Many construction companies are honest, decent firms which have considerable expertise in carrying out construction. They may justifiably believe that their work doesn't usually cause damage. But, it is undeniable that damage does occur to surrounding homes and buildings in some contractors' projects (see Is Damage Possible? for a geographical distribution; see Damage Statistics and Damage Prevalence in the CVDG Pro for an extensive discussion of the occurrence, causes, distribution and types of construction-caused vibration damage reported to Vibrationdamage.com).
People who report damage to their homes or buildings are often barraged with a series of assertions about the likelihood and causes of the damage by construction companies, project sponsors, insurers and their paid experts. Some of these assertions are either misconceptions generally or, at least, incorrect in the specific damage instance. In this chapter, I'll discuss a few of the most common such examples of potential misconceptions and misinformation. The discussion will also provide tips on how to clarify the factual basis, if any, on which they rest and judge the likelihood of their accuracy in the situation at hand.
"Construction Can't Cause Damage"
Almost everyone who reports damage from construction will be told this, or something very like it by those connected with the work in some way.1,5 Such statements are, at best, misconceptions, lacking any support whatsoever in the scientific literature of vibration effects and damage. These biases are so ingrained in the thinking of those who work in or with the construction industry that they may contribute to damage by providing a false sense of security to those doing the work. Because this bit of misinformation is so common, a whole chapter of the CVDG, Is Damage Possible?, is devoted to a consideration of it in greater detail.
"The Vibrations Met Standards."
People who report damage from construction or blasting are often told that the construction vibrations "met standards". While these or similar statements might be reassuring to some, they often have virtually no meaning from a scientific standpoint.
First, which standards were "met"? Blasting standards, like the US. Office of Surface Mining standard shown at right, are widely recognized throughout the scientific literature as inappropriate for construction, traffic or other settings with vibrations having durations more than a few seconds long. Yet, blasting standards are still routinely cited and relied upon by contractors and their paid vibration monitoring firms. Standards considered much more appropriate for construction, like the "Swiss" and related U.S. FTA standards,4 are rarely mentioned or adhered to by contractors.
Second, what is the frequency distribution of the vibration(s)? Most standards set lower allowable ground vibration velocities at lower vibration frequencies than at higher ones, due to low frequency resonance interactions with homes. Without knowing both the maximum velocity of the vibration and its complete frequency distribution (derived from Fast Fourier Transform analysis of the vibrations), any such statements about meeting standards cannot be verified.
Third, vibrations are only rarely monitored in construction settings. Too often, people depend upon vibration propagation "calculations", which are subject to many variables typically excluded from the calculations. The variables are excluded to make the calculations easier or because the information required to include them simply doesn't exist. Such calculations are frequently so inaccurate, when compared to measurements (i.e. when "validated"), that they are, at best, educated guesses, in absence of confirmation at the location in question. For more on this topic, see Vibration Regulation in the CVDG and the much more detailed Calculating Vibration Amplitudes in the CVDG Pro.
When faced with assertions about standards, the homeowner should ask to see ALL the supporting vibration monitoring data. He may (not) be surprised to find there are few or none which actually support the "met standards" claim. For a discussion of what ground vibration standards really mean and how they are properly used and interpreted, see Vibration Standards.
"Your Home Is Too Far Away to Have Vibration Damage"
Homeowners are often told by contractors and project sponsors that they are too distant from construction activities to have damage caused by the construction. Where homes are more than 500 feet or so from the construction, that could well be true, in many cases. However, often these assertions are made with no scientific justification whatsoever or on the basis of calculations whose assumptions and input parameters are inappropriate for the situation at hand.
As I've described elsewhere in the CVDG, there is no single PPV value or "safe distance" which is appropriate for all locales, structures and construction operations. The "safe distance" depends on the often complicated specifics of vibration propagation in the soil, the frequency distribution of the vibration, the specific way heavy equipment is used, and the extent to which reflections of vibration waves from surrounding structures augment the PPV through wave interference effects, among other variables. You can check such assertions by reading and using the graphics in our Vibration and Distance chapter, which provides an introduction to the relationship between vibration intensity (velocity) and distance. That chapter also discusses some of the complications that accompany any use of vibration calculations for estimating "vibration safety."
"We Followed (Federal, State, Local) Guidelines."
Construction companies often say things like this to those who report damage. These statements are sometimes false.2 For example, contracts for construction often require a
pre-construction survey and vibration monitoring during the work. Boilerplate language in the contracts usually make the contractor responsible for damage done during the project. Such requirements may also be part of the information for bidders on projects. While adherence to provisions of these sorts is highly variable, depending on locale,
project sponsor and bidder, such requirements are too often simply forgotten or ignored when the job is done.
"Our Employees Are Experts in Construction."
Contractors commonly make statements like this when faced with damage claims. Of course, any work that results in damage could be considered to argue against such declarations. But, all too often, those "experts" ignore operator's manuals for their heavy equipment, as well as contractor policies, when doing the work.
The "experts" in one project, who damaged many homes by pounding with an excavator bucket on asphalt pavement, disregarded both company policy and specific prohibitions in the operators manual for the excavator used. In another example, shown at right, a half ton piece of concrete was dropped repeatedly in front of both the seismograph and the damaged homes - months after the damage was reported.3 Undoubtedly, there are many responsible, knowledgeable construction employees out there doing careful work, but describing all construction employees that way would be much too charitable. If you can identify pieces of heavy equipment likely to be responsible for damage, you'll want to download copies of the operator's manual for that equipment to see if the construction workers really were as "expert" as claimed.
"The Damage Is Pre-Existing."
You will almost certainly hear some version of this rationalization, if you report damage. It is, by far, the most common counterargument (see Counterarguments in the CVDG Pro for a more extensive discussion of most of the common counterarguments) offered by contractors and their paid "experts". Such conclusions are usually made on the basis of nothing more than a brief (usually well under a minute at each damage site) visual inspection of (some) of the damage. Our own studies, reported briefly in the CVDG and in detail for more building material types in the CVDG Pro chapter, Estimating Damage Age, show that the time spans for visible changes in crack edges, due to erosion effects, to appear are frequently so long (often far longer than the project length) that it is difficult to draw any meaningful conclusions about crack age just by visual, macroscopic examination of the sort usually done.
An "expert" can offer an opinion about damage age, but real scientific data don't support simple visual inspection as a reliable means of arriving at the time of damage onset. When you hear such a statement, ask for the supporting, verifiable scientific facts behind the opinion. Broad claims of "experience" alone do not constitute scientific facts. The best way to combat such questionable conclusions is to have witnesses who can testify to the condition of the home as close to the onset of construction as possible. Real estate people are often excellent in this role, as they tend to look at a home more carefully than the average visitor.
A particularly harmful version of this "pre-existing damage" misconception is the claim that the damage was "latent" (i.e. about to happen, but not visible prior to the construction). Since latent damage prior to the construction work cannot be, and was not, seen, by definition, such a claim can neither be supported nor disproven with real scientific evidence. In the absence of some considerable and very specific scientific evidence proving that unseen damage was present in the structure in question, latent damage assertions should be considered not merely as unscientific, but anti-scientific. Ask for scientific proof, in the situation at hand, that latent damage was present, if you are presented with this assertion.
"We Have Never Had a Damage Claim Before."
Many contractors will make this representation in the face of a damage claim. It is sometimes false. Even the best, most careful contractors are likely to have experienced claims in the past, if they have done more than a few jobs. That is part of the reason contractors must carry insurance for every job. The contractor may not believe that the prior (or any other) claims were legitimate, but that belief (often completely unsupported with scientific evidence) does not change the fact that the claims were made. A quick search online of the contractor name will usually reveal at least some of the litigation claims made against the contractor, if they exist. This information can be especially valuable if the contractor makes similar "no prior claims" statements in litigation.
"We Did It the Only Way We Could."
This misconception takes many forms, and may only be implied, but it is almost always false. For example, asphalt pavement must be compacted to achieve acceptable densities, but there are lots of options for doing it. In urban areas, where vibration damage is a particular concern, the contractor can choose to use an oscillatory compactor, which has lower vibration associated with its use than vibratory compactors. Failing that, he can choose a vibratory compactor whose vibratory frequency is as high as possible, at least over 40 Hz, since resonant interactions with homes occur most strongly at frequencies below 40 Hz. In particularly sensitive areas, he can carry out static compaction, as advised by the Federal Transit Administration in its Noise and Vibration Manual (at left).4
Similarly, there are many options for demolition operations, some of which may be safe in the country, but not in the city. Pile driving also has considerable damage potential, if close enough to homes. Yet, the contractor can use a resonance pile driver, instead of a hammer pile driver, if he is within 100 feet of homes. There are always options which will mitigate vibration; the contractor just has to be aware of them and use them.
Homeowners, too, sometimes have misconceptions of their own about vibration damage. Their misconceptions are often more understandable, given their usual role as innocent, non-technically-trained, uninformed by-standers in construction. The two most common of these is concern over all felt vibrations and the idea that any cracking seen must be a result of nearby construction. Since damage potential is related to the velocity of vibrations (see at right), not all vibrations are damaging. Similarly, most homes more than a few years old will begin to have a few hairline cracks in drywall or plaster, unrelated to construction. For more about what vibrations to be concerned about, see the CVDG's Judging Vibrations. To learn about how to differentiate construction-related damage, read the CVDG's Recognizing Damage.
This chapter can't discuss all of the many examples of misconceptions and misinformation that one might hear with regard to a vibration damage claim. Its aim is to point out the ones most frequently heard and provide some ways of assessing their credibility. In the end, all parties should insist on real documentation for any claims made to them and real scientific evidence behind any "expert" opinion.
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