The ADSC has long been acknowledged as the industryleader for its commitment to, and support of, original re-search in the technologies represented by the association.These include research activities focusing on drilled shaftfoundations, anchored earth retention systems, soil nails,and micropiles. Over the past 40 years and through the In-dustry Advancement Fund, the International ADSC, andits nine regional and international chapters, the associa-tion and its members have provided over $10 million infunds and contributions-in-kind to support vital researchthat has advanced the industries beyond measure. The pro-gram described in the following article is one of the latestexamples of the association’s commitment to this impor-tant area of emphasis. (Editor)

The nature of geotechnical engineering is somewhatinexact. To some, this might be the understatement ofthe year. In the realm of structural engineering, steel issteel, concrete is concrete, and the behavior of a struc-ture can be determined whether it is in Bangor, Maine,or Mobile, Alabama. But the characteristics of founda-tion support materials vary widely, and the interactionsamong steel and concrete and those materials are as dif-ferent as the millions of different geological conditionsin which soil and rock were formed. The challenge with designing safe, cost-effective

foundation systems is to determine accurately soiland/or rock strength and behavior characteristics, andto determine whether the strength and stiffness pa-rameters assumed for design were appropriate for theactual in-situ performance of the foundation system.Many subsurface exploration programs are so limited

that sweeping assumptions must be made in design,leading to high costs needed to cover potential inaccu-racies. In many design projects a minimal number ofborings with standard penetration testing are the ex-tent of the standard exploration program. In addition,

most often load testing is not performed on the com-pleted foundation system, therefore no real correlationcan be made between the design assumptions, vaguethough they may be, and the in-situ behavior of the sys-tem when it is loaded. The only conclusion that isreached on a regular basis is that the design was ade-quate because the structure didn’t collapse.Due to the lack of data about foundations not used

frequently in a certain area, these generalized designassumptions often result in narrow scope when select-ing foundation type. This presents another layer of un-knowns. For many projects potentially suitablefoundation types are not even considered. Obviously,the lower the number of options for solving a problem,(in this case a design), the lower the possibility of max-imizing cost-effectiveness.Mandatory implementation of the American Associ-

ation of State Highway and Transportation Officials

FOUNDATION DRILLING January 2014 Page 23

(Continued on page 24)

FeatureADSC to Assist in

University of ArkansasDrilled Shaft Research Project

By Peggy Hagerty Duffy, P.E., ADSC’s Technical Adviser

The challenge with designing safe, cost-effective foundation systems is to determine accurately soiland/or rock strength and behavior characteristicsand to determine whether the strength and stiffness parameters assumed for design were appropriate for the actual in-situ performance ofthe foundation system.

NDT expert ADSC Technical Affiliate Member, Bernie Hertlein(left) and Sean B. Brady, Senior Instrumentation Specialist atGEI Consultants, Inc., who donated their services to the project.

(AASHTO) Load Resistance Factor Design (LRFD) standardsfor bridge projects has made the design process seem even morecomplicated on transportation projects than when allowablestress analysis (ASD) was the norm. As a result, many state high-way departments have been expanding exploration programsand performing full-scale load tests on completed projects to

amass a database of foundation performance in various geolog-ical environments. This is intended to aid in selecting appro-priate resistance factors, including factors applicable in onlyselected regions. In Arkansas, geotechnical explorations for the Arkansas High-

way and Transportation Department (AHTD) traditionally haveconsisted only of standard penetration testing with Shelby tube

samples obtained for minimal laboratory testing.Full-scale load tests of drilled shaft foundationshave not been conducted frequently, thereforecorrelations could not be made between the soiland rock data, (scarce that it was), and the actualload-carrying performance of the completedfoundation system. To complicate matters, thenortheastern portion of the state is located in theNew Madrid fault zone, thus adding seismic con-cerns to the mix. There really is no comprehen-sive collection of data on the behavior of drilledshafts in this specific environment during seis-mic events. As such, drilled shaft foundations arerarely used for transportation projects in the stateof Arkansas, despite the fact that utility trans-

mission projects all over the state are being com-pleted successfully and economically usingdrilled shafts.In order to improve the AHTD design process

Dr. Rick Coffman, of the University of Arkansas,recognized the need for more complete data. Heproposed a two-phase plan of research for testsites to the AHTD: an in-depth subsurface ex-ploration program using methods more compre-hensive and diagnostic than standard penetrationtesting; and full scale load testing on drilledshafts to be installed at each site. In order to cor-relate exploratory test results with strength char-acteristics, strength data obtained in theexplorations and laboratory testing phase wouldbe compared to actual resistance behavior exhib-

ited in the load tests. The plan would be implemented at threesites intended to represent most general subsurface conditionsthroughout the state of Arkansas. Data obtained from these sites

would form a basis for a database of conditions across the state.Future projects would add to the database. The underlying ex-pectation was that the load tests would demonstrate that drilledshafts could be a suitable and cost-effective foundation type formany projects within the state.In 2010 Dr. Coffman approached the Drilled Shaft Commit-

tee of the ADSC and inquired as to whether the association wasinterested in participating in the project. The potential benefitto association members was obvious. In April, 2011, the com-mittee pledged their support in a Letter of Commitment writtenby former ADSC Operations Director Tony Marinucci. TheAHTD subsequently accepted Dr. Coffman’s proposal and allo-

ARKANSAS RESEARCH Contd.

As such, drilled shaft foundations are rarelyused for transportation projects in the stateof Arkansas, despite the fact that utility transmission projects all over the state are being completed successfully and economically using drilled shafts.

Page 24 FOUNDATION DRILLING January 2014

As a result, many state highway departments have been expanding exploration programs and performing full-scaleload tests on completed projects to amass a database offoundation performance in various geological environments.

In order to improve the AHTD design process Dr. RickCoffman, of the University of Arkansas, recognized theneed for more complete data.

The forest provides a picturesque background for soil sampling.

cated $387,800 for the project. The ADSC’s contribution wasincluded as in-kind drilling, labor for concrete and steel place-ment, and materials (concrete andsteel). Osterberg load cells were to beprovided at cost by ADSC AssociateMember Loadtest, Inc.The first phase of the project involved

site selection. The three sites were in-

tended to represent three geologicalconditions prominent in Arkansas:

1) Bedrock material consisting oflimestone, sandstone, and/or shale com-mon in western and northern Arkansas,

2) Clay deposits common in south-western and eastern Arkansas, and,

3) Clay underlain by sand depositscommon in northeastern Arkansas.Three sites were evaluated and weredeemed to appropriately represent thegeological profiles. The sites were lo-cated in Siloam Springs, Turrell, andMonticello. The Turrell site is locatedwithin the New Madrid fault zone.Once the sites were confirmed, Dr.

Coffman and graduate students from theUniversity of Arkansas oversaw subsur-

face investigations at each site using equipment from the AHTD,the Missouri Department of Transportation, and the Universityof Arkansas. Fifteen soil test borings were advanced at each ofthe three sites. Six borings were made using a conventional drillrig to perform standard penetration testing and to obtain Shelby

tube samples for laboratory testing. Six borings were advancedusing standard penetration testing in sands, Osterberg hydraulicfixed-piston sampling in clay, Pitcher barrel sampling in stiffclay or soft rock, and a double swivel core barrel in hard rock.Five borings were made at sites containing clay using cone pen-etration test methods.Laboratory testing on the samples obtained from each site

also followed both the standard limited testing regime and amore expanded round of tests. As is usual for AHTD projectsvisual classifications, Atterberg limits tests, moisture contenttests, unit weight determinations, grain size analyses, calcium

ARKANSAS RESEARCH Contd.

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FOUNDATION DRILLING January 2014 Page 25

The AHTD subsequently accepted Dr. Coffman’s proposal and allocated $387,799.74 for the project. TheADSC’s contribution was included as in-kind drilling, laborfor concrete and steel placement, and materials (concreteand steel). Osterberg load cells were to be provided atcost by ADSC Associate Member Loadtest, Inc.

The underlying expectation was thatthe load tests would demonstratethat drilled shafts could be a suitableand cost-effective foundation typefor many projects within the state.

Soil samples evaluated.

All terrain soil sampling rig.(Continued on page 26)

carbonate tests, and specific gravity testswere completed. In addition, directshear, unconsolidated-undrained triax-ial compression, constant-rate-of-strainconsolidation, direct simple shear, andconsolidated-undrained triaxial com-pression and extension tests were con-ducted.During 2013, Dr. Coffman and his

team spent a number of months per-forming the laboratory testing and re-viewing and analyzing the test data.Each site now has a profile, which is acharacterization that can be used to pre-dict the behavior of drilled shaft foun-dations in each environment. Pending isthe second half of the correlation:“Road-testing” the assumptions, so tospeak. Three drilled shafts are beingconstructed at each site by ADSC con-tractor members, complete with Oster-berg load cells, so that accurate data canbe obtained about how the shafts behavewhen loaded. The load test data will provide information onhow the subsurface materials resist the loads from the drilledshaft, therefore providing a basis for comparison between theinferred actual properties and the strength assumptions made

from the laboratory and field test data. In addition, cross-holesonic logging will be performed on each shaft to confirm suc-cessful construction of the shafts as designed.

At press time, ADSC ContractorMember Aldridge Drilling, Inc., of Lib-ertyville, Illinois, had completed the firstsite in Siloam Springs. ADSC ContractorMember McKinney Drilling Company,of Memphis, Tennessee, was set to beginthe second site in Turrell.Construction and testing on each site

and the results and conclusions of thestudy will be detailed in upcoming is-sues of Foundation Drilling magazine.Future articles also will track the re-sponse from the AHTD to the research,as well as changes, if they occur, in theDepartment’s design policies.

Peggy Hagerty Duffy is the ADSC’sTechnical Advisor. She is the President ofHagerty Engineering, Inc., and a Principalin Construction Solutions, LLC, Jefferson-ville, Indiana.

ARKANSAS RESEARCH Contd.

Page 26 FOUNDATION DRILLING January 2014

University of Arkansas students observe Bernie Hertlein at work.

Soil sampling rig at other location on site.