LISTOFFIGURES-VolumeIIFigure 8-1.Failure modes for RSSs including internal failure within the reinforced soilzone, external failure entirely outside the reinforced soil zone, and compound..8-3failure starting behind and passing through the reinforced soil zone8-5Figure 8-2.Modified limit equilibrium analysis for reinforced slope design.8-9Figure 8-3.External failure modesforreinforced soil slopes...8-12Figure 8-4.Construction of reinforced soil slopes.Figure 8-5.Weldedwiremesh detail fortemporary (during construction)or permanent.8-15face support..8-17Figure 8-6.Componentsofavegetatedreinforcedslope(VRSS)system8-23Figure 8-7.DickeyLake site.Figure 8-8.8-25Salmon Lost Trail site..8-26Figure 8-9.Cannon Creek project.8-28Figure 8-10.PennsylvaniaSR54.Figure 8-11.Massachusetts Turnpikeduringconstruction,immediately afterconstruction.8-31and after the second growing season...Figure 8-12.Reinforced soil slopefor runway extension at Yeager Airport, Charleston8-33West Virginia.Figure 8-13.8-36Example of standard RSS design.9-2Figure 9-1.Flow chart of steps for reinforced soil slope design.9-4Figure 9-2.RequirementsfordesignofreinforcedsoilslopesFigure 9-3.Critical zone defined by rotational and sliding surface that meet the required9-6safety factor..Figure 9-4..*..9-8Rotational shear approachtodeterminerequired strength of reinforcement...Figure 9-5.Chart solution for determining the reinforcement strength requirements...9-10Figure 9-6.9-11Reinforcement spacing considerations for high slopes.Figure 9-7.9-14Developing reinforcement lengths.9-17Figure 9-8.Failure through the foundation.Figure 9-9.9-19Seismic stability analysis.Figure 9-10.9-20Subsurfacedrainageconsiderations.Figure 11-1.,11-12Casting yard for precast facing elementsFigure 11-2.Inspectreinforcingelements:topphotoshowsavarietyofreinforcementsincluding metallic strips, welded wire mesh, and geosynthetics and bottom11-14photo shows reinforcement length painted on geogrid reinforcement.Figure 11-3.Leveling pads: a) leveling the concrete, b) completed pad, and c) placing the11-17facing elements on the leveling pad.Figure 11-4.11-18Checking facing element batter and alignment.Figure 11-5.Full height facing panels require special alignment care..11-19.11-21Figure 11-6.Setting first row of precast facing elements..11-23Figure 11-7.Placementof reinforcedfillFigure 11-8.Compaction equipment showing:a)largeequipmentpermittedawayfrom11-24face;andb)lightweightequipmentwithin3ft(1m)oftheface11-27Figure 11-9.Facing connection examplesFigure 11-10. Geotextile joint cover and neoprene pads.11-29FHWA NHI-10-025Table of ContentsxiMSEWallsandRSS-VolIINovember2009
LIST OF FIGURES – Volume II Figure 8-1. Failure modes for RSSs including internal failure within the reinforced soil zone, external failure entirely outside the reinforced soil zone, and compound failure starting behind and passing through the reinforced soil zone . . 8-3 Figure 8-2. Modified limit equilibrium analysis for reinforced slope design. 8-5 Figure 8-3. External failure modes for reinforced soil slopes. . 8-9 Figure 8-4. Construction of reinforced soil slopes. . 8-12 Figure 8-5. Welded wire mesh detail for temporary (during construction) or permanent face support. 8-15 Figure 8-6. Components of a vegetated reinforced slope (VRSS) system . 8-17 Figure 8-7. Dickey Lake site. . 8-23 Figure 8-8. Salmon Lost Trail site. . 8-25 Figure 8-9. Cannon Creek project. . 8-26 Figure 8-10. Pennsylvania SR54. . 8-28 Figure 8-11. Massachusetts Turnpike during construction, immediately after construction and after the second growing season. . 8-31 Figure 8-12. Reinforced soil slope for runway extension at Yeager Airport, Charleston, West Virginia. 8-33 Figure 8-13. Example of standard RSS design. . 8-36 Figure 9-1. Flow chart of steps for reinforced soil slope design. . 9-2 Figure 9-2. Requirements for design of reinforced soil slopes. 9-4 Figure 9-3. Critical zone defined by rotational and sliding surface that meet the required safety factor. 9-6 Figure 9-4. Rotational shear approach to determine required strength of reinforcement. 9-8 Figure 9-5. Chart solution for determining the reinforcement strength requirements. 9-10 Figure 9-6. Reinforcement spacing considerations for high slopes. 9-11 Figure 9-7. Developing reinforcement lengths. . 9-14 Figure 9-8. Failure through the foundation. 9-17 Figure 9-9. Seismic stability analysis. . 9-19 Figure 9-10. Subsurface drainage considerations. . 9-20 Figure 11-1. Casting yard for precast facing elements. . 11-12 Figure 11-2. Inspect reinforcing elements: top photo shows a variety of reinforcements including metallic strips, welded wire mesh, and geosynthetics and bottom photo shows reinforcement length painted on geogrid reinforcement. 11-14 Figure 11-3. Leveling pads: a) leveling the concrete, b) completed pad, and c) placing the facing elements on the leveling pad. . 11-17 Figure 11-4. Checking facing element batter and alignment. 11-18 Figure 11-5. Full height facing panels require special alignment care. . 11-19 Figure 11-6. Setting first row of precast facing elements. 11-21 Figure 11-7. Placement of reinforced fill. . 11-23 Figure 11-8. Compaction equipment showing: a) large equipment permitted away from face; and b) lightweight equipment within 3 ft (1 m) of the face. . 11-24 Figure 11-9. Facing connection examples . 11-27 Figure 11-10. Geotextile joint cover and neoprene pads. . 11-29 FHWA NHI-10-025 Table of Contents MSE Walls and RSS – Vol II xi November 2009
TABLEOFCONTENTS-VolumeI1-1CHAPTER1INTRODUCTION1.11-1OBJECTIVES1-11.1.1Scope1-21.1.2SourceDocuments1-31.1.3Terminology1.21-4HISTORICALDEVELOPMENT1.31-12LOADANDRESISTANCEFACTORDESIGN(LRFD)2-1CHAPTER2SYSTEMSANDPROJECTEVALUATION2.12-1APPLICATIONS2-12.1.1 MSEWalls2-42.1.2Reinforced Soil Slopes.2.22-6ADVANTAGESANDPOTENTIALDISADVANTAGES2-62.2.1AdvantagesofMechanicallyStabilizedEarth(MSE)Walls2-62.2.2AdvantagesofReinforcedSoilSlopes(RSS)2-72.2.3Potential Disadvantages2.3.2-7RELATIVE COSTS.2.42-10DESCRIPTIONOFMSE/RSSSYSTEMS2.4.12-10Systems Differentiation2.4.22-11Types of Systems.2.4.32-12Facing Systems.2.4.42-16Reinforcement Types.2.4.52-17Reinforced Fill Materials2.4.62-18AppurtenantMaterialsofConstruction2.52-18CONSTRUCTIONSEQUENCE.2-182.5.1ConstructionofMSEWsystemswithprecastfacings2.5.2.2-24Construction of MSEsystems withFlexibleFacings2.5.3RSS Construction2-282.62-28SITE EVALUATION.2.6.12-28Site Exploration.2.6.22-30Field Reconnaissance...2-302.6.3Subsurface Exploration2.6.42-32Laboratory Testing..2.6.52-33Foundation Soils2.72-34PROJECTEVALUATION.2.7.12-34Structure SelectionFactors2-352.7.2Geologic and TopographicConditions2.7.32-36Environmental Conditions2.7.42-37Size and Nature of Structure.2.7.5.2-38Aesthetics2.7.6.2-38QuestionableApplications2.82-38ESTABLISHMENTOFPROJECTCRITERIA2-392.8.1Alternates2.8.22-39Facing ConsiderationsFHWA NHI-10-025Tableof ContentsxiliMSEWalls andRSS-VolIINovember2009
TABLE OF CONTENTS – Volume I CHAPTER 1 INTRODUCTION . 1-1 1.1 OBJECTIVES. 1-1 1.1.1 Scope . 1-1 1.1.2 Source Documents . 1-2 1.1.3 Terminology. 1-3 1.2 HISTORICAL DEVELOPMENT . 1-4 1.3 LOAD AND RESISTANCE FACTOR DESIGN (LRFD) . 1-12 CHAPTER 2 SYSTEMS AND PROJECT EVALUATION . 2-1 2.1 APPLICATIONS . 2-1 2.1.1 MSE Walls . 2-1 2.1.2 Reinforced Soil Slopes. 2-4 2.2 ADVANTAGES AND POTENTIAL DISADVANTAGES. 2-6 2.2.1 Advantages of Mechanically Stabilized Earth (MSE) Walls. 2-6 2.2.2 Advantages of Reinforced Soil Slopes (RSS). 2-6 2.2.3 Potential Disadvantages . 2-7 2.3 RELATIVE COSTS. 2-7 2.4 DESCRIPTION OF MSE/RSS SYSTEMS. 2-10 2.4.1 Systems Differentiation . 2-10 2.4.2 Types of Systems . 2-11 2.4.3 Facing Systems . 2-12 2.4.4 Reinforcement Types . 2-16 2.4.5 Reinforced Fill Materials . 2-17 2.4.6 Appurtenant Materials of Construction . 2-18 2.5 CONSTRUCTION SEQUENCE . 2-18 2.5.1 Construction of MSEW systems with precast facings . 2-18 2.5.2 Construction of MSE systems with Flexible Facings . 2-24 2.5.3 RSS Construction. 2-28 2.6 SITE EVALUATION . 2-28 2.6.1 Site Exploration . 2-28 2.6.2 Field Reconnaissance . 2-30 2.6.3 Subsurface Exploration . 2-30 2.6.4 Laboratory Testing . 2-32 2.6.5 Foundation Soils . 2-33 2.7 PROJECT EVALUATION. 2-34 2.7.1 Structure Selection Factors . 2-34 2.7.2 Geologic and Topographic Conditions . 2-35 2.7.3 Environmental Conditions . 2-36 2.7.4 Size and Nature of Structure. 2-37 2.7.5 Aesthetics. 2-38 2.7.6 Questionable Applications . 2-38 2.8 ESTABLISHMENT OF PROJECT CRITERIA . 2-38 2.8.1 Alternates . 2-39 2.8.2 Facing Considerations. 2-39 FHWA NHI-10-025 Table of Contents MSE Walls and RSS – Vol II xiii November 2009
2.8.312-40PerformanceCriteria.2.8.4DesignLife.2-462.92-46PROPRIETARYASPECTS2.102-47CASEHISTORIES--MSEWALLS.2-472.10.1Mn/DOTCrosstownProject MSEWalls.2-492.10.2VeteransMemorialOverpassTrueAbutmentMSEWalls.2-502.10.3 SEATACRunwayExtension Wall2-512.10.4GuanellaPassRoadwayReconstructionCHAPTER3SOILREINFORCEMENTPRINCIPLES.3-1AND SYSTEMDESIGNPROPERTIES3.1.3-1OVERVIEW3.2ESTABLISHMENTOFENGINEERINGPROPERTIESBASEDONSITE3-2EXPLORATIONANDTESTING3-23.2.11Reinforced Fill Soil..3-83.2.2RetainedBackfill and NaturalRetained Soil3-93.2.3Electrochemical Properties3.3.3-10REINFORCEDSOILCONCEPTS.3-103.3.1StressTransferMechanisms.3.3.23-12Mode of Reinforcement Action3-123.3.3GeometricCharacteristics..3.4SOIL REINFORCEMENTINTERACTION USING NORMALIZED3-13CONCEPTS3-133.4.1EvaluationofPulloutPerformance3.4.2Estimate of the Reinforcement Pullout Capacity in MSE Structures ...3-163-213.4.3Interface Shear.3.53-22ESTABLISHMENTOFSTRUCTURALDESIGNPROPERTIES3-22Strength Properties of Steel Reinforcements3.5.13-283.5.2StrengthPropertiesofGeosyntheticReinforcement.3-313.5.2.a Ultimate Tensile Strength, Tult..3-313.5.2.bInstallationDamageReductionFactor, RFD.3-323.5.2.cCreepReductionFactor,RFcR3-333.5.2.dDurabilityReductionFactor, RF.3-383.5.2.eDurabilityReductionFactor,RFp,atWallFaceUnit3-383.5.2.fLRFDGeosyntheticResistanceFactor,.3-393.5.2.g Preliminary Design Reduction Factor, RF.3-403.5.2.h Serviceability Limit State3.63-41FACING MATERIALS.3-413.6.11PrecastConcretePanels3-413.6.1.a Segmental Panels..3-423.6.1.b Full-Height Panels .3.6.2.3-43ModularBlock Wall (MBW)Units.3-463.6.3Welded Wire Mesh Facing3.6.43-47Geosynthetic Wrap-Around Facing3.6.53-47OtherFacings3.6.6..3-50Two-Stage Facings.FHWANHI-10-025Table of ContentsMSEWallsandRSS-VolIIxivNovember2009
2.8.3 Performance Criteria . 2-40 2.8.4 Design Life. 2-46 2.9 PROPRIETARY ASPECTS . 2-46 2.10 CASE HISTORIES - MSE WALLS . 2-47 2.10.1 Mn/DOT Crosstown Project MSE Walls. 2-47 2.10.2 Veterans Memorial Overpass True Abutment MSE Walls. 2-49 2.10.3 SEATAC Runway Extension Wall . 2-50 2.10.4 Guanella Pass Roadway Reconstruction. 2-51 CHAPTER 3 SOIL REINFORCEMENT PRINCIPLES AND SYSTEM DESIGN PROPERTIES . 3-1 3.1 OVERVIEW . 3-1 3.2 ESTABLISHMENT OF ENGINEERING PROPERTIES BASED ON SITE EXPLORATION AND TESTING . 3-2 3.2.1 Reinforced Fill Soil . 3-2 3.2.2 Retained Backfill and Natural Retained Soil . 3-8 3.2.3 Electrochemical Properties . 3-9 3.3 REINFORCED SOIL CONCEPTS . 3-10 3.3.1 Stress Transfer Mechanisms . 3-10 3.3.2 Mode of Reinforcement Action . 3-12 3.3.3 Geometric Characteristics . 3-12 3.4 SOIL REINFORCEMENT INTERACTION USING NORMALIZED CONCEPTS . 3-13 3.4.1 Evaluation of Pullout Performance . 3-13 3.4.2 Estimate of the Reinforcement Pullout Capacity in MSE Structures . 3-16 3.4.3 Interface Shear . 3-21 3.5 ESTABLISHMENT OF STRUCTURAL DESIGN PROPERTIES . 3-22 3.5.1 Strength Properties of Steel Reinforcements . 3-22 3.5.2 Strength Properties of Geosynthetic Reinforcement. 3-28 3.5.2.a Ultimate Tensile Strength, Tult . 3-31 3.5.2.b Installation Damage Reduction Factor, RFID . 3-31 3.5.2.c Creep Reduction Factor, RFCR . 3-32 3.5.2.d Durability Reduction Factor, RFD. 3-33 3.5.2.e Durability Reduction Factor, RFD, at Wall Face Unit . 3-38 3.5.2.f LRFD Geosynthetic Resistance Factor, . 3-38 3.5.2.g Preliminary Design Reduction Factor, RF . 3-39 3.5.2.h Serviceability Limit State . 3-40 3.6 FACING MATERIALS . 3-41 3.6.1 Precast Concrete Panels . 3-41 3.6.1.a Segmental Panels . 3-41 3.6.1.b Full-Height Panels . 3-42 3.6.2 Modular Block Wall (MBW) Units . 3-43 3.6.3 Welded Wire Mesh Facing . 3-46 3.6.4 Geosynthetic Wrap-Around Facing . 3-47 3.6.5 Other Facings . 3-47 3.6.6 Two-Stage Facings. 3-50 FHWA NHI-10-025 Table of Contents MSE Walls and RSS – Vol II xiv November 2009
4-1CHAPTER4DESIGNOFMSEWALLS4.14-1DESIGNMETHODOLOGYANDANALYSISMETHODS4-14.1.1LoadandResistanceFactorDesign(LRFD)Platform4-24.1.2Analysis Methods..4.2..4-3LOADSANDLOADCOMBINATIONS4.3.4-6DESIGNOFMSEWALLSUSINGLRFDMETHODOLOGY.4-74.3.1Design Steps.4.4MSE WALLS DESIGNGUIDELINES.4-9.4-94.4.1Step1-EstablishProjectRequirements4-94.4.2Step2-Establish Project Parameters4.4.3Step3-EstimateWallEmbedment Depth &Reinforcement Length...4-104.4.4Step 4 - Define Nominal Loads4-114.4.5Step 5 - Summarize Load Combinations, Load Factors, and Resistance4-17Factors.4.4.64-18Step 6- Evaluate External Stability.4-194.4.6.a Evaluate Sliding Stability.4-224.4.6.bEvaluateEccentricity4-264.4.6.cEvaluateBearingonFoundation..4-314.4.6.dSettlementEstimate4.4.7.4-31Step7-EvaluateInternal Stability.4-324.4.7.a Select Type of Reinforcement.4-334.4.7.bDefineCriticalSlipSurface4-354.4.7.cDefine Unfactored Loads4-384.4.7.d Establish Vertical Layout of Soil Reinforcements...4-394.4.7.e CalculateFactored TensileForces in Reinforcements...4-474.4.7.fCalculateSoilReinforcementResistance....4-494.4.7.g Select Grade of &/or Number of Elements at Each Level4-494.4.7.h Internal Stability with Respect to Pullout Failure4-524.4.7.iCheckConnectionStrength..4-574.4.7.j Lateral Movements....4-574.4.7.kVerticalMovementandBearingPads.4-584.4.8Step8-DesignofFacingElements...4-584.4.8.aDesign ofConcrete, Steel, and TimberFacings.4-594.4.8.bDesign of FlexibleWallFacings.4-594.4.9Step9-AssessOverall Stability4-614.4.10 Step 10 - Assess Compound Stability4-654.4.11 Step 11-WallDrainage Systems.4-654.11.aSurfaceDrainage4-654.11.b Surface Water Runoff4.11.cScour4-654.5..4-66TEMPORARYWALLS4.6.4-66DESIGNCHECKLIST..4.7.4-80COMPUTER-AIDEDDESIGN4.8.4-80VENDOR4.94-80STANDARDMSEWDESIGNSFHWA NHI-10-025Tableof ContentsMSEWallsandRSS-VolIIXVNovember2009
CHAPTER 4 DESIGN OF MSE WALLS . 4-1 4.1 DESIGN METHODOLOGY AND ANALYSIS METHODS . 4-1 4.1.1 Load and Resistance Factor Design (LRFD) Platform . 4-1 4.1.2 Analysis Methods. 4-2 4.2 LOADS AND LOAD COMBINATIONS . 4-3 4.3 DESIGN OF MSE WALLS USING LRFD METHODOLOGY . 4-6 4.3.1 Design Steps. 4-7 4.4 MSE WALLS DESIGN GUIDELINES . 4-9 4.4.1 Step 1 - Establish Project Requirements . 4-9 4.4.2 Step 2 - Establish Project Parameters . 4-9 4.4.3 Step 3 - Estimate Wall Embedment Depth & Reinforcement Length . 4-10 4.4.4 Step 4 - Define Nominal Loads . 4-11 4.4.5 Step 5 - Summarize Load Combinations, Load Factors, and Resistance Factors . 4-17 4.4.6 Step 6 - Evaluate External Stability. 4-18 4.4.6.a Evaluate Sliding Stability . 4-19 4.4.6.b Evaluate Eccentricity . 4-22 4.4.6.c Evaluate Bearing on Foundation. 4-26 4.4.6.d Settlement Estimate . 4-31 4.4.7 Step 7 - Evaluate Internal Stability . 4-31 4.4.7.a Select Type of Reinforcement . 4-32 4.4.7.b Define Critical Slip Surface . 4-33 4.4.7.c Define Unfactored Loads . 4-35 4.4.7.d Establish Vertical Layout of Soil Reinforcements. 4-38 4.4.7.e Calculate Factored Tensile Forces in Reinforcements. 4-39 4.4.7.f Calculate Soil Reinforcement Resistance . 4-47 4.4.7.g Select Grade of &/or Number of Elements at Each Level . 4-49 4.4.7.h Internal Stability with Respect to Pullout Failure. 4-49 4.4.7.i Check Connection Strength . 4-52 4.4.7.j Lateral Movements . 4-57 4.4.7.k Vertical Movement and Bearing Pads . 4-57 4.4.8 Step 8 - Design of Facing Elements. 4-58 4.4.8.a Design of Concrete, Steel, and Timber Facings . 4-58 4.4.8.b Design of Flexible Wall Facings. 4-59 4.4.9 Step 9 - Assess Overall Stability. 4-59 4.4.10 Step 10 - Assess Compound Stability . 4-61 4.4.11 Step 11 - Wall Drainage Systems . 4-65 4.11.a Surface Drainage. 4-65 4.11.b Surface Water Runoff . 4-65 4.11.c Scour . 4-65 4.5 TEMPORARY WALLS . 4-66 4.6 DESIGN CHECKLIST . 4-66 4.7 COMPUTER-AIDED DESIGN . 4-80 4.8 VENDOR. 4-80 4.9 STANDARD MSEW DESIGNS . 4-80 FHWA NHI-10-025 Table of Contents MSE Walls and RSS – Vol II xv November 2009
5-1CHAPTER5MSEWALLDESIGNDETAILS5-15.1TOPOFWALLELEMENTS5-15.1.1Copings.5-45.1.2Traffic Barriers.5-45.1.3Parapets..5-45.1.4Post and Beam Barriers.5-65.1.5DrainageRelated toTopof WallElements5.2BOTTOMOFWALLELEMENTS...5-65.3..5-8DRAINAGE...5-95.3.1Internal Drainage Systems5.3.25-17ExternalDrainage.5-245.3.3Filtration andDrainage SystemComponentRequirements.5.3.45-34Maintenance of Drainage.5.45-35INTERNAL DETAILS...5.4.15-35ContactBetweenDissimilarMetals.5.4.25-35Vertical Obstructions in Reinforced Soil Mass5.4.35-42Horizontal Obstructions inReinforced Soil Mass5-445.4.4Wall Face Penetrations5.4.55-46Slip Joints..5-475.4.6Wall Curves.5-515.4.7Wall Corners.5-525.4.8Two-StageFacing5.55-54WALLINITIATIONS AND TERMINATIONS5.65-56AESTHETICS6-1CHAPTER6DESIGNOFMSEWALLSWITHCOMPLEXGEOMETRICS.6-36.1BRIDGEABUTMENTS6-36.1.1MSEWAbutmentsonSpreadFootings.6.1.2MSEWAbutments on StubFootings SupportedbyDeepFoundations.6-6through Reinforced Wall Fill6.1.36-10Alternative Configuration of MSEWalls at BridgeAbutments6-116.1.4ProtectionofMSEWall atAbutments6.2.6-13SUPERIMPOSED(TIERED)MSEWALLS6-136.2.1 2-Tier Superimposed Wall6-156.2.2SuperimposedWallswithMorethan2-Tiers6.3.6-16WALLSWITHUNEVENREINFORCEMENTLENGTHS6.4.6-17BACK-TO-BACK(BBMSE)WALLS...6.5SHOREDMSEWALLSFORSTEEPTERRAINSANDLOWVOLUME6-19ROADS.6.66-26STABLEFEATURE MSE (SFMSE)WALLS.7-1CHAPTER7DESIGNOFMSEWALLSFOREXTREMEEVENTS.7-17.1SEISMICEVENTS.7-17.1.1 External Stability.7-97.1.2Internal Stability..7-117.1.2.a Tensile Failure7.1.2.b Pullout Failure.7-12FHWA NHI-10-025Table of ContentsxviMSEWallsandRSS-VolIINovember2009
CHAPTER 5 MSE WALL DESIGN DETAILS . 5-1 5.1 TOP OF WALL ELEMENTS . 5-1 5.1.1 Copings . 5-1 5.1.2 Traffic Barriers. 5-4 5.1.3 Parapets. 5-4 5.1.4 Post and Beam Barriers. 5-4 5.1.5 Drainage Related to Top of Wall Elements . 5-6 5.2 BOTTOM OF WALL ELEMENTS . 5-6 5.3 DRAINAGE. 5-8 5.3.1 Internal Drainage Systems . 5-9 5.3.2 External Drainage . 5-17 5.3.3 Filtration and Drainage System Component Requirements. 5-24 5.3.4 Maintenance of Drainage. 5-34 5.4 INTERNAL DETAILS . 5-35 5.4.1 Contact Between Dissimilar Metals. 5-35 5.4.2 Vertical Obstructions in Reinforced Soil Mass . 5-35 5.4.3 Horizontal Obstructions in Reinforced Soil Mass . 5-42 5.4.4 Wall Face Penetrations . 5-44 5.4.5 Slip Joints. 5-46 5.4.6 Wall Curves . 5-47 5.4.7 Wall Corners . 5-51 5.4.8 Two-Stage Facing . 5-52 5.5 WALL INITIATIONS AND TERMINATIONS . 5-54 5.6 AESTHETICS. 5-56 CHAPTER 6 DESIGN OF MSE WALLS WITH COMPLEX GEOMETRICS . 6-1 6.1 BRIDGE ABUTMENTS . 6-3 6.1.1 MSEW Abutments on Spread Footings . 6-3 6.1.2 MSEW Abutments on Stub Footings Supported by Deep Foundations through Reinforced Wall Fill . 6-6 6.1.3 Alternative Configuration of MSE Walls at Bridge Abutments . 6-10 6.1.4 Protection of MSE Wall at Abutments . 6-11 6.2 SUPERIMPOSED (TIERED) MSE WALLS. 6-13 6.2.1 2-Tier Superimposed Wall . 6-13 6.2.2 Superimposed Walls with More than 2-Tiers . 6-15 6.3 WALLS WITH UNEVEN REINFORCEMENT LENGTHS . 6-16 6.4 BACK-TO-BACK (BBMSE) WALLS . 6-17 6.5 SHORED MSE WALLS FOR STEEP TERRAINS AND LOW VOLUME ROADS. 6-19 6.6 STABLE FEATURE MSE (SFMSE) WALLS . 6-26 CHAPTER 7 DESIGN OF MSE WALLS FOR EXTREME EVENTS. 7-1 7.1 SEISMIC EVENTS . 7-1 7.1.1 External Stability . 7-1 7.1.2 Internal Stability. 7-9 7.1.2.a Tensile Failure . 7-11 7.1.2.b Pullout Failure. 7-12 FHWA NHI-10-025 Table of Contents MSE Walls and RSS – Vol II xvi November 2009