Appendix_6-PID_003876A_Tierra_Geotechnical_Report_2021-09-21.pdf

Tierra, Inc.

7351 Temple Terrace Highway • Tampa, Florida 33637

Phone (813) 989-1354 • Fax (813) 989-1355

September 21, 2021

VHB

225 E. Robinson Street, Suite 300 Landmark Center Two Orlando, Florida 32801-4326

Attn: Joe Perri SE Reg. Transportation Technology/ITS Manager

RE: Report of Geotechnical Engineering Services

Mast Arm Signal Pole Structures Countywide Mast Arm Hardening and Intersection Improvements Project Intersection of 49th Street N. and 70th Avenue N.

Pinellas County, Florida

PID: 003876A

Tierra Project No.: 6511-17-070-001

Mr. Perri:

Tierra, Inc. (Tierra) has performed a geotechnical study for the proposed mast arm signal pole structures associated with the above referenced project. This letter presents the findings of our field exploration, laboratory testing program and geotechnical recommendations for use in the design of the proposed mast arm signal pole structures. It is our understanding that the mast arm structure foundations will consist of drilled shafts.

Soil Borings

To evaluate the subsurface conditions, Tierra performed two (2) Standard Penetration Test (SPT) borings to a depth of approximately 30 feet below the existing ground surface. One (1) test boring was conducted in the vicinity of each proposed foundation location.

The SPT borings were located in the field by a representative of Tierra using design information provided by VHB and our hand-held, non-survey grade Global Positioning System (GPS) devices that have a manufacturer’s reported accuracy of ± 10 feet. The station, offset, and elevation of each boring location were estimated based on the GPS coordinates obtained in the field in conjunction with the project design files provided by VHB. Therefore, the boring locations and elevations should be considered approximate. If a more accurate determination of the boring locations and elevations is required, Tierra recommends the borings be survey-located by a professional land surveyor.

The SPT borings were performed with the use of a mechanical drill rig equipped with an automatic hammer using Bentonite Mud drilling procedures. The soil sampling was performed in general accordance with American Society for Testing and Materials (ASTM) test designation D- 1586. Due to the presence of existing utilities, the initial 4 feet of the SPT borings were advanced by manual auger to verify utility clearances. SPT N-values were then taken continuously to a depth of 10 feet and at intervals of 5 feet thereafter to the boring termination depths. Representative portions of these soil samples were sealed in glass jars, labeled and transferred to our laboratory for classification and analysis.

Report of Geotechnical Engineering Services Mast Arm Signal Pole Structures Countywide Mast Arm Hardening and Intersection Improvements Project Intersection of 49th Street N. and 70th Avenue N.

Pinellas County, Florida

PID: 003876A

General Soil Conditions

Based on the results of the SPT borings, the subsurface conditions in the vicinity of the proposed mast arm signal pole locations consist of loose to very dense sandy soils from the existing ground surface to the boring termination depth.

Soil stratification was determined based on a review of the recovered soil samples, laboratory classification tests and interpretation of the field boring logs. Stratification lines represent approximate boundaries between soil layers of different engineering properties; however, actual transitions between layers may be gradual. In some cases, small variations in properties that were not considered pertinent to our engineering evaluation may have been abbreviated or omitted for clarity. The soil profiles represent the conditions encountered at the boring locations and variations in soil conditions should be anticipated. Specific details about subsurface conditions and materials encountered at the test locations can be obtained from the Report of Core Borings sheet in the Attachments.

The groundwater level was encountered within the borings at depths ranging from approximately 2½ to 3 feet below the existing ground surface. The encountered groundwater levels are illustrated adjacent to the soil profiles on the Report of Core Borings sheet provided in the Attachments. It should be noted that groundwater levels tend to fluctuate during periods of prolonged drought and extended rainfall and may be affected by man-made influences. In addition, a seasonal affect will also occur in which higher groundwater levels are normally recorded in rainy seasons.

General Recommendations

Soil Parameters for Design of Mast Arm Signal Pole Structure Foundations

It is our understanding that the design of the proposed mast arm signal pole foundations will be performed by VHB utilizing the approved FDOT Mathcad program. The FDOT Mathcad program models the subsurface as a uniform soil type with consistent strength properties. However, the results of the borings indicate variable soil properties throughout the boring depths.

Recommended soil parameters for design of the mast arm signal pole foundations are provided in the Recommended Soil Parameters for Mast Arm Signal Pole Foundations table in the Attachments. These parameters include soil type, soil unit weight and internal friction angle. It is recommended that the foundations be designed based on saturated conditions, i.e. the groundwater table at the ground surface.

The current FDOT methodology for mast arm signal pole foundations reduces the torsional resistance factor (omega, ω) for sandy soils when the average SPT N-value of the sandy soils along the shaft is less than 15. Tierra recommends that the designer utilize a weighted average along the proposed shaft length within the portion of the sandy soils to determine the average SPT N-value. This may require iterations until the shaft meets the torsional resistance requirement. The SPT borings were performed with an automatic hammer. We recommend a

1.24 multiplier be applied to the SPT N-value (for example, if the average SPT N-value from the boring profile is 8, a value of 10 should be used in the analysis). We recommend that SPT N-values above 50 be truncated at 50 in the calculation of the average SPT N-value.

Countywide Mast Arm Hardening and Intersection Improvements Project Intersection of 49th Street N. and 70th Avenue N.

Pinellas County, Florida

PID: 003876A

Recommended average equivalent SPT N-values for the design of each mast arm signal pole foundation are provided in the Recommended Average N-Value for Mathcad Spreadsheet tables in the Attachments.

Shaft Embedment/Length

If the proposed structure foundations are to be installed within berms or embankments with side slopes steeper than 4H:1V, the foundation designer should include the portion of the shaft with less than 2.5D (D=shaft diameter) horizontal soil cover (face-of-shaft to face-of-slope) in the unsupported length, and design the portion of the shaft with more than 2.5D horizontal soil cover as though founded in level ground.

The foundations should not be tipped/embedded within one (1) shaft diameter above very loose soils with SPT N-values of 2 or less to reduce the risk of excessive settlement of the shaft and the potential for instability of the shaft bottom during construction. In the event that the shaft tip elevation is determined to be within one (1) shaft diameter above very loose soils (SPT N-value of 2 or less) based on the design calculations, the shaft should be extended below the very loose soils into denser underlying materials.

It is recommended that Tierra be provided the design shaft tip elevations for review prior to the final plans submittal.

Shaft Installation

The proposed mast arm signal pole structure foundations will consist of drilled shafts and should be installed in accordance with the FDOT and Pinellas County Specifications.

Very dense sandy soils were encountered within the borings performed at the proposed mast arm signal pole locations. Excavation into and/or through this material will be difficult and may require non-conventional construction techniques and the mobilization of specialized equipment.

Variations in the depth and relative density of this material should be anticipated.

Temporary casing methods for shaft installation beyond what is required in the FDOT Specifications may be required in order to prevent the collapse of sandy soils and/or groundwater intrusion during shaft construction.

Report Limitations

Our services have been performed, our findings obtained and our recommendations prepared in accordance with generally accepted geotechnical engineering principles and practices at the time of this report. Tierra is not responsible for the conclusions, opinions or recommendations made by others based on this data.

The scope of the exploration was intended to evaluate soil conditions within the influence zone of the proposed mast arm signal pole structure foundations. The analyses and recommendations submitted in this report are based upon the data obtained from the soil borings performed at the locations indicated. If any subsoil variations become evident during the

Countywide Mast Arm Hardening and Intersection Improvements Project Intersection of 49th Street N. and 70th Avenue N.

Pinellas County, Florida

PID: 003876A

course of this project, a re-evaluation of the recommendations contained in this report will be necessary after we have had an opportunity to observe the characteristics of the condition encountered. The applicability of the report should also be reviewed in the event significant changes occur in the design, nature or location of the proposed structures.

The scope of our services did not include any environmental assessment or investigation for the presence or absence of hazardous or toxic materials in the soil, groundwater, or surface water within or beyond the site studied. Any statements in this report regarding odors, staining of soils, or other unusual conditions observed are strictly for the information of VHB and their client. This report was prepared for the exclusive use of VHB and their client for evaluating the design of the project as it relates to the geotechnical aspects discussed herein.

Tierra, Inc. appreciates the opportunity to be of service to VHB on this project. If you have any questions or comments regarding this report, please contact our office at your earliest convenience.

Sincerely, TIERRA, INC.

Kaitlyn C. Waterman, E.I. Lawrence P. Moore, P.E.

Geotechnical Engineering Intern Principal Geotechnical Engineer Florida License No. 47673

Kevin H. Scott, P.E.

Senior Geotechnical Engineer Florida License No. 65514

Attachments:

Report of Core Borings Recommended Soil Parameters for Mast Arm Signal Pole Foundations Recommended Average N-Value for Mathcad Spreadsheet

V

V

V

L C

L B

L A

L C

L B

L A

V

SG-32+50R

70TH AVE N

SG-33+50L

T H

S T

70TH AVE. N.BL

BORING LOCATION PLAN

PLAN SCALE

0 50'

SOIL PROFILES

CHECKED BY:

DRAWN BY:

DATE:

APPROVED BY:

SCALE: PROJECT NUMBER:

ENGINEER OF RECORD:

LEGEND

KCW

SW

SEP 2021

LPM

NOTED 6511-17-070-001

PINELLAS COUNTY, FLORIDA

REPORT OF CORE BORINGS

SHEET 1

SP

N

HA

APPROXIMATE LOCATION OF SPT BORING

TIERRA

7351 Temple Terrace Highway Tampa, Florida 33637 Phone: 813-989-1354 Fax: 813-989-1355

HAND AUGERED TO VERIFY UTILITY CLEARANCES

SPT N-VALUE IN BLOWS/FOOT FOR 12 INCHES

OF PENETRATION (UNLESS OTHERWISE NOTED)

GRAY TO BROWN SAND TO SAND WITH SILT (SP/SP-SM)

12 TO 24

6 TO 12

24 TO 40

8 TO 24

3 TO 8

GREATER THAN 24

LESS THAN 3

GREATER THAN 40

LESS THAN 1

VERY LOOSE

HARD

VERY STIFF

STIFF

SILTS AND CLAYS

CONSISTENCY

FIRM

SOFT

VERY SOFT

LOOSE

MEDIUM

DENSE

VERY DENSE

3 TO 6

1 TO 3

RELATIVE DENSITY

GRANULAR MATERIALS- SPT

(BLOWS/FT.)

SPT

(BLOWS/FT.)

AUTOMATIC HAMMER

UNIFIED SOIL CLASSIFICATION SYSTEM (ASTM D

2488) GROUP SYMBOL AS DETERMINED BY VISUAL

REVIEW AND LABORATORY TESTING ON SELECTED

SAMPLES FOR CONFIRMATION OF VISUAL REVIEW

GROUNDWATER LEVEL ENCOUNTERED DURING

INVESTIGATION

LAWRENCE P. MOORE, P.E.

FLORIDA LICENSE NO.:

47673

INTERSECTION OF

49TH ST. N AND 70TH AVE. N

NOTES:

THE BORINGS WERE LOCATED IN THE FIELD BY A REPRESENTATIVE OF TIERRA, INC. USING

HAND-HELD, NON-SURVEY GRADE GARMIN ETREX GLOBAL POSITIONING SYSTEM (GPS) EQUIPMENT

WITH A MANUFACTURER'S REPORTED ACCURACY OF ± 10 FEET. STATION AND OFFSET OF THE

BORING LOCATIONS WERE DETERMINED USING THE GPS COORDINATES OBTAINED IN THE FIELD IN CONJUNCTION WITH PROJECT DESIGN FILES PROVIDED BY VHB. THE ELEVATIONS OF THE BORING LOCATIONS WERE DETERMINED USING PROJECT DESIGN FILES PROVIDED BY VHB BASED ON THE

APPROXIMATE BORING LOCATIONS. THE BORING LOCATIONS AND ELEVATIONS SHOULD BE

CONSIDERED APPROXIMATE.

VERY DENSE SANDY SOILS WERE ENCOUNTERED WITHIN THE BORINGS PERFORMED AT THE

PROPOSED MAST ARM SIGNAL POLE LOCATIONS. EXCAVATION INTO AND/OR THROUGH THIS

MATERIAL WILL BE DIFFICULT AND MAY REQUIRE NON-CONVENTIONAL CONSTRUCTION TECHNIQUES AND THE MOBILIZATION OF SPECIALIZED EQUIPMENT. VARIATIONS IN THE DEPTH AND RELATIVE

DENSITY OF THIS MATERIAL SHOULD BE ANTICIPATED.

TEMPORARY CASING METHODS FOR SHAFT INSTALLATION BEYOND WHAT IS REQUIRED IN THE FDOT SPECIFICATIONS MAY BE REQUIRED IN ORDER TO PREVENT THE COLLAPSE OF SANDY SOILS AND/OR

GROUNDWATER INTRUSION DURING SHAFT CONSTRUCTION

1.

2.

3.

-5

-10

-15

E L

E V

A T

IO

N

IN

F

E E

T

N A

V D

N

HA

HA

BOR # SG-32+50R

STA. 32+34

REF. 70TH AVE. N.

OFF. 33' RT.

ELEV. 17.1

DATE 9/3/2021

DRILLER I. POORAN

HAMMER AUTOMATIC

RIG D-25

N

HA

HA

BOR # SG-33+50L

STA. 33+70

REF. 70TH AVE. N.

OFF. 33' LT.

ELEV. 16.9

DATE 9/3/2021

DRILLER I. POORAN

HAMMER AUTOMATIC

RIG D-25

-5

-10

-15

E L

E V

A T

IO

N

IN

F

E E

T

N A

V D

BL BL

NAVD 88 NORTH AMERICAN VERTICAL DATUM OF 1988

BASELINE SURVEY OF 70TH AVE. NORTH 70TH AVE. N.BL

RECOMMENDED ENVIRONMENTAL CLASSIFICATION:

SUBSTRUCTURE CONCRETE: EXTREMELY AGGRESSIVE

SUBSTRUCTURE STEEL: EXTREMELY AGGRESSIVE

-200 PERCENT PASSING #200 SIEVE

-200 = 2

-200 = 3

AutoCAD SHX Text

49TH ST N

AutoCAD SHX Text

ASPHALT

AutoCAD SHX Text

70TH AVE N

AutoCAD SHX Text

ASPHALT

AutoCAD SHX Text

70TH AVE N

AutoCAD SHX Text

ASPHALT

AutoCAD SHX Text

CROSSWALK

AutoCAD SHX Text

CROSSWALK

AutoCAD SHX Text

CONC MEDIAN

AutoCAD SHX Text

CONC MEDIAN

AutoCAD SHX Text

CONC SWK

AutoCAD SHX Text

4' CLF

AutoCAD SHX Text

CONC SWK

AutoCAD SHX Text

CONC SWK

AutoCAD SHX Text

ASPHALT PARKING LOT

AutoCAD SHX Text

PLANTER W/SIGN

AutoCAD SHX Text

METAL

AutoCAD SHX Text

CONC SWK

AutoCAD SHX Text

WOOD

AutoCAD SHX Text

CONC

AutoCAD SHX Text

ASPHALT PARKING LOT

AutoCAD SHX Text

WOOD

AutoCAD SHX Text

WOOD

AutoCAD SHX Text

WOOD

AutoCAD SHX Text

CONC

AutoCAD SHX Text

METAL

AutoCAD SHX Text

ASPHALT PARKING LOT

AutoCAD SHX Text

15" RCP

AutoCAD SHX Text

15" RCP

AutoCAD SHX Text

15" RCP

AutoCAD SHX Text

12" RCP

AutoCAD SHX Text

ES-01

AutoCAD SHX Text

ES-02

AutoCAD SHX Text

ES-03

AutoCAD SHX Text

ES-04

AutoCAD SHX Text

15" RCP

AutoCAD SHX Text

15" RCP

AutoCAD SHX Text

15" RCP

AutoCAD SHX Text

12" RCP

AutoCAD SHX Text 252+00

AutoCAD SHX Text 253+00

AutoCAD SHX Text 254+00

AutoCAD SHX Text 32+00

AutoCAD SHX Text 33+00

AutoCAD SHX Text 34+00

Station

(feet)

Offset

(feet) Reference

1 33+52 44' LT. B/L 70TH AVE N. MAST ARM SG-33+50L SAND 112 50 30 Refer to N-Average Table

2 32+43 37' RT. B/L 70TH AVE N. MAST ARM SG-32+50R SAND 112 50 30 Refer to N-Average Table

Notes:

(1) Recommend analysis based on saturated conditions, i.e. analyze with the groundwater at the surface.

(2) Effective unit weight based on saturated conditions.

Signal

Pole No.

Structure

Type

Friction

Angle

(φ,°)

Recommended

N-Value

Total

Saturated

Unit Weight

(γ, lb/ft (1)

Effective

Unit Weight

(γ, lb/ft (2)

Reference

Boring Soil Type

Signal Pole Location

Tierra Project No.: 6511-17-070-001

Recommended Soil Parameters for Mast Arm Signal Pole Foundations

Countywide Mast Arm Hardening and Intersection Improvements Project

Pinellas County, Florida

PID: 003876A

Intersection of 49th Street N. and 70th Ave. N.

Reference Boring: SG-33+50L

Boring Station & Offset:

(B/L 70TH AVE. N.)

33+70, 33' LT.

16.9 Structure Station & Offset:

(B/L 70TH AVE. N.)

33+52, 44' LT.

Approximate Shaft

Depth

(feet)

Approximate

Shaft Elevation

(feet, NAVD 88)

Automatic Hammer SPT

N-Value

Corrected Safety Hammer

N-Value (2)

Average Weighted N-Value for use in MathCAD Torsional

Calculation

1 15.9 HA

(3) 4.0 4

2 14.9 HA

(3) 4.0 4

3 13.9 HA

(3) 4.0 4

4 12.9 HA

(3) 4.0 4

5 11.9 8 9.9 6

6 10.9 8 9.9 7

7 9.9 11 13.6 8

8 8.9 11 13.6 10

9 7.9 12 14.9 11

10 6.9 12 14.9 11

11 5.9 12 14.9 12

12 4.9 12 14.9 12

13 3.9 12 14.9 13

14 2.9 55 50.0 13

15 1.9 55 50.0 13

16 0.9 55 50.0 13

17 -0.1 55 50.0 13

18 -1.1 55 50.0 13

19 -2.1 50 50.0 14

20 -3.1 50 50.0 14

21 -4.1 50 50.0 14

22 -5.1 50 50.0 14

23 -6.1 50 50.0 14

24 -7.1 61 50.0 14

25 -8.1 61 50.0 14

26 -9.1 61 50.0 14

27 -10.1 61 50.0 14

28 -11.1 61 50.0 14

29 -12.1 73 50.0 14

30 -13.1 73 50.0 14

Recommended Average N-Value for MathCAD Spreadsheet

Countywide Mast Arm Hardening and Intersection Improvements Project

Intersection of 49th Street N. and 70th Ave. N.

Pinellas County, Florida

PID: 003876A

Tierra Project No.: 6511-17-070-001

Approximate Structure Ground Elevation

(feet, NAVD 88):

N/A

(1)

Approximate Boring Ground Elevation

(feet, NAVD 88):

Pole 1

(2) Automatic Hammer SPT N-Value is corrected by a factor of 1.24 to equivalent Safety Hammer N-Value in accordance with

FDOT Specifications.

(1) Approximate ground elevation at structure location not available.

(3)

HA: Hand augered. Corrected Safety Hammer N-Value treated as 4.

Reference Boring: SG-32+50R

Boring Station & Offset:

(B/L 70TH AVE. N.)

32+34, 33' RT.

17.1 Structure Station & Offset:

(B/L 70TH AVE. N.)

32+43, 37' RT.

Approximate

Shaft Depth

(feet)

Approximate

Shaft Elevation

(feet, NAVD 88)

Automatic Hammer SPT

N-Value

Corrected Safety Hammer

N-Value (2)

Average Weighted N-Value for use in MathCAD Torsional

Calculation

1 16.1 HA

(3) 4.0 4

2 15.1 HA

(3) 4.0 4

3 14.1 HA

(3) 4.0 4

4 13.1 HA

(3) 4.0 4

5 12.1 11 13.6 7

6 11.1 11 13.6 9

7 10.1 8 9.9 9

8 9.1 8 9.9 9

9 8.1 7 8.7 9

10 7.1 7 8.7 9

11 6.1 7 8.7 9

12 5.1 7 8.7 9

13 4.1 7 8.7 9

14 3.1 36 44.6 9

15 2.1 36 44.6 10

16 1.1 36 44.6 11

17 0.1 36 44.6 11

18 -0.9 36 44.6 11

19 -1.9 46 50.0 12

20 -2.9 46 50.0 12

21 -3.9 46 50.0 12

22 -4.9 46 50.0 12

23 -5.9 46 50.0 13

24 -6.9 48 50.0 13

25 -7.9 48 50.0 13

26 -8.9 48 50.0 13

27 -9.9 48 50.0 13

28 -10.9 48 50.0 13

29 -11.9 63 50.0 13

30 -12.9 63 50.0 13

(3)

HA: Hand augered. Corrected Safety Hammer N-Value treated as 4.

(2) Automatic Hammer SPT N-Value is corrected by a factor of 1.24 to equivalent Safety Hammer N-Value in accordance with

FDOT Specifications.

(1) Approximate ground elevation at structure location not available.

Approximate Structure Ground Elevation

(feet, NAVD 88):

N/A

(1)

Approximate Boring Ground Elevation

(feet, NAVD 88):

Pole 2

Tierra Project No.: 6511-17-070-001

Recommended Average N-Value for MathCAD Spreadsheet

Countywide Mast Arm Hardening and Intersection Improvements Project

Intersection of 49th Street N. and 70th Ave. N.

Pinellas County, Florida

PID: 003876A