GUEST EDITORIAL For building projects utilizing driven pile foundations, commonly used design processes often result in overly conservative solutions that could be made substantially more efficient through better coordination between structural and geotechnical engineers, use of best-value geotechnical testing techniques, and incorporation of local historical experience. The design process varies from project Engineering Collaboration for More Efficient Driven Pile Foundations From a geotechnical engineering firm’s to project, but typically begins with engaging a geotechnical engineer to report on subsurface conditions and to make general recommendations. Recommen- dations for deep foundations typically provided in a report include advice on site design, with the knowledge that field testing must substantiate the geotechnical analysis. The result is often a pile foun- dation proposed by the geotechnical engineer, without significant input by the structural engineer, and then specified by a structural engineer, without significant geotechnical input. The expectation of this process resulting in the most economical solution is unrealistic. From a structural engineering firm’s perspective, the shortcomings of the design process are a function of the design sequence and internal organization of a typical firm offering SER services. For deep foundation projects the focus of the The expectation of this process resulting in the most economical solution is unrealistic. preparation, paving, slab system require- ments and seismic risk assessment. Deep foundation recommendations are often limited to relatively few options and based on minimal information regarding the structure. This is somewhat reasonable since this report is generally written prior to the completion of any substantive struc- tural design, which could advise a more targeted approach. As a preliminary assessment to be used in future collaboration between engineer- ing disciplines this information may be adequate. All too often, however, the scope of geotechnical work is complete (test pile and field monitoring not withstanding) upon issuing the initial subsurface report, leaving what would be a good initial step in developing an efficient foundation solution as final options for selection by the structural engineer of record (SER). At this point, the SER becomes responsible for choosing a single pile type, which is based primarily on the worst case axial and lateral reactions, often without significant local experience. A plurality of that single pile type is then proportioned to provide a safe foundation may occur at two distinct points in the design process: preliminary budgetary foundation package submittal and final design package submittal. In general the final design is the result of a substantially better understanding of the foundation reactions when compared to the budgetary package; an improved under- standing that results from significant architectural coordination culminating in the final building concept. The geotech- nical engineer is not typically engaged during this development. Quite often, in fact, the structural engineer utilizes the initial subsurface report for the final design, without additional geotechnical study. In addition, SER firms are commonly selected for projects due to specialized expertise in a particular construction type or building usage. Development of valuable skills required to efficiently design particular types of structures for specific uses is geographically transferrable and does not necessarily indicate development of design knowledge required to most efficiently design all foundations options available to the owner. perspective, design shortcomings generally mirror those of the structural engineer. On many projects, the geotechnical engineer is contracted very early in the design process, often during the due diligence and con- ceptual phase. Involvement during the early phases of a project creates many difficulties for geotechnical design, but generally originates from lack of structural loading information and limited scope of work. While a geotechnical engineer’s investigative efforts focus on determining soil strength, the design efforts can depend heavily on the loading provided by the structural engineer. If these are not available, the geotechnical engineer must make assumptions which can lead to overly conservative design. Some of this conservatism can typically be eliminated if the final geotechnical analysis follows the determination of final building reactions. However, the scope of work proposed by the geotechnical firm may not allow for additional design efforts to fully evaluate all aspects of a foundation design. A final deep foundation design requires coordinated efforts between the geotechnical and structural engineer including design itera- tions during which different foundation types, sizes and loads are evaluated. For a geotechnical engineering firm this could involve higher level geotechnical analysis that evaluates pile/shaft setup/relaxation, group effects or multiple loading scenarios. These types of design efforts many not be included in a scope that was set based on conceptual design information. Vast improvements to the efficiency of a driven pile foundation could result from much closer interaction between the AUTHORS: John C. Ryan, Ph.D., P.E., Ryan Structural Engineers, Mount Pleasant, SC Brian Shiver, P.E., Terracon, Charleston, SC DEEP FOUNDATIONS • JULY/AUG 2012 • 87
