The standard situation can be described as follows: Adjacent to existing buildings construction activities are planned. These activities include e.g. using of heavy equipment, blasting or ramming. The owners of the existing buildings want to make sure their structures are not damaged due to the planned construction activities.
As a first step, the state-of-health of the existing buildings (cracks) has to be carefully defined and documented by a third party. We rely on Corak Engineering here.
As a second step, instrumentation and admissible levels of vibration, in most cases of velocity (see last parapraph) have to be defined. Based on our experience we can offer consultancy here.
The standard procedure consists of installing two measurement devices, one on the foundation, the other one at the top floor. These usually consist of a GeoSIG VE 33 geophone plus a GMS-24 recorder with GSM-modem. They measure, acquire and store the 3D-velocity vibrations. Unless the admissible level is surpassed, the daily report contains a graphic display of the measured maximum values per minute. In case of the admissible value being surpassed immediate action is taken (see below) (Project Stallikon).
Monitoring and Signal Processing
The GeoSIG GeoDAS software package is applied.
Permanent Recording: The admissible level not being surpassed, the GMS-24 device stores the maximum-per-Minute velocity value for all three directions plus the vectorial sum of the three on a local chip. Daily or weekly downloading of this data is performed using a GSM connection between GMS-24 and our office.
Event Recording: In case the admissible level being surpassed, two things happen: a) A respective alarm is distributed via SMS to up to ten recipients, and, b) the GMS-24 stores the measured signals continuously during a time window and with pre- and post-trigger times to be chosen. The sampling rate can be chosen to e.g. sR = 100 Hz, sR = 200 Hz or sR = 500 Hz. Downloading of the stored time signals can also be performed using the GSM connection.
Comprehensive solutions. There are cases where more than one structure is to be monitored and/or where monitoring consists of high-frequency, 24-hours-per-day data acquisition for several weeks. It is then necessay to dispose of a high-speed internet connection. (Mainau Office Building).
Rating of measured vibration levels:
Structures: SNV 640’312a, DIN 4150-2. These standards offer very vague rules when it comes to rating the probability of damages due to vibrations. We offer consultancy in this quite delicate matter.
Human Beings: ISO 2631, DIN 4150-3. These standards are formulated very clearly and are hence easy to use.