Mechanically Stabilized Earth Walls on the Interstate Highway System

32 TR NEWS 249 MARCH–APRIL 2007 Vancouver, Washington. Lands HighwayDivision, Leader, Western Federal Geotechnical Team and Barrows is Lakewood, Colorado; Geotechnical Engineer, Alzamora is Administration: Federal Highway The authorsare withthe RESEARCH M Interstate HighwaySystem Earth Walls onthe Mechanically Stabilized oped andbegancompetingwith eachother. significant asmore typesofreinforcement were devel- affected thecalculations.Stiffness becameincreasingly but inhowthestiffness ofthereinforcement elements differed notonlyinhowtocalculatethevertical stress calculate thesystem’s internalstability. Theapproaches verify. Eachdesignmethodoffered adifferent wayto prietary MSEwallsystemsandoftenwere difficult to the reinforcing elementsofMSEwalls. interaction, thefacedeformation,anddurabilityof remained—particularly aboutthesoil-reinforcement unproven structures. Manytechnicalquestions suade decisionmakerstotakeontheriskofnew, would produce costsavings,however, couldnotper- from thestatusquo.Theargument thatthechange track record. TheMSEconceptwasaradicaldeparture concrete andsteel;thisapproach hadanexemplary ments constructedfrom traditionalmaterialssuchas Retaining wallspreviously were rigidstructuralele- Problem DANIEL ALZAMORAANDRICHARDJ.BARROWS Thirty Years of Experience dard retaining wallforfillorembankmentsupport. accepted bymosttransportation departments asastan- then, MSEwallshavegainedpopularityandare Highway 39,northeast ofLosAngeles,in1972.Since in theUnitedStateswasconstructedonCaliforniaState approximately 34years.OneoftheearliestMSEwalls 50th anniversaryin2006,hasusedMSEtechniquesfor pressures. behaves asagravitymassthatretains lateralearth capacity. Thecombinationofsoilandreinforcement by frictionandconfinementprovide tensile can beeithersteelorsynthetic,interactwiththesoil and embankments.Thereinforcing elements,which PAYS OFF The earlydesignmethodsmostlyappliedtopro- The InterstateHighwaySystem,whichcelebratedits ing elementstobuildretaining walls layers ofcompactedsoilandreinforc- construction techniquethatalternates echanically stabilizedearth (MSE)isa develop aprocedure foranytypeofreinforcement ( design andconstructionguidelines,whichsetoutto geosynthetic sheets,soilnails,andanchored systems. and slopesystemsevaluatedbarmats,strips, Behavior ofReinforced Soil tration (FHWA) produced aresearch document, practical experience.TheFederalHighwayAdminis- undergone significantchangesthrough research and walls haveinvolvedseveraldesignmethodsand researchers. into thedomainofpracticingengineersand ing MSEwalldesignoutofthecommercial realm and designs, anddurability. Thiswasthefirststepinbring- forcement mechanisms,behavior, applications, reviewed earth reinforcement systems,aswellrein- literature review ofMSEsystems( Slopes andEmbankments gram’s The NationalCooperativeHighwayResearch Pro- Solution Cross sectionofatypicalMSEwall. ferred design approach. TheAmericanAssociationof of thiswork,aneffort tomerge andclarifythepre- The simplifiedcoherent gravitymethodwastheresult This research wasthefoundationforFHWA’s The guidelinesfortheinternalstabilityofMSE CR eot20 Reinforcement ofEarth NCHRP Report290: assembled acomprehensive , thatexaminedMSEwalls 1 ). Thereport 2 ). TR NEWS 249 MARCH–APRIL 2007 33 Suggestions for Pays Off” “Research welcome. topics are Contact G. P. Jayaprakash, Transportation Board, Research Keck 488, NW, 500 Fifth Street, DC Washington, 20001 (phone 202- 334-2952, e-mail gjayaprakash @nas.edu). The 140-ft high MSE wall The 140-ft at Seattle–Tacoma Airport International a critically allowed for needed third runway. . FHWA- TRB, National . TRB, National Reinforced Soil Struc- Reinforced NCHRP Report 290: Rein- : Appreciation is expressed to G. P. is expressed : Appreciation OTE N S ’ For more information contact Daniel Alzamora, For more forcement of Earth Slopes and Embankments forcement D.C., 1987. Council, Washington, Research and J. Dunnicliff. Schlosser, Mitchell, F. 1: Design and Construction Guidelines Volume tures, RD-89-043, Federal Highway Administration, November 1990. MSE Concrete 1414: Segmental Record Research Transportation and Soil Nailing. Geogrid Reinforcements, Walls, 1993. D.C., Council, Washington, Research The introduction of MSE walls more than 30 years of MSE walls more The introduction DITOR Jayaprakash, Transportation Research Board, for Board, Research Jayaprakash, Transportation in developing this article. his efforts E References 1. C. B. Villet. Mitchell, J. K., and W. 2. 2. I. Juran, J. K. Giroud, S. A. Gill, J.-P. B. R., Christopher, 3. Geotechnical Engineer, Federal Highway Administra- Geotechnical Engineer, Suite Dakota Avenue, 12300 West Center, tion, Resource 340, Lakewood, CO 80228, 720-963-3214, fax 720-963- J. Barrows, 3232, [email protected]; and Richard Federal Highway Adminis- Leader, Geotechnical Team Federal Lands Highway Division, 610 tration, Western 98661, 360-619-7704, fax WA Vancouver, East 5th Street, dot.gov. 360-696-7945, rich.barrows@fhwa. ment than can CIP concrete walls. MSE walls therefore ment than can CIP concrete that otherwise viability to some design schemes offer could not be possible. of high- ago has changed the design and construction for realized ways. The benefits of MSE walls will be pio- to come. Two changes are another 30 years; more the neers of this technology should be acknowledged: who developed Henri Vidal, architect–engineer, French State Dick Bell of Oregon MSE; and metallic-reinforced MSE. Also geosynthetic who introduced University, and development the many research are noteworthy and public agencies. by academia, industry, efforts , ). The construction of MSE 3 and the FHWA report refer- report and the FHWA provided case histories of the use and of the case histories of the provided Mechanically Stabilized Earth Walls and Rein- Earth Walls Mechanically Stabilized Method for Internal Development of the Simplified , from the Washington State Department of Department State Washington the , from Transportation Research Record 1414: Segmental Record Research Transportation MSE walls also have greater flexibility and can tol- flexibility MSE walls also have greater NCHRP Report 290   Ongoing research activities include the MSE Wall Ongoing research enced all of the MSE-related research that had been research enced all of the MSE-related then, significant research as of 1990. Since performed has included the following: Benefits (CIP) con- Gravity walls or cantilever cast-in-place economical for walls have worked well and are crete some situations but in most cases cannot compete with MSE walls. The construction of MSE walls has economical, particu- and more faster, become easier, because the backfill material larly for fill projects, sometimes is available onsite. In addition, MSE walls materials such prefabricated can be built quickly from panels or modular blocks. concrete as precast and Soil Geogrid Reinforcements, MSE Walls, Concrete Nailing of MSE walls made of seg- construction performance units ( mental concrete settle- and differential total erate significantly more walls generally costs 30 to 50 percent less than that of walls generally costs 30 to 50 percent on the wall height. The walls, depending CIP concrete the con- savings from estimated annual cost current struction of MSE walls instead of CIP walls on the Interstate system is $180 million. Application than 60,000 MSE walls U.S. highways now have more 35 feet. commonly constructed to heights that exceed wall is an impres- The highest transportation-related runway at sive 140 feet, along the third more Today International Airport. Seattle–Tacoma built for feet of MSE walls are than 9 million square applications each year. transportation State Highway and Transportation Officials’ technical Officials’ and Transportation State Highway calibrated the and walls on substructures committee for case history data with full-scale new procedure and adopted the procedure. MSE walls from FHWA (FHWA-SA-96-071); and (FHWA-SA-96-071); FHWA from which is Pooled Fund Study and its extension, the design of MSE walls using marginal addressing 24-22, Selecting backfill soils; and NCHRP Project which also Backfill Materials for MSE Retaining Walls, backfill soils. the use of marginal is addressing forced Soil Slopes Design and Construction Guidelines Soil Slopes Design and Construction forced Stabilized Earth (MSE) Stability Design of Mechanically Walls 513.1). WA-RD Report (Research Transportation