For the engineering geologist, site investigation forms a vital part of the project feasibility study and his role in investigation is usually concerned with the planning and perhaps control of the aspects of the fieldwork. As a member of the project team his particular contribution is based on a thorough grounding in the fundamentals of geology and his working knowledge of the requirements and procedures of foundation engineering.
Considered in rather broad terms, site investigation has two main objectives—firstly to obtain a qualitative picture of the sub-surface conditions in the project area and secondly to obtain quantitative estimates of the engineering properties of the soils and rocks. The latter is used in the analytical predictions of the behaviour of the proposed construction (Davis & Poulos, 1967).
In this contribution only one aspect of investigation will be considered, that is the taking of samples in the field. It has long been recognised by engineers that the actual method used to obtain the sample during an investigation is of major significance to the accuracy and value of the test results subsequently obtained in the laboratory. The disturbance which the sample* receives during its collection directly affects the engineering properties of the test specimens. Broadly speaking this effect is at a minimum in hard rocks, e.g. granite, and is at a maximum in sediments or soils, e.g. soft clay. The comments which follow are therefore largely concerned with clayey sediments. Not only has much work been done on these materials, but