BRIDGE FOUNDATION DESIGN. Local Agency Workshop February, 2009 Jan Six, P.E. Sr. Geotechnical Engineer ODOT Bridge Engineering Section. ODOT FOUNDATION DESIGN. Standards Foundation Design Process Foundation Reports Plans & Specifications Construction Assistance. Standards.
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Local Agency Workshop
Jan Six, P.E.
Sr. Geotechnical Engineer
ODOT Bridge Engineering Section
Standards Foundation Design Process Foundation Reports Plans & Specifications Construction Assistance
ODOT Geotechnical Design Manual (GDM) (available from ODOT Geo-Environmental web site)AASHTO LRFD Bridge Design SpecificationsODOT Bridge Design & Drafting Manual ODOT Standard SpecificationsFHWA Design Manuals (Geotechnical Circulars)
To determine the bridge foundation system that will result in the most cost effective bridge design, taking into account all the appropriate foundation design and construction considerations.
Scoping & Field Reconnaissance Field Explorations Laboratory Testing Foundation Design Foundation Reports Specifications Construction Support
Scoping and Field Reconnaissance
Identify Foundation Design Elements of Project New Bridge Foundations Bridge Widening Retaining Walls Culverts Conduct Office Data Research Old Foundation Data on Existing Structure Pile Record Books Maintenance Records
Observe Site Conditions affecting Exploration, Design and/or Construction Surface Conditions/ Obstructions (logs, riprap) Wetland Areas, R/W or other access restrictions Bridge Condition (settlement, corrosion) Scour or stream bank erosion Utilities (buried & overhead) Slope instabilities (slides, settlement, water problems) Locate Exploration Holes (test pits)
Typically done by contract drillers under contract to ODOTObtain Preliminary Bent LocationsTypically Locate Drill Holes at all Bridge Bents (per AASHTO)Identify Permits of Entry and Environmental ClearancesUtility Locations & Notifications
Standard Penetration Resistance Test (SPT ‘N’ value)Undisturbed Samples (Laboratory Testing)Rock Core Drilling (Rock hardness, RQD)Special In-Situ Tests (Cone Penetrometer, Pressuremeter)
Standard Penetration Resistance Test 140lb. hammer, 30” drop #blows/6” increment SPT ‘N’ value = #blows/last 12”
Undisturbed Sample (Shelby Tube)
Amount depends on the soils and project designPurpose of obtaining engineering properties of soils and rock materials for use in designTypical Lab Tests: Shear Strength of Soils Unconfined Compressive Strength (rock) Consolidation Tests (settlement) Unit Weight & Index Tests
Construct Subsurface Profile Stratigraphy & Geologic Model Groundwater Conditions Engineering Design Parameters Foundation TypeSeismic Analysis
Seismic Analysis (Earthquake Design)Two Level DesignSeismic design is evaluated in terms of the overall bridge performance using the 500 yr. & 1000 yr. mean return period earthquakes. Bridge performance must meet “Serviceability” criteria for 500 year event and Life Safety criteria (no collapse) for 1000 yr event.
Seismic Analysis (cont.) Ground Acceleration (PGA) 2002 USGS Maps Site Specific Analysis (optional) Liquefaction Analysis Lateral Spread, Slope Instability Approach Fill Settlement Bridge Damage Potential Mitigation Measures
Foundation type depends on combinations of: Foundation Materials & Conditions Structure Type & Loads Performance Criteria Site Conditions/Construction Constraints Extreme Event Effects Seismic Loads (Liquefaction Potential) Scour Depths Costs & Construction Time
Other Project Considerations: In-Water Work Periods Environmental Restrictions Noise or Vibration Constraints Construction Access/Traffic Control
Shallow Foundations Spread Footings (on engineered fill) MSE Abutment Wall w/ Spread FootingDeep Foundations Driven Piles Drilled Shafts Micropiles
Types of Foundations
Pile Design Bearing Resistance (compression and tension) Lateral Resistance Settlement and Downdrag Analysis Corrosion Potential/Protection Tip Protection Pile Drivability (construction) Group Settlement, Group Effects
Drilled Shafts High bearing resistance High lateral resistance Cost-effective in river environments Can be socketed into bedrock Potential construction issues Hole stability (caving, groundwater) Difficulty with drilling obstructions Need very good subsurface data Need good experienced contractors
Micropiles Small diameter, drilled-in-place piles Rarely used Relatively expensive Applicable for: low overhead clearance boulders in foundation soils underpinning projects
Project description (scope & purpose) Office research & summary of pertinent records relating to foundation design and construction. Description of the geologic setting Summary of hydraulics information affecting foundation recommendations Subsurface explorations and conditions Boring logs Groundwater conditions Special field testing Laboratory test results
Seismic Analysis & Recommendations 500 yr. and 1000 yr. event analysis Peak Ground Acceleration (PGA), Sa & S1 AASHTO soil site class and response spectra Liquefaction Assessment Extent of Liquefaction & Potential Impacts Lateral Spread Potential Reduced Foundation Capacities Settlement, Downdrag Potential Liquefied Soil Parameters for Bridge Analysis Mitigation Recommendations Site Specific Analysis & Response Spectra (optional)
Spread Footings Recommended Footing Elevation(s) Nominal Bearing Resistance Factored Bearing Resistance (Allowable Bearing Capacity) Nominal bearing resistance for service limit state (settlement)Description and properties of the anticipated foundation material
Pile FoundationsType (Pipe Pile, H-pile, Concrete or Timber) Size or Dimensions (O.D., wall thickness, etc.) Material Specification (e.g., ASTM spec & grade of steel), Tip Treatment (PP open or closed-end, reinforcement) Nominal Bearing Resistances, estimated tip elevation for bearing estimated cutoff elevation, “estimated” or “order” lengths Minimum Required Tip Elevation (reason for req’d. tip elev.) Resistance Factors (f factor) and Factored Resistances Nominal (Ultimate) Uplift Capacities Soil Parameters for Lateral Load Analysis Pile Group Settlement
Pile Foundations (continued) Downdrag Effects (reduced capacities or mitigation) Liquefaction Effects: reduced pile capacities (axial, uplift, lateral, etc) Pile Drivability Analysis Wave Equation Parameters (for special provisions/contractors)
Drilled ShaftsShaft Type (i.e., end-bearing, friction or both) Nominal Resistance for various diameters and lengths Estimated Shaft Settlement vs. Shaft Diameter and Load Factored Resistance and Resistance Factors Soil Parameters for Lateral Load Analysis Liquefaction Effects: reduced shaft capacities (axial, uplift, lateral, etc) Load Test recommendations (if appropriate)
Construction & Specification Recommendations Pile Foundations Pile Driving Criteria Wave Equation Input Criteria (if applicable) Number of Pile Splices Is Set Period (freeze) acceptable? Is Preboring or Jetting acceptable? Effects of driving on adjacent structures Potential Driving Obstructions (e.g., boulders, existing piles, utilities) been identified?
Construction & Specification Recommendations Drilled Shafts End bearing or friction shaft designation Temporary or Permanent casing recommendations Groundwater conditions Boulders and/or obstructions expected to be encountered Cross Hole Sonic Logging (CSL) Quality Control
Structural Defect Produced by Interruption in Concreting and Low Slump Concrete
Construction & Specification RecommendationsOther Foundation Recommendations Detour Bridge Recommendations Falsework Support Falsework foundation type recommendations Foundation Excavations Groundwater conditions & possible mitigation Shoring and Bracing Cofferdams Unique Special Provisions Specific Geotechnical/Geologic information
Foundation Data Sheet (part of bridge plans) Locations all explorations (borings, test pits, hand augers, etc.) Explorations plotted in elevation view Subsurface conditions depicted with soil and rock unit descriptions SPT (“N” values), Undisturbed Samples Highest measured groundwater levels and the date measured Percent rock core recovery and rock hardness.
Distributed To: Structural Designer(s) Specification Writer Project Manager’s Office (inspector) Project Team Leader Region Geo-Office HQ Bridge Engineering Office FHWA (for large projects)
Plans ReviewPile type, size and grade Drilled Shaft size, tip elevations, min. rock socket depth Nominal Resistances Resistance Factors Pile Driving Criteria Required Pile Tip Elevation Pile Tip treatment Splicing Detail Footings: Nominal Resistance Maximum Footing Elevation
SpecificationsPiling (Section 520)Estimated Pile Lengths (steel piles) Number of Pile Splices Tip Treatment (open or closed end, reinforcement) Driving Criteria Wave Equation Input (if applicable) Pile freeze, preboring or jetting allowed
Specifications Shafts (Section 512)Designated Friction or End Bearing Permanent Casing Requirements Crosshole Sonic Log (CSL) testing required
Pile Hammer & Equipment Review & Approval Pile Driving Criteria (inspectors graph) Pile Driving Problem Solving Pile Record Books Drilled Shaft Installation Plan Drilled Shaft Construction Forms Review of CSL test results Materials Substitutions Foundation Inspection Assistance Claims Resolution