Issue link: https://geospatial.trimble.com/en/resources/i/1479770
/ that it is a problem." The tunnel surveyors move the instrument position one or two times each week. Between advances, the Towill team works on advancing the horizontal and vertical control. They also conduct as-built measurements on the more than 5,000 concrete rings that line the tunnel. Each ring is measured in four locations; Fitzpatrick uses the data to compute best-t circles and prepare reports on each ring's circularity. With assistance from Trimble, Fitzpatrick developed a style sheet for Trimble Access that calculates and outputs the differences between the measured locations and design proles. Working in a tunnel presents unique challenges for the surveyors. They comply with the project's strict safety regulations and coordinate their work with the multiple trades and contractors working in the conned space. One of the key needs is to maintain the lines of sight needed for control and measurements to the prisms on the TBM. It's not a simple task: The tunnel is lled with machinery, piping, people and materials vying for access. Even the tunnel environment itself can be an issue. The main portion of the tunnel can be as cool as 55 F. But when working near the TBM, the machine's powerful electric motors and hydraulics can drive the temperature up to 90 F, with a signicant increase in humidity. The team must plan their work to include time for the instruments to acclimate to the variable environmental conditions. "It's a very professional work setting, and everything is built on respect," Fitzpatrick says. "Your primary responsibility is safety for yourself and everybody else in that tunnel. You know your job and have a plan. You communicate your plan to your people and the people that are waiting on you." As the TBM moves eastward beneath the bay, MJC has started work on the receiving shaft in Newark. Because of wet conditions and environmental concerns, MJC is freezing the ground around the shaft. The shaft will be driven into the frozen ground and lined with concrete. When the TBM arrives, a large steel sleeve with an elastomeric gasket seal will connect it to the shaft and provide a dry work environment. The TBM will punch into the sleeve, and then an inatable bladder will release the gasket and seal the machine to the sleeve. Once the seal is fully applied to the outer skin of the TBM, crews will take the TBM apart and lift it out of the receiving shaft. From ve miles away, the sleeve is a tiny target. The clearance between the TBM and seals is just 4 inches (10 centimeters), and the grinding face of the machine must not be allowed to contact the seals. Yet neither Whitman nor Fitzpatrick is visibly nervous about guiding the TBM to the required location. Fitzpatrick expects to slow the TBM as it approaches the sleeve, and possibly take additional gyro and total station measurements to conrm any nal adjustments to the TBM's trajectory. When the machine reaches the Newark shaft in late 2012, Fitzpatrick expects it to end up within 2.5 inches (6 centimeters) of the center axis of the sleeve.