U.S. cities have become increasingly focused on maintaining vibrant downtown areas, not only to work but live and spend free time. As this results in renovations and new high-rise buildings, it’s important to note the damaging vibrations construction may have on nearby, existing buildings—particularly those of historical significance.
Many municipalities, transportation departments and regulatory organizations have placed limits on the ground vibrations that can occur within a given distance from a structure. Vibrations limits can also be based on potential damage, especially for historical structures which can incur more damage than modern buildings.
Some of the construction activities that can cause damage include the blasting of bedrock, demolition of existing structures, pile driving, equipment operation during site preparation and ground improvement.
As the vibrations from the sources move away through the soil or rock, they are attenuated or damped depending on the characteristics of the material. According to the National Cooperative Highway Research Program (NCHRP), as the seismic wave travels out from the source of the vibration (during a pile driving operation or from a blast epicenter, etc.) the individual soil or rock particles move back and forth over very small distances. The velocity at which these particles can move varies from barely measurable to over 5 inches per second. The maximum velocity at which these particles move is defined as the Peak Particle Velocity (PPV) measured in inches per second.
In addition to the PPV, the duration of the vibration must also be considered. The duration of the vibration can either be a “steady state” from vibratory compactors during fill placement or “intermittent” or “transient” from blasting or pile driving using an impact hammer.
While the primary focus of monitoring and controlling vibrations on and near a construction site is to protect structures, the effects on the people who occupy the structures cannot be ignored. The Federal Transit Administration (FTA) suggests that the root mean squared (RMS) amplitude describing a “smoothed” vibration amplitude is more appropriate for human response as “the human body responds to an average vibration amplitude.”
In addition to PPV and RMS, the frequency of the vibrations is also a factor to consider in the assessment of potential damage annoyance to humans. The NCHRP and FTA have developed damage potential threshold criteria and vibration annoyance criteria along with summary guidelines for vibration levels for construction equipment 25 feet from the source.
To implement one of these programs, it is necessary to develop a screening process and plan for monitoring.
The screening process and plan will typically include but is not limited to:
- Assessment of the vibration sources and levels expected for the project
- Location and condition of structures
- Screening evaluation of expected vibration levels at existing structures based on the vibration source
- Evaluation measures for reducing vibrations, if necessary
- Pre-existing condition survey of structures in question
- Development of a monitoring plan for the building(s)
Some of these steps will require the architect/engineering (A/E) firm, the geotechnical engineer, and the contractor to work together to develop the plan.
PSI works with the owner, A/E firm and contractor during the pre-construction screening process and in the development of the assessment and monitoring plans for the surrounding structures. PSI also provides vibration monitoring services and data during construction to assist the design and construction teams in limiting the exposure of construction-related vibrations to surrounding facilities.
The following PSI personnel should be contacted for assistance in vibration monitoring and additional contacts in PSI:
Mahmoud El-Gamal, Pd.D., P.E., Chief Engineer, District Manager
Phone – (734) 453-7900
Email – firstname.lastname@example.org
John Gordon, P.E., Chief Engineer, Principal-in-Charge for Geotechnical Services
Phone – (901) 365-1802
Email – email@example.com
William Ciggelakis, P.E., FACI, Chief Engineer, Principal-in-Charge for Construction Services
Phone – (214) 330-9211
Email – firstname.lastname@example.org