Continuous Vibration Monitoring of a Demolition Site in Central London

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In this case study we take a look at how Vibration Monitoring Services Limited have been using the RDL//Vibe for demolition vibration monitoring – tracking vibrations generated on a construction / redevelopment site in central London. 

The Demolition Vibration Problems

As residential neighbourhoods grow, developers and site managers face a problem in the decrease of space available for construction activities such as demolition and piling.

Vibration Monitoring Services Limited (VMS) were employed by Crest Nicholson London to protect buildings surrounding a demolition site in the centre of London, to allow them to redevelop the area, combining the historically important parts of the existing building with the new build which contains a mix of residential and commercial space.

Among other properties surrounding the demolition site, within close proximity there is a Church, glass house and Artists’ studio. The Roman Catholic Church of our Lady of Salette was built in 1861, a decade later a school building was built attached to the church, in later years the school was extended before the site was remodelled in the Post War period following bomb damage, a new church hall was built in the 1960’s and the school closed around 1970.  The School buildings were then subsequently occupied by Southwark College and leased to the City Banking College and London School of Commerce who vacated the premises in 2012.

Church and Glass House

The Manna Centre has occupied part of the site since opening in March 1983.  The organisation provides a crucial outreach service to homeless people in the area and the presbytery provides sheltered accommodation for the adjacent church and is a further source of community use on the site.  The project is to be carried out in two phases to ensure the Manna Centre can continue to operate throughout the project.  The project is expected to be completed in February 2016.

Without continuous vibration monitoring, vibration levels could exceed safe levels and not only cause minor damage to the sensitive structures but also cause distress for occupants of the church, the artist’s studio and other neighbouring buildings.

The Demolition Vibration Monitoring Solution

Over the last year VMS have been conducting continuous vibration monitoring of a demolition site which sits in close proximity to a Church, Glass House and artists’ studio.

Reasons for Monitoring

  • Document the ground vibrations generated by demolition work
  • Provide real time updates on the vibration levels allowing the site manager to make immediate remedial adjustments to work methods

VMS deployed several vibration monitoring units positioned in key areas throughout the site. In the current second phase they are protecting the Church, surrounding offices backing on to the site and the Glasshouse Artists Studio.  These are self-contained units within secure cases with a geophone attached and will remain in situ during the works, these will continue to collect data and notify of vibration levels during this second phase of demolition.

Vibration Limits

In the case of Melior Street, London as this has different types of structures surrounding the site from The Glass House to the Church the vibration levels, monitored in Peak Particle Velocity (PPV), had a limit set at 6mm/sec during demolition works.

However, as a starting level we use a British Standard guideline for vibration chart but each building/construction is assessed on it’s own merits, whether it is a concrete/steel/brick or block construction and the age of the structure is a major consideration as some buildings have no foundation to absorb ground vibration. All the alarm levels are flexible dependent upon the frequency of vibration generated and some projects have levels set by the Client, protecting gas mains, e.g. low pressure 8mm/sec or high pressure 6mm/sec, Network Rail Viaduct 5mm/sec, Building Server rooms 2mm/sec and underground water services 4mm/sec. We also use ISO 4866:1990 (E) Categorisation of structures and classification of buildings’ resistance to vibration and BS 7385-2:1993 Transient vibration guide values for cosmetic damage chart. In some cases we would also carry out a baseline vibration survey to ascertain the ambient levels prior to setting the pre-set alarm level.

What Remote Monitoring Systems Offer

  • Capture any events over pre-defined ‘acceptable’ thresholds, transmit this to a secure server for storage – then finally send out messages via SMS and email to key personnel
  • The system also takes a snapshot of data and makes a connection to the server at regular intervals to confirm the system is still active

Constant access to data is available on site, on the move or from the comfort of an office through the CDLSmartHub where Data can also be visualised in graph format. Reporting functions allow users to review events and vibration levels in any given time frame, allowing VMS to be able to offer weekly and monthly reports, with ease, showing vibration levels over time.

Project Engineer, Crest Nicholson London, “VMS offered a complete vibration monitoring solutions. By employing experts in the field of vibration monitoring we felt free to continue our work knowing VMS would contact us if the vibration generated from our work was at risk of causing damage to the surrounding sensitive structures.

“As yet we have not incurred any damage to the properties nearby”

About Vibration Monitoring Services Limited

Now in its 10th year offering specialist vibration monitoring to the construction industry, machine monitoring and thermal imaging. VMS has seen a steady increase over the years in the vibration monitoring of construction sites during demolition and piling.

VMS have gained a reputation for providing quality monitoring from start to finish, with projects all over the UK protecting everything from large sites to domestic buildings and everything in between, from excessive vibration. VMS is also responsible for monitoring a range of sensitive structures such as railway viaducts, railway lines, electrical sub stations and gas mains.

The monitoring systems and solutions used offer Clients the peace of mind that the demolition or piling work that is being carried out, doesn’t adversely affect the surrounding properties or structures.

About Our Demolition Vibration Monitoring Equipment

Products RDLVibeThe RDLVibe offers an innovative yet cost effective vibration monitoring solution for civil and structural engineers.

Whilst continuously monitoring sensor vibration levels, the RDLVibe seamlessly transfers the data to secure data servers. The data is then made available via a web based data management, reporting and monitoring platform called the CDLSmartHub.

Julie Collins, Vibration Monitoring Services Limited, “The RDLVibe was able to find mobile network coverage with ease by using roaming sims that offer an uninterrupted supply of data”

Key features include:

  • Up to 12 month battery life
  • Wireless communication with roaming sims
  • Frequency range from 0.3Hz to 500Hz
  • Real time alarms for user set alarm thresholds (i.e. against British Standards or independent limits)
  • Complete un-editable audit trail of all events and alarms

Commonly found monitoring vibration levels on or near construction sites, the RDLVibe was recently given a seal of approval in it’s use by Plymouth University’s School of Marine Science and Engineering, where a research team working in partnership with Trinity House have been using the systems to better understand the dynamic structural response, of one of the most iconic lighthouse’s in the British Isles, to wave and wind loading.

Eddystone Lighthouse which sits approximately 13 miles off the coast of Plymouth, on a dangerous rocky reef, offered a unique yet familiar challenge to Caption Data due to the remoteness of site and low power availability.

Even through these challenges the RDLVibe was able to continuously monitor vibration levels and provide an uninterrupted supply of data via the CDLSmartHub.

Case study written in partnership with Vibration Monitoring Services Limited. Updated 18/03/2015.

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