GCG was part of the design team advising on geotechnical issues including site investigation, earthworks (soil stabilisation and temporary cut slope stability), design of piles in swelling ground and the predictions of ground and tunnel movements. A key role was the design, supervision and interpretation of a site investigation aimed at making the best estimate of the in situ stiffness, strength and expansibility of the London Clay. Rotary cored samples were taken from two adjacent boreholes, one for detailed logging and one for selection of samples for laboratory testing.  A third co-linear borehole was drilled from which pushed thin wall tube samples were tube taken. Sample quality was assessed on the basis of simultaneous measurements of suction, using the Imperial College suction probe, and of shear wave velocities using bender elements.  Soil stiffness was measured in locally instrumented triaxial tests, also with measurements of shear wave velocity. The co-linear boreholes have been used for in situ geophysical measurements of crosshole and downhole shear wave velocities, natural gamma and electrical resistivity.

References

Hight, D.W., Gasparre, A., Nishimura, S., Minh, N.A., Jardine, R.J. & Coop, M.R. (2007). Characteristics of London Clay from the Terminal 5 site at Heathrow Airport. Géotechnique 57, No. 1, 3-18.

Jardine R.J., Potts D.M., Fourie A.B. & Burland J. B. (1986). Studies of the influence of non-linear stress-strain characteristics in soil-structure interaction. Géotechnique 36, No. 3, pp 377-396.