geotechnical and structural engineers at critical points in the design process and possibly involvement of a deep foundation specialist, who has fundamental under- standing of structural and geotechnical considerations. From a structural engi- neer’s standpoint, the availability of additional geotechnical study at an advanced stage of building design allows for more thorough optimization of the foundation with full understanding of what is required for the complete project. Questions regarding pile type and depth can then be most effectively answered to customize the foundation system for the structural reactions. Can pile depth be varied for widely differing ranges of reactions? If steel H-piles are chosen for lateral resistance requirements, can a less expensive pile type be used for non-lateral load resisting elements? Is it possible to optimize structural capacity and cost of piles with increased length? Contract limitations with regard to budgets and schedules often constrain this important interaction. Can locally available products reduce the cost of the project? However, additional cost associated with coupling a geotechnical study in the design phase with an advanced understanding of the structural system is most often offset by many times with savings in the pile foundation and elimination of “unfore- seen” challenges in the construction phase. Collaboration Leads to Savings The following brief examples of driven pile foundations illustrate the improved efficiency due to coordination between structural and geotechnical engineers, and incorporating best practice geotechnical engineering techniques in the field. NASA Taurus II Rocket Launch Complex – Wallops Island, Va. The original design concept for this project was based on standard design processes resulting in specification of either steel H-pile or prestress concrete pile options. Only two standard pile depths were considered to accommodate a wide range of service loads. The owner invested in geotechnical and structural engineering coordination late in the design process, and 88 • DEEP FOUNDATIONS • JULY/AUG 2012 a thorough dynamic load test pile program during production. Pile lengths were thereby customized. The engineering focus on optimizing the pile foundations allowed for the consideration of spliced concrete piles, which were crucial for adjusting pile lengths during production and meeting an aggressive schedule. As a result, a signifi- cant cost savings was reportedly realized compared to the original design concept. Pile driving was completed in 2010 by Sun Pile Driving, Frankford, Del. Police Station – Alberta, Canada For this project, a strict interpretation of the initial subsurface investigation yielded a foundation design comprised of 10 in to 24 in (254 mm to 609.6 mm) open-ended pipe pile, driven to a refusal in the till at a depth of approximately 75 ft (22.8 m). A structural and geotechnical design team, hired by the contractor, evaluated the initial geotechnical report and final building concept. An approach that utilized higher skin friction values and full structural capacity of steel pipe piles, validated through a more rigorous dynamic load test program, was accepted by the owner. As a result, 40% of the piles were 8 in (203.2 mm) diameter, reaching design capacity at approximately 40 ft (12 m). Approximately 60% of the piles were 12 in (304.8 mm) dia- meter driven to the till. Significant cost savings resulted from reduced pile length, decreased pile size, elimination of splices and sche- dule improvement due to reduced driving length. Pile driving was completed in 2011 by Force Pile Driving, Red Deer, Canada. NASA Taurus II Rocket Launch Complex Flood Wall for Waste Water Treat- ment Facility – New Orleans, La. For this project, 120 ft (36.5 m) long steel H-piles (14 x 117), installed on a 1:3 batter, were originally specified to resist substantial hydrostatic loads imposed by an 18 ft (5.4 m) tall flood wall. Subsequent to establishing preliminary cost with the original concept, the owner was presented with a possible prestressed concrete pile alternative. To determine the viability of the concept, additional structural engineering design and geotechnical engineering coordination was necessary. The concept involved utilizing 10% shorter piles, a quick-coupling mechanical splice, high strength concrete and additional deformed reinforcing at locations of excessive moment and tension. A substantially coordinate effort between the geotechnical and structural engineer yielded the most efficient solution for concrete piles. Bids for both options were solicited. The low bid for the concrete option was more than 25% less than the low bid for the steel option. The project is scheduled for construction in 2012. While these projects were in unrelated markets, with differing soil conditions, load requirements and pile types, they were similar in one way. In each case the owner or contractor invested some modest time and expense into additional engineering analysis for developing the most econo- mical driven pile solution. This allowed careful coordination between geotechnical and structural engineers, increasing the confidence by each discipline. Return on this investment was substantial, as the overall costs of the foundations were reduced with improved concept development through engineering.
