Att J - Vail-Tortolita_Tumamoc Hill_Geotech Report.pdf

Report Cover Page

Vail-Tortolita 230-kV

Transmission Line

Geotechnical Engineering Report

November 29, 2023 | Terracon Project No. 63225031A

Prepared for:

Civil Design & Engineering, Inc.

618 East Route 66

Flagstaff, Arizona 86001

355 S Euclid Ave, Ste. 107

Tucson, Arizona 85719

P (520) 770-1789

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

November 29, 2023

Civil Design & Engineering, Inc.

618 East Route 66

Flagstaff, Arizona 86001

Attn: Mr. Cole Shinaman, PMP

P: (602) 935-2024

E: c.shinaman@cdeinc.org

Re: Geotechnical Engineering Report

Vail-Tortolita 230-kV Transmission Line

Tumamoc Hill

Pima County, Arizona

Terracon Project No. 63225031A

Dear Mr. Shinaman:

We have completed the scope of Geotechnical Engineering services for the above referenced project in general accordance with Terracon Proposal No. P63235031A, Revision No. 1 dated August 21, 2023. This report presents the findings of the subsurface exploration and provides geotechnical engineering recommendations concerning the design and construction of foundations for the proposed project.

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

Sincerely, Terracon

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

Geotechnical Group Manager Sr. Consultant/Sr. Principal

Geotechnical Engineering Report

Vail-Tortolita 230-kV Transmission Line | Pima County, Arizona

Table of Contents Page Number

Introduction

Project Description

Site Conditions

Geotechnical Characterization

Regional Geology

Local Geology

Subsurface Conditions

Groundwater Conditions

Seismic Site Class

Liquefaction

Frost Action

Geotechnical Overview

Deep Foundations

Design Recommendations

Drilled Shaft Construction Recommendations

General Comments

Attachments

Exploration and Testing Procedures Site Location

Geophysical Site Map

Geologic Map

Exploration Results

Note: This report was originally delivered in a web-based format. Blue Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com. Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our geophysical exploration and Geotechnical

Engineering services performed for the proposed Vail-Tortolita 230-kV Transmission Line project located on the Tumamoc Hill in Pima County, Arizona. The approximate location of the project is shown on the attached Site Location map. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil and bedrock conditions

■ Groundwater conditions

■ Seismic considerations

■ Foundation design and construction

■ Excavation considerations

The geotechnical engineering Scope of Services for this project included geological mapping and field reconnaissance along the alignment, 16 geophysical surveys to develop compression wave (p-wave) and shear wave (s-wave) velocity data, engineering analyses, and the preparation of this geotechnical engineering report. Note that based on shallow bedrock at a majority of the geophysical survey locations, the shear wave velocities were difficult to measure. Only five (5) shear wave velocity profiles were able to be generated confidently due to the interference from shallow bedrock at a majority of the locations. Compression wave velocities were generated at all 16 geophysical survey locations.

Maps showing the seismic refraction survey locations and mapped geologic conditions are shown on the attached Geophysical Site Map and Geologic Map. The velocity profile results of the 16 geophysical surveys are presented in the Exploration Results section of this report as well.

Facilities | Environmental | Geotechnical | Materials 2

Project Description

Our initial understanding of the project was provided in our proposal and our final understanding of the project conditions is as follows:

Item Description

Project

Description

Terracon previously provided a Geotechnical Engineering Report for the Vail-Tortolita 230-kV Transmission Line, Project No.

63225031, dated January 18, 2023. 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.

We understand due to the culturally sensitive area at Tumamoc

Hill, soil borings were not able to be performed. We have performed geophysical exploration services for approximately

2.7 miles near the Tumamoc Hill area to assist in developing engineering parameters for foundation design as outlined in this report.

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

(provided)

• 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 several tower locations, at various locations across the alignment, that will need to be designed for 10 feet of scour/erosion.

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

Terracon should be notified if any of the above information is inconsistent with the planned construction, especially the grading limits, as modifications to our recommendations may be necessary.

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.

Facilities | Environmental | Geotechnical | Materials 3

Item Description

Location

Information

The project is located around Tumamoc Hill in Pima County, Arizona.

See Site Location for additional site information.

Existing

Improvements

This portion of the alignment is primarily adjacent to Anklam

Road, Greasewood Road, and Starr Pass Boulevard.

Current Ground

Cover

Based on field exploration and site reconnaissance, the ground cover across the alignment generally consists of bare soil with variable amounts of vegetive cover.

Existing

Topography

The area generally slopes downward away from Tumamoc Hill, and the general region slopes downward towards the northeast in the direction of the Santa Cruz River.

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, 1988).

The southern portion of the Basin and Range province is situated along the southwestern flank of the Colorado Plateau and is bounded by the Sierra Nevada Mountains to the west. Formed during middle and late Tertiary time (100 to 15 million years ago), the

Basin and Range province is dominated by fault-controlled topography. The topography consists of mountain ranges and relatively flat alluvial valleys. Typically, the ranges in this area are of a small areal extent but protrude significantly above adjacent wide alluvial 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:

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

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

3 Demsey, 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.

Facilities | Environmental | Geotechnical | Materials 4

Feature Description

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

Inselbergs Isolated hills or mountains, usually maintain their relief after the erosion of surrounding rock

The site lies within the Tucson Basin. The 1,000 square-mile basin is a northwest-trending valley that 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, and is estimated to have a displacement as much as 27.5 km (4Dickinson, 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 uplift which created the Tucson Basin exposed these rocks beginning approximately 12 million years ago (5Anderson, 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 (6Davidson, 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, literature review, and seismic refraction surveys. Geologic field reconnaissance of the proposed transmission line alignment was conducted on September 18, 2023, and seismic refraction surveys were conducted on October 16th through October 20th, 2023. Geologic reconnaissance was limited to areas that were accessible at the time.

According to the Arizona Geological Survey, Geophysical Survey Lines 1, 2, 5, 7, 8, and

9 are mapped as Quaternary surficial deposits, shown on the attached Geologic Map.

This unit includes coarse, poorly sorted alluvial fan and terrace deposits on middle and

4Dickinson, 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.

5Anderson, 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, 6Davidson, 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.

Facilities | Environmental | Geotechnical | Materials 5 upper piedmonts and along large drainages; sand, silt, and clay on alluvial plains and playas; and wind-blown sand deposits (0-2 Ma).

Geophysical Survey Lines 10 and 15 are mapped as early Tertiary to Late Cretaceous volcanic rocks. This unit locally includes thick welded ash-flow tuffs, rhyolite, and andesite and associated sedimentary and intrusive rocks (50-82 Ma).

Geophysical Survey Lines 3, 4, 6, 16, and Lines 12 through 14 are mapped as middle

Miocene to Oligocene volcanic bedrock deposits. This unit includes tuff, fine-grained intrusive rock, and diverse pyroclastic rocks consisting of basalt, andesite, dacite, and rhyolite (11-38 Ma).

Note that Geophysical Line 11 straddles the two volcanic geologic units described above.

Geophysical Survey Line 3 is located approximately 200 feet northeast of outcrops noted from geologic reconnaissance consisting of middle Tertiary (~26-28 Ma) gray tuff containing lithic fragments locally named Tumamoc tuff and approximately 600 feet north of Tumamoc basaltic andesite outcrops (~23-24 Ma). Geophysical Survey Line 16 is located approximately 1,100 feet southwest from a bedrock outcrop consisting of early

Tertiary to late Cretaceous tuffaceous sandstone, shown on the attached Geologic Map

(7Spencer et al., 2003).

Geophysical Survey Line 6 is located approximately 700 feet north of mapped bedrock of middle Tertiary age (~23-24 Ma) locally named Tumamoc basaltic andesite. Geophysical

Survey Line 4 is located approximately 1,100 feet northeast of the same bedrock outcrop, and Geophysical Survey Line 5 is located approximately 750 feet northwest of a different outcrop of the same geologic unit (7Spencer et al., 2003).

The seismic refraction survey recorded P-wave velocities consistent with expected velocities of weathered to strong volcanic rocks, at variable depths, at all survey locations.

Subsurface Conditions

We have developed a general characterization of the subsurface conditions based upon our review of the geologic setting and results of our seismic refraction surveys. This characterization forms the basis of our geotechnical engineering calculations and evaluation of the site. Conditions observed at each seismic refraction survey location are

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.

Facilities | Environmental | Geotechnical | Materials 6 indicated on the individual refraction profiles. The individual profiles can be found in the

Exploration Results attachment of this report.

Based on the mapped geology and results of the seismic refraction survey, subsurface conditions on the project site have been generalized as follows:

Layer

Approximate

Depth to Bottom of Stratum (feet)

Interpreted/Correlated

Materials

Compressional Wave

Velocity (feet/second)

1 0 to 25 Loose to Medium Dense

Granular Soil Up to 3,000

2 0 to 40 Dense to Very Dense

Granular Soil 3,000 to 4,500

3 5 to 57 Weathered Volcanic Rock 4,500 to 6,500

4 30 to 57 1 Strong Volcanic Rock Greater than 6,500

1. Refraction profiles from 30 to 57 feet in depth were developed based on the seismic refraction survey lines.

Groundwater Conditions

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

Groundwater Data website (https://gisweb.azwater.gov/waterresourcedata/GWSI.aspx), the depth to regional groundwater was most recently measured in 2019 to be approximately

142 feet below the ground surface (approximate elevation of 2,194 feet above mean sea level) at an Arizona Department of Water Resources (ADWR) monitored well site (Local

I.D.: D-14-13 11BAD) located approximately one (1) mile northeast of the Geophysical

Survey Line 1.

Zones of perched and/or trapped groundwater may also occur at times in the subsurface soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock materials. The location and amount of perched water is dependent upon several factors, including hydrologic conditions, type of site development, irrigation demands on or adjacent to the site, fluctuations in water features, seasonal and weather conditions.

The possibility of groundwater being encountered in drilled shaft excavations should be considered when construction plans and specifications for the project.

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

Facilities | Environmental | Geotechnical | Materials 7

Seismic Site Class

The seismic design requirements for 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 seismic shear wave velocity profiles the

Seismic Site Classification is C with the average shear wave velocity of the upper 100 feet (Vs100) ranging between 1,300 to 1,960 ft/sec. The shear wave velocity profiles are found in the Exploration Results attachment of this report.

Liquefaction

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 or lack of any groundwater, and low seismic potential in the site region, liquefaction is not considered a hazard along this portion of the transmission line alignment.

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. However, frost is not a design concern for deep or shallow foundations in the

Tucson area.

Geotechnical Overview

The site appears suitable for the proposed construction based upon geotechnical conditions encountered in the geophysical survey lines, provided that the geotechnical engineering recommendations provided in this report are implemented in the design and

Facilities | Environmental | Geotechnical | Materials 8 construction phases of this project. The following geotechnical considerations were identified:

Difficult drilling conditions should be expected where dense to very dense coarse-grained soils and weathered to intact bedrock is expected 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 very dense soils and rock drilling techniques will be required where rock is expected on the project.

Considering the sandy and dry nature of the subsurface soils in the area along the proposed alignment, there is a potential of caving of uncased drilled shaft excavations.

Zones of perched and/or trapped groundwater may also occur at times in the subsurface soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock materials. Therefore, the construction of drilled shaft foundations may necessitate the use of temporary casing.

The recommendations contained in this report are based upon the results of field exploration (presented in the Exploration Results), 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.

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 or rock, 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. Please note that the design values provided in these tables are based upon correlations between the geophysical data and engineering properties of soil and rock in published literature or based upon Terracon experience with similar rock formations within the Tucson area.

Also note, the bottom depth of each layer was based upon an interpretation of the average depth across each Geophysical Survey Line. This is evident as shown on the combined Refraction Profiles that are plotted to elevation along the alignment in the

Facilities | Environmental | Geotechnical | Materials 9

Exploration Results section. Variations in the bottom depth to each layer should be expected at the actual locations of each tower along the alignment and should be accounted for in the design plans and specifications for the project.

GEOTECHNICAL PARAMETERS – Geophysical Survey Line 1

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 17 Granular 100 1.5 31 -- -- -- 250 7,200

3 27 Granular 125 5.0 38 -- -- -- 600 24,000

4 45 Rock 140 440 33 2.5 30 100 -- 24,000

5 57 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS – Geophysical Survey Line 2

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 23 Granular 100 1.5 31 -- -- -- 350 7,200

3 32 Granular 125 5.0 38 -- -- -- 750 24,000

4 43 Rock 140 440 33 2.5 30 100 -- 24,000

5 47 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

Facilities | Environmental | Geotechnical | Materials 10

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 3

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)3

1 5 Disregard Due to Potential Erosion

2 30 Rock 140 440 33 2.5 30 100 -- 24,000

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

2. Rock sockets should be designed only using rock/concrete bond strength or end bearing, but not a combination of both.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 4

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 7 Granular 100 1.5 31 -- -- -- 50 --

3 18 Granular 125 5.0 38 -- -- -- 350 24,000

4 34 Rock 140 440 33 2.5 30 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 5

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 18 Granular 125 5.0 38 -- -- -- 350 24,000

3 35 Rock 140 440 33 2.5 30 100 -- 24,000

4 45 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

Facilities | Environmental | Geotechnical | Materials 11

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 6

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 12 Granular 100 1.5 31 -- -- -- 150 --

3 30 Granular 125 5.0 38 -- -- -- 650 24,000

4 45 Rock 140 440 33 2.50 30 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 7

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 8 Granular 100 1.5 31 -- -- -- 100 --

3 20 Granular 125 5.0 38 -- -- -- 400 24,000

4 40 Rock 140 440 33 2.5 30 100 -- 24,000

5 47 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 8

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 7 Granular 100 1.5 31 -- -- -- 50 --

Facilities | Environmental | Geotechnical | Materials 12

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 8

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)1,2,3

Allowable

End

Bearing

(psf)2,3

3 28 Granular 125 5.0 38 -- -- -- 550 24,000

4 39 Rock 140 440 33 2.5 30 100 -- 24,000

5 45 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 9

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 7 Granular 100 1.5 31 -- -- -- 50 --

3 18 Granular 125 5.0 38 -- -- -- 350 24,000

4 35 Rock 140 440 33 2.5 30 100 -- 24,000

5 48 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 10

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 9 Granular 100 1.5 31 -- -- -- 100 --

3 30 Granular 125 5.0 38 -- -- -- 600 24,000

4 50 Rock 140 440 33 2.5 30 100 -- 24,000

Facilities | Environmental | Geotechnical | Materials 13

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 10

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)1,2,3

Allowable

End

Bearing

(psf)2,3

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 rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 11

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 10 Granular 100 1.5 31 -- -- -- 150 --

3 22 Granular 125 5.0 38 -- -- -- 500 24,000

4 45 Rock 140 440 33 2.5 30 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 12

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 12 Granular 100 1.5 31 -- -- -- 150 --

3 28 Granular 125 5.0 38 -- -- -- 600 24,000

4 45 Rock 140 440 33 2.5 30 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

Facilities | Environmental | Geotechnical | Materials 14

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 13

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 27 Granular 125 5.0 38 -- -- -- 500 24,000

3 42 Rock 140 440 33 2.5 30 100 -- 24,000

4 47 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 14

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 11 Granular 125 5.0 38 -- -- -- 150 24,000

3 25 Rock 140 440 33 2.5 30 100 -- 24,000

4 44 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 15

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 27 Granular 125 5.0 38 -- -- -- 500 24,000

3 40 Rock 140 440 33 2.5 30 100 -- 24,000

4 45 Rock 150 970 36 3.3 45 100 -- 24,000

Facilities | Environmental | Geotechnical | Materials 15

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 15

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)1,2,3

Allowable

End

Bearing

(psf)2,3

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 rock/concrete bond strength 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.

GEOTECHNICAL PARAMETERS - Geophysical Survey Line 16

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)1,2,3

Allowable

End

Bearing

(psf)2,3

1 5 Disregard Due to Potential Erosion

2 11 Granular 100 1.5 31 -- -- -- 100 --

3 22 Granular 125 5.0 38 -- -- -- 500 24,000

4 36 Rock 140 440 33 2.5 30 100 -- 24,000

5 42 Rock 150 970 36 3.3 45 100 -- 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/rock are not saturated below the level of potential erosion.

3. Rock sockets should be designed only using rock/concrete bond strength 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.

The load capacities provided herein are based on the stresses induced in the supporting soils. The structural capacity of the shafts should be checked to assure that they can safely accommodate the combined stresses induced by axial and lateral forces.

Furthermore, the response of the drilled shaft foundations to lateral loads is dependent upon the soil/structure interaction as well as the shaft’s actual diameter, length, stiffness and “fixity” (fixed or free-head condition). All drilled shaft foundations should be reinforced full-depth for the applied axial, lateral and uplift stresses imposed.

Minimum reinforcement of at least one percent of the cross-sectional area of each drilled shaft should be specified.

Settlement of the pole foundations designed and constructed in accordance with the recommendations in this report should be less than 1-inch.

Facilities | Environmental | Geotechnical | Materials 16

Drilled Shaft Construction Recommendations

Difficult drilling conditions should be expected where dense to very dense coarse-grained soils and weathered to intact bedrock is expected 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 expected on the project.

Considering the sandy and dry nature of the subsurface soils in the area, there is a potential of caving of uncased drilled shaft excavations. Zones of perched and/or trapped groundwater may also occur at times in the subsurface soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock materials.

Therefore, the construction of drilled shaft foundations may necessitate the use of temporary casing.

Temporary casing should also be used whenever shafts are installed adjacent to any existing structures or improvements, to reduce the potential for ground loss and movement due to drilled shaft excavation.

If casing is used for drilled shaft construction, it should be withdrawn in a slow continuous manner maintaining a sufficient head of concrete to prevent the creation of voids in the drilled shaft concrete. Drilled shaft concrete should have a relatively high fluidity when placed in cased holes or through a tremie. Concrete with a slump in the range of 6 to 8 inches is recommended. Drilled shaft concrete should be placed immediately upon completion of drilling, cleaning and placement of the reinforcement.

If the drilled shaft concrete cannot be placed in dry conditions, a tremie should be used for concrete placement. Free-fall concrete placement in drilled shaft excavations will only be acceptable if provisions are taken to avoid striking the concrete on the sides of the hole or reinforcing steel. The use of a bottom-dump hopper, or an elephant's trunk discharging near the bottom of the hole where concrete segregation will be minimized, is recommended. Due to potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes.

Shaft bearing surfaces should be cleaned prior to concrete placement. A representative of Terracon should inspect the bearing surface and shaft configuration. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required.

Directly Embedded Pole Recommendations

We understand that directly embedded poles may be installed for the proposed transmission line structures. These are typically installed in an oversized excavation to the design depth and then backfilled with crushed stone in approximately 12-inch lifts, Facilities | Environmental | Geotechnical | Materials 17 or, alternatively, some form of low strength concrete slurry can also be utilized. At a minimum, we recommend that the excavation hole be at least 12 inches larger than the pole outer diameter. We understand that a compressed air tamper is commonly used on the stone backfill to achieve some degree of compaction on each lift. Care should be taken to prevent bridging of backfill material around the pole, and smaller lifts could be used to help reduce the potential for bridging. Granular backfill having a maximum particle size less than ¼ of the minimum distance between the pole and hole/casing

(approximately 1½ inches for a 6-inch annular space) along with slow, controlled placement will reduce the potential for bridging and development of voids along the sides of the pole. As an alternative, lean concrete could be considered as a backfill material around the poles if a casing is used. The skin friction values provided in the

Design Recommendations subsection are for compressive loads with concrete backfill and it is assumed that there will be adequate shear transfer between the pole and the concrete backfill.

It is our understanding that 2-inch minus crushed stone is typically used as backfill around direct embedment poles. As noted above, a smaller maximum particle size of

1½ inches is recommended. The granular material is typically compacted with an air tamper. For design purposes, an effective unit weight of 125 pcf and an internal friction angle of 38 degrees could be used for the crushed stone. The skin friction parameters provided in the Design Recommendations subsection are appropriate for concrete drilled shafts or at an intimate soil-casing interface for poles placed in holes supported by a corrugated steel casing/sleeve. Due to tapered poles, skin friction should be ignored and the axial design should be based on end bearing alone. Lateral deflection would also be significant until movement was sufficient to engage the surrounding soil.

These values do not include any factor of safety.

General Comments

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration.

Variations will occur between exploration point locations or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. Terracon should be retained as the

Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner

Facilities | Environmental | Geotechnical | Materials 18 is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client. Reliance upon the services and any work product is limited to our client and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly effect excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety and cost estimating including excavation support and dewatering requirements/design are the responsibility of others.

Construction and site development have the potential to affect adjacent properties. Such impacts can include damages due to vibration, modification of groundwater/surface water flow during construction, foundation movement due to undermining or subsidence from excavation, as well as noise or air quality concerns. Evaluation of these items on nearby properties are commonly associated with contractor means and methods and are not addressed in this report. The owner and contractor should consider a preconstruction/precondition survey of surrounding development. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

Attachments

Exploration and Testing Procedures

Field Exploration

The approximate seismic refraction survey locations at the project site are shown on the

Geophysical Site Map, and the location and length of the geophysical survey locations are summarized in the following table:

Number of

Surveys Survey ID Nos.

Approximate Survey

Length (feet) Location

Line 1 thru

Line 16

Proposed Transmission

Line Alignment

Geophysical Investigation: Terracon performed 16 seismic refraction profile surveys along the proposed transmission line alignment, as provided by the Western Area Power

Administration. A total of 16 seismic refraction test lines were performed where soil borings were not able to be performed. The seismic system consisted of a linear series of

24 seismic sensors (geophones) and an impulse energy source (sledgehammer and metal plate). Refer to Image 1 below for a typical seismic array setup. A series of seismic records were collected along the geophone array and combined to produce a continuous, 2-D profile of compressional wave (P-wave) velocities. The refraction method correlates with the material strength (higher velocity indicates potentially higher strength) and is limited to the concept of increasing velocity with depth. Refraction surveys are not capable of modeling lower velocity zones within a higher velocity layer.

Image 1: Towable seismic array

In addition to refraction, a shear wave test was completed at each location, using the same array setup as the refraction survey. Shear wave velocities are derived from slower seismic energy compared to compressional waves and can be limited in areas of shallow bedrock. A series of impulse energy sources along the array, combined with ambient vibrational noise (i.e., traffic), generates a 1-D vertical profile at the midpoint of the array and a weighted average of the top 100 ft (Vs100). Only five (5) shear wave profiles were able to be generated confidently due to the interference from shallow bedrock at a majority of the locations.

The seismic refraction method of field exploration consists of measuring (at known points along the surface of the ground) the travel time of compressional waves (p-waves) generated by an impulsive energy source, recorded by a detector (geophone). The field data recorded consists of the time it takes the compressional wave to travel from the source to the detectors, and the distance between the detector and the source. Depending upon the hardness and depth of subsurface materials, the travel time of the compressional waves are shortened and refracted as the material becomes harder with depth.

The data obtained from our field exploration was evaluated and interpreted using Snell's law to determine the compressional wave velocities of each strata. From these interpretations, the depth to various strata was determined along the alignment of each of the survey lines.

Site Location and Exploration Plans

Contents:

Site Location

Geophysical Site Map

Geologic Map

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Site Location

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS

Project:…