Editorial Note – Issue 1 (2018)

Abstract

We are thrilled to present another DFI Journal issue with a variety of research and case studies on deep foundation design, construction, and testing. Kershaw and Luna open the issue with a model scale investigation of the effect of vertical loading on the response of micropiles in sand. The authors tested 17 instrumented model micropiles in a laboratory setting to study the effect of combined axial and lateral loading on the nonlinear soil-structure interaction response of the foundation system. Particularly for loose sands and for piles with lack of head restraint, Kershaw and Luna observed a more pronounced and sudden failure under combined loading compared to observations for laterally-only loaded micropiles. Another micropile application is presented by authors Nodine, Eggers, Walker and Aubrecht, who describe a clever solution for difficult below-groundwater soil conditions at a site in Buffalo, New York. This case study explains the revitalisation of the former Buffalo Memorial Audtorium site, which was constructed in 1940 and founded on H-piles. Micropiles were used to support the new building and provide additional capacity for the four-story construction to be erected. Primary challenges and solutions described in the study include the drilling through the existing slab, the development of a water proofing system, construction obstructions encountered during the drilling and construction process, as well as challenges posed by the asymmetric foundation geometries. The performance of helical pile foundations under lateral loading is documented by Sakr who experimentally investigated the nonlinear response behaviour of helical and driven piles on five different sites in Alberta, Canada. Direct comparisons between the load-displacement behaviour as well as comparisons with commercially available foundation design software showed that lateral resistances for piles with similar geometries were close to each other despite the different installation methods. Soil disturbance was found to play a bigger role at large pile displacement levels, and especially when the predrilling process used auger equipment that matched the diameter of the anticipated helical pile. Recommendations with respect to the installation and construction based on the observed load test results are offered by the author. Another load test case history is presented by Oweis and Erdman, who describe a series of dynamic pile load testing on H-Piles driven into fractured shale rock. The CAPWAPmethodology was utilised to analyse the pile driving performance and determination of resistance to axial loading. The authors observed side resistances in good agreement with published recommendations by the local State Department but achieved average tip resistances approximately four times higher than predictions by design provisions. A local case study at the Lagos and PortHarcourt industrial cities of Nigeria is presented by Bolarinwa, Kalatehjari and Ogunwole. The authors conducted low strain integrity testing on bored piles and auger cast-in-place piles during the construction of local oil tank farm facilities. The in-situ integrating testing allowed for better assessment of structural quality and integrity and identified a small amount of piles with inadequacies, while the overall majority of the piles were installed to QA/QC satisfaction. Classification categories from literature were used and expanded and are described in detail in the manuscript. Costello, Baker, and Mullins tackle an interesting challenge in evaluating a threshold amount of binder needed to improve the strength of organic soils. Traditionally, ground improvement through soil mixing has been difficult for organic materials and strength gains remain primarily unpredictable. The authors used laboratory experiments and field studies to gain insight into binder contents for soils with various water contents, organic contents and soil compositions. An alternative design approach to the traditional w/c ratio approach, namely a binder factor approach, is introduced and explained. A set of strength curves are presented which show prediction curves that are based on a more direct cement factor, and consider the organic content and soil porosity in their prediction analysis. We hope our readers will enjoy the variety of topics covered in this issue, and 2018 DFI Board of Trustees