Pre-Emptive Demolition

A Rammer 3288 hammer is playing a key role in a project that will bring much needed relief to Kent’s car users and travelers to the Garden of England.

As anyone that has ever spent a day taking an afternoon’s drive along its country roads will testify, Kent is not blessed with a road network designed for modern traffic levels.  

But that is slowly changing.   Work is underway on the £66 million East Kent Access Road, a major road improvement around Manston airport, Ramsgate and Sandwich, aimed at relieving traffic congestion on A256, close to the Pfizer works.   Somewhat ironically, work started on the scheme just a few months after the pharmaceutical giant moved out.

Ingenious Plan

Part of this scheme is the Cliffsend Underpass that will join the Manston Road to the Sandwich Road by passing beneath the main Ramsgate to Dover railway.    It was vital that this line remain open throughout the construction works, so an ingenious plan was devised to build the tunnel in situ, and push tunnel sections into place without disruption to the mainline service.

Main contractors Volker-Fitzpatrick, Hochtief (VFH) excavated on either side of the railway and constructed a pair of three metre high, 132 metre long access tunnels under the line.  Local demolition contractor DDS Demolition was contracted to break open the tunnel portal walls, so that 256 concrete piles – each of 450 mm diameter - could be constructed on either side, eventually to take the weight of the new £22 million tunnel.   This was successfully completed by DDS in two and a half days, well ahead of the four days scheduled by VFH.

For the next stage, VFH constructed the casting yard where it would manufacture six tunnel sections, each measuring 22 metres in length, 2.7 metres in height, and weighing 2,500 tonnes.   These sections will span the entire 25.8 metre width of the new road.

VFH then constructed the skidding yards where the completed tunnel sections would be pushed into place on rails by giant hydraulic jacks as part of the largest operation of its type in the world.

Finally VFH completed 20 post-tension ground anchors (although only 14 were actually used) on either side of the tunnel.   These were used to pull against the jacks as they moved the tunnel sections into place.

Demolition Planning

Before this work started, and using just the contractors drawings, DDS was asked to calculate the cost of the demolition of these preparatory works - together with the thrust blocks, key shields and the protective cutting shield on the first tunnel section - before they had even been constructed.

"As it turned out, our calculations proved remarkably accurate," says DDS managing director Wesley Ray.   "Even though we had to accelerate our programme to accommodate the shortened chalk season earthworks needed on the approach road banks.  We had to split the demolition north-south, removing all of the southern side's temporary structures to allow access for VFH's ADTs. That meant that the working area was very much constricted with a lot more site traffic than originally planned.   But it's amazing what a bit of good planning and some strategic overtime can achieve."

Ray reports that his company firstly tackled the Southern thrust block moving onto the 60 metre long casting yard.   Next came the 120 metre long skidding yards, where the 5.5 metre wide reinforced concrete slab was 500 mm thick with a raised 250 mm rail on top.   Demolition of the thrust blocks and TBM launch pads alone generated 1,300 m3 of concrete and 220 tonnes of rebar.  Overall the temporary structure removal generated in excess of 400 tonnes of rebar and approximately 3,000 m³ of concrete in a 3.5 week program.

UPDATE

The opening of the new dual carriageway on the 23rd May 2012 was achieved five months ahead of schedule. More than 2,500 people were involved in the construction of this contract and over 1,250,000 man hours worked.