Foundation Design and Construction for our Structural ...

1 Technical Excellence Practical Experience Client Responsiveness Foundation Design and Construction for our Structural Brethren Deep Foundation Design Basic Cookbook A Presentation on Special Foundation Topics to the Delaware Valley Association of Structural Engineers 4 February 2015 Technical Excellence Practical Experience Client Responsiveness Today s Presenters Marc Gallagher, , LEEDAP Michael Fritzges, Senior Principal New York Office Project Engineer Philadelphia Office Technical Excellence Practical Experience Client Responsiveness Today s Topics Deep foundations Driven Piles Types Benefits - Disadvantages Costs Equipment Drilled Piles Types Benefits - Disadvantages Costs Equipment Technical Excellence Practical Experience Client Responsiveness Deep foundations Introduction When do we use deep foundations ?

2 However, we can save 700 lira by not doing I don t think we need piles Technical Excellence Practical Experience Client Responsiveness Deep foundations Introduction When do we use deep foundations ? Soft soils such as marsh/wetlands Poor fill in a loose condition Liquefiable soils High groundwater Contamination Very high Foundation loads High loads in limited footprint Sensitive adjacent structures (subways) Reduce settlement Technical Excellence Practical Experience Client Responsiveness Types of Deep foundations Driven Piles Driven into the ground with impact hammer Drilled Elements Drilled hole filled with concrete/grout/steel Other Helical piles Rammed piers Technical Excellence Practical Experience Client Responsiveness Driven Piles basics Design theory Installation requirements Equipment Problems in Construction Technical Excellence Practical Experience Client Responsiveness Driven Piles - basics Pile driving has been around for 1000 s of years Pile hammer imparts energy to the pile to drive into the ground Driving into harder material requires more energy More energy

3 Into the pile yields higher capacity Technical Excellence Practical Experience Client Responsiveness Technical Excellence Practical Experience Client Responsiveness Driven Piles - basics Advantages Relatively inexpensive $75-$100/ft for steel/concrete $25-$35/ft for timber Numerous contractors Material readily available Equipment fairly standard Equipment fairly low-tech Technical Excellence Practical Experience Client Responsiveness Driven Piles - basics Disadvantages Practically limited to about 250 to 300 tons with the exception of very large marine applications Vibrations Noise Obstructions Technical Excellence Practical Experience Client Responsiveness Driven Piles - basics Timber H-Pile Pipe Pile Taper Piles Precast Concrete Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory End bearing Side friction Combination Factor of Safety Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory tipsideultRRQ FSQQ ultallow Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory End bearing SPT (limited to 40N)

4 Bearing Capacity tiptiptipAqR* qfctipNDcNBNq 21 BLNqbtip**4 Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory Sand C=0 Limited to Df = 10 to 20 * Diameter Clay Last term ~ 0 Nc = 9 qfctipNDcNBNq 21 Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory Side friction Sand Normal force & friction coefficient Clay Depends on the cohesion or Su (undrained shear strength) frictionadhesionfside perimetersidesAfR* Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory fs for cohesive reduces to first term fs for cohesionless reduces to second term tan*'verticalsAskcf Ca = Adhesion factor relating cohesion to friction along shaft ks = coefficient of lateral earth pressure (generally 1 to 2) Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory Sand Rule of Thumb #1 a 12 pile in dense sand will give about 1 ton allowable capacity per foot of embedment perimeterhorizontaltipqfultAANDQ)tan*()

5 ( Technical Excellence Practical Experience Client Responsiveness Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory Clay Rule of Thumb #2 Call a geotech for piles in clay perimeterAtipultAcAcQ**9 Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory Load Transfer Load shed into soil along shaft and at tip Side friction starts with little displacement End bearing requires significant displacement but can be up to 50% or more of capacity, even for friction piles Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory Group effects Acts more like a block than n individual piles Reduced capacity Pgroup Psingle * n Both axial and lateral Increased settlement Sgroup > Ssingle Technical Excellence Practical Experience Client Responsiveness Driven Piles Design Theory Factor of Safety on a Design is directly related to field verification program.)

6 Technical Excellence Practical Experience Client Responsiveness Driven Piles Installation Requirements Driven to a resistance Called the pile set Referenced as Blows per inch or foot Technical Excellence Practical Experience Client Responsiveness Driven Piles Installation Requirements ENR Formula Empirical based on 100 years of pile driving experience Input hammer energy (weight * drop) Output required resistance or set (s) **2 SHeightWeightQDropHammerallowTechnical Excellence Practical Experience Client Responsiveness Driven Piles Installation Requirements Wave Equation Analysis WEAP Computer analysis based on elastic (spring) theories Input hammer type, pile type, soil properties Output a graph showing capacity v blow count Indicates estimated pile stresses CRITICAL FOR CONTRACTOR!

7 Technical Excellence Practical Experience Client Responsiveness Technical Excellence Practical Experience Client Responsiveness Driven Piles - Equipment Pile driving rig Base unit is usually a crane Leads hold the pile and hammer Fixed Hanging Hammer Technical Excellence Practical Experience Client Responsiveness Driven Piles - Equipment Technical Excellence Practical Experience Client Responsiveness Driven Piles - Equipment Technical Excellence Practical Experience Client Responsiveness Driven Piles - Equipment Technical Excellence Practical Experience Client Responsiveness Hammer Types Gravity Steam Diesel Hydraulic Single Acting Double Acting Driven Piles - Equipment Technical Excellence Practical Experience Client Responsiveness Driven Piles Installation Problems Technical Excellence Practical Experience Client Responsiveness Driven Piles Installation Problems Vibrations Obstructions (any) Sweep (pipe, tapered, H) Dog leg (pipe, tapered, H) Crumple (end bearing steel) Rupture (pipe, tapered) Breaks (timber, concrete) Yields (steel) Tension cracking (concrete)

8 Technical Excellence Practical Experience Client Responsiveness Drilled Piles basics Design theory Installation requirements Equipment Problems during Construction Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Pile is drilled into the ground not driven Very large diameter and very high capacities possible essentially unlimited Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Advantages No vibrations Limited noise Can penetrate obstructions Small rigs, limited access/headroom Disadvantages Relatively expensive Micro-pile $200-$400/ft Auger Cast $100-$200/ft Drilled Shaft/Caissons $500-$2,500/ft Limited contractors Materials can be limited Equipment is highly specialized Equipment often high-tech Can be required to carry unskilled union contingent (operator, mechanic, etc) who are not familiar with drilling Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Micropiles Auger cast piles Drilled shafts Caissons Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Micro-piles (mini-caissons)

9 50 to 500 tons 5 to 14 inches Casing, grout and reinforcement Drill with fluid to flush cuttings Pressurized in soil Soil or rock socket Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Drilled shafts 500 to 5,000 tons+ Very large diameters, up to 12 feet have been drilled Very high capacity Can be belled at the bottom Drilled with slurry to support hole Installed with casing Temporary or Permanent Difficult in glacial and fill areas Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Drilled shafts Technical Excellence Practical Experience Client Responsiveness Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Caissons Really a drilled shaft into rock Large diameters Extremely high capacity-10,000 tons highest to date?

10 Casing and/or slurry for support Rock socket used for capacity Technical Excellence Practical Experience Client Responsiveness Drilled Piles - basics Auger cast piles 50 tons to 300 tons Typically 12 to 30 inches Larger diameters more common now Fast installation in right environment Relatively cheap Auger is screwed into the ground, concrete injected as auger is withdrawn Technical Excellence Practical Experience Client Responsiveness Technical Excellence Practical Experience Client Responsiveness Drilled Piles Design Theory Who designs drilled piles? There is no I in Team Geotechnical engineer = minimum length and diameter of the pile, axial reinforcement Structural engineer = Pile connection and verification of axial steel arrangement Technical Excellence Practical Experience Client Responsiveness Drilled Piles Design Theory Geotechnical - similar to driven piles End bearing Side friction Combination Structural Geotechnical capacity is typically much greater than driven piles, therefore the Structural Design is often a limiting factor Typical ASD Design per building code factors Rebar throughout length