Development of a “Smart Laser Projector” for Guiding Tunnel Boring Construction

Abstract

Engineering design of a drainage tunnel specifies start/end positions, alignment, grades, and tunnel diameter/lining material. Tunnel construction faithfully transforms engineering design into the built structure in the underground space. In construction, the guidance system of the tunnel boring machine (TBM) is crucial to ensure all design specifications are met within tight tolerances. The laser-based guidance system has been the mainstream solution in practice. However, laser system setup and calibration demands experience and expertise from a survey crew and also results in frequent construction shutdown over extensive time periods. In (1) straight tunnel sections with highly restrained survey window or (2) curved tunnel sections, the line of sight between the laser station and TBM can be easily blocked. Thus, tunnel construction has to be more frequently shut down solely for the sake of calibrating or relocating the guidance system, causing substantial productivity loss. To improve productivity of tunnel construction and enhance current practice of TBM guidance, this paper introduces research and prototyping of the Smart Laser Projector system. Unlike the traditional laser system, the Smart Laser Projector does not rely on maintaining the parallelism between the tunnel alignment and the laser beam. The system calculates the as-designed coordinates of the center in the same cross section of the as-designed tunnel model and projects a laser spot at the exact as-designed position of the center of the target board. It presents the as-designed position information to guide the operator just like the conventional laser, but its operations take much less effort of the surveyors, and the same level of accuracy and reliability can be maintained. A lab test is provided to demonstrate the concept and prototype.