ky cable rail

Kentucky Cable Rail

Erik Scott, P.E.Kentucky Transportation Cabinet,

Geotechnical Branch

Outline:

I. General cable rail info/considerationsII. Overview of cable median barrier in KYIII. KY’s Geotechnical Investigation Process IV. Anchor & Post Foundation Design Overview

General Cable Barrier Info• Where?

– Locations picked based on traffic volume / crash history and potential.

– Mostly interstates/highways in urban areas• (increasing use in rural areas)

• Why Cable Barrier?– Lower Cost: $140K to $150K per mile in KY– Much less than W‐beam, concrete, box beam

General Cable Barrier Info• Why Cable Barrier?

– Increased Safety – Reduce severe crashes/fatalies

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

Total Crashes Disabling Crashes Fatal Crashes Fatal & Disabling Crashes

Median Cross‐over Crash Rates in Washington State3(Per 100 Million Vehicle Miles Traveled)

Before CableBarrier

After CableBarrier

Cable Median Barrier in Kentucky• KY cross‐over crashes in recent cable rail areas:

– McCracken‐Marshall project area: last 3.5 yrs, 27 cross‐over, 4 fatalities

– Christian Co project area: last 3.5 yrs, 25 cross‐over, 4 fatalies

Cable Median Barrier in Kentucky• 266 miles installed in Kentucky currently.• 3 Systems allowed in KY (all high tension):

– CASS – (Trinity)– GIBRALTOR CABLE BARRIER SYSTEM– WRSF (Brifen USA, Inc.)

Brifen USAhttp://www.brifenusa.com/

Trinity Highway Productshttp://www.highwayguardrail.com/products/cb.html Gibraltar Cable Barrier Systems, L.P.

http://gibraltartx.com/

Cable Median Barrier in Kentucky

• Components:– Retro‐Reflective

Sheeting– Line Post– Steel Cable– Concrete Mow

Strip– Anchor

Cable Median Barrier in Kentucky• Components – Line Posts:

– Spacing: 10.5’ on center– Plastic or metal sleeves in concrete foundation– Gasket to prevent debris entering post

Cable Median Barrier in KentuckyTypical Layout and Placement:

• Min. 8’ from edge of travel lane (9’ common)• Horizontal curves: generally adjacent to inside shoulder on

outside of curve

Reference (2)

Reference (2)


• Mow strip / trench– Facilitate Maintenance– Added Overturning Stability1

(Reference 4)


• Anchor Types– Typically use anchor blocks

• Anchor Locations– Bridges– U‐turn crossovers– Other end points

• Shield Anchors When Possible– Behind existing hardware (guardrail end treatments, bridge ends, etc.)

KY Geotechnical Investigations• Boring Plan

– Done after barrier and anchor location selection– Drill at anchor locations

• (previously drilled minimum of 1 per mile)– 8’ from edge of shoulder– Driller’s Notes:

• Granular or cohesive soil?• Cut or Fill?• Were boulders encountered?• Is area wet? Depth to water table (if present)?

KY Geotechnical Investigations• Drilling & Sampling

– Changes in sample type:

– Standard Penetration Test (SPT) @ depths of 2’, 7’, 12’ and 15’

– Maximum depth of 15’, or top of bedrock

1 Bag Sample continuous SPTs Current: 4 SPTs per hole(bag if < 6” recovery)

KY Geotechnical Investigations• Drilling & Sampling

– Expedited schedule is typical– Drilling Work often contracted (statewide contract); also use in‐house crews

– Information provided to Contractors in proposal prior to project letting

More subsurface info = Lower/more competitive bids

KY Geotechnical Investigations• Soil Testing

– AASHTO & USCS Classifications – Natural Moisture Content– Normally expedited– Done in‐house or with statewide contracts– Data provided before project letting, included in proposal if possible

KY Geotechnical Investigations

KY Geotechnical Investigations

• Karst Topography– No additional drilling specified currently– Sinkholes investigated/mitigated during roadway geotechnical investigation (consider review of prior geotechnical roadway investigation)

– But sinkholes could develop after construction – Possible additional note for boring plan: Direct driller to obtain soundings for sinkholes encountered, or suspected, near anchor locations.

Anchor / Line Post FoundationsAnchor Foundation Types:• Anchor blocks (common in KY)• Drilled shafts (common in other states)

– Typical 2’ diameter, 12’ depth (but designed site‐specific)

• Concrete driven piles• Driven piles / Helical piles

– Have been explored, but not economical

Anchor / Line Post Foundations• Anchor Blocks:

– Loading based on rope contraction in cold temps– Use minimum extreme temperature graph from previous year (Climate Predication Center)

(Reference 5)

Anchor / Line Post Foundations• Anchor Blocks:

– Cast in place concrete w/ No. 4 bar reinforcement– Typical size: 3.5’ wide X 3.5’ deep X 10‐12’ long– Designed to resist overturning (Safety Factor of 1.5)– Water table presence increases block size (due to using buoyant unit weight of concrete)

Anchor Load (tensioning & temperature effects)

Block weight

Passive Force (from cohesion)Passive Force (from unit weight)

d/3

d/2

Anchor / Line Post Foundations• Drilled Shafts for Line Posts:

– Check overturning (lateral capacity), Brom’s Method• Max. Lateral Deflection = 1”• Ignores axial load on pile (OK for this application)

– Check uplift (Alpha & Beta methods)– Water table presence may warrant switch to block foundation

Construction Issues / Notes• Past Issues Reported by Contractor

– Shaft system with strut connecting multiple shafts: rebar cage not extended to bottom of shaft, sheared at base of cage

– Shallow rock: when encountered for line post foundations, typically extend into rock ½ remaining required depth

– Saturated soils

Special Thanks To:Jim Wilkerson, XD Engineering, PLC

Sanford Vice, George B. Stone Co

Kentucky Transportation Cabinet Staff:

Kevin Martin, Div of Highway Design, Developmental Branch

Jason Wright, Div of Structural Design, Geotechnical Branch

Matthew Graves, Construction Section Supervisor, Owenton Office, District 6.

Kentucky Cable Rail

Any Questions?

Kentucky Cable RailReferences:

1.) D. Marzougui et. al. NCHRP Report 711. Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems. Transportation Research Board. Washington, D.C. 2012.asdf

2.) Scott A. Cooner, et al. Development of Guidelines for Cable Median Barrier Systems in Texas.Texas Transportation Institute, The Texas A&M University System. College Station, Texas. December 2009.

3.) M. H. Ray. Independent Expert Report, An Evaluation of WSDOT’s Cable Median Barrier Policy. Washington State Department of Transportation. Olympia, Washington. April 2007.

4.) Kentucky Transportation Cabinet, Department of Highways. Previous Construction Proposals [online]: http://transportation.ky.gov/Construction‐Procurement/Proposals/201‐CHRISTIAN‐MARSHALL‐MCCRACKEN‐141230.pdf (Christian‐Marshall‐McCracken Counties, I‐24, Cable Guardrail. Primary Completion 11‐15‐14. Link Accessed 10‐15‐14.

5.) National Weather Service, Climate Prediction Center – Regional Climate Maps [online]: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/us_12‐month_mint.shtml (Modified 2‐2‐14). Link Accessed 10‐14‐14.

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