Chapter 8 Spread Footings Synthesis
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Transcript of Chapter 8 Spread Footings Synthesis
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Priyantha Jayawickrama, Ph.D.Associate ProfessorChapter 8:Shallow Foundations-SynthesisTexas Tech UniversityDepartment of Civil and Environmental Engineering
CE 4321: Geotechnical Engineering Design
Spread Footings-Geotechnical Design8.1 Design for Concentric Downward Loads8.2 Design for Eccentric or Moment Loads8.3 Design for Shear Loads8.4 Design for Wind or Seismic Loads8.5 Lightly Loaded Footings8.6 Footing on or Near Slopes8.7 Footings on Frozen Soils8.8 Footings on Soils Prone to Scour8.9 Footings on Rock
CE 4321: Geotechnical Engineering Design
Design for Concentric Downward LoadsAllowable Bearing Pressure MethodDesign Chart Method
CE 4321: Geotechnical Engineering Design
Foundation Depth
CE 4321: Geotechnical Engineering Design
Minimum DepthSquare & Rectangular Footings
CE 4321: Geotechnical Engineering Design
Minimum Depth-Continuous Footings
CE 4321: Geotechnical Engineering Design
Other Considerations; Minimum DepthDepth to competent soilDepth of frost penetration (Figure 8.15)Presence of expansive soilsPotential for scourPossibility of a shallow landslide
CE 4321: Geotechnical Engineering Design
Considerations; Maximum DepthPotential undermining existing foundations, utility lines etc.Desire to avoid ground water tableDesire to avoid the need for excavation shoring
CE 4321: Geotechnical Engineering Design
Allowable Bearing Pressure MethodAllowable bearing pressure, qa is the largest bearing pressure that satisfies both bearing capacity and settlement criteria.Select depth of embedment, DDetermine the allowable bearing pressure based on bearing capacity analysis using the smallest applied load
CE 4321: Geotechnical Engineering Design
Allowable Bearing Pressure MethodDetermine the allowable bearing pressure based on settlement analysis using the largest applied loadSelect qa as the lower value of the two allowable bearing pressures.
CE 4321: Geotechnical Engineering Design
Example 8.1
CE 4321: Geotechnical Engineering Design
Example 8.1A site for a new parking garage; an urban re-development projectColumn loads range from 250k to 900k a = 1.0 inches and Da = 0.6 inchesSite was occupied with old commercial buildingsOld buildings were demolished and their basements backfilled with SW, sandy silt, silty sands
CE 4321: Geotechnical Engineering Design
Example 8.1A series of five exploratory boringsGWT at depth of 200 ftUpper 10ft excavated and recompacted to provide uniform supportEstimated OCR = 3 and N60 = 60C= 0 and =35
CE 4321: Geotechnical Engineering Design
CE 4321: Geotechnical Engineering Design
Example 8.1
CE 4321: Geotechnical Engineering Design
CE 4321: Geotechnical Engineering Design
CE 4321: Geotechnical Engineering Design
CE 4321: Geotechnical Engineering Design
Design Chart Method
