Pioneering research, testing and analysis has helped deliver
significant time and cost savings on delivery of foundations for
Terminal 5.
The project involved Mott MacDonald excavating by far the largest
basement ever attempted in London clay, which is prone to long-term
swelling, pushing foundation design and construction beyond the
limits of previous experience and existing knowledge.
Excavation and foundations construction had to be carried out
without disturbing existing infrastructure, including rail tunnels
and without compromising the schedule for construction of the
terminal’s basement and superstructure. Design of foundations had
to finely balance the opposing uplift forces imposed by the
swelling clay with the variable compressive force applied by the
terminal buildings.
Original research and testing enabled a far more economical piling
design to be used than was initially thought practical, saving on
materials and improving safety.
Value engineering and close attention to the sequencing of work
enabled excavation within mere metres of rail tunnels, without
impacting on safety or affecting the tunnel geometry.
