Tunnel Construction Wireless Monitoring for the Los Angeles Metro++

COUNTRY:
United States of America

PROJECT TYPE:
Metro Tunnel Construction monitoring

SECTOR:
Construction - Tunnels

MAIN PRODUCT:
Loadsensing

Challenge

The Purple Line Extension Project spans a total of 14 kilometers (9.1 miles) and passes through Wilshire Boulevard, one of the busiest streets in Los Angeles.

The project was already equipped with sensors for monitoring various parameters such as 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 others. Some of these sensors were placed in boreholes drilled from the road surface or sidewalk. The project developers wanted to avoid interrupting traffic every time a sensor needed to be checked, but the alternative of installing cables to power and read the sensors, was too expensive because it would have required digging trenches for the cables. This made wireless monitoring the best solution.

Solution

The project conducted a range of coverage tests of several wireless monitoring providers. According to the test results, the Loadsensing gateway coverage circumference reached 3000 feet in adverse conditions, double the distance of the other wireless monitoring provider.

For section 1 and 2 alone, 6 (soon to be 7) Loadsensing gateways are gathering data from more than 600 (soon to be more than 1100) Loadsensing data nodes that are connected to various sensors such as vibrating wire piezometers, multi-point borehole extensometers (MPBX), strain gauges, load cells, liquid levels and tiltmeters. With the opening of section 3, more gateways and nodes are also expected to be installed.

Loadsensing uses LoRa connectivity: a long-range, low-power wireless technology used by IoT networks worldwide. Loadsensing uses a star network topology that can cover a range of up 9 miles/15 km without any repeaters. The wireless data nodes are also IP-67 certified and have been tested in temperatures ranging from -40C to +80C, making them very robust and able to withstand the harshest environments.

Benefits

Loadsensing 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 measure tunneling effects once the movements reach the surface and the buildings and this makes it difficult to anticipate and prepare countermeasures for accidents. Loadsensing and in-ground sensors make it possible to measure the causes of the ground movements and to check if the performance of structural elements in the shafts is as predicted. 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 insight 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 real-time from the beginning to the completion of the project.

Through Loadsensing, the LA Metro expansion project is able to gather data on the stability of the tunnels in an unobtrusive way through the data units that are connected to sensors inside manholes. This helps to ensure the safety not only of the construction site but also the surrounding areas.

Loadsensing data nodes and gateways have been deployed to perform remote wireless monitoring of the LA Metro Purple Line Extension to provide automatically-collected data from geotechnical instrumentation to reveal hidden threats and reduce uncertainties which are inherent in geotechnical construction projects. The wireless deployment also helps minimize costs from cabling and avoid traffic interruptions.

Advantages

  • Gateways and nodes that can cover distances twice as far versus other monitoring systems
  • Less traffic interruption than with manual monitoring
  • More cost-effective than monitoring using cables that require digging trenches

Tunnel Construction Wireless Monitoring for the Los Angeles Metro

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