All fill material placed should consist of soil that is free of organics, contaminants, debris, and rock fragments larger than 3 inches. In addition, fill material should be placed in horizontal lifts, with the loose lift thickness not to exceed 8 inches for heavy equipment compactors and 4 inches for hand-operated compactors and be compacted to a dense and unyielding condition. Thinner lifts may be required, depending on the contractor’s equipment.

Backfill Material (Section 704.03 of FP-14) or other granular soils (AASHTO classification A-1, A-3, A-2-4, and A-2-5 soils) should be moisture treated to within 2 percent of optimum moisture content and compacted to at least 95 percent of the maximum dry density, as determined by AASHTO T180. Existing onsite soils or other cohesive soils (AASHTO classification A-2-6, A-2-7, A-4, A-6, and A-7-6 soils) should be moisture treated between optimum and 2 percent over optimum moisture content and compacted to at least 95 percent of the maximum dry density, as determined by AASHTO T99.

8.3 Riprap

Riprap placed at the site should meet the requirements outlined in FP-14, Section 705.02. It is anticipated that the limestone rock outcrops from approximately Stations 30+00 to 220+00 may satisfy the durability requirements outlined in FP-14. The sandstone rock outcrops from approximately Stations 220+00 to 308+63.17, likely will not satisfy the durability requirements and should not be considered in the estimation of onsite riprap quantities. Should testing by the

Contractor indicate the sandstone does meet durability requirements, placement should be directed by the Contracting Officer (CO). Basalt rock should not be used as riprap unless testing by the Contractor indicates that it satisfies durability requirements and the CO approves placement.

9.0 CONSTRUCTION OBSERVATION

Geotechnical design recommendations are developed from a limited number of explorations and tests. Therefore, recommendations may need to be adjusted in the field. To this end, we recommend that a construction observation and monitoring program be implemented for the project and that Shannon & Wilson be retained to monitor the geotechnical aspects of construction, particularly the installation of culverts, excavations, and fill placement. This monitoring would allow us to confirm that conditions encountered are consistent with those indicated by the explorations and provide recommendations should conditions be revealed during construction that are different from those anticipated.

10.0 LIMITATIONS

The analyses, conclusions, and recommendations presented in this report are based on our understanding of the project, a limited surficial reconnaissance, and a limited number of subsurface explorations and laboratory test results. We assume that these explorations are representative of the subsurface conditions beneath the site; that is, the subsurface conditions everywhere are not significantly different from those disclosed by the explorations.

This report was prepared for the exclusive use of CH2M and CFLHD for the use in design of the

Navajo Lake Road Project. It should be made available to prospective contractors and/or the

Contractor for information on factual data only, and not as warranty of subsurface conditions,

11.0 REFERENCES

American Association of State Highway and Transportation Officials (AASHTO), 2014, AASHTO LRFD bridge design specifications, Customary U.S. units, 7th edition:

Washington, D.C., American Association of State Highway and Transportation Officials.

American Concrete Institute (ACI), 2011, Building Code Requirements for Structural Concrete and Commentary, Farmington Hills, Michigan, ACI 318-11.

Average Annual Precipiation for Utah, http://www.currentresults.com/Weather/Utah/average-yearly-precipitation.php accessed on 08/18/15 12:40 PM.

Black, B.D., and DuRoss, C.B., and Hylland, M.D., and McDonald, G.N., and Hecker, S., compilers, 2004, Fault number 998a, Hurricane fault zone, Cedar City section, in

Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/hazards/qfaults, accessed 06/18/2015 01:34 PM.

Doelling, H.H., Davis, F.D., and Brandt, C.J. 1989. The geology of Kane County, Utah –

Geology, Mineral resources, Geologic hazards. Utah Geological and Mineral Survey

Bulletin 124, scale 1:100,000.

Roberge, P.R., 1999, Handbook of Corrosion Engineering, McGraw-Hill.

Shannon & Wilson, Inc., 2015, Pavement Design Report, Navajo Lake Road Design, Dixie

National Forest, Kane County, Utah: Report prepared by Shannon & Wilson, Inc., Denver, CO, 23-1-01373-107, for CH2M, Inc. Denver, CO, August 28.

U.S. Frost Depth Map. http://sqfoot.com/pdf/US_Map_Frost_DepthAVG.pdf, accessed on

7/21/2015 at 1:20 PM.

U.S. Department of Transportation (U.S. DOT) and Federal Highway Administration (FHWA), 2007, Draft Technical Guidance Manual: U.S. Department of Transportation and Federal

Highway Administration, available from http://flh.fhwa.dot.gov/resources/design/pddm/Geotechnical_TGM.pdf

U.S. DOT and FHWA, 2014, Federal Standard Specifications for Construction of Roads and

Bridges on Federal Highway Projects, FP-14 English Units: U.S. Department of

Transportation and Federal Highway Administration, available from http://flh.fhwa.dot.gov/resources/pse/specs/.

U.S. Geological Survey (USGS), 2014, U.S. Seismic Design Maps Web Application: available:

http://earthquake.usgs.gov/designmaps/us/application.php.

http://www.currentresults.com/Weather/Utah/average-yearly-precipitation.php%20accessed%20on%2008/18 http://www.currentresults.com/Weather/Utah/average-yearly-precipitation.php%20accessed%20on%2008/18 http://earthquakes.usgs.gov/hazards/qfaults http://sqfoot.com/pdf/US_Map_Frost_DepthAVG.pdf http://flh.fhwa.dot.gov/resources/design/pddm/Geotechnical_TGM.pdf http://flh.fhwa.dot.gov/resources/pse/specs/ http://earthquake.usgs.gov/designmaps/us/application.php

APPENDIX A

SUBSURFACE EXPLORATIONS

A.1 INTRODUCTION .......................................................................................................... A-1

A.2 EXPLORATIONS .......................................................................................................... A-1 A.2.1 Soil and Rock Classification System ................................................................ A-2 A.2.2 Standard Penetration Test (SPT) ...................................................................... A-2 A.2.3 Bulk Samples .................................................................................................... A-2

A-1 Soil Classification and Log Key (3 sheets) A-2 Rock Classification and Log Key (2 sheets) A-3 Log of Boring SW-P-1 A-4 Log of Boring SW-B-1 A-5 Log of Boring SW-P-2 A-6 Log of Boring SW-B-2 A-7 Log of Boring SW-P-3 A-8 Log of Boring SW-B-3 A-9 Log of Boring SW-P-4 A-10 Log of Boring SW-B-4 A-11 Log of Boring SW-P-5 A-12 Log of Boring SW-P-6 A-13 Log of Boring SW-B-5 A-14 Log of Boring SW-P-7 A-15 Log of Boring SW-B-6 A-16 Log of Boring SW-P-8

23-1-01373-107-R3-AA 23-1-01373-107

A-1

A.1 INTRODUCTION

The field exploration program for the Navajo Lake Road Design Project consisted of drilling and sampling 14 geotechnical borings on June 9 through 10, 2015 designated as SW-P-1 through SW-P-8 and SW-B-1 through SW-B-6. The letter P designates a pavement boring while the letter B designates culvert borings. Approximate boring locations are indicated on Figure 2. A representative from Shannon & Wilson observed the drilling and sampling operations, retrieved representative samples for laboratory testing, and prepared logs of our subsurface explorations.

The methods used to conduct the field exploration program are described below.

A.2 EXPLORATIONS

The borings were coordinated (including subcontractor coordination and utility locates) by Shannon & Wilson. Individual boring logs are presented in Figures A-3 through A-16. These exploration logs represent our interpretation of the contents of the field logs and select results of laboratory testing. All borings were drilled by Elite Drilling Inc. (under subcontract to Shannon & Wilson) using a track-mounted CME 55 drill rig.

Pavement borings were generally sampled to an approximate depth of 6.5 feet below the road surface and culvert borings were sampled to a depth of 15.5 feet. All borings were advanced using 6-inch-diameter hollow-stem-auger and base course thicknesses were measured after the auger was pulled out. All borings were backfilled with drill cuttings.

During the drilling of boring SW-P-6, a culvert was encountered at approximately 2 feet. The auger drilled through the culvert to the bottom of the boring at 5 feet but was not observed until after drilling was completed. Drive sample S-1 was taken 12-inches above the culvert and had an artificially high blow count the last 1-inch of the drive. We disregarded the blow count for this sample since it was being driven onto the culvert. Due to limited materials and remote access to supplies, a temporary repair was constructed to allow for traffic to continue and prevent the culvert from filling up with material. The repair consisted of placement of a traffic cone upside-down in the hole. The traffic cone was filled halfway with coarse gravel and cobbles and then filled with the existing fill to the top of the roadway surface. The culvert is currently planned to be replaced during construction activities.

23-1-01373-107-R3-AA 23-1-01373-107

A-2

A.2.1 Soil and Rock Classification System

During drilling, the Shannon & Wilson representative collected soil/rock samples and prepared a field log of the boring. Soil classifications were based on ASTM D 2487, Standard Test Method for Classification of Soil for Engineering Purposes, and ASTM D 2488, Standard Recommended Practice for Description of Soils (Visual-Manual Procedure). The system is called the Unified Soil Classification System and is summarized in Figure A-1. Our representative classified rock samples in general accordance with the International Society of Rock Mechanics classification method. According to this system, rocks are classified based on the stratigraphic structure, rock strength, degree of weathering, and other properties. The rock classification system is summarized in Figure A-2.

A.2.2 Standard Penetration Test (SPT)

Disturbed samples were obtained in general accordance with the Standard Penetration Test (SPT) (ASTM Designation: D 1586). The SPT consists of driving a 2-inch outside diameter (O.D.), 1.375-inch inside diameter (I.D.) split-spoon sampler a distance of 18 inches with a 140-pound hammer free-falling a distance of 30 inches. An automatic hammer system was used to advance the samplers. During sampling, the Shannon & Wilson field representative recorded the number of blows for each 6-inch increment of penetration and summed the blow counts for the last two 6-inch increments. This sum is recorded as the penetration resistance number, or N-value. If high penetration resistance prevented driving the total length of the sampler, the Shannon & Wilson field representative recorded the partial penetration depth and blow count. The N-values provide a means for evaluating the relative density or compactness of cohesionless (granular) soils and consistency or stiffness of cohesive (fine-grained) soils (see Figure A-1). The N-values are shown in the individual boring logs. Representative portions of the split-spoon sample were placed in an airtight jar and transported to our laboratory for further analysis.

A.2.3 Bulk Samples

Bulk soil samples were also obtained by collecting the drill cuttings, generally from 1 to 5 feet of select borings. Approximately 30 to 40 pounds of cuttings were placed in a plastic bag and transported to our laboratory for further analysis and testing. A total of 6 bulk samples were obtained during the drilling program.

Dixie National Forest Kane County, Utah

23-1-01373-107August 2015

Geotechnical and Environmental Consultants

Absence of moisture, dusty, dry to the touch

Damp but no visible water

Visible free water, from below water table

FIG. A-1

Shannon & Wilson, Inc. (S&W), uses a soil identification system modified from the Unified Soil Classification System (USCS). Elements of the USCS and other definitions are provided on this and the following pages. Soil descriptions are based on visual-manual procedures (ASTM D2488) and laboratory testing procedures (ASTM D2487), if performed.

STANDARD PENETRATION TEST (SPT)

SPECIFICATIONS

Hammer:

Sampler:

N-Value:

Dry

Moist

Wet

MOISTURE CONTENT TERMS

Modifying (Secondary)

Precedes major constituent

Major

Minor Follows major constituent

1All percentages are by weight of total specimen passing a 3-inch sieve.

2The order of terms is: Modifying Major with Minor.

3Determined based on behavior.

4Determined based on which constituent comprises a larger percentage.

5Whichever is the lesser constituent.

COARSE-GRAINED

SOILS

(less than 50% fines)1

NOTE: Penetration resistances (N-values) shown on boring logs are as recorded in the field and have not been corrected for hammer efficiency, overburden, or other factors.

PARTICLE SIZE DEFINITIONS

RELATIVE DENSITY / CONSISTENCY

Sand or Gravel 4

30% or more coarse-grained:

Sandy or Gravelly 4

More than 12% fine-grained:

Silty or Clayey 3

15% to 30% coarse-grained:

with Sand or with Gravel 4

30% or more total coarse-grained and lesser coarse-grained constituent is 15% or more:

with Sand or with Gravel 5

Very soft Soft Medium stiff Stiff Very stiff Hard

Very loose Loose Medium dense Dense Very dense

RELATIVE

DENSITY

FINE-GRAINED SOILS

(50% or more fines)1

COHESIVE SOILS

< 2 2 - 4 4 - 8

8 - 15 15 - 30

> 30

1Gravel, sand, and fines estimated by mass. Other constituents, such as organics, cobbles, and boulders, estimated by volume.

2Reprinted, with permission, from ASTM D2488 - 09a Standard Practice for Description and Identification of Soils (Visual-Manual Procedure), copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428.

A copy of the complete standard may be obtained from ASTM International, www.astm.org.

140 pounds with a 30-inch free fall.

Rope on 6- to 10-inch-diam. cathead 2-1/4 rope turns, > 100 rpm

NOTE: If automatic hammers are used, blow counts shown on boring logs should be adjusted to account for efficiency of hammer.

10 to 30 inches long Shoe I.D. = 1.375 inches Barrel I.D. = 1.5 inches Barrel O.D. = 2 inches

Sum blow counts for second and third 6-inch increments.

Refusal: 50 blows for 6 inches or less; 10 blows for 0 inches.

RELATIVE

CONSISTENCY

N, SPT,

BLOWS/FT.

5% to 12% fine-grained:

with Silt or with Clay 3

15% or more of a second coarse-grained constituent:

with Sand or with Gravel 5

< 5%

5 to 10%

15 to 25%

30 to 45%

50 to 100%

Surface Cement Seal

Asphalt or Cap

Slough

Inclinometer or Non-perforated Casing

Vibrating Wire Piezometer

N, SPT,

BLOWS/FT.

< 4 4 - 10

10 - 30 30 - 50

> 50

DESCRIPTION

< #200 (0.075 mm = 0.003 in.)

#200 to #40 (0.075 to 0.4 mm; 0.003 to 0.02 in.)

#40 to #10 (0.4 to 2 mm; 0.02 to 0.08 in.)

#10 to #4 (2 to 4.75 mm; 0.08 to 0.187 in.)

SIEVE NUMBER AND/OR APPROXIMATE SIZE

#4 to 3/4 in. (4.75 to 19 mm; 0.187 to 0.75 in.)

3/4 to 3 in. (19 to 76 mm)

3 to 12 in. (76 to 305 mm)

> 12 in. (305 mm)

Fine Coarse

Fine Medium Coarse

BOULDERS

COBBLES

GRAVEL

FINES

SAND

Sheet 1 of 3

S&W INORGANIC SOIL CONSTITUENT DEFINITIONS

CONSTITUENT2

COHESIONLESS SOILS

Silt, Lean Clay, Elastic Silt, or

Fat Clay 3

PERCENTAGES TERMS 1, 2

Trace

Few

Little

Some

Mostly

WELL AND BACKFILL SYMBOLS

Bentonite Cement Grout

Bentonite Grout

Bentonite Chips

Silica Sand

Perforated or Screened Casing

SHANNON & WILSON, INC.

SOIL DESCRIPTION

AND LOG KEY

_B O

R

IN

G _C

LA

S

S

3-

1-

3-

N A

JA

V

O L

A K

E D

E S

IG

N

.G P

J S

W N

E W

.G D

T

/3 1/

Dixie National Forest Kane County, Utah

August 2015

GC

SC

Inorganic

Organic

(more than 50% of coarse fraction retained on No. 4 sieve)

MAJOR DIVISIONS GROUP/GRAPHIC

SYMBOL

CH

OH

ML

CL

TYPICAL IDENTIFICATIONS

Gravel

Sand

Silty Sand; Silty Sand with Gravel

Clayey Sand; Clayey Sand with Gravel

Clayey Gravel; Clayey Gravel with Sand

Sheet 2 of 3

Gravels

Primarily organic matter, dark in color, and organic odor

SW

(more than 12% fines)

Silts and Clays

Silts and Clays

(more than 50% retained on No.

200 sieve)

(50% or more of coarse fraction passes the No. 4 sieve)

(liquid limit less than 50)

(liquid limit 50 or more)

Organic

Inorganic

FINE-GRAINED

SOILS

SM

Sands

Silty or Clayey Gravel

Silt; Silt with Sand or Gravel; Sandy or Gravelly Silt

Organic Silt or Clay; Organic Silt or Clay with Sand or Gravel; Sandy or Gravelly Organic Silt or Clay

HIGHLY-

ORGANIC

SOILS

COARSE-

GRAINED

SOILS

GW

Geotechnical and Environmental Consultants

SHANNON & WILSON, INC.

(less than 5% fines)

PT

(more than 12% fines)

MH

SP

GP

GM

Silty or Clayey Sand

Silty Gravel; Silty Gravel with Sand

(50% or more passes the No.

200 sieve)

SOIL DESCRIPTION

AND LOG KEY

Elastic Silt; Elastic Silt with Sand or Gravel; Sandy or Gravelly Elastic Silt

Fat Clay; Fat Clay with Sand or Gravel;

Sandy or Gravelly Fat Clay

Organic Silt or Clay; Organic Silt or Clay with Sand or Gravel; Sandy or Gravelly Organic Silt or Clay

Poorly Graded Sand; Poorly Graded Sand with Gravel

Well-Graded Sand; Well-Graded Sand with Gravel

Well-Graded Gravel; Well-Graded Gravel with Sand

Poorly Graded Gravel; Poorly Graded Gravel with Sand

Lean Clay; Lean Clay with Sand or Gravel; Sandy or Gravelly Lean Clay

NOTES

1. Dual symbols (symbols separated by a hyphen, i.e., SP-SM, Sand with Silt) are used for soils with between 5% and 12% fines or when the liquid limit and plasticity index values plot in the CL-ML area of the plasticity chart. Graphics shown on the logs for these soil types are a combination of the two graphic symbols (e.g., SP and SM).

2. Borderline symbols (symbols separated by a slash, i.e., CL/ML, Lean Clay to Silt; SP-SM/SM, Sand with Silt to Silty Sand) indicate that the soil properties are close to the defining boundary between two groups.

Peat or other highly organic soils (see

ASTM D4427)

FIG. A-1

OL

(less than 5% fines)

_B O

R

IN

G _C

LA

S

S

3-

1-

3-

N A

JA

V

O L

A K

E D

E S

IG

N

.G P

J S

W N

E W

.G D

T

/3 1/

NOTE: No. 4 size = 4.75 mm = 0.187 in.; No. 200 size = 0.075 mm = 0.003 in.

UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)

(Modified From USACE Tech Memo 3-357, ASTM D2487, and ASTM D2488)

Dixie National Forest Kane County, Utah

August 2015

Angular

Subangular

Subrounded

Rounded

Flat

Elongated

Sharp edges and unpolished planar surfaces.

Similar to angular, but with rounded edges.

Nearly planar sides with well-rounded edges.

Smoothly curved sides with no edges.

Width/thickness ratio > 3.

Length/width ratio > 3.

Narrow range of grain sizes present or, within the range of grain sizes present, one or more sizes are missing (Gap Graded). Meets criteria in ASTM D2487, if tested.

Full range and even distribution of grain sizes present. Meets criteria in ASTM D2487, if tested.

Crumbles or breaks with handling or slight finger pressure Crumbles or breaks with considerable finger pressure Will not crumble or break with finger pressure

Weak

Moderate

Strong

VISUAL-MANUAL CRITERIA

A 1/8-in. thread cannot be rolled at any water content.

A thread can barely be rolled and a lump cannot be formed when drier than the plastic limit.

A thread is easy to roll and not much time is required to reach the plastic limit. The thread cannot be rerolled after reaching the plastic limit. A lump crumbles when drier than the plastic limit.

It take considerable time rolling and kneading to reach the plastic limit. A thread can be rerolled several times after reaching the plastic limit. A lump can be formed without crumbling when drier than the plastic limit.

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants Sheet 3 of 3

Interbedded

Laminated

Fissured

Slickensided

Blocky

Lensed

Homogeneous

Alternating layers of varying material or color with layers at least 1/4-inch thick; singular: bed.

Alternating layers of varying material or color with layers less than 1/4-inch thick; singular:

lamination.

Breaks along definite planes or fractures with little resistance.

Fracture planes appear polished or glossy;

sometimes striated.

Cohesive soil that can be broken down into small angular lumps that resist further breakdown.

Inclusion of small pockets of different soils, such as small lenses of sand scattered through a mass of clay.

Same color and appearance throughout.

At Time of Drilling Diameter Elevation Feet Iron Oxide Gallons Horizontal Hollow Stem Auger Inside Diameter Inches Pounds Magnesium Oxide Millimeter Manganese Oxide Not Applicable or Not Available Nonplastic Outside Diameter Observation Well Pounds per Cubic Foot Photo-Ionization Detector Pressuremeter Test Parts per Million Pounds per Square Inch Polyvinyl Chloride Rotations per Minute Standard Penetration Test Unified Soil Classification System Unconfined Compressive Strength Vibrating Wire Piezometer Vertical Weight of Hammer Weight of Rods Weight

ATD

Diam.

Elev.

ft.

FeO gal.

Horiz.

HSA

I.D.

in.

lbs.

MgO mm

MnO

NA

NP

O.D.

OW

pcf

PID

PMT

ppm psi

PVC

rpm

SPT

USCS

qu

VWP

Vert.

WOH

WOR

Wt.

STRUCTURE TERMS1

SOIL DESCRIPTION

AND LOG KEY

1Reprinted, with permission, from ASTM D2488 - 09a Standard Practice for Description and Identification of Soils (Visual-Manual Procedure), copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM International, www.astm.org.

2Adapted, with permission, from ASTM D2488 - 09a Standard Practice for Description and Identification of Soils (Visual-Manual Procedure), copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM International, www.astm.org.

ACRONYMS AND ABBREVIATIONS

Poorly Graded

Well-Graded

Irregular patches of different colors.

Soil disturbance or mixing by plants or animals.

Nonsorted sediment; sand and gravel in silt and/or clay matrix.

Material brought to surface by drilling.

Material that caved from sides of borehole.

Disturbed texture, mix of strengths.

Mottled

Bioturbated

Diamict

Cuttings

Slough

Sheared

DESCRIPTION

Nonplastic

Low

Medium

High

ADDITIONAL TERMS

PLASTICITY2

CEMENTATION TERMS1

GRADATION TERMS

APPROX.

PLASITICTY

INDEX

RANGE

< 4

4 to 10

10 to 20

> 20

PARTICLE ANGULARITY AND SHAPE TERMS1

FIG. A-1

_B O

R

IN

G _C

LA

S

S

3-

1-

3-

N A

JA

V

O L

A K

E D

E S

IG

N

.G P

J S

W N

E W

.G D

T

/3 1/

Roadway Surfacing - 3.5 inches Tan to light brown, Poorly Graded Sand with Silt and Gravel (SP-SM); dry-moist.

Medium dense, brown, Clayey Gravel with Sand (GC); moist; clasts of pumice [A-2-4].

Fill.

BOTTOM OF BORING

COMPLETED ON 6/9/15

S-1

G-1

S-2

G ro un dw at er n ot e nc ou nt e re d du ri ng d ri lli ng

0.3

6.5

S ym bo l

Refer to the report text for a proper understanding of the subsurface materials and drilling methods. The stratification lines indicated below represent the approximate boundaries between material types, and the transition may be gradual.

SOIL DESCRIPTION

NOTES

1. Refer to Figures A-1 and A-2 for explanation of symbols, codes, abbreviations and definitions.

2. The stratification lines represent the approximate boundaries between soil types, and the transition may be gradual.

3. The discussion in the text of this report is necessary for a proper understanding of the nature of the subsurface materials.

4. Groundwater level, if indicated above, is for the date specified and may vary.

5. USCS designation is based on visual-manual classification and selected lab testing.

Navajo Lake Road Dixie National Forest Kane County, Utah

0 60

Total Depth:

Top Elevation:

Vert. Datum:

Horiz. Datum:

20 40

Geotechnical and Environmental…