Laserfiche WebLink
• CAUSE <br />The pre-slide slope, which was concluded to be of marginal <br />stability in the RMG report, has experienced a slope failure due to <br />changes in natural conditions. The changed natural conditions has <br />caused a general slope weakening because of a variation in the <br />elevation of groundwater and a change in the slope's subsurface <br />flow which created new seepage forces, and the weakening of <br />subsurface soil because of change in the groundwater flow. These <br />increased seepage flows, or excess pore water pressures, had the <br />effect of weakening the subsurface soils and lowered the strength <br />and stability of the slope. In addition, the heavier than normal <br />amounts of precipitation, which occurred in the recent weeks prior <br />to the slide, contributed to the instability of the slope by <br />saturating the near surface soils, which increased the weight of <br />the slide material and added to the forces acting on the steep weak <br />slope. This infiltration of water into the near surface soils <br />• could theoretically increase the normal weight of that material by <br />as much as 508, consequently decreasing the stability of the slope. <br />in other words, the cause of the slide can be attributed to <br />the presence of water which effected the previously marginal stable <br />slope in the following two ways; 1) Snow melt and recent <br />precipitation ran down from the slopes above the slide and flowed <br />into the colluvium through the sands and gravels present in the <br />slope, raising the groundwater level, increasing the subsurface <br />pressures which effectively attempt to float the slope material <br />and; 2) Snow melt and recent precipitation infiltrated into the <br />soils on the slope from the surface increasing the amount of weight <br />the moderately weak soils had to hold on the steep slope. <br />This particular landslide had a progressive failure with a <br />small slide at the base of the slope which left the slope above <br />unsupported, and so another slide occurred terminating in the mine <br />portal access road above. Refer to drawing No. 21-3 for the <br />locations of both slope failure scarps. <br />CJ <br />21-6 <br />