Hydraulic Roughness of Untroweled Field Cement Mortar Lined Olmsted 102-in. Diameter Pipeline

The Olmsted 102-in. diameter welded steel pipeline was originally constructed in the 1950s and conveys water to the 11 mega-watt Olmsted Hydroelectric Power Plant. As part of the rehabilitation and replacement of the Olmsted Power Plant in 2018, an in-place cement mortar lining was installed inside the pipeline in accordance with AWWA C602, Standard for Cement-Mortar Lining of Water Pipelines in Place—4 in. (100 mm) and Larger. It was decided during construction that the field-installed cement mortar lining would not require a finished troweled surface because of concerns related to the out-of-round and elliptical shape of the pipe. It was also assumed that the untroweled cement mortar lining would exhibit a hydraulic surface roughness similar to that of the surface of an orange, as suggested in AWWA C602. This paper will present the hydraulic capacity and roughness characteristics of the untroweled cement mortar lining along with the field-measured and calibrated roughness characteristics for this pipeline based on the original bare steel lining and subsequent field-installed epoxy lining used in the existing 102-in. diameter pipeline. The hydraulic roughness was determined by measuring free water surface elevations and installing manometers along the pipeline to collect hydraulic grade line data for flows between 100 and 400 cubic feet per second (cfs). The roughness and surface profile of the field cement mortar lining will also be presented based on collected samples of the lining once it was removed. The benefits of this paper will be a presentation of roughness coefficients for a large-diameter pipeline that utilized different lining systems, all field-measured and calibrated under similar flow and hydraulic conditions. The subject matter will be useful for pipeline designers and utility owners considering different options for the rehabilitation of linings in large-diameter pipelines.