- Devising and Installing the System
- Requirements and Challenges
- Serving the Data to the Client
- Managing Data and Alarms
- Analyzing the Data
- The Value of Innovation
The site already includes a very busy railway corridor, a bus tunnel and a historic building. This required Watpac to provide assurances to the owners of those assets — Queensland Rail, TRANSLink and the South Bank Corporation, respectively — that the 12-month construction process would not damage them. With this in mind, the company needed a geospatial solution to monitor the work in real time, non-stop, from start to completion, and alert it to any deformation that could lead to a collapse and endanger lives — so that trains and busses could be stopped before they entered the hub and construction personnel could be evacuated in time.
“Our goal was to provide a level of assurance that there was no effect on the tunnel or the rail line,” says Dave McIlwraith, a Watpac project manager. “It was very important to us to provide the stakeholders comfort that what we were doing would not affect their infrastructure.”
Land Solution Australia Pty. Ltd., a private consulting firm, came up with a complete geospatial solution that included total stations, geotechnical sensors, and a wired and wireless communication system to feed the data to Watpac’s Trimble 4D Control software platform.
“This solution collects different data types from many sources, manages them in near real time via a secure central server, and allows a host of users the ability to analyze or combine the data in a variety of ways, for different purposes,” said Lee Hellen, a professional surveyor and Land Solution’s director. “We negotiated the terms for the installation with the client and integrated the different technology partners on the project. As registered surveyors, we had an understanding of the client’s accuracy requirements, geospatial context and IT needed to support the solution. To deliver this project, we relied heavily upon the equipment and expertise of our technology partners — namely, UPG (a distributor of positioning technology and software), two geotechnical companies, Saros and ES&S, and IT company Runge ICT — to provide the vibration and geotechnical sensors and IT knowledge.”
The installation began in April 2014 in the bus tunnel and took around a month, including configuration, baseline observation, and communications and IT. Land Solution attached 36 monitoring prisms to the capping beam and the tunnel lining by drilling and grouting, and further attached 102 prisms to the running rails of the tracks using epoxy. Land Solution installed one total station in the tunnel and a second one on an adjoining building. Overall, it took less than two months to install the total station sensing components and about 20 geotechnical sensors, including logistical delays caused by site access constraints required to prevent interference with the buses and trains. Among the challenges was trying to deliver a monitoring system while construction had commenced and the site was constantly evolving, according to Simon Sprague, a geospatial technical consultant with UPG.
The monitoring system will be removed as soon as a sufficient structure has been built to hold the basement together, McIlwraith pointed out. This is expected to take about 55 weeks.
The project required geotechnical and survey observations with 24-hour automated alarming whenever realistic engineering design tolerances were exceeded. Delivering the complete system required technical expertise in surveying and vibration, as well as communications and IT.
“Various levels of precision were required across the site for the survey and geotechnical monitoring,” Hellen said. “In all cases, a baseline was observed to ensure realistic limits could be achieved after the system and site constraints were identified.” In the bus tunnel, if the survey tolerances were exceeded by 0.5 millimeters (0.02 inches), the system would send out a warning. If the tolerances were exceeded by 2 millimeters (0.08 inches), it would issue an alarm. The capping beams were expected to deflect by 6-7 millimeters (0.24-0.28 inches) and the rail track by 10-15 millimeters (0.4-0.6 inches).
Therefore, all the observations had to be extremely accurate and had to correct for changes in the environment. However, it was very difficult to monitor temperature in the tunnel, because the atmosphere was not constant throughout the 24-hour cycle. During the day, the buses were stirring up the air, but at night it settled into different layers. In addition, the tunnel’s exhaust fans were switched off at night. “We had to observe the total stations observations through layers of different temperature,” said Hellen. “This presented some difficult challenges in terms of vertical angle refractions for the observations. To solve this problem, we isolated some of the alarms at different times of night during the project, to allow for the unpredictability of atmospheric effects that we could not control.” Additionally, to help maintain the precision of the observations, the tunnel operators agreed to run the fans at night, which kept the atmosphere constant.
A separate challenge was the extent of the communications required to provide the data to the customer in real time, reliably, and constantly for a year.
Finally, McIlwraith points out, there was the challenge of “liaising with the different departments to put the monitoring plan in place and to insure that there was no negative effect.”
All of the sensors were connected to an outside server, which ran Trimble 4D Control (T4D) software. “One of the real challenges — which makes this project quite unique — is the way in which we serve up the data to our client,” said Hellen. This is accomplished by means of a web user interface, desktop software, and SMS and e-mail messages.
It would have been highly problematic to send data directly from the total station in the tunnel to the server by radio. So, instead, it is sent to an adjacent communication box that converts it to a TCP/IP format.
The output from that box is then sent along the bus tunnel, through about 100 meters (330 feet) of Ethernet cable, to a radio housed in another communication box positioned for a clear and uninterrupted signal to another radio located across the rail lines and the excavation, about 150 meters (490 feet) away from the server. The second total station, which is on top of a 15-story building, has a direct radio link to the server. Three on-site field data loggers use GSM modems to send the data to an on-site server and 900 MHz radio connections control the total stations through a Trimble Pivot infrastructure software platform.
Watpac engineers access the monitoring data via a web user interface from the T4D software. It enables limited access, if needed, to control the alarm levels and it determines who receives which alarms. For example, some engineers might be interested in certain geotechnical data, but not in the data from the total stations.
Depending on the severity and type of the alarms, the T4D software automatically sends SMS or e-mail messages to specific contacts, so users can log in at any time and determine the legitimacy or severity of the alarm.
The T4D web user interface also allows Watpac’s engineers to analyze the data, look at trends and data for periods of their choice, and plot various data types against each other. The monitoring system effectively measures movement over time in horizontal and vertical axes. The geotechnical data is sent as a DAT file via the 3D data connection from the data logger on site to a server, where it is ingested by the T4D software, which automatically processes the data and provides analysis output.
According to Hellen, every day the survey equipment delivers 8,400 measurements, and the environmental and geotechnical sensors deliver possibly tens of thousands of observations. The public stakeholders can access all of them via the web portal. The site is updated automatically and key people regularly access it 24 hours a day to analyze the data for specific purposes. This sets a new benchmark in the way construction sites can be monitored.
“We are using the data daily during the excavation to monitor, because things are moving,” said McIlwraith. “For example, by monitoring the data, we can ensure that the beam on top of the piles is moving within the calculated engineering parameters.”
The monitoring data is analyzed in real time through the Trimble Pivot platform — which collects the data from the field, processes it, and then sends it through to the database, which then serves it up online to be viewed and analyzed.
Trimble T4D was configured by Land Solution Australia to include standard reports, as requested by the engineers, and allows them to customize the reports should they wish to create their own. The engineers on site, who are required to monitor specific trends, can use it to select the data of interest to them — for instance, between two dates — and create their own trend analysis. T4D will then retrieve the appropriate information and graph it for them. For example, they might want to plot a temperature trend against that of the movement of a prism over the course of a day. “Our job is to provide high-quality reliable data to the engineers so they can interpret it,” Sprague said. Users can also access the T4D database using SQL to produce custom reports and analyses.
The monitoring project combines data from several different mature technologies. “The innovation in this project has to do with the challenges and constraints,” said UPG’s Rodd Yann. “We had to deal with the constraints of a live project, in the sense that there were very busy public transport utilities always being utilized. So, it was innovative in the way we went about doing that with T4D.”
The project also was innovative because it brought the geotechnical sensors into a single platform, as well as graphed and reported the geospatial information that surveyors conventionally deal with, and did so harmoniously. Hellen hopes that it will soon be possible to visualize monitoring in 3D, using computer graphics. “In addition to graphs and 2D representations of the data, we believe it could be even simpler to interpret the results of our monitoring using a 3D animation or fly-through inspection in the near future,” he said. “So, we are looking to gaming experts from our local community to visualize the results, creating greater meaning for the stakeholders.”
The dynamic nature of any construction project poses unique challenges for monitoring. From the beginning, decisions such as where to place the total stations, sensors and server — and how to connect them — required a solid understanding of the construction project and of how it would grow and evolve. It was also critical to put in place a good IT infrastructure and test the technology as much as possible off-site before installing it. Finally, it was important for the team to have good relationships with all the parties involved. Management of the solution by a professional surveyor committed to the needs of his client was critical for the successful delivery of the project.
The Southpoint geospatial solution has contributed to the safety of both the workers on site and of the public who use the public transport corridors. It also serves as a powerful risk management tool for Watpac, providing it the data it needs to limit the risk of damage to surrounding assets during the construction project. According to McIlwraith, the monitoring project has been “quite a learning experience” and “it has been very good.”
By collecting and serving a variety of real-time geospatial and geotechnical data that the client can easily combine and analyze, the Southpoint project provides a model for monitoring complex and dynamic work sites.
Matteo Luccio earned a Master’s Degree in political science from MIT. He began his career as a magazine writer and editor, about 20 years ago, as co-founder and editor of a public policy magazine. He switched to geospatial technologies 14 years ago and has been covering them as a freelance writer ever since. He lives in Portland, Oregon.