Regina Beach — a town on a landslide

Abstract

The town of Regina Beach is constructed on landslides along the Last Mountain Lake valley, a glacial meltwater channel in south-central Saskatchewan, Canada. The landslides are retrogressive in nature and are seated in bentonitic clay shale of the Bearpaw Formation. A study was conducted at Regina Beach to determine the sensitivity of the slopes to changes in slope geometry as a result of regrading, or groundwater changes. Back-calculated shear strength was compared with values from the laboratory and from other landslides in Cretaceous bedrock shales. Modest changes in grading of the toe areas would result in significant reductions in the local stability and future movements of upslope portions of the landslide. Development should minimize the amount of grading. Increased slope movement due to breaks in watermains was observed and measured. This correlated well with analysis. Development in landslide areas must assume that differential vertical and horizontal movements will occur. Proper site reconnaissance should identify optimum locations for buildings and services such that the risk of rupture or damage is minimized. Key words: landslide, retrogressive, back analysis, residual shear strength, Bearpaw Formation, inclinometer, slope movement.