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Wireless Tunnel Construction Monitoring: The Key Questions & Answers

Using wireless technologies for construction monitoring and instrumentation during tunneling projects is nothing new, but generally these technologies are not optimized for the challenges of technical monitoring. This is where the new generation of IoT wireless monitoring technologies has the advantage, offering new possibilities for low-power, long-range, and low-cost data aggregation, transmittance and analysis.

Worldsensing joined Jim Rush, the editor and publisher of Tunnel Business Magazine, for a webinar discussing how wireless monitoring systems can help track performance, identify issues and decrease operational risk during tunnel construction projects. This webinar invited a number of questions from the public – for this article, we have chosen our favorite questions and offer answers below from wireless monitoring expert, Juan Pérez. Juan is a Geotechnical Engineer and Product Owner of the globally recognized wireless monitoring system, Loadsensing. He has a background in geotechnical and structural instrumentation and has been leading the product development of wireless monitoring at IoT pioneer Worldsensing since 2013.

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What differentiates modern IoT wireless monitoring from traditional wireless monitoring?

IoT wireless monitoring is both long-range and low-power. Wireless solutions based on mobile technology (GPRS/3G) – the traditional kind – are more power demanding. As a consequence, with these solutions, the GPRS data-loggers only transmit the data once a day or once a week, especially if they are powered with internal batteries. With mobile technology, operators have to pay according to their monthly plan for each device that they want to connect. With private IoT networks, the operators of the wireless monitoring systems can be the owner of the infrastructure so the data transmission can be free. And most importantly, they can deploy the infrastructure depending on their needs without requiring an agreement with the provider of telecommunications services. They just need to connect the gateway to the Internet with a sim card or ethernet connection in the most suitable location according to the tunnel project.

Other solutions like wireless mesh networks (XBee, IEEE 802.15.4) are powerful for areas with a high density of nodes and can transmit higher volumes of data. However, their short range limits their application in tunnel construction monitoring projects, where the monitoring points are spread over a wide area.

In summary: traditional wireless monitoring is based on mobile technologies, which are power-demanding, short-range and expensive. IoT wireless monitoring, in contrast, offers both long-range wireless connectivity, free data transmission and low-power usage.

What is the radio system based on?

The radio we use for our wireless monitoring system, Loadsensing, which featured in the webinar, is LoRa because we at Worldsensing consider this the best technology available to cover the requirements of the geotechnical monitoring sector. We are constantly evaluating new radio technologies as they emerge and look for the best technology for each application. Our parking management system, for example, also uses Sigfox and has some pilots with NarrowBand-IoT.loadsensing_nodes

Wireless data nodes based on IoT technology deployed in a tunnel construction project

Within construction projects, can the data acquisition system be used for application areas such as water/sewer trenches?

To put it simply: yes, it can. We have projects where wireless data acquisition is used in geotechnical monitoring projects but the system is also featured in cases related to ground-water monitoring (water level, water quality) and other industrial applications.

In our experience, the system best suited for areas such as water/sewer trenches are analog nodes which are flexible and can read up to four sensors of different interfaces (voltage, 4-20 mA, potentiometer, full Wheatstone bridge, thermistor and PT100). They allow monitoring water levels, temperature and also pH, Oxidation reduction potential (ORP) and other parameters related to the quality of the water.

What time span from instrument to server side do you consider “real time”?

There are many factors that can affect data transmission, but based on our experience, the minimum latency is approximately 25 seconds. We consider “near-real-time”, the “almost real time” of the system, when compared to manual readings. In tunneling monitoring, the processes are typically slower so remote wireless data acquisition systems can be considered as “near-real-time”. With wireless IoT systems, the reading can reach the gateway within a few seconds or a few minutes; it all depends on the sampling rate and the size of the network.

We are working on developing something that might be termed a “fast mode” for certain field tests related to Structural Health Monitoring. When operators need to reduce the latency for a project they usually contact us and we find a solution for their specific industry and application area.

What are the power requirements for deploying the data acquisition system?

The data nodes are powered by their own internal batteries, meaning that power requirements only apply to the gateways here. One of the most notable advantages of our system is that the nodes are battery-powered and have a low-power design, meaning that the battery life can last a number of years sampling and transmitting every hour. The power consumption of the gateway is roughly 3W. It is also possible to power the gateway with a solar kit.

What type of data nodes is your wireless monitoring system using with what type of sensors?

We use different kinds of data nodes according to the chosen sensor-type. Below is a table listing the pairs:

Node Types
Compatible sensor
Wireless Tiltmeter
Integrated with its own sensor
Vibrating Wire Node 5 channels
Vibrating Wire
Vibrating Wire Node 1 channel – aluminum box version
Vibrating Wire
Vibrating Wire Node 1 channel – polycarbonate box version
Vibrating Wire
Digital node
Currently:
– Chains of in-place inclinometers and digital tilt beams from Sisgeo, Geosense and RST.
– MDT SMART MPBX extensometer
Analog node 4 channels
– Voltage
– Current loop
– Potentiometer
– Full Wheatstone bridge
– Thermistor
– PT100
– Chains of DGSI Slope Indicator Serial HD In-Place Inclinometers

How can you handle gassy conditions in excavations with a wireless data acquisition system?

A system like Loadsensing is not certified for explosive atmospheres such as coal mines, oil and gas wells. However, a cable can be extended from the sensor to the data node located in an open area (think, for example, of gas pipelines) that does not have gassy conditions.

Conclusion:

Wireless monitoring systems are essential for tunneling projects because the excavation site is a constantly changing and busy working environment, with risks arising all the time. In contrast to manual readings, wireless sensors are easy to install and once there, can transmit real-time data immediately every 5 – 15 minutes. The wireless monitoring system of choice should include data nodes that can be both connected to the wide variety of different sensors used for tunneling projects and configured with a simple app. The information gathered also needs to be sent to one gateway, which should use new wireless protocols facilitated by the IoT.

Wireless systems like Loadsensing are particularly useful during tunneling projects, as not only can the data nodes be configured easily and require little maintenance through low-power consumption, but the internet connection between the data nodes and gateways is very strong. This allows the tunnel construction to be monitored both inside and out as sensors can transmit data up to two miles within the tunnel, and also through manholes or boreholes, and buildings on the surface.

Overall the advantages of IoT-driven data acquisition systems for tunnel monitoring far outstrip the capabilities of traditional wireless and wired monitoring systems, offering a new, cheaper, and streamlined way to make tunneling safer, more cost-effective and more efficient.

Industrial IoT

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