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Scanning Total Stations Improve Tunnel Surveying from Start to Finish

Digging into the Trimble SX12

The Trimble® SX12 Scanning Total Station is the complete instrument for tunnel surveying. It combines innovative technology with simple and intuitive functionality to help you save time, maximize efficiency and get more done in the field. No longer do you need to carry a robotic total station and a scanner down the tunnel; only one instrument is required!

Surveyors can use the SX12’s high powered laser pointer and Trimble Access™ Tunnels field software for underground construction surveys, Tunnel Boring Machine (TBM) guidance and more. With these tools in place, you can efficiently stakeout key features such as rock bolts, anchors, blast holes, guide road headers, drilling jumbos and other construction equipment. Users can then create comprehensive excavation control and overbreak/underbreak reports quickly and easily by scanning to collect tunnel as-built data, then automatically clean and process that data with the Trimble Business Center™ (TBC) Tunneling module.

The SX12 benefits surveyors throughout the tunnel construction process, including setting the initial control network, guiding the drill and blast equipment, verifying the constructed tunnel, monitoring for convergence, and inspecting finished tunnels.

Control and Traverse Surveys


  • High accuracy total station with 1” angular accuracy and 1 mm + 1.5 ppm EDM
  • Lock on to prisms in challenging environments using the Autolock® and Finelock capabilities
  • Trimble MagDrive™ technology designed to withstand the harshest conditions such as dust and moisture
  • Perform network adjustments with confidence by combining SX12 total station measurements, level, and GNSS in one software, TBC.

Tunnel control networks are critical to ensuring tunnel construction operators have accurate references to build the tunnel to the correct alignment and dimensions. The Trimble SX12 is a high accuracy robotic total station that efficiently collects prism measurements using the Finelock capabilities to automatically lock on to targets in dusty and humid environments. Even after hundreds of sets have been measured in these conditions, the robotic drive, tilted MagDrive, continue to operate reliably. Once the data has been collected, TBC performs a rigorous network adjustment of the SX12 total station measurements and incorporates GNSS and level.

Drill, Blast, and Excavation Guidance

SX12 and TA Tunneling

  • Accurate and visible stake out using the smallest laser spot size in the industry 
  • Automated and semi-automated set-out of rock bolts and blast holes using Trimble Access Tunnels
  • Comprehensive analysis and customized reporting using on field data in TBC Tunneling

Trimble Access Tunnels field software and the SX12 provide construction operators efficient set-out and excavation positioning. The high-powered green laser pointer can be seen in difficult, dark, and dusty conditions often present in tunnels, while upping your set-out game by using Trimble Access to automate blasthole set-out. The total station automatically finds set-out locations and will move to the next location after a pre-set time elapses, allowing you to focus on marking the point in the tunnel surface.

For further analysis, data from the SX12 can be imported into TBC where as-built reports can be automatically generated.

Construction As-Built Verification and QC


  • Automated collection of as-built data using Trimble Access Tunnels
  • In-field reporting of over/underbreak areas for construction quality control
  • Automatically geo-referenced point cloud data and noise removal using TBC Tunneling

The SX12 and Trimble Access reduce field time by automating the as-built data collection process when performing excavation control, shotcrete, and tunneling lining checks. Simply set up the instrument, backsight, and start as-building. This removes the  need to manually collect detailed as-built measurements. 

Back in the office, provide clients with detailed reports verifying tunnel as-built position and over/underbreak values using TBC Tunneling. For more detailed analysis, customize your as-built reports to suit the client and project needs.


Convergence Monitoring


  • Autolock and Finelock to reliably lock on to prisms in high-volume prism areas typically required for tunnel convergence
  • Combine with Trimble Access Monitoring to automate collection of total station rounds reducing field operator errors and time in the field
  • Process, view, and analyze total station convergence measurements in the same software used to create as-built reports (TBC)

Performing convergence measurements typically involves measuring a large quantity of prisms in a narrow corridor. The SX12’s Finelock ability ensures the instrument reliably locks on to each prism as it collects measurements. Combined with Trimble Access Monitoring, measurements can be automated to collect pre-defined sets to each convergence point. In the office, TBC Monitoring produces displacement reports to provide engineers with data to ensure proper convergence tolerances are met.

Inspection and Maintenance


  • Collecting total station, dense point cloud, and high resolution imagery from one instrument
  • Enhanced navigation and documentation with the Trimble VISION™ camera system
  • Tunnel scan classification and extraction tools using point cloud and imagery in TBC Tunneling 

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 VISION combined with laser scanning capabilities allows you to quickly collect data in a tunnel’s high traffic areas from a safe distance. Using TBC, CAD data can be extracted from the scan and imagery, using automated and manual tools. 


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.