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“Improving Alaska’s quality of transportation through technology application, training, and information exchange.”TECHNOLOGYFORA Transpor tationlaskanSpring 2003January–AprilVolume 28, Number 1In this issue . . . Loftus Road ExtensionPlanning, Design, andField Notes Flooding in Salcha a YearRound Event Detectible Warnings Ditch Basics Shaping Gravel Drivewaysand Intersections Snow Site Storage Designand PlacementAnnouncements Research and TechnologyLibrary Available On Line Keith B. Mather LibraryAvailable On Line Now Available: NCHRPReports Willow Guide NowAvailableTraining and MeetingsCalendarLocal Technical Assistance ProgramLoftus Road Extension:ACE & ThermosyphonDesign FeaturesAdapted in part from ACE and Thermosyphon Design Features Loftus Road ExtensionProject, by Douglas Goering, and UAF gets new connection to Geist, by Bill O’Neill,UAF Sun StarScarce snowfall and mild springtemperatures may not be ideal forthe ski or snowmachine enthusiastbut it made for an easier start onthe Loftus Road Extension projectin Fairbanks. The short piece ofhighway between Geist Road andTanana Drive on the Universityof Alaska Campus is to be namedMorris Thompson Drive, after thelate Alaska Native leader.The design of the project requires that the embankment remainfrozen. Beginning construction inApril helped to minimize thaw andmaintain the integrity of the permafrost. The Alaska Department ofTransportation & Public Facilities(ADOT&PF) will include uniqueexperimental features designed tomaintain underlying permafrost,extending the project life andcreating a safer, more efficientroadway.The technology employed inthe Loftus project isn’t new; ratherit is new adaptations of proventechnologies: Thermosyphons Air convection embankments(ACE) Air convection embankmentsideslopes (ACE sideslope)Thermosyphons: Necessity isOften the Mother of InventionDuring the design of the TransAlaska Pipeline, engineers hadthe problem of laying hot pipe ontop of frozen ground. Settling andshifting would cause obvious problems. Keeping the ground frozenand stopping the transfer of heatwas the solution. The metallic finsthat protrude up from the pipeline’svertical support members are partof a thermosyphon, a device usingtemperature changes in the environment to remove heat from thecontinued1

“Improving Alaska’s quality of transportation through technology application, training, and information exchange.”ground. The pipeline employs approximately 62,000of them.A New Application of a Proven TechnologyThe Loftus extension will be constructed over astretch of permafrost. In order to prevent thaw settlement the permafrost must remain frozen. Since the design of the Loftus project includes concrete sidewalksit is imperative to avoid thaw settlement. In order tomaintain the integrity of the base it became necessaryto employ innovative techniques.AKDOT&PF will use a new technique called ahairpin thermosyphon to help keep the ground frozen.“Hairpin” thermosyphons are filled with liquid carbondioxide. During winter months, when the ground iswarmer than the air, the carbon dioxide turns into gasat 31 degrees Fahrenheit and travels up the thermosyphon where it cools, turning back into liquid form.This will cause the roadbed to cultivate freezing temperatures during the winter months. During summermonths the cooling unit will remain stagnant and willrely on the rigid insulation board to keep heat frompenetrating the permafrost. The theory of the coolingunit is to keep the road cold enough, long enough, sothat the residual cold will last through the summer andprevent ground thaw.The experimental design for the cooling unit iscompletely buried underneath the roadway around alayer of rigid insulation board.Air Convection Embankment ConceptThis process involves the use of uniformly sizedrock, with no fines content, in the construction of theembankment or sideslope. The voids within the material permits airflow and the ACE process.The hairpin thermosyphons lie horizontally spaced everyfew feet, entirely embedded in the embankment. Conceptdrawings by Russell Mitchell.PavementCondenserRigid insulation boardrHeat transfeEvaporatorPermafrost2ThermosyphonHeat (warmer than outside air)

“Improving Alaska’s quality of transportation through technology application, training, and information exchange.”Embankment EffectDuring winter months, the coarse material in theembankment provides an opportunity for convectioncells to occur, through the natural upward flow ofwarm air and downward flow of cool air. As the coolair circulates it draws the relatively warm air out ofthe embankment and cools the ground The embankment acts as a one-way heat transfer device efficientlyremoving heat from the embankment and underlyingfoundation soil during the winter months without reinjecting heat in summer. The passive cooling effectcan prevent thaw of underlying permafrost, eliminating thaw settlement.PavementConvectioncells formThree Passive Cooling Systems Included inLoftus DesignThe Loftus project is divided into three test sections where the previously discussed cooling systemsare implemented. Each section required a variation orcombination of ACE and thermosyphon adaptations,depending on the height of the embankment.Test Section One: ACE Sideslopes andThemosyphons in the EmbankmentThe ACE sideslopes and thermosyphons will provide a high level of cooling in the embankment duringthe winter months, while the rigid insulation board willhelp maintain residual cold in the summer.PavementACE material(course rock)Cold air sinksCold air sinksRigid insulation boardACE material (coarse rock)Warm air risesWarm air risesPermafrostThermosyphonPermafrostHeat (warmer than outside air)Embankment effect.Chimney EffectThe ACE chimney effect also acts as a one-wayheat transfer device. When ACE material is placedon the sideslope, the movement of cold air passing through cools the embankment adjacent to thesideslope and transfers the heat to the air. The air iswarmed slightly by the warm embankment and thenescapes up through the rock.Test section one.ACE material(course rock)PavementWarm airCool airACE sideslopes with thermosyphons.Heat (warmer than outside air)PermafrostChimney effect.continued3

“Improving Alaska’s quality of transportation through technology application, training, and information exchange.”Test Section Two: ACE Material Under Pavement andon the SideslopesTest section two was designed for use on the northside of the railroad tracks, where the embankment is10 m to meet the railroad overpass. The system proposed for this section is a 2.5 m layer of ACE materialplaced on the upper portion of the embankment (belowthe pavement), with ACE sideslope layers extendingdown both shoulders. The core of the embankmentconsists of conventional base material.Tanana loopTraffficcircle#1Tanana loopACE material under pavementand on sideslopesA.R.R.PavementACE embankmentACE sideslopeConventionalbase materialThompson Dr.#2ACE sideslopesand thermosyphonsThermosyphonsonly#3GEIST ROADPermafrostTest section locations on Loftus Road Extension project.Test section two.Test Section Three: ThermosyphonsThe third passive cooling system proposed consistsof thermosyphons. This section is near the Geist Roadintersection, where the embankment height is inadequate for an ACE installation. An ACE would notprovide enough chimney for the configuration to operate properly.PavementCondenserRigid insulation boardEvaporatorPermafrostTest section three.4ThermosyphonWhat do we expect?We hope to reduce or eliminate thawing of the underlying permafrost and maintain the integrity of theroadway. The innovative and experimental featuresused on the Loftus project will play a key role in howwe build roads in permafrost environments in thefuture.

“Improving Alaska’s quality of transportation through technology application, training, and information exchange.”Planning, Design, and Field NotesFlooding in Salcha a Year-Round Event“It’s the nature of the Tanana River to change channels and it has been migrating northward for years,”said Ed Plumb, a hydrologist for the National WeatherService, who believes several factors contributed tothis flood event.Sedimentfrom theAlaska Rangecontinues to fillthe valley andslowly push theTanana Rivernorthward.Old Richardson Highway northbound.An ice jam, combined with record warm temperatures, caused flooding in the Salcha area for the secondspring in a row. The water spilled over a 1 mile erosion control dike and found its way along old riverchannels.This isn’t the first time. As recently as last January,overflow from the Tanana River plugged culverts andovertopped the Old Richardson Highway. Nearly 30Salcha families were stranded until Alaska Departmentof Transportation Maintenance & Operations crews assembled an EZ Bridge, set it in place, and constructedtemporary abutments.“We can speculate the unseasonably warm temperatures in November initiated a short breakup, causingice to jam in the Tanana River near the Boondox Bar.The following cooler temperatures and continuedOld Richardson Highway southbound.Ice jam downstream of Boodox Bar. Photo courtesy ofNational Weather Service.During the April flood, nearly 90 homes were either surrounded or damaged and another 50 were injeopardy before water subsided slightly. The floodingcaused an estimated 2 million in damages to homesand roads throughout the Salcha area.Water from Tanana River spills over erosion control dike.Photo courtesy of National Weather Service.continued5

“Improving Alaska’s quality of transportation through technology application, training, and information exchange.”Planning, Design, and Field Notesoverflow events over the winter added to the jam sizeand likely locked it in place. The record high temperatures in late April created a large influx of water intothe Tanana River Drainage lifting more ice onto thejams. These local ice movements are the primary effect of the flooding. With all the melt water comingdownstream up against these jams, we saw water levels rise 5 feet in half an hour, contributing to the worstof the flooding.”Much of the work done this past winter to repairroad damage will need repair again. The abutments toFriday May 2,2003. Photo courtesy of National WeatherService.the EZ Bridge washed out, the erosion control dike isno longer intact, and portions of the Old Rich Highway will need improvements.Salcha is about 35 miles southeast of Fairbanks onthe Richardson Highway.One of many Salcha residents begins clean up. Nearly 2feet of water swept through lower level of this home duringthe crest of the flood.Benerth residence, Wednesday April 30, 2003. Photocourtesy of National Weather Service.6An airboat on the Old Richardson Highway on January5, 2003. Photo courtesy of Sam Harrel, Fairbanks DailyNews-Miner.

“Improving Alaska’s quality of transportation through technology application, training, and information exchange.”Planning, Design, and Field NotesDOT Maintenance workers place an EZBridge in place on the Old RichardsonHighway. Crews previously created thechannel by removing ice-clogged culvertsto drain overflow which had backed up andthreatened local homes (Jan. 2003).DOT Maintenancecrew built up anabutment, held it inplace, and fastenedit to EZ Bridge inpreparation for theconstruction of theapproach. See alsothe back page ofthis newsletter foranother photo (Jan.2003).7