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06/25/97 ~rl;D 10:12 FA.[ 503 $84 0954 CARLSON TESTING ~]002 <br /> <br />97-G116 <br />Roberts and Alton Residences <br />Page 2 <br /> <br />SUBSURFACE CONDITIONS <br /> <br />The borings indicate that the upper 30 feet of sandy flood deposits is only loose to medium dense. <br />No continuous dense gravel layers were encountered to the depths explored, such as the lens <br />exposed below the Alton Residence. Below 30 feet, ~n older flood deposit with coarse sand and <br />blue/grey sandy silt was encountered. Groundwater was perched above this layer to a level of about <br />25 to 29 feet deep on the day of our explorations. <br /> <br />CONCLUSIONS AND RECOMMENDATIONS <br /> <br />Based on our findings, it is our opinion that the best and most economical method of slope stability' <br />improvement is to drive steel H piles towards the base of the riverbank. The wooden piles driven for <br />the dock stairs appear to have been enough to keep the bank intact at these locations: all of the failed <br />areas were between the stairs and had no pilings. This is also the repair that was recommended and <br />installed at the nearby Ragan residence. <br /> <br />The steel H piles should be a minimum of 40 feet long driven to 30 feet depth at 10 feet center-to- <br />center. The pile size should be a minimum size of HP10x42. Between the piles, we suggest <br />P~acement of Hollowcore 4CF8 extruded concrete spans (4.7 strand), cut to 10 foot lengths as <br />lagging. The lagging should be backfilled with gravel. See attached detail. <br /> <br />CLOSING <br /> <br />Our reports pertain to the material tested/inspected only. Information contained herein is not to be <br />reproduced, except in full, without prior authorization from this office. If there are any questions, <br />please do not hesitate to contact this office. <br /> <br />Respectfully submitted, <br />CA R L S Oj~L-,~:E-~_T.I~ G, INC. <br /> <br />James D. I~e, P.E. ' ' <br />G~technical Engineer <br /> <br />Attachment: Slope Shoring Detail - Figure 1 <br /> Boring Logs - Figures A-1 and A-2 <br /> <br /> <br />