Aerodrome Road, Barnet

Simplex Westpile delivered this piling contract, consisting of 8 2.1m diameter piles to a depth of 24m, and 106 900mm diameter piles to 16m depth in a £2m joint venture project for main contractor, Norwest Holst Limited.

In a field in which these two businesses would normally be rivals, they supplied crews and rigs as a team to install piles for the foundations of two replacement bridges beneath two rail lines. The client, London Borough of Barnet commissioned these new structures to create increased vehicle headroom from the current 11’ 6” restriction plus road widening for local traffic.

Specifically these logistics were, that the M1 motorway, and both the Brighton to Bedford and the Midland Main Line run parallel at this section. These transport routes are all elevated above Aerodrome Road and to create areas for cranes and rigs to be supported and function, twin working platforms were constructed up to rail track level using a system of retaining walls formed from gabion baskets, with access ramps leading up from road level.

Timing issues centred on the requirement to install the 8 2.1m main bridge foundation piles over a series of four consecutive weekend railway possessions — from 10.00pm on Saturday to 5.00 am on Monday. Each possession was planned for the installation of two piles by two rigs and four crews, with shifts working round the clock — one supplied by Westpile and the other by Simplex. The smaller piles for the bridge wall wings were installed during the weekdays in between and also required a number of short four hour possessions to access those piles in close proximity to the tracks.

All 2.1 diameter piles were required to be permanently cased, with all 4 piles on the southern elevation being slip coated to prevent load transfer to a Thames Water sewer in close proximity. The slip coat approved for use on this project is a gloss finish paint designed for increased corrosion protection as well as providing a smooth surface. Permanent casings were manufactured by Deepdale and painted by Surface Technik. The permanent casings extend to 12m depth below rail level.

To be able to place a casing of that length, it was necessary to first bore at 2.4m diameter and case at this size for the first 6m. The 2.1m casings were then placed inside and below the outer casing. The wider casings were also installed to be permanent, saving one operation at the end of the pile construction process. Also they would be difficult to extract and their extraction could be damaging to the rail and ballast structure.In preparation for the installation of the final pair of 2.1m piles over the final weekend possession, temporary track crossings were constructed to enable the piling rigs to reach the narrow, work platforms sandwiched between the M1 and the rail track. Since there was no space here for the usual service cranes supporting each rig, a single 160t capacity crane was required to service both rigs from the opposite side of the track.