Movement behaviour of the Little Chief Slide

The Little Chief Slide has been extremely slow moving at a rate of 4–14 mm/year since the late 1960s. The 800 million m3 slide lies about 3 km upstream of Mica Dam in British Columbia. The extremely slow rate was not affected by the Mica Dam reservoir filling in the 1970s. Although the Little Chief Slide is classified as a rock slide, the extremely slow movements take place on seams of soft materials composed mainly of micaceous clay gouge. The characteristics of the movement trends with time were investigated at six zones using in-place inclinometers (IPIs). The trends of the movement with the reservoir level fluctuations and pore pressure changes were investigated to quantify the contribution of steady-state creep to the total in situ movements. The creep behaviour of the clay gouge materials forming the movement zones was also investigated in the laboratory. The laboratory and field creep behaviours were then compared. The movement could be partitioned into steady-state creep and seasonally induced creep movements. This partitioning identified the locations where the seasonal movements are the highest, and, hence, where drainage measures could have the biggest impact.