Laserfiche WebLink
Lyman Henn collected 5 bulk samples (PERM -1 through PERM -5, stations 0 +00, 15 +00, 29 +95, 45 +00, <br />and 60+00) of SB backfill for permeability performance testing. Knight Piesold performed permeability <br />testing in accordance with ASTM D5084 using 25 psi confining pressure. Table VI presents the results <br />for each sample. Appendix B contains the permeability test reports from Knight Piesold. <br />3.5 Deviations from the Plans and Specifications <br />The aspects of the SB slurry wall construction that differed from the design plans and specifications during the <br />construction phase are summarized below. <br />1. The actual depth to unweathered bedrock varied from the design depths. The top of bedrock profile presented <br />on the design plans was determined by interpolation and extrapolation of test boring information along the <br />slurry wall alignment. The actual depth to unweathered bedrock was determined in the field by Hall -Irwin <br />and confirmed by Lyman Henn as excavation proceeded. Recorded depths determined during construction <br />are provided in Table III of this report. <br />2. Occasionally the final key depth would extend beyond the minimum 4 -ft requirement. The greater key depth <br />would generally be the result of an elevation change in the unweathered bedrock. To make certain the <br />minimum key depth was obtained, the contractor made a smooth transition from one set to the next, resulting <br />in greater than 4 -ft key depths in the areas where the bedrock elevation rose abruptly in the direction of <br />excavation. Areas particularly along the southeast, east, and northeast edge of the perimeter were keyed <br />greater than 4 ft. below top of bedrock due to dramatic elevation changes. <br />3. Areas of very hard siltstone and/or limestone concretions were encountered during construction that could not <br />have been anticipated from the ground conditions encountered during geotechnical investigation performed <br />for the design phase of the project. Hall -Irwin implemented their rock clause (stating that if bedrock cannot <br />be excavated 6 inches within a 10 ft. section in 30 minutes, then work could proceed forward). The rock <br />clause was in the contract between Hall -Irwin and Weld County, but not in the project specifications. <br />Between stations 23 +80 and 23 +90 a key was not achieved at all, however, a significant amount (7 ft.) of <br />brown /tan/orange weathered bedrock and clay was excavated just above unweathered bedrock. Numerous <br />areas where the rock clause was used had less than a 4 ft. key. Most instances had a substantial amount of the <br />brown/tan/orange weathered bedrock and clay just above competent bedrock. Weathered bedrock ranged <br />anywhere from 1 to 11 ft thick with thicker areas located where bedrock was shallow and substantially harder. <br />The slurry wall key shown on Sheet 1 through 3 displays the thickness of the key. <br />4. The slump of the SB backfill was specified between 3 and 6 inches. The Contractor was notified when slump <br />was above and below the slump specifications. Six of the 315 slumps tested resulted in tests that were greater <br />than 6 inches. The slump results are included in Table V of this report. <br />5. Of the tests performed on the in- trench bentonite slurry, 79% were found to have a sand content greater than <br />the specified 20 percent. The test results are included in Table II of this report. <br />6. The construction staking of the alignment totaled 7,184 ft. The as -built alignment totaled 7,015 ft. The <br />difference of 169 feet (2.4 %) between the design alignment and as -built is a result of the moving the eastern <br />boundary to the west approximately 75 ft. <br />G \PROJECTS\2011 Projects B11025 Gecsert Gravel Pa Slurry Wall \O \OI \Con trucuon report \LH Construuton Report- BS.doc <br />5 <br />