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Real-time vibrations monitoring (SPPV) and automatic alert notification

Case studies

Geobit, September 2016

1. Vibrations Monitoring

The purpose of this system is to record vibrations in buildings being caused by human activity or construction works, for example industrial vibrations or construction/demolition works that may be carried out in the monitored building’s neighborhood. The monitoring is performed in real time 24/7, and it is intended to analyze the velocity spectrum and calculate velocity magnitude of the movement of the building.   The user can make decisions about actions that have to be taken for reducing the level of the vibrations in order to protect the building.

Thresholds for each sensor can be set separately. If the threshold level is exceeded by the amplitude of the oscillation caused by the nearby activities, alert messages are generated and sent until the velocity level falls back below the activation limit.

2. Instruments

The recording system consists of the following parts: three-axis velocity sensor, seismic digitizer, central datalogger as well as the necessary power supply and surge protection equipment.

2.1 Seismic Sensors

Modified C100 type, 3 channel velocity seismic sensors, can be used (Fig 1 and 2). The sensor ranges from 0.005 mm/sec to 100 mm/sec, and has frequency response from 1 Hz to 300 Hz and a dynamic range 138 dB. Two types of the sensor are available based on installation requirements, a surface type and a borehole type.

2.2 Seismic Digitizer

The digitizer of the application (Figures 3 and 4) is the SRi32S datalogger unit, which includes a three seismic channels digitizer unit and a local recorder, and supports real-time data transmission over the seedlink protocol. It also includes a GPS receiver in order to provide high precision timing. The unit has low power consumption, thus it can operate continuously for many days getting powered from a 12-volt battery.

Figure 1

C100 borehole sensor

Figure 2

C100 surface sensor

Figure 3: SRi32S Digitizer/Recorder

Figure 4: SRi32S Digitizer/Recorder back view

Figure 5: Central recording PC

2.3 Central Recording System

The central recording system (Figure 5) consists of a small linux PC which supports industrial type hardware to withstand outdoor conditions. It has low power consumption, it does not require cooling fans, and provides all the necessary peripherals for collecting, storing and transmitting the data from the interconnected digitizers in real time.

3. Installation

The borehole type sensors can be settled into a shallow hole (small post hole) in the ground. The surface type sensors can be mounted using quick dry cement. The cables must me passed through flexible plastic protective tube. The shelter that houses the instruments has to be a metallic box suitable for outdoor use.

Figure 6: Surface type sensors

Figure 7: Borehole type sensors

Figure 8: Installation in progress

Figure 9: Monitoring system shelter

4. Automatic real-time ground vibration velocity calculation (SPPV) – Software (GEOShock)

The communication and analysis software (GEOShock) is running on a linux pc, with the following features: Signal waveform plot, FFT analysis, spectrum response, energy content per frequency, file conversion in ASCII format, individual trigger level set of each sensor, alert via e-mail or sms when SPPV exceeds predefined limits etc. The software can be installed into any computer and thus the user can receive data in real time and have them processed in multiple receiving points. The software includes the data plot software “SeisGram2k” and the SPPV monitor.

The implementation of the software has been developed in such a way that it provides continuous monitoring and recording of the vibrations in real time, calculating in parallel for every minute, how many times the SPPV limit has been exceeded (if so). The SPPV limit is not constant but linear to the frequency from 10 to 100Hz and can be derived from the structural study of the building.

The software has the ability to send automated email notifications to the user in case of a limit is exceeded.

Figure 10: Real-time velocity waveforms from the six sensors (18 channels)

The SPPV velocity calculation is automatically performed from the monitor service program GEOshock that processes the data in real time, calculates the SPPV magnitude and displays it in a plot as a function of frequency. It also plots the maximum SPPV value calculated for every minute.  If the SPPV threshold is exceeded, the user receives an alert e-mail containing the maximum value that exceed the threshold.

Figure 11: SPPV vs frequency

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