Bridges constitute a very important component of the transportation network. As they are a major investment for society and are at the core of public transport and usage, it is extremely crucial to keep an eye on their safety and maintenance. This is achieved through geotechnical instrumentation and monitoring, which is involved in the pre, post, and after-construction phases.
Safety in bridges is a bigger concern than in other parts of the transport system since any damage or collapsing of the structure can lead to magnanimous devastation to life and property with severe consequences. With this understanding in mind, Encardio Rite makes use of modern technologies, instruments, sensors, and real-time assessment of the bridge to observe and keep track of all the activities that might affect the foundation of the structure.
In this article, we are taking a look at one such project that was carried out by Rite Geo System, Encardio Rite’s USA Subsidiary. We will be discussing the reason for monitoring, the solutions involved, and the instruments used along with the conclusive result.
Why is Bridge Monitoring Important?
The easy answer to this question is that monitoring is needed to enhance the life of any structure. As mentioned, bridges are a huge investment, and are a part of the everyday transport system; shortening routes, avoiding the lagging traffic, and improving the quality of life of many citizens.
Geotechnical Monitoring and Instrumentation play a huge role in determining the safety and reliability of these structures; alerting when needed. This ensures a longer service life and also avoids any mishaps that might lead to a complete collapse of the bridges. This is not just applied to the new bridges but also takes care of existing structures demanding maintenance and care.
According to the ASCE Infrastructure Report Card of 2017, almost 56,000 bridges (10% of them) in the United States are reported to have some sort of structural deficiency, making them susceptible to unforeseen incidents. This makes us aware of the importance of Bridge Monitoring which involves measurements by sensors, identification of weak points, processing data, and analysing the result and decision-making.
Let’s move forward with our case study of the Harry W. Nice Memorial Bridge.
Harry W. Nice Memorial Bridge – An introduction
The Harry W. Nice Memorial Bridge runs between Newburgh in Charles County, Maryland, and Dahlgren in King George Virginia, USA. It is a 2.7 km two-lane continuous truss bridge, which was inaugurated by Franklin D. Roosevelt in 1938. It was originally named the Potomac River Bridge but was renamed Harry W. Nice in 1967, after the governor of Maryland.
The bridge features an approximate total length of 10,050 ft from the VA shore abutment to the MD shore abutment. It has four 12-foot (3.7m) lanes, 2 in each direction, full shoulders, and a 55 mph (89 km/h) speed limit. The bridge also has 59 lower approach bents placed between 61.5 ft and presents 19 raised spans and piers spaced from 116 to 800 feet. It makes use of reinforced concrete piles and steel H-piles up to the length of 115 ft in its bent/pier foundations.
Monitoring Needs – Harry W. Nice Bridge
The Harry W. Nice Bridge Monitoring plan was formulated to ensure the safety and protection of existing bridges, structures, and facilities which may be affected during the construction of the new Nice Middleton Bridge, embankments, and other similar development.
The monitoring plan is intended to gauge and judge the current structural health of the existing bridge and identify the bridge movements with regard to daily and seasonal weather/climate changes, traffic operations, and the effects of the passing watercraft.
Monitoring Solutions & Instruments
The bridge monitoring project was handled by Rite Geosystems Inc, Encardio Rite’s USA Company. The aim was to provide instrumentation and monitoring for the Harry W. Nice Bridge during the pre-construction and construction phases.
The Scope of work included the supply of geotechnical instruments, Automatic monitoring and survey with compact data loggers and total stations. RGS also made use of an Online web-based data management system (WDMS) and generated daily, weekly, and monthly reports.
Instruments Used
The instrumentation period was divided between the existing bridge monitoring and the construction phase of the new monitoring. Let’s take a look at the instruments used in each of the stages.
Existing Bridge Monitoring
Strain gauges – These were used to measure the strain on girders and trusses.
Tilt meters – They were employed for the accurate measurement of tilt and rotation on trusses and decks.
Crack meters – They are employed to observe any changes in the existing crack and on the epoxy-repaired piers.
Prism Targets – These were installed on piers, decking, trusses, and girders to monitor the X-Y-Z movements.
Datalogger – Automatic compact data loggers with GSM/GPRS modems were used for the monitoring of existing bridges.
Automated Total Station – The ATS System and in-house developed controlled box with GSM/GPRS and suitable software were installed for the remote control of the total station.
New Bridge Monitoring
Piezometers – These were used for the accurate monitoring of groundwater levels and pore water pressure at the land-based foundation construction.
In-place Inclinometer – These sensors are used to confirm whether the movement of embankments, adjacent structures, and retaining walls is well within the planned design.
Borehole extensometer – The extensometer is used to observe the subsurface settlement of underground structures and critical utilities that are near the construction zone.
Settlement points – Similar to IPI systems, these are used to monitor the settlement of embankments and adjacent structures to confirm that they are within design tolerances.
RGS also provided the complete online cloud-based monitoring solution for the project.
Conclusion of the Monitoring Project
The above-mentioned instruments were executed successfully. The real-time data from the tiltmeters, strain gauges, inclinometers, and other installed geotechnical instruments have been made accessible to the consultant/contractor at their work desk. This allows them to have constant and continuous information about the construction activities, without any lag or failures.
In case any of the data crosses the pre-set review and levels, the software has been equipped with the feature to send out warning signs or alarms by SMS/email. Moreover, real-time data assists in the seamless and cost-effective progress of the construction work.
Monitoring platform showing location and IDs of instrument installed
This brings us to the end of our case study on Harry W. Nice Bridge Monitoring and Instrumentation. Hope this was informative.
If you have any questions or doubts, feel free to comment below and we’ll get back to you.
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