Introduction

In recent years there has been a trend in overseas countries and also in Australia towards the regular and systematic application of geological science to the planning, investigation, design and construction of major civil engineering undertakings, particularly those involving the construction of large dams and hydroelectric schemes. Whereas formerly recourse was had to geology only occasionally when individual geologists or state geological organizations were called upon as consultants in connection with particular problems, now it is common to find geologists as regular staff members of the engineering organizations. At the same time, engineering geology is developing as a distinct, well-recognized branch of applied geology.

The Snowy Mountains Hydro-electric Authority soon after its inception established an Engineering Geology group, the professional staff of which is at present nine geologists and one geophysicist. The work of this group is very closely integrated with, and depends upon, that of the several civil engineering groups, and thus for each project in the Scheme the geological investigations have evolved in distinct stages in phase with the engineering developments. Its work covers the investigation of sites for dams, tunnels, power stations, aqueducts and roads, and also the finding, exploration and petrographic examination of concrete aggregates and of materials for earth dam construction and for road building.

The first stage of any project is that of preliminary investigation, when the geological aspects of various alternative proposals are studied and compared, providing an important part of the data for determining which alternative is most favourable.

The objectives of the work at this stage are to establish the geological feasibility and practicability of each feature of the various alternative layouts, to determine the general nature of the geological problems involved and whether any particular difficulties are to be anticipated, and to obtain sufficient information about each of the most promising alternatives to enable a realistic comparison to be made between them.

This usually requires a geological reconnaissance mapping of the whole area, together with a limited amount of exploration of sites and materials sources, usually by diamond drilling, trenching and test pits, and seismic refraction surveys.

In the second stage, detailed studies are made of the adopted layout and of the sources of constructional materials, to obtain all geological data required for final pre-construction designs and estimates. This requires geological mapping in close detail on large scales, and usually considerable exploration by means of diamond drilling, trenching and test pits.

The third stage is that of construction. Systematic inspection and detailed geological mapping of the important excavations are carried out, and the results reviewed and correlated with all other geological data previously obtained from surface geological mapping and explorations. The purpose of this work is to provide assistance with immediate construction problems, to obtain records of the foundations of the important structures in case difficulties should arise during the operation of the project, and to collect geological data and experience bearing on future projects.