What Technology are Tunneling Surveyors Using Today?
- Robotic Total Stations (Trimble S-Series)
- Surveying Field Software (Trimble Access)
- 3D Laser Scanning (Trimble SX and X Series)
- Office Software (Trimble Business Center)
The workhorse on any tunnel construction project is a robotic total station. It is used for multiple tasks — set out, machine positioning, as-built profiles, monitoring and more. Trimble has a complete line of robotic total stations with all the tools needed to survey a tunnel: highly visible laser pointer, accurate direct-reflex measurement, ruggedized enclosure and long-lasting robotic drives for tough environments.
A Trimble S5 robotic total station surveys the tunnel geology during construction to assist in decision making.
If I already have a Trimble total station can I use it for tunneling?
Yes. Trimble Access (field software) supports a variety of Trimble and non-Trimble instruments. The key to having a complete system is the field and office software you use to perform the tunnel work.
Is there other technology being used in tunnel construction?
3D laser scanning is on the rise in tunnel construction. The increased resolution of point cloud data supports more accurate volume and surface analysis during construction, in addition to painting a detailed picture of the final tunnel position and assets. High-definition laser scanners like the Trimble X7 are improving the infield workflows while reducing the time needed in the office to process the data. As sensor fusion becomes more prevalent, such as the integration of total stations and laser scanners, the need for two independent hardware products decreases and the workflow is centralized. The Trimble SX10 scanning total station can be used to set out key points in the tunnel and also scan the finished lining as-built. The scan data is automatically geo-referenced to the survey control, which saves time back in the office.
The Trimble SX10 combines a total station and scanner in one instrument.
There is also specialized equipment utilized for tunnel surveys. For example, instead of a prism on a range pole, it is often attached to a mount on the wall or a screw in the tunnel side wall. Due to the construction traffic and congestion, you typically can’t place a tripod in the middle of the tunnel.
Mounting instruments and targets outside of the construction path but in line of sight is a challenge on tunnel projects.
What software does a surveyor need for tunneling?
The differentiator is the field and office software which provide tailored workflows for tunnel survey-specific activities. For example, measuring the tunnel surface in a semi-automated way to answer the questions, “How much material was excavated and do we need to continue to excavate?”
Trimble Access is the bread and butter field application for surveyors. The Tunnel module provides specific tunnel workflows for getting design data to the field, such as the alignment and cross-sections. From here, the design can be used to set out key positions like blast holes and rock anchors, collect as-built profiles for volume and undulation analysis, and guide drilling and excavating machines like the drilling jumbo. Find out more on the Trimble Access website.
Trimble Access Tunnels provides unique workflows for tunnel surveys such as auto scan profiles and set out key points.
Connecting the field and design together is the office software, Trimble Business Center (TBC) – the complete field to finish software for surveyors. The real power of TBC is the ability to combine all survey data, such as total station, GNSS, level, and 3D laser scanning, in one software. Before the tunnel construction begins, adjust your control network to ensure the construction stays on line; prepare the design data before taking it to the field; and when data have been collected in the field, process, and analyze all from one software. Finish off the workflow by creating reports to assess the over and underbreak, as well as finished cross-section and plan view plotting.
Mixed fleet of instruments? No problem. Import data from non-Trimble instruments into TBC as well. Once the analysis is done, field and design data can be exported out in a variety of formats such as DWG, DXF, PDF, and many more. Find out more about the TBC Tunneling module here.
Scan and survey data from the Trimble SX10 shown in Trimble Business Center.
What other products are useful for tunnel surveys?
Survey accessories, such as tunneling specific prisms or reflector targets, can really improve your results. These tools enable you to make difficult measurements in a challenging tunnel environment. I see a lot of unique gear in tunnels. One of the most useful things is to have bi-reflex targets. When it comes to performing convergence monitoring in tunnels, hundreds (sometimes thousands) of targets are needed along the tunnel alignment. Buying this many prisms is not cost effective so targets that are both accurate and easily replaceable are useful.
An example of a total station/prism wall mounting bracket that keeps the surveying equipment out of the construction equipment path in the center of the tunnel.
Gyroscopes are specialized instruments used in tunneling and mining to determine azimuths underground to a high accuracy. They are usually integrated with a theodolite or total station so the azimuth can be measured relative to a set of control points in the tunnel. This improves the accuracy of the tunnel control network as the traverse accuracy degrades over long tunnel bores.
Why should surveyors consider tunneling opportunities?
Tunnels are a growing industry with plenty of opportunities for survey companies to offer new services like scanning, BIM, and geodetic knowledge. Every tunnel requires an accurate control network to ensure that it stays on the correct path. This specialized knowledge is crucial for the project and should be provided by a survey company.
As 3D laser scanning becomes the norm, we will see more and more tunnels being as-built using this technology. The rich and descriptive information from point cloud data allows stakeholders to understand and visualize tunnels to a high level of accuracy.
Scanning the final tunnel lining position using a Trimble TX8 high accuracy scanner.
In tandem with scanning, BIM (Building Information Modeling) is starting to be used in a variety of tunnel projects from start to finish. Being complex geometric structures with a variety of assets, tunnels are the ideal candidate to benefit from BIM. Survey services are mandatory to provide the necessary 3D data to produce BIM deliverables of new and existing infrastructure.
Tunnel structure BIM design showing the main tunnel bore and entrance shafts in Tekla Structures software.