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Vibrations cannot be completely avoided during any type of demolition and earthworks. Falling or rebounding demolition parts transmit vibrations via the ground to the foundations of neighbouring buildings. Vibrations can also be triggered during dynamic soil compaction work with heavy construction equipment and vehicles, for example in the case of deep foundations within less load-bearing soils.
Vibrations are mechanical vibrations of solid bodies that can cause damage or nuisance depending on their strength and emission location. These generally include
- Effects on humans and animals in buildings,
- Impacts on structures,
- Impacts on the subsoil beneath structures,
- Effects on technical devices.
The specifications of DIN 45669-2, June 2005, Measurement of vibration immissions - Part 2: Measurement methods and the specifications and reference values from DIN 4150-3, December 2016, Vibrations in buildings - Part 3: Effects on structures provide an evaluative framework.
The vibration velocities, measured in [mm/s] and vibration frequencies in [Hz], are relevant for the assessment. The DIN 4150-3 provides tabular reference values for these two variables for various building types (categories) and components (foundation area, top ceilings). Unacceptable vibration effects on the surroundings can be allocated to the cause and, if necessary, to other sources by means of metrological recordings during construction. After analysing the data in the context of the construction process, and if necessary the construction diary, the data is usually displayed using the date and time.
If the vibration loads during the construction period are below the DIN reference values, the results can be used to avert unjustified claims.
Measuring principle
The vibrations are recorded by geophones in the three perpendicular spatial axes (X, Y and Z). The geophones have vials for adjusting the position in the room and markings on the X and Y measurement axes; the Z axis is the vertical axis. There is the option of wall mounting or stable mounting feet are used. A handy, portable computer contains the data logger and interfaces and is connected to the geophone. The computer is customised according to the desired or necessary specifications. The measuring interval and duration of the measurements are programmed manually or via software, for example, and the device is put into operation on site. Limit and alarm values can be specified, which can be sent wirelessly as text messages or by e-mail to programmed recipients.
A well-known manufacturer is the company Profound from the Netherlands. It supplies a series of devices called VIBRA and VIBRA+.
Prof. Burmeier Ingenieurgesellschaft mbH carries out vibration measurements as part of evidence preservation procedures and thus helps to prevent damage to buildings caused by construction work.
