Letters (February 01, 1999)

Dear editor:

Vibration from construction equipment, or blasting operations commonly results in claims from nearby homeowners for structural damage to their residence. It is now common to conduct pre-construction surveys of such residences to document any existing damage prior to starting the construction project. This is especially true if blasting is to occur.

There are still many instances where damage is claimed, but there is no pre-construction survey, so the adjuster must decide whether the cause of damage was related to the work done by their insured contractor. There are analytical techniques available to assist this decision, so adjusters should be aware of this and hire experts as required.

Homeowners are often convinced that the vibration cracked their home, so the claims are not fraudulent. However, homeowners are often mistaken in their belief, so it takes an expert opinion report to convince them of the real cause of damage.

Over the years, there have been numerous tests and studies of construction vibrations. Papers have been published throughout the world on this topic. The International Standards Organization has published a Standard ISO 4866, first edition 1990, to provide guidelines for measurements and evaluations of vibration effects on buildings.

Soil vibration is measured in different ways, but one common measurement is peak particle velocity (PPV). Testing indicates PPV of 0.01 in/sec is perceptible to humans, while PPV of 0.30 in/sec is disturbing to humans. When humans detect vibrations in this range, they then assume that these vibrations are damaging their structure.

In fact, vibration damage thresholds for structures start at 2.0 in/sec PPV, based on testing. At this level, “cosmetic damage”, such as hairline cracks in drywall can begin. To reach the second level of damage, “minor”, where cracks through bricks can occur, requires at least 5.4 in/sec PPV, and “major” damage, such as foundation shifting, can begin at 7.6 in/sec PPV.

Variables, such as magnitude and frequency of vibration, soil type, and distance from source to structure, are important in estimating the PPV in any given situation. An expert can visit the site, examine the damage, collect the necessary data, and estimate PPV exposure to the structure. This can then be compared to damage thresholds, and an opinion on the cause of damage can be developed.

When faced with vibration claims, don’t get “shook up” about it; just call an expert to tell you whether cause is vibration, settlement or some other mechanism.

Yours truly,

Rene G. Caskanette, B.A.Sc., P.Eng.

Caskanette & Associates Consulting Engineers