W912PL19R0011_Amendment0001_Part3.pdf

Preliminary Geotechnical Report Integrated Fixed Tower Sites and Associated Access Roads Tucson Sector, Ajo and Casa Grande Stations Tohono O’odham Nation Lands, Pima County, Arizona

December 17, 2014 (Revised February 6, 2015; August 28, 2015)

Prepared for

U.S. Army Corps of Engineers P.O. Box 532711

Los Angeles, CA 90053-2325

Prepared by

Diaz•Yourman – GeoPentech – Kinnetic Laboratories / Joint Venture 1616 E. 17th Street

Santa Ana, CA 92705-8509

(714) 245-2920

DY Project No. 2011-026.06, GP Project No. 09021A

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TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 GENERAL

1.2 PROJECT DESCRIPTION

1.3 SCOPE OF SERVICES

2.0 FIELD INVESTIGATION AND LABORATORY TESTING

2.1 HOLLOW STEM AUGER AND CORE BORINGS

2.2 TEST PIT EXCAVATIONS

2.3 GEOPHYSICAL SURVEYS

2.4 GEOLOGIC MAPPING AND DOWNHOLE OPTICAL TELEVIEWER SURVEYS

2.5 LABORATORY TESTING

3.0 GEOLOGIC CONDITIONS

3.1 REGIONAL GEOLOGY

3.2 SITE TOPOGRAPHY AND SURFACE CONDITIONS

3.3 LOCAL GEOLOGIC CONDITIONS

3.3.1 Colluvium

3.3.2 Alluvium

3.3.3 Crystalline Bedrock

3.4 ROCK MASS DISCONTINUITIES

3.5 GROUNDWATER

3.6 GENERAL CHARACTERIZATION FOR ENGINEERING ANALYSIS

4.0 POTENTIAL GEOLOGIC HAZARDS

4.1 FAULT SURFACE RUPTURE

4.2 SEISMIC SHAKING

4.3 LIQUEFACTION POTENTIAL

4.4 SEISMICALLY INDUCED SETTLEMENT

4.5 SEISMICALLY INDUCED FLOODING

4.6 EROSION, FLASH FLOODS, AND DEBRIS FLOWS

4.7 EARTH FISSURES

4.8 SLOPE INSTABILITY

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 CODE BASED SEISMIC PARAMETERS

5.2 EARTHWORK

5.2.1 Site Preparation and Grading

5.2.2 Material for Fill

5.2.3 Excavations and Temporary and Permanent Slopes in Alluvial and Fill Soils

5.2.4 Rock Slope Stability at IFT Sites AJO-0446 and AJO-0450

5.3 DEEP FOUNDATIONS

5.3.1 Drilled Shafts

5.3.2 Rock-Socketed Shafts

5.3.3 Drilled Shaft Installation Considerations

5.4 MAT FOUNDATIONS

5.5 ACCESS ROADWAYS

5.5.1 Drainage

5.5.2 Culvert Design

5.6 SOIL CORROSION POTENTIAL

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5.7 RESISTANCE TO LATERAL LOADS AND LATERAL EARTH PRESSURES

5.8 UTILITY TRENCHES

6.0 PLAN REVIEW, CONSTRUCTION OBSERVATION, AND TESTING

7.0 LIMITATIONS

8.0 REFERENCES

LIST OF TABLES

Table 1 - IFT LOCATIONS Table 2 - PREDOMINANT LITHOLOGIC GROUP PROPERTIES Table 3 - ASSIGNED IFT SITE LITHOLOGIC GROUP Table 4 - SEISMIC SITE CLASSIFICATION Table 5 - IMPORT FILL AND SELECT BACKFILL CRITERIA Table 6 - IFT DEEP FOUNDATION SUMMARY Table 7 - SOIL INPUT PARAMETERS FOR LPILE

LIST OF FIGURES

Figure 1 - VICINITY MAP Figure 2 - SITE PLAN Figure 3a - SITE GEOLOGIC MAP Figure 3b - LEGEND TO ACCOMPANY GEOLOGIC MAP Figure 4 - AXIAL DRILLED SHAFT CAPACITIES - CAG SITES Figure 5 - AXIAL DRILLED SHAFT CAPACITIES - AJO COARSE-GRAINED SITES Figure 6 - AXIAL DRILLED SHAFT CAPACITIES - FINE-GRAINED SITES Figure 7 - AXIAL DRILLED SHAFT CAPACITIES - CRYSTALLINE BEDROCK SITES Figure 8 - DRILLED SHAFT INSPECTION PIPES Figure 9 - LATERAL EARTH PRESSURES Figure 10 - RETAINING OR BASEMENT WALL DRAINAGE Figure 11 - PIPELINE BACKFILL SCHEMATIC

LIST OF APPENDICES

APPENDIX A - BORING AND TEST PIT LOGS

APPENDIX B - GEOPHYSICAL SURVEY

APPENDIX C - GEOLOGIC MAPPING AND DOWNHOLE OPTICAL TELEVIEWER SURVEYS

APPENDIX D - LABORATORY TESTING

APPENDIX E - IFT SITE SUMMARIES

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LIST OF ACRONYMS AND ABBREVIATIONS

AASHTO American Association of State Highway and Transportation Officials

ACI American Concrete Institute

AJO CBP Ajo Station

ASCE American Society of Civil Engineers

ASTM ASTM International

AZGS Arizona Geological Survey

BMP best management practices bpf blows per foot

CAB crushed aggregate base

CAG Casa Grande Station

CBP U.S. Customs and Border Protection Service

CBR California Bearing Ratio

Cc compression index

CD compact disc

CH clay of high plasticity, fat clay

CL Clay

CMB crushed miscellaneous base

Cr recompression index

DI design index

DY-GP-KL Diaz Yourman–GeoPentech–Kinnetic Laboratories, /JV ɛ50 secant modulus from triaxial compression

EPA U.S. Environmental Protection Agency

ER efficiency rating

FHWA U.S. Federal Highways Administration fps feet per second

FS factor of safety ft feet ft/sec feet per second

GC clayey gravel

GM silty gravel

GPS global positioning system

H:V horizontal:vertical

HMA hot-mix asphalt

HSG Hydrologic Soil Group

IBC International Building Code

ID identification number

IFT Integrated Fixed Tower

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ISRM International Society for Rock Mechanics

K Vertical modulus of subgrade reaction kip 1,000 pounds-force

KR Reduced modulus of subgrade reaction ksf Kip per square foot

ML Silt

NAD North American Datum

OSHA Occupational Safety and Health Administration pcf pounds per cubic foot pci pounds per cubic inch (per square inch per inch) ppm parts per million psf pounds per square foot psi pounds per square inch

SC clayey sand

SM silty sand

SP poorly graded sand

SPT standard penetration test

T.O.N. Tohono O’odham Nation

TP test pit

UCS unconfined compressive strength

UFC Unified Facilities Criteria

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey

VM Vamori

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1.0 INTRODUCTION

1.1 GENERAL

This report presents the results of the preliminary geotechnical study of 16 integrated fixed tower (IFT) sites and associated access roads within the U.S. Customs and Border Protection

Service (CBP) Tucson Sector. The IFT sites and access roads are located near and along the

U.S.-Mexico border within the main reservation of the Tohono O’odham Nation (T.O.N.) in Pima

County, Arizona.

This report was prepared by Diaz•Yourman–GeoPentech–Kinnetic Laboratories, Joint Venture

(DY-GP-KL) for the U.S. Army Corps of Engineers (USACE) to support the CBP IFT project.

This work was completed in accordance with Agreement No. W912PL-11-D-0015, Delivery

Order 0006, Purchase Request No. W81EYN40631952, dated March 10, 2014, between

USACE and DY-GP-KL.

1.2 PROJECT DESCRIPTION

In support of the CBP, the USACE will construct 15 IFT sites (this study includes 15 primary sites plus one alternative site for a total of 16 IFTs) and approximately 70 miles of unpaved roadways. Eight IFT sites are located within the area of the CBP Ajo Station (AJO) sector, and 8

IFT sites are located within the area of the CBP Casa Grande Station (CAG) sector. Figure 1 is a site vicinity map showing the location of the project and Figure 2 (which includes an imbedded digital Google Earth KMZ map file) is a site plan showing the location of the towers and access roads. The proposed 16 tower site designations and locations are listed in Table 1.

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Figure 1 - VICINITY MAP

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Table 1 - IFT LOCATIONS

IFT Site Latitude Longitude

AJ0-0446 31.76726643 -112.25812208

AJ0-0448 31.77219667 -112.41955046

AJ0-0450 31.80844001 -112.54179000

AJ0-0452 31.92701611 -112.57474901

AJ0-0454 31.97148333 -112.58217536

AJ0-0458 32.11807409 -112.63392140

AJ0-0460 32.15728128 -112.69316437

AJ0-0462 32.05266045 -112.61355810

CAG-0430 31.57297498 -111.68513605

CAG-0432 31.58358223 -111.77068857

CAG-0434 31.61814318 -111.83911187

CAG-0436 31.65739889 -111.91184358

CAG-0438 31.65098102 -111.99034199

CAG-0440 31.67309997 -112.04956801

CAG-0442 31.73489472 -112.11467013

CAG-0444 31.62068902 -111.90473101

At each IFT site, a 50-foot by 50-foot gravel pad is planned to be constructed within a 100-foot by 100-foot work limit. Specifics of the IFT towers are unknown at this time; however for the purposes of this report, the following were assumed:

3-sided, steel lattice structure, 180 feet tall.

Drilled shaft foundation spacings are typically 18.5 feet, in an equilateral triangular pattern.

Typical top of drilled shaft loads include:

o Maximum compression = 150 thousand pounds (kips) o Maximum uplift = 135 kips o Maximum shear = 15 kips

The project will also include the improvement of approximately 70 miles of existing dirt roads and construction of access roads to the IFT locations. We understand that these improvements will generally entail grading operations directed to widening and adjusting the current grades of the dirt roads and grading new access roads by using the minimum amount of grading.

Maximum cuts and fills will likely be approximately 5 feet (cuts and/or fill placement). At IFT locations AJO-0446 and AJO-0450, cuts as deep as 12 feet are planned.

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1.3 SCOPE OF SERVICES

The objective of this assignment was to perform investigations to collect surface and subsurface geological/geotechnical data and provide preliminary geological/geotechnical recommendations to assist with the design of the IFT sites and associated access roads.

In order to complete this preliminary investigation, the following tasks were performed:

Coordinated with T.O.N. for access to the project site.

Compiled and reviewed available and relevant planning documents provided by USACE and geologic and geotechnical information from existing publications completed in the vicinity of the project area.

Conducted a site reconnaissance at the 16 AJO-CAG IFT sites and along 70 miles of associated access roadway. This task included performing a geophysical investigation, consisting of seismic refraction surveys and Wenner array electrical resistivity soundings, at 16 IFT sites and across the Vamori Wash. The results of the site reconnaissance were documented in our site exploration plan (DY-GP-KL, 2014).

Performed subsurface investigations, which included a) drilling, logging and sampling 24 borings using both hollow-stem auger and rock coring methods and b) excavating and logging 23 test pits.

Characterized bedrock conditions in the vicinity of IFT Sites AJO-0446 and AJO-0450, which included a) performing geological surface mapping of bedrock exposures and b) performing downhole optical televiewer surveys within Borings AJO-446 and AJO-450.

Performed laboratory testing on selected soil samples collected from the borings to evaluate pertinent geotechnical properties; laboratory testing of soil samples from the test pits was not in the scope of services.

Performed preliminary engineering analyses and evaluations pertaining to the design and construction of the IFT sites and associated access roads.

Prepared this report.

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2.0 FIELD INVESTIGATION AND LABORATORY TESTING

The field investigation program for the IFT sites and associated access roads consisted of (1) collecting geophysical measurements (seismic refraction and electrical resistivity), (2) completing hollow-stem-auger and rock core borings, (3) performing geologic mapping of accessible bedrock exposures at two IFT sites, and (4) excavating test pits. The locations of the investigations are shown on Figure 2. Appendices A through D provide details of the field investigation and laboratory testing. Detailed maps showing individual exploration locations at each site are included in Appendix E.

2.1 HOLLOW STEM AUGER AND CORE BORINGS

A total of 24 borings were drilled, sampled, and logged as part of this investigation. The depths ranged from approximately 11 feet to 72 feet. Twenty three of the borings were completed at the

16 IFT sites and one boring was completed at the center of Vamori Wash adjacent to the Border

Road. The borings were drilled using hollow-stem auger methods, except at IFT Sites AJO-446 and AJO-450, which were drilled using rock coring methods, and CAG-444A and CAG-444B, which were drilled using a combination of hollow-stem auger and rock coring methods.

Additional details of the drilling program, including the boring logs, are included in Appendix A.

2.2 TEST PIT EXCAVATIONS

A total of 23 test pits (AJO-TP1 through AJO-TP9 and CAG-TP1 through CAG-TP14) were completed along the IFT site access roads. The test pits were excavated and logged to depths ranging between approximately 2 to 10 feet. The test pit logs and further details of the test pit program are provided in Appendix A.

2.3 GEOPHYSICAL SURVEYS

Seismic refraction measurements were obtained along 17 survey lines, one at each of the 16

IFT sites and one across Vamori Wash along the Border Road. Seismic refraction was performed to evaluate the geometry of the soil, bedrock, and groundwater surfaces, and to estimate rock rippability. Additionally, 16 electrical resistivity surveys were performed using

Wenner array methods at each of the 16 IFT sites to assess soil corrosivity. The results of the geophysical surveys along with other pertinent details are presented in Appendix B.

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2.4 GEOLOGIC MAPPING AND DOWNHOLE OPTICAL TELEVIEWER SURVEYS

Present and accessible exposures of bedrock were mapped in the vicinity of IFT Sites AJO-

0446 and AJO-0450. Exposures of the bedrock were observed at 8 mapping stations at AJO-

0446 and 12 mapping stations at AJO-0450. Additionally, downhole optical televiewer surveys to measure rock mass discontinuity data were performed in core holes AJO-446 and AJO-450.

The geologic mapping and downhole optical televiewer surveys were used to characterize bedrock conditions for rock slope stability analyses. The surface mapping and optical televiewer data and additional details are presented in Appendix C.

2.5 LABORATORY TESTING

Selected soil and rock samples recovered from the borings were tested at the geotechnical laboratories of Kleinfelder in Tucson, Arizona, to evaluate their physical and engineering properties. The scope of services did not include laboratory tests on soil samples from the test pits. The laboratory tests performed included: dry density, moisture content, sieve analysis, Atterberg limits, compaction, expansion index, one-dimensional consolidation, direct shear strength, unconfined compressive strength (UCS), and corrosion suite (pH, chloride, minimum resistivity, and sulfate). Testing was performed in general accordance with ASTM International

(ASTM) and U.S. Environmental Protection Agency (EPA) standards. The results of laboratory testing are included in Appendix D.

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3.0 GEOLOGIC CONDITIONS

3.1 REGIONAL GEOLOGY

The project is located in the Basin and Range Physiographic and Tectonic Province of southern

Arizona, which is characterized by low to mid-elevation mountain ranges and intervening broad basins or valleys. The basins and ranges are typically separated by inactive, buried normal faults. The late Cenozoic age basins are filled with alluvial material, generally consisting of sand and gravel, but also including silt and clay. Bedrock in the project area consists of Tertiary, Mesozoic and Precambrian age igneous rocks (generally of granitic composition), metamorphic rocks (mostly schist and phyllite), sedimentary rocks (generally sandstone and conglomerate), and Cenozoic age volcanic rocks.

Figure 3a shows the proposed IFT sites and associated access roads overlain on a regional geologic map of the area (Beikman et al., 1995). The legend for Figure 3a is presented on

Figure 3b. As shown on this geologic map, the IFT sites are predominantly underlain by

Quaternary surficial sediments (Qs) [herein referred to as alluvium] with the exception of IFT

Sites AJO-0446 and AJO-0450, which are underlain by volcanic bedrock. Also, the IFT access roads are primarily underlain by Quaternary sediments with the exception of some portions of access roads near or leading to IFT Sites CAG-0444, AJO-0446, AJO-0450, AJO-0452, AJO-

0460 and AJO-0462, which are underlain by volcanic or granitic bedrock. Volcanic and granitic rocks in the project area are also referred to herein as crystalline bedrock.

The project site is not located within a seismically active region. The U.S. Geological Survey

(USGS) Quaternary Fault and Fold Database (USGS, 2006) shows that there are no active faults within the study area. Also, the project area is not located near any mapped significant faults based on a review of the 2014 (USGS) National Seismic Hazard Maps. Additionally, the

USGS Arizona Seismic Hazard Map (USGS, 2014) shows that the study area has a relatively low seismic hazard potential.

3.2 SITE TOPOGRAPHY AND SURFACE CONDITIONS

The project area generally consists of gently sloping alluvial valleys and alluvial fans separated from one another by north to northwest-trending volcanic and igneous intrusive bedrock hills and mountains that rise to between 2,000 and 5,000 feet in elevation. Numerous ephemeral drainages cross the area, draining generally from south to north, from high to lower elevations, 9 2015-02-04 AJO-CAG IFT Geotech Report (08-28-2015).docx and in radial patterns around some of the bedrock hills. The IFT sites range between approximately 1,700 and 2,900 feet in elevation.

The IFT sites were accessible by existing dirt roads. Vegetation across the project area was sparse in some areas and relatively impenetrable in areas close to larger drainages, typical of the Sonoran Desert. The vegetation includes various cacti species, notably saguaro cacti, which are considered sacred by the T.O.N. Cattle stock ponds and cattle pens were scattered throughout the area.

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Figure 3a - SITE GEOLOGIC MAP

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Figure 3b - LEGEND TO ACCOMPANY GEOLOGIC MAP

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3.3 LOCAL GEOLOGIC CONDITIONS

The geotechnical investigation completed for this project encountered colluvium, alluvium, and crystalline bedrock (volcanic and granitic bedrock). Exposures of the geology were observed within the borings and test pits, as well as during geologic surface mapping. The geologic properties and descriptions of the geologic units observed during our investigation are discussed below.

3.3.1 Colluvium

At IFT Sites AJO-0446 and AJO-0450, colluvium was observed mantling the bedrock slopes to depths ranging between 2½ to 3½ feet below ground surface. The colluvium was composed primarily of blocky rock debris, generally consisting of gravel to boulder-size volcanic rock.

3.3.2 Alluvium

Alluvium was encountered at the IFT sites, excluding AJO-0446 and AJO-0450, and along the majority of the access roads. The alluvium observed in the investigation was predominantly coarse-grained. This coarse-grained alluvium predominantly consisted of sands with varying percentages of gravel (SC, SM, and SP) and gravels (GC, GM, and GP) with occasional clay

(CL) and silt (ML) layers. The coarse-grained alluvium was generally very dense with some loose to dense layers in the upper 5 to 10 feet below ground surface. The direct shear tests performed on coarse-grained alluvium samples (39 tests) had an average friction angle of approximately 37 degrees (standard deviation = 8 degrees) and an average cohesion of approximately 0.4 kip per square foot (ksf) (standard deviation = 0.4 ksf). Direct shear tests performed in the upper 20 feet of the CAG sites had a slightly lower average friction angle of 30 degrees (standard deviation = 5 degrees), and this layer was separated out for engineering analysis as discussed in Section 3.6.

The consolidation (confined compression) test results indicated that the coarse-grained alluvium was relatively incompressible because of static loading. The compression index (Cc) of the samples collected between 5 and 30 feet below ground surface within the coarse-grained alluvium generally ranged between 0.1 and 0.17, and the recompression index (Cr) ranged between approximately 0.01 and 0.02. The initial void ratio of these samples ranged between approximately 0.4 and 0.8. Additionally, laboratory tests within the upper 30 feet indicated the coarse-grained alluvium collapse ranged from approximately 0 to as much as about 7 percent

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Fine-grained alluvium predominantly consisting of clay (CL and occasional CH) and silt (ML) with varying percentages of sand was encountered at IFT Site AJO-0448 and IFT Site AJO-

0454 below a depth of about 20 feet. The fine-grained alluvium was predominantly hard with occasional layers that were very stiff. The plasticities of the fine-grained alluvium were in the slightly to highly plastic range. The direct shear tests performed on fine-grained alluvium samples (8 tests total) had an average friction angle of approximately 35 degrees (standard deviation = 7 degrees) and an average cohesion of approximately 0.9 ksf (standard deviation =

0.9 ksf).

Consolidation test results indicated that the fine-grained alluvium was relatively incompressible because of static loading. The Cc of the fine-grained alluvium ranged between approximately

0.11 and 0.18, and the Cr ranged between approximately 0.02 and 0.04. The initial void ratio of these samples ranged between approximately 0.6 and 0.7. Based on two samples tested, the fine-grained alluvium does not appear to be subject to a high degree of hydrocollapse; one sample swelled less than 1 percent and the other sample collapsed approximately 0.4 percent upon saturation.

Occasional caliche (also referred to as “hardpan”) layers composed of calcium carbonate-cemented sediments were encountered in our subsurface investigation. The caliche layers encountered were generally white or white and brown in color, very hard, well cemented, and composed of carbonate-veined silty sand, sand, and gravel. The caliche layers encountered in the test pits were difficult to excavate with a backhoe (Deere 410g).

3.3.3 Crystalline Bedrock

Volcanic and granitic crystalline bedrock was encountered within the project area as discussed below.

Volcanic Bedrock: Volcanic bedrock was encountered within the borings at IFT Sites AJO-

0446 and AJO-0450 and associated access road test pits to IFT Sites AJO-TP7 and AJO-TP8.

The volcanic rock observed at these locations generally consisted of latite that was predominantly strong to very strong, hard, slightly weathered to fresh, vesicular, with carbonate

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Pressure-wave velocities of the volcanic rock measured within the upper 10 feet ranged between approximately 4,590 and 8,630 feet per second (ft/sec). Based on these velocities, the upper 10 feet of volcanic rock at these IFT sites are rippable to non-rippable using a Caterpillar

D8R with a multi or single shank No. 8 Series D ripper or equivalent based on the Caterpillar

Performance Handbook (2014). Based on the seismic velocity measurements, the proposed cuts may locally encounter less weathered volcanic rock which may require bigger excavation equipment (e.g. Caterpillar D10R) or blasting.

Volcanic bedrock was also encountered within test pits AJO-TP3 (along the access road to IFT

Sites AJO-0462) and AJO-TP5 (along the access road to AJO-0452). At these locations, the volcanic rock generally consisted of vesicular basalt that was hard to very hard with carbonate fracture coatings and vesicle fillings.

Granitic Bedrock: Granitic bedrock was encountered beneath alluvial materials within Borings

CAG-444A and CAG-444B at a depth of 27 and 25 feet below ground surface, respectively. The granitic bedrock observed in these borings was generally strong to very strong, and hard.

Granitic bedrock was also encountered within test pits AJO-TP-1 and AJO-TP2 (along the access road to IFT Site AJO-0460). At these locations, the granitic rock observed was generally weathered, friable to hard, and coarse-grained.

3.4 ROCK MASS DISCONTINUITIES

Within the area of IFT Sites AJO-0446 and AJO-0450, the significant rock mass discontinuities observed were joints. The rock mass properties of these joints were observed during drilling, downhole optical televiewer surveys, and the surface geologic mapping (see Appendices A and

C). Stereonets showing the orientations of joint discontinuities (in dip/dip direction format) measured at Sites AJO-0446 and AJO-0450 along with tables of all of the discontinuity measurements are included in Appendix C.

IFT Site AJO-0446: The joints mapped in the vicinity of Site AJO-0446 predominantly dip at a high angle (generally 70 degrees or greater) to the west-southwest. Additional less pronounced joint sets dip between approximately 20 to 25 degrees to the northwest and north-northeast.

The joints are commonly very narrow to narrow (i.e. aperture less than about 0.1 inch) as

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IFT Site AJO-0450: The joints mapped in the vicinity of Site AJO-0450 predominantly dip at a high angle (generally 70 degrees or greater) generally between southwest and northeast. The joints were mapped as narrow (i.e. aperture less than about 0.1 inch) as observed in the rock core and very wide (i.e. aperture greater than about 0.4 inch) as observed in rock outcrop. The joints are typically continuous for about 3 to 10 feet.

3.5 GROUNDWATER

Groundwater was encountered in the vicinity of Vamori Wash adjacent to the border road within

Boring CAG-VM Wash1 at a depth of approximately 6 feet and within CAG-TP12 at a depth near 9 feet. Other than within the vicinity of Vamori Wash, groundwater was not encountered within our borings at the IFT sites and test pits along the access roads to the maximum depths explored (as deep as 72 feet).

Based on online groundwater data available on the Arizona Department of Water Resources

Well Registry Interactive Map (2014), groundwater is expected to be greater than 100 feet below ground surface in the vast majority of the project area with shallower groundwater measured adjacent to major washes.

3.6 GENERAL CHARACTERIZATION FOR ENGINEERING ANALYSIS

Based on similarities in material types, the geologic materials underlying the project area were categorized into the following three lithologic groups for our preliminary engineering analyses:

(1) coarse-grained alluvium, (2) fine-grained alluvium, and (3) crystalline bedrock. Table 2 summarizes the predominant lithology and engineering properties of each lithologic group and

Table 3 indicates the assigned group for each site. Because of the gravel in the alluvium, some of the blow counts are likely artificially high. Therefore, correlations with blow counts should be used with caution. The laboratory test results for dry density of the alluvial soils indicated lower than expected values based on the SPT blow counts. This discrepancy could be the result of sample disturbance associated with driven samples in granular soils. Sample disturbance affects the dry densities measured in the laboratory, which also affects the soil shear strength and consolidation properties measured during laboratory testing.

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Table 2 - PREDOMINANT LITHOLOGIC GROUP PROPERTIES

LITHOLOGIC

GROUP

PREDOMINANT

LITHOLOGY

TOTAL

UNIT

WEIGHT

(pcf)

FRICTION

ANGLE

(degrees)

COHESION

(psf)

UCS

(psi)

UNCORRECTED

SPT BLOW

COUNT, N

(bpf)

Coarse-grained Alluvium: 0-20 feet

(CAG)

Clayey to silty sand with gravel, and some gravel layers

107 281 -- -- 392

Coarse-grained Alluvium: 20-80 feet

(CAG)

Clayey to silty sand with gravel, and some gravel layers

109 38 -- -- >50

Coarse-grained Alluvium: 0-80 feet

(AJO)

Clayey to silty sand with gravel, and some gravel layers

113 37 -- -- >50

Fine-grained Alluvium: 0-80 feet

Lean clay and silt with sand 117 -- 1,500 -- >50

Crystalline Bedrock: 0-25 feet

Volcanic or Granitic Bedrock 153 -- -- 11,500 --

Notes:

1. From the surface to a depth of approximately 20 feet, the average friction angle was equal to 30 degrees with a standard deviation of 5.

2. The standard deviation was 29 bpf. The refusal blow counts were assumed to be 100 bpf and were included in the average and standard deviation calculation.

pcf = pounds per cubic foot psf = pounds per square foot bpf = blows per foot

The parameters selected for design are shown in Table 2. These parameters were based on the results of the field investigation and laboratory testing. Because of the gravel affecting the blow counts, and sample disturbance of the granular soils, a conservative approach was used to select the engineering parameters for design that are listed in Table 2.

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Table 3 - ASSIGNED IFT SITE LITHOLOGIC GROUP

IFT TOWER SITE LITHOLOGIC GROUP

AJ0-0446 Crystalline Bedrock

AJ0-0448 Fine-grained Alluvium

AJ0-0450 Crystalline Bedrock

AJ0-0452 Coarse-grained Alluvium

AJ0-0454

Coarse-grained Alluvium (0-20 ft depth) Fine-grained Alluvium (>20 ft depth)

AJ0-0458

Coarse-grained Alluvium AJ0-0460

AJ0-0462

CAG-0430

Coarse-grained Alluvium

CAG-0432

CAG-0434

CAG-0436

CAG-0438

CAG-0440

CAG-0442

CAG-0444

Coarse-grained Alluvium (0-25 ft depth) Crystalline Bedrock (>25 ft depth)

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4.0 POTENTIAL GEOLOGIC HAZARDS

The following sections describe the potential for various geologic hazards at the IFT sites.

4.1 FAULT SURFACE RUPTURE

Large earthquakes in Arizona are rare, and no earthquakes in Arizona have ruptured the ground surface in historic time. As discussed above, the USGS Quaternary Fault and Fold Database

(USGS, 2006) shows that there are no known active faults within the project area, and the 2014

USGS National Seismic Hazard Maps show the project area is not located near any mapped significant faults. Therefore, potential for fault surface rupture at the IFT sites is considered negligible.

4.2 SEISMIC SHAKING

The area of the site is not prone to significant earthquakes. As discussed above, the USGS

Arizona Seismic Hazard Map (USGS, 2014) shows that the study area has a relatively low seismic hazard potential. This geotechnical investigation did not include a project specific evaluation of ground motions. Rather, as discussed below, code based seismic coefficients were provided as discussed in Section 5.1.

4.3 LIQUEFACTION POTENTIAL

Liquefaction can be defined as significant and relatively sudden reduction in stiffness and shear strength of saturated sandy soils caused by a seismically or statically induced increase in pore water pressure. The potential for seismically induced liquefaction exists whenever saturated, relatively loose, sandy soils exist with a high groundwater level, and/or there exists a potential for long duration high seismic shaking. Typically, liquefaction potential is greatest where submerged, loose fine sands occur within a depth of approximately 50 feet.

Considering that groundwater was not encountered in the IFT borings to a depth of over 70 feet, the general very dense subsurface conditions encountered in our borings, and the low probability of strong seismic shaking in this area; the potential for liquefaction at the IFT sites is considered negligible. Although liquefaction at the IFT sites is considered negligible, preliminary information from our limited investigation along the Border Road in the area of Vamori Wash (11

½ foot deep boring) suggests the presence of shallow groundwater and loose sand with gravel material, which is indicative of high liquefaction potential.

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4.4 SEISMICALLY INDUCED SETTLEMENT

Seismically induced settlement is often caused when unsaturated loose to medium-dense granular soils are densified during ground shaking. Due to the low probability of strong seismic shaking in this area and the relatively dense sandy soils encountered in our borings, the potential for seismically induced settlement is considered to be negligible.

4.5 SEISMICALLY INDUCED FLOODING

The potential hazard for seismically induced flooding is generally associated with a body of water located adjacent to the site, or from seismically induced failure of a reservoir located on a drainage upstream of the site. Because there are no bodies of water located upstream of the project sites, the potential for seismically induced flooding is considered to be negligible.

4.6 EROSION, FLASH FLOODS, AND DEBRIS FLOWS

The numerous drainages that traverse the project area are evidence of the seasonal occurrence of surficial runoff and erosion in the project area. Evidence of flash flooding and erosion (water-deposited debris and brush observed in stream drainages in the project area) was also observed along some of the larger drainages in the study area. Erosion is a concern within the project area and the potential for erosion is highest in areas located in alluvium, particularly those areas located within or close to ephemeral drainages and adjacent to slopes.

Flooding during heavy rainfall is also a concern, with the most vulnerable areas located near waterways. The potential for erosion can be reduced by covering critical surfaces with concrete, asphalt, rip-rap, or vegetation. The potential for flooding and erosion can be additionally reduced by controlling/diverting surface runoff (e.g. with a drainage channel) to carry water away from critical areas.

Debris flows are mixtures of water and debris that move downslope under the influence of gravity. They entrain and transport particles ranging from clays, silt, and sand to boulders tens of feet in maximum dimension. In Arizona, debris flows are particularly prevalent during monsoonal storms in recently burned terrain. Steep, mountainous topography with abundant poorly consolidated alluvial material is generally necessary to generate debris flows during a heavy rainstorm. This type of topography and deposits are not generally present in the project area, therefore the debris flow potential is considered to be low.

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4.7 EARTH FISSURES

Earth fissures generally form in deeper alluvial basins as a result of land subsidence driven by groundwater withdrawal. The Arizona Geological Survey (AZGS) has published earth fissure maps (AZGS, 2014a), and their online Earth Fissure Map Viewer shows that no earth fissures have been identified in the study area (AZGS, 2014), although it appears that their mapping effort is ongoing. No earth fissures were observed during our work, and since there is no known extraction of fluid in the project area, the potential for earth fissures is considered negligible.

4.8 SLOPE INSTABILITY

The planned grading and modifications to existing slopes at IFT Sites AJO-0446 and AJO-0450 can increase the potential for unstable slopes. This risk at these two sites and their mitigation are addressed more specifically in Section 5.2.4. Other than these two locations, slope instability is not considered to be a hazard at the other IFT sites.

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5.0 CONCLUSIONS AND RECOMMENDATIONS

Based on geotechnical and geologic considerations, the IFT sites are suitable for the proposed project. The proposed IFT tower structures can be supported on shallow (mat) or deep foundations. IFT structures at Sites AJO-0446 and AJO-0450 can be supported on surface bedrock, with rock sockets providing uplift resistance. At the other sites, the IFT structures can be supported on drilled shafts or mat foundations. However, we judge that drilled shaft foundations will be more cost efficient than mat foundations because of the relatively high uplift loads. Ancillary support structures can be supported on mat foundations placed on a layer of compacted fill, deep dense natural soils, or competent bedrock (AJO-0446 and AJO-0444).

Conclusions and recommendations summaries of individual IFT sites and related access roads are presented in tabular form in Appendix E for convenience. The following recommendations are applicable to the IFT sites and access roads, except as noted in Appendix E.

5.1 CODE BASED SEISMIC PARAMETERS

Based on the review of the local geologic conditions, results of the field investigation, Seismic

Site Class is defined in Table 4 in accordance with the 2012 International Building Code (IBC;

International Code Council, 2012).

Table 4 - SEISMIC SITE CLASSIFICATION

SEISMIC

SITE

CLASS

IFT SITE LOCATIONS IFT SITE PREDOMINANT LITHOLOGIC TYPE

B AJO-0446, AJO-0450 Crystalline Bedrock

CAG-0444 Coarse-grained Alluvium (0-25 ft depth) Crystalline Bedrock (>25 ft depth)

C

AJO-0452, AJO-0458, AJO-0460, AJO-0462 Coarse-Grained Alluvium

CAG-0430, CAG-0432, CAG-0434,

CAG-0436, CAG-0438, CAG-0440, CAG-0442 Coarse-Grained Alluvium

AJO-0454 Coarse-Grained Alluvium (0-20 ft depth) Fine-Grained Alluvium (>20 ft depth)

D AJO-0448 Fine-Grained Alluvium

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5.2 EARTHWORK

Minor earthwork (cuts and fills less than approximately 5 feet) are anticipated to be required for development of the IFT sites and access roads. However, bedrock cuts up to 12 feet high are required to create the IFT pads at Sites AJO-0446 and AJO-0450.

5.2.1 Site Preparation and Grading

Areas where improvements are planned, including fill areas, should be cleared and stripped of all debris, deleterious matter, organic material and vegetation, and remnants resulting from demolition of any existing foundations or facilities. Cleared and grubbed material should be disposed of off site.

Where improvements are planned at existing grades, the existing subgrade should be proof rolled to check for loose or soft soils.

Compacted fill should be placed immediately upon approval of the prepared subgrade by the geotechnical engineer of record. Prior to placement of the first lift of fill, the subgrade soils should be:

Scarified to a depth of 8 inches.

Moisture-conditioned to above optimum moisture content.

Compacted to at least 95 percent relative compaction.1

The bottom of the excavation should be firm, hard, and unyielding.

Where loose and/or soft soils at the bottom of the excavation preclude compaction, they should be excavated to a sufficient depth such that a firm and unyielding surface is achieved at the planned bottom of excavation or the base of fill. Generally, an overexcavation depth of 1 to 2 feet is sufficient. Using geogrids and/or easily compactable material such as crushed rock can reduce the depth of excavation. Geogrids, if necessary, should satisfy the requirements of the

Uniform Facilities Code (UFC).

1 Relative compaction refers to the in-place dry density of soil expressed as a percentage of the maximum dry density of the same material, as determined by CE 55, MIL-STD-621Test Method 100. Optimum moisture content is the moisture content corresponding to the maximum dry density, as determined by the CE 55, MIL-STD-621Test Method 100. MIL-STE-621 Test Method 100 test procedure is similar to ASTM D1557 test procedure.

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Fill and backfill should be compacted by:

Placing in loose layers less than 8 to 12 inches thick.

Moisture-conditioning to within 2 percent of optimum.

Compacting to at least 95 percent relative compaction for subgrades below mat foundations and roadways.

The compacted subgrade soils should be firm, hard, and unyielding.

Concrete flatwork (i.e., slabs-on-grade, sidewalks, hardscape, curbs, and gutters) should be underlain by a minimum of 12 inches of engineered soil compacted to at least 95 percent relative compaction and at least 2 percent above-optimum moisture content.

Site grading may be accomplished with conventional heavy-duty construction equipment (See

Caterpillar Performance Handbook, 2014). Examples of conventional heavy-duty construction equipment are Caterpillar 815 to 825 series compactors or Caterpillar 816 to 850 series front-end loaders (see Caterpillar Performance Handbook, 2014). The compactors total weights range from 45,000 to 72,000 pounds. The axle weights for the compactors range from approximately 21,000 to 37,000 pounds. The front end loader axle weights vary depending on the load in the bucket, but are in a similar range. Ground contact pressures can vary from 20 to over 1,000 psi depending on the compactor wheel tip penetration. The ground contact pressures for the front end loaders also vary significantly. Therefore, we do not recommend that ground contact pressures be used to select compaction equipment. If compaction equipment is specified, the equipment type, vehicle weight, and/or axle weight should be used.

To avoid overstressing retaining walls, backfill behind walls should be compacted using lightweight compaction equipment or the walls should be braced. Note that the choice of equipment should be left to the contractor as a part of their means and methods.

5.2.2 Material for Fill

All on-site granular soils (sands, silty sands with gravel) can be used as engineered fill. The clay soils encountered are not considered suitable for use as compacted fill beneath concrete walks and paving. Oversize material (larger than 6 inches in diameter) should not be used in the fill.

Any required import material should be approved by the geotechnical engineer of record prior to being placed at the site. Requirements for imported fill material or select backfill taken from on-site materials are summarized in Table 5 below.

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Table 5 - IMPORT FILL AND SELECT BACKFILL CRITERIA

CRITERIA IMPORT FILL SELECT BACKFILL

Maximum particle size (inches) 4 1 Maximum liquid limit (%) 10 5 Maximum plasticity index (%) 5 0 Maximum percentage passing the No. 200 sieve (%) 40 15 Minimum sand equivalent 10 20

The field density of fill should be measured in accordance with the sand cone method (ASTM

D1556) or the nuclear method (ASTM D6938).

5.2.3 Excavations and Temporary and Permanent Slopes in Alluvial and Fill Soils

The stability of temporary excavations is a function of several factors, including the total time the excavation is exposed, moisture condition, soil type and consistency, and contractor's operations. The contractor is responsible for excavation safety. As a guideline, temporary construction excavations greater than 3 feet but less than 15 feet deep in alluvial soils should be planned with slopes no steeper than 1 1/2H:1V (horizontal to vertical). Rock slope stability is discussed in Section 5.2.4. For steeper temporary construction slopes or deeper excavations in alluvium, shoring should be provided for stability and protection. The contractor should strictly adhere to grading requirements of Pima County and applicable health and safety regulations, including those of the Occupational Safety and Health Administration (OSHA).

Excavations at and near IFT Sites AJO-0446 and AJ-0450 will encounter rock. The ability to excavate or rip the rock is noted in Section 3.3.3. Difficult to very difficult ripping is anticipated, and blasting could be needed.

Permanent compacted fill slopes should be planned no steeper than 2H:1V. The slopes should be paved, rocked, treated, or covered with vegetation to reduce surface erosion.

5.2.4 Rock Slope Stability at IFT Sites AJO-0446 and AJO-0450

The stability of the proposed cut slopes extending into bedrock at IFT Sites AJO-0446 and AJO-

0450 were investigated using a kinematic slope stability analysis developed by Markland (1972).

In the kinematic analysis, two conditions must be met for sliding to occur. First, the discontinuity must have a dip angle that is steeper than its friction angle, and second, the discontinuity must daylight from the slope face in a down dip direction. This analysis is conservative because it

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At IFT Sites AJO-0446 and AJO-0450, the currently proposed slopes will be cut into bedrock at an angle 2H:1V or approximately 27 degrees (refer to Site Plans in Appendix E). The friction angle of the bedrock was estimated to be greater than 50 degrees based on methodology outlined in International Society of Rock Mechanics ([ISRM], 2007), which takes into consideration joint roughness, rock UCS, and effective normal stress. No critical failure zones are delineated for the proposed cuts at IFT Sites AJO-0446 and AJO-0450 because the slope angle is shallower than the friction angle estimated for the rock (i.e. discontinuities cannot dip out of slope at an angle that is greater than the friction angle).

Plane and wedge failures have the potential to occur in areas where bedrock cut slopes are steeper than approximately 50 degrees (e.g. potentially along road cuts at rock sites). If bedrock cuts are required at other project locations, cutting the rock slope to an angle less than about 50 degrees if space is available, would eliminate the critical zone for plane and wedge failures and, therefore, the potential for these failures to occur. A thin layer of colluvium (less than approximately 3½ feet) was observed to mantle the bedrock at IFT Sites AJO-0446 and

AJO-0450. These colluvial materials should be removed upslope of the permanent cuts as much as practical. If it is not practical to remove all the colluvial materials, cleanup of loose rock falls and slope sloughing may be required, especially after heavy precipitation.

5.3 DEEP FOUNDATIONS

The IFT site structures will be founded on coarse-grained alluvium, fine-grained alluvium, or bedrock. We recommend that tower structures on alluvial sites be founded on drilled shafts; for bedrock sites, rock-socketed small-diameter shafts are recommended. Both deep foundation types will derive their capacity from skin friction. The proposed structures can also be founded on mat foundations as discussed in Section 5.4, though we judge that drilled foundations will likely be more efficient. Each IFT site was classified by its predominant lithologic type and a summary is presented on Table 6. Note that this table includes references for the design foundation capacity figures applicable for each site.

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Table 6 - IFT DEEP FOUNDATION SUMMARY

DEEP

FOUNDATION

AXIAL

CAPACITY

FIGURES

IFT SITE LOCATIONS IFT SITE PREDOMINANT

LITHOLOGIC TYPE

Figure 4

CAG-0430, CAG-0432, CAG-0434,

CAG-0436, CAG-0438, CAG-0440, CAG-0442 Coarse-Grained Alluvium

CAG-0444 Coarse-grained Alluvium (0-25 ft depth) Crystalline Bedrock (>25 ft depth)

Figure 5 AJO-0452, AJO-0458, AJO-0460, AJO-0462 Coarse-Grained Alluvium

AJO-0454 Coarse-Grained Alluvium (0-20 ft depth) Fine-Grained Alluvium (>20 ft depth)

Figure 6 AJO-0448 Fine-Grained Alluvium

Figure 7 AJO-0446, AJO-0450 Crystalline Bedrock

0 100 200 300 400 Ultimate Axial Capacity (kips)

D ep th (fe et

UPLIFT

0 100 200 300 400 Ultimate Axial Capacity (kips)

D ep th

(fe et

COMPRESSION

Figure 4 - AXIAL DRILLED SHAFT CAPACITY - CAG SITES

Note:

1. Rock encountered during drilling at IFT Site CAG-444 at 25 feet bgs. Skin friction in rock assumed to be the same as soil at this site.

2. Depth referenced to the top of final grade that was assumed to be within 5 feet of the existing ground surface.

D ep th (fe et

UPLIFT

0 100 200 300 400 Ultimate Axial Capacity (kips)

D ep th

(fe et

COMPRESSION

Figure 5 - AXIAL DRILLED SHAFT CAPACITY - AJO COARSE GRAINED SITES

Note:

1. Depth referenced to the top of final grade that was assumed to be within 5 feet of the existing ground surface.

D ep th (fe et

UPLIFT

0 100 200 300 400 Ultimate Axial Capacity (kips)

D ep th

(fe et

COMPRESSION

Figure 6 - AXIAL DRILLED SHAFT CAPACITY - AJO FINE GRAINED SITES

1. Depth referenced to the top of final grade that was assumed to be within 5 feet of the existing ground surface.

D ep th (fe et

UPLIFT

0 100 200 300 400 Ultimate Axial Capacity (kips)

D ep th

(fe et

COMPRESSION

Figure 7 - AXIAL DRILLED SHAFT CAPACITY - AJO CRYSTALLINE BEDROCK SITES

1. Depth referenced to the top of final grade that was assumed to be within 2 feet of the existing ground surface.

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The following sections discuss the drilled shaft and rock-socketed pier foundations. Mat foundations are discussed in Section 5.4.

5.3.1 Drilled Shafts

The vertical capacities of drilled shafts were analyzed using the computer program SHAFT v2012 (Ensoft, 2012) which utilizes methodology described by the Federal Highway

Administration (FHWA; 1999, 2010). Estimated Drilled shaft lengths can be estimated from the ultimate capacity charts on Figures 4, 5, and 6 for drilled shaft diameters of 2, 3, 4, and 5 feet.

These figures correspond to the CAG sites, AJO coarse-grained alluvium sites, and AJO fine-grained alluvium sites, respectively. Table 6 summarizes the applicable design values for specific IFT sites.

Note that these capacities are presented for shafts up to a maximum length of 40 feet. The upper five feet of the drilled shaft has been neglected when computing the skin friction axial capacity of the shafts in accordance with FHWA (1999, 2010). End-bearing was neglected

(FHWA: 1999, 2010). Also note these axial capacities are nominal (i.e., ultimate) values and appropriate factors of safety should be used for design. The minimum required length of the drilled shafts may be determined based on the allowable axial capacities given; however, the shafts should be at least 20 feet long. Due to the presence of shallow bedrock, drilled shaft lengths should be limited to less than 25 feet at IFT Site CAG-0444 if practical.

A minimum factor of safety (FS) of 2 should be used for developing the allowable axial capacities from the minimal capacities presented on Figure 4 through Figure 6. (FHWA, 1999).

A one-third increase to the nominal capacities may be used for transient loads such as wind and seismic. Settlements of the proposed tower leg foundations will depend on the length and diameter of the shafts selected. Based on the anticipated design compressive axial load of 150 kips, these settlements may be about ½ inch. Differential settlement between similarly loaded shafts can be taken as ½ the total settlement.

To use end…