This blog post highlights the first segments of Dr. Storesund’s presentation covering the mechanics of vibration monitoring, key considerations to address when designing and implementing a ground vibration monitoring program, uncertainties often occurring as a result of ground vibration during construction and how to address them, and an overview of best practices when developing and implementing a ground vibration monitoring program for risk mitigation. Subsequent blog posts will elaborate on each best practice in depth, highlight a case study Dr. Storesund is actively monitoring in the field, and share the Q&A from this webinar.
Webinar Highlights
Inzwa and Dr. Rune Storesund, D.Eng. & Executive Director of UC-Berkeley’s Center for Catastrophic Risk Management, presented a webinar entitled, “Implementing Effective Risk‐Reduction Vibration Monitoring Programs” in which Dr. Storesund covered four key topics:
- Ground vibration mechanics, what they are, and why they are important.
- Key considerations when planning and implementing a ground vibration monitoring project.
- Uncertainties that can develop due to ground vibrations during construction and how to address them.
- Best practices associated with effective construction-induced ground vibration monitoring programs.
- A case study and a look toward future enhancements that could increase the.
- utility and robustness of construction ground vibration monitoring to minimize risk exposure.
Construction Ground Vibration Monitoring: Why?
Dr. Storesund outlines a few of the many reasons one might consider implementing a ground vibration monitoring program:
- It is required as part of the project’s specifications.
- Ground vibration data is desired to provide some protections against future litigation.
- Densely populated areas may cause one to try to self-limit ground vibrations to minimize the potential for complaints from homeowners surrounding the site.
Ground Vibration Mechanics: Three Types of Waves in Construction Ground Vibration Monitoring
Dr. Storesund also describes the different modes of ground vibrations typically measured during construction — P-Waves (compression waves), S-Waves (shear waves), and R-Waves (surface waves) – and how these three wave types travel at different speeds through a material. He explains why this is important: first, the total vibration energy is a composite of these different wave types; and second, these waves separate as time elapses and the equivalent magnitude of the vibration attenuates, resulting in less perceived vibration. The result? The further away you are from the source of the vibration, the less the experienced vibration. For most project sites, the decrease in experienced vibration is also going to be non‐linear.
Ground Vibration Mechanics Have Numerous Causes
Dr. Storesund further explains that the factors that can cause the propagation of ground vibrations during construction can be numerous and quite complex, including:
- Type of construction equipment, and how (and where) it will be used.
- Subsurface soil conditions on and adjacent to your site.
- Surface conditions – the composition and whether they are uniform or more heterogeneous.
- Other vibration-contributing sources on or near the site.
- Are harmonic or non‐harmonic waves being generated.
- Frequency distribution of wave energy being emitted.
These are but a few of the factors that should be considered when evaluating the need for ground vibration monitoring of a construction site.
Considerations When Implementing a Ground Vibration Monitoring Program
The list of considerations when approaching a potential new ground vibration monitoring project can be extensive, including questions such as:
- How large or small is the project site?
- What is the proximity of the project site and proximity of the ground vibration-inducing work to adjacent populated areas or structures?
- What is the distribution and density of people around the project site?
- What are the age, condition, and anticipated foundation types of surrounding structures?
- What are the specifics of the planned work, including the proximity and duration of the work to existing structures?
Citing different use cases, Dr. Storesund cautions that no two projects are alike and advises that each project should be approached considering its unique characteristics and situation.
Uncertainties that can Occur During Ground Vibration Monitoring
Dr. Storesund further describes the many uncertainties that can be associated with damage that can occur because of construction-induced ground vibrations. Ground vibrations occurring are not necessarily the problem; they may be more associated with the soil-structure interaction, where ground vibrations result in a physical change to a structure – usually a “crack” that is created (or worsened) as a result of ground vibrations transferring from the ground into the structure through the foundation system.
But here is where uncertainties can arise. What was the condition of the existing structure before the work started? Were there any existing cracks, and if so, what were their dimensions prior to construction? Were these existing cracks visible or hidden? For most typical construction projects, it can be infeasible to do detailed interior and exterior surveys of every house near a construction project.
Also, soil conditions beneath the construction work area can be variable and have the potential to contribute to the risk for construction-vibration-related damage to existing structures. Dr. Storesund recommends that an effective ground vibration monitoring program should take subsurface data and conditions into account to ensure there are no obvious zones of concern that need to be addressed.
Recommendation: Risk Mitigation through Use of Crack Gauges Prior to and During Construction
Dr. Storesund recommends that known cracks in existing structures be documented and measured during construction whenever and wherever feasible. “Much of the litigation associated with construction‐induced ground vibrations focus on either the appearance of cracks or the enlargement and reactivation of existing cracks,” He explains. “If you have the ability to install crack gauges on known cracks, you will be doing yourself and your client a tremendous service because now you have an established, site‐specific data point. If you can document the performance of an existing crack relative to the construction‐induced ground vibrations produced at the site, you stand a much better chance of developing a vibration‐crack relationship for your site and suite of structures.”
Five Best Practices in Ground Vibration Monitoring During Construction
Dr. Storesund also outlines and elaborates upon five best practices associated with developing and implementing an effective construction ground vibration monitoring program:
- Pre-project site screening to ascertain potential exposure to construction-induced ground vibrations.
- Identify mitigation opportunities for the reduction or elimination of substantial ground vibrations.
- Identify and implement management actions to help control vibrations during the course of the project.
- Monitor and enforce the appropriate vibration threshold levels for the project.
- Identify and implement the type of monitoring equipment, data collection, and dissemination protocols that will be needed to help ensure your ground vibration levels are minimized.
Subsequent blog posts will elaborate on each best practice in depth, highlight a case study Dr. Storesund is actively monitoring in the field, and share the Q&A from this webinar.
Also, we’ve gathered a collection of resources Dr. Storesund recommends on best practices in construction-related ground vibration monitoring.
