AZ FLAP PIM FR510-1 100 FINAL GEO and MNT Report.pdf

GEOTECHNICAL AND PAVEMENT REPORT

AZ FLAP PIMA FR510(1)

Sabino Canyon Park Road Improvements

Pima County, Arizona

Yeh Project No.: 221-083

August 29, 2023

Prepared for:

Atkins North America 7604 Technology Way, Suite 400

Denver, Colorado 80237 Attn: Ms. Heather Andrews, P.E.

Prepared by:

Yeh and Associates, Inc.

391 Front Street, Suite D

Grover Beach, California 93433 Phone: 805-481-9590

391 Front Street, Suite D Grover Beach, CA 93433

(805) 481-9590 www.yeh-eng.com

Colorado California Denver | Colorado Springs | Durango | Glenwood Springs | Grand Junction | Greeley Grover Beach | Ventura

GEOTECHNICAL AND PAVEMENT REPORT

AZ FLAP PIMA FR510(1)

Sabino Canyon Park Road Improvements

Pima County, Arizona

Yeh Project No.: 221-083

August 29, 2023

Prepared by:

Judd King, P.E. (CA, AZ), G.E. (CA) Geotechnical Engineer

Jamie L. Ross, P.E. (CA) Project Engineer

Independent Reviewer: Reviewed By:

Jonathan Blanchard, G.E. (CA) Robert F. LaForce, P.E. (CO) Principal Geotechnical Engineer Senior Materials Manager http://www.yeh-eng.com/ jking Pencil

Geotechnical and Pavement Report Yeh Project No. 221-083 Sabino Canyon Park Road Improvements August 29, 2023 i

TABLE OF CONTENTS

1. PURPOSE AND SCOPE OF STUDY

2. PROJECT UNDERSTANDING

3. EXISTING CONDITIONS

4. GEOTECHNICAL EXPLORATION AND TESTING

4.1 SITE RECONNAISSANCE

4.2 GEOLOGIC RECONNAISSANCE AND THIRTY PERCENT DESIGN VISIT

4.3 EXPLORATORY DRILLING

4.4 LABORATORY TESTING

5. SITE CONDITIONS

5.1 GEOLOGIC SETTING

5.2 TERRAIN AND VEGETATION

5.3 CLIMATE

5.4 EXISTING ROADWAY

6. SUBSURFACE CONDITIONS

6.1 EXISTING PAVEMENT AND SUBGRADE CONDITIONS

6.2 NEW PARKING LOT AREA

6.3 GROUNDWATER

7. GEOTECHNICAL ANALYSES AND EVALUATION

7.1 SEISMIC DATA

7.1.1 SEISMIC LATERAL EARTH PRESSURE FOR EXTREME LIMIT STATE

7.2 SLOPE STABILITY ANALYSES

7.2.1 SLOPE STABILITY CRITERIA

7.2.2 INPUT AND ANALYSES

7.2.3 RESULTS

8. CONCLUSIONS AND RECOMMENDATIONS

8.1 EARTHWORK - GENERAL

8.1.1 GENERAL GRADING

8.1.2 EARTHWORK FACTORS

8.1.3 EROSION AND SLOPE DRAINAGE

8.1.4 REUSE OF ONSITE SOIL

8.2 EMBANKMENT SLOPE DESIGN

ii

8.3 CUT SLOPE DESIGN

8.4 SUBEXCAVATION

8.5 PAVEMENT DESIGN RECOMMENDATIONS

8.5.1 DESIGN TRAFFIC VOLUME AND SUBGRADE

8.5.2 STRUCTURAL SECTION

8.5.3 BINDER AND MIX RECOMMENDATIONS

8.5.4 PAVEMENT MAINTENANCE

8.6 RETAINING WALLS

8.6.1 GABION WALL

8.6.2 PARKING LOT– WEST WALL (SOIL NAIL)

8.6.3 PARKING LOT - EAST WALL – (MSE)

8.7 PARKING LOT RESTROOMS

8.8 CORROSION CONSIDERATIONS

9. CONSTRUCTION CONSIDERATIONS

9.1 TEMPORARY SLOPES AND SHORING

9.2 GROUNDWATER CONSIDERATIONS

9.3 EXCAVATION CONSIDERATIONS

9.4 MATERIAL SOURCES

9.4.1 CONCRETE, ASPHALT CONCRETE AND AGGREGATE

9.4.2 GENERAL BORROW

10. LIMITATIONS

11. REFERENCES

List of Figures

FIGURE 1: PROJECT LOCATION MAP

FIGURE 2: EXISTING FAILING SOUTH RETAINING WALL

FIGURE 3: GEOLOGIC MAP (DICKENSON 1992)

FIGURE 4: PROPOSED 1V:1H CUT SLOPE (STATION 105+00)

FIGURE 5: SABINO CANYON PARK ROAD

FIGURE 6: TYPICAL EMBANKMENT CONSTRUCTION

FIGURE 7: SABINO CANYON PARK ROAD PAVEMENT RECOMMENDATIONS

FIGURE 8: PARKING LOT - GRANITIC BEDROCK

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List of Tables

TABLE 1: EXISTING PAVEMENT CONDITIONS ENCOUNTERED

TABLE 2: SUBGRADE PROPERTIES TEST SUMMARY

TABLE 3: PARKING LOT AREA SOIL PROPERTIES TEST SUMMARY

List of Plates

Field Exploration Plan – Proposed Project Limits .............................................................................................. 1a Field Exploration Plan – Proposed Parking Lot .................................................................................................1b

List of Appendices

Page Appendix A – Boring Logs Boring Record Legend ................................................................................................................ A-1 to 2 Boring Logs for 21E-01 to 03 ...................................................................................................... A-3 to 5 Boring Logs for 21P-01 to 03 ...................................................................................................... A-5 to 8 Boring Logs for 21W-01 to 04 ................................................................................................... A-9 to 12 Boring Logs for 22E-01 .................................................................................................................... A-13 Boring Logs for 22W-01 to 03 ................................................................................................. A-14 to 18 Drill Rig Set Up Photos ............................................................................................................ A19 to 25 Rock Core Photos ................................................................................................................... A-26 to 27 Appendix B – Results of Laboratory Testing Summary of Laboratory Results ................................................................................................. B-1 to 3 Mechanical Sieve Analyses ................................................................................................................ B-4 Proctor Compaction .......................................................................................................................... B-5 Corrosivity Test Summary (for chloride and sulfate) .......................................................................... B-6 R-Value ...................................................................................................................................... B-7 to 8 Consolidated Undrained Triaxial Test ....................................................................................... B-9 to 16 Unconfined Uniaxial Compressive Strength of Rock Cores ...................................................... B-17 to 20 Appendix C – Slope Stability Analyses Parking Lot West Wall – Soil Nail Wall Global Stability ................................................................ C-1 to 2 Parking Lot East Wall – MSE Wall Global Stability ............................................................................... C3 Appendix D – Pavement Design Calculations AASHTO Pavement Design Calculations ...................................................................................... D-1 to 2

1. PURPOSE AND SCOPE OF STUDY

Yeh and Associates was retained by Atkins to provide geotechnical recommendations for the design of roadway improvements as part of the Federal Highway Administration, Central Federal Lands Highway Division (FHWA-CFLHD) project for Sabino Canyon Park Road in Pima County, Arizona. The project is located on a 0.5-mile-segment of Sabino Canyon Park Road (Forest Road 510) along Sabino Creek within the communities of Mount Lemmon and Summerhaven. The site is approximately 19 miles northeast of the City of Tucson and at an elevation of approximately 7,700 feet and is shown in Figure 1.

The geotechnical evaluation consisted of a program of project coordination, field exploration, data review, laboratory testing, and engineering analyses as a basis for providing the recommendations in this report. This report provides recommendations for the design of parking and roadway improvements, culverts, retaining walls, public restrooms, and a multi-use parking lot.

2. PROJECT UNDERSTANDING

The layout of the project and stationing from the Atkins (2022) 30% plan submittal is shown on Plates 1a and 1b, Field Exploration Plan. The project generally consists of improvements to Sabino Canyon Park Road (also known as Forest Road 510) and the design of the new parking lot. The approximate project limits extend from the Forest Road gate at the south end of Sabino Canyon Road station (100+21) north to the intersection of Carter Canyon Road (station 123+50). The improvements are planned to improve roadway safety and mitigate congestion of vehicles parking along the existing roadway by providing additional parking for recreational uses. The proposed improvements along Sabino Canyon Park Road generally include the following:

• A new paved parking lot with 71 vehicle stalls, 4 Americans with Disabilities Act (ADA) accessible stalls, and two motorcycle stalls. The parking lot will be supported on the west side by a retaining wall. The west wall will be an approximately 608-foot-long soil nail wall that will support cut and fill heights that vary from 4 to 13 feet. The east side of the parking lot will be

Figure 1: Project Location Map supported on either a 1:2 (vertical to horizontal) fill slope or by a retaining wall. The east wall (if selected) will be an approximately 132-foot-long mechanically stabilized earth (MSE) wall and support fill heights of up to 17 feet. Walls will include sculpted shotcrete facing to match the context of the site and nearby rock exposures. Retaining walls will be contractor designed.

• Two vault type prefabricated public restrooms will be provided within the parking lot. The restrooms will have septic holding vaults up to 8 feet in depth.

• Sabino Canyon Park Road will be widened where practicable to two 11-foot-wide lanes with two 1-foot-wide paved shoulders and improvements along Sabino Canyon Park Road (including adding new street parking spaces asphalt surface rehabilitation). Cuts up to 15 feet high with anticipated gradients of 1v:1.5h (vertical to horizontal) are anticipated. A cut slope of 1v:1h is planned where rock is exposed along the west side of the road between approximate Stations 105+00 to 106+60.

• A new 5 to 6-foot-wide aggregate surfaced pedestrian path will be provided along Sabino Canyon Road and connect to the Arizona Trail.

• Drainage improvements will be made to Sabino Canyon Park Road including replacing an existing low water crossing with culverts and adding seven new culverts at other locations along the road with diameters of 24 to 38 inches.

• A new retaining wall along Sabino Creek that will be provided below the road from approximate station 106+96 to station 107+82. The new wall will replace an existing failed wire and rail post retaining wall that supported the roadway embankment adjacent to the creek. The new wall will be a gabion wall to support an embankment height of up to 8 feet (approximately 2 feet below the existing creek thalweg) designed by the contractor using standard details and drawings.

3. EXISTING CONDITIONS

Sabino Canyon Park Road (Forest Road 510) is an existing 18-to 22-foot wide, asphalt paved road with variable shoulders and a posted speed of 25 miles per hour. Cuts up to twenty feet and fills up to ten feet were constructed to support the roadway bench. Slope gradients are estimated at 20 to 40 percent along the roadway cuts and fills. The road is within the communities of Mount Lemmon and Summerhaven and serves as an access road to residences, the Pima County Wastewater Treatment Facility, and the Marshall Gulch Trailhead. Sabino Creek runs directly adjacent to the northbound lane of Sabino Canyon Park Road.

The existing low water crossing is located on Sabino Canyon Park Road near the entrance to the Pima County Wastewater Treatment facility at approximately station 118+00 that will be replaced with a new culvert as part of the project. An existing wire and rail post retaining wall that supports a portion of the road near the southern extent of the project (approximately station 107+15 to 107+82) was undermined 1 to 2 feet by Sabino Creek and will also be replaced as part of the project (see Figure 2).

A second existing wire and rail post retaining wall supports the road near the northern extent of the project (at about station 120+00 to 121+00). This northern wall will not be replaced as part of the project.

The proposed parking lot is within a forested portion of the project site. Th existing trees will be cleared from the parking lot area as part of the project.

The proposed parking lot area slopes eastward down to Sabino Canyon Road with variable gradients of 5 to 50 percent. An incised drainage with approximate variable depths of 3 to 8 feet is present at the south end of the proposed parking lot. Two smaller drainages cross the area where the parking lot is proposed.

4. GEOTECHNICAL EXPLORATION AND TESTING

The geotechnical exploration consisted of a program of geologic site reconnaissance, attendance of the 30-percent design review meeting at the site, exploratory drilling, and laboratory testing. The locations of the borings are shown on Plates 1a and 1b. The boring logs and photos of the rock cores are presented in Appendix A. Laboratory test results are presented in Appendix B.

4.1 SITE RECONNAISSANCE

Yeh personnel visited the project site on October 6, 2021, to mark boring locations in preparation for the 2021 exploratory drilling program as well as perform field cross sections for preliminary design.

Field cross sections were taken by Yeh personnel using tape and compass techniques at the two existing retaining wall locations, and the existing low water crossing location. Sections were also taken at the previously proposed restroom location and previously proposed roadway widening location at an existing rock outcrop which have since been removed from the project scope. Yeh personnel also reviewed the condition of the existing retaining walls and low water crossing. After additional subsurface exploration was needed in the revised parking lot area, Yeh visited the project on October 6, 2022 to mark boring locations in the parking lot area in preparation for the November 2022 exploratory drilling program and review site conditions.

4.2 GEOLOGIC RECONNAISSANCE AND THIRTY PERCENT DESIGN VISIT

Field reconnaissance was performed on as a part of the 30 percent design walk on March 29, 2022, with representatives from Atkins, Central Federal Lands, Pima County, and the United States Forest Service. The reconnaissance was performed to visually observe the condition of the roadway, low water crossing, proposed retaining wall areas, and proposed parking lot area. The 30-percent design

Figure 2: Existing Failing South Retaining Wall (Sta 107+15 to 107+82) plans were reviewed during the visit relative to field conditions including reviewing the proposed retaining wall and parking area locations as well as overall construction considerations for the project. The layout of the parking lot and restroom location was changed during the 30-percent design review which necessitated additional subsurface exploration for the updated parking lot layout.

4.3 EXPLORATORY DRILLING

Drilling for the project was performed in two phases. The first phase of drilling was performed prior to the 30-percent design submittal, and the second phase of drilling was performed following the 30-percent design submittal and subsequent revision of the parking lot location and layout. The drilling subcontractor for the first phase of drilling was Enviro-Drill, Inc. of Tucson, Arizona. Enviro-Drill drilled ten borings (21E-01 through 21E-03, 21P-01 through 21P-03, and 21W-01 through 21W-04) on Sabino Canyon Park Road on October 26 and 27, 2021. The borings were drilled using a truck-mounted CME- 75 drill rig equipped with 8-inch hollow-stem augers and were drilled to depths of approximately 5 to

20.4 feet below the road surface.

The drilling subcontractor for the second phase of drilling was Geomechanics Southwest, Inc. (GSI) of Tucson, Arizona. GSI drilled four borings (22E-01 and 22W-01 through 21W-03) at the proposed parking lot location on November 14 and 15, 2022. The borings were drilled using a track-mounted CME-75 drill rig equipped with 8-inch hollow stem augers and HQ rock coring equipment and were drilled to depths of 20 to 31.4 feet below the ground surface. Yeh personnel logged the subgrade conditions encountered and secured samples for subsequent laboratory testing for each phase of drilling performed.

Sampling within the borings was performed by driving either a modified California or standard penetration test (SPT) split spoon sampler at typical 2.5-foot intervals in the upper 5 feet and subsequently at 5-foot intervals below 5 feet. Bulk samples were also collected from the auger flights within the upper 5 feet of the boring. The SPT sampler has a 2-inch outside diameter, 1-3/8-inch inside diameter and is equipped for but was used without liners. The modified California sampler has a 3-inch outside diameter, 2-3/8-inch inside diameter and was used with 1-inch-high brass liners. The drive samples were collected using a 140-pound automatic trip hammer in accordance with ASTM D1586, Standard Penetration Test, procedures. The sampling depth, selected lab test results, recorded blow counts (N-values) for the driven samples, a description of subsurface conditions encountered, and method of backfilling the holes are presented on the boring logs in Appendix A.

Continuous coring was performed in rock encountered in borings 22E-01, 22W-01, and 22W-02 once drive sampling and auger drilling met practical refusal. Coring was performed using a double-walled

HQ continuous rock coring system with diamond bit core-barrels retrieved on a wire-line system. The HQ core barrel drilled an approximately 3.4-inch diameter hole and collected 2.5-inch diameter core samples. Core was collected in 3 to 5-foot runs and recovered from the hole on the wire-line system.

The percent recovery and the rock quality designation (RQD) were measured and reported on the logs for each run. Samples for laboratory tests were taken from the recovered core. Photographs of the equipment set up at each location and core samples are included in Appendix A.

4.4 LABORATORY TESTING

The results of laboratory tests are presented in Appendix B. Laboratory tests were performed on selected samples recovered from the field exploration program. Tests for moisture content, unit weight, percent passing the 200 sieve, sieve analyses, and pH and resistivity were performed at our laboratory in Ventura, California. Tests for Proctor compaction were performed at our laboratory in Grover Beach, California. Tests for soluble sulfates and soluble chlorides as well as R-Value were performed by Cooper Testing Labs in Palo Alto, California. Consolidated-undrained triaxial testing as well as unconfined compressive strength testing were performed by Cal Poly Geo-E Lab in San Luis Obispo, California. Testing was performed in accordance with American Society for Testing and Materials (ASTM) and American Association of State Highway and Transportation Officials (AASHTO) methods as noted on the lab reports. After the completion of the laboratory testing, the field descriptions were confirmed or modified as necessary and boring logs were prepared.

5. SITE CONDITIONS

5.1 GEOLOGIC SETTING

Published geologic information from Dickenson (1991) and the Dickenson (1992) geologic map were used to help characterize the regional geology in the site vicinity. The project limits are mapped within the Santa Catalina Mountains which reside within the Catalina Core Complex. The Catalina Core Complex is a metamorphic core complex which forms from “extensional displacements that form along brittle-ductile shear zones that penetrated to mid-crustal levels” (Dickenson 1991).

Geologic structure within the project vicinity includes two unnamed normal faults mapped by Dickenson (1992) approximately 3.0 miles north and 4.8 miles south of the project site. Dickenson (1992) also maps the pre-Quaternary age Pirate Fault, Mogul Fault, and Catalina Detachment Fault approximately 7.0 miles west, 8.4 miles north and 9.3 miles south of the project site, respectively.

The closest mapped Quaternary-age faults are the Whitlock Wash Fault, Little Rincon Mountains Fault, and Santa Rita Fault Zone mapped approximately 18.7 miles northeast, 21.0 miles southeast, and 30.5 miles south of the project site (USGS 2022).

The surface geology in the site vicinity, as mapped by Dickenson (1992), is shown on Figure 3.

Dickenson (1992) maps the surface geology within the project limits as Leatherwood quartz diorite

(Kgl). The Oracle/Ruin Grantic Suite was also mapped just south of the project limits and is described by Dickenson (1991) as “porphyritic granite with subhedral K-feldspar phenocrysts in a buff or tawny groundmass of coarse granular texture.” Outcrops of granite were observed along portions of Sabino Canyon Park Road, and completely weathered to fresh granite judged to be the Oracle/Ruin Granitic Suite was encountered in Yeh’s 2021 and 2022 borings along Sabino Canyon Road and in the proposed parking lot area.

5.2 TERRAIN AND VEGETATION

The project site is located near the summit of Mount Lemmon, the highest peak within the Santa Catalina Mountains. The Santa Catalina Mountains lie within the Coronado National Forest in southeastern Arizona and are generally characterized by steep slopes and deep canyons. Elevations along Sabino Canyon Park Road vary between approximately elevation 7,583 feet at the southern extents of the project (station 100+21) to approximately elevation 7,684 feet at the northern extents of the project (station 123+50) (Atkins 2022). The road is primarily constructed on cut and fill through the side hills of the canyon. Cuts up to twenty feet and fills up to ten feet were constructed to support the roadway bench. Slope gradients are estimated at 20 to 40 percent along the roadway

Figure 3: Geologic Map (Dickenson 1992) cuts and fills. Cuts are predominantly in alluvium over the underlying granite of the Oracle/Ruin Granitic Suite with some exposed cuts within the Oracle/Ruin Granitic Suite. A photo of a proposed cut slope at 1v:1h is shown in Figure 4.

Sabino Creek runs north to south directly adjacent to the northbound lane of Sabino Canyon Park Road with an average gradient of two to five percent. Vegetation in the project vicinity consists of alder trees, ferns, willows, and grasses along the creek banks as well as ponderosa pine trees along the slopes and hillsides. A forest fire impacted the region in 2003 and in 2020. Debris flows were reported by residents along drainages during monsoon season.

5.3 CLIMATE

Climate data from NOAA (2021a, 2021b) for Mount Lemmon, Arizona, reports an average annual rainfall of about 25 inches and about 10 inches of snowfall. Monthly average temperatures range from a low of 29 degrees Fahrenheit for December to a high of 91 degrees Fahrenheit in July (NOAA 2022). Intense precipitation events resulting in debris clogging culverts was reported by a local representative of the water company to occur during the summer monsoon season. The estimated frost depth for the project site is 24 inches per AZ Natural Resource Conservation Service (NRCS) (2010).

5.4 EXISTING ROADWAY

Sabino Canyon Road is an asphalt-paved road with typical lane widths of 10 to 11 feet. Portions of the roadway on the north end of the site (approximately station 117+50 to 123+00) are striped with centerline markings and edge of traveled way markings. Cut slopes border the roadway to the west and fill slopes and Sabino Creek border the edge of the roadway to the east.

6. SUBSURFACE CONDITIONS

The subsurface conditions encountered in the borings generally consisted of units of artificial fill (Af) and alluvium (Qa) overlying bedrock of the Oracle/Ruin Granitic Suite (Yo). The proposed parking lot area has an estimated 2-inch-thick layer of topsoil at the ground surface. The approximate locations

Figure 4: Proposed 1v:1h Cut Slope (Station 105+00)

Looking North of the borings are shown on the boring location plans shown on Plates 1a and 1b and noted on the logs in Appendix A. The subsurface conditions encountered within the roadway, parking lot and retaining wall areas are summarized below.

6.1 EXISTING PAVEMENT AND SUBGRADE CONDITIONS

The existing asphalt pavement is approximately 40 years old and has potholing as well as high severity transverse, block, and longitudinal cracking (see Figure 5). Moderate to severe raveling of the pavement surface was also observed. Much of the observed distress can likely be attributed to the age of the pavement and is further aggravated by associated clearing of the roadway of ice and snow after winter storms.

Existing Pavement. The existing structural section encountered in borings 21P-01 through 21P-03 and 21W-01 through 21W-04 drilled within Sabino Canyon Road generally consisted of variable thickness of hot-mix asphalt concrete pavement (HMA) overlying aggregate base coarse (ABC) as noted in Table

1. Existing pavement sections along the project limits consist of 3 to 8 inches of hot mix asphalt concrete pavement (HMA) over 4 to 12 inches of aggregate base coarse (ABC) based on Yeh’s 2021

Figure 5: Sabino Canyon Park Road

Top left: View looking south near Station 107+00; Top Right: View looking south near Station 107+50 Bottom left: View looking south near Station 118+50; Bottom Right: View looking south near Station 123+00 borings. Subgrade conditions encountered in the borings consisted generally consisted of silty and clayey sand with variable gravel concentrations associated with the units of artificial fill (Af), alluvium (Qa), and weathered rock from the Oracle/Ruin Granitic Suite (Yo).

Artificial Fill (Af). Artificial fill was encountered below the pavement section in boring (21W-04 drilled on Sabino Canyon Park Road) to the maximum depth explored of approximately 7 feet below the road surface. The fill consisted of loose to medium dense clayey sand with gravel (SC) with red clay pipe fragments encountered at approximately 6 feet below the ground surface. A representative from the Mount Lemmon Co-op Water Company was onsite during the drilling program and noted this was an abandoned water line. Boring 21W-04 hit refusal on Oracle/Ruin Granitic Suite (Yo) bedrock below the fill.

Alluvium (Qa). Alluvium was encountered in borings 21E-01 (drilled near the proposed parking area) and 21E-03 (drilled in the shoulder of Sabino Canyon Park Road) from the ground surface to the maximum depths explored of approximately 10.3 to 11.5 feet below the ground surface. The unit was also encountered below the pavement sections in borings 21P-01 through 21P-03 and 21W-03 (drilled along Sabino Canyon Park Road) to the maximum depths explored of approximately 5 to 9.5 feet below the ground surface as well as below the pavement sections in borings 21W-02 and 21W- 03 (drilled along Sabino Canyon Park Road) to depths of approximately 10 to 14 feet below the road surface. The alluvium consisted of loose to medium dense well-graded gravel with sand and varying amounts of silt (GW, GW-GM), very loose to medium dense poorly to well-graded sand with varying amounts of silt and gravel (SP-SM, SW), as well as very loose to dense silty to clayey sand with varying amounts of gravel (SM, SC). Oracle/Ruin Granitic Suite was encountered below the alluvium in borings 21E-02, 21W-02, and 21W-03.

Table 1 summarizes the existing pavement thicknesses and subgrade conditions encountered in the borings drilled in Sabino Canyon Park Road.

Table 1: Existing Pavement Conditions Encountered

Boring No. Station Asphalt

Thickness (inches Base Thickness

(inches) Subgrade AASHTO1 Comment

21P-01 120+15 3 12 Silty SAND with Gravel (SM) A-2 Northbound lane

21P-02 107+28 8 7 Poorly graded SAND with SILT (SP-

SM)

A-1/A-2

Northbound lane

21P-03 103+79 3 5 Clayey SAND with GRAVEL (SC) A-2 Northbound lane

1 AASHTO symbol may be based on manual classification of soil.

Boring No. Station Asphalt

Thickness (inches Base Thickness

(inches) Subgrade AASHTO1 Comment

21W-01 120+47 3 9 Clayey GRAVEL with SAND (GC) A-2 Northbound ETW

21W-02 118+51 4 10 Silty SAND (SM) A-2 Southbound lane

21W-03 107+40 8 7 Poorly graded SAND with SILT (SP-

SM)

A-1/A-2

Northbound lane

21W-04 103+19 2 4 Clayey SAND with GRAVEL (SC) A-2 Northbound lane

Table 2 summarizes laboratory test results on samples obtained within the upper 5 feet of the existing roadway for pavement reconstruction.

Table 2: Subgrade Properties Test Summary2

Geologic Unit Borings Dry Unit Wt.

Particle Size

Analyses Proctor Results R-value

Artificial Fill (Af)

21P-01, 21P-02, 21P-03, 21W-01, 21W-02, 21W-03, 21W-04 wo = 11%

27% G 41% S 32% F γd,MAX. = 132 pcf

WOPT. = 8%

Alluvium (Qa)

21E-01, 21E-02 21E-03, 21P-01, 21P-02, 21P-03, 21W-01, 21W-02, 21W-03 γd =76 – 123 pcf wo = 8 – 31%

0 – 76% G 20 – 71% S 4 – 43% F γd,MAX. = 118 - 126 pcf

WOPT. = 7 - 12 %

6.2 NEW PARKING LOT AREA

Borings drilled for the proposed new parking lot area and associated retaining walls include 21E-01, 21E-02, 22E-01, and 22W-01 through 03. Subsurface conditions generally consisted of Alluvium (Qa) overlying weathered and fresh Oracle/Ruin Granitic Suite (Yo) bedrock. Subsurface conditions encountered in the borings drilled for the proposed parking lot and associated retaining walls in the parking lot are described below.

Alluvium (Qa). Alluvium was encountered in borings 21E-01 from the ground surface to the maximum depths explored of approximately 10.3 to 11.5 feet below the ground surface. Alluvium was also encountered in borings 21E-02, 22E-01, and 22W-01 through 22W-03 to approximately 1.5 to 5.5 feet below the ground surface. The alluvium consisted of loose to medium dense well-graded gravel with sand and varying amounts of silt (GW, GW-GM), very loose to medium dense poorly to well-graded sand with varying amounts of silt and gravel (SP-SM, SW), as well as very loose to dense

2 Geotechnical properties are noted for dry unit weight (γd) and moisture content (wo); particle size as percent gravel (G), sand size (S) and fines content (F); electrical resistivity (ρ), soluble sulfates (SO42-) and soluble chlorides (Cl-); unconfined compressive strength (UCS) tests; effective friction angle (φ′) and r cohesion (c′) measured from consolidated undrained (cu) tests; permeability (k); maximum dry unit weight (γd,MAX) and optimum moisture content (wOPT).

silty to clayey sand with varying amounts of gravel (SM, SC). Oracle/Ruin Granitic Suite was encountered below the alluvium in borings 21E-02, 21W-02, and 21W-03.

Oracle/Ruin Granitic Suite (Yo). Oracle/Ruin Granitic Suite was encountered below the alluvium in borings 21W-02 and 21W-03 (drilled along Sabino Canyon Road) and in borings 21E-02, 22E-01, and 22W-01 through 22W-03 (drilled in the proposed parking lot area). The Oracle/Ruin Granitic Suite consisted of two predominant subunits as described below.

Yo1. The Yo1 subunit was encountered below the alluvium in borings 22E-01, 22W-01, and 22W-02 to depths of approximately 5.5 to 17 feet below the ground surface. The subunit was also encountered below the alluvium in borings 21E-02, 21W-02, 21W-03, and 22W-02 to the maximum depths explored of approximately 11.5 to 30.4 feet below the ground surface. The Yo1 subunit consisted of moderately to completely weathered, extremely weak to weak granite encountered as medium dense to very dense clayey sand (SC). The Yo2 subunit was encountered below the Yo1 subunit in borings 22E-01, 22W-01, and 22W-02.

Yo2. The Yo2 subunit was encountered below Yo1 subunit in borings 22E-01, 22W-01, and 22W-02 to the maximum depths explored of approximately 20 to 30 feet below the ground surface. The subunit consisted of fresh to slightly weathered, mica-rich granite with very closely to moderately spaced discontinuities.

Table 3 summarizes laboratory test results on samples obtained within the borings drilled for the parking lot and associated retaining walls.

Table 3: Parking Lot Area Soil Properties Test Summary3

Geologic Unit Borings

Dry Unit Wt.

and Moisture

Content Particle Size

Analyses Corrosion Strength

Parameters

Alluvium (Qa) 21E-01, 21E-02, 22E-01,22W-01, 22W-02, 22W-03 γd=91 – 108 pcf wo=15 – 31%

0 – 7% G 66 – 70% S 27 – 30% F

Oracle/Ruin Granitic Suite (Yo1)

21E-02, 21W-02, 21W-03, 22E-01, 22W-01, 22W-02, 22W-03 γd=63 – 113 pcf wo=4 – 18%

0 – 13% G 70 – 74% S 13 – 30% F pH = 6.53 - 7.99 ρ = 883 – 12,969 Ω-cm

SO4

2- = 8 - 11 mg/kg Cl- = <2 - 4 mg/kg φ’cu = 34° -38° c’cu = 100 - 400 psf

3 Geotechnical properties are noted for dry unit weight (γd) and moisture content (wo); particle size as percent gravel (G), sand size (S) and fines content (F); electrical resistivity (ρ), soluble sulfates (SO42-) and soluble chlorides (Cl-); unconfined compressive strength (UCS) tests; effective friction angle (φ′) and r cohesion (c′) measured from consolidated undrained (cu) tests; permeability (k); maximum dry unit weight (γd,MAX) and optimum moisture content (wOPT).

Geologic Unit Borings

Dry Unit Wt.

and Moisture

Content Particle Size

Analyses Corrosion Strength

Parameters

Oracle/Ruin Granitic Suite (Yo2)

22E-01, 22W-01, 22W-02 -- -- -- UCS:

4,180 – 8,100 psi

6.3 GROUNDWATER

Groundwater was encountered in borings 21E-03 and 21W-03 at approximately 10 feet below the ground surface and in boring 21W-02 at approximately 13.5 feet below the ground surface.

Groundwater encountered in these borings is likely associated with the flow within Sabino Creek as the depth to groundwater coincided with the depth to the water elevation within the creek. Perched water was also encountered in boring 22E-01 at a depth of 3 feet within alluvium above weathered bedrock. Soil moisture and groundwater conditions are likely to vary seasonally and in association with changes in precipitation, runoff, and other factors.

7. GEOTECHNICAL ANALYSES AND EVALUATION

7.1 SEISMIC DATA

Seismic data were estimated for the geotechnical evaluation in accordance with the AASHTO (2020) Bridge Design Specifications using the United States Geological Survey (USGS) Earthquake Hazards Program Unified Hazard Tool (USGS 2023) accessed February 10, 2023. The site is classified as boundary Site Class B/Site Class C, rock to very dense soil and soft rock. The site class was estimated for the site using subsurface exploration field blow counts and classifications for the soil and rock at the site from the borings in conjunction with Table C3.10.3.1-1 Method B of the AASHTO (2020) Bridge Design Specifications. The site coordinates were estimated near the center of the project as

32.4376 degrees latitude and -110.7593 degrees longitude. The design earthquake for the site is defined by a mean magnitude of 6.05 event and an estimated peak ground acceleration of 0.04g, corresponding to a 10-percent in 50 years probability of exceedance (475-year return period) per Section 6.4.11 of the PDDM.

7.1.1 SEISMIC LATERAL EARTH PRESSURE FOR EXTREME LIMIT STATE

Exhibit 6.4-B in the FHWA (2018) Federal Lands Highway Project Development and Design Manual (PDDM) notes that seismic factors of safety for retaining walls are only applicable when the peak ground acceleration is greater than 0.09g. The peak ground acceleration estimated for the site is 0.04g for the design earthquake. Therefore, seismic considerations are not needed for retaining wall design based on FHWA (2018) standards.

7.2 SLOPE STABILITY ANALYSES

Slope stability analyses were performed to provide a basis for the recommended minimum lengths, spacings, and strengths for the soil nails and geogrid reinforcement for the proposed parking lot retaining walls. The final design of the walls, including internal stability, will be contractor designed per Section 257 of FP-14. The slopes were analyzed using the computer program SLIDE2 (Rocscience 2022).

7.2.1 SLOPE STABILITY CRITERIA

In accordance with AASHTO (2020) LRFD Bridge Design Specifications Section 11.6.3.7, a slope is considered stable when a factor of safety of 1.5 was used for the global stability analyses for structures. Seismic considerations for slope stability were not needed based on FHWA (2018) standards (see Section 7.1.1)

7.2.2 INPUT AND ANALYSES

In SLIDE2, the user defines the surface and subsurface profile boundaries, groundwater conditions, the type of analysis to be performed, the layout and strength of any slope reinforcement, boundary loads, and the unit weight and strength of the soil and rock materials included in the analysis. The groundwater conditions modeled for existing slopes were based on groundwater levels encountered in the borings. The cross-sectional geometry used for modeling the slopes was based on design cross-sections and topography provided by Atkins (2023a, 2023b). Seismic loads for the design earthquake were not needed based on FHWA (2018) standards (see Section 7.1.1).

7.2.3 RESULTS

A factor of safety of at least 1.5 was estimated for global slope stability of the east and west retaining walls using the recommended minimum lengths, spacings, and strengths for soil nails and geogrid reinforcement presented in this report. The plotted results of those slope stability analyses are presented in Appendix C.

8. CONCLUSIONS AND RECOMMENDATIONS

8.1 EARTHWORK - GENERAL

8.1.1 GENERAL GRADING

The recommendations of this report assume that pavement and fill materials will be placed in general accordance with the Standard Specifications, FP-14. Compliance with those specifications is needed for the recommendations in this report to remain applicable. Site grading should conform to the applicable sections of FP-14 and the recommendations of this report. Temporary excavations should conform to OSHA requirements.

8.1.2 EARTHWORK FACTORS

The subgrade generally consisted of loose to medium dense gravel with sand and varying amounts of silt as well as very loose to dense sand with varying amounts of silt, clay, and gravel. Drive samples had dry unit weights that ranged from approximately 76 to 123 pounds per cubic foot. The maximum dry unit weight of the subgrade estimated from Proctor tests was approximately 118 to 132 pounds per cubic foot.

It is recognized that disturbance to drive samples occurs due to compaction of samples during driving, loosening of the soil when recovering the sampler from the boring and during trimming in the laboratory. Differences in the in-situ soil density likely occur in areas where the existing pavement subgrade and embankment fill materials were compacted as opposed to where the roadway was constructed in alluvium.

The estimated earthwork factors4 do not account for losses for removal of vegetation or unsuitable material. An average earthwork factor of 1.1 can be used considering the pulverization and compaction of the existing structural (FDR) section for the roadway reconstruction. Subgrade and areas adjacent to existing pavement for new shoulders and paved parking areas can assume an earthwork factor of 0.9. An average earthwork factor of 0.85 can be used for on-site borrow obtained from road cuts, and the earthwork for the parking lot. The earthwork factors are approximate and based on limited number of tests and may vary based on conditions encountered during construction.

8.1.3 EROSION AND SLOPE DRAINAGE

Erosion can occur where drainage runs uncontrolled along the edge of the roadway, such as between the edge of road and the base of cut slopes. Care should be taken so that roadway work does not block or prevent the flow of surface drainage that is provided by existing ditches. Rock lined swales can be provided along the edge of the roadway to help reduce the potential for erosion.

Graded slopes will be vulnerable to erosion. Maintenance and repairs to gullied or eroded areas should be performed promptly while vegetation is being established. Concentrated flows of runoff should not be allowed to run over slopes. Lined ditches, overside drains, and culverts should be provided to carry water to the base of slopes and reduce the potential for erosion. Energy dissipation

4 The earthwork factor represents the ratio of the existing in-situ unit weight of the soil before construction to the unit weight of the same soil after compaction. For example, an earthwork factor of 0.95 represents a 5 percent loss in the volume of soil following compaction. An earthwork factor of 1.05 represents a 5 percent gain in volume of the soil or pavement following compaction due to bulking of a relatively dense material.

devices should be provided at the outlet of pipes and along ditches to reduce the potential for erosion where there are concentrated flows of runoff.

8.1.4 REUSE OF ONSITE SOIL

Excavated onsite soil, cleansed of organic material, oversized rock, and other deleterious material, should be suitable for reuse as Unclassified Borrow per FP-14 Section 704.06 for general embankment construction. The excavated onsite material should not be considered suitable for reuse as select fill, such as aggregate base coarse, structure backfill, pipe bedding, or drainage material. Excess fill or cut material should be disposed of offsite, unless an onsite location has been identified for placement of excess fill on the project plans.

8.2 EMBANKMENT SLOPE DESIGN

Embankment fill should be keyed and benched into the existing slope where embankment fill will be placed on existing grades steeper than 1v:5h as detailed in Figure 6. This detail supersedes CFL Standard Plan C204-50 that shows 8-foot-high precut benches. The fill should be initiated from a base key excavated at the toe of the new embankment. The base key should be at least 2 feet deep and be excavated into firm and stable ground.

The new embankment can then be keyed and benched into the existing slope as the fill is placed and such that at least the outer 5 feet of the existing slope is removed. Excavated material removed during keying and benching can be incorporated into the new embankment as the fill is being placed.

8.3 CUT SLOPE DESIGN

Permanent cut slopes (with the exception of Stations 105+00 to 106+60) should be graded to inclinations of 1v:1.5h (vertical to horizontal) or flatter. Existing slopes along the road are cut at similar inclinations and appear to be generally stable. Yeh should be contacted if cut slopes steeper

Figure 6: Typical Embankment Construction than 1v:1.5h beyond the proposed 1v:1h cut slope (see below) are needed. Those slopes should be analyzed specifically as a basis for recommending allowable cut slope inclinations and may need to be reinforced or retained depending on the height or location of the slope.

Permanent cut slopes of 1v:1h are acceptable between approximate Stations 105+00 to 106+60.

Granitic rock of the Oracle/Ruin Granitic Suite is exposed on the existing cut slope. The cut slope should be reviewed by an engineering geologist or geotechnical engineer during construction to review for adverse bedding and the need to adjust slope inclinations. Rock excavation should be planned for this portion of the project.

8.4 SUBEXCAVATION

Yeh did not observe specific areas of existing pavement that indicate the need for subexcavation and subgrade stabilization. Depending on the time of year and moisture condition of subgrade soil, subgrade stabilization may be warranted in areas where unsuitable materials or soft subgrade conditions are encountered during construction that will not allow for proper compaction of the subgrade or roadway base materials, or where organic or other deleterious materials are encountered at the subgrade elevation that will not provide suitable foundation support for the new roadway. Subgrade stabilization should consist of subexcavating the existing soil to a depth at least 1-foot below the bottom of subgrade elevation. If the subgrade is wet or yielding, subexcavation should be performed using backhoe type equipment such that construction equipment will not operate on the exposed subgrade during excavation.

A geotextile conforming to Section 714.01, Class 1, Type E Geotextile of FP-14 should be placed over the undisturbed surface of the excavated subgrade following removal of the unsuitable material in accordance with Section 207 of FP-14. The geotextile should be placed without gaps or wrinkles.

Uniformly graded 3/8 to 1.5-inch Crushed Aggregate conforming to Section 703.6 of FP-14 should be placed over the geotextile. The aggregate should be fully encased in the geotextile to reduce the potential for the overlying base course or adjacent soil to erode into the gravel.

Project specifications should include a quantity for stabilizing the subgrade for the roadway, if needed. Project specifications need to address increasing or decreasing this quantity or deleting the quantity based on the conditions encountered during construction. The geotechnical professional or contracting officer should review the subgrade conditions encountered at the time of construction to evaluate whether stabilization of the subgrade is needed, and to recommend the depth and limits of the subexcavation and stabilization.

8.5 PAVEMENT DESIGN RECOMMENDATIONS

The new structural section for design of the Sabino Canyon Park Road improvements is recommended based on Chapter 11 of the FHWA (2018) Federal Lands Highway Project Development and Design Manual (PDDM) and the AASHTO (1993) Guide for the Design of Pavement Structures.

The new structural section should consist of hot mix asphalt concrete pavement (HMA) over full depth reclamation (FDR) as identified in the project Scoping Trip Report (Atkins 2021) for the pavement section along Sabino Canyon Park Road. The structural section for the new parking lot and parking areas consisting of HMA over imported aggregate base course (ABC), Type C per Table 703-2 of FP-14, is proposed for the parking lot and parking areas for the project. Supplemental Crushed Aggregate per Section 703.06 should be added to the FDR and blended if needed to provide sufficient material to meet finished grade and allow for the roadway widening. Preliminary pavement recommendations for these alternatives were provided to Atkins via email (Yeh 2022). The spreadsheet calculations for our recommended traffic loading and thickness recommendations are presented in Appendix D.

8.5.1 DESIGN TRAFFIC VOLUME AND SUBGRADE

The design traffic volume was estimated using traffic data provided in the Atkins (2021) Scoping Report and procedures in the PDDM (FHWA 2018). Average daily traffic (ADT) for both current (ADT = 150 vehicles per day) and seasonal (ADT = 325 vehicles per day) were considered for both 0-percent and 2-percent growth conditions. A mix of 70-percent passenger cars (Class 2) and 30-percent pickup trucks/vans (Class 3) were assumed for design. Yeh also evaluated the road for a portion of busses (Class 4) or 3-axle trucks (Class 6). A design life of 20 years was used in estimating the proposed structural sections. The estimated structural number of 1.52 is controlled by the minimum 50,000 equivalent single axle loads (ESALs) used for pavement design per the PDDM (FHWA 2018).

The subgrade encountered along Sabino Canyon Road was predominantly classified as silty to clayey sand with varying amounts of gravel (A-2) and is considered good support for the roadway. An R value of 59 was obtained on a test of subgrade material obtained from Yeh’s 2021 field exploration program. Variable soil conditions were encountered in borings and a design R-value of 50 was chosen for the design of the roadway. The recommended structural section thicknesses were estimated considering a resilient modulus (Mr) of 13,168 psi corresponding to an average R-value of 50.

8.5.2 STRUCTURAL SECTION

Recommended structural sections for the road rehabilitation (HMA over FDR) and the new parking lot areas (HMA over imported ABC) are shown in Figure 7. A minimum of 3 inches of HMA over a minimum 5 inches of FDR (per FP-14 Section 304) is recommended along Sabino Canyon Park Road. A minimum of 3 inches of HMA over a minimum of 5 inches of imported ABC is recommended for the new parking lot and roadside parking areas. The existing measured pavement thicknesses varied from 2 to 8 inches on Sabino Canyon Park Road. The FDR should consist of pulverizing the existing pavement and base to a depth of 9 inches (one inch deeper than the maximum measured AC thickness). We recommend a minimum pulverization depth of 9 inches to account for variable thickness of existing HMA and to provide a more consistent FDR material.

The FDR material may be harvested and regraded in some areas to provide for the new superelevation, a higher vertical profile, and/or portions of the roadway that are in cut or widening of the roadway (if needed). Imported Crushed Aggregate can be added to supplement the FDR if needed and depending on the final quantity of base course material needed for design. It should be anticipated that the FDR and any supplemental base course material will need to be compacted in a maximum 6-inch lift to achieve compaction. The FDR material should be moisture conditioned and compacted to at least 95 percent relative compaction in accordance with FP-14 Standard

Figure 7: Sabino Canyon Park Road Pavement Recommendations

Specifications. Subgrade below areas outside the existing pavement areas that will be paved (roadside parking areas and parking lot) should be scarified to a minimum depth of 9 inches and recompacted in accordance with FP-14 Standard Specifications.

Shoulder backing should be placed along the new edge of pavement (NEP) to support the pavement and reduce the potential for edge cracking of the pavement. A typical shoulder backing width of 3 feet is recommended but does not need to extend onto existing slopes above or below the road if where there isn’t sufficient room from the new edge of pavement. Shoulder backing should consist of Surface Course Aggregate conforming to Section 703.05.c of FP-14 and placed as Roadway Aggregate, Method 2 per Section 302. Shoulder backing should be at least 3 inches thick at the NEP and can be tapered out over the width of the backing.

8.5.3 BINDER AND MIX RECOMMENDATIONS

The recommended binder for this area was selected using Mohseni (2005) LTPPBind with considerations for local methodology. Asphalt binder should consist of PG 70-22 TR+ which is the performance grade binder for projects in Arizona above 4,000 feet in elevation (AZDOT 2021). This project is located near Tucson where the supply of hot-mix asphalt is readily available. A nominal 3/4

– inch grading per Table 703-4 of FP-14 should be used with the recommended binder. Loss of temperature and segregation of the hot asphalt mix can occur during transport. We recommend that the project specifications require the use of a material transfer device at the point of placement to allow for uniform temperatures and prevent segregation of the mix during placement.

8.5.4 PAVEMENT MAINTENANCE

The pavement condition should…