Investigation and Repair of an Ethanol Plant Mat Foundation

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Investigation and Repair of an Ethanol Plant Mat
Foundation

• 2008 Structures Congress
• Vancouver, BC
• Daniel J. Larson
• American Engineering Testing, Inc.
• St. Paul, MN

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U.S. Ethanol Production

• Since 2000, 80 biorefineries put into production
• 77 new or expanded facilities planned
• 13,500 million gallons per year

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HISTORIC U.S. FUEL ETHANOL PRODUCTION
Millions of gallons
Source Renewable Fuels Association, January 2008
Estimated
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Grain Silo Facts

• 74 feet in diameter
• 150 feet tall
• Slip-form construction
• 33 inch thick mat foundation

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N
Plan Silo and Tunnel Structures
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Geotechnical Review

• Topsoil underlain by sandy lean clay
• Bedrock 15 to 18 feet below grade
• 7 to 9 feet of additional fill to attain planned
  subgrade elevation
• Two foundation options considered
• Deep foundation system
• Mat foundation

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Investigative Borings

• Five standard penetration test borings
• Variable fill density and moisture
• Nine cone penetration test soundings
• Correlated with borings
• Estimated additional settlement of 2 to 6 inches
  if no remediation

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Vertical Control Monitoring

• Eight vertical control points
• Weekly readings
• Up to 2 inches of settlement before remediation
• Crack gauges

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Structural Investigation

• Visual documentation
• Nondestructive evaluation
• Sounding
• Impulse radar
• Impact-echo
• Invasive testing and sampling
• 17 cores

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Cracking Around Boot Pit
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Mat Foundation
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Upper Transfer Tunnel Wall
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Findings

• Differential settlement between mat and boot pit
  foundations caused distress
• Additional settlement of 2 6 inches of mat
  foundation unacceptable
• Differential settlement could not be accommodated
  by current design

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Repair Program

• Stabilize mat foundation
• Compaction grouting
• Micropiles
• Restore integrity of mat foundation and tunnel
  structures in boot pit area
• Create allowance for differential movement
  between mat and boot pit

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Sequencing of Repairs

• Compaction grouting
• Monitoring of vertical movement during controlled
  filling of silos
• Structural repairs

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Compaction Grouting

• Six foot on center spacing
• 178 grout columns installed
• 2,840 lineal feet
• 350 cubic yards of grout

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Schematic of Compaction Grouting
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Structural Repairs

• Partial and full-depth replacement of mat
  foundation
• Reinforced overlay on tunnels walls and floors
• Soft joint between top of boot pit walls and mat
  foundation

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Post Repair Performance

• No recurrence of distress
• Silos routinely filled to near capacity
• Unbalanced loading
• Long term settlement of mat unknown

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Lessons Learned

• Interaction between structural elements with
  different bearing strata
• Caution when using deep fills for foundation
  support
• Cooperative effort avoided delays

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Investigation and Repair of an Ethanol Plant Mat
Foundation

• 2008 Structures Congress
• Vancouver, BC
• Questions?