24124026 Butner Proposed Self Support Tower - Geotechnical Report (sealed).pdf

Engineered Tower Solutions, PLLC - 3227 Wellington Court - Raleigh, NC 27615

(919) 782-2710 – NC License # P-1016

GEOTECHNICAL REPORT OF SUBSURFACE INVESTIGATION

October 14, 2024

PROPOSED SELF SUPPORT TOWER

BUTNER (NEW)

HP-1040

Central Avenue

Butner, NC 27509

36.1432, -78.7678

Prepared for:

Prepared by:

Matt Nesbit, E.I. Jorge Varela, P.E.

Geotechnical Engineer I I Registered NC 051545

Geotechnical Report of Subsurface Investigation

BUTNER (NEW) HP-1040

Job Number: 23124026

October 14, 2024│1

Project Summary

Item Description

Project Description

A geotechnical exploration and report have been prepared for this proposed 380-foot self-supported tower with 20-foot lighting arrestor.

Included in this report are the results of the field exploration and the recommendations for the design of the foundation system.

Site Coordinates Latitude: 36.1432 Longitude: -78.7678

Site Condition The proposed tower will be installed at Central Avenue in Butner, North

Carolina.

Frost Depth

Based on the TIA Standard (TIA-222-H), dated October 2017, the recommended design frost penetration depth to be used for Granville

County, NC is 12 inches (1.0 ft).

Groundwater

Groundwater was encountered at 26 feet below ground surface at the time of drilling. Please note that subsurface water levels will fluctuate with seasonal and cyclical temperatures and precipitation and can be higher or lower at other times.

Proposed Foundation We assume the proposed foundation will be supported with either pad and pier or drilled shaft (caisson).

October 14, 2024│2

Field Exploration

Item Description

Date October 7th, 2024

Number of Borings 1

Location Latitude: 36.1432 Longitude: -78.7678

Equipment Used CME 45

Advancement Method Hollow Stem Auger (HSA)

Sampling Method ASTM D-1586 with 1.5 I.D. Split Spoon Sampler

Laboratory Classification and Testing

Standard Description

ASTM D2488 Standard Practice for Description and Identification of Soils

October 14, 2024│3

Subsurface Profile

Based on the results of our borings, the soils beneath the surface can be summarized in the table below:

Material Encountered Description Consistency / Density

CLAY Tan and orange sandy lean clay Medium Stiff to Hard

PWR

Partially Weathered Rock sampled as sandy lean clay

1. Refer to boring log for stratification boundaries.

Detailed descriptions of conditions encountered at each exploration point are indicated on the individual logs in the Appendix B. Stratification boundaries on the boring logs represent the approximate location of changes in soil types; in-situ, the transition between materials may be gradual.

Groundwater was encountered at 26 feet below ground surface at the time of drilling. Groundwater levels will fluctuate with seasonal and climatic changes and may be different at other times.

Earthwork Recommendations – Equipment Mat

Earthwork is anticipated to include excavations and fill placement. The following sections provide recommendations for use in the preparation of the equipment mat foundation area and access drive.

Site Preparation

The subgrade should be evaluated under the direction of the Geotechnical Engineer. Areas where soft material are present or excessively wet or dry material should either be removed, or moisture conditioned and recompacted.

October 14, 2024│4

Fill Material Types

Soil Type USCS Classification Acceptable Parameters (for Structural Fill)

Imported Low- to

Moderate- Plasticity

Soil 2

CL, ML, SC or SM All locations and elevations

Sand / Gravel with greater than 12% fines

GW/GP, SW/SP

Crushed stone base course may be used for the access roadway or beneath shallow foundations as a replacement material for overexcavated soils.

Near-Surface

On-site soils 2

CL

On-site soils generally appear suitable for use as fill when they contain at least 12% fines (clay and/or silt) and are compacted at an appropriate moisture content.

1. Controlled, compacted fill should consist of approved materials that are free of organic matter and debris. A sample of each material type should be submitted to the geotechnical engineer for evaluation.

2. Low- to moderate-plasticity cohesive soil or granular soil having at least 12% fines

Fill Compaction Requirements

Item Structural Fill General Fill

Maximum Lift

Thickness

8 inches or less in loose thickness when heavy, self-propelled compaction equipment is used Same as Structural fill

Minimum

Compaction

Requirements 1, 2

98% of max. below foundations and within 1 foot of finished pavement subgrade

95% of max. above foundations, below floor slabs, and more than 1 foot below finished pavement subgrade

92% of max.

Water Content

Range 1

Low plasticity cohesive: -2% to +3% of optimum

High plasticity cohesive: 0 to +4% of optimum

Granular: -3% to +3% of optimum

As required to achieve min. compaction requirements

1. Maximum density and optimum water content as determined by the standard Proctor test (ASTM D 698).

2. High plasticity cohesive fill should not be compacted to more than 100% of standard Proctor maximum dry density.

October 14, 2024│5

Excavations

Groundwater was encountered at 26 feet below ground surface at the time of drilling. Although not expected, if encountered in deep trench excavations during construction, groundwater or perched groundwater will require dewatering until backfilling operations are complete.

All excavations that may be required should, at a minimum, comply with applicable local, state and federal safety regulations, including the current OSHA Excavation and Trench Safety

Standards to provide stability and safe working conditions.

Slopes

For permanent slopes in unreinforced compacted fill areas, we recommended maximum configurations of 3:1 (Horizontal: Vertical) for the cohesive soils (clay) found at the site.

If steeper slopes are required for site development, stability analyses should be completed to design the grading plan. The face of all slopes should be compacted to the minimum specification for fill embankments. Fill slopes should be overbuilt and trimmed to compacted material.

Earthwork Construction Considerations

The near-surface, on-site soils will lose strength when exposed to moisture. To the extent practical, earthwork should be performed during drier periods of weather. Increased remedial measures due to wet and soft or otherwise unsuitable conditions should be expected if earthwork is performed during colder and wetter periods of weather.

A qualified geotechnical engineer should be retained during the earthwork phase of the project to observe earthwork and to perform necessary tests and observations during subgrade preparation;

to monitor proof-rolling, placement and compaction of controlled compacted fills, and backfilling of excavations to the completed subgrade.

October 14, 2024│6

Foundations Recommendations

The following recommendations are made based on our review of the test boring data and our past experience with similar projects and subsurface conditions. Ultimate soil strength parameters are presented on table below.

Ultimate Strength Parameters

Boring

Depth

(ft)

Unified Soil

Classification

Total Unit

Weight

(pcf)

Friction

Angle

(degrees)

Cohesion

(psf)

B-1

0.0 – 3.0 CL 105 -- 600

3.0 – 5.0 CL 105 -- 800

5.0 – 8.0 CL 115 -- 1,200

8.0 – 12.0 CL 115 -- 1,700

12.0 – 17.0 CL 115 -- 2,000

17.0 – 22.0 CL 115 -- 4,800

22.0 – 27.0 PWR 130 38 --

27.0 – 32.0 CL 130 -- 6,000

32.0 – 47.0 PWR 130 38 --

47.0 – 57.0 CL 115 -- 4,500

57.0 – 60.0 PWR 130 38 --

1. Groundwater was encountered at 26 feet below ground surface at the time of drilling. Utilize bouyon unit weight below this depth

Based on the subsurface conditions and typical design foundation loads for similar self-support towers, we recommend that either a caisson (drilled shaft) or a pad/pier be used to support the new tower.

October 14, 2024│7

Modulus of Subgrade Reaction

A vertical and horizontal modulus of subgrade reaction may be derived using the following equations and soils parameters expressed in the above table:

ks-υ = 12 ‧ SF ‧ qa ks-h = ks-υ ‧ B

Where:

qa = Allowable Bearing Capacity (ksf)

SF = Safety Factor

B = Base width (ft), use 1 if B< 1ft ks-υ =Vertical Modulus of Subgrade Reaction (kcf) ks-h = Horizontal Modulus of Subgrade Reaction (ksf)

Caisson (Drilled Shaft)

Should caissons (drilled shafts) be used, the caissons (drilled shafts) will achieve compressive

(downward) and tensile (uplift) resistance through skin friction along the sides of the shafts. In addition to skin friction, bearing resistance at the caisson’s tip will contribute to compressive capacity. We recommend the values given the table below be used for this project. Please note the tip bearing capacity and skin frictions are net ultimate and ultimate values respectively.

Appropriate factors of safety or resistance factors should be used. Lateral loads can be resisted by the lateral stiffness of the soil. Parameters for analysis of the laterally loaded caisson are also given the table below.

October 14, 2024│8

Caisson (Drilled Shaft) Parameters

Depth

(ft)

Net Ultimate

Tip Bearing

Capacity

(ksf)

Ultimate Skin Friction1

(ksf) Lateral

Modulus (pci) ε50

(in/in) Compressive Uplift

0.0 – 3.0 -- -- -- -- --

3.0 – 5.0 -- 0.4 0.4 500 0.007

5.0 – 8.0 -- 0.6 0.6 500 0.007

8.0 – 12.0 -- 0.9 0.9 1,000 0.005

12.0 – 17.0 18 1.0 1.0 1,000 0.005

17.0 – 22.0 40 2.4 2.4 2,000 0.004

22.0 – 27.0 40 1.4 1.4 125 --

27.0 – 32.0 40 3.0 3.0 2,000 0.004

32.0 – 47.0 40 2.5 2.5 125 --

47.0 – 57.0 40 2.3 2.3 2,000 0.004

57.0 – 60.0 40 3.2 3.2 125 --

1. We recommend the skin friction be ignored for the top 3 ft of the caisson

Based on the subsurface soil conditions, excavations for the caissons (drilled shafts) should be possible using a large, truck-mounted, hydraulic-advanced drill rig. All debris, loose or disturbed soil should be removed from the excavation prior to placing reinforced steel and/or concrete.

Reinforcing steel and/or concrete should be placed immediately upon completion of the excavation.

The excavations may be susceptible to caving. Drilling fluid or casing could be used to assist in keeping the drilled hole open. If casing is used, we recommend it be removed from the excavation as concrete is being placed. Continuous vibration or other approved methods should be used during casing withdrawal to reduce the potential for void-space formation within the concrete. If water is present during concrete placement and/or drilling fluids are used to maintain hole stability, concrete should be pumped or otherwise discharged to the bottom of the hole via a hose or tremie pipe. The end of the hose or tremie pipe must remain below the top surface of any water, drilling fluid and the in-place concrete at all times. Additionally, concrete should be consolidated using

October 14, 2024│9 vibration methods over the entire length and width of the caissons and the consolidation should be performed only after these fluids are removed and to the extent possible.

Pad & Pier / Single Mat Foundation

If the site has been prepared in accordance with the requirements noted in Earthwork

Recommendations – Equipment Mat, the tower’s foundation capacity can be determined using the soil’s bearing capacity, passive pressure resistance, and a sliding friction factor.

Net Ultimate Bearing Capacity and Sliding Friction Factor

Depth2

(ft)

Net Ultimate Bearing Capacity1

(psf) Sliding Friction Factor1

0.0 – 2.0 -- --

2.0 – 5.0 7,000

0.30 5.0 – 8.0 8,000

8.0 – 12.0 11,000

1. This value is a net ultimate value and an appropriate factor of safety or resistance factor should be used

Ultimate Passive Pressure and Friction Factor

Boring # Depth

(ft)

Ultimate Passive Pressure1

(psf)1

B-1

0.0 – 2.0 0 – 400

2.0 – 4.0 400 – 800

4.0 – 8.0 800 – 1,600

8.0 – 12.0 1,600 – 2,400

12.0 – 20.0 2,400 – 4,000

1. Ultimate passive pressure can be interpolated for foundation depths with the depth ranges given

Job Number: 23124026

October 14, 2024│10

Seismic Parameters

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)

Seismic Site Classification

Item Seismic Parameter

2018 International Building Code

Seismic Site Classification D1

Design Spectral Response Acceleration Parameters Sds = 0.125g

Sd1 = 0.093g

1. The IBC seismic site classification is based on the subsurface profile depth of 100 feet. The scope of work did not authorize exploration to a depth of 100 feet. A seismic Site Soil Classification of D should be used if insufficient details are known about the 100-foot soil profile.

LIMITATIONS OF REPORT

This report has been prepared in accordance with generally accepted geotechnical engineering practices for the specific application of this project. The conclusions in this report are based on the applicable standards of our practice in this geographic area at the time this report was prepared.

No other warranty, expressed or implied, is made.

The analyses and conclusions submitted herein are based, in part, upon the data obtained from the subsurface exploration performed for this analysis. The soil and ground water conditions can vary across the site. Opinions and conclusions are subject to change if new or additional information is submitted for review.

APPENDIX A

LOCATION INFORMATION

SITE LOCATION PLAN

October 14, 2024│12

BORING LOCATION PLAN

October 14, 2024│13

SITE PHOTO

October 14, 2024│14

APPENDIX B

SOIL TEST BORING

3-3-3 (6)

2-3-5 (8)

3-6-6 (12)

6-9-8 (17)

7-11-9 (20)

8-21-27 (48)

26-50/5"

21-32-28 (60)

33-50/5"

37-50/5"

41-50/5"

29-31-34 (65)

32-17-28 (45)

23-19-50/4"

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SANDY LEAN CLAY (CL), tan and orange, moist, medium stiff to stiff.

SANDY LEAN CLAY (CL), tan and orange, moist, very stiff to hard.

PARTIALLY WEATHERED ROCK (PWR), , sampled as sandy lean clay.

SANDY LEAN CLAY (CL), tan and orange, moist, hard.

PARTIALLY WEATHERED ROCK (PWR), , sampled as sandy lean clay.

SANDY LEAN CLAY (CL), tan and orange, moist, hard.

PARTIALLY WEATHERED ROCK (PWR), , sampled as sandy lean clay.

Bottom of borehole at 60.0 feet.

NOTES

GROUND WATER LEVELS:

AT TIME OF DRILLING 26.00 ft / Elev 358.00 ft

AT END OF DRILLING 26.00 ft / Elev 358.00 ft

AFTER DRILLING 26.00 ft / Elev 358.00 ft

LOGGED BY J. Varela

DRILLING METHOD Hollow Stem Auger (HSA)

DRILLING EQUIPMENT CME 45

DATE 10/7/2024 COORDINATES 36.143244, -78.767803

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MATERIAL DESCRIPTION

BORING NUMBER B-1

PROJECT NAME BUTNER (HP-1040)CLIENT NCSHP

PROJECT NUMBER 23124026 PROJECT LOCATION Central Avenue, Butner, NC 27509

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October 14, 2024│16