All-In-One Survey Solution Drives Efficiencies, Accuracies During Construction

25 June 2021

Like others in the infrastructure construction space, tunnel contractors are under increasing pressure to deliver projects faster to meet the needs of growing communities. History has shown that speed, accuracy and above all safety in these highly complex endeavors can only be achieved with help from technology, for both surveyors and contractors.

The role of a survey team on underground projects is one of continuous demand that ranges from setting geodetic control and collecting initial site surveys to guiding the excavation, drill and blast equipment, monitoring for convergence and final inspection of the tunnel construction. Conventional methods of completing these tasks often require multiple pieces of equipment, large survey teams and time-intensive post processing of data.

The Trimble® SX12 Scanning Total Station simplifies the process while opening new doors of opportunity in the challenging tunnel environment. The combination of advanced total station technology and laser scanning coupled with automated data collection, analysis and reporting capabilities offers tunnel surveyors a next generation improvement in meeting on-site demands while achieving unprecedented accuracy, speed and productivity.

Multi-Purpose Positioning

The SX12 Scanning Total Station combines a high accuracy robotic total station and 3D laser scanner in one instrument. For tunnel projects, accurate measurements for traversing and control can be performed alongside general construction set out, and as-built scanning. There are several key technology elements in the SX12 that make it the ideal tool for tunnel surveys.

First, the total station leverages Autolock® and Finelock technology to automatically lock on to prisms even in target-congested environments reducing the need for manual pointing and errors. This capability is especially useful when performing tunnel convergence measurements which typically involve measuring a large number of prisms in the narrow tunnel corridor. The SX12’s Finelock functionality ensures the instrument reliably locks on to each prism as it collects measurements.

Next, with the smallest laser spot size (3 mm diameter EDM laser spot at 50 m) in the industry, the SX12 provides a precise and clear set out of tunnel construction points. The green laser pointer provides additional differentiation from other red laser sources in the tunnel eliminating confusion for construction and survey crews.

Finally, the Trimble MagDrive™ robotic technology is designed to withstand the harshest conditions such as dust and moisture, decreasing service cycles and survey crew downtime by ensuring continued instrument operation.

Accurate, Automated Collection

The SX12 is currently in use on a two-year long project that includes the widening of the Norwegian Maursund underwater and Kågen road tunnels, which includes the upgrade of ventilation, drainage, utilities and safety systems.

Sylvia De Vuyst, a surveyor for the Norwegian enterprise Mesta AS, has been involved in the tunnel renovation project performing layouts. She said, “The combination of surveying and scanning technology makes the SX12 incredibly versatile. As I operate it in a very dynamic environment, the speed at which it operates really reduces the time required to do the scans and the layout tasks. It is easy to set up and the prisms can be quickly found.”

When asked about key features, De Vuyst said that her team loves the green laser. “The fact that the pointer is so clearly visible, in spite of being exceptionally small, is a big deal,” she added.

Another important advancement is the SX12’s automated and semi-automated features and functionality. Using Trimble Access Tunnels field software, which includes tools to define, survey, stakeout and report on tunnel operations, with the SX12, operators can automate the as-built data collection process, one of the most time consuming tasks in tunnel construction.

With the SX12, simply set up the instrument, backsight and start measuring. The total station automatically finds set-out locations and will move to the next design location after a pre-set time elapses, allowing the operator to focus on marking the point on the tunnel surface.

No need to manually point to each measurement. 

Easing Data Management

One of the big pain points in today’s technology-enabled operations is managing large data, particularly the quantity of data produced by 3D laser scanners, for construction verification and reporting.

Sifting through the noise, or the unwanted data, such as machinery, duct work, and workers, and aligning the scan data to the tunnel design is often tedious and costly.  The SX12’s optimal workflow, which includes Trimble Business Center™ (TBC) Tunneling is designed to simplify much of the data processing data. Scan data generated by the SX12 is automatically georeferenced to the survey control backsight or resection setup measurements eliminating the need for time intensive point cloud registration and processing. TBC Tunneling incorporates tools that automatically remove unwanted data, a step that saves considerable office technician time.

As well, with TBC Tunneling, surveyors can automatically generate detailed as-built reports verifying tunnel as-built position and over/underbreak values. In shotcrete and excavation quality control, the SX12 scanning data can be used to generate heat map reports to verify thickness, undulation, and conformity to the design. For more flexibility, these reports can be customized to suit the client and project needs using Microsoft Word templates.

De Vuyst confirmed the data verification benefits, and added, “TBC software prepares the data to be automatically georeferenced, while the Tunnel function is taking care of the auto-classification of the point cloud regions.”

Another benefit is the ability to collect, analyze and report on total station convergence measurements reducing the need for multiple software packages or managing monitoring data in cluttered spreadsheets. Combined with Trimble Access Monitoring, measurements can be automated to collect pre-defined sets for each convergence point. In the office, TBC Monitoring produces comprehensive displacement reports to provide engineers with data to ensure proper convergence tolerances are met.

De Vuyst concluded, “All in all, the SX12 has a significant impact on our efficiency and safety on the project as it reduces set-up and scan time. It can even be used in live traffic situations as the software allows me to filter out the noise from the point cloud generated by moving traffic.”

Inspection and Maintenance

Once the tunnel is in operation, the structural integrity and assets need to be collected to provide data for informed maintenance decision making. The SX12’s high resolution imagery capture using enhanced navigation and documentation features of the Trimble VISION™ camera system combined with laser scanning capabilities allows surveyors to quickly collect data in a tunnel’s high traffic areas from a safe distance.

The Trimble SX12 is the complete instrument for tunnel surveys from start to finish. View this webinar recording for an overview of how to use the SX12, Trimble Access, and TBC for tunnel surveys. 

Contact the Trimble Tunneling team for more information here.