Laserfiche WebLink
iVf 1!V ~1 <br />MONTGOMEflYWA7SON HAa2A <br /> <br />~~~, <br />LJ <br />B J.Pellfcer Date 21~1un-O6 Client Seneca Sheet 1 of 2 <br />Chkd. B C.Tusin Desch tion Seneca IIW Slo a Failure Back Anal sis and Re rade 16Jun-2006 Job A 1004337 <br />Purpose: <br />This analysis was performed in order to determine the in-situ shear strength of the soil material that <br />failed at the IIW mine. Based on the results of the back-analysis, a revised slope configuration was <br />developed to meet the State of Colorado's static safety factor of 1.30 for reclaimed slopes. <br />References: <br />1. None used. <br />Procedure: <br />• Atwo-material geologic model was used in the back analysis. Based on conversation with Seneca <br />personnel, aerial photo observation, and a site visit, soil material overlies undisturbed bedrock <br />material that dips to the west. <br />• An infinite slope back analysis was completed for [he failed soil material that overlies the bedrock. <br />This was done to determine the overall soil strength. <br />• Roclab Ver. 1.021 was used to estimate the rock shear strength. Roclab uses estimates for the <br />unconfined compressive strength, intact rock fabric, geologic strength index, and disturbance factor <br />to obtain an overall curvi-linear strength envelope. <br />• A rotational search routine was estimated by SLOPE/W. <br />Soil Back-analysis: <br />- The overall failure plane depth was estimated to be approximately 15 feet. <br />- The slope was saturated due to the culvert supplying water to the slope from rain and snowmelt. <br />- Based on the overall slope angle prior to failure, saturated groundwater conditions, a friction angle <br />of 37° and a cohesion of 200 psf yielded a safety factor of slightly less than one (1.00). See <br />Attachment 1. <br />Regraded Soil Analysis: <br />- Seneca will regrade the soil portion at the upper elevations that overlies the rock to a 3H:1 V slope. <br />This is consistent with other reclaimed soil slopes at the mine site. The revised grading plan is <br />shown on Drawing 1 and 2. <br />- A surface water ditch will be constructed across the upper potions of the slope to collect and route <br />rain water and snowmelt off the slope and direct it to the drainage located to the south (see <br />Drawing 1). <br />~~ <br />