Cape Leeuwin Lighthouse Foundations

Determining whether boreholes have terminated on boulders or competent basement rock is as much a problem for geotechnical engineers today as it was for the designers of the Cape Leeuwin Lighthouse in 1894.

First proposed in 1881 by the Colonial Secretary’s Office, the Cape Leeuwin Lighthouse is located on the southwest corner of the Australian continent. The name was taken from the adjoining area which was called Leeuwin’s Land by Dutch navigators after the East India Company’s ship ‘Leeuwin’ (Lioness) which was in the vicinity in March 1622.

Constructed at a time when most Australia-bound ships travelled via the Cape of Good Hope, Cape Leeuwin Lighthouse was often their first ‘sight of Australia’

The lighthouse was designed by W. T. Douglas, Consulting Engineer of Westminster, London. Tenders for its construction were called in January 1895 and the contract was awarded to Messrs Davies and Wishart in April of the same year. The contract price was 7800 pounds.

When excavation for the foundations be9an it became apparent that considerable changes to the foundation would be required. The bores on which the original design had been based had been terminated on ‘granite’ (?) at a depth of 6-8 feet. However excavation showed this to be in the form of boulders. Bedrock was not reached until 22 feet.

Exact details of the Concrete foundations are difficult to determine. A ‘Drawing No. l’ dated 10-5-1895 entitled ‘Revised Section of Foundation’ shows a square mass concrete foundation with an octagonal hole in the centre, ‘to be filled with clean stone and sand, rubbish or muck, in layers 9 inches thick and rammed’. Hardly select fill by 1988 standards! This drawing is however endorsed ‘not adopted’ and the author has been unable to locate a final ‘as executed’ plan.

The revised foundations are reported to have involved 1000 cubic yards of concrete (Watson 1978).

The Cape Leeuwin Lighthouse is a well designed and constructed structure which stands today showing no signs of foundation settlement or distress.