Ground vibrations is a technical term that is being used to describe mostly man-made

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

s of the ground, in contrast to natural vibrations of the Earth studied by

seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

. For example, vibrations caused by explosions, construction works, railway and road transport, etc. - all belong to ground vibrations.

General information

Ground vibrations are associated with different types of

elastic waves Linear elasticity is a mathematical model of how solid objects deform and become internally stressed by prescribed loading conditions. It is a simplification of the more general nonlinear theory of elasticity and a branch of continuum mechani ...

propagating through the ground. These are

surface waves In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occur within liquids, at ...

, mostly

Rayleigh waves Rayleigh waves are a type of surface acoustic wave that travel along the surface of solids. They can be produced in materials in many ways, such as by a localized impact or by piezo-electric transduction, and are frequently used in non-destruc ...

, and bulk longitudinal waves and

transverse waves In physics, a transverse wave is a wave that oscillates perpendicularly to the direction of the wave's advance. In contrast, a longitudinal wave travels in the direction of its oscillations. All waves move energy from place to place without tr ...

(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

microseism In seismology, a microseism is defined as a faint earth tremor caused by natural phenomena. Sometimes referred to as a "hum", it should not be confused with the anomalous acoustic phenomenon of the The Hum, same name. The term is most commonly used ...

s, and they are normally associated with natural phenomenae, e.g.

water waves In fluid dynamics, a wind wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result of the wind blowing over the water's surface. The contact distance in the direction of the wind is k ...

in the oceans. 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. Magnitudes of ground vibrations are usually described in terms of particle vibration velocity (in mm/s or m/s). Sometimes they are also described in

decibel The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a Power, root-power, and field quantities, power or root-power quantity on a logarithmic scale. Two signals whos ...

s (relative to the reference particle velocity of 10⁻⁹ m/s). 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. Magnitudes of ground vibrations that are considered to be able to cause structural damage to buildings are above 10–20 mm/s.

Ground vibrations from railways

The main sources of ground vibrations generated by railway trains are dynamic forces transmitted from tracks to the ground. These forces are associated with complex processes of interaction of moving train axles with railway tracks supported by the elastic ground. The magnitudes of these forces generally increase with the increase of train speeds. Therefore, the levels of generated ground vibrations may be substantial in the case of high-speed trains. If a train speed becomes larger than Rayleigh wave velocity in the ground, an additional very large increase in generated ground vibrations takes place. This phenomenon is termed ground vibration boom, and it is similar to

sonic boom A sonic boom is a sound associated with shock waves created when an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to ...

generated by supersonic aircraft.

Ground vibrations from road traffic

The main mechanism responsible for generation of ground vibrations by moving cars and lorries is the dynamic forces associated with vehicle passage over road irregularities, such as bumps, peats, etc. These forces, and hence generated ground vibrations, can be reduced by keeping road surfaces in good condition.

Ground vibrations at construction

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.

References

* Skipp, B.O. (ed)
''Ground Dynamics and Man-made Processes''
The Institution of Civil Engineers, London, 1998. * Krylov, V.V. (ed),
''Noise and Vibration from High Speed Trains''
Thomas Telford Publishing, London, 2001. * Santos, J.A. (ed),
''Application of Stress-Wave Theory to Piles: Science, Technology and Practice''
IOS Press BV, Amsterdam, 2008. * Bull, J.W. (ed),
''Linear and Non-linear Numerical Analysis of Foundations''
Taylor & Francis, New York, Abingdon, 2009.

External links