Environmental Vibration

Adjacent to London Bridge Station and Guy’s Hospital…

Whilst the Shard is the tallest building in the UK, we were involved when it was just a hole in the ground. The location abuts London Bridge Station with Guy’s Hospital just across the road. You could scarcely have asked for a site that was potentially more sensitive to noise and vibration.

Explosive demolition

Keltbray, the demolition contractor, wanted to use the technically advanced explosive demolition techniques developed by the Controlled Group to remove the pile cap in the basement of the office block on the site. Breaking up this massive slab of concrete by conventional means would have extended the project by c 2 – 3 months - and the consequent noise and vibration were potential deal-breakers. Explosive demolition offered the opportunity to minimise both the noise and vibration from the site and the programme duration.

Noise and vibration predictions

We were asked to provide the noise and vibration predictions, logging, monitoring and mitigation expertise required to justify the decision both in terms of potential risks and to minimise both the duration of the process and the environmental impact.

Noise and vibration presentations and PR

We also generated and presented multi-media presentations to all the parties involved (station, hospital, security, police etc) to present the predictions and to provide the technical reassurance necessary to assuage any concerns about noise and vibration issues.

The project was very successful with zero complaints re the pile cap demolition.

Building a new terminal 3 multi-storey car park above the Heathrow Express underground station was a major technical challenge. As part of the process, piles had to be bored 40m into the ground very close to access and train tunnels – without disturbing structures or personnel. There were also additional complications arising from the necessity to carry out work at night within a very limited time-window and without interfering with the station operation or the marring the look...

BAA selected us to carry out an extensive vibration and noise monitoring programme over several months. The turn-key project involved developing a bespoke vibration monitoring system and installing an array of transducers in the tunnels with detailed analysis and continuous remote monitoring of the piling vibration. The INVC designed system also included a facility to alert key personnel automatically via SMS text message if the vibration exceeded threshold trigger values.

Noise monitoring and mitigation programmes were also initiated to ensure the minimum disturbance of passengers during working hours,

Demolition vibration was causing problems in the adjacent lightweight steel construction office block. A very extensive and costly array of conventional vibration monitoring systems was in use as part of a time consuming and unsuccessful vibration complaint management process that led to potentially very costly delays to the project.

Our detailed building and operational vibration analyses proved that the cost and hassle of the extensive vibration monitoring programme could be completely eliminated. We developed and introduced a number of innovative - and sometimes counter-intuitive - demolition vibration management procedures that substantially reduced the problems in the offices. Coupled with developing a purpose-designed project vibration management software tool, the “best practice” noise and vibration management process for the project was simplified and re-defined to minimise the likelihood of further costly delays.

One of the open-plan office floors in the very prestigious new Mailbox office development had been designed with a very low profile floor to provide more space within the building. Unfortunately the design had a natural frequency of 3.6Hz and had very low damping.

Consequently, as staff walked across the floor, the vibration amplitude would rapidly build-up and after a few steps, the whole floor would be oscillating with quite high amplitude. This caused PC monitors to sway and some staff to complain of incipient motion sickness.

Based on a detailed analysis of the structure and response, a minimal set of disguised stiffening beams were designed and fitted (to avoid impinging on the open feel of the office). These increased the vertical stiffness by 70% and introduced more damping, solving the problem.

A Local Authority had been investigating complaints about ground vibration from residents near a factory using rolling mills. Narrow band frequency analysis of the vibration revealed two distinct and separate types of vibration – tonal vibration at 18.25 Hz (and harmonics) plus a regular “thump”. The source of the “thump” was traced to roller backlash caused by bearing wear at the transfer gear end of a particular mill.

The tonal component was diagnosed as excessive vibration at the tooth mesh frequency of the pinion on another mill caused by worn teeth on the gear. The “thump” could be eliminated by replacing the bearings. However, as production requirements precluded immediate down-time, the interim solution recommended was to avoid running at idle and to adjust the clamping force to minimise the backlash. Inspection of the pinion gear source showed very worn pinion drive tooth flanks in mesh with “new” flanks on the driven gear. The tonal vibration was eliminated “on-the-spot” by reversing the pinion.

This case study illustrates the benefits of sophisticated diagnosis coupled with engineering expertise. A low cost solution to a complex and intractable problem was implemented within hours of arriving on site.

We have considerable experience in the establishment of ground and building borne vibration limits and specifications for a range of vibration sensitive equipment. These range from computer systems and hard disks, servers, metrology equipment, electron microscope and nanotechnology facilities and electronic fabrication plant.

Our speciaiist expertise allows us to determine the best practice building vibration monitoring and control regimes for these vibration sensitive facilities and, if necessary, to design bespoke vibration monitoring and control systems.

A detailed vibration assessment of the impulses from a drop-hammer piling operation was carried out in response to concerns from local residents about potential structural damage to their houses. The results showed that the vibration level was very close to the DIN 4150 damage limit guidelines which posed a question as to possible claims for compensation.

Instead of halting piling operations, a detailed vibration analysis allowed modifications to be developed for the pile helmet. These reduced the ground vibration by 65% to well below the structural damage criteria, allowing the project to continue on schedule. In a similar case involving piling near a railway line, we reassured the residents by demonstrating that whilst the piling operations were subjectively very evident, the passage of trains actually generated a very similar level below the structural vibration damage criteria.