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� �.. r . . <br /> OF'�fC I <br /> �: 9�` <br /> G <br /> V 70 <br /> �1L����' i <br /> %l lINO�`'� <br /> July 31, 1996 ' <br /> PUBLIC WORKS MEMORANDUM <br /> NO. 96 - 51 <br /> MEMORANDUM TO: Honorable Mayor and City Council <br /> FROM: Daniel R. Sommerfeldt, Acting City Manager <br /> Bruce A. McNabb, Director of Public Works � <br /> Stephen P. Swanson, City Engineer�'J <br /> SUBJECT: Lake Decatur Dam Spillway Rehabilitation <br /> E3ctra Concrete Rehabilitation Work <br /> In the process of beginning the repairs to the north and south wingwalls of the Lake Decatur <br /> Dam, it was discovered that the deterioration of the concrete surface of the wingwalls was much � <br /> more extensive than originally estimated. The original estimate was based on non-destructive , <br /> testing by Black & Veatch, the City's consultant, in the process of preparing the plans and ; <br /> specifications. This testing involved doing soundings on the existing concrete surface to detect ', <br /> any voids or "soft" concrete. This is typically done by dragging a chain across the surface of the � <br /> concrete or tapping with a hammer. �, <br /> When the contractor started his work, it became evident that the specified repair strategy , <br /> needed to be modified to make the appropriate repairs. This matter was reviewed by City staff il <br /> and discussed with Black & Veatch. It was determined that an estimated 3,400 square feet of � <br /> surface area was going to have to be milled off to a depth of about three and a half inches. After <br /> the milling, the surface would be prepared and then a Microsilica Shotcrete applied to the surface <br /> to restore the wingwalls to an acceptable condition. <br /> Staff and Black& Veatch agreed that the work needs to be done and that it is timely and cost <br /> effective for it to be done at this time. The wingwalls are a critical part of the dam, as they serve <br /> as retaining walls to hold back embankments on each side and aid in supporting the dam. The <br /> work typically involves a contractor having to work from below the face of the dam to remove <br /> deteriorated portions of the wingwall faces and make the repairs. In addition, it is important that <br /> the surface areas be dry so the shotcrete will adhere to the milled surface. Osage has the work <br />