Dirt and Steel - UMN CCAPS · Dirt and Steel: The Case for Collaboration between ... •...
Transcript of Dirt and Steel - UMN CCAPS · Dirt and Steel: The Case for Collaboration between ... •...
Dirt and Steel:The Case for Collaboration between
Geotechnical and Structural Engineers
Minnesota Power Systems ConferenceNovember 9, 2016
Marlon W. Vogt, PE, MASCE. F.SEI
Heroic Engineering?
The Big IdeaThere is project value when geotechnical and
structural engineers collaborate
Scope and Planning
Design
Construction
The Plan
OwnerEngineer
Contractor
The Project Team
Geotechnical AND Structural?
Scope and Planning
The Project Kickoff
Detailed Sharing
• Project Description• Site Plan• Schedule
• Milestones• Deadlines
• Safety
Soil is VariableRock Fill
Contamination
Groundwater
Granular Cohesive
Slope InstabilityWeak Layers
Expansive
Anticipate and Prepare
Historical Data
Desktop Study
Electrical ClearancesUnderground Facilities
Safety
Important for Utilities
Structures, Foundations, Loads
All Are Relevant to the Geotech
Early in the ProcessA Few Common Systems
Different Load MagnitudesInterrelated Systems
Tangent Structures
Often Directly Embedded
Typical LoadsAxial – 20kShear – 25k
Moment – 1500ft-k
Guyed Angle StructuresMedium or Two-Way Deadend
Bisector GuysGuyed Each Direction
Embedded or Piers
Typical LoadsAxial – 140kShear – 3k
Moment – 200ft-kAnchor tension – 40k
Self-supporting Structures
Medium Angle or Two-Way DeadendPartial or No Guying
Typical LoadsAxial – 35k
Shear – 125kMoment – 7000ft-k
Spread Footings
Primarily Vertical LoadsTransmission and Substation
Match Geotech Approach to Structures and Foundations
Soil Sampling and Testing
Geotechs Can Provide Value for these Decisions
Match to Structures and Loads Cohesive/Non-cohesive/Rock/Swamp, etc.
Consolidation - SettlementCoordinate with Foundation Design Methodology
Holes – Field Investigation
Geotechs Can Provide Value for this Decision
One per Soil TypeOne per Mile for Transmission
One per StructureDepth - Sampling - Testing
Cost-driven Soil Investigations
This Can Have $$$$ Implications
Design
Capacity vs. PerformanceCapacity
Performance
• Based on largest applied loads• Designed to prevent failure
• Designed to perform well
Capacity = Performance
Deflection vs. Rotation
• Pole top deflection limits• Foundation deflection• Foundation rotation
Which is More Critical?
Pole Top Deflection
• Sag• Tension
• Clearances
Important Limitation
Pole Top Deflection Example
Rotation >>> Deflection
• 100 ft. pole• 3 inch top of foundation deflection• 1 degree top of foundation rotation
Pole Top Displacement (Deflection) = Foundation Deflection = 3 inches
Pole Top Displacement (Rotation) = 1.75 ft = 21 inches
Total pole tip displacement (deflection and rotation) = 3in + 21in = 24 in
Foundation Design Options
Appropriate Soil Properties
Direct Embed Design Options
Get Soil Tests to Match
• Brom’s (cohesionless and cohesive)• Hansen’s Method
• MFAD
Guy Anchors
Accurate Soil Classification
Design Guidance by Manufacturers
Spread Footings
ACI Standards
More Common Foundation Design Methodologies
General Design Comments
Get Soil Tests to Match
• Non-utility Soil Parameters• Coordinate Safety Factors
• Total vs. Differential Settlement• Axial Capacity• Skin Friction
Construction
Contractor on Team
Biggest Friend or Toughest Foe
Construction Issues
Geotechs Can Contribute Solutions!
• QA/QC• Equipment Recommendations
• Groundwater• Surprise Soil Characteristics
• Slope Instability• Bedrock
C’mon Man!
Pole with the Wobbles
Upon Further Review
Throw the Flag!
Searching for Answers
Damage Assessment
Missing Pieces
This is Not Supposed to Happen
Geotechnical Engineers – Structural EngineersA Valuable Partnership