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This work analyses the effect of the change in the initial stiffness on the behaviour of two geotechnical structures performed on/in overconsolidated clays: an embankment built on Boston blue clay and a tunnel dug in London clay. The numerical predictions are performed with the MIT-E3 model, which reproduces the small strain nonlinearity and hysteretic stress–strain response observed in unload-reload cycles. Firstly, the performance of the constitutive model to replicate an unload-reload cycle of a consolidation test is validated. The initial stiffness is varied by changing the κ o parameter of the MIT-E3 model. Thus, several numerical predictions of the two geotechnical structures, performed for different κ o values are compared with each other and field measurements, in terms of settlement and horizontal displacements. The results show that the variation in initial stiffness has a greater effect on the behaviour of the tunnel than the embankment. In fact, in the case of the tunnel, the majority of the stress paths occur inside the yield surface, where the stiffness is the key parameter. On the other hand, for the embankment, the yield occurs in the major part of the domain, therefore the stiffness effect is less significant. [ABSTRACT FROM AUTHOR]