I.I. Rockfall Hazard RatingRockfall Hazard Ratingfor Road Cuts between Rolla and Viennafor Road Cuts between Rolla and Vienna

II. Site Remediation and Mitigation Plan for II. Site Remediation and Mitigation Plan for Site ESite E

Four Miles North of Rolla, MO on Highway 63Four Miles North of Rolla, MO on Highway 63

► Daniel StoutDaniel Stout► Evan StevensEvan Stevens► Brian MullenBrian Mullen

Part 1: Rate all Rock Cuts on Highway 63 Part 1: Rate all Rock Cuts on Highway 63 between Rolla and Vienna, MObetween Rolla and Vienna, MO

► Both use similar factors Both use similar factors to rate rock fall hazardsto rate rock fall hazards

► Oregon system tailored Oregon system tailored for mountainous terrainfor mountainous terrain

► Missouri system Missouri system designed for more designed for more moderate terrain; moderate terrain; includes karst variablesincludes karst variables

► How?How? Missouri Rock Fall Missouri Rock Fall

Hazard Rating Hazard Rating System System

► Maerz et. al., 2005 Maerz et. al., 2005 ► ““Missouri System”Missouri System”

Oregon Rock Oregon Rock Hazard Rating Hazard Rating System System

► Pierson & Van Pierson & Van Vickle, 1993 Vickle, 1993

► ““Oregon System”Oregon System”

In the beginning…In the beginning…

► 36 individual sites36 individual sites► L & R sides rated L & R sides rated

separatelyseparately► Digital video analysis Digital video analysis

and site visits used and site visits used to gather datato gather data

““Missouri System”Missouri System”

► RISKRISK Slope heightSlope height Slope angleSlope angle Rock face instabilityRock face instability Weathering & Weathering &

ErosionErosion Rock strengthRock strength Face irregularityFace irregularity Face loosenessFace looseness Block sizeBlock size WaterWater KarstKarst

► CONSEQUENCECONSEQUENCE Ditch widthDitch width Ditch volumeDitch volume Rockfall quantityRockfall quantity Slope angleSlope angle Shoulder widthShoulder width Number of lanesNumber of lanes Daily trafficDaily traffic Average vehicle riskAverage vehicle risk

► (Cars/day * (Cars/day * length)/(Speed limit * cut length)/(Speed limit * cut length)length)

Decision Sight Decision Sight DistanceDistance

Block sizeBlock size

““Missouri System”Missouri System”► Rate factors, then sum risk 1-100Rate factors, then sum risk 1-100► Rate factors, then sum consequence 1-100Rate factors, then sum consequence 1-100

0

50

100

0 25 50 75 100Consequence Value

Ris

k V

alu

e

““Oregon System”Oregon System”► FactorsFactors

Slope heightSlope height Ditch effectivenessDitch effectiveness AVRAVR DSDDSD Structural condition Structural condition

& erosion& erosion Block size/quantityBlock size/quantity Climate/WaterClimate/Water Rock fall historyRock fall history

► Each factor ratedEach factor rated 3 (good)3 (good) 9 (fair)9 (fair) 27 (poor)27 (poor) 81 (bad)81 (bad)

► Summation of all Summation of all values gives score; values gives score; maximum 810maximum 810

► >500 needs >500 needs “immediate action”“immediate action”

► 300-500 “of 300-500 “of concern”concern”

““Missouri system” resultsMissouri system” results

Site E

Site D

Site K

““Oregon Oregon System” System” resultsresults

► Sites E, D, and K Sites E, D, and K elevated in this model elevated in this model tootoo

► E = 222/810E = 222/810► Other sites (red Other sites (red

arrows) perhaps arrows) perhaps “inflated” by AVR“inflated” by AVR

Part I ResultsPart I Results► Site E clearly Site E clearly

highest rated site highest rated site by both methodsby both methods

► A few other sites A few other sites may need may need attentionattention

““Site E”Site E”

► Four miles north of Rolla, Four miles north of Rolla, fifth cut on rightfifth cut on right

► Just past Capital QuarryJust past Capital Quarry

www.terraserver.comEarth.google.com

The PaleosinkholeThe Paleosinkhole

► Cut is approx. 50 years oldCut is approx. 50 years old► Stands at 76 degreesStands at 76 degrees► Heterogeneous jumbled Heterogeneous jumbled

up massup mass

► Matrix like a calcrete or Matrix like a calcrete or calichecaliche

► Dolomite boulders and Dolomite boulders and broken stratabroken strata

► Left and right contactsLeft and right contacts

► Jumbled mass of dolomite in Jumbled mass of dolomite in a calcrete mixa calcrete mix

► Overhanging slab at topOverhanging slab at top

► Ravel PileRavel Pile

A short slideshowA short slideshow

► Right contactRight contact

► DryDry► Slumping/slumpedSlumping/slumped► Ditch along topDitch along top

► Left contactLeft contact

► WetWet► Highly eroded; Highly eroded;

water off top and water off top and along jointsalong joints

Approx. 2’

Current Mitigation PracticeCurrent Mitigation Practice

Possible Remediation or Possible Remediation or MitigationMitigation

► ExcavationExcavation► BermsBerms► RockshedsRocksheds► DitchesDitches► Rock traps and fences Rock traps and fences ► Retaining walls and Retaining walls and

GabionsGabions► Mesh drapingMesh draping► Rock nettingRock netting► ShotcreteShotcrete► RockboltingRockbolting► Soil nailingSoil nailing

Spang, 1987

Chosen Chosen Methods to Methods to InvestigateInvestigate

► Gabion WallsGabion Walls► Mesh Draping (w/ and w/o Mesh Draping (w/ and w/o

rock fencing)rock fencing)► ExcavationExcavation

Gabion wall on I-44

Mesh draping on a similar slope (Goodman, 1989)

Gabion WallsGabion Walls► ““Natural looking” stacked Natural looking” stacked

baskets of rockbaskets of rock► Low maintenanceLow maintenance► Restraining massRestraining mass► Local experienceLocal experience

► AssumptionsAssumptions Phi = 35 degreesPhi = 35 degrees C = 300 psfC = 300 psf Values consistent with a Values consistent with a

strong soilstrong soil Unit weight = 160 pcfUnit weight = 160 pcf

► AssignmentsAssignments Wall batter = 6 degreesWall batter = 6 degrees Porosity of 50 percentPorosity of 50 percent 2.7 mm PVC coated wire2.7 mm PVC coated wire Top slope of 3 degreesTop slope of 3 degrees 3 ft top surface height 3 ft top surface height

(depth of lowest layer of (depth of lowest layer of gabions) aids FOSgabions) aids FOS

Design 1: Half-slope Gabion Design 1: Half-slope Gabion WallWall

► 24 ft gabion wall24 ft gabion wall► Benched back 12 Benched back 12

ft.ft.► Bench covered w/ Bench covered w/

rip-raprip-rap

► $70-$80,000 $70-$80,000 depending upon depending upon optionsoptions

► Overall FOS 1.91Overall FOS 1.91

Design 2: Full-slope Gabion Design 2: Full-slope Gabion WallWall

► 48 ft gabion wall48 ft gabion wall► Four tiersFour tiers

► $180-$220,000$180-$220,000► Overall FOS 1.69Overall FOS 1.69

Design 3: Staggered half-slope gabion Design 3: Staggered half-slope gabion wallswalls

► Two 24’ gabion Two 24’ gabion walls staggered walls staggered with a 12’ (9’) with a 12’ (9’) benchbench

► Bench covered w/ Bench covered w/ rip-raprip-rap

► $105-$135,000$105-$135,000► Overall FOS 1.97Overall FOS 1.97

Design Cost ComparisonDesign Cost Comparison

Design Comparison 2Design Comparison 2

Maintenance/ Maintenance/ RecommendationRecommendation

► Design 1Design 1► Why?Why?

Lowest costLowest cost Best FOSBest FOS No FOS < 1.50No FOS < 1.50 Others are overkillOthers are overkill

► Not Designs 2 & 3Not Designs 2 & 3► Why?Why?

High costHigh cost Poor overturning FOSPoor overturning FOS

► Low maintenanceLow maintenance Clear out vegetation, or Clear out vegetation, or

allow it cover if wantedallow it cover if wanted Check regularly for wire Check regularly for wire

breaksbreaks Clean benches (if any) Clean benches (if any)

periodicallyperiodically

Mesh Draping - GeneralMesh Draping - General► A flexible facing such as A flexible facing such as

wire rope nets or wire rope nets or conventional wire meshes conventional wire meshes are draped over the slope are draped over the slope for passive rock fall for passive rock fall protection. protection.

► The draping does not The draping does not stop rock falls, but rather stop rock falls, but rather controls the velocity of controls the velocity of falling rocks by limiting falling rocks by limiting the horizontal the horizontal component. component.

► Anchored from above and Anchored from above and simply hangs over slopesimply hangs over slope (Hoek, 2006)

Mesh Draping - ProcedureMesh Draping - Procedure► Clean and scale slopeClean and scale slope► Choose net sizeChoose net size► Anchor support cablesAnchor support cables

Could be problematic Could be problematic given the paleosinkhole given the paleosinkhole material naturematerial nature

Need 20 kips supportNeed 20 kips support Muhunthan et. al. (2005)Muhunthan et. al. (2005)

Optional Rock FencingOptional Rock Fencing

Energy absorbing rock fence that can be used alone or in addition to

other methods

(Hoek, 2006)

► Design may or may Design may or may not include rock not include rock fencing as a design fencing as a design elementelement

Design 1: 40’ drape w/ rock Design 1: 40’ drape w/ rock fencefence

► 40’ mesh draping over 40’ mesh draping over paleosinkpaleosink

► 4” x 4” mesh4” x 4” mesh► 120’ rock fence across center120’ rock fence across center

Design 2: Full-slope drapingDesign 2: Full-slope draping

► 55’ draping covers full slope55’ draping covers full slope► 4” x 4” mesh4” x 4” mesh

Draping ComparisonDraping Comparison

Draping Comparison 2Draping Comparison 2

► Draping with fence provides perhaps the Draping with fence provides perhaps the best protection of all designs, but:best protection of all designs, but: Removal of accumulated debris is problematicRemoval of accumulated debris is problematic Periodic fence replacement costly (~$21,000)Periodic fence replacement costly (~$21,000)

► Full-slope draping alleviates above Full-slope draping alleviates above concernsconcerns

Draping RecommendationDraping Recommendation► Full-slope drapingFull-slope draping

Keeps all but the Keeps all but the very smallest and very smallest and largest rock falls in largest rock falls in the ditchthe ditch

Requires little to no Requires little to no maintenancemaintenance

Relatively cheap Relatively cheap compared to compared to massive excavation massive excavation or gabion walls.or gabion walls.

► ProblemsProblems Paleosink material Paleosink material

problematic for problematic for placing anchorsplacing anchors

No protection No protection against rotational against rotational failurefailure

ExcavationExcavation► Removal of two Removal of two

linear yards into linear yards into paleosink along paleosink along entire faceentire face

► 1080 c.y. @ 1080 c.y. @ $28/c.y.$28/c.y.

► ~$30,000~$30,000► Note: the $28/c.y. Note: the $28/c.y.

price is a high bid; price is a high bid; could be done could be done cheapercheaper

► What does this do?What does this do? TemporaryTemporary

► Removes Removes weathered faceweathered face

► Decreases Decreases loosenesslooseness

► Decreases face Decreases face instabilityinstability

PermanentPermanent► Increases ditch Increases ditch

width and volumewidth and volume► Slight decrease in Slight decrease in

slope angle to 70 slope angle to 70 degreesdegrees

Excavation effectExcavation effect

(49,67)(58,79)

Comparison of all DesignsComparison of all Designs

Recommended DesignRecommended Design► Full-slope draping at $53, Full-slope draping at $53,

414414► Very good results w/ usage Very good results w/ usage

so far, for more info see:so far, for more info see:► Muhunthan et. al. (2005) Muhunthan et. al. (2005)

Analysis and Design of Wire Analysis and Design of Wire Mesh / Cable Net Slope Mesh / Cable Net Slope Protection, Washington Protection, Washington State Transportation State Transportation Center, April 2005.Center, April 2005.

AfterthoughtsAfterthoughts► We’ve noticed numerous We’ve noticed numerous

paleosinkholes over paleosinkholes over Missouri in the middle of Missouri in the middle of similar rock cuts that now similar rock cuts that now sit at ~30 degrees and sit at ~30 degrees and are heavily vegetated. If are heavily vegetated. If excavation could be done excavation could be done cheap, cut it back to <30 cheap, cut it back to <30 degrees and vegetate it degrees and vegetate it

► As we went through this As we went through this exercise—even at the exercise—even at the very end—we continued very end—we continued to discover alternativesto discover alternatives There are numerous There are numerous

simple retaining wall simple retaining wall structures that might structures that might work just fine if all we work just fine if all we want to do is control rock, want to do is control rock, ravel, and roll.ravel, and roll.

Sheet piles, bin walls, etc.Sheet piles, bin walls, etc.

The next road cut down from Site E has a degraded paleosinkhole…

In reality…In reality…► The slope will probably sit The slope will probably sit

and ravel…and ravel…

Questions?Questions?