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Driven Pile Foundation Support-Cost Components

Driven Pile Foundation Support-Cost Components. 2009 PDCA Professors’ Driven Pile Institute June 15-16, 2009 Van E. Komurka, P.E. Wagner Komurka Geotechnical Group, Inc. Talk Outline. Define support cost. Discuss support-cost components: Pile Conventional Profile (as a function of depth)

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Driven Pile Foundation Support-Cost Components

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  1. Driven Pile Foundation Support-Cost Components 2009 PDCA Professors’ Driven Pile Institute June 15-16, 2009 Van E. Komurka, P.E. Wagner Komurka Geotechnical Group, Inc.

  2. Talk Outline • Define support cost. • Discuss support-cost components: • Pile • Conventional • Profile (as a function of depth) • Cap • Column (matching allowable pile loads to structure column loads) • System • Present case histories (large and small) illustrating load-matching approach.

  3. Sup•port' Cost (Sŭ•pōrt' Kŏst) The cost of an installed or constructed foundation element or system divided by its allowable load, usually expressed in dollars per ton (i.e., how many dollars it costs to support one ton of load).

  4. Sup•port' Cost (Sŭ•pōrt' Kŏst) • As a normalized parameter, allows direct (apples-to-apples) economic comparison of different foundation alternatives: • Shallow vs. deep (e.g., spread footings vs. piles) • Deep vs. deep (e.g., drilled piers vs. piles) • Pile section vs. pile section (e.g., 10.75” vs. 12.75”) • Pile capacity vs. pile capacity (e.g., 70T vs. 150T) • Allows economic evaluation and optimization of deep foundation system cost components

  5. Design Column Load Deep Foundation System Components Column Cap Piles

  6. Pile Support Cost Pile Cost = Allowable Pile Load • In general, higher allowable pile loads result in lower pile support costs: • Spread pile length invested to penetrate through poor soils over more capacity • In competent soils, capacity generally increases faster with depth than does cost

  7. Pile Support Cost Pile Cost Pile Support Cost = Allowable Pile Load $1,500 per pile $3,000 per pile = $30 / ton = $20 / ton 50-ton allow. load 150-ton allow. load

  8. WKG2 Pile Support Costs

  9. Pile Support Costs – WKG2 Projects Pile Support Cost, dollars per allowable ton Allowable Pile Load, tons (factor of safety = 2.0)

  10. Pile Support Costs – Sixth Street Viaduct Replacement • Various: • Pile Diameters (10.75- and 12.75-inch- O.D.) • Safety Factor (from 2.0 to 2.5) • Installation Criteria (WEAP, Modified EN) • Subsurface Conditions (from till at 4 feet, to 60 feet of organic silt) Pile Support Cost, dollars per allowable ton Allowable Pile Load, tons

  11. Achieving Higher-Capacity Piles • Use larger section, larger hammer, drive piles “harder,” perhaps deeper. • Incorporate soil/pile set-up: • Use displacement pile. • Adjust testing program (wait longer to test, restrike testing, etc.). • Increase design stresses (e.g., from 9-12 ksi to 16 ksi) • Use higher-strength concrete (e.g., in concrete-filled pipe piles from 3-4 ksi to 6 ksi)

  12. Cap Support Cost Cap Cost = Design Column Load Higher allowable pile loads result in fewer piles, smaller caps, and therefore lower cap support costs. Minimized cap support cost results from using the minimum required number of piles.

  13. Cap Support Costs Cap Support Cost, dollars per allowable ton Design Column Load, kips

  14. Column Support Cost Pile Cap Cost + Σ Pile Costs = Design Column Load Measures how well the allowable pile load, in conjunction with the minimum required number of piles, matches the design column load. Minimum column support cost results from using the optimum allowable pile load.

  15. 900K Optimum Allowable Pile Load Design Column Load = Minimum Req’d No. of Piles • Design Column Load = 900 kips • Minimum Req’d No. of Piles = 3 • Optimum Allowable Pile Load = 900 kips 3 piles = 300 kips/pile = 150 tons/pile

  16. Lower-Than-Optimum Allowable Pile Loads • Increased pile support costs – each ton of allowable pile load costs more than it would have with higher-capacity piles. • Increased cap support costs – each cap is larger than it would have been with higher-capacity piles. • Increased column support costs – for a given column load, pile and cap costs are higher than they would have been with higher-capacity (closer to optimum allowable load) piles. • Increased number of pile installations – may increase total project drive time.

  17. Higher-Than-Optimum Allowable Loads • Increased column support costs – although pile support costs are low, and cap costs are minimized, unnecessary capacity is installed (unnecessary cost is incurred). All you need. Low unit cost.

  18. Match Allowable Pile Loads to Column Loads! • Piles are below-grade structural extensions of above-grade structural elements; their design should be integrated with the above-grade design. • Using one allowable pile load for a project is analogous to using one beam or column design throughout a building. • Two fixed design components: • Structural loads to support (column load schedule). • Soil/pile resistance behavior to support structural loads (depth vs. capacity relationships). • Deep foundation system design flexibility (choice of pile type, section, allowable load, safety factor, etc.) allows accommodating fixed design components.

  19. System Support Cost Σ Deep Foundation System Costs = Σ Column Design Loads Measures overall cost-effectiveness of deep foundation system. Provides basis for comparison of viable design and installation options.

  20. Load-Matching Design Approach • Obtain foundation layout, column load schedule, and the minimum required number of piles at each cap, from structural engineer. • Calculate optimum allowable pile load for each cap. • If desired, calculate required “ultimate” pile capacity for each cap. To evaluate the cost-effectiveness of field testing, this can be done for a range of factors of safety.

  21. Pier Wisconsin

  22. Load-Matching Design Approach • Obtain foundation layout, column load schedule, and an indication of the minimum required number of piles at each cap, from structural engineer. • Calculate optimum allowable pile load for each cap. • Calculate required “ultimate” pile capacity for each cap. To evaluate the cost-effectiveness of field testing, this can be done for a range of factors of safety. • Generate histogram of optimized allowable pile loads (or of “ultimate” pile capacities).

  23. Allowable Pile Load Histogram Pier Wisconsin Optimum (Minimum) Required Number of Piles Allowable Pile Load, tons

  24. Load-Matching Design Approach • Obtain foundation layout, column load schedule, and an indication of the minimum required number of piles at each cap, from structural engineer. • Calculate optimum allowable pile load for each cap. • Calculate required ultimate pile capacity for each cap. To evaluate the cost-effectiveness of field testing, this can be done for a range of factors of safety. • Generate histogram of optimized allowable, and/or ultimate, pile capacities. • Select appropriate allowable pile loads (or “ultimate” pile capacities), with design-team input.

  25. Allowable Pile Load Histogram Pier Wisconsin 91 tons 180 tons 251 tons Optimum (Minimum) Required Number of Piles Allowable Pile Load, tons

  26. Load-Matching Design Approach (continued) • Select viable pile type(s) and section(s) for selected allowable loads/capacities (91T, 180T, and 251T) {borings}. • Estimate individual pile lengths required for selected pile capacities.

  27. Estimated Ultimate Pile Capacity - Borings 13.375-inch-diameter Pipe Piles Pile Toe Elevation, feet Estimated “Ultimate” Pile Capacity, tons

  28. EOID Capacity Pile Test Program Capacity Profile Set-Up Pile Toe Elevation, feet Long-term Capacity Estimated “Ultimate” Capacity, tons

  29. Load-Matching Design Approach (continued) • Select viable pile type and section for selected pile capacities. • Estimate individual pile lengths required for selected pile capacities. • Estimate total pile lengths required for project. • Using representative prices, estimate total pile cost for project.

  30. Allowable Pile Load Histogram Pier Wisconsin 91 tons 180 tons 251 tons Optimum (Minimum) Required Number of Piles Allowable Pile Load, tons

  31. $21.61 / ft $27.97 / ft

  32. Load-Matching Design Approach (continued) • Select viable pile type and section for selected pile capacities. • Estimate individual pile lengths required for selected pile capacities. • Calculate total pile lengths required for project. • Calculate total pile cost for project. • Perform additional iterations as desired.

  33. $19.16 / ft $21.61 / ft $27.97 / ft

  34. $19.16 / ft $21.61 / ft $27.97 / ft

  35. Pile Support Costs – WKG2 Projects Pile Support Cost, dollars per allowable ton Allowable Pile Load, tons (safety factor = 2.0)

  36. First Place Condominiums • Relatively small project, approximately 200 piles required. • Renovation of a former storage warehouse into condominiums. • Piles required only beneath small building addition. • Existing geotechnical engineering report prepared for different site development plans. • A review of existing recommendations relative to currently proposed development was desired.

  37. Optimum Allowable Pile Load Histogram First Place Condominiums Optimum (Minimum) Required Number of Piles Allowable Pile Load, tons

  38. First Place Condominiums - Proposed Designs Allowable Number Estimated DesignLoad, tonsof PilesFootage Original 70 205 15,580

  39. Optimum Allowable Pile Load Histogram First Place Condominiums Optimum (Minimum) Required Number of Piles Allowable Pile Load, tons

  40. First Place Condominiums - Proposed Designs Allowable Number Estimated DesignLoad, tonsof PilesFootage Original 70 205 15,580 Revised 72 180 14,040 SAVE: 25 1,540 $34,250 + cap costs on $346,500 worth of piles

  41. First Place Condominiums - Proposed Designs Allowable Number Estimated DesignLoad, tonsof PilesFootage Original 70 205 15,580 Revised 72 180 14,040 Alternate 100 130 $60,000 savings 72 tons per pile x 180 piles = 12,960 tons to support 12,960 tons / 100 tons per pile = 130 piles Save 50 piles & $60,000 ?

  42. Optimum Allowable Pile Load Histogram First Place Condominiums Optimum (Minimum) Required Number of Piles Allowable Pile Load, tons

  43. 72-ton allowable 100-ton allowable 72 tons 72 tons 72 tons 100 tons 100 tons 100 tons

  44. First Place Condominiums - Proposed Designs Allowable Number Estimated DesignLoad, tonsof PilesFootage Original 70 205 15,580 Revised 72 180 14,040 Alternate 100 164 15,744 SAVE: 16 (not 50) -1,704 ($37,897) (if same pile section is used)

  45. Conclusions • Consider using higher-capacity piles (when building loads warrant) • Lower pile support cost • Lower cap support cost • Consider matching (optimizing) allowable pile loads to column loads • Lower column support cost • Evaluate design options/alternatives using actual column loads and allowable pile load histogram • All should result in more-cost-effective driven pile foundations

  46. Questions / Comments?

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