letter
What bornhardts teach
King, Lester
Zeitschrift für Geomorphologie Volume 21 Issue 3 (1977), p. 366 - 367
published: Sep 27, 1977
ArtNo. ESP022002103011, Price: 29.00 €
Abstract
Dr. Twidale and others who suppose that weathering occurs deep down fissures in bornhardts have not, so far as I am aware, been inside one to see. I have. In the Valley of a Thousand Hills in Natal, South Africa, the nascent bornhardts have been pierced at many levels by aqueduct tunnels carrying the water supply from Nagle Dam to Durban (Fig. 1). The first line of tunnels was driven in the 1940s. Dr. Alex du Toit, the doyen of South African geologists, was consultant, and I, as assistant on some aspects of the scheme, took the opportunity to examine every tunnel as it was being driven and made collections of the rock types passed through. The work was hard-rock tunnelling throughout, and only the floor and the sides to a height of three feet were lined with concrete to serve as an aqueduct. The upper parts of the sides and the roof were seldom supported in any of the tunnels.
Keywords
weathering • bornhardts • aqueduct tunnels • Valley of a Thousand Hills • Natal • South Africa