Leveraging Data for Tunneling

How Technology Is Improving Design, Construction and Management

In modern tunneling applications, data is everything, especially as we move towards more digital construction and operations. Whether it is gathering geotechnical information for design purposes, or collecting as-builts to validate construction processes, having accurate and validated data can help ensure that projects are completed properly and efficiently by providing stakeholders with greater insights.

One of the workhorse tools in tunnel surveying data collection is a robotictotal station. Used in conjunction with a suite of available software tools, modern total stations can provide the basis for contractors, engineers and owners to make decisions and provide validation and quality control for all types of tunnels, including mechanized (segmental and two-pass) and conventional tunneling. Over the years, improvements to the total station such as combining laser scanning and imagery capabilities, along with data processing and management capabilities, have vastly improved the ability for contractors to collect and utilize the information they need.

Improved robotics and sensor fusion – as referenced above, combining tools like laser scanning with optical imaging capabilities – are improving safety and reducing the time needed to gather information, all while providing additional levels of detail and safety. An example of this is the Trimble SX12, which is a scanning total station that allows the conventional survey workflow while enabling mass data capture through cameras and laser scanning sensors in one system.

As the tools have evolved, increased demands have been placed on contractors to provide more detailed information, according to Riley Smith, marketing director for the industrial technology company Trimble. “An ongoing trend in the industry is that requirements for data collection are growing but the same level of accuracy is required for contractors to meet as they are building tunnels,” he said. “In particular, there is a high priority placed on shotcrete analysis where safety and reducing waste are key. There are requirements to validate thickness, and also other parameters including volume and waviness criteria. With modern equipment, we are able to measure with very high accuracy – to the millimeter level – and can automatically extract insights from the data using infield software tools.”

Additionally, structural health monitoring is an increasing priority for both tunnel construction and operations. “We’re seeing increased requirements for settlement and convergence monitoring to validate safety,” Smith said. “And now we can collate this information alongside geotechnical data such as temperature, groundwater pressure, and more into a single software platform with alarm reporting capabilities, and share that information with owners and others who may need it in real-time, keeping workers out of potentially unsafe conditions.” Surveying principles are key to gathering accurate data for deformation monitoring analysis of the structure and surrounding ground.

On the operations side, monitoring equipment can be used to collect ongoing data on the tunnel structure or key features such as rail track geometry. Again, more stringent requirements are being implemented to increase the frequency of data collection when nearby construction may affect existing tunnel structures. For example, boring a parallel tunnel or drilling foundations next to an operating subway. Using modern survey equipment, crews can collect this information quickly, reducing intervals from hours to minutes, thereby minimizing impacts on tunnel construction crews.

In the Field

One company using Trimble technology is New York Geomatics, which worked on all three tunneling sections of the Purple Line Extension project for the Los Angeles Metro. The services included providing QA/QC information for the contractor, and surveying for the construction management team. Sean Fitzpatrick of New York Geomatics says his team relied on the Trimble SX10/12 scanning total station and Trimble Access field software in collecting survey data, which represents a big step forward from how information was collected in the past.

“Collecting the data used to be a time-consuming process,” he said. “Using the modern survey tools in combination with the tunnel software, we can collate all the data and provide a 3D as-built of the entire tunnel, and export that data into other platforms the client may need. This can be helpful if the clients wants to do an airflow analysis or utility piping work. Having that information stored in an as-built eliminates the need for a survey crew to go back in the tunnel and collect data again, which reduces downtime and increases safety.”

For the Purple Line project, New York Geomatics could typically scan and collect data for about 300 ft sections of tunnel at a time using the SX10 scanning total stations – about 150 ft in each direction. This length varies by the diameter and geometry of the tunnel.

The information can also be included in a GIS database where it can be used by operations staff for asset management and regulatory compliance purposes, Fitzpatrick says.

While the Los Angeles Metro Purple Line tunnels were TBM-driven, the Trimble equipment is also well-suited for conventional tunneling projects, particularly the Sequential Excavation Method (SEM). Using this method, accurate survey data is critical in both tracking the excavated profile of the tunnel, as well as the thickness of the shotcrete used to support the mined tunnel.

“Our equipment is being used regularly in SEM projects for quality control and verification,” Smith said. “In drill-and-blast tunnels, for example, contractors need to validate whether they have blasted to the correct tolerances by checking overbreak and underbreak. We are also seeing a high priority placed on shotcrete analysis to ensure safety of operations and temporary foundation stability.”

The evolution of technology allows for more detailed information, while decreasing the amount of time needed to collect the data. “Now, a client can go out, take a scan, perform an analysis and make a decision using the field software within 10 minutes,” Smith said. “Using traditional tools, it could take multiple hours to collect the data and process it back at the office.”

Tying all the information together is Trimble Business Center (TBC) office software, which allows clients to efficiently calculate earthwork and material quantities for bids, prepare data for construction stakeout, build 3D models to optimize construction operations and surveying, track productivity, and prepare insights for clients such as customizable reports, point clouds, and as-built models. New tools in TBC such as deep-learning based feature extraction and segmentation, optimize the time spent in the office to create client deliverables.

The new age of digital tunnel construction requires contractors to rethink how they perform operations such as surveying and monitoring to maintain accuracy while meeting client deliverables. With rapid evolution in geospatial technology, surveying operations can be used to provide new insights during construction and operations as well as validate structural safety and digitizing the construction process.