The Natural Hazards of Drilled Shaft Construction on Herrington Lake Darrin Beckett, P.E. Kentucky Transportation Cabinet Division of Structural Design, Geotechnical Branch 17th Purdue Geotechnical Society Workshop April 26, 2019 West Lafayette, Indiana Photo Credit: Walsh Rev. 04/23/2019 Presentation Overview • How natural hazards impacted drilled shaft construction (March – June 2018) at Pier 1 of the new bridge over Herrington Lake in Kentucky, with some design considerations. • What Natural Hazards Affected this Project? • Consequences of Potential Dam Break (Design Considerations) • Deep Water & Rapid Variations in Lake Levels (Construction Impacts) • Karstic Features in Limestone Bedrock (Design & Construction Impacts) • These hazards made for an interesting & challenging project, although they do not rise to the level of earthquakes, hurricanes & meteorites! #1 - 2:00 Project Site West Lafayette About 160 Miles [258 km] Northwest of Louisville Herrington Lake About 75 Miles [121 km] Southeast of Louisville, Kentucky #2 - 2:30 Major Project Team Organizations Owner Design Consultant Geotechnical Consultant General & Drilled Shaft Contractor Kevin Buch, P.E. Walsh Project Manager BSCE from Purdue (December 2007) #3 – 3:00 Project Overview Bid Price ≈ $30M “This was the most technically challenging • Three Span Bridge bridge foundation we’ve ever worked on.” • Incidental Roadway Work Joel Halterman of Walsh • Remove Existing Structure at Ribbon Cutting on 12/21/2018 Presentation Focuses on Four Shafts at Pier 1 (≈ $10M or about 1/3 of bid) Near Vertical ≈ 1½ H:1V Rock Cliff Rock Slope #4- 3:30 Herrington Lake • Dam on the Dix River was constructed in the 1920’s to generate hydro-electric power and for flood mitigation • When constructed, Dix Dam was the largest rock fill dam in the world at ≈ 287 ft. [88 m] high • Lake & Dam owned by Kentucky Utilities (KU) • Deepest lake in KY - Max. Depth ≈ 249 ft. [76 m]; Avg. ≈ 78 ft. [24 m] • Approx. 35 miles [56 km] long & up to about 1200 ft. [366 m] wide Reference: Herrington Lake Conservation League (www.hlcl.org) #5 - 4:30 North End of Herrington Lake Kentucky Utilities (KU) Dix Dam E.W. Brown Generating Station • Hydro Electric ≈ 5 miles [8 km] • Coal downstream • Natural Gas • Solar Reference: www.lge-ku.com Contractor’s Lake Access & Staging Area Three ≈ 3 miles [5 km] Marinas & Docks downstream Bridge Construction Site #6- 5:00 Dix River Palisades Dix Dam Dix River Rainfall events can lead to quick & significant lake water level Kentucky River changes due to: ≈ 3 miles [5 km] • Relatively narrow lake downstream from dam • Steep underwater rock slopes • No overbank 03/26/2019 #7- 6:00 Pier 1 Geotechnical Conditions & Considerations • < 10 ft. [3 m] of Overburden • One exploration boring at each of the four shafts, w/ ≈ 90 to 100 ft. [27 to 30 m] of rock core • Bedrock consists of Dolomitic Limestone • Average Unconfined Compressive Strength ≈ 19,000 psi [131 MPa] • Voids/highly fractured zones above El. ≈ 523 ft. [159 m] ≈ 20 to 25 ft. [6.1 to 7.6 m] into bedrock • Rock socket imaging & cavity stabilization included in contract due to these karstic features • Bedrock above El. 523 ft. [159 m] neglected for design • ≈ 40 ft. [12 m] long, 8.0 ft. [2.4 m] dia. rock sockets w/ ≈ 15 ft. [4.6 m] long “design rock sockets” #8 - 7:00 Pier 1 Construction Tolerances: water ≈ 170 ft. [52 m] & 185 ft. [56 m] deep • Within 6 inches [150 mm] of plan at “winter & summer pools” respectively position both at top of shaft & top of rock socket • Vertical alignment of the rock sockets within 2% slope ≈ 60 ft. [18 m] intermediate braces ≈ 60 ft. [18 m] for stiffness ≈ 180 ft. [55 m] tall at approx. 1/3 points 8.5 ft. [2.6 m] dia. cased sections ≈ 60 ft. [18 m] ≈ 40 ft. [12 m] long ≈ 15 ft. [4.6 m] long 8.0 ft. [2.4 m] dia. 8.0 ft. [2.4 m] dia. rock sockets “design” rock sockets #9 – 8:00 How Would a Dam Break Affect the Bridge? • Water velocity forces resulting from ≈ 287 ft. [88 m] rapid lake draining were considered but found to be insignificant due to the ≈ 5 miles [8 km] distance from dam. • In final design, wind loads were applied over the entire height of Pier 1 to evaluate the drained-lake condition. Photo Credit: Herrington Lake Conservation League (www.hlcl.org) #10- 8:30 Project Site in October 2017 New Bridge Alignment • Original bridge built in 1920’s before lake was impounded. • Closed in March 2018 due to structural deficiencies. 10/09/2017 #11 – 9:00 Barge Anchoring System & Ground Prep anchors drilled into rock cliffs * Contractor’s Means & Methods Plan View anchor cables (min. 20 ft. [6 m] below water surface) clam shelled overburden & chiseled bedrock to relatively level surface * Contractor’s at ≈ Elev. 546 ft. [166 m] Means & Methods (verified using sonar) Elevation View #12 - 9:30 Casing Assembly and Lowering Sequence Subsequently, unit was lowered, upper brace constructed, & top ≈ 60 ft. [18 m] of casings spliced. ≈ 60 ft. [18 m] of Lower Intermediate Casings Spliced Concrete Brace Above Brace Constructed Above Water ≈ 60 ft. [18 m] of Casings Below Brace * Contractor’s Means & Methods 11/29/2017 #13 - 10:30 Casing Assembly and Lowering Sequence slack in cables monitored & adjusted as water levels changed Poured ≈ 5 ft. [1.5 m] thick tremie seal & lowered casings to bedrock surface relatively level through plastic concrete. rock surface * Contractor’s Means & Methods #14 - 11:00 2018 (January – September) Herrington Lake Water Levels Significant Schedule 2018 Wettest Year on Record in & Logistical Lexington, KY: 72 inches (1830 mm) Impacts Source: National Weather Service >30 ft. [9 m] Variation “Summer Pool” Elev. ≈ 738 ft. [225 m] Rose up to ≈ 1.5 ft./hr. [0.5 m/hr.] “Winter Pool” Elev. ≈ 725 ft. [221 m] Pier 1 Foundation Construction Activities 03/16/18 - 06/07/18 #15 - 12:30 Drilling Equipment Casing Mounted Drill Rig Reverse Circulation Rock Roller Bit 06/14/2018 05/15/2018 #16- 13:00 Sonar Calipering Imaging to Evaluate Cavities Approx. Bottom What could go wrong during a of Casing & Top shaft pour in a socket like this? of Bedrock • Clay & gravel from cavities could Karstic features fall into the socket & contaminate (clay- & gravel-filled concrete voids) measured up to ≈ 18 in. [460 mm] • Concrete loss in cavities beyond nominal socket wall • Potential of a “blowout” due to cavities near top of socket & concrete head up to ≈180 ft. [55 m] ≈ Elev. 523 ft. [159 m] ≈ 40 ft. [12 m] • Slow concrete loss or blowout Rock Socket could result in the need to stop a w/ ≈ 15 ft. [4.6 m] pour and leave a “cold joint” Design Socket #17 - 14:00 Consequences of a Cold Joint Post-Stabilized Socket • Leaves a plane of weakness. • Latency (formed at the top of concrete in an underwater tremie pour) would not rise to the surface for disposal. • Any attempt to repair a cold joint at water depths on the order of 200 ft. [60 m] would have been very expensive and posed significant safety risks. Cavity Stabilization Method: Pour unreinforced concrete in the rock socket & re-drill it. #18 - 15:00 Bridge Profile with As-Built Sonar Scan #19- 15:30 Bridge Opened to Traffic December 21, 2018 11 Months Ahead of Schedule in Spite of High Water Delays 03/26/2019 #20- 16:00 Thank You 03/26/2019 .