21 Moorfields – Civil Works

Project: Civil Works

Client: Mace Group Limited

Works Value: £170,000

 

As part of the works at 21 Moorfields, ground bearing piles were installed to support a new structure to be built above Moorgate Station.  D&D Rail were tasked with casting concrete slabs at the base of these piles, down at platform level.

All areas to be concreted were prepared/ excavated by others.  Our works at each location commenced with the laying and compacting of MOT type one material in the excavation.  A layer of DPM was then placed on the type one before the area was handed over to our steel fixers who drilled holes in the surrounding concrete slab to allow starter bars to be chem-fixed in place.  They then built the rebar cages or formed the rebar as dictated by the bar bending schedule issued by our client.

All rebar was tied in place with tying wire and also tied to the starter bars.  The rebar was installed ensuring that there was sufficient cover for the concrete.  Concrete spacers were placed on the DPM and fibreboard and compressible board was fixed to the piles with the aid of tek screws to prevent the concrete being cast directly against the pile.

Plywood/ timber shutters were made up on site by our carpenters, fixed into position and braced ready for the concrete pour.

Following a pre-pour inspection by our clients’ structural engineer, we commenced the concreting works with concrete delivered to the work site by a concrete pump.  The pipeline had to drop 5 metres down to platform level and the run from the pump was 130m to the furthest location.  Where it was not practical to run a pipeline from the pump we utilised a concrete column skip for delivery.  The concrete skip was filled at the delivery point and lowered to the location of each pile base by the site crane.  This process was repeated until the excavation was at the required level.

The concrete surface was vibrated, levelled off and floated to a finish.  Concrete cubes manufactured at the time of the pour were sent for compressive strength testing at intervals requested by the engineer.  Following a suitable curing period the plywood shutters were removed and the site was cleared.

2no. soakaways were hand dug and installed in the location of the pile bases with gully covers installed above the soakaways at the levels requested by our client.  These covers were backfilled with bagged C40 concrete to the level of the surrounding slab.

We were also instructed to cast a ground strengthening beam.  Prior to our arrival on site 6no. 50mm core holes were drilled to a depth of 3m into the pile cap at the angle specified by our client. Our operatives roughened up the internal surface of these core holes before mixing and pouring Fosroc Lockfix S25 grout and inserting 3m long, 40mm diameter dowel bars into the core holes to the required levels.  We then drilled the existing slab and inserted the starter bars which were chem-fixed in place.

The rebar cage was made up as shown on the schedule for this beam and tied in place.  Our Carpenters then made up plywood/ timber shutters which were braced off the existing slab. Following a pre-pour inspection by our clients’ structural engineer we poured the slab using bagged C40 concrete which was vibrated, levelled and floated to a finish.  Concrete cubes manufactured at the time of the pour were sent for compressive strength testing at intervals requested by the engineer.  Following a suitable curing period the plywood shutters were removed and the site was cleared.

Finally, we were instructed to reduce the level of the concrete inside pile 13 to allow a pile head to be installed by others.  Once installed we poured high strength concrete around the pile head.  Works commenced with our trained operatives core drilling around the internal perimeter of the pile down to the required depth.  Once the perimeter was cored we used a dustless grinder to score the surface of the existing high strength concrete.  The concrete was then broken out to the required level with the aid of a heavy duty 110v breaker, bagged up and removed from site.  A steel base plate was then fixed to the existing concrete at the required level by others.

We formed a timber shutter around the base plate before mixing and pouring 5 star grout between the concrete and the underside of the plate.  Our steel fixers then tied rebar as detailed on the schedule, to the pile head and around the external perimeter of the bars cast into the pile.  The pile head was lowered into position by others prior to the concrete pour.  Our operatives poured high strength concrete through the gaps in the pile head.  The concrete was placed with the aid of a concrete column skip lowered into place by the site crane.  The concrete was vibrated with a poker throughout the delivery to ensure the void beneath the pile head was completely filled.  Concrete cubes manufactured at the time of the pour were sent for compressive strength testing at intervals requested by the engineer.

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