inclinedtoward)theeast.Theresultissimilartoastackofcardstiltedinaneastwarddirection. <br />Planesofweaknesscausedeitherbythebeddingintherockorbyweakbedsthemselves(suchas <br />clayeydecomposedashlayers)aremuchmorelikelytoslideinadirectionparalleltothe <br />eastward-inclinedbeddingthanwestward,wherefailuresareforcedtobreakthroughthepackage <br />ofbeddedrocks.ThisisreflectedintheDOGAMISLIDOmapofthelargerarea,whereclearly <br />themajorityofthemappedslidesoriginateoneast-facingslopes. <br />Thispropensityforeast-facingslopestobelessstablethanwest-facingslopesiscausednotonly <br />byinclinedplanesofweakness,butalsobygroundwaterflowanddischargeareas.Precipitation <br />fallingontotheentireridgepartiallysinksintothegroundandsomeofitinfiltratesintomore <br />permeablebedsintherock(e.g.sandstone),flowinginitiallydownward,untilitencountersan <br />impermeablestratum(e.g.siltstoneorclaystone).Becausethisstratumwillbefollowingthe <br />generaleastward-dippingtrend,thewaterthen“runsdown-dip”ontopoftheimpermeableunit. <br />Inthismanner,notonlywaterfallingontheeast-facingslopeoftheridgewillbetransmittedto <br />baseofthatslope,butalsosomewaterfallingonthewest-facingslopeoftheridgewillalsobe <br />transmittedeastward.Wherethiswaterexitstherockunderlyingtheslopeontheeast-facing <br />slope,itemergesasseeps.Iftherockinthatvicinityiscoveredwithanimpermeableclayeysoil <br />layer,thewaterwillbuildupintherockuntilthepressureissufficienttoeitherbreakthrough <br />thesoillayer,ordislodgeportionsofthesoillayerbyreducingthefrictionbeneaththemin <br />mannerverysimilartotheoilpressureinacar’sengine.This“excessporepressure”isvery <br />likelymostlyresponsibleforthemultitudeofslopemovementsontheeast-facingslopesofthe <br />hillsintheEugene-Springfieldarea. <br />TheApplicant’sgeotechnicalassessmentcompletelyignorestheseaspectsofstructuralgeology. <br />Therefore,itfailstoinvestigatetheportionoftheproposedCHPUDthatismostsensitiveto <br />slopemovementsresultingfromlocationsonadipslopeinanareawheregroundwatercould <br />developsignificantporepressures.Instead,thesubsurfaceexplorationwaslimitedtothelow- <br />slopingareaatthetopoftheridge. <br />4.TheProposedCHPUDDesignExacerbatesExistingSlopeStabilityIssues <br />Giventhatthegeotechnicalassessmentwasconductedinalimitedmannerandpossibly <br />restrictedintentionallytotheareasoftheproposedCHPUDthatmostlikelywouldbewithout <br />slopestabilityissues,thedesignisseeminglyunfetteredbygeotechnicalconstraints.Althoughit <br />mightbepossibleforadifferentPUDdesigntoeffectivelyaddresstheseissues,theproposed <br />CHPUDasdesignedexacerbatesexistingslopestabilityproblems.Asproposed,theroad <br />infrastructure(CupolaDriveandthedrivewaystolots9/10,17/18and19/20)andthebuilding <br />sitesforlots8through20arelocatedalongthetopofthesteepeast-facingslope.Theresultis <br />thatfillembankmentswillbeplacedatthetopofthesteepslope,insomecaseswithfillslopes <br />upto1.5H:1V,whichisinitselfquite“optimistic.”Normally,fillslopesaredesignedtonot <br />exceed2H:1V.TheexcessivelysteepfillslopesproposedfortheCHPUDareemployedhereto <br />limittheeastwardanddownslopeextentofthetoeofthefills,becausetheywouldlikelyreach <br />theeastpropertylineoftheproposedCHPUDoreventheRibbonTrailifinstalledalternatively <br />atappropriatelyconservativeslopeangles.Thus,theresultofconstructingthesesteepfillsonthe <br />upperportionsoftheeast-facingslopewouldbeloadingthetopofthatslope. <br />113 <br /> <br />