The importance of vibration monitoring

From a piling contractor's point of view - Aarsleff

Piles are the permanent foundation support to many structures in certain areas of the UK, whether they are bridge abutments for major infrastructure, a hospital, school, factory or residential development.

As such, it is vital to know the likelihood of disruption that could be caused by installing piles, so as to minimise or alleviate it. An increasingly key aspect of project management during construction is to understand the impact of ground-borne vibration on the surrounding community.

Driven piling involves displacing soil as the pile penetrates ground. The energy produced by the piling hammer to achieve this will result in a degree of ground vibration. Yet a vibration's magnitude generated by wellmanaged driven piling operations can be kept well within limits and is unlikely to cause structural
damage, albeit these vibration levels will be noticed by residents nearest a construction site.

Complaints out of anxiety that structural damage might occur can be allayed by good communication and demonstration of vibration monitoring at sensitive
locations.

When planning a new project, a thorough site investigation must be carried out. This will then determine the piling operation's suitability and highlight areas of concern. Vibration criteria can be detailed in the piling specification.

To ensure conformance, the use of vibration-monitoring equipment during driving is generally employed by the contractor or an independent third party.

In instances where known issues are specific to a particular region or site, the vibration criteria may outline monitoring of the operation so as to manage the change to procedures, like hammer fall height or frequency, working hours to avoid disruption at certain times of the day, or the introduction of pre-drilling.

There is little doubt that the operation of a continuous-flight auger or bored piling rig creates less vibration than a driven piling operation, though on sites underlain by weak soils, the extra wheeled transport and tracked excavators associated with the technique will create noticeable levels of vibration, which would
also benefit from vibration monitoring.

Kevin Hague, general manager at Aarsleff, comments: "Remote vibration monitoring will allow the industry to dispel myths and understand the potential for damage caused by driven piling and appreciate some of the precautionary measures that should take place at the planning stages, plus manage the change of operational procedures should problems occur."

The future of vibration monitoring

From a vibration monitoring consultant's point of view - Vibration Monitoring Services

With changes in legislation, working practices, advances in technology and machinery, vibration monitoring could look very different in 5-10 years.

Companies are already asked to take care planning the sequence of works so that the transfer of vibration to nearby properties is minimised, and in some cases project managers are instructed to monitor ground-borne vibrations, react and adjust work methods to ensure vibration levels remain low.

In future, a wider scale of building specifications could insist on ground or party-wall vibration monitoring as an essential tool to monitor vibration levels arising from piling and other construction activities.

As available space becomes tighter, it will be imperative to protect surrounding properties from the effects of excessive vibration during such works.

Advances in technology will be key to monitoring residential properties and sensitive structures like electrical sub-stations, railway viaducts, gas mains and buildings of all types.

Vibration monitoring consultant Stuart Collins adds: "Advances in remote monitoring technology make remote vibration-monitoring systems like the RDL//Vibe an effective tool within the vibration-monitoring industry."

When carrying out works that may produce vibration, all potential receptors must be considered, with particular attention paid to occupiers and users of buildings, hospitals or laboratories, as well as cosmetic or structural damage to buildings or heritage sites.

People's responses and complaints to perceptible vibration are usually concerned with fear of the unknown and the potential effects of relatively low levels of vibration in buildings. Concerns are best addressed by monitoring affected areas to assess the levels of vibration being generated, keeping this to a minimum and providing reassurance to affected parties.

How is technology shifting?

From a vibration-monitoring equipment manufacturer's point of view - Caption Data

Remote shock- and vibration-monitoring products now fall under the overall description of the Internet of Things, a rapidly growing industry in itself which will exceed 4.9 billion connected devices by the end of 2015.

Specific developments to benefit these products include:

• • Availability
  Through globalisation and developments in manufacturing processes the world over, key components that make up remote shock- and vibration-monitoring systems have much shorter lead times, as a result shortening lead times on monitoring systems, allowing vibration-monitoring projects to begin in days (in most cases) as opposed to weeks, or more.
• • Robustness battery life
  Advances in circuitry design, components and manufacturing make modern monitoring products very robust. Caption Data's latest remote monitoring product consumes micro-amps and offers up to six years of battery life.
• • Connectivity
  For many applications, GSM is still a favoured solution, and improvements in roaming along with unsteered SIM card technology virtually abolish reception black holes. Alter­natives such as Ethernet, Wi-Fi and whitespace (if available) are all possibilities too. For example, Caption Data was able to provide a remote-monitoring solution to a lighthouse, situated about 13 miles (21km) offshore, allowing a team of researchers to understand more effectively the dynamic structural response of one of the most iconic lighthouses in the British Isles.
• • Local intelligence
  The RDL//Vibe by Caption Data offers local intelligence and will monitor up to six channels locally in real time at 500Hz, comparing to your alarm thresholds (which can be set and changed via the CDLSmartHub). If any events exceed the alarm threshold of a particular unit, the RDL//Vibe will collect the data for the duration of the event and e-mail a notification.
• • IOT controls and intelligence
  This refers to the ability to add third-party algorithms, aggregate data from multiple sources, view units on dashboards with automatic geo-pin markers offering status inform­ation, receive alerts with audit trails, download and share information digitally with colleagues or third parties, and more.
• • Secure data
  Data is stored on secure servers managed by Caption Data. The RDL//Vibe was designed to be robust enough for use in harsh environments such as construction sites yet simple to use and sensitive enough to capture low-frequ­ency vibrations. Since the product's initial launch, Caption Data has added a range of developments which include:
  • • Roaming sims - to reduce signal-related issues
  • • Doubled battery capacity - increasing field life up to 12 months, in some instances
  • • Extended range of geophone frequencies
  • • PPV (Peak Particle Velocity) measurement
  • • Low-profile/high-signal antennae for increased signal range
  • • Enhanced cloud features through the CDLSmartHub.

Other reasons for vibration-level monitoring

• • Formal risk analysis
  Given the known risks of vibration to buildings and structures, any serious risk assessment is going to consider these and likely recommend monitoring.
• • International, national & corporate standards
  A range of standards exists for measuring shock and vibration in buildings - for example, BS 7385, the British Standard for evaluation and measurement for vibration in buildings, as well as corporate standards published by the International Organization for Standardization (ISO) such as ISO 4866:2010 and ISO/TS 10811-1:2000.
• • Culture of prevention rather than cure
  Quite rightly, we are all interested in solutions that prevent problems rather than fix them afterwards. Monitoring shock and vibration in buildings and structures is a growing requirement.