Ground Engineering Solutions

Three Key Geotechnical Takeaways from Rankine Lecture

  • A super contribution from a great practitioner

We didn’t have the pleasure of attending this year’s lecture1) but caught the live stream. Dr. O’Riordan certainly had some big shoes to fill following a super treatise last year from Prof. Alonso but ably stepped in with a great discourse on dynamic soil structure interaction. There had been some debate in industry circles with regards to the balance of academia and practitioners in what has been, with a few notable exceptions, a forum dominated by academics. Without doubt, the practitioner didn’t disappoint. We took these salient points from the lecture:

  1. Being aware of the dense urban fabric, above and below ground

The Anthropocene is not a geological age that gets a lot of discussion outside of climate change circles and not nearly enough in geotechnical circles but Dr. O’Riordan brought it to life here for geotechnical engineers with some outstanding work. The second phase beating of the earthquake event induced by the Anthropocene postulated in Mexico City is a fascinating example of its influence. Indeed, Mexico City is such a classical example being developed on lake deposits with enough of the basin remaining undeveloped for the effects to be studied.

We also thought the work on the San Francisco Transbay Transit Centre, which was studied with and without the surrounding structures, is so important. There’s some terrific slides which demonstrate how the entire Transit Centre (which is a 20m deep multi-propped excavation) behaves as a deep beam for load transfer in a seismic event and how the imposition of the Salesforce Tower dramatically alters the response during the same event (increasing the loads transferred very significantly). Really great demonstration in the consideration of the macro-concept with far-reaching implications for city planners and developers.

  1. Using well thought-out and executed field testing to calibrate numerical modelling

Not a novel idea, but two outstanding examples here. Firstly, use of the pressuremeter in South Africa to calibrate the design of viaduct structures to account for sinkhole formation. A combination of the calibrated horizontal ground stiffness (derived from the pressuremeter) and dynamic large strain analytics to model sinkhole formation to establish a robust design for the viaduct foundations in terms of lateral earth pressures induced by the sinkhole formation.

Secondly, following some great discussion on the importance of strain rate on the dynamic behaviour of soils, some large strain modelling of CPT penetration demonstrated that varying the rate of penetration could be used to calibrate numerical models for rate effects – marvelous stuff with real practical applications.

  1. Detailed case histories informing the design approach

Throughout his lecture, Dr. O’Riordan espoused the use of case histories to inform a design approach, focussing in particular on a paper2) which informed the design approach of the new air traffic control tower at Mexico City airport4), 5). The detailed measurements of the case history recorded during an actual earthquake event were used to calibrate the model and mechanism of compensated foundations in order to go forward with a design concept for the NAIM Tower and unique terminal building. Reference to detailed case histories is commonplace in geotechnical engineering – it has to be – but it’s great to see this used to such great effect on a project of such complexity.

There are, of course, many other excellent nuggets in the lecture (performance-based design, “big geotechnical data”, soil-structure-soil interaction to name but a few) and we’d encourage any engineer with even a passing interest in the dynamic behaviour of soils to study this lecture. We also think there’s a really important concluding point stated as: “we now have the tools to articulate to stakeholders the consequences of extreme events on foundation systems”. It’s a bit of a call to arms for practicing geotechnical analysts – go forth with your sophisticated design tools, complex constitutive models and innovative ideas, and go forth with confidence. This is not a dark art – it’s a deeply scientific, data-driven practice capable of contributing to a resilient future for infrastructure and the broader built environment.

Three cheers for Dr. O’Riordan.

Sources / references

  1. https://www.jstage.jst.go.jp/article/sandf1995/40/4/40_4_143/_pdf/-char/en
  2. https://www.fosterandpartners.com/projects/new-international-airport-mexico-city/
  3. https://en.wikipedia.org/wiki/New_International_Airport_for_Mexico_City

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