Construction & Machine Vibrations
Exponent engineers and scientists use many tools to measure, characterize, and evaluate the source and magnitude of induced vibration and its effects on structures and sensitive equipment. Key elements in these investigations include establishing baseline conditions (e.g., prior to construction activities), assessing sources of vibrations, analyzing the magnitude and zone of influence of vibrations on both the structure and the soil supporting it, evaluating damage, and preparing conceptual recommendations for repair.
Construction activities, machinery operation, and large blasts produce ground vibrations that can cause damage to nearby structures either directly from wave propagation or indirectly, primarily through soil densification. Construction activities such as pile driving, blasting, breaking pavement, and vibratory fill compaction, can produce strong levels of vibration and are commonly cited as the cause of damage to nearby structures. Vibrations of smaller magnitude, such as those induced by traffic, construction equipment, rail operations, and oscillating machinery are also alleged to cause damage but are more likely to be felt without causing damage. Vibration effects on structures can include cosmetic cracking of walls and facades, while they rarely cause damage affecting the structural integrity of the building. Vibrations can also have adverse impacts on sensitive equipment.
Exponent engineers and scientists have broad experience investigating damage due to construction vibrations for small and large-scale projects. Key elements in an investigation depend on site characteristics and the needs of the client and may include:
- Determination of the types and extent of damage to structures from vibrations
- Pre- and post-construction condition assessment surveys of buildings
- Pre-construction review of construction plans and activities
- Monitoring, recording and evaluation of vibrations prior to and during construction
- Monitoring with geotechnical and structural instruments and equipment, including: manometers, tiltmeters, slope inclinometers, strain gauges, piezometers, and extensiometers
- Damage assessment at adjacent properties
- Analysis of ambient ground vibrations
- Analysis of measured vibrations induced by construction activities
- Analysis of level survey data and geotechnical and structural instrumentation
- Data Acquisition and Monitoring System Architecture
Exponent consultants utilize a modular data acquisition system to record and monitor construction vibrations that can be adapted to the project’s specific needs. The system uses NI-DAQmx modules to perform analog to digital conversion, allowing nearly all types of sensors to be used with the system. Signals can be sent via wired or wireless connection based on project requirements. The data is then collected and processed on a laptop computer. Remote data access is provided via a 3G/4G data card installed on the laptop computer, or any common internet connection.Exponent’s system is ideal for projects that require distributed data acquisition. The system is portable and can be powered by a variety of power sources, including solar panels. It can be installed in open areas with up to one mile line of sight using a high-gain wireless antenna.
Exponent owns various types of sensors including accelerometers, geophones, tiltmeters, string potentiometers, hygrometers, thermometers, soil pressure sensors, microphones, video cameras, and others. Individual specialty sensors can be purchased and integrated into the data acquisition system.