City Park 1

The first stage of this contract began with the 34,000m3 basement excavation, which started in early July. This enabled completion of the car park facility, which included a basement tank comprising a raft slab and perimeter retaining walls.

The foundation works entailed the construction of a 1m thick raft slab within the basement covering an area of 6,500m2. We also erected a reinforced concrete perimeter retaining wall of approximately 3.5m in height and approximately 415m in length. A second 180m external precast retaining wall was also erected within the lower car park to enable the area to be upfilled, creating space for an external structure and additional car parking.

For the upfilling process we used the existing material from the bulk excavation, which was treated by the addition of lime stabilisation to produce the engineering fill. These stabilisation works were carried out by a specialist subcontractor working with our team.

It was particularly important to monitor the temperature of the concrete used in the retaining walls as there was a concern that a thermal differential might induce cracking. Our engineers used thermocouples, (devices that produce a voltage to mark differences in temperature), to monitor the heat gain. In order to meet the stringent architectural specifications, the concrete formula was designed in conjunction with an external designer and concrete supplier, Breedon Aggregates.