I was reading the Preface of Tony Brinks Engineering Geology of Southern Africa Volume 4 and am still astonished and in awe of the massiveness of the undertaking to produce those four ground-breaking volumes on the geology and geotechnical characteristics of Southern Africa. The scope and breadth of the undertaking is still breathtaking, and to quote Brink himself, ‘what as envisaged as a two year, two volume project has turned into a seven-year, four-volume marathon.
All respect is due to Brink, but we must also acknowledge the visionaries who made time and finance available for him to do his work. Back in the day there used to be a system of patronage in which artists or clever and capable men were supported. I not being sexist here when I use the term men – women unfortunately weren’t included in any of those patronage systems. But I digress. Full marks to the Geotechnical Division of SAICE and AEG for providing the necessary to for this project – visionaries indeed.
Thirty years later those four volumes are still the go-to publications for us engineers and geologists when we need some information on the geotechnical conditions underlying our site. Indeed they have stood the test of time. It also amazes me that all the 929 figures and tables were plotted by hand with Rotring pens and stencils in the days before Word and Excel.
It is also lovely to look at the case studies and get insights into what was being built in the 1980’s – projects that are now successes and all adding to the quality of our lives. Alas many of those contributors are now no longer with us, Tony Brink included.
Brink’s Coastal Deposits
I thought it might be useful to have series of articles on some of subjects covered by Brink, to remind myself and others of his genius and the breadth of his knowledge. Of course these newsletters cannot hope to cover all the ground which his four volumes, but might rekindle an interest in those chapters which may lie obscurely in those dusty tomes. So starting at the top, and on materials which are relevant to us who ply our trade on the East Coast, are the sediments recently deposited within the proximity of the current shoreline.
South Africa’s coast has been affected by fluctuations in sea levels which occurred during the Cainozoic Era – the Cainozoic stretching from 66 million years ago to the present. Cainozoic means ‘new life’ for those who were guessing. Fluctuations in sea levels led to marine incursions – more correctly termed transgressions – up to 300 m above the present shoreline. During the Pleistocene there were more frequent sea level changes in response to changing volumes of the polar ice caps. These were of major importance in generating extensive Quaternary sequences which are now preserved close to the present coast.
With transgressions come regressions as sea levels rise and fall, with the major local regression taking place during the Weichselian (115 000 years ago) when sea levels fell by 100 m below the current level. This caused the eastward flowing rivers to incise deep valleys seaward of the present shoreline. Large areas of the continental shelf were exposed during this regression, with the exposed shelly sands redistributed by winds to form long dunes. These coastal dunes are preserved as calc-arenite ridges with the Aliwal and Protea shoals off the KZN south coast and the Bluff as good examples – the two former now currently submerged.
The most extensive on shore occurrences of marine sedimentation are preserved on the Zululand coastal plain, extending northwards into Mozambique.
So how does all of this lovely geological history affect us who have to dig around in the substrate? Well, the Berea sands are infamous for their collapsible fabric, the Bluff sandstones are variable in hardness with calcified beds underlain by weak compressible horizons with attendant difficulties, and the Port Durnford Formaton which underlies much of the Zululand coastal plain and is characterised by shallow perched water tables and great variability in shear strength and compressibility. Then there are the black hippo muds and unconsolidated sediments that were deposited in those delightfully beautiful lagoons that give the KZN coast its special appeal. Great for hippos, but not great for founding on.
And all of that out of Brink. So beware when founding on those beautiful ridges or alongside the mangrove fringed lagoons of the KZN Coast.
Do have a very splendid day