The Use of Lidar in Mapping and Assessing Bedrock Foundations

The USACE geologists at the Bluestone Dam Phase 5 Dam Safety Assurance (DSA) Megaproject in Hinton, WV have employed the use of Terrestrial LiDAR scanning and photogrammetry for the purpose of mapping and documentation of stilling basin foundation conditions. Following the excavation and cleaning of a 60-foot by 60-foot monolith foundation, a Trimble SX-10 scanning total station is used to capture high density 3D scans, imagery, and survey measurements of the monolith floor and adjacent side walls. This data is used to generate high density point clouds of the entire foundation and sidewalls, which in turn facilitate the creation of numerous products that aid in the documentation and future assessment of the project foundation. These products include high resolution true color orthophotos, detailed topographic maps, excavation reports, and 3D models. Quarter scale orthophotos of the foundation and sidewalls are printed out and used as base maps for geological field mapping, allowing for greater accuracy and faster execution time when compared to traditional field mapping methods. Topographic maps, orthophotos, and data obtained from excavation reports contribute to the generation of detailed and accurate Foundation, Completion, and Geotechnical Reports, and will help inform the project Post Implementation Evaluation (PIE). Annotated 3D models, with the future incorporation of virtual/augmented reality technology, will allow design personnel, project delivery teams, and risk assessment teams to virtually inspect bedrock conditions and better identify any underlying geological conditions that impact post-construction performance of the project. This innovative approach has allowed project geologists to exceed the requirements for foundation mapping and documentation as outlined in ER 1110-2-1156. The quality and volume of spatial and geological data collected using this method has allowed for a faster and more efficient foundation approval process, reducing the time during which the foundation is exposed during construction and lowering risk at the project.