Issues Related to Construction Vibrations in Densely Populated Cities

Existing buildings near active construction sites experience vibrations. When they are not properly mitigated, these construction-induced vibrations can disturb occupants, cause service interruptions, and/or result in damages to adjacent buildings. Due to the increasing density of buildings, issues related to construction-induced vibrations are emerging as a concern in many cities across the United States. Besides a few exceptions, limited guidance is available in local building codes to assist engineers, building officials, developers, contractors, owners, and building occupants to proactively evaluate the risks associated with vibrations from adjacent construction.

What Are Construction Vibrations?

Vibrations are the cyclic motion of a physical object with respect to its position at rest. Objects vibrate when excited by dynamic actions. Buildings, for example, vibrate side to side when subjected to wind or seismic forces. Building floors vibrate up and down when people walk across them. Similar to wind, seismic, and footfall actions, construction equipment is a source of vibrations that affects the buildings we live in.

Construction activities, such as pile drilling, pile driving, soil excavation, soil compaction, demolition, heavy vehicle traffic, etc., cause local disturbances to the soil particles which result in three-dimensional ground motions (or vibrations) that propagate away from the source. The intensity (or amplitude) of the induced ground vibrations depends primarily on the type of construction equipment, the energy imparted to the soil, the types of soil the waves travel through, and the relative position of the receiving object from the wave source.

The amplitude of ground vibrations is measured as the velocity (or, interchangeably, displacement or acceleration) of a particle in the ground as it moves from its position at rest. Vibration amplitude is often the only parameter used to assess the severity of construction-induced vibrations. While there are many circumstances that prove this concept true, it is not always correct. In fact, objects respond differently to vibrations of the same amplitude, but different frequency. Vibration frequency is the number of full cycles completed by an object (or a soil particle) every second. The frequency at which soil particles vibrate due to construction activities is a variable of the construction equipment and the soil medium.

As construction vibrations travel through the soil, they shake the buildings that are in close proximity to the construction site. This shaking can cause discomfort to the building occupants, can disrupt operations of vibration-sensitive equipment, and/or can damage building components. As urban density is in constant growth in cities across the United States, owners, developers, contractors, and engineers are becoming more sensitive to the negative effects that construction vibrations may have on adjacent buildings. Failures in anticipating and/or mitigating these negative effects often lead to legal disputes.

What are the Effects of Construction Vibrations on Buildings?

Construction vibrations transmit through the foundations to the walls and floors of the adjacent buildings. When the floor vibration amplitudes exceed levels that are perceivable by the human body, the adjacent building residents’ initial reaction is likely to worry complain. They complain because it is annoying having to perform daily activities while their floors vibrate. They worry because they believe that the vibrations are damaging their buildings. Anecdotal evidence also shows that adjacent residents tolerate construction vibrations more when the adjacent construction project is perceived as useful to them.

Potential issues also arise when construction activities occur in the proximity of facilities housing vibration-sensitive equipment, such as electronic precision instruments, operating theater equipment, optical balances, electron microscopes, etc. This type of equipment requires a quiet environment to operate safely. Construction vibrations can add up to normal ambient vibrations and cause service interruptions.

Construction vibrations can also damage adjacent buildings. As buildings shake, wall and floor finishes deform. When these vibration-induced deformations exceed the materials’ strengths, the architectural finishes crack. The majority of vibration-induced cracks in adjacent buildings are generally cosmetic. Cosmetic cracks are superficial, hairline cracks in the architectural finishes that do not affect the load-bearing capacity of the building and, therefore, do not constitute a life threatening concern. Often, special care should also be devoted to hardscape features and artwork. A correlation between critical vibratory thresholds and the appearance of cosmetic cracks in plaster and drywall finishes are a ressult of experimental research in the mining industry. These vibratory thresholds, expressed as functions of soil particle velocity and frequency, are used today to control the effects of construction activities.

Buildings crack naturally as they age. Thermal expansion and contraction, changes in material properties, fatigue, structural overloading, foundation settlements, construction defects, etc., are examples of mechanisms that cause building cracks. Distinguishing between normal wear and tear cracks and vibration-induced cracks is often a challenging task without a thorough documentation of the building’s condition predating the start of the adjacent construction.

Pre-Construction Evaluation

Before a new construction project begins, it is good practice for the new construction team to alert their future neighbors of the upcoming project. Adjacent owners and residents should be educated on the type of construction activities that will take place, the anticipated vibrations levels the neighbors will experience, and the measures that will be implemented to minimize the risk of causing damage. It is also of paramount importance to document the existing condition of the adjacent buildings. The preconstruction condition assessment should be detailed and exhaustive.

Adjacent residents and owners generally pay closer attention to the status of their buildings upon feeling construction vibrations and often notice preexisting cracks for the first time. This often constitutes the basis for complaints and, eventually, legal disputes. A preconstruction survey provides critical information on how to resolve such disputes.

Construction Vibration Monitoring

The cooperation and dialogue between construction team and neighbors should continue during construction. The most common and effective way to document the effects of the ongoing construction activities is through monitoring the induced ground vibrations. Construction vibrations are commonly monitored using seismographs placed at critical locations around the construction site and in proximity of the adjacent buildings. Acceptable vibration thresholds (expressed in terms of particle velocity) should be determined on a project-by-project basis and be approved by both the construction team and the adjacent building owners. Special attention should be given to events that cause vibration levels in excess of the approved thresholds. It is critical to understand the cause of these events in a timely manner and remediate any detrimental effects of the construction activities in a timely manner.

Conclusions

The industry-accepted best practice for limiting complaints and legal disputes from excessive construction vibrations generally includes the following:

• The construction team should engage the adjacent building residents and owners before construction begins and educate them on the effects of the future construction activities.
• The condition of the adjacent buildings should be thoroughly evaluated and documented before construction begins.
• The effects of construction activities, in primis through vibration monitoring, should be continuously evaluated and reviewed with the adjacent residents and owners for the entire duration of the construction.

The lack of specific guidance from local codes may leave the execution of these challenging tasks up to contractors and developers. Engaging experienced matter experts to guide the construction team before putting shovels in the ground is generally a good strategy to limit neighbors’ complaints.