2022-114-E-Plannng-Schnabel Engineering South-Contract Amendment #1 – Lake Orange Gate and Spillway Channel Repairs

Browse Search

Orange County Lake Orange Intake Tower Additional Services Project 20P21019.01 / January 25, 2022 Page 2 Schnabel Engineering South, P.C. sluice gates. This proposal includes additional inspections and evaluations of the intake tower to help obtain a better understanding of its condition prior to moving forward with sluice gate replacement. OBJECTIVE AND SCOPE OF SERVICES Our existing scope of services are organized into five tasks and they are described in our existing agreement. The proposed additional services are presented below as Task 6. The objective of the Task 6 services is to gather additional information on the intake tower condition. Task 6 services are organized into two subtasks and will be performed under the responsible charge of a Professional Engineer licensed in the state of North Carolina. Task 6.1 – Additional Dive Inspection Observation It is our understanding that Orange County plans to contract with In-Water to bring them back onsite to further observe the tower. A Schnabel representative will coordinate with and direct the In-Water diver to gather additional observations and measurements of the intake tower and low level outlet structure. We have assumed this would include a single day on-site with a memo summarizing the observations. Task 6.2 – GPR to Locate Reinforcing Steel in the Intake Tower Since no steel reinforcement (rebar) was observed in the concrete spalls on the exterior of the intake tower, Schnabel recommends utilizing ground penetrating radar (GPR) to locate rebar in the intake tower walls. This work will consist of two Schnabel representatives accessing the intake tower via a boat launched from the upstream slope of the embankment to visually inspect the above-water portions of the intake tower and locate the rebar using GPR when the reservoir is lowered to for other repairs to the dam. The objective of the GPR survey will be to identify the typical pattern of rebar within the intake tower concrete walls including the configuration, orientation, spacing, and approximate depth of rebar within the wall. Schnabel personnel plans to perform the GPR survey at one location on each of the four exterior tower walls for a total of four locations, but will adjust the approach based on observations in the field. GPR data will be collected on a 2 ft by 2ft grid at each location. We have included as Attachment 1 a data sheet with additional information on the use of GPR to evaluate concrete reinforcing steel. We will mark the locations on the concrete surface, will photo document our markings. The effectiveness of GPR is dependent on many factors, such as cultural features, concrete age, concrete materials, moisture contents, additives and overlays, and metallic objects on top of and within the concrete. Results may vary depending on actual site conditions; from our understanding of the site conditions for this project, the GPR method is well suited for the objective here. If a reinforcing bar is located directly above and parallel to a deeper reinforcing bar, the deeper bar will be shadowed by the top bar and may not be observable in the GPR data. While we do not anticipate metallic interference being an issue for identifying the rebar within the intake walls and measuring wall thickness, it is important to note that GPR signal does not penetrate metallic objects, such as sheet metal or wire mesh reinforcing with spacing less than about 2 inches. Smaller metallic objects, such as individual pipes or reinforcing bars, reflect part of the GPR signal and may allow the remainder of the GPR signal to pass around the object, penetrating deeper into the subsurface. The resolution of the GPR is such that we expect to identify the depth to the reinforcing steel bars and slab thickness to within ¼ to ½ inch of their actual depth. Based on the project’s goals, we do not plan to DocuSign Envelope ID: 3667B243-40E4-479A-AE63-F797402CD54A