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2.0 Haul Road HR -1 Slump <br />A northward moving, pre-existing earth slide body was observed during the spring of 2011, hereafter <br />referred to as the East Slide, in a portion of haul road HR -1 that was under construction at the time. <br />Actions were immediately taken to control the slide and minimize its impact. A second earth slide, <br />hereafter referred to as the West Slide, associated with the same conditions that caused the first slide, <br />occurred on December 21, 2011, on the west end of the first slide. Investigation, repair design, <br />construction activities, and analysis of constructed repairs are provided in this section. <br />The Haul Road HR -I slide locations are shown on Figure 2. Details of the slide development and <br />cause of the slide are provided below. <br />The location of the East Slide was approximately between Haul Road HR -1 Stations 8+00 and <br />12+00, and extended up to a large sandstone outcrop just below the upper haul road leg at Station <br />18+50 as shown in Figure 2. Also as shown in Figure 2, the width of the displaced mass (east -west) <br />was about 400 feet, and the length of the rupture surface (north -south) measured about 300 feet with <br />the vertical offset measuring about 5 feet at the headscarp. The material that comprised the sliding <br />mass was colluvium consisting of sandy lean clay with gravel, though sandstone cobbles and <br />boulders were also present in the material. <br />The location of the West Slide was approximately between Haul Road HR -1 Stations 6+00 and 8+00 <br />as shown in Figure 2. As is also shown in Figure 2, the width of the displaced mass (east -west) was <br />about 200 feet and the length of the rupture surface (north -south) measured about 200 feet with the <br />vertical offset measuring about 4 feet at the headscarp which was located within the haul road itself. <br />The material that comprised the sliding mass appeared to be identical to the material in the first slide. <br />The likely cause of the slides was very wet colluvial soils. It is believed that the native soils <br />overlying the bedrock in this area had created "dams" over bedrock seeps and caused pressure <br />buildup, which eventually resulted in saturated soils and failures as observed. Repairs, primarily <br />consisting of excavation, drains and slope reconstruction, are presented on Figures 3 and 4. <br />2.1 Site Characterization <br />This section of the report documents site geometry, site soil geotechnical characteristics, and <br />groundwater conditions. The conditions described in this section were used as a basis for <br />stabilization feature design and modeling of conditions as the slope was reconstructed. <br />P:\Mpls\06 CO\26\06261003 Haul Road Slide Repair\WorkFiles\Report\MCC_Slump_Repaa-Instrumentation-Drain Rev 2012-12-12.docx 3 <br />