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SUBGRADESUBGRADEHOW TO DEAL WITH HOW TO DEAL WITH

SOFT SPOTSSOFT SPOTS

BY BY JIM FIFEJIM FIFE

KOECHLEIN CONSULTING KOECHLEIN CONSULTING ENGINEERS, INC.ENGINEERS, INC.FEBRUARY 2009FEBRUARY 2009

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PAVEMENT SECTIONPAVEMENT SECTION

RECONDITIONED 8” TO 12” OF RECONDITIONED 8” TO 12” OF SUBGRADESUBGRADE

SUBBASESSUBBASES

BASESBASES

SURFACE COURSES (CONCRETE OR SURFACE COURSES (CONCRETE OR ASPHALT)ASPHALT)

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SUBGRADESUBGRADE

ALL SOILS BELOW THE PAVEMENT ALL SOILS BELOW THE PAVEMENT SECTIONSECTION

INCLUDES THE 8’’ TO 12” SUBGRADE INCLUDES THE 8’’ TO 12” SUBGRADE RECONDITIONINGRECONDITIONING

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SUBGRADE SOIL TYPESSUBGRADE SOIL TYPES

FINE GRAINED - PASSING #200 SIEVEFINE GRAINED - PASSING #200 SIEVE– CLAYSCLAYS– SILTSSILTS

SAND – GREATER THAN #200 SIEVE SAND – GREATER THAN #200 SIEVE AND SMALLER THAN #4 SIEVEAND SMALLER THAN #4 SIEVE

GRAVEL – LARGER THAN #4 SIEVEGRAVEL – LARGER THAN #4 SIEVE

COMBINATION OF THE ABOVECOMBINATION OF THE ABOVE

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FIELD IDENTIFICATIONFIELD IDENTIFICATIONCLAYS – CANNOT SEE PARTICLES CLAYS – CANNOT SEE PARTICLES – SHEENSHEEN– ROLLROLL– HOLD MOISTUREHOLD MOISTURE– MAINTAIN SHAPE WHEN DRYMAINTAIN SHAPE WHEN DRY

SILTS – CANNOT SEE PARTICLESSILTS – CANNOT SEE PARTICLES– WILL NOT ROLL OR SHEENWILL NOT ROLL OR SHEEN– WILL PASS WATERWILL PASS WATER– WILL CRUMBLE WHEN DRYWILL CRUMBLE WHEN DRY

SANDS – CAN SEE INDIVIDUAL PARTICLESSANDS – CAN SEE INDIVIDUAL PARTICLESGRAVEL – LARGER THAN ¼ INCHGRAVEL – LARGER THAN ¼ INCH

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SOIL TYPE CHARACTERISTICSSOIL TYPE CHARACTERISTICS

CLAYS – SHRINK / SWELL POTENTIAL CLAYS – SHRINK / SWELL POTENTIAL WITH CHANGES IN MOISTURE WITH CHANGES IN MOISTURE CONTENTCONTENT

SILTS – LONG TERM CONSOLIDATION SILTS – LONG TERM CONSOLIDATION (SHRINAGE)(SHRINAGE)

SANDS – OFTEN NOT STABLESANDS – OFTEN NOT STABLE

GRAVEL – MOST DESIRABLE FOR GRAVEL – MOST DESIRABLE FOR CONSTRUCTIONCONSTRUCTION

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DETERMINING SUBGRADE DETERMINING SUBGRADE STRENGTHSTRENGTH

ASTM D 1883-05 “STANDARD TEST ASTM D 1883-05 “STANDARD TEST METHOD FOR CBR (CALIFORNIA BEARING METHOD FOR CBR (CALIFORNIA BEARING RATIO) OF LABORATORY-COMPACTED RATIO) OF LABORATORY-COMPACTED SOILS” (AASHTO T 193)SOILS” (AASHTO T 193)ASTM D 4429-04 “STANDARD TEST ASTM D 4429-04 “STANDARD TEST METHOD FOR CBR (CALIFIRNIA BEARING METHOD FOR CBR (CALIFIRNIA BEARING RATIO) OF SOILS IN PLACE”RATIO) OF SOILS IN PLACE”ASTM D 2844-01 “STANDARD TEST ASTM D 2844-01 “STANDARD TEST METHOD FOR RESISTANCE VALUE AND METHOD FOR RESISTANCE VALUE AND EXPANSION PRESSURE OF COMPACTED EXPANSION PRESSURE OF COMPACTED SOILS” (R-VALUE), (AASHTO T 190), CP-L SOILS” (R-VALUE), (AASHTO T 190), CP-L 31013101

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SOIL STRUCTURESOIL STRUCTURE

IN ENGINEERING, A SOILS IN ENGINEERING, A SOILS STRUCTURE IS COMPOSED OF:STRUCTURE IS COMPOSED OF:– GASES (AIR AND SOMETIMES METHANE)GASES (AIR AND SOMETIMES METHANE)– LIQUIDS (WATER)LIQUIDS (WATER)– SOLIDS (SOIL PARTICLES AND SOLIDS (SOIL PARTICLES AND

DEPOSITED CRYSTALS)DEPOSITED CRYSTALS)

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GASES (AIR)

LIQUIDS (WATER)

SOLIDS (SOIL PARTICLES)

SOIL PROFILES

GASES (AIR)

LIQUIDS (WATER)

SOLIDS(SOIL PARTICLES)

GASES (AIR)

LIQUIDS (WATER)

SOLIDS(SOIL PARTICLES)

1 2 3

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TEST PROCEDURES TO MEASURE TEST PROCEDURES TO MEASURE SUBGRADE STRENGTHSUBGRADE STRENGTH

PRIOR TO SATURATION, LABORATORY PRIOR TO SATURATION, LABORATORY TEST PROCEDURES ARE PERFORMED AT TEST PROCEDURES ARE PERFORMED AT OR NEAR MAXIMUM DENSITY AND OR NEAR MAXIMUM DENSITY AND OPTIMUM MOISTURE CONTENTOPTIMUM MOISTURE CONTENT

CLAY SOILS HAVE LOW PERMEABILITY CLAY SOILS HAVE LOW PERMEABILITY WHEN COMPACTEDWHEN COMPACTED

SOAKING DOES NOT ALWAYS SOAKING DOES NOT ALWAYS SIGNIFICANTLY CHANGE MOISTURE SIGNIFICANTLY CHANGE MOISTURE CONTENT OR DENSITYCONTENT OR DENSITY

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DESIGN CHALLENGEDESIGN CHALLENGELABORATORY TEST RESULTS DON’T LABORATORY TEST RESULTS DON’T ALWAYS REPRESENT THE LONG TERM ALWAYS REPRESENT THE LONG TERM MOISTURE CONTENT OF THE SOILS BELOW MOISTURE CONTENT OF THE SOILS BELOW THE PAVEMENTTHE PAVEMENTIN THE FIELD, AS A SOIL GAINS MOISTURE IN THE FIELD, AS A SOIL GAINS MOISTURE IT’S STRENGTH IS COMPROMISEDIT’S STRENGTH IS COMPROMISEDRESULTING PAVEMENT SECTION RESULTING PAVEMENT SECTION SUBGRADE MAY NOT BE STRONG ENOUGH SUBGRADE MAY NOT BE STRONG ENOUGH TO SUPPORT TRAFFIC LOADSTO SUPPORT TRAFFIC LOADS

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IMPORTANCE OF DRAINAGE WITHIN IMPORTANCE OF DRAINAGE WITHIN AND BELOW THE PAVEMENT SECTIONAND BELOW THE PAVEMENT SECTION

MAINTAIN UNIFORM MOISTURE MAINTAIN UNIFORM MOISTURE CONTENT CONTENT

REDUCE POTENTIAL FOR REDUCE POTENTIAL FOR SATURATION SATURATION

MAINTAIN STRENGTH OF SUBGRADE MAINTAIN STRENGTH OF SUBGRADE

MAINTAIN STRENGTH OF PAVEMENT MAINTAIN STRENGTH OF PAVEMENT SECTION LAYERSSECTION LAYERS

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IDENTIFYING SOFT SUBGRADEIDENTIFYING SOFT SUBGRADE

VEGETATION CHANGESVEGETATION CHANGESPOOR DRAINAGE / RECENT POOR DRAINAGE / RECENT IRRIGATION / PONDING WATERIRRIGATION / PONDING WATERRIVER OR STREAM MEANDERSRIVER OR STREAM MEANDERSSHEENING SURFACESSHEENING SURFACESSATURATED AREASSATURATED AREASSIGNS OF RUTTING/CRACKINGSIGNS OF RUTTING/CRACKINGPROOF ROLLINGPROOF ROLLINGTESTINGTESTING

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MEDIATION OF SOFT MEDIATION OF SOFT SUBGRADESUBGRADE

REMOVAL & REPLACEMENT USINGREMOVAL & REPLACEMENT USING– SIMILAR SOILSSIMILAR SOILS– GRANULAR MATERIALGRANULAR MATERIAL– MILLED TAILINGSMILLED TAILINGS– HMA MATERIALHMA MATERIAL

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MEDIATION OF SOFT MEDIATION OF SOFT SUBGRADESUBGRADE

REINFORCEMENTREINFORCEMENT– GEOGRIDSGEOGRIDS– WOVEN GEOTEXTILESWOVEN GEOTEXTILES– NON-WOVEN GEOTEXTILESNON-WOVEN GEOTEXTILES

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MEDIATION OF SOFT MEDIATION OF SOFT SUBGRADESUBGRADE

SOIL MODIFICATIONSOIL MODIFICATION– REMOVE AND REPLACE SAME SOILREMOVE AND REPLACE SAME SOIL– COLLAPSE SOIL STRUCTURE WITH COLLAPSE SOIL STRUCTURE WITH

DYNAMIC FORCEDYNAMIC FORCE– PLACE SURCHARGE WEIGHTPLACE SURCHARGE WEIGHT– DE-WATER SOIL STRUCTUREDE-WATER SOIL STRUCTURE– SOIL CEMENT SOIL CEMENT – LIME STABLIZATIONLIME STABLIZATION– EMULSIONSEMULSIONS

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SPECIAL CONSIDERATIONS FOR SPECIAL CONSIDERATIONS FOR POOR SUBGRADE CONDITIONSPOOR SUBGRADE CONDITIONS

KEEP CONSTRUCTION WITHIN THE UPPER, DRIER KEEP CONSTRUCTION WITHIN THE UPPER, DRIER SOIL HORIZONSOIL HORIZON

LIMIT CONSTRUCTION EQUIPMENTLIMIT CONSTRUCTION EQUIPMENT

MAINTAIN POSITIVE DRAINAGE DURING MAINTAIN POSITIVE DRAINAGE DURING CONSTRUCTIONCONSTRUCTION

SUBGRADE SURFACE SHOULD HAVE MINIMUM 2% SUBGRADE SURFACE SHOULD HAVE MINIMUM 2% SLOPESLOPE

POSITIVE SURFACE DRAINAGE AWAY FROM POSITIVE SURFACE DRAINAGE AWAY FROM ROADWAYROADWAY

REQUIRE MOISTURE CONDITIONING AND REQUIRE MOISTURE CONDITIONING AND COMPACTION OF UTILITY BACKFILL SOILSCOMPACTION OF UTILITY BACKFILL SOILS

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SPECIAL CONSIDERATIONSSPECIAL CONSIDERATIONSDON’T PLACE GRANULAR BASES UNDER DON’T PLACE GRANULAR BASES UNDER ADJACENT SIDEWALKS THAT BACK AGAINST ADJACENT SIDEWALKS THAT BACK AGAINST IRRIGATED AREASIRRIGATED AREASISOLATE SIDEWALKS FROM ROADWAYSISOLATE SIDEWALKS FROM ROADWAYSMAKE SURE CONCRETE GUTTERS & CROSS PANS MAKE SURE CONCRETE GUTTERS & CROSS PANS ARE LARGE ENOUGH AND DRAIN CORRECTLYARE LARGE ENOUGH AND DRAIN CORRECTLYCRACK SEAL INTERFACES BETWEEN GUTTER & CRACK SEAL INTERFACES BETWEEN GUTTER & CROSS PANS AND PAVEMENT CROSS PANS AND PAVEMENT PREVENT OR REPLACE LEAKING UTILITIES & PREVENT OR REPLACE LEAKING UTILITIES & STORM DRAINSSTORM DRAINSPREVENT INFILTRATION GALLERIES FOR PREVENT INFILTRATION GALLERIES FOR COLLECTING WATERCOLLECTING WATER

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QUESTIONS ?QUESTIONS ?

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THANK YOUTHANK YOU