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BOLTON 8i- NA 1 N Consulting Engineers Surveyors Date: October 19, 2010 To: Terry Maurer, P.E., Public Works Director Kristine Giga, P.E., Civil Engineer Michelle Olson, Parks and Recreation Manager From: Travis Winter, P.E., LEED® AP Subject: CP Rail Bridge Trail City of Arden Hills Project No.: T16.100325 review and authorization. 12224 Nicollet Avenue Burnsville, MN 55337 Phone (952) 890 -0509 Fax (952) 890-8065 www.bolton- menk.com MEMORANDUM During the capacity testing of the helical pile anchors installed as a part of the retaining wall for the CP Rail Bridge Trail Crossing Project, the contractor discovered that six of the eight anchors in the upper row did not meet the capacity requirements of the design. These six anchors held approximately half of the planned working load. To remedy this issue, the contractor submitted a revised design that called for the installation of an additional six helical pile anchors. The revised design information along with field installation logs for the original 16 anchors was submitted to Bolton Menk and LHB Corporation for The field logs from the anchor installations indicate that the upper row of anchors hit obstructions that prevented them from being installed to the planned depth of 50' The contractors anchor design set the depth of the anchors based on the soils information that was available. It relied on the anchors advancing into a layer of stiff clay till in order to develop high enough installation torque values which would translate into adequate bearing capacity. The obstructions that were encountered could not have been foreseen based on the soils information that was available. It is our opinion that the Contractor's original design was adequate, consisting of reasonable anchor depths and substantial anchor size. This design would have met the requirements if the anchors had been installed without obstruction. We concur that installation of the additional anchors is necessary to meet the needed 50 -kip working load. This loading was computed to restrain the bridge abutment and protect the existing bridge structure. It was developed using what would be considered a standard factor of safety for public works projects and is consistent with Mn/DOT design practices. Due to this change in conditions the Contractor is eligible for additional compensation for the work to complete the project. We have worked with the contractor and were successful in negotiating a price reduction from what the work would have cost at the contract price for each of the additional anchors. F:\ Civil\ ARDH\ T16100325 \Corres \memo_101910.doc DESIGNING FOR A BETTER TOMORROW Bolton Menk is an equal opportunity employer