GROUND VIBRATION DAMAGE ON THE RISE

Ground vibrations can originate from a number of common sources, some of which are – rail and vehicular traffic, jackhammering, bulldozing, pavement milling, vibratory compaction, pile driving, and blasting. The magnitude of these vibrations can range from being entirely unnoticeable, to a minor nuisance, to extremely damaging. Generally speaking, factors that dictate the effect that ground vibrations may have are the strength of the source vibrations, duration of exposure, distance from the source, type and condition of the affected building, and the local soil type. But here is the reality of the matter: Urban development is on the rise and frequently, construction is taking place alongside aging building stock and infrastructure. Consequently, there will probably be an increase in vibration damage claims and here is what you will need to know.

Direct Damage

To best explain this, it is necessary to get technical. Ground vibrations are typically quantified in terms of Peak Particle Velocity (PPV), which can be expressed in millimetres per second (mm/s). Stronger vibrations have a higher PPV. While in Canada there is no national standard for ground vibrations, in other countries it is generally agreed that ground vibrations should not exceed 5 mm/s.

This 5 mm/s threshold is intended to minimize the risk of cosmetic cracking in drywall, plaster, and old unreinforced masonry. If the building is well constructed and in good condition, or if exposure to the vibration is very brief, it is possible for a building to tolerate even stronger vibrations. On the flipside, while instances of this are rare, it is also possible for damage to occur at levels lower than 5 mm/s. But this threshold applies to direct damage only; vibrations can also cause damage indirectly, as a result of soil movements caused by the vibrations.

Indirect Damage

Vulnerability to indirect damage depends on the local soil and the duration of exposure. Soils such as sand, gravel, and some fine-grained soils known as loess, can be compacted and compressed by vibrations, which in turn can result in foundation movement and cracking. Imagine the particles in loosely compacted sand like a house of cards: The vibration makes the particles move around and fall into a more compact configuration, like when a house of cards collapses. Unlike direct damage, there are no standards limiting vibrations to prevent soil consolidation because more research into the problem is needed. However, damage to buildings has occurred in some susceptible soils at vibration levels below 1 mm/s. Therefore, when investigating a vibration damage claim, both the soil characteristics and the ground vibrations need to be considered.

The Human Factor

Building occupants are usually much more sensitive to vibrations than the structures themselves. Vibrations of just 0.3 mm/s can be enough to disturb some homeowners, and vibrations of about 1 mm/s are likely to result in complaints. A vibratory roller compactor working in an area with very hard soils might cause complaints more than 400 feet away! This is why the sensitivity of the occupants is frequently an issue with vibration damage claims. Often, when building owners notice these vibrations, they go looking for damage afterwards. They may find a number of cracks they had never noticed before, which in many cases were actually pre-existing.

Documentation and Communication

Cracking caused by ground vibrations may be indistinguishable from other types of damage. Therefore, a vibration damage investigation involves a lot more than a visual examination. Additional information needs to be considered, including the local soil conditions, the type of building involved, general condition of the building, and the duration, frequency, and source location of the vibrations. But the most valuable information can be documentation of pre-existing conditions. Unfortunately, that information is rarely available.

If you look hard enough, you will find cracks in any house. As a homeowner, it is a good idea to go looking for those pre-existing cracks, and take photographs, as soon as you see any construction work going on nearby. That way, if damage does occur, you will have some documentation of existing conditions from when the construction work started. That record of pre-existing conditions will help in determining the extent of the damages.

If you are a contractor, the best way to prevent complaints is to inform residents if they should expect ground vibrations, and to conduct pre-construction surveys to document existing cracks. Nuisance vibrations are more tolerable when they are expected, and if you do a pre-construction survey, owners will not be discovering pre-existing cracks while the construction work is going on. If vibration damage does occur, a record of pre-existing conditions will help limit the costs of the claim.

Hit the Ground Running

Whether caused by jackhammering sidewalks, new road construction, pile driving, or rock blasting, ground vibrations are a complex matter. They could be nothing more than a nuisance, cause superficial damage to your home, or they could even cause serious foundation damage. Our forensic structural engineers have the necessary experience and expertise to help you with your next vibration damage claim.

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About the Author: 

ADAM LOHONYAI, Forensic Engineer, MEng, PEng

Adam specializes in structural forensic investigation and holds a Master of Engineering degree from the University of Alberta. He is currently a professional engineer licensed in both Ontario and Alberta. Adam’s background includes work as a structural engineer providing design services for new building construction, personal fall arrest systems, roll-over protection systems, and repairs to existing structures, in addition to conducting structural condition assessments and failure investigations. He also has experience teaching engineering labs and conducting research on building envelopes, structural health monitoring, and masonry walls at the University of Alberta.