ronment. With its ease of use, short learning curve, simple and intuitive functionality and seamless workflow integration, I felt I would be in good hands with the SX12 for my first project with Mesta,” Based on progress to date, it seems the SX12 and the surveying tasks have been in good hands with De Vuyst. Where are we As darkness is the one constant in the tunnels, it has been crucial for crews to have reliable reference points to know where they are physi - cally in the tunnel and where specific work needs to be done. So one of De Vuyst’s main tasks has been to seamlessly switch between the SX12’s total station and scanner to provide that guidance. Using the instrument’s robotic total station, she has been establishing ground control by setting out prisms at 80-m intervals along the tunnel walls. With those fixed points, De Vuyst maintains a project control network accurate to 0.005 meters. To easily and reliably guide the four teams of 40-50 people working in the tunnel, De Vuyst uses the total station scanner to establish and measure a “meter line”, a horizontal line sprayed every 10 m that indi- cates the 1-meter mark above the Maursund’s future new road. “The existing road has steep grades descending down around 80 m and it curves so it isn’t a reliable reference,” says De Vuyst. “We know the elevation and design of the new road so I can use that theoretical data and the SX12 to measure and set out the meter line, which not only gives crews a physical position in the tunnel, it provides a marker to follow for determining their own work such as laying cables or install - ing reinforcing materials on the walls. To lay that out with a traditional total station would require hours of multiple set ups but with the green laser range and speed of the SX12, I can capture the survey data in minutes from one position.” Volumes of volumes If there is one word that often dominates De Vuyst’s day, it is “volume”. With the routine blasting and digging to both widen and heighten the Maursund, De Vuyst is constantly checking and calculating volumes to confirm teams have removed enough material to create a 6-m-wide carriageway with a 1.2-m shoulder on each side and a clear height of 4.6 meters. And she has had to be creative with machine control since none of the diggers on site are connected to universal total station (UTS) position- ing technology. To resolve this, De Vuyst first created a 3D model of the tunnel’s “driving box”, the pre-defined height and width needed to allow vehicles to safely drive through. Scanning 60-m sections of the tunnel, she imported the 3D data into Trimble Business Center (TBC) to create a model of the road and then input the 6-m-wide and 4.6-m- high driving box dimensions to produce a linear 3D drawing of the box. She imported it into Trimble Access Tunnels software and saved it as master file on a Trimble TSC7 controller, enabling her to quickly check earthworks progress any time by positioning the SX12, measuring any point, and immediately identifying any underbreak in relation to the driving box perimeter visible on the controller’s graphical interface. She has also been creating 3D “profile prints”, drawing files that pro-
needed to be constructed and assembled into a confined space with a tolerance of 0.5 m. When the renovation first began in January 2021, the original plan was to run one, two-person survey team with a total station and occasional scanning, and they would alternate every week. However, given the scale, setting and project deadlines, this approach proved problematic within the first two months of work. “Measuring and establishing control for the carriageway––one of the most essential jobs to ensure we create the required width and height–– with a total station requires constant setting up, measuring and setting out, which is quite time consuming,” says De Vuyst. “So in order to keep up, they had to be on site every day and night taking measure - ments. Laser scanning is far more efficient. With my scanning total station, I can scan 500 meters to measure control at a precision of .005 meters in four hours; that would take the total station team two days. That efficiency has not only enabled me to manage all surveying tasks by myself, it’s allowed me to limit my time on site to only four days every other week, saving us survey costs and positively impacting the project’s budget.” The scanning total station that De Vuyst is referring to is the Trimble SX12, a total station and scanner combination that is particularly well suited for underground projects like tunnels. It can scan a full dome at 100 m with a point density of 0.1 m in 11 minutes, lock onto a prism in five seconds, and pinpoint a 3-mm diameter spot at 50 m with its green, eye-safe laser pointer. “We chose the SX12 based on extensive demos we received on it as well as our experience with previous Trimble SX models,” explains De Vuyst. “The combination of surveying and scanning technology makes it incredibly versatile––I can perform multiple functions from the same set up. It’s fast and precise which is important for such a dynamic envi -
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csengineermag.com
November 2021
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