Attch 2 Geotechnical Report.pdf

Geotechnical Investigation & Report Hayden Peak Radio Tower

Mojave County, Arizona

Submitted to:

United States Department of the Interior

Bureau of Land Management

Kingman Field Office

7/21/2020

TABLE OF CONTENTS

Page

1.0 INTRODUCTION

2.0 PROJECT DESCRIPTION

3.0 SITE CONDITIONS

3.1 CLIMATE

3.2 GEOLOGIC SETTING

4.0 ROCK MAPPING AND GEOTECHNICAL INVESTIGATIONS

4.1 ROCK MAPPING

4.2 SEISMIC REFRACTION SURVEY

4.3 RESISTIVITY SURVEY

5.0 GEOTECHNICAL DESIGN PARAMETERS OF GRANITE

6.0 FOUNDATION SELECTION

6.1 ROCK ANCHOR FOUNDATION

6.2 MICROPILE FOUNDATION

6.3 PAD AND PIER FOUNDATION

7.0 CONSTRUCTION RECOMMENDATIONS AND CONCLUSIONS

7.1 CONSTRUCTION RECOMMENDATIONS FOR ROCK ANCHORS

7.2 CONCLUSIONS

7.3 LIMITATIONS

8.0 REFERENCES

LIST OF FIGURES

Figure 1: Site Location Map Figure 2: Hayden Peak Tower Figure 3: Existing Foundation System Figure 4 Illustration of Granite Tors with Cell Towers Figure 5 Hayden Peak Discontinuities pattern Figure 6 Photo of Hayden Peak Seismic Line Layout SL-2 Figure 7 Seismic Refraction Array Line SL-1 Figure 8 Seismic Refraction Array Line SL-2

LIST OF TABLES

Table 1 Rock Mass Rating Table 2 Resistivity Results Table 3 Design Parameters

APPENDIX

1. Exhibit 1-Geology Map

2. Exhibit 2-Geotechnical Exploration Map

3. Rock Mapping Study

4. General Construction Drawings

Final Geotechnical Report:

Hayden Peak Radio Tower Site YeDoma Project 62159

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1.0 INTRODUCTION

YeDoma Consultants, LLC. (YeDoma) was authorized by the Bureau of Land Management

Arizona State Office (BLM-AZ) through Contract Order No. 140L6420P0022 to conduct geotechnical investigations and report for the Hayden Peak radio communication tower (Refer to

Figure 1 for site location). The objective of the consultant led geotechnical investigation was to investigate site subsurface conditions and evaluate options for remediating the existing tower foundation.

YeDoma was onsite in May 2020 and conducted rock mapping of the site. As the site access was constrained, the technical approach included collecting rock discontinuity data to evaluate the rockmass and surveying the site using seismic refraction compression waves (P-wave) and resistivity probing. This report includes the findings and results of the field investigation, engineering analyses, and recommended criteria for a foundation type.

Figure 1: Site Location Map

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2.0 PROJECT DESCRIPTION

The Hayden Peak Tower is used for communications by the United States Department of the Interior, Bureau of Land Management’s Kingman Field Office. A photo of the tower is illustrated in Figure 2. The site is located about 11 miles southeast of Kingman, Arizona via Hualapai Mountain Road. The site has controlled access which is shared with Hualapai Mountain Park User’s Group and respective local entities. The Hayden Peak Tower is perched on a granite outcrop, refer to Figure 2 within the BLM Wilderness Area at an elevation of 8340 feet.

Figure 2: Hayden Peak Tower

It is our understanding that the communication tower is used for fire dispatch and has periodically been offline due to environmental and structural loading related distress on the tower. The rugged access makes it less accessible for maintenance and repairs. The access road to the tower is steep with switchbacks and considered an unimproved 4-wheel drive only switchback trail, at the time of visiting the site the roadway was not traversable until mid-May and required a vehicle with adequate ground clearance. In winter, the road conditions can present treacherous access due to drifting, ice and wind elements, while in summer, storm events could also present challenges.

At the time of the investigation, it is noted that the communications were offline, a maintenance crew was conducting work at the time of YeDoma’s investigations, bringing the cell service back online. The existing foundation system is described as concrete pedestals bearing on granite.

The foundation is illustrated in Figure 3.

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Figure 3: Existing Foundation System

3.0 SITE CONDITIONS

The rugged rocky terrain characterizes the site. Equipment and supplies must be hauled in and hauled out by carting the supplies up and down a three-hundred-foot staircase.

3.1 Climate

The site is within the semi-arid southwest region of the USA. Daily fluctuations in temperature and seasonal changes along with precipitation events are key factors that contribute to seasonal frost and construction considerations. Thermal expansion and contraction, expansive behavior of subsurface material, loss of shear strength can vary based on seasonal climatic conditions. The average wind speed for the area from March to August is about 14 mph which can cause the lateral force for the tower. In the local area, the access road to the Hayden Peak radio tower was inaccessible with a motor vehicle though the winter months. We anticipate that extreme weather conditions occur throughout the year. The TIA Standard was used as the basis of determining the design frost depth of 36 inches.

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3.2 Geologic Setting

The northeastern part of Arizona terrain is described as within a converging zone between two prominent physiographic provinces which define the western region of the United States, the

Basin and Range and the Colorado Plateaus. The mountain ranges in this area include the Black, Cerbat, Hualapai, Mohave, McCracken and Aquarius Mountains, generally ranges trend northwest with expansive structural basins between them. The geologic mapping in the area is based on 1959 mapping (Refer to Exhibit 1 in the Appendix). The pinnacle formations capping the peaks are tors, erosion and weathering of rock landforms. The granite tors at Hayden Peak are described as massive boulders, comprised of crystalline basement rocks, uplifted from deep in the continental crust, the rock unit has gradational contacts separating the granite and gneiss.

The discontinuities are spaced several feet apart and the core blocks of the granite are monolithic.

Geologically, the rock unit mapped at the site is Proterozoic granite, Xg (Similar to the Unit

Mapped in the Kingman 7 ½’ Quadrangle, Mohave County, Arizona). The unit is visually described as a K-feldspar porphyritic granite. The phenocrysts of K-felspar range in size up to 5

cm. The granite has a gradational contact with gneiss, Xgn, the gneiss is visually distinguished from the granite by the biotite foliation planes. An image of the site, with a nest of cell towers perched on the top of granite tors at Hayden Peak is presented below.

Figure 4 Illustration of Granite Tors with Cell Towers

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4.0 ROCK MAPPING AND GEOTECHNICAL INVESTIGATIONS

On May 21st, YeDoma conducted the site work with a three-person field crew. The work included geological mapping of the granite, seismic refraction surveying and resistivity surveys.

4.1 Rock Mapping

Discontinuities in the rock mass were evaluated, including spacing, orientation, and width of planes, joints and fractures. The massive outcrops of granite were mapped, rock discontinuity patterns were assessed by geotechnical engineers, Jesse Reinikainen, PE and Hamid Ranjkesh using a Brunton compass and chain to measure spacing of the prominent joints and shears. The data was plotted in the office using a stereographic projection software program and the basis for identifying major joint patterns. Figure 5 present the discontinuities pattern for the project area which illustrates three main clusters of joint sets with the dip direction of Southwest, East and

Southeast. A minor joint set is noted with dip direction to the Southwest. A layout is also included in the Appendix with the rock data collected from the site.

Figure 5 Hayden Peak Discontinuities pattern

The rock mass rating was evaluated for the site and presented in Table 1.

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Table 1 Rock Mass Rating

Parameter/Rating Typical condition

1. Uniaxial Compressive Strength of Intact material (MPa) 55

Rating 7

2. Interpreted Drill Core Quality (RQD) (%)

75 – 90 %

Rating 17

3. Spacing of Discontinuities 0.2 – 1.0 m

Rating 12

4. Discontinuity Length 1 – 3 m

Rating 4

5. Discontinuity Separation 1 – 5 mm

Rating 1

6. Roughness of Discontinuities Rough

Rating 5

7. Discontinuity Infilling Hard filling & < 5 mm

Rating 4

8. Weathering Slightly weathered

Rating 5

9. Groundwater Condition in Joints Completely dry

Rating 15

10. Strike and Dip Orientations of Discontinuities Favorable

Rating -2

RMR 68

Rock Mass Class II

Description Good rock

Cohesion of Rock Mass (kPa) 300 – 400

4.2 Seismic Refraction Survey

A 24- channel Geode instrument with two-foot spacing on the 10-Hertz geophones array was surveyed in the field (Refer to Figure 6). The Geode and the 2D Seisimager software used to evaluate the data was developed by Geometrics, Inc. YeDoma processed the data using signal enhancement (filtering and stacking shots) to improve the signal to noise ratio. An aluminum plate was used to dampen the energy of a 12-pound sledgehammer. The crew evaluated the first picks initially in the field using a laptop computer and finalized the subsurface strata in the office.

The seismic data together with rockmass quality was used to correlate geotechnical parameters of the granitic rock.

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Figure 6 Photo of Hayden Peak Seismic Line Layout SL-2

The refraction data at the site included collecting travel times of a compressional (P-wave) seismic wave measured to each geophone directly through subsurface layers of rock. The study was conducted to calculate seismic velocities and evaluate the depth and thickness (geometry) of subsurface layers. The depth to bedrock was also evaluated to aid in assessing rock quality and rippability of rock. It is noted that the seismic refraction method has limitations. The seismic profiles may include hidden zones due to higher velocity material overlying lower velocity (i.e., competent rock over weaker rock) and depth of sections is typically limited to about 1/3 of the length of the seismic lines. Two seismic lines were conducted (Refer to Exhibit 2 in the Appendix and Figure 7 on the adjacent page).

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Figure 7 Seismic Refraction Array Line SL-1

Figure 8 Seismic Refraction Array Line SL-2

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Seismic Refraction Discussion:

The seismic data was evaluated in the office. Two layers were modeled, the overburden is comprised of three to five feet of soil. This layer has an average seismic velocity of about 2200 feet per second, which is typical for a dense sandy gravel engineered fill material. The irregular boundary separating the two units is interpreted to be the contact with the granite tors erosional surface. The core blocks of granite bedrock are characterized by an average seismic velocity of about 5600 feet per second. The depth of the seismic lines was limited to about fifteen feet due to the site constraints; lines were about 50 feet in length. The two seismic arrays provide similar findings and basis for evaluating the site.

4.3 Resistivity Survey

The electrochemical properties underlying the tower site was evaluated using soil resistivity lines (4-point Wenner method). Line 1 was setup at an azimuth of 60° and Line 2 setup at an azimuth of 300°. Electrical resistivity sounding measurements involve placing four electrodes (stainless steel probes) in a straight line. A current is injected into the outer two probes, and the potential difference is measured across the inner two probes. The resistance is calculated from the known current and the measured voltage. The results of the two resistivity soundings are summarized in Table 2. The electrical resistivity results are consistent with near surface granite.

Table 2 Resistivity Results

Site Line Spacing (feet) Resistivity Units

Hayden Peak

2 64727 Ohm.cm

4 48564 Ohm.cm

6 70548 Ohm.cm

8 72616 Ohm.cm

2 102644 Ohm.cm

4 109000 Ohm.cm

6 104673 Ohm.cm

10 125241 Ohm.cm

13 120740 Ohm.cm

5.0 GEOTECHNICAL DESIGN PARAMETERS OF GRANITE

The geotechnical parameters are presented in Table 3.

Table 3 Design Parameters

RMR Description Unit Weight

(pcf) Static Modulus

(psi) Estimated UCS* (psi)

Bond Strength** (psi)

68-Good Rock

Granite 140 1x105 4000-8000 400

UCS*=Unconfined Compressive Strength based on Seismic Velocity Bond Strength**=Ultimate Bond Strength for Rock/Grout based on Good to Fair Rock

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6.0 FOUNDATION SELECTION

The foundation selection considered the geotechnical design parameters and a lightly loaded tower. General Construction Drawings are illustrated int the Appendix. The granite unit is characterized as competent rock based on mapping rock discontinuities, seismic velocity properties. The following subsections include a general alternative analysis of different methods considered at the site for provisions of bearing resistance to structural loads. Rock anchors are feasible from a geotechnical viewpoint and provide the most resilient form of foundation given the site constraints. The access to the site will be difficult and may require slinging the equipment in with a helicopter. Assuming the access is manageable, rock anchors are the preferred alternative due to ease of construction and competency of rock conditions.

6.1 Rock Anchor Foundation

Anchors are three-part systems consisting of (1) steel tendons or reinforcing bars, (2) cement or resin grout, and (3) the rock mass itself. The components of the rock anchor include a bonded anchorage, free stressing length and a tendon bond length. Generally, the free stressing length should remain unbonded after stressing unless provisions are included to satisfy structural requirements. For conventional rock anchors installed in competent rock, the bond stresses are typically concentrated at the top of the bond length. The maximum strain in the tendon bond length occurs at the top of the tendon bond length and some load redistribution is anticipated within a small cone of rock as the peak stress migrates down the tendon bond length. A load is applied to the tendon, which is designed to transfer tensile forces and bending moments that imposed on the tower by high wind loads to the rock mass through shear stresses in the grout. At the Hayden Peak based on the seismic refraction data the rock mass is competent which is advantageous for rock anchors. The design and analysis of anchors is to determine the anchors load, spacing, depth and bonding of the anchor. The anchor should be designed to resist overturning and uplift loads associated with the heavy-duty tower and resist tensile failure of the tendons and pullout of the tendons from the grout. The anchor depth should be designed depend on type of rock and anchor pattern to develop the anchor force required for stability. The geotechnical considerations included in this report are limited to evaluating the grout-rock interface and rock mass uplift. The rock mass uplift failure mechanism can be analyzed using the parabolic equation P=6D, where P = capacity in kN and D= depth of embedment in meters

(Pease, 1984). Construction of the Rock Anchors should follow recommendations for prestressed rock and soil anchors (latest version of Post-Tension Institute PTI DC-35: Prestressed Rock and

Soil Anchor Committee). The Load Factor Design method is specified for the project, based on

TIA-222 guidance; therefore, a nominal and a factored bearing resistance are provided as design guidelines. As the founding material is rock, the factor used for self-supporting structures is

Fs`=0.75. The nominal resistance multiplied by the factor is the factored bearing resistance to the strength load combination case. If allowable design is used, the nominal resistance shall be determined by multiplying the allowable resistance by a safety factor of 2.0.

6.2 Micropile Foundation

Micropiles are small diameter drilled and grouted non-displacement pile and used when there are difficult ground conditions. Micropiles have high performance and capacity which can withstand relatively significant axial, tension and lateral loads, and transfer the structural loads through competent foundation. They can be installed at any angle and where access is restrictive. The

11 | P a g e micropiles have a diameter in range of 3 to 12 inches that can extend to depth of 200 feet. In this technique the casing will be drilled to design depth and steel reinforcing is inserted into the micropile casing. Pile is grouted with rich grout of cement and fine sand with water cement ratio of 0.5 and this grout shall have compressive strength of minimum 480 kg/cm2 on 28 days. We anticipate that the design length of the pile will be primarily dependent on the embedment/lateral capacity required to resist live loading. The safe vertical and lateral load capacities for micropiles are respectively from 25 to 35 Mt and 2 to 4 MT.

6.3 Pad and Pier Foundation

Pad and Pier footings or massive footing section with interior pier cages to tie in with the tower legs are common foundations for cell towers due to ease of construction when access is reasonable and conventional earthmoving equipment can rip into the subsurface. Individual footings are one of the most common and simple types of spread footing foundation. They are used when the load of the structure is carried only by the same columns. The footing is just a square or rectangular pad of concrete on which the column sits. For this project, the spread footing should be founded on sound rock and notched into a rock. At Hayden Peak, the bedrock is hard granite rock, the excavation should be at least 12 inches deep and encompass the entire tower footprint. The spread footing shall be sufficiently thick so that the footing does not require punching shear or beam shear reinforcement. Spread footings should be sized for eccentric loading at the strength limit state and checked for bearing at the service and strength limit states. For spread footings, on rock, the eccentricity of the loading at the strength limit state shall not exceed 0.45 of the footing dimensions in any direction.

7.0 CONSTRUCTION RECOMMENDATIONS AND CONCLUSIONS

The construction of anchors is to be carried out in a manner consistent with this geotechnical report and PTI DC35.1-14 guidelines with respect to drilling, corrosivity mitigation, and proof testing. The foundation system will require helicopter supported operations, slinging equipment to the top of the mountain peak. A helipad is in the vicinity for staging purposes.

7.1 Construction Recommendations for Rock Anchors

YeDoma recommends extending the free stressing length of the prestressing steel about three feet into the bond length (fifteen feet free stressing length) so that the bond length is partially loaded in compression. A sacrificial pile should be used to load test the foundation. The recommended test load for evaluating deflection and suitability is 133% with a minimum of 10-minute hold. Every anchor should be tested with proof or performance test procedures. The project should include a Quality Control (QC plan) and a quality assurance geotechnical engineer to evaluate actual conditions and document the load testing process. YeDoma is available to conduct construction phase engineering to review Contractor submittals and supply a field technician to conduct Quality Control testing and log geotechnical downhole conditions and load evaluate the load tests during production. This includes compressive strength and regular fluid grout testing to verify the correct specific gravity. The QC testing is a major step in resolving construction related issues and confirm design parameters. The test load should not exceed 80% of the ultimate strength of the steel.

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7.2 Conclusions

The foundation improvements at Hayden Peak are anticipated to require rock anchors to reduce unacceptable movement of the tower during storm events and increase reliability of the infrastructure. Rock anchors are the preferred method of resisting design loads. Stability of the tower should be verified by the design engineer for overturning, sliding, and uplift in addition to bearing resistance.

7.3 Limitations

This report is intended solely for the use private owner, and its subcontractors for the specific

Hayden Peak radio tower project use and in the context and for the express purpose for which it has been delivered. YeDoma makes no warranty either or implied. Our conclusions are based on the information made available to the project team. Recommendations are based on accepted professional engineering principles and practices. Any other use or reliance on this document by any third party is at that party’s sole risk and responsibility.

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8.0 REFERENCES

Pease, K.A., Kulhawy, F.H., 1984, EL-3777 Load Transfer Mechanisms in Rock Sockets and

Anchors, Cornell University prepared for Electric Power Research Institute, California

PTI DC-35, 2014 Recommendations for Prestressed Rock and Soil Anchor Committee, Post-

Tensioning Institute, New York, NY

Richard, Stephen M., et al. “AZGS Document Repository.” Digital Graphics Files for the

Geologic Map of Arizona, a Representation of Arizona Geological Survey Map 35, v. 1.0 | AZGS

Document Repository, 2002, repository.azgs.az.gov/uri_gin/azgs/dlio/632.

Bieniawski, Zdzisław Tadeusz, and Z. T. Bieniawski. Engineering rock mass classifications: a complete manual for engineers and geologists in mining, civil, and petroleum engineering. John

Wiley & Sons, 1989.

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Appendix:

1. Exhibit 1-Geology Map

2. Exhibit 2-Geotechnical Exploration Map

3. Rock Mapping Study

4. General Construction Drawings

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