i

THE ROAD TAKEN:

MY FWD EXPERIENCE

By:

Scott O. Cosby

Scribd Edition

* * * * *

PUBLISHED BY:

Scott O. Cosby on Scribd

Copyright © 2012 by Scott O. Cosby

ii

About this E-book

This e-book offers the reader a conversational tone into my primary career as a Falling

Weight Deflectometer (FWD) Operator for a state government agency in Oklahoma.

Covered will include: an introduction of the FWD, how the FWD is used in the

Geotechnical Branch with two (2) actual projects presented as case studies, FWD

Calibration, a brief section on the analysis of FWD data, and a guide for anyone

interested in a career as an FWD Operator.

iii

Dedication

This e-book is dedicated to those who have emotionally supported me in all things I’ve

attempted in writing: J’Layne (love of my life) and her family, my parents, and other

friends who have enjoyed these e-books.

iv

Acknowledgements

I would additionally like to thank the following people for their professional support of

this e-book: Materials Division Engineer; Reynolds Toney, P.E., Geotechnical Branch

Engineer; Vincent (Butch) Reidenbach, Ph.D., P.E., Geotechnical Lab Supervisor;

Christopher Clarke, P.E., Dave Morrow of Dynatest’s Production & Support Center

(PSC) in Starke, Florida, and John Ragsdale at the Texas Transportation Institute (TTI)

- Texas A&M University, Riverside Campus in College Station, Texas.

v

Contents

Title Page…………………….……………..……i

About this E-book.…………………….......….....ii

Dedication..……………………………….……..iii

Acknowledgements ……………………...……..iv

Introduction…………………………..…….........1

FWD Introduction.…….………………….……..3

Recommended FWD Reading ………….……11

Branch FWD Use………………………..……...12

Branch FWD Analysis…………………….……18

FWD Calibration………………………………...23

FWD Operator Career Guide……………..……27

FWD Project Photographs….……………..…...28

About the Author…………….……………..……31

1

Introduction By the time this e-book is self-published, I will be well beyond my fifteenth (15th) year anniversary with the State of Oklahoma’s Oklahoma Department of Transportation (ODOT) as a Transportation Specialist II with the Materials Division, Geotechnical Branch in Oklahoma City, Oklahoma. On the Materials Division website; it states, “The mission of the Materials Division is to provide quality sampling, testing, analysis and inspection programs for the transportation industry, in order to ensure that highway materials meet quality and performance standards.”

Oklahoma Department of Transportation (ODOT) Logo

I spent the first six (6) years of my ODOT career from 1997 to 2003 as a member on a Geotechnical Branch Core Drilling Crew, which required full-time travel anywhere in the State of Oklahoma. A core drilling crew member assists the driller in the field sampling and testing operations of highway construction materials (e.g. soil and/or rock) with a truck-mounted drill rig.

Driller - Joe Redenbaugh (left) and I (right) are working the rig near Altus, Oklahoma (1998).

Sulfate Testing in the Geotechnical Lab

2

I moved into the Geotechnical Lab in 2003, and began to perform soil classification and sulfate testing, prepared branch reports, and often aided the Geotechnical Engineer of that time in special projects. Additionally; I began to learn to operate the FWD (Falling Weight Deflectometer) through the infinite patience and assistance of Christopher Clarke, P.E. (Professional Engineer), the FWD determines the condition of an existing road structure. I’ve completed a total of over 75 FWD jobs and road tested a total of almost 300 miles in Oklahoma as of the self-publishing of this e-book. The Branch FWD is the only Falling Weight Deflectometer operated by the State of Oklahoma to cover the state for Project Level FWD testing (which will be discussed later).

Branch Falling Weight Deflectometer (FWD) Trailers; older model in the foreground and newer model (2009) in the background of this photograph.

My educational background includes a Bachelor of Science (B.S.) degree in Geography from Oklahoma State University (OSU) Stillwater, OK in May 1994, and very close to two (2) Associate in Applied Science (A.A.S) degrees in Electronic Technology (1988 to 1990) and General Engineering (2002 to 2003) at OSU - Oklahoma City Campus.

The next sections of this e-book will examine the FWD in introductory detail, how the FWD is used in the branch with two (2) actual Branch FWD projects explored as case studies, FWD data analysis, FWD Calibration, recommended FWD reading, and a brief guide for those interested in pursuing this interesting career.

3

FWD Introduction The Falling Weight Deflectometer (FWD) is composed of a towing vehicle and FWD (trailer) unit (see FWD Unit Figure), and designed to simulate a traffic load along a road section and record the response in the form of deflection values.

FWD Unit Figure - Tow Vehicle and FWD Trailer The FWD generates a load pulse by dropping a weight onto a road’s surface. This load pulse is transmitted into the pavement through a circular load plate (see FWD Concept Figure). The load pulse generated by the FWD momentarily deforms the pavement under the load plate into a bowl shape (see Deflection Basin Figure). From a side view, the shape of the deformed pavement surface is called a Deflection Basin.

FWD Concept Figure

4

Deflection Basin Figure

An FWD has two (2) types of primary measurement devices. The first is a load cell, located directly above the load plate, and it measures the force imparted to the pavement. The second is a deflection sensor, or also known as a geophone which measures the momentary deflection of the deflection basin (see Geophone Figure). The Branch FWD unit is usually set-up for seven (7), but can be easily refitted for nine (9) geophones placed at fixed distances from the load plate to obtain a more defined shape of the deflection basin (see FWD - Lower Parts Figure).

FWD - Lower Parts Figure

5

Geophone Figure

The Dynatest geophones (seismic velocity transducers) have the following advantageous characteristics:

• Small, light-weight design • Weather proof • Maintenance free • Damping easy to control (and keep constant) • Excellent calibration stability

Dynatest additionally developed a (proprietary) method of processing taking place within a fraction of a second (Source: White paper by Dr. Anders Sorensen, Technical Director, Dynatest International A/S, Denmark on the company’s website; http://www.dynatest.com/papers-2-4.php). This website paper is very technical, but good information on the geophone.

The FWD – Upper Parts (see FWD - Upper Parts Figure) produces the load pulse by dropping the weight package which is transmitted into the pavement through the circular load plate and deflection data is collected through the geophones and the laptop in the van.

6

FWD - Upper Parts Figure from a Dynatest Truck-Mounted Deflectometer (TMD). This is essentially the same set-up in the Branch FWD.

The FWD operates through complex (to mention in this e-book) electronic and hydraulic means. The Model 8002 FWD Trailer is the newest, most sophisticated Dynatest FWD Test System, which is the same model as the Branch FWD operated by me. The Branch FWD consists of four (4) primary Dynatest components (see the Dynatest FWD

Components Figure):

1. Model 8002 FWD Trailer (see Dynatest Model 8002 FWD Trailer Figure). 2. Compact15 Embedded Processor (see the Branch FWD Compact15 Figure). 3. Remote Control Box / Wireless Router (not pictured). 4. IBM compatible notebook or laptop with Windows®, and the FwdWin field data

collection program loaded.

7

Dynatest Model 8002 FWD Trailer

Dynatest FWD Components

8

Branch FWD Compact15

FwdWin is Dynatest’s field data collection programmed in Visual Basic 6 meaning that it is an object oriented program with a graphical user interface. FwdWin functions much like any other Windows based programs. The program is mouse driven, but there are keyboard shortcuts to help reduce the requirement for mouse operation. In addition to the data collection screen (see the Data Collection Screen Figure), the FwdWin interface is composed of a number of extra components (sub-windows) that the user may choose to display or hide. The additional components (see the FwdWin Sub-Windows Figure) are:

• LED Panel

• Distance Display

• Geographic Position Data

• Thermometers Display

• Time Histories Plot

• Surface Modulus Plot

• Surface Moduli Chart

• Back Calculation

• Back Calculation Chart

• Camera

9

Data Collection Screen

FwdWin Sub-Windows, including the Data Collection Screen

10

The data collection screen and the additional components sit within another panel

known as the Tray. The Tray can be regarded as a desktop container that can hold all

of the various components that make up the FwdWin program. The tray is capable

auto-sizing when the components are selected.

Prior to running an FWD test, it is assumed that the following functions have been

performed (in addition to driving to the site and positioning on the first test point):

• The program has been configured for the appropriate FWD trailer

• A proper test setup has been created (or loaded).

• The location information has been entered.

• The data file has been created.

The data collection screen serves as the primary control interface. At first glance, it may

seem complicated, but after a short time the operator will become quite familiar and

comfortable with it.

The testing process is fairly simple. When the vehicle is located in the appropriate test

position, the operator merely clicks the Action button to start the test sequence. When

the sequence completes, the computer will issue one of a variety of sounds indicating

that the plate has been raised to the transport position and it is OK to move to the next

test point.

If an error or other problem occurs during the test sequence, a pop-up window will

appear indicating the nature of the problem or error. If so equipped, the computer may

also issue an audible version of the error message.

During the test sequence, there is generally nothing for the operator to do until it is

complete. This is a good time to scan the surroundings to make sure persons stay clear

of the equipment and that traffic is not posing a hazard.

After each drop, the load and deflection data are written to the data collection window.

This provides a convenient method for monitoring the progress of each test sequence.

FwdWin stores data in several formats. The primary format is Microsoft Access 2000

(MDB), which is the most versatile and highly recommended. The remaining formats are

all text based. The first three (F25, F20, FWD) are earlier Dynatest ASCII formats.

Pavement Deflection Data Exchange (DDX) was developed by AASHTO in 1998.

Extensible Markup Language (XML) is a structured format developed by the World Wide

Web Consortium (W3C).

11

Recommended FWD Reading

Long-Term Pavement Performance Program Manual for Falling Weight Deflectometer Measurements, FHWA-HRT-06-132, December 2006. 79 pages. Even though this manual was developed for the FHWA (Federal Highway Administration) Long-Term Pavement Performance (LTPP) program; it’s a good general manual for Falling Weight Deflectometer - Data Collection.

This manual is available for free download at the following website:

http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/06132/06132.pdf

Long-Term Pavement Performance Program Falling Weight Deflectometer Maintenance Manual for Falling Weight Deflectometer Measurements, FHWA-HRT-05-153, December 2006. 88 pages. This manual provides guidance on most FWD related repairs, maintenance, and troubleshooting.

This manual is available for free download at the following website: http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/05153/05153.pdf

12

Branch FWD Use

An FWD job is requested, the Geotechnical Branch will obtain a project plan set and a letter of request which details the project and tests requested by the Roadway Division. The normal FWD Testing Interval as specified by Branch specifications: 250 feet (ft) from a beginning to ending point. The Load Level will depend on the type of road tested (e.g. State Highway, Interstate, US Highway, or County Road). Load Level refers to the load in pounds per square inch (psi) or pounds per force (lbf), or height the weight package is dropped in FWD testing. Research and some special request projects often require a closer FWD testing interval (100 or 150 ft). The testing interval and load level will depend on the entity requesting the research and/or special project. Closer FWD testing intervals will yield more detailed FWD data collected for a more in-depth analysis. There are two (2) types of known FWD data collection: 1.) Network Level. 2.) Project Level. Network Level FWD data collection encompasses a large area; for example, the entire length of US-412 from Woodward to Tulsa (approximately 202 miles). ODOT’s Planning and Research Division administers Network Level FWD data collection anywhere in the State of Oklahoma. The Geotechnical Branch is responsible for the Project Level FWD data collection anywhere in the state. Project Level FWD data collection can be considered a narrower, forensic examination of road section on any County Road, State Highway (SH), US Highway, or Interstate Highway in Oklahoma. Occasionally, the branch is asked to collect and analyze FWD data from various rural airport runways in the state as well. ODOT FWD operator(s) also must comment on site conditions encountered during testing that might reasonably be expected to cause anomalous deflection value measurements. These conditions usually are cracks or other pavement surface distresses. These conditions and comments must be combined and reported in a Pavement Surface Condition Survey separate from the FWD report along with site photographs. Pavement surface condition surveys are described according to the distress patterns in various FHWA (Federal Highway Administration) publications. The best way to illustrate how the Geotechnical Branch uses its FWD unit is to examine case studies of actual FWD jobs requested and recently completed by me. I have gathered information on two (2) FWD case studies approximately fourteen (14) miles apart on Interstate 35 (I-35) in Norman and near Purcell, Oklahoma. The first case study in Norman (Cleveland County) is a standard requested project from the Roadway Division, and the second near Purcell (a research project through the cooperation of the Oklahoma Department of Transportation (ODOT), University of Oklahoma (OU), and the National Center for Asphalt Technology (NCAT) based in Auburn, Alabama. These two (2) case studies will specifically examine basic project information with available maps and photographs, project scope, and FWD related matters.

13

Case Study #1: I-35/SH-9 in the Norman area: The Geotechnical Branch received a formal request from the Roadway Division for this project on: April 12, 2011. The location was from the South Canadian River and North for 5,914 feet (1.12 miles) which was near the Main Street exit for the I-35 part, and from 24th Ave SW to McGee Drive which was 2,640 feet (.50 miles) in length (see FWD Test Areas Map for I-35/SH-9).

FWD Test Areas Map for I-35/SH-9 (In yellow.) The specific FWD Testing request included all three (3) of the Northbound (NB) and Southbound (SB) lanes as well as the shoulder of the I-35 portion which totaled out to be around nine (9) miles tested. The SH-9 portion totaled about one (1) mile tested, and no shoulder testing only the Outside (right) lane going Westbound (WB) and Eastbound (EB) of SH-9. FWD Testing and Coring for I-35 took place on July 11 - 13, 2011, and the SH-9 was done August 30, 2011. This project was essentially a normal requested FWD testing and coring project, but the actual testing and coring was anything but normal. Sometimes, an FWD Operator must adapt to an alternate work schedule. I-35 and SH-9 has a high ADT (Average Daily Traffic) rating, so the FWD Testing and Coring was done at night from about eight (8) pm to two - three (2-3) am the following morning for a total of four (4) nights. A contract

14

traffic control crew closed off each lane for FWD Testing and Coring which was done in tandem. Night-time FWD Testing and Coring operations can create more unpredictable situations than during the day. The overall operation went well with only a few tense moments around an off-ramp on I-35 and right at dusk with the traffic in the area.

Case Study #2: I-35 near the Purcell area:

FWD Test Area Map for I-35 Purcell Research Project (Blue X).

Imagery (Source: Google Earth) of the I-35 Purcell Research Project (in Blue).

15

This research project and Geotechnical Branch involvement begin in 2007 and 2008 with several emails and a meeting or two at the request of the ODOT’s Planning & Research Division and the University of Oklahoma (OU) which there is often research project cooperation between the state’s universities and ODOT. The entire length of the I-35 Purcell research project in McClain County, Oklahoma is 1000 feet (0.19 miles) with six (6) FWD Test Locations (see Project Plan Figure).

Project Plan Figure

The research project test area was designed and constructed by the Oklahoma Department of Transportation (ODOT) in conjunction with a National Center for Asphalt Technology (NCAT) research team. The objectives of this research project was to determine effects of fatigue and rutting in pavement design through a prescribed road design and instrumentation (e.g. temperature and moisture probes, strain gauges, Earth Pressure Cells (EPCs) within the various layers of the road section. Also, a Weather Station was placed at the site several feet west of the I-35 project. Field data collection (including FWD testing) done quarterly over a period of five (5) years which ODOT could use the performance data in comparison of long-term road service life studies. An FWD Operator must adapt quickly to each project, especially research projects. My actual participation began on May 8, 2008 when the subgrade layer was ready for FWD testing (see I-35 Purcell FWD Testing Photographs) to the present (2012, with the last quarterly done on May 2nd) with quarterly testing requests. In addition, before the project was opened to traffic there was FWD testing done at night and during the day to

16

obtain pavement stiffness (moduli) data at multiple temperatures throughout a day (24 hours). All of the FWD data was collected, and turned over to University of Oklahoma (OU) research participants for analysis through the aid of a flash-drive. Chris Clarke, P.E. and I provided technical assistance for the FWD analysis in the beginning.

I-35 Purcell FWD Testing Photographs

These photographs will include the older / newer FWD model, which was built / picked up at Dynatest’s Production & Support Center (PSC) in Starke, Florida and brought back to Oklahoma City, Oklahoma in 2009. That was a trip!

FWD Testing on Subgrade Layer (8 May 2008).

17

FWD Testing on Aggregate Base Layer (13 May 2008).

FWD Testing on finished Asphalt Layer (16 May 2008).

18

Branch FWD Analysis

I began performing FWD data analysis at about the same time as becoming the operator. I eventually discovered that each and every FWD project analyzed is unique with none presenting similar results. FWD Analysis or Backcalculation can be a laborious process; requiring a high degree of skill, and considered an art as well as a science. A definition for Backcalculation is described as an analytical technique that uses a mathematical description (elastic moduli) of a road’s layers which is deformed through a force applied to it by the FWD. This elastic moduli of road layers corresponding to measured FWD’s load and deflections. A firm knowledge of how the Falling Weight Deflectometer (FWD) collects data and knowledge about the data itself can ease the process of Backcalculation. The Backcalculation method used by the Geotechnical Branch is the Iterative method with the Modulus software developed by the Texas Transportation Institute (TTI) at Texas A&M University. The iterative analysis involves assuming “seed” moduli values for the layers of a road (see Layers of a Road Figure), computing the surface deflection at several radial distances from the load, comparing the computed and measured deflections, and repeating the process, changing the layer moduli each time, until the difference between the calculated and measured deflections are within selected tolerance(s) or the maximum number of iterations has been reached.

Geotechnical Branch FWD Analysis Process:

1. File Preparation

2. Temperature Analysis

3. Backcalculation (Modulus software)

4. Result Decision

5. Core Report Generation

6. FWD Report Generation

Note: The table above is meant only as a generic process model. There may be some overlap and departures from the process table.

Layers of a Road Figure

19

AC (Asphalt Concrete), the majority of roads in Oklahoma are of this material as the surface. Base(s) can be composed of aggregate (rock) of varying sizes or other materials. In some road construction projects, a Sub-Base is included for additional support. The Subgrade is the foundation of the road layers, and can sometimes be chemically stabilized, but must be able to support the upper layers for quality road structure. These layers are also included in concrete roads with the often addition of a metal inner structure (or rebar, etc.).

Modulus Icon

Modulus Start Figure

20

Modulus Read FWD File Figure

Modulus 6.0 software (see Modulus Icon and Start Figures) operation basically entails reading the FWD (.fwd) file (see Modulus Read FWD File Figure) into the program, drop and station selection if necessary, then selecting the Backcalculation tab to set the parameters (see Modulus Inputs Figure), and finally clicking run to see the Modulus results (see Modulus Result Figure), but the entire FWD Analysis process is more involved than anyone realizes.

Modulus Inputs Figure

21

Modulus Result Figure

The process works on the assumption that the road structure can be modeled as a linear-elastic layered system. A likely range of “probable” layer moduli provided by the program user facilitates the process by forming the basis of a small internal database against which mathematically generated deflection bowls are compared to the actual measured deflection bowl by the software. The final decision on the FWD analysis done by me is made by the Geotechnical Engineer or the Geotechnical Lab Supervisor on the viability of the backcalculation result(s) generated to proceed to final report preparation. It is desirable for the Branch FWD analysis to limit the error per sensor (%) in the Modulus Results to approximately 2%. This is not always possible and in most cases, errors in the 3-5% range may not adversely affect the subsequent analysis. From my past FWD analysis experiences; error per sensor issues can be the result of pavement distresses (e.g. cracking, patching, surface defects, etc.) or the geophones are not sitting firmly on the road surface.

22

Recommended Reading on FWD Analysis (Which can be found on the internet through Google, Yahoo, and other internet search engines): American Society of Testing Materials (ASTM) Standard: D 5858, Guide for Calculating In Situ Equivalent Elastic Moduli of Pavement Materials Using Layered Elastic Theory. American Association of State Highway and Transportation Officials (AASHTO) Standard: T 256-01, Standard Method of Test for Pavement Deflection Measurements (2006). Federal Highway Administration (FHWA) Publications: FHWA-RD-98-085, Temperature Predictions and Adjustment Factors for Asphalt Pavements. SHRP-P-665, SHRP's Layer Moduli (FWD Analysis) Backcalculation Procedure. The software MODULUS 6.0 for Windows can be obtained through request by contacting:

Texas Transportation Institute (TTI) Texas A&M University System

3135 TAMU College Station, Texas 77843-3135

(979) 845-1713 (979) 845-9356 (FAX)

pubquest@ttimail.tamu.edu For more information on MODULUS 6.0 for Windows; the user’s manual is available for free

download at the following website:

http://tti.tamu.edu/documents/1869-2.pdf

23

FWD Calibration The FWD calibration for the Branch unit is done annually at the Texas Transportation Institute (TTI) - Texas A&M University, Riverside Campus in College Station, Texas. This regional FWD calibration center is supported by Texas Department of Transportation under the supervision of Dr. Magdy Mikhail. The Falling Weight Deflectometer (FWD) calibration procedure ensures that the data collection and pavement analysis is accurate and repeatable. FWD calibration is a complex process that requires specialized equipment (see FWD Calibration Equipment Figure), procedures, and personnel.

FWD Calibration Equipment Figure

--------------------------------------------------------------------------------------------------------------------- The information on the calibration process below was provided by John Ragsdale at the Texas Transportation Institute (TTI) - Texas A&M University, Riverside Campus in College Station, Texas: The calibration process of a Falling Weight Deflectometer (FWD) is focused on the

seismic sensors and the force sensor. The FWD Calibrations Center operator is

certified annually by the AASHTO Materials Reference Laboratory (AMRL).

24

There are two important reasons to have a FWD calibrated. The first reason is to

maintain quality data and consistent data for pavement evaluation. The second reason

is to find broken sensors on the FWD. The FWD calibration process takes about a day

without major sensor failure.

Before the FWD operator brings the FWD unit to the Calibration Center he/she needs to

check over the FWD to insure it is proper operational condition.

These checks include but are not limited to:

• checking all cables, cable connections, mechanical connections, and electro-

mechanical connections, repairs are to be done when required

• lubricate all required points

• check all sensors and electronic cables

• bring manufacturer operating manuals

• check all batteries and replace any nonfunctioning batteries

• check air, hydraulic or magnetic systems depending on the manufacture, repair if

necessary

• have the calibration FWD testing setup programmed

• bring past calibration data

• set typical load levels to 6000, 9000, 12,000, 16,000 pounds force

The day of the FWD calibration the FWD operator will remove all of the seismic

sensors, these are normally geophones. The geophones will need to be connected to

the FWD but each of the geophones will be placed on a comparison stacker. The

comparison stacker will be at the back of the FWD. Each geophone will be inspected

before placement on the stacker, if an issue is discovered it will be corrected before

calibration.

The FWD operator will give the Calibration Center operator an electronic data file so the

gains and serial numbers of the sensors will be input into the Calibration Center

computer.

The seismic sensors will be compared to the reference or the accelerometer on the

stacker. When this data is accepted then the seismic sensors will be compared to each

other. After these comparisons are complete and the data is accepted the seismic

sensors calibration is complete.

The next part of the calibration is the load sensor. The load-cell is compared to a

reference load-cell that is National Institute of Standards and Technology traceable

through AMRL. After the load data is accepted the calibration is done but not complete.

25

The Calibration Center operator will present the FWD operator with a certificate with

new sensor gains. These gains will be entered into the FWD operating computer to

complete the calibration.

The calibration process helps to ensure that the data from different FWDs of the same

manufacturer or different FWD manufactures is equivalent.

---------------------------------------------------------------------------------------------------------------------

The two (2) photographs below presents the Falling Weight Deflectometer (FWD) Calibration process:

Reference (Load Cell) Calibration

26

Relative (Geophones) Calibration Preparation

Note: The photographs taken above were of the older branch FWD unit and a 2007 calibration visit to College Station, Texas. The calibration process has now become a less complicated and streamlined process due to equipment and procedure improvements as of 2009. I occasionally attend FWD Users Group (FWDUG) meetings which is composed of various state DOTs, private firms, and university groups who utilize Falling Weight Deflectometers. I remember reading a presentation from the 2000 meeting in Ithaca, New York which described FWD Calibration with unique imagery: Think of Falling Weight Deflectometer (FWD) calibration as shots at a target (see the image on the next page):

27

The #1 target shows a non-calibrated FWD system, off the target. The #2 target is the Reference (Load Cell) Calibration where the shots are more defined and closer to the intended target. The #3 target or Relative (Geophone) Calibration; the shots are very close and in the target’s bulls-eye. (Source: Falling Weight Deflectometer (FWD) Reference

Calibration: An Overview Demonstration by Andrew Brigg, LAW PCS - A Member of the LAWGIBB Group; 2000 FWDUG Meeting - Ithaca, New York, October 1-3, 2000).

The Red Dots indicate FWD Calibration Centers with Certified Operators.

Each center and operator is evaluated for compliance to AASHTO R 32, Standard

Recommended Practice for Calibrating the Load Cell and Deflection Sensors for a

Falling Weight Deflectometer by AASHTO Materials Reference Laboratory (AMRL)

staff. Each operator will be expected to perform the calibration independently,

demonstrating proficiency in use of the calibration software and equipment.

28

FWD Operator Career Guide

Becoming an FWD Operator is a rewarding and fascinating career. I was told; by Dave Morrow of Dynatest’s Production & Support Center (PSC) in Starke, Florida, that there are probably only 200 - 300 FWD Operators in the United States. This is a specialized career, but people move on to other positions, retire, and so on. The best FWD Operator employment sources are government agencies (Federal and State DOTs) and private engineering firms (e.g. Terracon, Fugro, etc.). There are certain personality traits that the potential FWD Operator must have to be successful in this career. First; travel or the psychological conditioning of travel, to and from work sites are a major reality of this career as well as living in hotels within other metro and rural areas of the state.

Map of Cities in Oklahoma

I was well accustomed; regarding this first trait, after a six (6) year tour on the Branch

Drill Crew. I suggest obtaining practical field experience either in college or in a

professional job setting. Second; patience, the FWD is a complex machine to learn and

proper FWD data collection will take time. Even to this day, I continue to learn more

about the FWD and its operation. The Branch’s FWD manufacturer Dynatest and their

support staff are excellent informational sources when problems arise or answering

operational questions. A third trait is the desire to learn, to stay current on FWD

technology as well as operational and analysis techniques. I research internet sources

weekly on known and new FWD related matters. Planning Skills are the fourth trait.

29

FWD operations are meticulously planned out before execution. The Branch process

includes: initial planning with Google Maps and ODOT documentation, FWD and Core

locations planned, traffic control set-up through ODOT maintenance/division yards, or

safety consultant firms, travel to the location, site reconnaissance, and finally FWD

testing and core location(s) marking is done. I repeat; this overall process is carefully

planned out, and not an on-the-fly operation.

The FWD Operator must also have multi-tasking abilities. FWD testing requires

getting to a precise test location while maintaining watch of traffic in the area (even with

traffic control), operating the equipment and examining the data collected, and all of

these tasks are done at the same time safely.

Education is a necessity for the potential FWD operator either through a college degree

or a variety of courses, such as basic engineering, hydraulics, and electronic

(especially troubleshooting and repair) courses. Local technology (or vo-tech) centers

are excellent educational opportunities as well. Another educational necessity for the

potential FWD Operator is computer skills, especially with laptops which is the primary

operational and data collection medium in FWD testing.

Panasonic Toughbook model is used in the Branch FWD.

Based on Murphy’s Law regarding technology: anything that can possibly go wrong will go wrong. The only thing that the FWD operator can rely on is his or her experiences, knowledge of the FWD equipment, and a competent traffic control crew to keep the operation safe. The ODOT Video Production Branch and I produced a video demonstration on the Branch FWD in 2010 after a project East of Oklahoma City. This video is available on the YouTube.com website. The video title: FWD Unit Demo.

Link: http://www.youtube.com/watch?v=k-U8LS43dbQ This video really presents Falling Weight Deflectometer (FWD) operation in vivid detail.

30

FWD Project Photographs

US-287, North of Boise City, Cimarron County (Oklahoma Panhandle) in 2009. Beginning of

Project (BOP) to start FWD testing is marked in the photograph.

SH-3, Northwest of Broken Bow, McCurtain County (Southeast Oklahoma) in 2011. FWD in action.

31

About the Author

Scott O. Cosby, in 2006 began a second career in freelance writing later specializing in

technical writing. In six (6) years; I have over seventy (70) articles in print and more than

five hundred (500) articles as web content on a variety of subjects. I have three (3) other

titles self-published on the Scribd website, these titles are: Infinite Possibilities: A

Freelance Writer's Journey (July 2011), Superheroes of my World (January 2012),

and A Fan’s Guide of Science Fiction Comics (February 2012).

32

FWD Testing at I-35 Research Project near Purcell, OK on February 16, 2010.

That’s me behind the laptop with the “Grizzly Adams” look!