Ground vibration comes from many sources in the construction, mining and energy development industries – but no matter where it comes from, it can create a wide range of concerns for adjacent neighbors and structures. When dealing with man-made vibration, you must understand and quantify the amplitude, frequency and duration of the vibration event. You must also understand the unique engineering properties of the structure to understand its dynamic response and ultimate susceptibility to vibration. GeoSonics/Vibra-Tech’s vibration monitoring services provide the solid technical information and vibration data needed to assess such concerns and devise solutions.
Why do you need to monitor vibration?
In order to manage your vibration, you need to know what you are trying to protect. Once you know what you need to protect, you can set vibration limits. Monitoring is done for a number of different reasons, including
- Permitting
- Project specifications
- Regulatory compliance
- Community relations
- Litigation
In any of these situations, you will need vibration data to verify you are staying within set limits specific for your project. Monitoring data allows you the confidence to know you are operating at levels that are safe for the structures you are concerned about, thus giving you peace of mind and the ability to mitigate your vibration risk.
How do you measure vibration?
Seismographs are digital instruments used to measure ground vibrations. In order to characterize ground vibrations, data is collected in three independent directions of motion (x, y and z). Seismographs used for blasting and construction vibration monitoring measure ground vibration in terms of particle velocity and operate over a 1 Hz to 250 Hz frequency range. Most vibration criteria developed to prevent damage to offsite structures is set in terms of particle velocity.
On-site or remote monitoring: Which is better for your project?
In the past, vibration monitoring was conducted on‐site by a technician. Today, Re:mote Monitoring Technology allows you to access your project vibration data anytime on any device.
An on-site monitoring unit requires someone to be on-site to set up and man the instrument. They would use the instrument to monitor vibration and report any changes or concerns. They can also move monitors based on the location of the vibration source.
Re:mote monitoring requires an instrument to be installed at a strategic location to constantly monitor and report vibration levels. It can be set to send alerts when levels near programmed limits.
What is your vibration impact?
To assess your vibration risk you need to first define all the variables on the project that influence the vibration impact. The two primary factors that will control the vibration impact for your project are the distance from the vibration producing event and the energy output of the equipment that will be utilized.
When assessing the vibration impact, start by defining areas of concern and determine their distances from the vibration inducing activities. Next understand the means and methods for each task of the project and if it will produce vibration. If so, gather specifications on energy output and operating frequency for the equipment that will be utilized. All this information is critical for predicting expected vibration levels and determining standoff distances for equipment.
The variables off‐site that can influence the vibration impact of the project are the type and condition of the adjacent structures.
- Are the structures residential, commercial, or industrial?
- Are they single or multi‐story?
- What type of foundation might they have? Are they in good condition or poor condition?
- How far are the structures from the vibration source?
Additional factors of concern are sites that have vibration sensitive soils. These sites are usually characterized by loosely consolidated silts and sands that may be water saturated. Gather any geotechnical information that may be available for the site.
Special attention should also be paid to structures that may have vibration sensitivities such as hospitals, museums, laboratories or manufacturing facilities. In these facilities, understand the particular piece of equipment or procedure that may be vibration sensitive and gather any information on the make and model of the equipment and/or it’s vibration tolerance.
How do you develop a vibration monitoring and control plan?
The single, most important factor for mitigating vibration risk is determining appropriate vibration limits for the project. If you have a project that requires vibration monitoring, you should ask yourself, “Why am I monitoring?” If the answer is, “to protect myself in case of a claim”, then the vibration limit is critical to your defense and must be justified by a sound engineering decision and supported by science.
Vibrations have a very real potential to cause damage or unnecessary annoyance if not properly limited. There are several different sources of vibrations such as blasting, pile drivers, compaction equipment, hydraulic hammers, rock wheels or tracked vehicles that may operate in close proximity to adjacent structures.
These pieces of equipment operate in different frequency ranges and can have various levels of energy output depending on the manufacturer and model. If the operating frequency of the equipment is near the natural frequency of the structure, there is a very efficient transfer of energy from the ground to the structure.
How do vibrations affect structures?
Because of the nature of vibrations, the vibrations can affect adjacent structures in two ways. The vibrations may cause the structure to respond and shake the structural elements causing cracking conditions to occur or the vibrations may cause a softening of the soil beneath the structure which leads to settlement and cracking conditions in the structure. The vibration limit for one may be different than the other. Vibration criteria should identify the most critical concern.
What should be included in a vibration monitoring plan?
One of the key elements to managing construction vibration risk is to develop a vibration monitoring and control plan for the project. A vibration monitoring and control plan is usually developed by a professional engineer with many years of vibration experience. The plan should detail the location for the monitoring equipment, the type of equipment and sensors to be utilized, and the method for coupling the sensor. The plan should also specify the maximum allowable vibration level at each monitoring location based on all of the site‐specific variables.
The plan should also establish a warning level less than the criteria and determine key personnel to be notified once this level is reached. At the action level the plan should specify if work stops, who is responsible for stopping work, and what changes could be made to equipment or methods to reduce vibrations.
Finally, the Vibration Monitoring and Control Plan should make predictions of vibration levels at critical locations from the various pieces of equipment proposed for use and determine zones of influence and the associated vibration risk for each piece of equipment.
Learn more about mitigating your vibration risk. Contact GeoSonics/Vibra-Tech for a customized vibration control plan for your project today.