AARSLEFF PILING has installed tubular steel piles to support overhead sign gantries on the M42 south of Birmingham. It forms the third phase of the Highways Agency's Active Traffic Management (ATM) pilot project in which innovative solutions, such as automatic queue detection and variable message sign gantries aim to improve this busy 16km section of motorway.
Overseeing design by a partnership of 15 consultants, Mouchel Parkman is also managing the pilot with main contractor Birse Civils. The ATM will operate between junctions 3a and 7 of the M42, which forms part of the major network distributing local and national traffic and serving the NEC and Birmingham International Airport.
Aarsleff Piling is using one of its Banut 700 self-erecting fixed leader hydraulic piling rigs, with 5t drop hammer, to pitch and drive 84 tubular steel piles, 508 mm diameter and between 8m and 10m long.
Each gantry, typically every 500m with adjacent emergency lay-by refuges, requires a pair of steel foundation piles, which are driven up to 6m into underlying clays and Keuper Marl next to the hard shoulder.
Birse expected that pile locations would need preboring to achieve the penetration required.
However, the high impact energy of Aarsleff's hammer eliminated the need for this, resulting in time and cost savings.
'We could not start piling until 11pm or midnight, after Birse occupied the relevant carriageways at about 9pm and installed the traffic management system, ' says Aarsleff piling manager Phil Chippindale.
'We could then take the rig on a low loader to the designated location. Depending on the location and driving conditions we were able to install piles to one or two structures each night.
'The Banut had to be off the motorway before the traffic management was removed at 5am.'
Aarsleff believes the use of tubular steel piles offers considerable programme advantages and confidence over conventional bored piles for supporting motorway sign gantries.
'Normal bored cast insitu piles on this project would probably require a minimum of two shifts to complete the works at each location, with all the associated added plant and wagons needed to take muck away and bring in concrete and reinforcement.
'A further seven days would have to elapse for curing the concrete before pile testing could be carried out. The fact that all the tubular steel piles are pre-formed gives greater confidence to the performance, integrity and quality of the foundations and allows faster follow on access to build the pile caps and gantry bases, ' adds Chippindale.