Desert Island Geotechnical Papers

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The process of returning to work offices in mid-2021 following a year and half of working from homes has prompted another (probably 4th time in 32 years) major purge of our company “hard” technical libraries.  Over the past 18 months I’ve personally struggled in not having my paper “hard” technical library available to me, and in particular those proven “old” papers that we refer to time and time again.

This most recent major purge made me reflect that the digital business world that we work in is not perfectly suited to learning, remembering and using the lessons that our forebears took the effort to write down and disseminate.  Of course, some technical papers can be found “digitally” in pdf format somewhere on the internet, some legally accessible, albeit surprisingly costly.  However large hardback volumes of proceedings from e.g. the international conferences of the 1970s and 1980s etc. aren’t so easily accessible online.

In parallel I reflected on how I learned much of my own personal “geotechnique” over several decades, and I reflected that a lot of it came from sitting on floors in various company, Institution and university libraries in between bookshelves, seeking out and reading papers in Géotechnique, QJEG, Canadian Geotechnical Journal, the numerous ASCE proceedings, Soils & Foundations to name but a few.  A positive by-product of that was the list of further references in all those papers, along with the other papers in whichever volume I was looking at, which then took me off on other journeys of discovery.

Therefore, in the spirit of prompting and promoting the dissemination of lessons learned long ago, this paper is the first in hopefully a series of articles on technical papers that experienced geotechnical practitioners rely on and return to over and over.

The following is a selection of 6 of my “go to” papers, which have been most useful to me over 3 decades plus of geotechnical engineering practice, mainly in design, along with some notes of why I find them useful or what they mean to me.  These are Technical papers, from conferences and proceedings – not books, not technical reports.  They are the ones that are in the folder immediately to hand (pre-COVID), and are well worn and have been stapled and sellotaped together several times.  They have personal annotations over figures and highlighter shading of key paragraphs.  I have deliberately limited myself to only 6 papers – it would have been easier to have 12 or 22 or more ! As a result I haven’t included a number of great papers on for example, railway track and sub-grade engineering from India, Japan, and the US which were vital in the early 2000s when the UK were designing and constructing both light rail systems without a modern UK track-bed and subgrade design method – if you are interested, then research the papers of Gerald Raymond, J T Shahu, and Li & Selig.

I add the caveat I am not including any of the Rankine Lecture papers – they are well known, free and online .  It was nice re-reading the list of Rankine lecturers again whilst preparing this article.  Sutherland’s 1987 lecture on Uplift Resistance was my first during my industrial year when I was encouraged to attend by my work colleagues.  I regret missing Peter Vaughan’s in 1994 while working away, but particularly memorable and useful lectures to me were those by Poulos 1989, Burland 1990, Simpson 1992, Clayton 2010, Lacasse 2015 and Jardine 2016. My personal close winner is the still unpublished David Hight lecture in 1998.  I look back at those papers in particular and note however that my preferences might be biased by being lucky to have worked alongside those authors at some point in my career, or used their work for my own research.  If you haven’t read the Rankine Lectures, I encourage you to do so, and those might be interesting ones to start with.

In concluding, it occurred to me that the following 6 papers appear to be the source of widely used design charts and rules of thumb, and I then wondered how this non-digital knowledge and “rules of thumb” will be used in “digital” and AI-influenced designs of the future.  And that reinforced my resolve to start off this series of papers.

Fraser & Wardle”  (1976) “Numerical analysis of rectangular rafts on layered foundations” Geotechnique 26 No 4 pp613 – 630

This, along with my Craig “Soil Mechanics” 3rd Edition textbook is probably the most “re-sellotaped” in my collection.  The paper is primarily focussed on design charts derived from 1970s numerical analyses for the design of uniformly loaded rafts for settlement and bending moment, taking into account the relative stiffness of the raft and the ground.  Graphs of influence factors, settlement correction factors and bending moment influence factors are simply presented for a variety of relative stiffnesses (“Stiffness factor”) across various geometries of raft.  The results are extended to address infinite depth or multi-layered ground, and herein lies one of the “golden nuggets” of this paper.  The combination of Stiffness Factor of the raft/soil system and varying soil stiffness with depth allows the user,  probably after several uses of the method, to really get an understanding of the operating zone of influence beneath a slab, and what depth is most important to best characterise accurately by investigation to optimise settlement and bending moment, and hence slab thickness.  This acquired knowledge is vital to good geotechnical and structural engineering design.  The method and learning substantially avoids the need for complex numerical modelling, or at least allows one to challenge the predicted behaviours in numerical models.

James Penman extended this work in the early 1990s in his Imperial College MSc thesis using axisymmetric FLAC analyses, and this has proved to be useful for e.g. buried reservoir structures at the column/slab interface where moments and shears peak and change direction, and are therefore key elements of design of those structures.

Burland, Simpson & St John” (1979) “Movements around excavations in London Clay”. Proceedings of the Conference “Design Parameters in Geotechnical Engineering” BGS London Vol 1pp 13 – 29

This is a good and comprehensive paper discussing  real ground movements and the factors controlling movements around deep excavations.  The paper presents back analyses and provides information on applicable operating ground design parameters, and provides a good summary of the real scale of movements to be anticipated.

What is particularly useful is the discussion around K0 and earth pressures.  The Initial K0 for embedded wall design can be a highly dominant factor in ground movement predictions, and values determined from e.g. Self Boring pressuremeters certainly, and to a certain extent from suction measurements on thin wall samples, can be very high.  The paper includes a very useful figure presenting horizontal and vertical effective stress and K0 during unloading and reloading.

Burland & Coatsworth”, (with acknowledgement to Burbidge) (1987) “Estimating the settlement of foundations on sands and gravels”  Proceedings  Int. Conference on Foundations and Tunnels, London, 24–26 March 1987 Vol 1, P1–6.

Marcus Burbidge’s original MSc thesis and his subsequent paper with Professor Burland was based on a very large number of case records of settlements of foundations, and this led to a relatively simple empirical basis for settlement prediction, and one which reflected reality whilst predicting settlements much less than many common approaches.  Coatsworth extended this original study with additional case records.

It is noted that for the most part, SPTs from the original case records were NOT corrected for overburden pressure, that the dominating depth of influence was <breadth of foundation, and that SPT be averaged only over that zone.  A simple Compressibility Index is derived and then used to determine settlements “at the end of construction”.  A really interesting and useful aspect of the method is that it also predicts long term (30 years) settlements, with these being larger than the end of construction settlements.  Many books tell you that settlements on granular materials are (substantially) complete at end of construction, yet the empirical results suggest that total settlements at 30 years are 150% for static loads, and 250% for fluctuating loads.

Apart from this really interesting facet, the great advantage of this empirical method is that one doesn’t have to try and work out what value of E’/N is applicable to a foundation load case, noting that the range of E’/N for granular foundations of varying load intensity is massive ! (see CIRIA R143 Clayton (1995))

(Note – you may wonder why I use the Burland & Coatsworth paper rather than the original Burland & Burbidge paper ?  Well, for daily design I only need the few graphs and equations which are summarised neatly on one single page in the B&C version, and hence that’s the one I reach for in my folder of useful papers!  But please do go and dig out the original B&B paper in the 1985 ICE Proceedings which has a lot more useful information and background to the method.)

Bica & Clayton” (1992) – “The preliminary design of free embedded cantilever walls in granular soil” Proceedings of the Retaining Walls conference, ICE, Cambridge University, July

Adriano Bica’s PhD at University of Surrey was on free embedded cantilever walls in granular soils, and this paper to the Retaining Wall conference presents a number of highly useful design charts for depth of embedment and bending moment for embedded cantilever walls, based on model wall experiments  The experimental values of depth of embedment at failure were normalised and presented in design charts which are excellent and simple tools for very quick preliminary design without having to do WALLAP / FLAC etc. analyses.

Black & Lister” (1978)– “The strength of clay fill subgrades : its prediction and relation to road performance” Proceedings of the conference Clay Fills, ICE London pp 37 – 48

This useful paper is a great summary of the relationships between CBR and shear strength for clays  – coarse granular soils are generally far less of an issue because their CBR is much higher, hence it is the low strength and plastic materials that cause us most concern.  As UK pavement design standards (e.g. the DMRB etc.) have ben updated and superseded several times, it is often difficult to know where the background and science supporting those methods lies.

Boscardin & Cording” (1985) – “Building Response to excavation induced settlement

Journal of Geotechnical Engineering,  ACSE 115 No1 January

There is a lot more in this excellent paper than just 2 key figures and 1 useful table, but those are what I reach for first . Figure 4 provides a chart of Horizontal Strain vs Angular Distortion and plots zones of differing damage showing the inter-relation and importance of these 2 factors in determining how much settlement is too much.  Figure 11 provides useful definitions of various different terminology used, which is helpful when speaking to asset owners and other engineers.  Table 2 provides the very widely used Damage Classification by description or by crack width.

In concluding, it occurred to me that these 6 papers appear to be the source of widely used design charts and rules of thumb, and I wondered how this non-digital knowledge and “rules of thumb” will be incorporated into “digital” and AI-influenced design approaches of the future.  And that reinforced my resolve to start off this series of papers, and hopefully will prompt other readers and practitioners to propose their own similar sets of “desert island geotechnical papers”.

Article by Steve Everton, Jacobs