AARSLEFF PILING's big Hitachi KH180.3 GLSK self-erecting leader rig has saved time and money on a major road project in Essex.
The 105t Hitachi rig, the largest of its type in the UK, allowed Aarsleff to handle, pitch and drive 24.5m long steel columns for the abutments of three bridges in a single piece. This was much faster than using a smaller rig, welding shorter sections of pile together and driving in two stages.
Aarsleff's client Balfour Beatty Civil Engineering (BBCE) has a £75M contract for Essex County Council, on behalf of the Highways Agency, to design and build a new 24km stretch of the A120 trunk road.
The road will connect Stansted Airport and the M11 motorway with the Braintree bypass with an upgraded dual two-lane carriageway. The project, which includes 32 structures, started in summer 2001 and is scheduled to finish in summer 2004.
The scheme was designed for BBCE by its consultant WS Atkins, which has adopted a standard 56m span design with pier support in the central reservation for all the bridges.
For the vast majority of the bridges, BBCE is forming deep excavations and building up concrete columns from a mass concrete pad foot base slab in each of the abutments.
But a plethora of fibre optic cables near one ofthe bridges prevented excavation and led Balfour Beatty to look at alternative steel piled abutments.
Aarsleff won the £75,000 contract to drive the 305mm square, 240kg/m section universal columns. The firm initially planned to use one of its Banut 700 selferecting leader rigs with a 5t drop hammer to drive the piles in two sections with radiography tested and ultrasonically inspected insitu butt welded joints.
But for its first visit to site in April 2002, to drive a row of eight columns at each of the two abutments, Aarsleff was unexpectedly able to divert its big Hitachi rig to the A120 scheme just before it started work installing precast concrete piles on a section of the Channel Tunnel Rail Link.
'The bigger rig became available and Aarsleff were able to install the piles in one piece and save time on driving, ' says Balfour Beatty Civil Engineering construction manager Ian Cook.
'Aarsleff installed the 32 universal columns in the first phase in a very slick and fast operation so we reprogrammed the piling on the third bridge to coincide with the availability of the big rig in autumn 2003. Aarsleff drove eight piles, four at each abutment, in two days.'
Aarsleff equipped the rig with a Banut 5t drop hammer to drive the steel H section columns, at 1.5m centres, through alluvial deposits, Kesgrave Sand and about 12m into the underlying stiff clay.