Micropiles and the FHWA Micropiles and the FHWA 30 Years of Implementation 30 Years of Implementation International Workshop on Micropiles International Workshop on Micropiles Schrobenhausen, Germany Schrobenhausen, Germany 6 May 2006 6 May 2006 Barry D. Siel, P.E. Barry D. Siel, P.E. Senior Geotechnical Engineer Senior Geotechnical Engineer FHWA-Resource Center FHWA-Resource Center
FHWA Micropile Projects FHWA Micropile Projects Mendocino Pass Slope Retention, 1978 Mendocino Pass Slope Retention, 1978 Linn Cove Viaduct, Blue Ridge Pkwy, 1980 Linn Cove Viaduct, Blue Ridge Pkwy, 1980 Marble Fork Bridge, Sequoia NP, 1992 Marble Fork Bridge, Sequoia NP, 1992 Chilnualna Bridge, Yosemite NP, 1994 Chilnualna Bridge, Yosemite NP, 1994 Foothills Parkway Bridge, 1998 Foothills Parkway Bridge, 1998 Madrone Lake Dam Crossing, 2000 Madrone Lake Dam Crossing, 2000 Going-to-the-Sun Guardwalls, 2002 Going-to-the-Sun Guardwalls, 2002 Deer Canyon Bridge, 2003 Deer Canyon Bridge, 2003 Gibbon Falls Retaining Wall, 2004 Gibbon Falls Retaining Wall, 2004
FHWA Micropile Projects FHWA Micropile Projects Examples include bridge pier and Examples include bridge pier and abutment foundations, slope retention, abutment foundations, slope retention, and retaining wall foundations and retaining wall foundations Our terminology has evolved from pali Our terminology has evolved from pali radice , to microshaft , to drilled shaft , to radice , to microshaft , to drilled shaft , to micropile micropile Let’s take a closer look Let’s take a closer look
Pali Radice Pali Radice Mendocino Pass, 1978 Mendocino Pass, 1978 – 721 127 mm piles, 15 to 24 m long – 721 127 mm piles, 15 to 24 m long – 8.25 piles per meter – 8.25 piles per meter – Wall designed for shear, piles in compression – Wall designed for shear, piles in compression – Slide in 1990s revealed wall, which still – Slide in 1990s revealed wall, which still performed well performed well
Linn Cove Viaduct Linn Cove Viaduct Deliver the Project ‘Top-down’ Deliver the Project ‘Top-down’ Limited exploration Limited exploration
Linn Cove Viaduct Linn Cove Viaduct Two uses for ‘Microshafts’ Two uses for ‘Microshafts’ – Pier foundations – Pier foundations – Sliding resistance – Sliding resistance
Linn Cove Viaduct Linn Cove Viaduct Load testing Load testing – Design load of 130 tons compression, 50 tons tension – Design load of 130 tons compression, 50 tons tension – Tested simultaneously to approx. 200% DL – Tested simultaneously to approx. 200% DL
Marble Fork Bridge, Sequoia NP Marble Fork Bridge, Sequoia NP Foundation retrofit when poor bearing conditions Foundation retrofit when poor bearing conditions encountered along two sides of the abutment encountered along two sides of the abutment
Chilnualna Bridge, Yosemite NP Chilnualna Bridge, Yosemite NP 15 years after Linn Cove 15 years after Linn Cove Follows Marble Fork Bridge, Follows Marble Fork Bridge, Sequoia NP Sequoia NP – Contractor design – Contractor design
Chilnualna Bridge, Yosemite NP Chilnualna Bridge, Yosemite NP Still calling them shafts Still calling them shafts 74 kips capacity 74 kips capacity Led to 20-inch Louis Led to 20-inch Louis Lake DH Hammer Spec. Lake DH Hammer Spec.
Foothills Parkway, GSMNP Foothills Parkway, GSMNP Late 1990s Late 1990s Similar to Linn Cove Similar to Linn Cove
Madrone Lake Dam Madrone Lake Dam New retaining wall on 75-year old, New retaining wall on 75-year old, marginally stable dam marginally stable dam
Madrone Lake Dam Madrone Lake Dam Battered piles Battered piles No testing No testing
Going to the Sun, Glacier NP Going to the Sun, Glacier NP Avalanche Resistant Wall Install micro-piles Form work Masonry work
Deer Canyon Bridge, California Deer Canyon Bridge, California Changed site conditions, bedrock lower than anticipated Boulders preclude drilled shafts Differential settlement preclude spread footing Change order design for micropiles
Gibbon Falls, Yellowstone NP Gibbon Falls, Yellowstone NP Historic wall stabilization Historic wall stabilization Extension of guardwall Extension of guardwall
FHWA Micropile Projects FHWA Micropile Projects FHWA – One of the pioneers of the technology FHWA – One of the pioneers of the technology Most every project an innovation Most every project an innovation Still not employed where they could be (?) Still not employed where they could be (?) – Frenchman Lake, Challone Creek, Foothills Parkway (?) – Frenchman Lake, Challone Creek, Foothills Parkway (?) Not yet routinely utilized and accepted technology Not yet routinely utilized and accepted technology – Seismic design – Seismic design – Quality assurance – Quality assurance It/ bring micropiles into the mainstream of FHWA It/ bring micropiles into the mainstream of FHWA practice practice
QUESTIONS? QUESTIONS? International Workshop on Micropiles International Workshop on Micropiles Schrobenhausen, Germany Schrobenhausen, Germany 6 May 2006 6 May 2006 Barry D. Siel, P.E. Barry D. Siel, P.E. Senior Geotechnical Engineer Senior Geotechnical Engineer FHWA-Resource Center FHWA-Resource Center
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