Construction Vibrations and Damages
Year after year contractors are involved in claims due to vibration from construction activity. Vibration can result from activities such as blasting, pile driving, sheet pile installation, demolition, truck and excavating equipment operation, as well as vibrating compactors during backfill operations. Many of these claims can be avoided by conducting a pre-construction survey of current vibration levels with additional monitoring during the activities that may increase vibration.
Residents and businesses in the vicinity may notice cracks in walls and foundations after activity commences. Many of these, however, were pre-existing and are just now being noticed. It is usually impossible to determine when these cracks occurred; therefore, we have only the resident’s or business owner’s word that they are new and need to be fixed. A little pre-planning and preparation can save a contractor from potential problems.
Pre-Construction Survey
As the name implies, this survey needs to be completed prior to any activity on the project. It is important to evaluate and describe the location of the project. For example, a project being constructed in a remote location where traffic is minimal and no surrounding homes or businesses are located is unlikely to need a vibration level determination. However, if you are constructing in a city or built-up area where traffic is continually streaming, then you will need to measure the existing effect that cars, trucks, buses, etc., are having on surrounding sidewalks/footpaths, buildings and homes.
Seismographic monitoring should be conducted by an independent, qualified consulting company before and during operations. You must first establish a base line vibration level from regular traffic and then evaluate the potential for damage with the increased activity. In many cases, the background vibration is equal to or greater than the vibrations caused by construction.
Photographing or videotaping pre-existing cracks in surrounding buildings and sidewalks/footpaths can help reduce the potential for future claims. If existing cracks are found, crack monitors should be placed across the gap to evaluate the effects of construction activities.
Historical Data
Cracks in buildings may result from a host of sources separate from construction activity. Along with the other typical sources of cracks, such as normal settling and dewatering, you must consider the seismological activity that is occurring or has occurred. Many countries are susceptible to seismic activity on a regular basis. This activity falls short of being classified as an earthquake.
Some research may show the occurrence of a seismic event of a magnitude that could have caused stresses or damage to structural components of the building. Another option is to evaluate past construction or demolition activities in the area to see if there have been vibration issues.
Areas experiencing severe drought may also see cracks develop from settling, due to the lowering of the water table.
Expert Evaluations
On many projects the contractor is able to evaluate and document the surrounding building exteriors for obvious existing damage prior to the start of a project. This documentation must be dated and identified by location. Where strong vibrations are expected (such as pile driving or blasting), it is prudent to hire an expert in seismographic monitoring to conduct pre-construction surveys.
They also should conduct monitoring during construction operations at locations they determine will best reflect the vibration levels that impact surrounding buildings and structures where damage may occur.
If you are using explosives, qualified persons should be used to design all shots in order to minimize vibrations. This could involve methods such as increasing the number of delays or delay periods, decreasing pounds of explosives per delay, or other means.
Documentation and records of inspection are your strongest ally should you be required to defend against a claim. Retain these records in your project files since claims may be made several years after project completion. Project records should be kept at least as long as required by the municipality or local legislation.
