Biggin Hill Airport Limited
Biggin Hill Airport Construction of New Hangar
Faithorn Farrell Timms (FFT) were approached by London Biggin Hill Airport Ltd in July 2016 to provide professional consultancy services for the construction of a parking hangar with office accommodation and car parking.
The hangar building is over 132m long, 43m deep and 15.5m high with an attached three-storey office building. It was a design requirement that the frontage was enclosed with six retractable sliding doors and the internal space needed to be free of columns and structural support except along the centre line where there had to be an opening large enough to move aircraft from one side of the hangar to the other from within. Therefore, the structure had to be self-supporting and the roof had to span 66m to create this open space.
London Biggin Hill Airport Ltd were to fund the project themselves and our initial involvement was to provide a value for money assessment in order that the scheme could receive final Board approval.
Our initial appraisal of the financial viability of the project was favorable, however we raised a number of significant issues concerning general due diligence and were concerned that there appeared to be no contractual framework under which this project, at a value in excess of £6M, was going to be undertaken.
After FFT highlighted a number of risks with the project, our client that they needed to appoint a client’s representative to advise them upon the contractual requirements necessary to demonstrate due diligence and to monitor and implement these throughout the construction process.
In addition to advising our client on the contractual requirements, setting up the necessary documentation and undertaking the negotiations with the contractor, Civils Ltd, we additionally advised collateral warranties to be signed to include all sub-consultants with a design responsibility and bind them in contract with the Airport.
For the duration of the construction phase, we provided construction monitoring by fortnightly site inspections, undertook valuations and certified work satisfactorily completed for payments to be made in accordance with the contract. Upon completion of the construction phase, FFT certified practical completion and inspected again at the end of the twelve months defects liability period whilst maintaining sufficient involvement with the project so that our client could call upon us at any time for advice.
- The chosen construction site was on made-up ground and the load bearing capacity was insufficient for a ground bearing slab suitable for the purpose of the building to store multiple executive aircraft, therefore the soil had to be stabilized before any construction work could be started.
- The site was extensively bombed during World War 2 and also used for the storage of munitions, therefore an unexploded bomb (UXB) survey had to be completed before any works could be considered to start.
- The location capacity and adequacy of existing services connections for water, electricity, gas and sewage had not been fully investigated and therefore the viability of the project and final out-turn cost could not be known until these investigations were completed and the scheme proposals finalized.
- At the time of placing the contract with Civils coincided with the period of instability and considerable price inflation for the supply of structural steel. As the entire building was to be steel frame and steel clad the cost uncertainty for the project, general cost and instability and the virtual certainty for unknown cost increases was of major concern to our client.
To address the ground bearing conditions and increase the ground bearing strength, the site was levelled and then a specialist vehicle was imported from Germany that was designed for lime entrainment. This was a long process on a site of this size and was undertaken over several months with numerous tests being undertaken to establish the improvement in the ground bearing resilience. Work was only concluded when the tests achieved the required capacity. Upon completion the site was completely level and well consolidated. The site was so large that the land levelling equipment, graders, bulldozers etc were effectively controlled by GPS in three dimensions with the vehicle operatives only being present to obey the instructions provided via their on-board computer.
We worked with the contractor and recommended to our client that, in order to remove as much potential for price fluctuations in the capital cost of steel, the full order should be placed and paid for upon delivery at the very earliest date even if this meant paying additionally for storage of the material at the fabricator’s yard. This saved our client approximately £65,000 in the capital cost of the steel.
We monitored the development of the hangar building at all key stages throughout its construction. The accuracy with which the holding down bolts were pre-fitted to the foundation pads in readiness for receiving steel columns was absolute and no on-site adjustments were required to either the holding down bolts or to the fabricated steel components therefore no construction delays resulted from re-fabrication of any components.
The enormous sliding doors to the front elevation arrived from the specialist supplier in kit form and had to be site assembled. The foundation concrete for the running rail had to be constructed as close to perfectly level as possible. Upon completion it was found to be just 3mm out of level from one end to the other and perfectly flat. Externally the new apron and taxi ways were constructed progressively as, weather permitted, in large bays of expansion joints between. Once cured each bay was perfectly flat, no water ponding occurred, and the quality of finish was equal to that of any internal concrete floor.
The hangar was completed just prior to Christmas which was three months ahead of the scheduled completion date for the project, therefore sectional completion was accepted and allowed the parking hangar to be used significantly earlier than anticipated. The office areas were then fitted out over the following three months with overall project completion achieved on-time in March.