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3) Due to the presence of sands and groundwater in the test holes, the use of casing will most likely <br />be required to prevent caving and reduce the infiltration of water into the pier holes. The <br />placement of concrete in the piers immediately upon cleaning and approval can sometimes reduce <br />the need for casing. <br />4) The presence of cobble to boulder sized bedrock fragments in the fill materials could complicate <br />the pier drilling operations. The drilling subcontractor should be made aware of the subsurface <br />conditions and mobilize drilling equipment with sufficient size and operating condition to achieve <br />the required depth and bedrock penetration, as well as to properly handle the temporary casing. <br />5) Concrete utilized in the piers should be a fluid mix with sufficient slump so it will fill the voids <br />between the reinforcing steel and the sides of the pier hole and casing. The concrete should have a <br />slump ranging from 5 to 8 inches and provide a minimum 28 -day compressive strength of 4,000 <br />psi at this slump. <br />6) A representative of NWCC should observe the pier drilling operations, as well as the reinforcing <br />steel and concrete placement on a full -time basis. <br />The slopes situated within the failed area and downhill of the pier wall should be regraded to a 2 <br />(Horizontal) to 1 (Vertical) or flatter slope configuration. The on -site materials removed during the <br />regrading of the slope should be suitable for use as fill materials in the access road. Fill materials used for <br />the access road embankment should be uniformly placed and compacted in 6 to 9 inch lifts to at least 95% <br />of the maximum standard Proctor density and within 3 percent of the optimum moisture content as <br />determined in accordance with ASTM D698. <br />The soil and groundwater conditions exposed at the toe of the failure area after the slope has been regraded <br />should be evaluated by NWCC. If groundwater seepage or saturated soils are encountered in the cut slope <br />above the railroad tracks, additional stabilization and dewatering measures may be required. Measures may <br />include the placement of a free draining rock buttress fill. <br />Limitations <br />The recommendations provided in this report are based on the soils, bedrock and groundwater conditions <br />encountered in the test holes, and those exposed during this investigation. We believe that this information <br />gives a high degree of reliability for anticipating the performance of the reconstructed /stabilized slope; <br />however, our recommendations are professional opinions and cannot control nature, nor can they assure the <br />soils, bedrock or groundwater profiles beneath or adjacent to those observed. We do not guarantee the <br />performance of the stabilized/reconstructed slopes in any respect, only that our engineering work and <br />judgments meet or exceed the standard of care of our profession at the time they were rendered. <br />Tnh Ni imher 1 1 _R970 <br />NWCC, h,c Pave 6 <br />