Having faced the afore-mentioned challenges on prior slip lin- ing projects, which inherently resulted in multiple construction delays and change orders, the City of Milwaukee DPW began working with raSmith who utilized static LiDAR coupled with conventional survey control and tools to create current and very accurate as-built documentation of the pipes. The City required a series of deliverables including an alignment and profile of the existing CSO invert, 2D pipe sections at 100-foot stations in the tangent sections of the pipe, and 25-foot stations in the curved sections of the pipe. Additional sections were also required at any observed deflection or deformation points. raSmith tackled the project by first establishing tight survey control at ground level. This included establishing a series of control points along the corridor and near the various manhole access points. Survey control points were also established in the bottom of the pipes at the manholes by inverting a static LiDAR scanner over the manhole and conducting a series of inverted scans that captured control points both above ground and down in the pipe. Additional below ground control points were then established between the manhole access points, and basic sta- tioning was established. raSmith then used a static LiDAR scanner to scan the inside of the pipe throughout the entire 3,700-foot length to create a 3D point cloud of the interior conditions. During the field work data collection period, there was also approximately 6 to 8 inches of flow (primarily ground water infiltration) in the pipe, which prevented the capture of reliable point cloud data below the water surface, obscuring the pipe invert as well as some of the sediment buildup and deposits. raSmith utilized a robotic total station to map those features with a conven- tional survey approach to supplement the point cloud data. This approach allowed raSmith’s office technicians to not only create the alignment and plan and profile documents, but also specifically map the areas with sediment buildup and wander- ing deposits, which may also potentially hinder the slip lining construction process. Furthermore, the series of cross sections clearly illustrated the existing profile of the pipe compared to a perfectly round pipe of the same size and alignment. As a value- added deliverable, raSmith also provided the City of Milwaukee with the 3D point cloud data and a 3D surface of the inside surface of the pipe. All of the resulting documentation was included in the bid document package sent to general contractors to assist them with properly planning for and bidding on the subsequent construction work. Of the general contractors that utilized this information in their planning and budgeting efforts, their bids inherently were very similar and considerably lower than those general contractors who did not utilize that same information. The DPW issued a contract in November 2019 to slip line three of the tangent sections and two of the radii that were sur- veyed using static LiDAR; the other tangent and radius will be
raSmith inverted a scanner over each manhole access point in order to capture control points above and below ground simultaneously.
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november 2020
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