Developers are keen to get their basements built because they do not want to be affected by a restriction imposed by the Crossrail Bill which will prohibit work on foundations during nearby tunnelling work.
The restricted zone is expected to be nearly 30m across covering the route of the 7m wide running tunnels and a 3.5m zone either side of each tunnel, which was designated to allow for slight deviations to the alignment.
The restriction is expected to affect tall building projects in Canary Wharf and the City of London and also "over station developments" at Crossrail stations along the route of the tunnelled section between Paddington and Liverpool Street and Canary Wharf spur.
WSP technical director Sam Wong said his firm had been instructed to start designing basements for several major projects along the route before the tunnelling starts.
"We are working on foundations and piling now so that we can carry on building above the tunnel corridor when tunnelling starts," said Wong.
"If we don't, there will be a moratorium period of as much as a year when we can't do any piling or excavation above the tunnel."Tunnelling work is expected to start in 2010.
"It depends on where the tunnelling starts and when it crosses sites but while tunnelling, lining and grouting takes place, they don't want excavation or piling during that period," added Wong.
He would not reveal the identity of projects where advanced works were taking place but added that advanced piling works were much more expensive because so many more piles were being driven than was usually the case.
This is because developers want options because they had yet to finalise the design of the building overhead and needed more piles to give them options of where heavier loads would be placed.
"We have to come up with more foundation options that are more expensive – more piling is needed so there is more flexibility as to where to put the building's core," said Wong.
"The piling guys are putting in a lot more than they normally do."
A spokeswoman for Crossrail said: "Crossrail safeguarding prevents new deep foundations from impinging on the alignment, which would have resulted in the project being changed or made more expensive.
"Planned schemes and development within the safeguarded areas, including those adjacent to future works or over deep tunnels, must be vetted by Crossrail on a case-by-case basis."