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York University – Chemistry Department Water Tower & Laboratory Block D
The project commissioned by York University consisted of the demolition and the safe dismantling of the University Landmark Water Tower, and the demolition of the Chemistry Laboratory Block D. The Tower (seen above) comprised of an inverted 21metre diameter conical tank which was made up of 32 pre cast concrete petals each weighing 8.5 tonne. The Overall Height of the Tower was approximately 28 metres, the central core stem being 2.3 metres diameter .
One of the main features of the project was its environmental surroundings. The Tower sat in a quadrangle which is in the middle of the Chemistry Department at the University. The Chemistry Department is a collection of single and two storey structures containing operational lecturing, teaching and research facilities. Covered Walkways surround the perimeter of the quadrangle and are used by students, staff and visitors on a daily basis. One of the main challenges facing Connell Brothers was to maintain access to the department throughout the proposed works, with as little disruption to every day life at the University as possible. As can be seen by the photograph below, due to the extremely condensed environment of the project, safety was of paramount importance. Also with the village of Heslington in close proximity there were traffic and access considerations which had to be taken into account. Connell Brothers adopted an innovative approach from early Tender Stage of the Project and throughout the execution of the works.
Close Liaison with the University was an essential factor to the smooth running of this project. The prime concerns of the university were those of noise, dust and vibration which can effect the workings of instruments within the laboratory. Connell Brothers kept the use of percussive tools to a minimum in order to limit vibration levels. Regular background noise readings were taken to ensure that noise levels were kept to a minimal level. Dust arising from the operation was also a main factor for consideration and the Project included implementing a strict regime of dust control measures. Also specialist filters were procured and fitted to the Laboratories Air inlet systems to prevent dust contamination, which would seriously effect sensitive experiments taking place inside the buildings. It was also essential to provide protection for gullies and drains to prevent dust/debris entry. This was necessary as local lagoons contained rare Coy Carp and could not be polluted by any means. Further liaison was also required with regards to working hours. Works had to be liased and phased around the Chemistry Departments busy experimental schedule to take account of any possible emissions resulting from the experiments.
The demolition of Block D was done by a specialist excavator fitted with a hydraulic grapple attachment. This part of the project was complicated by the large amounts of asbestos located in the structure. This required the specialist removal under all current legislation prior to the structure being demolished. The Demolition of the Block enabled the crane to be located in the footprint of the building to allow careful dismantling of the petals. It also allowed access at a future date within the contract for the high reach machine to demolish the remaining stem.
There was a degree of uncertainty surrounding the demolition of the pre cast structure of the Tower as it had been subject to deterioration since erection. At Tender stage, the 32 petals forming the bowl of the water tank were described as each individually being restrained by wire ropes to the central core. Upon opening up the works, it was found that the stated 32 restraining Ropes had only been used during the construction of the bowl and had been removed, therefore the petals of the tank were gaining support from the ring beams.
The lack of the restraining ropes, contrary to that described in the tender documents necessitated Connell Brothers to carry out a full structural reappraisal of the dismantling techniques to be employed. On completion of the appraisal, it was decided that 32 restraining ropes to the outer edge of the petals and a further 32 restraining ropes to the inner edge of the ring beam would require installing to enable safe dismantling of the petals. A proactive approach was adopted to the immediate sourcing, fabrication and installation of the ropes. A fully designed structural scaffold was erected to take the self-weight of the petals.
Once the scaffold and restraining ropes were installed, a planned sequence of dismantling was undertaken by cutting the petals in half at the point of intersection of the central ring beam and lifting in sequence therefore maintaining the overall integrity of the structure. Repetitive lifting operations were carried out by removing the outer sections of the petals in the first phase and inner sections of the petals in the second phase, leaving the stem exposed along its full height.
The top section of the stem weighing 16 tonnes was a heavily reinforced structure containing the 64 holes, which were incorporated during construction for restraining the petals. The top section was separated from the reminder of the stem and lifted down to ground level in one operation. Once at ground level excavators fitted with hydraulic attachments reduced the structure by munching down.
With all high level works complete, the supporting scaffold was taken down to enable access for the Long Reach Machine. With protection still in place to the covered walkways and the entire quadrangle secured as an exclusion zone the munching down of the remaining stem commenced. The stem was successfully removed within a 6 hour period, thus minimizing disruption to the campus users.
The Management of the Project was carried out in close liaison with Faber Maunsell and the University. The Project was headed by Mr. J. Connell, Projects Director, with Site Supervisors, Foremen, Safety Advisor, Structural Consultants, Monitoring Consultants and a team of highly trained (CITB) demolition Operatives and machine Operators. The Management called for regular Safety Audits of the site, weekly Tool Box Talks with regards to safety, regular Method Statement Induction courses for all Operatives on site, fortnightly Progress and Safety Meetings with Faber Maunsell. Regular auditing was undertaken to ensure that the Project Management procedures were followed. The project took 20 weeks to complete and throughout the works, safety to all Personnel on site and the General Public was of paramount importance. A strict regime of safety procedures was implemented and Connell Brothers can report that no notifiable incidents occurred throughout the 20 week project period.