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' Hall-Irwin Corporation <br /> Hokestra Slurry Walls <br /> October 30, 2014 <br /> ' Page 5of8 <br /> The Contractor placed the SB backfill mixture into the trench using a lead-in slope or on top of <br /> previously placed backfill. The backfill formed a slope of approximately 2.5:1 to 5:1 (horizontal to <br /> ' vertical) in the trench, advancing through the trench by a sliding and slumping displacement action. The <br /> toe of the backfill slope was typically maintained within 0 to 30 ft. of the excavation end of the open <br /> trench. Batches were prepared and placed in approximately 20-30 minutes. <br /> ' As a daily routine, prior to placing backfill, the bottom of the trench was measured (sounded) by Hall- <br /> Irwin to ensure the trench bottom was free of caved material and sand accumulation. The soundings <br /> ' also determined the toe location and the profile of the backfill slope. The Komatsu PC 800 was used to <br /> clean out the trench bottom and determine the location of the backfill toe. <br /> 2.5.3 Soil-Bentonite Backfill Sampling Procedure <br /> Brierley collected 71 samples from the backfill prior to placing it into either of the trenches. A sample <br /> was collected twice per day to determine slump and density, and once per day for moisture content and <br /> grain size distribution. Slump tests were performed according to ASTM C143-90a. Density tests were <br /> performed using a 0.25 cubic foot bucket according to ASTM C 138-92. Moisture and grain size <br /> distribution were performed using ASTM D 2216 and ASTM C 136, respectively. Tables III & IV <br /> present the results for each sample. <br /> Brierley collected a total of 5 bulk samples for the northern and southern slurry walls. The northern wall <br /> had two samples (PERM-1 through PERM-2, stations 0+00, 15+20) of SB backfill that were collected <br /> ' for permeability performance testing. The southern wall had three samples (PERM-1 through PERM-3, <br /> stations 4+75, 23+90, and 44+50) of SB backfill that were collected for permeability performance <br /> testing. Knight Piesold performed permeability testing in accordance with ASTM D5084 using 20 psi <br /> ' confining pressure. Table VII presents the Permeability results. <br /> 2.6 Deviations from the Plans and Specifications <br /> ' The aspects of the SB slurry wall construction that differed from the design plans and specifications <br /> during the construction phase are summarized below. <br /> 1. The actual depth to less weathered bedrock varied from the design depths. The top of bedrock <br /> profile presented on the design plans was determined by interpolation and extrapolation of test <br /> boring information along the slurry wall alignment. The actual depth to less weathered bedrock was <br /> ' determined in the field by Hall-Irwin and confirmed by Brierley as excavation proceeded. Recorded <br /> depths determined during construction are provided in Table VI of this report. <br /> ' 2. The slump of the SB backfill was specified between 3 and 6 inches. The Contractor was notified <br /> when slump was above and below the slump specifications. One of the 71 slumps tested resulted <br /> in a test that was greater than 6 inches. The slump results are included in Table IV of this report. <br /> ' 3. Of the tests performed on the in-trench bentonite slurry, 17% were found to have a sand content <br /> greater than the specified 20 percent. The test results are included in Table II of this report. <br /> 4. The construction staking of the northern alignment totaled 4,358 ft. The as-built alignment totaled <br /> 4,358 ft. A difference exists of 0 feet (0%) between the design and as-constructed alignments. The <br /> BRIERLEY <br /> ASSOCIATES <br /> ' Creating Space Underground <br />