The Modern Wireless Monitoring for Tunnel Construction in North America++

COUNTRY:
United States of America

PROJECT TYPE:
Tunnel Monitoring

SECTOR:
Construction - Tunnels

MAIN PRODUCT:
Loadsensing

Challenge

The Purple Line Rail Link in Washington D.C. is a 16.2 mi (26.1 km) light rail line under construction to link the Maryland suburbs to the Washington metropolitan area. The line will allow riders to move between the other lines of the Washington Metro transportation system without needing to ride into central Washington, D.C. Meanwhile, the Purple Line Extension in Los Angeles, formerly known as the Westside Subway Extension and the Subway to the Sea, is a new heavy rail subway corridor in Los Angeles County, extending the Metro Purple Line from its current terminus at Wilshire/Western station in Los Angeles to the Westside region.

The two projects had similar pain points. While installing cables, some of the sensors were placed in boreholes drilled from the road surface or sidewalk. Installing cables to power and read the sensors were too expensive due to the necessity of trenches. The instrumentation monitoring in a tunnel is crucial not only during the initial phase of tunnel boring but also for some time after project completion. During the initial tunnel construction stages, it is very costly and inefficient to conduct monitoring using cabling because of the rapidly changing environment as the tunneling progresses, difficult access areas, etc. The sensors could be read manually but it required traffic interruptions and resulted in sporadic data acquisition. Also, the nodes are usually installed underneath manholes covered with a metal lid which is a very limiting condition for the radio transmission.

Solution

Loadsensing wireless data nodes are successfully collecting and transmitting data from different types of sensors installed deep in the tunnels, on the ground surface and in surrounding buildings.
Loadsensing has been proven to work excellently in spite of harsh conditions during tunnel monitoring. The wireless nodes are collecting and transmitting pore water pressure, subsidence above tunnels, ground movements in depth, horizontal displacements in depth, induced movements in buildings (settlements and tilt), stresses in structural elements, stresses in tunnel linings and other required parameters.
Loadsensing uses LoRaWAN: a long-range, low-power wireless technology used by IoT networks worldwide. The wireless data units also operate on ISM sub 1 GHz operating frequency bands adjustable to each territory requirement, are highly sensitive (down to -137 dBm) and with a transmission of +14dBM high efficiency / +20 dBM. This is why Loadsensing is able to achieve efficient communication in conditions where other wireless nodes cannot. Lastly, Loadsensing units are IP67 certified and tested from -40C to +80C making them highly robust and protected.

Benefits

Loadsensing easily provides real-time data from the sensors installed in-ground and helps in measuring the impact of the construction project. A monitoring program based on geodetic survey monitoring can only work when the movements reach the surface but the irregularity of the data acquisition makes accidents difficult to anticipate. With Loadsensing, any deviation from the predicted performance can be detected earlier and makes it possible to implement remedial or preventive actions.

A wireless monitoring system that is able to monitor the preliminary phases of a project can bring a wealth of data and overall project visibility that was not previously available or feasible. With the easy to install, battery powered and long range Loadsensing wireless nodes, it is possible to collect automatic readings in near-real time from the beginning to the completion of the project.

Through Loadsensing, the metro expansion projects are able to gather data on the stability of the tunnels in an unintrusive way through the data units that are connected to their sensors even inside the metal-covered manholes. This helps to ensure the safety not only of the construction site but also thsurrounding areas.

Click here for the Loadsensing webinar for more details on tunnel construction monitoring.

The Loadsensing monitoring system was deployed in some of the biggest metro extension projects in North America such as the Purple Line Rail Link in Washington D.C. and the Purple Line Extension in Los Angeles to enable the wireless monitoring of the stability of the surrounding ground structures during the metro extension.

Advantages

  • Real-time, wireless monitoring of sensors in harsh environments
  • Compatibility with multiple types of sensors from different manufacturers
  • Minimal maintenance required for the low-power wireless data nodes

A lot of tunnel projects have a mishmash of systems. They could use 3 or 4 systems because operators feel like they have to use a specific system for a certain type of sensor. On our project, for the first time, we are using an integrated, automated data acquisition system. We are using the Loadsensing system for pretty much everything. In fact, Loadsensing is being used for every single monitoring sensor we’re deploying.

Dots Oyenuga Ph.D., P.E., ASC

The Modern Wireless Monitoring in North America

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