With increasing activities in and around our cities the importance of vibration has become a prominent feature. You might have heard of PPV, but what exactly is it and how does that affect us and our projects?
VIBRATION (PPV) – ALL THE ANSWERS!
What is vibration and where does it come from?
Ground vibrations are associated with different types of elastic waves propagating through the ground. These are surface waves, and bulk longitudinal waves and transverse waves (or shear waves) propagating into the ground depth. Typical frequency range for environmental ground vibrations is 1 – 200 Hz. Waves of lower frequencies (below 1 Hz) are usually called microseisms, and they are normally associated with natural phenomenae, e.g. water waves in the oceans.
Ground vibration is measured in terms of Peak Particle Velocity (PPV) with units in mm/s or mm/s-1. It should be noted that the PPV refers to the movement within the ground of molecular particles and not surface movement. The displacement value in mm refers to the movement of particles at the surface (surface movement).
Environmental ground vibrations generated by rail and road traffic may cause annoyance to residents of nearby buildings both directly and via generated structure-borne interior noise. Very strong ground vibrations, e.g. generated by heavy lorries on bumped roads, may even cause structural damage to very close buildings. Typical values of ground vibration particle velocity associated with vehicles passing over traffic calming road humps are in the range of 0.1 – 2 mm/s.
The main sources of ground vibrations at construction are pile driving, dynamic compaction, blasting, and operation of heavy construction equipment. These vibrations may harmfully affect surrounding buildings, and their effect ranges from disturbance of residents to visible structural damage.
Why do we monitor and what are the limits?
Ground vibration can cause serious structural damage but can also be a nuisance to local residents. There are clear limits mentioned for vibration due to construction/demolition in BS 5228-2. In table B.1 - page 36 of BS 5228-2 you will find the guidance on effects of vibration levels. These levels set out the human response to vibration, as in nuisance. When we look at potential damage to buildings table B.2 comes into place. Depending on the type of building there are different limits which are generally higher than the nuisance limits. In general, magnitudes of ground vibrations that are considered to be able to cause structural damage to buildings are above 15 mm/s.
Every ground vibration can be recorded and measured automatically. Since it is simple for everyone to protect people, buildings, infrastructure, soil, air and watercourses from negative environmental impact these days we see more and more demand for continuous automated monitoring so construction & demolition can move forward and communities can be developed with minimal disturbance.
To minimize the impact of vibration caused by construction & demolition works governing bodies often set limits that are aimed to protect individuals from levels likely to cause nuisance and potential cosmetic damage to buildings. You will often see limits of 10 mm/s which is a level likely to cause complaints and is close to the level of potential cosmetic damage in lightweight structures. Amber alerts can also be sent at lower levels to give warning that vibration levels are getting closer to the limits.
It is also useful to store a waveform (very detailed data) when high vibration levels are recorded. This enables you to investigate the actual frequency content of the vibration event. BS 5228-2, table B.2 gives separate limits by frequency which can therefore be accurately assessed.
Please note that the levels in the tables below are for guidance. You will see separate guidance/ limits on vibration close to historic buildings, utilities infrastructure and sensitive measurement equipment found in universities and hospitals.
HOW CAN CAMPBELL ASSOCIATES ASSIST YOU?
The AVA vibration monitor, processes and temporarily stores measurement data from vibrations and air shock waves locally in the instrument. Measurement data is automatically transmitted over the mobile phone network and the Internet to the AvaNet web-based measurement system according to an individual and adjustable schedule. Alerts are automatically sent by e-mail and SMS to those responsible when a measurement is registered that exceeds set limits or if a failure occurs, such as a cable break.
The monitor is fully automated and has full remote access to view & download data, print reports, set alerts and change settings. The AVA vibration monitor is easy to install, maintain and can easily be relocated on site to ensure you can work confidently on site knowing you are working safely within vibration limits.