Use of Launched Soil Nails toStabilize Landslides in Summit County, Ohio
Use of Launched Soil Nails toUse of Launched Soil Nails toStabilize Landslides in Stabilize Landslides in Summit County, OhioSummit County, Ohio
Mitchell W. Weber, P.G.Mitchell W. Weber, P.G.Gannett Fleming Engineers & Architects, P.C.Gannett Fleming Engineers & Architects, P.C.
Greg Bachman, P.E., P.S.Greg Bachman, P.E., P.S.County of Summit EngineerCounty of Summit Engineer
Robert K. BarrettRobert K. BarrettSoil Nail Launcher, Inc.Soil Nail Launcher, Inc.
Geologic SettingGeologic SettingNW part of Summit County lies NW part of Summit County lies within the Glaciated Allegheny within the Glaciated Allegheny Plateau.Plateau.–– Uplands and many slopes composed Uplands and many slopes composed
of End or Ground Moraine. of End or Ground Moraine. 33% Sand, 34% Silt, 32% Clay33% Sand, 34% Silt, 32% Clay
–– Cuyahoga River valley and base of Cuyahoga River valley and base of slopes composed of glacialslopes composed of glacial--lacustrine lacustrine deposits.deposits.
0% Sand, 39% Silt, 60% Clay0% Sand, 39% Silt, 60% Clay
Typical Slide CharacteristicsTypical Slide Characteristics
Glacial Till(SM-SC)
Glacial-Lacustrine(ML-CL)
21
± 46 ft.
10 – 12 ft.
OBSERVED SLIDE TYPES
• Earth Slumps
• Earth Flows
• Earth Block Slides
Slide TriggersSlide Triggers
Increased Driving Forces (IDF)Increased Driving Forces (IDF)–– Saturation. (Saturation. (above average rainfall in 2003 & 2004above average rainfall in 2003 & 2004))–– Toe undercutting by stream erosion.Toe undercutting by stream erosion.–– Lateral Lateral ‘‘squeezesqueeze’’ of basal lake deposit.of basal lake deposit.
Decreased Resisting Forces (DRF)Decreased Resisting Forces (DRF)–– Softening of basal clay through desiccation and Softening of basal clay through desiccation and
wetting cycles.wetting cycles.
Rain, Rain, Go AwayRain, Rain, Go Away……
The Memorial Day (2004) weekend rains triggered The Memorial Day (2004) weekend rains triggered several landslides within the County, two resulted several landslides within the County, two resulted in immediate road or lane closures.in immediate road or lane closures.By June 2004, Summit County had 9 slides that By June 2004, Summit County had 9 slides that required required ““immediateimmediate”” attentionattentionCounty forces were occupied with other storm County forces were occupied with other storm damage clean up.damage clean up.County Engineer sought a County Engineer sought a ““good, fast, cheapgood, fast, cheap””solution. solution.
Selection of Launched Soil NailsSelection of Launched Soil NailsIn consultation with GF and SNL, nine In consultation with GF and SNL, nine ““emergencyemergency”” landslides site were selected landslides site were selected for remediation with launched soil nails.for remediation with launched soil nails.
Soil NailingSoil Nailing
Consists of reinforcing the ground with closely Consists of reinforcing the ground with closely spaced, passive inclusions (nails), to create inspaced, passive inclusions (nails), to create in--situ situ a coherent gravity structure which results in an a coherent gravity structure which results in an increase of the overall shear strength of the inincrease of the overall shear strength of the in--situ situ soil. soil. Basic design concept Basic design concept -- transfer the resisting transfer the resisting tensile forces generated in the nails into the tensile forces generated in the nails into the ground through the friction mobilized at the ground through the friction mobilized at the interfaces. interfaces.
Ref: FHwA –SA-96-069R
Soil NailsSoil NailsNails typically consist of :Nails typically consist of :–– Steel bars or other metallic elements that Steel bars or other metallic elements that
resist tensile & shear stresses and bending resist tensile & shear stresses and bending moments. moments.
–– Soil nails are not prestressed but are closely Soil nails are not prestressed but are closely spaced (e.g., one driven nail per 2.5 ftspaced (e.g., one driven nail per 2.5 ft²², one , one grouted nail per 10grouted nail per 10--50 ft50 ft²²) to provide an ) to provide an anisotropic apparent cohesion to the native anisotropic apparent cohesion to the native ground. ground.
Ref: FHwA –SA-96-069R
Suitable Ground ConditionsSuitable Ground Conditions
Favorable ConditionsFavorable Conditions–– Clays Clays –– Sandy soilsSandy soils–– Weathered rock; talus slope depositsWeathered rock; talus slope deposits–– Heterogeneous and stratified soils Heterogeneous and stratified soils
Soil nailing is generally not practical in: Soil nailing is generally not practical in: –– Soft, plastic claysSoft, plastic clays–– Organics/PeatOrganics/Peat–– Loose (N<10), low density and/or saturated soils Loose (N<10), low density and/or saturated soils
Launched Nail AdvantagesLaunched Nail Advantages
EffectiveEffective–– IncreasesIncreases shear resistance while shear resistance while decreasingdecreasing
shear stresses.shear stresses.Unobtrusive Unobtrusive –– Equipment can reach Equipment can reach ±± 20 20 -- 25 feet downslope.25 feet downslope.–– Articulating head facilitates working around Articulating head facilitates working around
trees and utility poles.trees and utility poles.–– Usually only shoulder or single lane closure Usually only shoulder or single lane closure
required.required.
Launched Nail AdvantagesLaunched Nail Advantages
Fast InstallationFast Installation–– 10 nails/hour, 100 nails/day.10 nails/hour, 100 nails/day.Immediate ResultsImmediate Results–– No waiting for grout set.No waiting for grout set.Single Process with small crew Single Process with small crew –– Performed by a laborer and a operator.Performed by a laborer and a operator.CostCost--effectiveeffective–– Average range of $200 $400/lf of crown length.Average range of $200 $400/lf of crown length.
Launched Soil NailsLaunched Soil Nails
Soil Reinforcing Elements Soil Reinforcing Elements –– 11--inch diameter, hollow steel tubes.inch diameter, hollow steel tubes.–– 2020--foot long.foot long.–– Perforated for drainage.Perforated for drainage.Installed by a Proprietary LauncherInstalled by a Proprietary Launcher–– Launcher mounted on an excavator.Launcher mounted on an excavator.–– Has 360Has 360ºº mobility.mobility.
Typical Launched Soil Nail Typical Launched Soil Nail Application Application
Slide Mass
Failure Surface
Launched Soil Nails3 or 4-foot c-c
2-3 rows
Typical Launched Soil Nail Typical Launched Soil Nail Application Application
Slide Mass
Failure Surface
Launched Soil Nails3 or 4-foot c-c
2-3 rows
Summit CountySummit County’’ssLaunched Soil Nail StatisticsLaunched Soil Nail Statistics
11 sites have been nailed, repairing 1,000 lf 11 sites have been nailed, repairing 1,000 lf of roadway .of roadway .About 1,200 launched soil nails installed in About 1,200 launched soil nails installed in less than a 4 week time frame.less than a 4 week time frame.Cost of Cost of ±± $480,000.$480,000.County crews monitor repaired sites on County crews monitor repaired sites on monthly schedule, no renewed movement to monthly schedule, no renewed movement to date.date.
Design ResourcesDesign Resources
FHwAFHwA--SASA--9696--069R069RUSFS EMUSFS EM--71707170--13, Volumes I 13, Volumes I –– III.III.