Van Elle are currently on site in the heart of Nottingham city centre, Thomas Fish are constructing apartments and retail units on behalf of the developer Southreef and have contracted Van Elle to carry out piling works. The project started on 30th May and is due to finish on 6th July the value of the contract is in excess of £350,000.

The site had always been used for industrial purposes, with a saw mill and corn warehouse being recorded on the land in 1884. At the turn of the century a railway line cut through the site and remained there until 1991 when it was dismantled. Three different levels of foundations were dug through as the site was excavated prior to the piling.

The site is rectangular with the canal running at the back and a road running along the front. There are also buildings situated along the north and south end of the site. Before any main piling works could commence the four sides of the site had to be sheet piled to retain both the canal and the road and stop any building slippage.

Due to the location of the site next to roads and other buildings CFA piles were used.

"The benefits of using CFA piles," Andy Sneddon Director of Van Elle's Piling Division explains, "is the lack of vibration and noise. The lack of vibration minimises the risk of damage to the surrounding structures, whilst the reduction in noise makes the site a better neighbour to the people living and working in this part of the city."

The interesting thing about this project is the fact that Van Elle had to work at two levels into a 4.5m deep coffer dam.

The first phase of piling was to provide access for the cranes. A hardcore bridge was constructed across the site towards the canal, essentially splitting the site into two halves of 4.5m deep. Piles were then installed using a Llamada rig through the hardcore bridge into good ground beneath. This allowed the cranes access across the bridge to their operating positions at the rear of the site. It also allowed the concrete wagons access to the piling concrete station. The piles within the hardcore bridge would be taken out at a later date and discarded.

The second phase involved the Llamada rig being tracked along the roadside to the southern end of the site. A ramp was built parallel to the road, running from ground level into the 4.5m deep coffer dam. The next step was for a 5m wide gap to be dug out of the hardcore bridge to allow the rig access along the full length of the site to the northern 'half' to continue piling. The bridge then had to be 'plugged' once the rig was through in order to allow the concrete wagons continuous access.

Once the piling had been completed in the northern 'half', the process of digging out and plugging the hardcore bridge began again and the rig was moved to the southern 'half' of the site to complete the piling.

The complex logistics on site went hand-in-hand with some tough ground conditions; the ground consisted of sandstone which was extremely hard.

Ian Jones, Contracts Director for Van Elle, explains the difficulties which were overcome.

"The piles had to penetrate between 3.5m to 4.5m into very hard sandstone. Our Llamada rig gave us the high torque capabilities we required coupled with its pull-down facility and the specially made cutting heads."

Van Elle installed 580 No 500mm diameter CFA piles, installed to depths between 8m - 14m through the sandstone. These load bearing piles were designed to take the load capacity of the new structure, whilst at the same time they also created a piled wall for the new basement area of the building.

With the site being next to the canal the lower level needed de-watering to 17m below ground level in order to stabilise the ground.