Complying with municipal bylaws for good vibrations

An example of vibration measurement equipment, along with a box to capture and store data.
Photos courtesy Aercoustics Engineering Limited

By Nicholas Sylvestre-Williams, M.Eng., P.Eng.
The Crosstown, a light rail transit (LRT) project set to run across Eglinton Avenue, is expected to make it easier to traverse Toronto when finished. Unfortunately, that is not much consolation to residents and businesses in the middle of the construction zone. According to Metrolinx, the agency responsible for road and public transport in the Golden Horseshoe region, more than 200 complaints about the tunnel-boring have been received since November 2015. The new LRT is not the only project to garner complaints in the area. From new buildings at Ryerson University to condo tower construction, the City of Toronto has fielded numerous calls about construction noise and vibrations.

Toronto is only one of many municipalities to receive resident complaints about this issue. In Ottawa, multiple homes in the Lowertown neighbourhood were left with damage after experiencing strong vibrations from an adjacent condo development site. Residents blamed the excavation, sheet piling, dewatering, and drilling for ceilings dropping, drywall cracks, and other damage.

Large and small construction projects alike can cause problems. For instance, Edmonton’s infill housing program may be upgrading neighbourhoods, but it can also cause issues with adjacent properties if no one controls the amount of vibration. Damaged fences are usually easy to mend, but flooded basements and vibrations causing tiles and drywall to crack are more concerning. In both Ottawa and Edmonton, construction sites did not violate existing bylaws, but likewise did not make for friendly neighbours.

Having learned from these kinds of conflicts, more cities are starting to explore bylaws to help protect neighbouring sites when a construction project gets underway. The concern is always the impact of the project on its surroundings—by having bylaws related to vibration, municipalities can protect themselves from risk, placing the responsibility on builders and their clients.

Toronto has a bylaw on this matter already, under Chapter 363 of the Toronto Municipal Code. Implemented in 2008, it requires construction companies to monitor anything potentially having vibrations—large or small. However, there is a significant difference between a noticeable shake and vibrations actually causing structural damage.

Measuring vibrations
A condo tower resident could feel vibrations on the 10th floor of his or her building and raise the alarm, but this may not mean there is actually a problem. The average person will feel a vibration at around 0.1 mm/sec—however, for a vibration to cause structural damage, it needs to be at 8 mm/sec, about 80 times higher. Drilling into bedrock and digging holes produce very different vibration levels, not all of which will cause issues with the neighbouring building.

Vibration measurement equipment can be modified to fit in the necessary space on a construction site. Here, the box is attached to a steel beam to measure ground vibrations.

Even when a bylaw exists, its enforcement relies on construction companies monitoring their own sites. There is a possibility a location’s vibration measurements may never be reviewed, but if there is a problem with a neighbouring site, the company would be required to produce its data to show the project’s vibration levels. The most crucial times for vibration monitoring are the demolition, excavation, and drilling stages.

One of builders’ biggest misconceptions is thinking vibration monitoring is just an optional ‘check mark’ to complete before starting a project. Prior to the bylaw in Toronto, there was no accountability for this kind of problem, but now there is a risk with construction that needs to be mitigated. The requirement for companies to monitor vibration in turn calls for engineers with equipment suitable for measuring vibrations accurately.

Standard equipment usually includes an accelerometer or geophone to measure vibration, along with a box to capture and store the data. Simpler units only measure data and store it for later review, while other systems are equipped with cell modems offering more than just a single vibration level result. These systems allow professionals to measure a vibration, record a sample, store and send data, and set up alerts for any issues via e-mail or phone text.

Monitoring vibrations
Pre-condition surveys are needed before construction can begin, and vibration monitoring usually requires equipment to be set up in multiple locations. If the ideal vibration levels are exceeded, the project team must stop work immediately and determine how to solve the issue. Exceeding the vibration limit does not mean neighbouring sites are automatically affected, but it is a problem that must be investigated before work can continue.

In Toronto, any vibration overages must be reported to the client and city. However, before an incident is reported, an engineer should review and confirm the monitoring results. If a brick falls next to a monitoring station, for example, it may cause an overage not actually reflecting what is happening at the site. Thus, it is best for an acoustical engineer to provide confirmation.

Demolition, excavation, and drilling are the major causes of vibration on a construction site. These vibrations need to be monitored regularly to ensure there is no damage to any neighbouring projects.

Working within the limits
For work exceeding the acceptable vibration limits, there are options. A mix of equipment and manual labour may be required. If a project abuts a heritage building, there is a good chance smaller pieces of equipment will have to be used, and it will take longer to complete the construction. However, these steps mean the structure of the historic building will remain secure.

Cracks—in the drywall, for example—do not necessarily indicate damage, structural or otherwise. Assessing structural damage goes beyond the visual—for instance, assessments may involve watching the size of a crack to determine if it grows larger or longer during construction, but structural damage can also mean things start to tilt, lean, or settle.

Projects in Toronto are also required to respond to any complaints from neighbours. However, since projects can take months or years to complete, good neighbour relations should go beyond responding to complaints; a team should be proactive about any onsite activity.

The City of Toronto is currently reviewing construction noise bylaws to see if they need to be changed. As with vibration, these laws will not require all noise to cease, but they may be updated to reflect change in the Toronto construction market. With more home and infrastructure construction expected across Canada within the next few years, the need to monitor vibrations and their impact on the surroundings will increase.

It is important to remember shaking ground may not indicate damage. However, professionals must also be aware vibrations need to be monitored throughout the construction process to ensure surrounding structures suffer no ill effects.

Nicholas Sylvestre-Williams, M.Eng., P.Eng., is a registered Professional Engineer and Designated Consulting Engineer in the field of acoustics, noise, and vibration, with 13 years of experience. He is a partner at Aercoustics Engineering Ltd., a privately held engineering consulting company. Sylvestre-Williams works on architectural and environmental projects, and has completed many studies on noise and vibration impacts for many proposed and existing buildings. He has presented at national and international conferences on acoustics and vibration, taught acoustic theory and practice for various organizations, and served as an expert witness for the Ontario Municipal Board (OMB). Sylvestre-Williams can be reached at nicholass@aercoustics.com.

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