Geotechnical Illustrated: Good Vibrations or Not?

Heavy construction in densely populated cities can be conducted near neighboring buildings. Vibrations induced by such heavy construction are one of the most claimed causes of adjacent building damage. These vibrations can be generated by multiple types of equipment such as pavement breakers, excavators, or pile drivers. Such activities can generate short term vibrations or contribute to longer periods of increased vibration levels.

Property owners experiencing construction-induced vibrations may file claims for nuisance or cosmetic/architectural and structural damages. Since the vibration threshold for nuisance is typically lower than the threshold to cause any damage, property owners may express concerns about vibrations that are not substantial enough to damage their property. During the COVID-19 era, more residents stay and work from home, giving a rise to construction-induced vibration claims.

Construction activities cause vibrations of various amplitudes and frequencies that propagate within the subsoils. The waves propagated through the soils typically attenuate with distance. Wave attenuation is caused by geometric and material damping. Geometric damping is caused by the spreading of the wave front over an increasing area. Material damping is caused by energy converted to thermal energy within the subsoils. The attenuation of vibrations with distance is typically estimated by a straight line in a double logarithmic plot of peak particle velocity (PPV) versus distance.

Construction vibrations are typically a nuisance to residents; however, many times they can contribute to property damage. Ground vibrations may be of sufficient magnitude to cause direct damage to structures. The magnitude of vibrations that causes damage varies with the type and the vibration response of the structure. For example, generally historic buildings are more sensitive to vibrations compared to modern residential or commercial buildings. Vibration damage can vary from threshold damage such as paint loosening, or minor damage such as masonry cracks to major damage that can cause structural weakening and distress. Various levels of threshold PPVs have been evaluated in the industry for different structures and damage levels. For example, Caltrans (2004) has proposed threshold PPVs as low as 0.12 inches per second for extremely fragile historic buildings to 2 inches per second for modern industrial buildings.

Vibrations can also cause indirect damage. For example, they can cause densification of loose soils beneath buildings, resulting in differential settlements. Vibrations can also cause partial loss of strength of loose saturated subgrade soils and hence contribute to loss of bearing capacity. Both for densification and for partial loss of strength to occur, a sufficient shear strain within the subsoils should be triggered (i.e., threshold shear strain) and enough vibration cycles should occur.

Vibration levels can be measured by geophones (i.e., velocimeters) or accelerometers. Geophones have been traditionally used in construction and is a proven technology. Accelerometers historically were less effective for the lower frequencies of construction vibrations, however modern accelerometers may be competitive with geophones. Such devices can relate to data collection systems, which automatically stream data to interfaces such as Geocomp’s iSiteCentral® portal. Such systems can also automatically provide text or email alerts to all involved stakeholders.

The vibration data measured at a site can be compiled, and over-laid with a series of other data such as aerial imagery, property parcels, tax assessor information, city maps, surface elevations or others. These publicly available geospatial data and project specific data, including damage claim data, can be combined within GIS software to create an incredibly robust tool to efficiently perform sophisticated analyses of damage claims. Once the data are input in a GIS system, the user can create graphics and statistics that allow for analysis of the specific issues of each property. Moreover, the graphics produced can become very compelling exhibits in a dispute (e.g., court exhibits). 

Compiled publicly available geospatial data and project specific data, along with any pre and post construction surveys of any adjacent buildings are efficiently analyzed to answer both simple and more complicated questions such as:

  1. Are construction activities sufficiently close to cause damage to the subject property? An overlay of construction drawings, field records, along with aerial photos allows for estimation of the distance of the subject property and the limits of various construction activities such as pavement removal, excavations, and pavement compaction with private buildings and improvements.
  2. Can construction-induced vibrations contribute to the claimed conditions? A geospatial overlay of the measured peak vibration levels can indicate whether significant vibrations occurred within a construction period and at what distances from the subject properties.
  3. Are there any effects of non-construction activities that need to be considered? For example, has the damaged property ever been flooded from a large flooding event? A simple overlay of the property and an inundation map could show if that ever occurred. Can vegetation affect the measured cracking within a building? An overlay of a city-wide tree map and aerial imagery can show whether any trees exist that can contribute to this damage mechanism. 

Fortunately, many effects of construction vibrations can be mitigated. If damage in a building is claimed due to construction vibrations, then the above mechanisms can be investigated to demonstrate cause-and-effect.

Antonios Vytiniotis is the Director/Group Lead of the Massachusetts Consulting Group at Geocomp. Antonios has wide experience in evaluating and mitigating damages from machine and construction vibrations.

Published by Geocomp Blog

Geocomp is a company of people dedicated to delivering best-value services and solutions to help clients identify and manage risks to natural and built environments using innovative applications of science and technology.

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