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CVDG - Executive Summary
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The Construction Vibration Damage Guide (CVDG)Executive Summary
Construction vibration damage to homes and other structures is increasingly recognized around the world as both real and much too frequent. While there are no readily obtained estimates or studies of the occurrence of construction vibration damage worldwide or in the U.S., virtually every U.S. state and territory and over 100 other countries outside the U.S. are among those who have registered copies of the free Construction Vibration Damage Guide (CVDG) PDF at Vibrationdamage.com. Explicit damage reports among those registrations currently relate to well over 1600 different construction and/or blasting-related projects worldwide. When misused, or used properly too close to homes and other structures, heavy construction equipment can, and does, damage them. Those involved in or with the construction industry routinely say, in effect, that construction can't cause damage. Such statements are, at best, based on highly selective readings of the scientific literature and inappropriate application of clearly unsuitable blasting-derived vibration standards, if they are based on any scientific understanding at all. The all-too-common use of blasting vibration standard limits in construction settings not involving blasting is directly scientifically contradicted. Inappropriate application of blasting vibration limits results in a high probability of damage to structures. Many construction contractors are responsible and mindful to avoid damage from their operations. Much of the far too common damage which occurs is brought about by operations performed improperly and/or in violation of both company policy and the use manual instructions for the equipment involved. Even some "properly done" construction operations, e.g. impact pile driving and use of vibratory compactors in compaction operations, are known to produce vibrations which can cause damage, if done too close to the nearby property and structures. There are well-known mitigation actions which contractors can take at minimal time and monetary expense to reduce or avoid damage. Not all vibrations felt by people generate damage to structures. People can perceive vibration at about a factor of ten lower ground peak particle velocity (PPV) than the lowest vibration standard limit for homes and other structures. The ground vibration velocities which are sufficiently large to have a potential for causing immediate damage are considerably higher than those usually encountered. Construction vibration damage can take many different appearances and be both cosmetic and structural in nature. Cracking in wall finishes, both interior and exterior, is the most commonly observed damage manifestation (especially along approximate diagonals to wall penetration corners). Wall cracking is also sometimes accompanied by door and window misalignments, slab and other concrete cracking, masonry damage, damage to exterior property walls, plumbing and HVAC damage, and property damage separate from that done to structures. These damage types are often traceable to vibration-caused shearing ("racking") of the structure and its components. Damage may or may not appear with or immediately after the vibrations; it can take months to become fully evident, as the structural stresses produced by the vibration are slowly resolved. Much of what is known about vibration damage to structures has been gleaned from extensive studies of blasting vibration effects, particularly by the United States Bureau of Mines (USBM). Blasting vibrations last for a few seconds at most, less than the duration of the vibrations induced in a home by nearby blasting. Continuous or long-lasting (more than "a few seconds") construction vibration enhances resonance and fatigue effects in home vibrations, which are far less significant in short duration, relatively infrequent and relatively widely-spaced blasting events. Construction vibrations last far longer than the natural duration of home vibrations, allowing resonance and fatigue effects far more time to do damage through additive build-up of vibrations in the structure, a process referred to as "amplification". Further, typical heavy equipment-caused construction vibrations have vibration frequency components which are mostly within the resonance frequency regimes of homes (below 40 Hz in frequency). This is well shown by an extensive set of Fast Fourier Transform-derived dominant vibration frequency data from a road reconstruction job, involving virtually all the common types of construction heavy equipment. Ground impact-related vibrations generally are particularly worrisome in this regard. A quantitative analysis of vibrations from a road reconstruction project shows that total movement in construction vibration can be from tens to hundreds of times that generated in a "worst-case" mine blasting setting over the same period of time. Construction vibration standards set substantially lower velocity limits for vibration than those set for blasting. Historic buildings and cultural assets require still lower vibration velocity limits. The relative scarcity of directly relevant studies of construction vibration effects leaves many of the most critical scientific questions unanswered. Vibration attenuation equations are often used to calculate vibration velocities at distance and to estimate safe distances. While valuable, these must be properly used and at least a factor of two safety margin applied to any calculated result to account for a host of variables not included in the typical calculations. Homeowners with valid damage claims face many obstacles in handling their claims and pursuing repair reimbursement for damage done to their homes and property. Most home insurance policies carry exclusions for "earth movement", which are often invoked by insurers, with little or no scientific justification, to avoid paying claims in construction vibration damage cases. Construction companies are well-experienced in dealing with claims and have money and legal resources to support their positions, placing the homeowner at an additional disadvantage. Structure owners with vibration damage damage must have extensive documentation of the damage and of the construction procedures and equipment used to establish the causal link to the construction activity necessary to pursue successfully a claim for damages. The best approach is to head off vibration damage problems prior to construction by documenting the house condition and register your concerns in public comment meetings. A homeowner should give serious consideration to how to pursue a claim, perhaps even getting an attorney, if the repair cost for the damages will justify the time and expense. There are currently few, if any, real checks and balances either to limit or remedy construction vibration damage. While science-based national vibration standards exist for various vibration sources, state and local implementations of vibration regulations are mostly limited or non-existent, making it difficult for those with damage to pursue their claims or for local agencies to stop unnecessarily risky and/or damaging work. Most vibration damage is easily prevented by good planning and proper use of equipment. In the end, we all pay a price for construction vibration damage, even if the burden falls disproportionately and unfairly on those whose homes or buildings are unnecessarily damaged by construction vibration. A more extensive summary of the information available on Vibrationdamage.com can be found in the CVDG Introduction and Summary, which we suggest all visitors to Vibrationdamage.com read.
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