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F I N A L G E O T E C H N I C A L D E S I G N R E P O R T

Kolob Canyons Road UT FTNP Zion 13(1)

Prepared for

Federal Highway Administration Central Federal Lands Highway Division

January 2018

CH2M HILL Inc.

322 East Front Street Boise, ID 83702

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Contents Section Page

1.0 Introduction

1.1 Purpose and Scope

1.2 Project Description

1.3 Existing Conditions and History

Kolob Canyons Road Scenic Drive

1.4 Pavement Conditions

2.0 Technical Data

2.1 Geotechnical Field Exploration Program

2.2 Laboratory Testing

2.3 Subsurface Conditions

2.4 Groundwater Conditions

2.5 Regional Geology

2.6 Inclinometers

3.0 Design Recommendations

3.1 Drainage

3.2 Pavement Design

3.2.1 Resilient Modulus

3.2.2 Forecasted Traffic and ESALS

3.2.3 Pavement Design Parameters

3.2.4 Performance-graded Binder Type

3.2.5 Recommended Pavement Sections

3.3 Roadway Slumping and Landslide Stabilization

Existing Conditions - MP 2.1 (STA 114+00 to 116+00) Recommended Mitigation Solution Existing Conditions - MP 2.35 (STA 127+50 to 129+00) Recommended Mitigation Solution

3.4 Bearing Resistance

3.5 Sliding Resistance

3.6 Lateral Earth Pressures

3.7 Seismic Design Parameters

3.8 Soil Corrosivity

3.9 Frost Action

3.10 Expansive Soil

3.11 Construction Considerations

4.0 Potential Geologic Hazards

5.0 Limitations

6.0 References

FINAL GEOTECHNICAL DESIGN REPORT

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Appendixes A Exploratory Boring Location Maps B Soil Boring Logs C Pavement Core Photographs D Laboratory Test Results E Traffic Analysis F Calculations

Tables

1 Existing Pavement and Subgrade Conditions along Kolob Canyons Road 2 Soil Boring Summary 3 Laboratory Test Results Summary 4 Laboratory Corrosivity Analysis Results 5 Design Soil Profile at MP 2.1 (STA 114+00 to 116+00) 6 Design Soil Profile at MP 2.35 (Taylor Creek Landslide - STA 127+00 to 129+00) 7 UDOT CBR Correlations for Subgrade Resilient Modulus, MR 8 Zion Park Shuttle Bus Daily Trips 9A Transmark Shuttle Bus – Current Bus Fleet 9B Catalyst E2 – New Bus Fleet 10 Forecasted Traffic and ESALs 11 Summary of Required Structural Number 12 Pavement Section Thickness Recommendations for Kolob Canyons Road 13 Pavement Section Thickness Recommendations for Scenic Drive – Zion Lodge Intersection 14 MP 2.1 MSE Wall configuration 15 Reinforced Soil Slope at MP 2.35 16 Summary of Static Lateral Earth Pressure Coefficients 17 Seismic Design Ground Motion Parameters

Figures

1 Location Map and Vicinity Map

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1.0 Introduction

This report provides geotechnical design recommendations for pavement improvements and mitigation of landslide areas and roadway slumps for the Kolob Canyons Road Project, a 3R project in Zion National Park Utah. The proposed pavement improvements to the roadway include 5.35 miles of pavement rehabilitation, several culvert replacements, slope stabilization, curb and pullout removal or replacement, and parking lot/pullout reconfigurations. In addition, there is the potential for pavement reconstruction at the intersection of Scenic Drive and the Zion Lodge entrance.

CH2M performed a geotechnical field investigation that included pavement coring and soil borings for support of pavement evaluation and design of roadway improvements, and soil borings for the purpose of evaluating slope movements that are damaging the roadway. In addition, CH2M advanced soil borings and installed two inclinometers at two locations where embankment and pavement damage from slope movements has occurred previously. The soil boring locations are shown on the Exploratory Boring Location Maps in Appendix A.

1.1 Purpose and Scope

The purpose of this technical memorandum is to present the findings of the geotechnical field exploration program and provide geotechnical design recommendations to the CH2M design team.

The scope of work consisted of the following:

• Conduct a geotechnical investigation, including a pavement condition survey

• Collect background information and review traffic information provided by the National Parks Service (NPS) consisting of monthly traffic counts from 1991 to 2016

• Complete a geotechnical field exploration program at the project site consisting of pavement cores and soil borings. Identify poor soils and/or poor drainage conditions within soil borings, locate sub-excavation zones, and determine thickness of existing asphalt concrete pavement.

• Perform laboratory testing of selected samples. Estimate appropriate parameters for pavement thickness design

• Develop a pavement rehabilitation and/or reconstruction recommendations for the existing asphalt pavement section, and develop flexible pavement sections for Kolob Canyons Road mainline, pullouts, and parking lots

• Develop a rigid and flexible pavement section for the Scenic Drive and Zion Lodge Intersection

• Provide a performance-graded (PG) binder recommendation

• Develop a soil profile(s)

• Conduct geotechnical analyses, including slope stability evaluation(s)

• Evaluate and develop construction options

• Prepare a Final Geotechnical Design Report

1.2 Project Description

The Central Federal Lands Highway Division (CFLHD) of the Federal Highway Administration (FHWA), in cooperation with the National Park Service (NPS), are proposing improvements to Kolob Canyons Road and Scenic Drive in Zion National Park, which sees more than 4.3 million visitors each year. Kolob

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Canyons Road, Route 13, is 5.35 miles long and is owned and maintained by the NPS. Kolob Canyons Road is located to the east of I-15 at Exit 40 in the State of Utah.

The existing topography within the limits of Kolob Canyons Road is mountainous, with steep cut and fill slopes. The road begins at the junction of I-15 and Kolob Canyons Road, climbs up the Taylor Creek drainage and through a section of Kolob Canyons along various side slopes, valleys, and multiple drainage crossings, then terminates at the Kolob View Point parking lot/turn-around. The road consists of two travel lanes with shoulders and various pullouts, parking areas, and overlooks.

The project proposes to pulverize the existing pavement section and place a new wearing course on Kolob Canyons Road for the entire 5.35 miles, with possible areas of roadway realignment to provide two 12-foot wide travel lanes and 3-foot wide shoulders. Pavement that is outside of this roadway template and is not part of a pullout or parking lot will be removed.

The proposed road improvements will closely follow the existing road, with minor realignments as needed to improve safety. Improvements will require grading of roadside ditches, curbing to accommodate a constant typical section, and removing pullouts to reduce impacts and reduce the paved area along the route. Two parking lots will be reconfigured, which will require removal and relocation of culvert drop inlets and outlet pipes. Existing culverts and drop inlets that are damaged or full of sediment will be replaced to improve roadway drainage.

Figure 1. Location Map and Vicinity Map

Begin Project Milepost 0.0

End Project Milepost 5.35

South Fork Taylor Creek

Milepost 3.34

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1.3 Existing Conditions and History

Kolob Canyons Road At the time of our explorations, the existing pavement condition was poor to fair with transverse cracking and occasional longitudinal and alligator cracking, as well as shoulder deterioration. The current roadway surface consists of a chip-seal coating with reddish aggregate. Several asphalt patches consisting of thin localized overlays to repair surface settlement and pavement cracking, or “blade patches”, were evident at areas of significant pavement distress along with occasional pothole repairs.

According to the NPS, the construction history of Kolob Canyons Road includes the following:

• Original Construction in late 1960s – included 2 to 2.5 inch hot asphalt concrete pavement (HACP).

• In 1979, 3 landslides were observed along the route that closed the road, including a landslide at MP

2.3. This slide was described in a Federal Highway Administration report dated June 1979 as fill slope failure exhibiting principally translational movement, 40 feet in length, having occurred during late winter under wet conditions. The scarp at the head of the slide was semi-circular, extending within 4 feet of the centerline. According to the report, this initial slide likely occurred at the uphill section of an existing pavement distress related to more recent slope movement. FHWA advanced a single soil boring at centerline above the slide, and encountered 4.5 feet of red-brown sandy and silty gravel road fill overlying 11 feet of native red-brown sandy clayey silt and talus. A soft red-gray shale formation was encountered at a depth of 17 feet. Undocumented repairs were completed and the road was re-opened.

• In 1983, new landslide movement at MP 2.3 was observed. The National Park Service prepared a Narrative Statement that described a slump area in excess of 100 feet in length from the toe of the cut slope to the stream below, caused by excessive moisture conditions during the winter of 1982-

83. The road surface settled approximately 10 feet with the entire slope moving. On 4/1/83, temporary measures were taken to place approximately 9 feet of fill over the slump, with approximately 1 foot of base gravel placed on the fill to bring the area back to road grade. Within 2 days, the slump area settled an additional 2 feet. After one month, the slump appeared to stabilize, at which time the 1 foot of base gravel was removed and the slump area backfilled with additional fill material, followed by base rock. These repairs, ultimately consisting of up to 12 feet of fill placed in the slump area, were completed in June 1983. A previous drain system is noted, possibly installed in 1979.

• In September 1983, the National Park Service road crew excavated as much of the road bed as possible. After the excavation, approximately 150 to 200 feet of 8-inch diameter flexible drain pipe was installed. An 18-inch thick drain layer of 2- to 4-inch diameter lava rock was placed with filter fabric over the drain layer. The slump area was then built up to subgrade with 12-inch lifts of 2-inch minus washed rock with filter fabric between each lift.

• In 1988, additional repairs were completed at the landslide at MP 2.3, and a 1.5-inch-thick HACP, overlay was placed over the entire roadway. The Division of Construction and Maintenance prepared a Memorandum dated November 21, 1988 regarding the Zion pkg. #B00, overlay route 7 (Kolob Canyons Rd). An inspection of the slide area on Route 7 near milepost 2.3 was discussed, and memo comments suggest that the 1983 repair worked for 5 years, but renewed slumping resulted in a 2” deep tension crack crossing the pavement and 12-inch wide cracks appearing in the embankment slope below the road. The Memo reported that the slide was caused by the stream undercutting the roadway embankment toe during storm runoff, resulting in an over-steepened embankment. The memo also references installation of 24-inch minimum diameter riprap as a channel liner/buttress at the toe of the slide.

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• Since 1988, there have been 3 or 4 chip seal applications, with the last one occurring in 2009.

• In 1991, there was additional slope movement at MP 2.3. The Division of Construction and Maintenance prepared a Memorandum dated February 19, 1991, which described “continual movement of the area” and documented a survey of the slide area. The opinion of the author was “it appears that the cause of the slide is erosion at the toe and not intrusion of water in the testholes above the slide, but there is recent evidence of movement within the slide area.” This memo also discusses the possibility of placing riprap at the toe of the slide to act as a buttress.

The most recent “blade patch”, consisting of an HACP overlay of roadway slides and slumps, occurred in 2013. Since then, there has been less observed roadway movement in slide areas than seen prior to 2013.

The roadway prism includes through-cuts, through-fills, balanced cut-fill sections, and sliver fills along the route. The existing roadway embankments consist primarily of loose clayey sand and were constructed at a slope ratio of 1.5H:1V. As described above, the existing embankment slopes have not performed well over the years, requiring repeated slope repairs at MP 2.35 and pavement overlays at MP 2.1, 2.35, and other locations along the route.

Scenic Drive There is the potential to reconstruct the existing pavement at the intersection of Scenic Drive and the Zion Lodge entrance. There is notable rutting and shoving of the existing asphalt pavement surfaces, up to 2 inches in depth, due in part to the turning and stopping of the shuttle fleet buses during hot days and perhaps an insufficient asphalt binder grade for the temperature range actually experienced at the site.

The maintenance history of Scenic Drive includes a 2004 3R road rehabilitation, consisting of 8 inches asphalt stabilized full depth pulverization with a 2.5-inch-thick overlay of HACP.

1.4 Pavement Conditions

Table 1 summarizes the existing pavement and subgrade conditions along Kolob Canyons Road based on the geotechnical exploration program.

Table 1. Existing Pavement and Subgrade Conditions along Kolob Canyons Road

MP

Start

MP

End

Total AC Pavement Thickness (inches)

Chip Seal Surface

Thickness (inches)

Existing Base Thickness (inches) Subgrade Soil Type Pavement Distress

0.0 0.4 3.5 0.5 7 Lean clay with sand, moist, stiff

Minor transverse and structural cracking

0.4 1.05 6 0.5 8 Clayey sand, moist, dense

Structural cracking and minor rutting at MP 0.5 and 0.9

1.05 2.06 7 0.5 6 – 12 Silt with sand, moist, very stiff

Structural cracking, minor rutting, and cut bank springs at

MP 1.9

2.06 2.14 9.5 – 16 None 16 – 24 Lean clay with sand, moist, firm to stiff

Outside lane slump with severe longitudinal cracking

2.14 2.33 7 0.5 6 – 12 Silt with sand, moist, very stiff

Minor transverse and structural cracking

2.33 2.37 36 – 42 None 12 Silty sand with gravel, moist, loose

Roadway slide, pavement severe cracking

2.37 2.4 10.5 0.5 11 Lean clay with sand, moist, stiff

Minor transverse and structural cracking

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Table 1. Existing Pavement and Subgrade Conditions along Kolob Canyons Road

MP

Start

MP

End

Total AC Pavement Thickness (inches)

Chip Seal Surface

Thickness (inches)

Existing Base Thickness (inches) Subgrade Soil Type Pavement Distress

2.4 2.65 4.5 0.5 10 – 11 Lean clay with sand, moist, stiff

Structural cracking, minor rutting inside lane, cut bank spring at MP 2.5 to 2.65

2.65 3.1 3 – 10.5 0.5 10 – 11 Lean clay with sand, moist, stiff

Transverse cracking with structural cracking and rutting at wheel paths, pothole repairs at MP 2.8 to 3.0

3.1 3.3 5.5 – 6 0.5 10 – 12 Elastic silt with sand, dry to moist, stiff

Minor transverse and structural cracking

3.3 5.3 3.5 - 6 0.5 8 - 12 Lean Clay with sand, moist, very stiff

Sunken shoulder at MP 4.2, minor structural and transverse cracking along road shoulder at MP 4.5 to 5.25

2.0 Technical Data

This section of the report presents the data collected from the field exploration program and laboratory testing program for the project.

2.1 Geotechnical Field Exploration Program

The geotechnical field exploration program consisted of advancing 22 shallow pavement borings along Kolob Canyons Road and Scenic Drive, and nine geotechnical soil borings up to a depth of 45 feet along Kolob Canyons Road, between September 11 and September 23, 2017. The pavement and soil borings were completed to explore subsurface conditions, determine the thickness of the existing pavement section, investigate groundwater, roadway slumping, and an existing landslide, and to collect material for laboratory testing for classification and determination of pavement thickness design parameters.

Cascade Drilling, Inc of Salt Lake City, UT drilled the geotechnical pavement and soil borings using a Mobile B57 and a CME 85 truck mounted drill rig. The pavement borings were backfilled and compacted using the excavated native soil, and the pavement was repaired with cold patch.

At each soil boring, bulk samples consisting of 5-gallon buckets were collected at the depth corresponding to the pavement subgrade elevations for soil classification, gradation, moisture-density testing, and R-value testing. Disturbed soil samples obtained from Standard Penetration Test, or SPT, sampling per ASTM D1586 were visually classified in accordance with ASTM D2488, Standard Practice for Description and Identification of Soils (Visual-Manual Procedure) and stored in zip lock plastic bags for selective testing.

The soil boring locations were selected by CH2M. The soil boring locations are shown in Appendix A, and boring logs are included in Appendix B. Pavement core photos are included in Appendix C. A summary of the boring locations and exploration depths is presented in Table 2.

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Table 2. Soil Boring Summary

Boring ID Location Approximate

STA

Total AC thickness (inches)

Existing Base thickness (inches)

Completion Depth

(feet, bgs)

P-1 MP 0.3, outside lane 19+50 3.5 7 11.5 P-2 MP 0.5, inside lane 30+00 5.5 8 6.5 B-1 MP 0.65, outside lane 40+00 6 24 25.3 P-3 MP 1.4, outside lane 78+50 7.5 6 2.1 P-4A MP 1.9, inside lane 106+00 7 6 6.5 P-4B MP 1.95, inside lane 107+50 7 12 5.8 B-2 MP 2.10, outside lane – shoulder slump 115+10 9.5 24 31.0 B-3 MP 2.14, outside lane – shoulder slump 116+10 16 16 41.5 B-4/B-5A MP 2.35, outside lane – landslide 128+50 42 6 45.3 B-5 MP 2.36, outside lane – landslide 128+90 36 -- 32.9 B-6 MP 2.37, outside lane 129+50 10.5 11 21.0 P-5A MP 2.6, inside lane 141+75 4.5 11 3.1 P-5B MP 2.6, inside lane 142+50 4.5 10 14.0 B-7 MP 2.7, outside lane 146+50 10.5 7 27.2 P-6 MP 2.8, outside lane 149+75 3 11 6.5 P-7 MP 3.05, outside lane 165+00 8.25 9 5.5 P-8 MP 3.2, inside lane 173+00 5.5 10 6.5 P-9 MP 3.25, parking lot 176+00 6 12 4.3 P-11 MP 3.4, outside lane 184+00 5 8 2.7 B-8 MP 3.8, outside shoulder 205+50 3.5 11 16.5 P-12 MP 4.2, inside lane 225+00 3.5 9 2.8 P-13 MP 4.45, outside pullout 238+00 3 10 6.5 P-14 MP 4.5, outside lane 240+50 6 11 6.5 P-15 MP 4.9, outside lane 263+50 3.5 11 6.5 P-16 MP 5.25, outside lane 280+50 3.25 10 6.5 P-17 MP 5.3, parking lot 282+50 3.5 12 5.8 B-9 MP 5.3, parking lot 283+00 3 12 12.5 P-18 Scenic Dr. P-1 at MP 2.8 - Zion Lodge intersection -- 12 10 6.5

P-19 Scenic Dr. P-2 at MP 5.3, inside lane -- 10.5 12 6.5 P-20 Scenic Dr. P-3 at MP 6.1, inside lane -- 14 10 6.5

The sampling intervals and the field classifications of the soil samples are recorded on the soil boring logs included in Appendix B. Selected soil samples from the soil borings were tested in a laboratory to aid in soil classifications and to provide data for use in engineering analyses. A more detailed discussion of the laboratory testing program is provided below.

2.2 Laboratory Testing

Laboratory testing for this project was performed by Terracon Consultants Laboratory in Las Vegas, NV, on selected soil samples. Laboratory testing was performed using the following test methods:

• AASHTO T99, Standard Test Methods for Moisture-Density Relationship of Soil Using Standard Effort

• ASTM D2844, Standard Test Method for R-Value of Soils

• AASHTO T265, Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass

• AASHTO T89/T90, Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils (Atterberg Limits)

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• AASHTO T27, ASTM D6913, Standard Test Method for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis

• AASHTO T11, ASTM D1140, Standard Test Method for Amount of Material in Soil Finer than the No.

200 Sieve

• Corrosion Suite (pH – AASHTO T289, sulfate content – AASHTO T290, chloride content – AASHTO T291, resistivity – ASTM G57)

• ASTM D4829 – Expansion Index of Soil

• ASTM D3080 – Direct Shear Test

A summary of the laboratory test results is presented in Table 3. The complete laboratory test results are presented in Appendix C.

Table 3. Laboratory Test Results Summary

Boring ID Sample

ID

Sample Depth (feet)

USCS

Class

Water Content

P200

Liquid Limit

Plastic Limit

Plasticity Index

(%) Other Tests

P-1 SS-3 &

SS-4

5 – 11.5

GM

with sand

2 37 NP NP NP Corrosivity Analysis

P-2 Bulk 2 - 5 SC with gravel

33 41 25 12 13 Standard Proctor (combined with P-5B), R-value = 16.0

P-4A & P- 4B

SS-3 5 – 6.5 CL-ML 6 66 24 20 4 Corrosivity Analysis

P-5B Bulk 2 - 5 CL 11 53 28 16 12 Expansion Index, Standard Proctor (combined with P-2), R-value = 11.0

P-8 Bulk 2 - 5 MH 6 63 54 33 21 Expansion Index, Standard Proctor (combined with B-9), R-value = 5.0

P-11 Bulk 1 - 3 6 39 -- -- -- R-value = 30.0 P-14 Bulk 2 - 4 CL 5 -- 21 17 4 Expansion Index, Standard Proctor

B-2 SS-1 &

SS-2

2.5 - 5 SC -- 35 25 16 9

B-2 SS-3 10 –

11.5

-- 27 -- -- --

B-2 SS-4 15 –

16.5

CH 21 90 54 23 31

B-2 ST-5 17.5 -

CL 4 26 17 9 Direct Shear (phi = 8 deg, c = 2316 psf)

B-4/B-5A ST-5 20 –

20.8

CL 14 55 25 16 9

B-4/B-5A SS-6 20.8 –

22.3

SM 12 47 23 20 3

B-4/B-5A SS-7 25 –

26.5

CL-ML 13 55 24 17 7

B-4/B-5A ST-8 27 - 29 CL 12 60 30 15 15 Direct Shear (phi = 20 deg, c = 1431 psf)

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Table 3. Laboratory Test Results Summary

Boring ID Sample

ID

Sample Depth (feet)

USCS

Class

Water Content

P200

Liquid Limit

Plastic Limit

Plasticity Index

(%) Other Tests

B-4/B-5A GRAB 25 - 30 CL -- 57 27 15 12 Reconstituted Direct Shear (phi = 30 deg, c = 10 psf)

B-5 SS-4 20 –

21.5

CL 12 63 26 18 8

B-5 SS-5 25 –

26.5

SM 14 49 21 18 3

B-8 SS-3 &

SS-4

10 – 16.5

SM

with gravel

8 47 NP NP NP Corrosivity Analysis

B-9 Bulk 2 - 5 CL 14 58 34 18 16 Standard Proctor (combined with P-8), R-value = 9.0

B-9 SS-3 &

SS-4

5 – 11.5

SM 10 42 NP NP NP Corrosivity Analysis

Scenic Dr P-1

Bulk 2 - 5 SM 3 8 -- -- -- Standard Proctor, R-value = 50.0

Scenic Dr.

P-3

Bulk 2 - 5 SM 23 37 NP NP NP Expansion Index, R-value = 53.0

Notes:

% = percent P200 = Percent of material passing the No. 200 sieve CL = Lean Clay SM = Silty Sand SC = Clayey Sand GC = Clayey Gravel USCS = Unified Soil Classification System

Table 4. Laboratory Corrosivity Analysis Results

Boring ID Sample ID

Sample Depth (feet)

USCS

Class

Water Content

(%) pH

Saturated Resistivity (ohm/cm)

Soil Chloride, Cl (ppm)

Soil Sulphate, SO4

(ppm)

P-1 SS-3 & SS-4 5 – 11.5 GM with sand

2 8.0 732 33 33

P-4A & 4B SS-3 5 – 6.5 CL-ML 6 8.1 825 48 30

B-8 SS-3 & SS-4 10 –

16.5 SM with gravel

8 8.6 2304 38 55

B-9 SS-3 & SS-4 5 – 11.5 SM 10 8.6 2643 29 87

Notes:

ppm = parts per million

2.3 Subsurface Conditions

The site subsurface profile generally consists of 2 to 20 feet of native soils overlying siltstone or sandstone. The native subgrade soil is generally a stiff to very stiff lean clay with sand. The segment from MP 3.1 to 3.7 consists of a stiff elastic silt to silt with sand.

Beginning from the ground surface downward, the generalized soil profile at MP 2.1 and 2.35 consists of the following:

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• Existing Pavement Section. The existing pavement consists of 12 to 36 inches asphalt concrete (AC) pavement over varying thickness of aggregate base.

• Lean Clay with sand (CL). This subgrade layer starts just below the existing pavement section and was encountered to a depth of approximately 9 feet below ground surface (bgs) at MP 2.1. This layer was not encountered at MP 2.35. It is brown to red-brown, moist, stiff, with fine-grained sand.

Field SPT N-values ranged from 7 to 9, indicating a firm to stiff consistency.

• Silty Sand with gravel (SM). This upper gravel embankment layer was observed below the subgrade layer to a depth of approximately 15 feet bgs at MP 2.1 and 18 feet bgs at MP 2.35. It ranged from 5 feet thick at MP 2.1 and 15 to 17 feet thick at MP 2.35, and consists of brown, light gray, and light purple, dry to moist, fine to coarse sand, sub-rounded to sub-angular gravel up to 1-inch. Field N-values ranged from 2 to 10 in the upper portion of the layer to 17 to 24 in the lower portion, indicating a loose to medium dense relative density.

• Lean to Fat Clay with sand (CL/CH). Below the subgrade layer and the upper gravel layer, this potential embankment layer was found to a depth of 19 to 25 feet bgs at MP 2.1 and 30 feet bgs at MP 2.35. The layer thickness ranged from 4 to 10 feet at MP 2.1 and 10 to 12 feet at MP 2.35, and is red-brown and olive-gray, moist, with fine- to coarse-grained sand. Field N-values ranged from 10 to 18 at MP 2.1, indicating a stiff consistency. At MP 2.35, field N-values ranged from 4 to 11, indicating a soft to stiff consistency.

• Sandy Clay (CL). Below the embankment layers, this native soil layer is a shale formation. Thickness ranged from 2 to 6 feet and is greenish-gray to olive-gray, moist to wet, low plasticity, with 44 to 49 percent fine-grained sand. Field N-values ranged from 44 to refusal at MP 2.1 and from 26 to 30 at MP 2.35, indicating a very stiff to hard consistency.

Tables 5 and 6 present the design soil profiles, along with the measured and interpreted engineering properties.

Table 5. Design Soil Profile at MP 2.1 (STA 114+00 to 116+00)

Soil Type Layer Thickness

(feet) Consistency/ Density Field SPT N-Value γwet (pcf) sU (psf) φ’ (deg)

Lean Clay with sand (subgrade)

8 Stiff to very stiff 7 to 9 110 n/a 30

Silty Sand with gravel (embankment)

5 Loose 5 to 10 120 n/a 34

Lean to Fat Clay with sand (embank/native)

5 to 8 Stiff 10 to 18 110 n/a 30

Poorly-graded Sand with Silt (native)

0 to 8 Very dense 100 125 n/a 38

Sandy Clay/Shale (native) 10 Hard 44 to 100 110 100 35

Notes:

SPT = standard penetration test wet = in situ wet unit weight of soil pcf = pounds per cubic foot ’ = effective (drained) friction angle su = undrained shear strength

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Table 6. Design Soil Profile at MP 2.35 (Taylor Creek Landslide - STA 127+00 to 129+00)

Soil Type Layer Thickness

(feet) Consistency/ Density Field SPT N-Value γwet (pcf) sU (psf) φ’ (deg)

Silty Sand with gravel (embankment)

11 Loose 2 to 7 120 n/a 30

Silty Sand with gravel (embankment)

4 Medium dense 17 to 24 120 n/a 34

Lean Clay with sand (native)

12 Soft to Firm 4 to 11 110 n/a 20

Lean Clay with sand (native)

5 Very stiff 26 to 30 110 100 30

Lean Clay (Shale) 10 Hard 100 120 2000 30

Notes:

SPT = standard penetration test wet = in situ wet unit weight of soil pcf = pounds per cubic foot ’ = effective (drained) friction angle su = undrained shear strength

The wet unit weights and drained soil strength properties for the gravel and sand materials were estimated from Figure 7, “Correlations of Strength Characteristics for Granular Soils,” page 7.1-149 in NAVFAC DM-7.1 (Naval Facilities Engineering Command, 1986) using estimated relative densities based on SPT N-values, moisture content, and other information from the field exploration for the material types. For effective stress (drained) analyses, cohesion was assumed equal to zero for the cohesionless materials.

2.4 Groundwater Conditions

Groundwater was not encountered in the soil borings to the maximum depth of 45 feet below existing ground surface (bgs). However, pavement distress and site history information indicates the presence of stormwater seepage. Therefore, surface drainage improvements and pavement edge drains are recommended in specific areas in the design to minimize subgrade infiltration and improve pavement drainage where signs of cut bank and ditch seepage are evident.

Groundwater table measurements at standpipe piezometers installed at MP 2.1 and 2.35 indicate a groundwater table below a depth of 25 feet and 30 feet bgs, respectively, on 11/16/2017.

2.5 Regional Geology

Kolob Canyon is drained by Taylor Creek to the west and La Verkin Creek to the south, and is at the western margin of the Colorado Plateau, which consists of several sedimentary formations that dip gently to the east. The Colorado Plateau is considered a tectonically stable region underlain by generally horizontal sedimentary strata that are locally disrupted by early Tertiary Laramide basement-block uplifts, Oligocene/Miocene igneous intrusions, and late Tertiary to Quaternary basaltic lava flows. The Hurricane fault, which bisects the quadrangle, is the eastern-most major fault of the Basin and Range Province in southern Utah. The formation of the Kolob Canyons resulted from weathering and erosion of an elevated portion of the Colorado Plateau.

As described in the Geologic Map of the Kolob Arch Quadrangle and Part of the Kanarrabille Quadrangle, Washington and Iron Counties, Utah (Biek 2007), Kolob Canyons Road crosses colluvial and talus deposits generally less than 20 to 30 feet thick, members of the Navajo Sandstone and Kayenta Formation, and landslide deposits. The Navajo Sandstone is described as moderate-reddish-orange, massively cross-bedded, poorly to moderately well-cemented, well-rounded, fine- to medium-grained

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quartz sandstone. The Kayenta Formation is described as interbedded, thin- to very thick bedded moderate-reddish-brown siltstone, fine-grained sandstone, and mudstone with planar, low-angle, and ripple cross-stratification.

The landslide deposits are described as very poorly sorted, clay- to boulder-size, and locally derived material deposited principally by rotational slides. They are characterized by hummocky topography, numerous internal scarps, and chaotic bedding attitudes. The younger landslides (Qmsy) may have historical movement, but are typically characterized by slightly more subdued landslide features indicative of early Holocene to late Pleistocene age. They are typically several tens of feet thick, but some deposits may exceed 200 feet thick.

2.6 Inclinometers

Two inclinometer casings (inclinometers) were installed in select boreholes during the geotechnical field exploration for periodic observation of any possible ground movement of the existing slopes at MP 2.1 and 2.35. The inclinometers consist of a 2.75-inch-diameter plastic casing with grooves oriented at 90 degrees. The casing includes quick connect joints that ensure the grooves remain properly aligned and sealed to prevent intrusion of cement grout during installation. Once the entire length of casing was installed in the open borehole, cement grout was placed in the annulus space using a tremie pipe. Initial baseline inclinometer surveys have been performed on 9/24, 11/1, and 11/16/2017. Minor inclinometer displacements of less than 0.25 inches have been observed to date, but they appear to be related to grout setup and not ground movement.

3.0 Design Recommendations

This section provides recommendations for design and construction of the project.

3.1 Drainage

The pavement evaluation indicates the pavement distress along Kolob Canyons Road is caused by aging of the asphalt concrete and poor subsurface and surface (stormwater) drainage. In areas of active seepage or evidence of cut bank seepage, edge drains or highway interceptor drains are recommended along the inside curb lines or below roadside ditches, with equally spaced cross drains trenched through the subgrade or connecting to a culvert.

3.2 Pavement Design

The following pavement design parameters and design thicknesses conform to values presented in the U.S. Department of Transportation and Federal Highway Administration (FHWA) Federal Lands Highway Project Development and Design Manual (PDDM), dated March 2008, and the 1998 UDOT Pavement Management and Pavement Design Manual, updated 2008 (UDOT 1998). Where they have different recommendations, the UDOT suggested value was used. Traffic analysis was completed using methods presented in the 1993 American Association of State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures (AASHTO 1993), with truck factors from Exhibit 11.2-A of the Federal Highway Administration’s Federal Lands Highway Design Manual (FHWA 2014). Pavement thickness design calculations and required structural numbers (SN) were computed using the computer program WinPAS 2012 (American Concrete Pavement Association 2012) in combination with a CH2M developed computation spreadsheet. Both of these tools are based on the AASHTO 1993 pavement thickness design methodology.

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3.2.1 Resilient Modulus

Material parameters for design were estimated based on soil exploration by CH2M and laboratory testing completed by Terracon in Las Vegas, NV. R-value testing was conducted on 6 separate bulk samples of subgrade soils collected by CH2M during the geotechnical investigation.

According to the Draft Federal Lands Highway Project Development and Design Manual (PDDM), guidance for determining the effective soil resilient modulus is provided in AASHTO 1993, and equations for correlating soil index properties to resilient modulus are provided in the Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures (NCHHRP 1-37A, 2004). Correlation equations developed by individual state DOTs may also be used as appropriate.

Material parameters for design were determined by conversion of R-value to resilient modulus values according to AASHTO methodology. For comparison, California Bearing Ratio (CBR) values were calculated from soil index properties according to the Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures (NCHHRP 1-37A, 2004), then converted to resilient modulus using UDOT methodology.

Based on criteria established in AASHTO 1993 and the PDDM, the following equation was used to convert the laboratory R-value to a subgrade resilient modulus for design:

MR = 1,000 = 555 * R-value (for fine-grained non-expansive soils)

Four bulk samples (P-2 Bulk, P-5B Bulk, P-8 Bulk, and B-9 Bulk) were identified for testing from the subgrade along Kolob Canyons Rd, and 2 bulk samples were identified for testing along Scenic Dr. For Kolob Canyons Rd, Hveem Stabilometer (R-value) tests per ASTM D2844 resulted in R-values of 9.0, 11.0, and 16.0 for lean clay subgrade soils, and an R-value of 5.0 for elastic silt subgrade soils. For Scenic Dr., the R-value tests on the silty sand subgrade soil resulted in R-values of 50.0 and 53.0.

Using the above correlation, the MR for lean clay ranges from 5,995 to 7105 psi for R-values of 9.0 and 11.0, respectively. According to the UDOT 2014 Pavement Design Manual (UDOT 2014), the typical range for AASHTO Soil Class A-6 (lean clay) is 7,250 (low) to 14,500 (mean) psi. Therefore, a design MR of 5,995 (from MP 3.7 to 5.3) and 7,105 psi (from MP 0.0 to 3.1) were selected for the lean clay soils.

As a conservative check of the Kolob Canyons Road flexible pavement design, a design MR of 3,775 psi was selected for the elastic silt subgrade soils encountered at MP 3.2 (from MP 3.1 to 3.7). According to the UDOT Pavement Design Manual (UDOT 2014), the typical range for AASHTO Soil Class A-7-6 (fat clay) is 5,750 psi (low) to 11,500 psi (median), and 7,750 psi (low) to 15,500 psi (median) for AASHTO Soil Class A-5 (MH). A design value of 3,775 psi is below the typical ranges included in the UDOT Pavement Design Manual for elastic silt and fat clay subgrade soils, but is the recommended value for this design.

For Scenic Drive, a design MR of 12,000 psi was selected. The typical range for AASHTO Soil Class A-2-4 (silty sand and clayey sand with PI < 10) is 10,750 psi (low) to 21,500 psi (median).

The UDOT 2008 Pavement Design Guide (UDOT 2008) and the UDOT 2014 Pavement Design Manual of Instruction (UDOT 2014) present the following equations to estimate the subgrade resilient modulus from CBR Values: the Level 2 correlation of subgrade resilient modulus with CBR is:

MR = CBR * 1500 CBR Correlation #1

MR = 2,555 x CBR^0.64 CBR Correlation #2 (Level 2 correlation)

Using the following CBR correlation for soil index properties from NCHRP 1-37A (for plastic soils, with P200 equal to percent passing the No. 200 sieve used as a decimal, and PI equal to the plasticity index used as a percent):

CBR = 75 / (1+ (0.728 * (P200 * PI)))

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Calculated CBR values for the clay soils range from 9.7 to 15.4, and the calculated CBR for the elastic silt is 7.1. According to NCHRP 1-37A, CBR values typically range from 5 to 15 for lean clays, and from 2 to 8 for elastic silts.

Using the UDOT CBR correlations for comparison, the MR values presented in Table 7 were estimated and compared to the design MR values.

Table 7. UDOT CBR Correlations for Subgrade Resilient Modulus, MR

R-value Soil Type Estimated CBR

MR from CBR Correlation #1

(psi)

MR from CBR Correlation #2

(psi)

Design MR

(psi)

5 MH 2 – 3 3,000 to 4,500 3,982 to 5,161 3,775

9 CL 5 7,500 7,157 5,995

11 CL 5 7,500 7,157 7,105

50 SM 19 28,500 16,819 12,000

3.2.2 Forecasted Traffic and ESALS

The Park provided traffic data in the form of monthly vehicular counts from 2006 to 2017. No data was provided regarding the percentage of trucks. These traffic counts were taken at the Visitor Center entrance where traffic counts range between 1643 to 21094 vehicles per month. This use is comprised of a combination of Park visitors and I-15 freeway pass through vehicles. The Park stated that a significant portion of the vehicles that are counted at the Visitor Center entrance do not proceed beyond the Visitor Center. Therefore, the number of vehicles that use the entire 5.3 miles of Kolob Road can be assumed to be less than those counted at the Visitor Center entrance. For the purposes of this design, a conservative approach was used and the traffic counts at the Visitor Center entrance were not reduced. In addition, subsequent review of traffic counts resulted in a significant reduction in the ADT values. Refer to the Project’s 100 Percent Design Technical Memorandum for the description of the change to the traffic ADTs (seasonal ADTs of 290 and 590 for 2018 and 2038, respectively). However, since this resulted in a slight reduction in the design ESALs, the traffic analysis presented here was not modified and is considered conservative.

The types of vehicles accessing the roadway are mainly comprised of passenger vehicles and recreational vehicles such as motorhomes and trailers. Occasionally, pick-up trucks pulling horse trailers are present to facilitate equestrian use on some of the trails. In addition to these uses, there is a very limited number of tour busses that occasionally travel to the end of the road. There is no other known reason for other heavy truck usage on the roadway. Based on discussion with the Park during the Scoping Meeting Site Visit and the 70% Review Site Visit, there was no indication that the types of uses would change in the future.

The monthly traffic counts were used in coordination with assumed values of weekend usage to determine the current ADT. The busiest months of the past 5 years were used to determine an average busiest month traffic count. An assumption that 40% of the that monthly traffic was used to calculate the ADT on a weekend day. This provided the ADT on a weekend day during, on average, the busiest month of the year. The resulting ADT was 678, rounded up to 680 vehicles/day.

The future ADT was determined by graphing the past 10 years of vehicles/year data, and then projecting a linear trend line using Microsoft Excel to project count data 20 years into the future. The trend line resulted in a future yearly vehicular count of 162,361 vehicles. On average over the past 10 years, 14.7% of the yearly traffic occurred during the busiest month of the year. This average was applied to the future vehicle count to arrive at a 2036 monthly maximum vehicle count of 23,903 vehicles/month.

Again, 40% of these vehicles were assumed to use the road on the weekend, resulting in a weekend ADT of 1195 vehicles/day, rounded up to 1200 vehicles/day on a weekend day during the busiest month of

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the year. This is equivalent to a 2.2% growth rate over 20 years. Again, heavy vehicle usage is not anticipated to increase beyond its current percentage over the next 20 years.

These ADT values are conservative in that they represent all the traffic being counted at the Visitor Center on a weekend day during the busiest month of the year. If the provided traffic counts reduced to reflect less usage beyond the Visitor Center, are spread out over the course of the year, and not adjusted for the busier weekends, the ADT values would be lower.

Scenic Drive provides park visitor access to Zion Lodge and several viewpoints and shuttle bus stops within Zion Canyon primarily by shuttle bus. A traffic analysis was conducted for Scenic Drive based on an average number of buses per day from the Zion Park Shuttle Schedule included on the Zion National Park Fall/Winter Info Sheet, dated 9/21/17. Shuttle bus spacing varies from 7 to 15 minutes. According to the Fall/Winter Info Sheet, shuttle buses do not run during the months of December through March.

A total of 200 daily two-way vehicle trips were estimated for each month, as private vehicles can access Scenic Drive during the winter months, but are not allowed on Scenic Drive while the shuttle buses are operating. Average daily bus trips per month are presented in Table 7 below.

For flexible pavements, a 20-year design life was selected in accordance with the PDDM for 3R rehabilitation projects that increase the structural capacity of the pavement. This is the standard design life for flexible pavements per the UDOT 2014 Pavement Design Manual. For rigid pavements, UDOT recommends a 40-year design life (UDOT 2014).

Table 8. Zion Park Shuttle Bus Daily Trips

Month First bus Last bus # hours/day of bus operation Average bus spacing

(min) Average # bus trips/day

April – Sept 7:00 AM 8:30 PM 13.5 10 81 Oct 7:00 AM 7:30 PM 12.5 10 75 Nov 7:00 AM 7:00 PM 12 10 72

To determine an equivalent Truck ESAL Factor for the Zion National Park shuttle bus fleet, the General Axle Factor, GAF, was used:

GAF = (W / 18,000)3.8, where W is equal to the axle load of any type or spacing in pounds.

Per FHWA, GAFs have similar meaning and roughly the same magnitude as the AASHTO Load Equivalency Factors, or LEFs (FHWA 2000). Therefore, General Axle Factors and Truck ESAL Factors are considered equivalent.

The current bus fleet consists of Transmark-RE-29 Paratransit shuttle buses with Transmark-RE-29 trailers. Each shuttle bus and trailer has two axles (4 total per vehicle).

Table 9A. Transmark Shuttle Bus – Current Bus Fleet

Vehicle Type/Axle GAWR Truck ESAL Factor per Axle

Shuttle Bus – Front Axle 10,000 lbs 0.11 Shuttle Bus – Rear Axle 19,000 lbs 1.23 Shuttle Trailer – Front Axle 12,000 lbs .21 Shuttle Trailer – Rear Axle 12,000 lbs .21 Total Truck ESAL Factor for design = 1.8

Notes:

GAWR = Gross Axle Weight Rating ESAL = Equivalent Single Axle Load

The proposed new shuttle bus fleet will consist of Catalyst E2 electric buses, with 2 axles (2 total per vehicle).

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Table 9B. Catalyst E2 – New Bus Fleet

Vehicle Type/Axle GAWR Truck ESAL Factor per Axle

Catalyst E2 – Front Axle 16,094 lbs 0.65 Catalyst E2 – Rear Axle 25,906 lbs 3.99 Total Truck ESAL Factor for design= 4.6

Notes:

GAWR = Gross Axle Weight Rating ESAL = Equivalent Single Axle Load

Therefore, the Truck ESAL Factor for the Transmark Shuttle Bus and Trailer was set at 1.8, and 4.6 for the Catalyst E2 electric bus.

The traffic analyses are attached, and are summarized in Table 10 below. Base year average daily traffic (ADT) is two-way traffic. The number of bus trips per day is not expected to increase, as this is governed by the shuttle bus fleet size and the number of bus stops along the route. Therefore a zero growth rate was used to determine the design life ESALs for Scenic Drive. 20-year design life ESALs are provided for flexible pavement designs and 40-year design life ESALs are provided for rigid pavement designs.

Table 10. Forecasted Traffic and ESALs

Pavement Section Base Year ADT

(2016)

Total Design Equivalent Single Axle Loads (ESALs)

Base Year ESALs (2016) Design Life ESALS

Pavement Type

Kolob Canyons Rd (20-yr design life)

680 6,033 160,311 (2.2% annual traffic growth) Flexible

Scenic Dr – Existing Bus Fleet (20-yr design life)

200 53,516 1,070,430 (zero growth) Flexible

Scenic Dr – Existing Bus Fleet (40-yr design life)

200 53,883 2,155,740 (zero growth) Rigid

Scenic Dr – New Bus Fleet (20-yr design life)

200 136,676 2,733,788 (zero growth) Flexible

Scenic Dr – New Bus Fleet (40-yr design life)

200 137,043 5,482,789 (zero growth) Rigid

3.2.3 Pavement Design Parameters

The AASHTO 1993 and PDDM procedures require the use of specific design parameters for pavement thickness design. These parameters are variable based on the functional classification of the facility, local material sources, agency requirements, and judgement of the pavement designer.

Pulverized full depth reclamation (FDR) is the preferred alternative being considered for rehabilitation of the existing pavement section in Kolob Canyon. An untreated pulverized FDR layer can be created by pulverizing and mixing the existing HACP with the underlying base layer. This pulverized FDR layer can be incorporated into the proposed pavement section as a base layer for a new HACP layer. The PDDM indicates that the layer coefficient for pulverized FDR is appropriate for material with less than 25 percent fines. Therefore, pulverization will be limited to the existing HACP and the upper portion of the existing base layer. Practical limits for depth of pulverization is 12 inches for a single equipment pass.

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There are three types of rigid Portland cement concrete pavements (PCCP): plain jointed concrete pavement (PJCP), jointed reinforced concrete pavement (JRCP), and continuously reinforced concrete pavement (CRCP). UDOT prefers plain jointed concrete pavement (PJCP), with load transfer as required for traffic loading (UDOT Pavement Design guide, 2008).

The sections below indicate which parameters are necessary for project pavement design and provide a brief explanation of the selected parameter.

Reliability. The reliability factor for the design was set at 75 percent, based on PDDM for routes other than interstates with less than 2500 ADT. A reliability factor of 75 percent is also recommended in AASHTO 1993 for a local rural roadway or facility. For Scenic Drive, a reliability factor of 90 percent was selected to minimize future maintenance costs and the associated traffic delays to park visitors during roadway maintenance activities. For rigid pavement, UDOT recommends a reliability of 90 percent for roadways other than interstate highways (UDOT 2008).

Standard Deviation. A standard deviation value of 0.45 was selected, in accordance with UDOT 2008 and AASHTO 1993 for flexible pavement sections. For rigid pavements, a standard deviation of 0.35 was chosen in accordance with the PDDM. A standard deviation of 0.35 is recommended for rigid pavement by UDOT 2008.

Rupture and Elastic Modulus. For rigid pavement, a rupture modulus value (S’c) of 650 psi and an elastic modulus of 4,000,000 psi was selected in accordance with UDOT 2008.

Load Transfer. According to UDOT 2008, load transfer requirements for PJCP can be accomplished with a variety of devices, including smooth dowels in the transverse joints. The recommended load transfer coefficient with and without load transfer devices is 3.0 and 4.0, respectively, with no edge support.

Loss of Support. According to UDOT 2008, the loss of support value for the layer immediately below the PJCP is 1.0 for unbound, well-graded granular materials.

Initial Serviceability. An initial serviceability of 4.2 was selected for flexible pavement, in accordance with AASHTO 1993 and the PDDM. For rigid pavement, an initial serviceability of 4.5 was selected in accordance with UDOT 2008 and the PDDM.

Terminal Serviceability. For flexible and rigid pavements, a terminal serviceability of 2.5 was selected in accordance with PDDM and UDOT 2008 for roadways with an ADT between 500 and 5000.

Drainage Coefficient. This parameter modified the structural layer coefficients for untreated based materials based on the influence of potential water in the pavement section. The roadway design should address surface and subsurface drainage so that a value of 1.0 can be used appropriately.

Structural Layer Coefficients for Flexible Pavement Section. The layer structural coefficients are the backbone of AASHTO’s flexible pavement design. The coefficients were selected based on PDDM and UDOT 2008 recommendations. The assigned values for layer coefficients for this project are as follows:

• Hot Asphalt Concrete Pavement (HACP) – 0.40

• Pulverized Full Depth Reclamation (FDR) – 0.12

• Imported Untreated Base Course (UTBC - Aggregate Base) – 0.10

• Existing Untreated Base Course – 0.08

3.2.4 Performance-graded Binder Type

The performance-graded (PG) binder type was determined using the computer program LTPPBind v.3.1 Beta (Pavement Systems, LLC 2005) for a desired reliability of 98 percent at the pavement surface. At Kolob Canyons Road, the recommended performance-graded binder type is PG 64-28. This binder type is adjusted for design ESALS of less than 3 million and slow traffic speeds. At Scenic Drive, the

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recommended performance-graded binder type is PG 70-28. This binder type is adjusted for design ESALS of 3 to 10 million and slow traffic speed.

3.2.5 Recommended Pavement Sections

Based on the above pavement design parameters and a design life of 20 years for flexible pavement, the following required pavement structural numbers (SN) were developed:

Table 11. Summary of Required Structural Number

Road Section Design Period (years) Reliability (percent) Subgrade MR (psi) Required SN

Kolob Canyons Rd.

MP 0.0 to 3.1

20 75 7,105 2.36

Kolob Canyons Rd.

MP 3.1 to 3.3

20 75 3,775 3.01

Kolob Canyons Rd.

MP 3.3 to 5.3

20 75 5,995 2.52

Scenic Drive with New Buses

20 90 12,000 3.43

Kolob Canyons Road For Kolob Canyons Road, a rehabilitated flexible pavement section consisting of 3 inches of HACP over 8 inches minimum of pulverized full-depth reclamation over 4 to 6 inches of existing untreated base course is recommended.

From MP 3.1 to 3.3, the pulverization depth should be increased to 12 inches. Pulverized full-depth reclamation that extends below the existing asphalt and into the existing base will prevent reflective cracking. Based on the conservative subgrade modulus assigned to this section, a SN of 2.96 is considered adequate.