TECH BULLETIN - CONSTRUCTION VIBRATIONS
October 2011

Introduction

Construction activities have the potential to cause vibrations that are perceptible to the occupants of nearby buildings. Common construction activities which cause concern are quarry and construction blasting, vibratory compaction, and pile driving. Vibrations may result in annoyance and be the suspected cause of cracking or other damages. In many cases, particularly with heavy construction in close proximity to occupied structures, documentation and monitoring should be considered prior to construction. If concerns surface after the construction is complete, the level of vibrations that occurred at a particular building can still be estimated using engineering analysis. In most cases, the determination of whether or not a certain construction activity caused particular damage can be made within a reasonable degree of engineering certainty.

Fig. 1 - Blasting at Construction Site
Fig. 2 - Pile Driving at Bridge Construction

General

The strength of vibrations at a given building depends upon the work performed, the proximity of the building to the vibrations, the structure of the building and the soil conditions. If the vibration energy created by the work is near and great enough, vibrations can cause building damage, typically in the form of cracks. However, the level at which vibration energy is felt by people is typically well below the vibration energy required to cause damage to a building. This often leads a building occupant to suspect that newly discovered cracks were caused by recent vibrations, when the damage may have pre-existed the vibrations.


Pre-Construction Surveys

Pre-construction surveys can play a significant role in vibration damage claims and litigation. A pre-construction survey should include the documentation of cracks and other damages in and around buildings near the intended work.

When building access is permitted, inspection and documentation of the interior and exterior should be performed. If permission to access the property is not given, photographic documentation of the building exterior from the nearest public right of way is a viable option. Seismographic monitoring is an important component of vibration analysis. If permission is granted by the building owner, the monitoring equipment should be placed adjacent to the building. Otherwise, the equipment can be placed at a distance from the work that is similar in distance and direction to the nearest building. A plot of the seismographic data is developed from which vibration strength at any given distance from the work may be predicted.

Fig. 3 - Driving Sheet Piles
Fig. 4 - Seismographic Equipment
Fig. 5 - Sample Vibration Attenuation Curve

Post-Construction Investigations

Fig. 6 - Single Drum Vibratory Roller

The second phase of a vibration claim investigation is research into the work performed and equipment used. A visit to the work site is often helpful in conjunction with the property damage inspection. The goal is to obtain information regarding dates and nature of work, construction equipment used, pre-construction surveys if available, seismographic monitoring reports, and geotechnical reports. A written request for information is typically made to the parties responsible for the construction. Finally, after the construction data has been obtained, engineering analysis is performed to estimate the vibrations and determine the potential for damage due to direct vibrations and or settlement. The determination as to whether or not vibrations from construction activities were responsible for cracking or other damage requires the study of two mechanisms by which damage may occur. First, the direct vibrations or shaking of the structure as a result of the construction activities must be determined and compared to known thresholds for damage. Second, in the case where the structure is founded on a cohesionless soil such as sand, the potential for settlement of the structure as a result of vibrations can be approximated by rational analysis.


Closing

Vibration damage claims can be reduced by pre-construction surveys to document existing cracks and other conditions. Seismographic monitoring provides actual ground vibration experienced by nearby structures. In the absence of seismographic data, engineering analysis can be used to estimate the maximum vibrations at a given structure. The vibration data is used to determine whether the vibrations could have caused the damage.



Please contact us at The Pepper Engineering Group if you have any questions or need assistance.

THE PEPPER ENGINEERING GROUP, INC.
6135 NW 167th Street, Suite-26 Miami, Florida 33015
(305) 655-1115 / www.pegroup.com