PHOTOGRAPHIC TECHNIQUE FOR DETECTION AND MONITORING OF GROUND MOVEMENTS ASSOCIATED WITH MINING AND QUARRYING

Ground movements resulting from opencast or underground mining lead to concerns over safety and are often the cause of unforeseen costs to t he extractive industries. Sudden slope failures and surface collapses are usually preceded by small, and much slower, displacements. The det ection and monitoring of these minor changes to the ground surface pro vide a means of assessing the likelihood of failure. It is that conven tional surveying and from installed instrumentation be by a visual app roach that enables changes occurring between, but not affecting, the p oints of measurement to be recognized. An optical system that incorpor ates a 35-mm camera has been devised to allow the current vie-cv of a scene to be immediately compared on site with a record of the same sce ne ill the form of a colour transparency taken during a previous inspe ction visit. The observer fuses the transparency stereoscopically with the directly viewed scene. The impression is close to that of normal vision except that differences in detail that have occurred since the transparency was taken are immediately obvious, enabling a qualitative assessment of changes to be tirade on site. If repeat photographs are considered necessary, they can be taken with exactly the same alignme nt and coverage. Two images of the same scene are then available in th e office for quantitative analysis by the simplest techniques of micro -photogrammetry. An example is presented of a non-quantitative applica tion of the technique in a china-clay pit.