Measuring Ground Movement by Precise Survey
Chursinoff, Roy Wayne
The three dimensional surface movements of the retrogressive landslides at Beaver Creek were monitored from May, 1978 to August, 1979 using precise surveying techniques. A comprehensive, parametric, least squares adjustment computer program was developed to assist in the determination of the limit of accuracy, selection of the most desirable configuration and field procedure given the equipment available at the University of Saskatchewan, Saskatoon, Saskatchewan. The computer program was also used in the subsequent· analysis of the field results, calculation of statistical accuracies and checking the reliability of the data. The study indicated that the rate of horizontal surface movement of the landslides increased from the scarp to the toe, with as much as 100 mm of surface movement occurring from May, 1978 to August, 1979. This observed movement agrees with the current retrogressive slide model. Vertical surface movement was as much as 30 mm downward in the same time period. Slide blocks near the scarp exhibited predominantly rotational movement whereas slide blocks near the toe exhibited predominantly translational movement. This observed behavior also agreed with the current retrogressive slide model. A seasonal trend in the rates of movement was also apparent suggesting a correlation between slide movement and environmental effects such as freeze-thaw, rainfall or river level. Surveying accuracies expressed in the form of 95 percent error elliptical cylinders were in the order of 7 mm horizontally and 2 mm vertically at distances of 150 metres. This accuracy was more than adequate considering the relatively large amount of slide movement. The techniques and procedures set forth in this study should be used as guidelines when employing surveying techniques in future geotechnical field investigations.