Att I - Vail-Tortolita_Geotech Report.pdf

REPORT COVER PAGE

Geotechnical Engineering Report

Vail-Tortolita 230-kV Transmission Line

Pima and Pinal County, Arizona

January 18, 2023

Terracon Project No. 63225031

Prepared for:

Civil Design and Engineering, Inc.

Phoenix, Arizona

Prepared by:

Terracon Consultants, Inc.

Tucson, Arizona

Terracon Consultants, Inc. 355 S. Eucl id Ave. Suite 107 Tucson, Ar izona 85719

P [520] 770-1789 F [520] 792-2539 terracon.com

REPORT COVER LETTER TO SIGN

Civil Design and Engineering, Inc.

14001 N. 7th Street, Suite C-106

Phoenix, Arizona 85022

Attn: Mr. Cole Shinaman

P: (520) 307.3864

E: c.shinaman@cdeinc.org

Re: Geotechnical Engineering Report

Vail-Tortolita 230-kV Transmission Line

From TEP Vail Substation to Tortolita Substation

Pima and Pinal County, Arizona

Dear Mr. Shinaman:

Terracon Consultants, Inc. (Terracon) has completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with Terracon

Proposal No. P63225031, Revision No. 2 dated June 14, 2022. This report presents the findings of the subsurface exploration and provides geotechnical engineering recommendations concerning the design and construction of deep foundations for the planned transmission line.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon Consultants, Inc.

Louis D. Braun, P.E. Donald R. Clark, P.E.

Geotechnical Group Manager Sr. Consultant/Sr. Principal

Copies: Addressee (1 via email)

Vail-Tortolita 230-kV Transmission Line ■ Pima and Pinal County, Arizona

January 18, 2023 ■ Terracon Project No. 63225031

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

FROST ACTION

CORROSIVITY

SEISMIC CONSIDERATIONS

LIQUEFACTION POTENTIAL

GEOTECHNICAL OVERVIEW

DEEP FOUNDATIONS

GENERAL COMMENTS

Note: This report was originally delivered in a web-based format. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

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INTRODUC TION

Geotechnical Engineering Report

Vail-Tortolita 230-kV Transmission Line

From TEP Vail Substation to Tortolita Substation

Pima and Pinal County, Arizona

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed Vail-Tortolita 230-kV Transmission Line project located from

TEP Vail Substation to Tortolita Substation in Pima and Pinal County, Arizona. The purpose of these services is to provide information and geotechnical engineering recommendations relative to the following:

■ Subsurface soil and bedrock conditions ■ Foundation design and construction

■ Excavation considerations ■ Groundwater conditions

■ Recommended cement type for concrete below grade

■ Seismic site classification per IBC

The geotechnical engineering Scope of Services for this project included the advancement of 73 test borings/corings to depths of ranging from approximately 25 to 61½ feet below existing site grades, laboratory testing of samples collected from our field exploration, engineering analyses and the preparation of this geotechnical engineering report. Based on discussions with Western

Area Power Administration (WAPA), the scope of services has been reduced from the original 76 to

73 exploration locations, primarily due to site accessibility and cultural limitations.

Maps showing the site and boring locations are shown in the Site Location (Exhibit A1) and

Exploration Plan with Geology (Exhibits A2 thru A5) sections, respectively. The results of the laboratory testing performed on soil and rock samples obtained from the site during the field exploration are summarized in part on the boring logs and are included in graphical and tabular form in the Exploration Results section.

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PROJECT DESCRIPTION

Our understanding of the project is based on the information provided in the Geologic Investigation

Statement of Work (SOW) prepared by Western Area Power Administration, titled Geologic

Investigation Statement of Work, Vail-Tortolita 230-kV, Transmission Line Project. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Item Description

Information Provided

Terracon received the following documents detailing project information:

■ Geologic Investigation Statement of Work, Vail-Tortolita 230-kV, Transmission Line Project developed by Western Area Power Administration (WAPA).

■ kmz file outlining proposed transmission line alignment and boring locations

■ V-T Scour Design Locations Excel file dated September 30, 2022

Project Description

We understand that WAPA is working with Tucson Electric Power (TEP) to design a new 230-kV double-circuit steel pole transmission line to replace an existing 115-kV transmission line along the project alignment. The total transmission line alignment for the project is approximately 64 miles in length.

Construction

The transmission line poles will be supported on reinforced concrete drilled shaft foundations, or, alternatively, the proposed transmission line will be supported on fully embedded poles.

Maximum Loads

■ Moment = 25,400 ft-k

■ Shear = 209 kips

Erosion/Scour Depth

We understand the majority of the proposed transmission line poles will designed for 5 feet of scour/erosion. TEP has provided a number of tower locations, at various locations across the alignment, that will need to be designed for 10 feet of scour/erosion, and 16 towers near the Santa Cruz

River that will be designed for 30 feet of scour/erosion.

Grading/Slopes Minimal to no grading is anticipated for the project.

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SITE CONDITIONS

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available topographic maps.

Item Description

Location Information

The project extends from TEP’s Vail Substation located southeast of Tucson in Pima County to TEP’s Tortolita Substation located north of Marana in Pinal

County, Arizona

See Site Location (Exhibit A1) for additional location information.

Site Layout See Exploration Plan with Geology (Exhibits A2 thru A5) sections.

Existing

Improvements

There is an existing transmission line along a majority of the proposed alignment.

Current Ground

Cover

Primarily light to moderate growth of desert brush, native trees, and other vegetation.

Existing Topography

The transmission line alignment appears to generally slope downward towards the northwest as it follows the Santa Cruz River. Based upon information interpolated from Google Earth Pro, the ground surface elevation of the high point, at the southeast end of the alignment (near BH76), is approximately

2,980 feet (ft) above mean sea level (MSL). The topography slopes downward toward the Santa Cruz River, with a crossing between Boring Nos. BH55 to

BH56, and a streambed low point of approximately 2,416 ft MSL. From the

Santa Cruz River Crossing the elevation climbs gradually at first and then steepens as the alignment extends into the Tucson Mountains. One peak is crossed along the alignment with a high point of approximately 2,668 ft MSL

(BH54), before oscillating up and down slightly as the alignment wraps around

Tumamoc Hill. The alignment continues to slope downward as it approaches and crosses the Santa Cruz River two more times, between Boring Nos. BH47 to BH48 and BH41 to BH42, with streambed low points of approximately 2,295 ft and 2,278 MSL, respectively. The topography slopes downward as the alignment continues northwest running along the west edge of the Santa Cruz

River. The topography continues to slope generally downward until the alignment crosses over Rattlesnake Pass with a high point of approximately

2,184 ft MSL (BH28). The topography slopes downward following Rattlesnake

Pass, with a final Santa Cruz River crossing between Boring Nos. BH09 and

BH11, and a streambed low point of approximately 1,841 ft MSL. From the

Santa Cruz River crossing, the elevation climbs gradually as the alignment tends to the northeast towards the Tortolita Substation.

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GEOTECHNICAL CHARACTERIZATION

Regional Geology

The project area is located in the Basin and Range physiographic province (1Cooley, 1967) of the

North American Cordillera (2Stern, et al, 1979) of the southwestern United States. The Basin and

Range Province is defined by wide alluvial valleys and varied topography and is split into five distinct sections; the topography is defined by the features found in the Mexican Highlands and

Sonoran Desert sections (3Demsey, 19884).

The southern portion of the Basin and Range province is situated along the southwestern flank of the Colorado Plateau and is regionally bounded by the Sierra Nevada Mountains to the west.

Formed during middle and late Tertiary time (100 to 15 m.y. ago), the Basin and Range province is dominated by fault-controlled topography. The topography consists of mountain ranges and relatively flat alluviated valleys. Typically, the ranges in this area are of small areal extent but protrude significantly above adjacent wide alluviated plains and valleys. These mountain ranges and valleys have evolved from generally complex movements and associated erosional and depositional processes. Dominant features in the province consist of:

◼ Pediments: Gently dipping slopes formed due to an underlying rock erosional surface;

◼ Alluvial fans: Sediments deposited in outwash plains at areas of low water velocity;

◼ Bajadas: Alluvial fans which combine at the base of mountains; and, ◼ Inselbergs: Isolated hills or mountains, usually that maintain their relief after erosion of surrounding rock.

The site lies within the Tucson Basin. The 1,000 square-mile basin is a northwest-trending valley which is bounded by mountains on the eastern and western sides. The most significant structure that contributes to the formation of this Basin is the Catalina Detachment Fault. This Tertiary-aged normal fault gently dips to the southwest, is estimated to have a displacement as much as 27.5 km (5Dickinson, 1991). Extensive deformation of many of the basement granitic and meta-sedimentary rocks in the Tucson area occurred at 8 to 15 km depth, until local Basin and Range

1Cooley, M.E., 1967, Arizona Highway Geologic Map, Arizona Geological Society.

2Stern, C.W., et al, 1979, Geological Evolution of North America, John Wiley & Sons, Santa Barbara, California.

3Demsey, K, 1988, Geologic map of Quaternary and Upper Tertiary alluvium in the Phoenix North 30’x60’ Quadrangle, Arizona. Arizona Geological Survey, Open File Report 88-17, Map Scale 1:100,000, revised 1990.

5Dickinson, 1991. Tectonic setting of faulted Tertiary strata associated with the Catalina core complex in southern Arizona. Geological Society of America Special Paper 264, 106 p., 1 sheet, scale 1:125,000.

Responsive ■ Resourceful ■ Reliable 5 uplift which created the Tucson Basin exposed these rocks beginning approximately 12 million years ago (6Anderson, 1987).

The current hydrogeologic gradient is to the northwest, and groundwater is generally obtained from sedimentary rock layers which are approximately 2,000 feet thick, underlying the basin

(7Davidson, 1973). The estimated thickness of “basin-fill” sediments and rock of Cenozoic age or earlier is 20,000 feet (Anderson, 1987).

Local Geology

Local geology has been defined from geologic reconnaissance, exploration borings, and from literature review. See the attached Exploration Plan with Geology (Exhibits A2 thru A5) for the location of borings and local geology within 5,000 feet of the proposed transmission line corridor.

In these maps, Quaternary units consist of older alluvium and floodplain deposits (Q) and

Holocene-age fluvial and floodplain deposits (Qr). Bedrock units expected near Rattlesnake Pass consist of Tertiary volcanics (Tv), and bedrock near Borings BH52 through BH54 consist of late-

Cretaceous to Tertiary volcanics (Kv and Tv).

The proposed transmission line stretches from Red Rock, Arizona and heads generally southeast to Vail, Arizona. At the first borehole, approximately 2 miles southeast of Red Rock, Quaternary-aged sheet flood deposits are encountered which consist of dark brown to brown, unconsolidated to occasionally weakly cemented, fine-grained, silty and clayey sediments with occasional sandy lean clays. These deposits continue to Boring BH09, at which point fluvial materials were encountered in the uppermost 10 feet consisting of soft, sandy silts with no plasticity. These soils were deposited recently and lack any soil development in the form of cementation. Recently carved channels and ditches are prevalent continuing east to Boring BH23. It is clear that the sedimentology in this zone has been altered by seasonal monsoon-driven erosion. These deposits are described in literature as being deposits of the Brawley Wash. The Brawley Wash is a tributary to the Santa Cruz River and is the largest watershed in Pima County, and stretches generally south to north starting in the Roskruge and Coyote Mountains (8PCFCD). Soil development in these deposits is expected to be minimal (9Pearthree et al., 2020). Borings consist

6Anderson, 1987. Cenozoic stratigraphy and geologic history of the Tucson Basin, Pima Country, Arizona.

U.S. Geological Survey, Water Resources Investigation Report 87-4190. Demsey, K, 1988, 7Davidson, 1973. Geohydrology and water resources of the Tucson Basin, Arizona. In cooperation with City of Tucson, U.S. Bureau of Reclamation and University of Arizona. Geological Survey Water-supply Paper 1939- E.

8Pima County Flood Control District (PCFCD). Date Unknown. Brawley Wash watershed map. Accessed online, webcms.pima.gov, November 16, 2022.

9Pearthree, Youberg and Skotnicki, 2020. Geologic map of the west of Avra 7.5’ Quadrangle, Pima County, Arizona. Arizona Geological Survey Digital Geologic Map. Map Scale of 1:24,000.

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Continuing southeast, near Boring BH23, coarser-grained alluvial fan sediments consisting of medium- to coarse-grained sands mixed evenly with silts and clays are encountered. The sediments typically are fine- to coarse-grained, nonplastic to medium plasticity, with common weak cementation with calcium carbonate. These alluvial sediments are deposited as a result of the erosion of the Tucson Mountains to the southeast. These coarser grained soils are tightly interfingered with thin beds of dominantly fine-grained material, presumably the result of yearly fluvial and flood deposits.

At Boring BH28, the transmission line crosses over Rattlesnake Pass. Previous soil studies at this location suggest that Rattlesnake pass is located between two (one northerly and one southerly) heavily eroded peaks, the northern most extent of the Tucson Mountain range. The subsequent erosion of these peaks filled the valley between the two, building up alluvial sediments and allowing for the construction of Twin Peaks Road. These two peaks are comprised of Tertiary-aged porphyritic rhyolitic tuffs and ash flows, as determined from exploration borings and in literature (10Lipman, 1993). Boring BH28 did not encounter rock, and consisted of very dense, medium- to coarse-grained sands and gravels with nonplastic to medium plasticity fines. The SPT blowcounts indicate very dense materials for the entire depth and might indicate residual soils are present.

From Rattlesnake Pass to Vail, the surface geology is that of a proximal to distal alluvial fan deposits with variable provenance, interfingering with overall finer grained sheet flood and fluvial deposits from the Santa Cruz River. Fluvial deposits may extend deeper from the surface, especially as boreholes gain proximity to modern washes and the ancestral river beds that coincide, e.g. near Silverbell Road which follows the meandering path of the Santa Cruz

River/Wash. Material is commonly nonplastic, and there is an increase in gravel content with these Quaternary soils compared to the soils of the same age encountered west of Rattlesnake

Pass. Alluvial deposits from Rattlesnake Pass to Vail display coarser grained and boulder-sized, angular to sub angular sediments (proximal fan deposits) when the boreholes occur close to the

Tucson Mountains. Conversely, they display finer-grained sediments of sub rounded and subangular gravels, cobbles, sands and silts when the boreholes are located further from their source rocks. Basin-fill deposits which have experienced weak to moderate soil development were encountered near the end of the alignment, and are best observed in Borings BH75 and

BH76, where very dense sands were encountered near the surface.

Rhyolite bedrock was encountered at Borings BH52 through BH54. The geology in the area is consistent with that of the Tucson Mountain volcanics. They are primarily porphyritic rhyolitic ash

10Lipman, P.W., 1993. Geologic map of the Tucson Mountains Caldera, Southern Arizona. U.S. Geological Survey map I-2205. Map Scale of 1:24,000.

Responsive ■ Resourceful ■ Reliable 7 flows and welded ash flow tuff with sanidine and were likely formed by volcanic vents. The rhyolite rock encountered in borings was typically massive, coarse-grained, moderately to slightly weathered and intensely to moderately fractured. In a moderately weathered state, rock is strong, and in a slightly weathered state, rock is very strong.

Land Subsidence and Earth Fissures

Based on a review of available Arizona Department of Water Resources (ADWR), the project alignment is not within a mapped land subsidence area.

Earth fissures develop within land subsidence areas where a significant thickness of compressible alluvium overlies shallow irregular bedrock surfaces such as ridges and fault scarps or other subsurface features. Based on a review of the Earth Fissure Map of the Avra Valley Study Area:

Pima County, Arizona (11AZGS, 2014) prepared by the AZGS, there are no earth fissures mapped along the project alignment. The nearest mapped earth fissure is approximately 2,650 feet southeast of Boring BH28 and 1,360 feet south of the nearest proposed tower location (SAG-TUC

18/5).

Subsurface Profile

Specific conditions encountered at the boring locations are indicated on the individual boring logs.

Stratification boundaries on the boring logs represent the approximate location of changes in soil types; in-situ, the transition between materials may be gradual. Details for each of the borings can be found on the boring logs included in Exploration Results section of this report. Based on the results of the borings, subsurface soil conditions on the project site can be generalized as follows:

Borings BH01 thru BH08

Description

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 18 Primarily Sand with variable amounts of

Clay, Silt and Gravel / Sandy Lean Clay

Primarily Loose to

Medium Dense /

Very Stiff to Hard

Stratum 2 34 Primarily Sand with variable amounts of

Clay, Silt and Gravel / Sandy Lean Clay

Medium Dense to

Very Dense / Hard

Stratum 3 61½ Primarily Sand with variable amounts of

Clay, Silt and Gravel / Sandy Lean Clay

Primarily Dense to

Very Dense / Hard

11 Arizona Geological Survey (AZGS), 2014, Earth Fissure Map of the Avra Valley Study Area: Pima County Arizona, Digital Map

Series – Earth Fissure Map 27, DM-EF-27 version 1.0.

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Borings BH09 thru BH14

Description

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 10

Primarily Lean Clay with variable amounts of

Sand; Sandy Silty Clay; Sandy Silt / Silty

Sand; Silty Clayey Sand

Primarily Medium

Stiff to Stiff

Stratum 2 19

Primarily Lean Clay with variable amounts of

Sand / Sand with variable amounts of Clay, Silt and Gravel; Poorly Graded Gravel with

Silt and Sand

Primarily Stiff to

Very Stiff / Primarily

Loose to Medium

Dense

Stratum 3 34

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Clayey Gravel / Lean

Clay with variable amounts of Sand

Primarily Medium

Dense / Stiff to Very

Stiff

Stratum 4 43 Sand with variable amounts of Clay, Silt and

Gravel

Primarily Medium

Dense

Stratum 5 61½

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Poorly Graded Gravel with Silt and Sand

Medium Dense to

Very Dense

Borings BH15 thru BH19

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 10 Primarily Sand with variable amounts of

Clay, Silt and Gravel

Primarily Medium

Dense

Stratum 2 18 Primarily Clayey Sand / Sandy Lean Clay with Gravel

Primarily Very

Dense / Hard

Stratum 3 30

Primarily Clayey Sand; Poorly Graded Sand with Gravel / Sandy Lean Clay with variable amounts Gravel

Medium Dense to

Very Dense / Hard

Stratum 4 48

Primarily Sand with variable amounts of

Clay, Silt and Gravel / Sandy Lean Clay with variable amounts Gravel

Medium Dense to

Very Dense / Hard

Stratum 5 61½ Primarily Sandy Lean Clay / Clayey Sand;

Poorly Graded Sand with Gravel Hard / Very Dense

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Borings BH20 thru BH27

Description

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 10 Primarily Clayey Sand; Silty Sand with

Gravel / Sandy Lean Clay

Primarily Medium

Dense to Dense /

Very Stiff

Stratum 2 38

Primarily Clayey Sand; Silty Sand; Well

Graded Sand with Silt; Poorly Graded Sand with Gravel / Sandy Lean Clay

Primarily Dense to

Very Dense /

Primarily Hard

Stratum 3 61½

Primarily Sand with variable amounts of

Clay, Silt and Gravel / Sandy Lean Clay; Fat

Clay with Sand

Primarily Dense to

Very Dense /

Primarily Hard

Boring BH28

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 10 Clayey Gravel with Sand Dense

Stratum 2 60½ Gravel with variable amounts of Clay, Silt and Sand; Clayey Sand with Gravel

Borings BH29 thru BH34

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density

Stratum 1 18 Sand with variable amounts of Clay, Silt and

Gravel; Silty Gravel with Sand

Primarily Loose to

Dense

Stratum 2 34

Sand with variable amounts of Clay, Silt and

Gravel; Poorly Graded Gravel with Clay and

Sand

Primarily Medium

Dense to Dense

Stratum 3 61½

Gravel with variable amounts of Clay, Silt and Sand; Sand with variable amounts of

Clay, Silt and Gravel

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Borings BH35 thru BH37

Description

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 30

Sand with variable amounts of Clay, Silt and

Gravel; Poorly Graded Gravel with Silt and

Sand

Loose to Very

Dense

Stratum 2 48

Sand with Gravel and variable amounts of

Clay and Silt; Poorly Graded Gravel with Silt and Sand

Primarily Dense to

Very Dense

Stratum 3 61½

Sand with Gravel and variable amounts of

Clay and Silt; Poorly Graded Gravel with Silt and Sand

Borings BH38 thru BH51

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 28

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Poorly Graded Gravel with Sand / Lean clay with variable amounts of Sand

Primarily Loose to

Medium Dense / Stiff to Very Stiff

Stratum 2 37

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Gravel with variable amounts of Clay, Silt and Sand

Medium Dense to

Very Dense

Stratum 3 61½

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Gravel with variable amounts of Clay, Silt and Sand / Sandy Lean

Clay

Primarily Very

Dense / Primarily

Hard

Boring BH52

Approximate Depth to

Bottom of Stratum (feet) Material Encountered

Relative Density/

Strength

Stratum 1 7 Clayey Sand with Gravel Very Dense

Stratum 2 28 Slightly to Moderately Weathered

Rhyolite Bedrock

Medium Strong to

Very Strong

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Boring BH53

Description Approximate Depth to

Bottom of Stratum (feet) Material Encountered

Relative Density/

Strength

Stratum 1 10 Clayey Gravel with Sand Dense

Stratum 2 20 Poorly Graded Gravel Very Dense

Stratum 3 40 Highly Weathered Rhyolite

Bedrock

Weak to Medium

Strong

Boring BH54

Approximate Depth to

Bottom of Stratum (feet) Material Encountered

Relative Density/

Strength

Stratum 1 3½ Clayey Sand ---

Stratum 2 25 Moderately Weathered Rhyolite

Bedrock

Medium Strong to

Very Strong

Borings BH55 thru BH61

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 10

Primarily Silty sand with Variable amounts of

Gravel; Clayey Sand / Lean Clay with Sand;

Silty Clay with Sand

Loose to Medium

Dense / Very Stiff

Stratum 2 28

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Poorly Graded Gravel with Silt and Sand / Sandy Lean Clay; Sandy

Silt

Medium Dense to

Very Dense / Very

Stiff to Hard

Stratum 3 61½

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Gravel with variable amounts of Clay, Silt and Sand / Sandy Lean

Clay with variable amounts of Gravel

Primarily Dense to

Very Dense / Very

Stiff to Hard

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Borings BH62 thru BH68

Description

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 10

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Clayey Gravel / Sandy

Lean Clay

Loose to Dense /

Stiff

Stratum 2 37

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Gravel with variable amounts of Silt and Sand / Lean Clay with variable amounts of sand; Sandy Silt

Primarily Dense to

Very Dense / Hard

Stratum 4 44

Primarily Lean Clay with variable amounts of

Sand; Gravelly Fat Clay with Sand; Sandy

Silt / Clayey Sand; Gravel with variable amounts of Silt and Sand

Stiff to Hard /

Medium Dense

Stratum 3 61½

Primarily Lean Clay with variable amounts of

Sand; Gravelly Fat Clay with Sand / Sand with variable amounts of Clay, Silt and

Gravel; Poorly Graded Gravel with Silt and

Sand

Primarily Very Stiff to Hard / Dense to

Borings BH69 thru BH76

Approximate

Depth to

Bottom of

Stratum (feet)

Material Encountered Relative Density/

Consistency

Stratum 1 14

Primarily Clayey Sand with variable amounts of Gravel; Silty Gravel with Sand / Sandy

Lean Clay

Loose to Dense /

Hard

Stratum 2 23

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Gravel with variable amounts of Clay, Silt and Sand / Sandy Lean

Clay

Primarily Dense to

Very Dense / Hard

Stratum 3 61½

Primarily Sand with variable amounts of

Clay, Silt and Gravel; Poorly Graded Gravel with Silt and Sand / Sandy Lean Clay

Very Dense / Hard

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Field and Laboratory Test Data

Laboratory tests were conducted on selected soil samples and the test results are presented in the Exploration Results and are summarized in the following table:

Laboratory Test Summary of Test Results

Atterberg Limits

The Atterberg limits test results of the on-site soils exhibit plasticity characteristics ranging from non-plastic to high plasticity (ranging from 0 to

42 with an average of approximately 11).

Grain Size/Gradation

The gradation test results of the on-site soils indicate these soils contain percent fines (percent passing the sieve No. 200) ranging from approximately 5 to 94 percent, percent sand ranged from approximately 6 to 88 percent, and percent gravel ranged from about 0 to 52 percent. These materials are classified as SC, SM, SP-SM, SW-SM, GC, GM, CL, ML, CL-

ML and CH according to the Unified Soil Classification System.

Moisture Content/Dry

Density

Testing of selected samples obtained from the borings indicated in-situ dry densities ranging from approximately 80 to 132 pounds per cubic foot (pcf) with an average of approximately 108 pcf; and in-situ moisture contents ranging from approximately 1 to 31 percent.

Unconfined

Compression Test - Soil

Three unconfined compressive strength tests were performed on selected soil samples. The unconfined compression strengths of the clay soils ranged between 2,929 psf and 19,583 psf with an average of approximately 9,348 psf.

Unconfined

Compression Strength -

Rock

Ten unconfined compressive strength tests were performed on the rhyolite bedrock samples obtained from Boring Nos. BH52 thru BH54. The unconfined compression strengths ranged between 659 psi and 27,249 psi with an average of approximately 14,123 psi.

Direct Shear

Seventeen (17) direct shear tests were performed on selected soil samples.

The friction angle of the granular soils based on maximum shear stress varied from 24 degrees to 65 degrees (with an average of approximately 44 degrees) with cohesion varying from 0 pounds per square foot (psf) to 2,313 psf (with an average of approximately 438 psf). The friction angle of the granular soils based on maximum displacement varied from 24 to 63 degrees (with an average of approximately 40 degrees) with cohesion varying from 0 to 2,051 psf (with an average of approximately 267 psf).

Groundwater Conditions

Groundwater was not observed in a majority of the test boring locations at the time of our field exploration. The boreholes were observed while drilling for the presence and level of groundwater

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Water levels observed in the boreholes can be found on the boring logs in Exploration Results, and are summarized in the following table.

Boring Number Approximate Depth to

Groundwater while Drilling (feet)

BH42 50

BH43 45

BH46 45

BH47 36

BH58 50

BH59 50

BH60 50

BH61 46

BH62 55

BH63 60

1. Below ground surface

Groundwater was not observed in any of the other test borings at the time of field exploration. These observations represent groundwater conditions at the time of the field exploration and may not be indicative of other times, or at other locations. Groundwater conditions can change with varying seasonal and weather conditions, and other factors.

Based on information obtained from the Arizona Department of Water Resources – Groundwater

Data website (https://gisweb.azwater.gov/waterresourcedata/GWSI.aspx), the following table shows the depth to regional groundwater measured at Arizona Department of Water Resources

(ADWR) monitored well sites in the vicinity of the proposed project alignment.

https://gisweb.azwater.gov/waterresourcedata/GWSI.aspx

Responsive ■ Resourceful ■ Reliable 15

FROST ACTION

Based on data obtained from the National Resources Conservation Service (NRCS) reported frost depth across the location of the proposed alignment varies from 3 to 12 inches.

CORROSIVITY

The following table lists the results of laboratory testing performed to evaluate the corrosive characteristics of the on-site soils.

Boring

No.

Sample

Depth (feet)

Soluble

Sulfate1

(mg/kg {%})

Soluble

Chlorides

(mg/kg) pH Minimum Resistivity

(ohm-cm)

B-3 8-10 60 {0.006} 175 7.5 1,755

B-6 0-5 98 {0.0098} 363 7.4 702

B-11 0-5 53 {0.0053} 213 7.5 4,233

B-15 0-5 96 {0.0096} 155 7.4 4,750

B-18 0-5 50 {0.005} 200 7.5 5,576

B-22 0-5 10 {0.001} 225 7.5 1,033

B-24 0-5 57 {0.0057} 188 7.4 2,375

Location Depth to Groundwater

Measured (ft)

ADWR Monitored Well

Site I.D.

Approximate Elevation

Above Mean Sea Level (ft)

Near BH-6 194 D-10-10 21BCC 1,671

Near BH-12 175 D-11-10 08DDD 1,709

Near BH-17 181 D-11-11- 31CCB2 1,791

Near BH-30 113 D-12-12 27CBB 2,023

Near BH-48 140 D-14-13 03ADD 2,172

Near BH-53 98 D-14-13 27DCA 2,308

Near BH-61 44 D-16-21 15AAB1 2,424

Near BH-66 74 D-15-14 31CBB2 2,523

Near BH-71 37 D-16-14 S04ADD 2,673

Near BH-76 410 D-16-15 04DDA 2,535

Responsive ■ Resourceful ■ Reliable 16

Boring

No.

Sample

Depth (feet)

Soluble

Sulfate1

(mg/kg {%})

Soluble

Chlorides

(mg/kg) pH Minimum Resistivity

(ohm-cm)

B-27 0-5 276 {0.0276} 338 7.5 723

B-30 0-5 51 {0.0051} 250 7.1 2,581

B-34 0-5 124 {0.0124} 231 7.1 4,233

B-40 0-5 7 {0.0007} 188 7.2 1,962

B-43 0-5 150 {0.015} 213 7.3 1,549

B-46 0-5 47 {0.0047} 231 7.4 2,788

B-50 0-5 700 {0.07} 738 7.3 320

B-55 0-5 66 {0.0066} 219 7.5 1,859

B-60 0-5 41 {0.0041} 369 7.3 847

B-64 0-5 958 {0.0958} 438 7.3 630

B-68 0-5 59 {0.0059} 169 7.4 1,549

B-72 0-5 163 {0.0163} 175 7.6 2,065

B-75 8-10 225 {0.0225} 344 7.5 1,466

Results of soluble sulfate testing indicate that a sample of the on-site soils tested has an exposure class of S0 when classified in accordance with Table 4.3.1 of the ACI Design Manual. The results of the testing indicate ASTM Type I portland cement is suitable for project concrete on and below grade. However, if there is no (or minimal) cost differential, use of ASTM Type II portland cement is recommended for additional sulfate resistance of construction concrete. Concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4.

These values should be used to help determine potential corrosive characteristics of the on-site soils with respect to contact with the various underground materials which will be used for project construction. The corrosion information presented is specific to the samples tested. If the actual soils that will be in contact with the structures at the site are different than those tested, then additional corrosion testing should be performed. Terracon is not a corrosion engineer, and our scope of work was limited to performing corrosion laboratory tests on selected samples, presenting these results, and providing a brief comparison of the results to selected criteria. A qualified corrosion engineer should be consulted if corrosion of underground utilities and structures is a concern.

Responsive ■ Resourceful ■ Reliable 17

SEISMIC CONSIDERATIONS

The seismic design requirements for buildings and other structures are based on Seismic Design

Category. Site Classification is required to determine the Seismic Design Category for a structure.

The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7 and the International Building Code (IBC).

Based on the soil properties encountered along the alignment and as described on the exploration logs and results, our professional opinion of the Seismic Site Classification is outlined in the table below:

Borings Seismic Site Classification

BH01 to BH23 D

BH23 to BH28 C

BH29 to BH51 D

BH52 to BH54 B

BH55 to BH68 D

BH69 to BH76 C

Subsurface explorations at this site were extended to a maximum depth of 61½ feet. The site properties below the boring depth to 100 feet were estimated based on our experience and knowledge of geologic conditions of the general area. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

LIQUEFACTION POTENTIAL

Liquefaction is a process in which strong ground shaking causes saturated soils to lose strength and behave as a fluid (Matti and Carson, 1991). Ground failure associated with liquefaction can result in severe damage to structures. The geologic conditions for increased susceptibility to liquefaction are:

■ Shallow groundwater (generally less than 50 feet in depth);

■ The presence of unconsolidated sandy alluvium, typically Holocene in age; and,

■ Strong ground shaking.

All three of these conditions must be present for liquefaction to occur. Based on the density of geologic materials underlying the site, the depth to groundwater, and low seismic potential in the site region, liquefaction is not considered a hazard along the transmission line alignment.

Responsive ■ Resourceful ■ Reliable 18

GEOTECHNICAL OVERVIEW

The site appears suitable for the proposed construction based upon geotechnical conditions encountered in the test borings and provided the geotechnical engineering recommendations contained in this report are implemented in the design and construction of the project.

Drilling of foundations to design depths should be possible with conventional drilling equipment using single flight power augers where granular soils of medium dense or lower relative density or cohesive soils of stiff or lesser consistency are encountered. However, difficult drilling conditions should be expected where weathered to intact bedrock, dense to very dense coarse-grained soils or very stiff to hard cemented clay soils will be encountered. Consideration should be given to obtaining a unit price for difficult excavation in the contract documents for the project.

Specialized drilling equipment will likely be required to advance drilled shaft excavations in areas of cemented soils and rock drilling techniques will be required where rock is encountered on the project. Considering the sandy and dry nature of the subsurface soils in some areas along the proposed alignment, there is a potential of caving of uncased drilled shaft excavations. Therefore, construction of drilled shaft foundations may necessitate the use of temporary casing and/or wet drilling methods. Construction of drilled shaft foundations will necessitate the use of temporary casing and/or wet drilling methods at locations where groundwater conditions were encountered near Borings BH42, 43, 46, 47, 58, 59, 60, 61, 62 & 63.

Other than drilled shaft foundation excavations, no other types of excavations are anticipated for construction of this transmission line project. In the event that other types of excavations may be required, it is anticipated that any shallow excavations can be accomplished with conventional earthmoving equipment, including backhoe type equipment. It should be noted that very dense materials were encountered below a depth of four feet in some of the borings, and increased excavation efforts may be necessary for excavations extending into these materials.

Geotechnical engineering recommendations for foundation systems and other earth connected phases of the project are outlined below. The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration Results section of this report), engineering analyses, and our current understanding of the proposed project.

The General Comments section provides an understanding of the report limitations.

DEEP FOUNDATIONS

The proposed transmission line structures can be supported by drilled shaft foundations or directly embedded poles. Design recommendations for the foundations for the proposed structures and related structural elements are presented in the following paragraphs.

Responsive ■ Resourceful ■ Reliable 19

Design Recommendations

Drilled shaft foundations or directly embedded poles with a minimum embedment depth of 12 feet or 4B (where B is the shaft diameter), whichever is greater, into native soils, are recommended for support of the proposed transmission line poles. Deep foundations can be evaluated using the allowable end-bearing pressures and allowable skin-friction values tabulated below.

Additionally, the tabulated values can be used for axial and lateral load analyses using the computer program MFAD.

GEOTECHNICAL PARAMETERS

Borings BH01 thru BH08

Layer

Bottom Depth

Below Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 18 Granular 110 1.4 31 225 7,200

3 34 Granular 120 3.9 37 725 19,200

4 60 Granular 125 4.7 40 1,100 24,000

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for each granular stratum should be reduced by 150 psf.

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

GEOTECHNICAL PARAMETERS

Borings BH09 thru BH14

Layer

Bottom Depth

Below Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 10 Cohesive 95 0.6 0.75 50 ---

3 19 Cohesive 115 1.2 1.875 400 6,700

4 34 Granular 105 1.7 32 700 8,600

5 43 Granular 110 2.4 34 925 12,000

6 60 Granular 120 4.4 38 1,050 21,600

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

Responsive ■ Resourceful ■ Reliable 20

Borings BH15 thru BH19

Layer

Bottom Depth

Below Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 10 Granular 110 1.4 31 125 ---

3 18 Granular 120 4.9 38 400 14,400

4 30 Granular 115 3.4 36 725 14,400

5 48 Granular 115 2.9 35 1,000 14,400

6 60 Cohesive 130 4.7 7.5 950 19,000

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

Borings BH20 thru BH27

Layer

Bottom Depth

Below Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 10 Granular 105 1.4 31 125 ---

3 24 Granular 120 4.9 38 500 24,000

4 38 Granular 120 4.9 38 900 24,000

5 60 Granular 120 4.8 38 1,125 24,000

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

Responsive ■ Resourceful ■ Reliable 21

Boring BH28

Layer

Bottom Depth

Below Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 10 Granular 120 7.3 38 225 ---

3 24 Granular 130 10.0 41 900 24,000

4 60 Granular 130 10.0 41 1,575 24,000

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

Borings BH29 thru BH34

Layer

Bottom Depth

Below Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 18 Granular 110 1.4 31 225 7,200

3 34 Granular 115 3.4 36 725 16,800

4 60 Granular 125 10.0 40 1,575 24,000

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

Borings BH35 thru BH37

Layer

Bottom Depth

Below Existing

Grade (ft) 1

Layer

Type

Total

Unit

Weight

(pcf)1

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf) 2

Allowable

End Bearing

(psf) 2

1 30 Disregard Due to Potential Erosion/Scour

2 48 Granular 120 4.9 38 100 24,000

Responsive ■ Resourceful ■ Reliable 22

Borings BH35 thru BH37

Layer

Bottom Depth

Below Existing

Grade (ft) 1

Layer

Type

Total

Unit

Weight

(pcf)1

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf) 2

Allowable

End Bearing

(psf) 2

3 60 Granular 130 7.3 41 275 24,000

1. The depth to groundwater should be set to 0 feet. This assumes the use of the program MFAD that automatically calculates the buoyant unit weights below groundwater depth.

2. The axial parameters outlined above assume the soils are saturated below the level of potential erosion/scour.

Borings BH38 thru BH51

Layer

Bottom Depth

Below Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion/Scour

2 14 Granular 100 1.4 31 200 7,200

2 28 Granular 100 1.4 31 575 7,200

3 37 Granular 120 4.4 38 825 21,600

4 60 Granular 125 5.8 40 900 24,000

1. For specific tower locations with 10 feet of potential erosion/scour, the average allowable skin friction value for each granular stratum should be reduced by 150 psf.

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

3. The depth to groundwater should be set to 36 feet for locations near BH47, and 45 feet for locations near

BH42, BH43 and BH46. This assumes the use of the program MFAD that automatically calculates the buoyant unit weights below groundwater depth.

Boring BH52

Layer

Bottom

Depth Below

Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective

Friction

Angle

(degrees

Effective

Cohesion

(ksf)

RMR76

Allowable

Rock/Concrete

Bond Strength

(psi)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 7 Disregard Due to Potential Erosion/Shallow Competent Rock Depth

2 28 Rock 150 973 36 3.28 45 100 3,000 24,000

Responsive ■ Resourceful ■ Reliable 23

Boring BH52

Layer

Bottom

Depth Below

Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective

Friction

Angle

(degrees

Effective

Cohesion

(ksf)

RMR76

Allowable

Rock/Concrete

Bond Strength

(psi)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1. The axial parameters outlined above assume the soils/rock are not saturated below potential erosion level.

2. Rock sockets should be designed only using skin friction or end bearing, but not a combination of both.

Boring BH53

Layer

Bottom

Depth

Below

Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective

Friction

Angle

(degrees

Effective

Cohesion

(ksf)

RMR76

Allowable

Rock/Concrete

Bond Strength

(psi)

Average

Allowable

Skin Friction

(psf)1, 3

Allowable

End Bearing

(psf) 3

1 5 Disregard Due to Potential Erosion

2 10 Granular 120 7.3 38 --- --- --- 200 21,100

3 20 Granular 125 10.0 41 --- --- --- 800 24,000

4 40 Rock 150 440 33 2.50 33 100 3,000 24,000

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for each granular stratum should be reduced by 150 psf.

2. The axial parameters outlined above assume the soils/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using skin friction or end bearing, but not a combination of both. If the shaft extends into rock, axial resistance in the soils overlying rock should be ignored.

Boring BH54

Layer

Bottom

Depth Below

Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective

Friction

Angle

(degrees

Effective

Cohesion

(ksf)

RMR76

Allowable

Rock/Concrete

Bond Strength

(psi)

Average

Allowable

Skin Friction

(psf)1

Allowable

End Bearing

(psf) 1

1 5 Disregard Due to Potential Erosion

2 25 Rock 150 1,292 38 3.75 52 100 3,000 24,000

1. Rock sockets should be designed only using skin friction or end bearing, but not a combination of both.

Responsive ■ Resourceful ■ Reliable 24

Borings BH55 thru BH61

Layer

Bottom Depth

Below Existing

Grade (ft) 3

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 10 Granular 100 1.4 31 125 ---

3 28 Granular 120 3.9 37 475 19,200

4 60 Granular 120 4.9 38 1,050 24,000

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for each granular stratum should be reduced by 150 psf.

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

3. The depth to groundwater should be set to 46 feet for locations near BH58 to BH61. This assumes the use of the program MFAD that automatically calculates the buoyant unit weights below groundwater depth.

Borings BH62 thru BH68

Layer

Bottom Depth

Below Existing

Grade (ft) 3

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 10 Granular 105 1.4 31 125 ---

3 20 Granular 120 4.4 28 450 10,800

4 37 Granular 120 4.4 28 825 10,800

5 44 Cohesive 120 1.9 3.0 650 10,800

6 60 Cohesive 125 2.8 4.5 875 16,200

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for each granular stratum should be reduced by 150 psf.

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion level.

3. The depth to groundwater should be set to 50 feet for locations near BH62 and BH63. This assumes the use of the program MFAD that automatically calculates the buoyant unit weights below groundwater depth.

Responsive ■ Resourceful ■ Reliable 25

Borings BH69 thru BH76

Layer

Bottom Depth

Below Existing

Grade (ft)

Layer

Type

Total

Unit

Weight

(pcf)

Deformation

Modulus

(ksi)

Effective Friction

Angle (degrees)/

Undrained Shear

Strength (ksf)

Average

Allowable

Skin Friction

(psf)1, 2

Allowable

End Bearing

(psf) 2

1 5 Disregard Due to Potential Erosion

2 14 Granular 105 1.9 32 200 9,600

3 23 Granular 125 5.4 39 550 24,000

4 40 Granular 125 7.3 41 900 24,000

5 60 Granular 125 7.3 41 1,175 24,000

1. For specific tower locations with 10 feet of potential erosion, the average allowable skin friction value for

2. The axial parameters outlined above assume the soils are not saturated below the level of potential erosion.

The geotechnical parameters provided assume the groundwater level remains below the maximum depth of the deep foundations except for where outlined within the above tables. The load capacities provided herein are based on the stresses induced in the supporting soils.