Construction vibrations can impact all three areas of concern: human perception, harmful effects, and structural damage, and special care must be taken to mitigate their effects, particularly for pile driving or other vibratory impact operations. Dowding (1996) provides an excellent resource for understanding the issues surrounding construction vibration monitoring.
The general issues involving human perception are the same as outlined under Traffic Vibrations.
Procedures for measurement
The guidelines and procedures outlined under Traffic Vibrations above are entirely applicable here.
Traffic Vibrations Table 10 applies for construction vibration concerns as well.
The general issues involving harmful effects are the same as outlined under Traffic Vibrations.
Damage to Structures
Besides blasting operations, construction vibrations also have potential for damaging structures. This is particularly true for pile-driving operations, pipe pulling/driving, tunneling, and other methods that require high vibratory energy.
Figure 224. CVM-2 continuous vibration monitor. (OZA)
As with blasting, special procedures are recommended to mitigate or minimize the potential for litigation (Dowding, 1996). These include the following:
- Calculations of probable motions (peak particle velocity) at the nearest structure using empirical formula.
- Preconstruction tests, to directly measure attenuation characteristics.
- Preconstruction crack surveys, to web manual the existing status of nearby homes.
- Monitoring, using more than one instrument, preferably one next to the closest structure or residence in each direction.
- Control of construction operations, using instrument data, i.e., evaluate predictions in the light of actual data and make adjustments.
- Careful and thorough web manualation.
Procedures for Measurement
Most blast monitoring seismograph manufacturers have begun to supply instruments capable of also recording construction vibrations, and particularly vibrations from pile-driving operations. However, there are differences. A blast seismograph is designed to record a single, short- duration blast event, and in the presence of a pile-driving operation, its memory capacity will be rapidly exhausted. Manufacturers have modified these instruments so that once the memory is filled, new events will be evaluated, and if the amplitudes exceed the stored data, the instrument will overwrite the data. This means that when a day's recording is completed, only the maximum events are stored in memory. Vibration Recommendations Table 11 provides links to these manufacturers. Following the manufacturers instructions is generally all that is necessary.
It is vital that the instrument be placed in a location where the sensor can be firmly coupled to soil. This is often accomplished by using spikes on the bottom of the instrument, but sometimes it is necessary to dig down to remove loose soil.
Modern construction vibration monitoring seismographs (figure 224) automatically provide analysis according to requirements, and compare this analysis to the Office of Surface Mining and Reclamation and Enforcement (OSMRE) guidelines. This is appropriate, even though these are not blast vibration events, because the OSMRE guidelines are essentially response spectra. The limitation of using the OSMRE curve for construction vibrations is that response spectra do not properly represent energy. Obviously, there may be a greater impact from a pile-driving operation that lasts for weeks, than a single blast.