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Allowing the transitory attainment of bearing capacity of caisson foundations supporting bridge piers during strong seismic events can lead to substantial optimisation in their design and major cost savings. If the approach of capacity design is applied to geotechnical systems, the temporary triggering of plastic mechanisms may be permitted if the resulting permanent displacements are smaller than given threshold values. To validate this design approach, the seismic performance of caisson foundations was assessed through dynamic centrifuge testing on reduced-scale models. This paper presents the results of two tests in which a caisson–pier–deck system was embedded in a typical alluvial deposit and subjected to a series of earthquakes of different intensities. The caissons were founded on soft and very soft clay, to either avoid or induce the attainment of plastic soil behaviour under the same seismic inputs. It is shown that both yielding and failure of the layer of very soft clay limit inertial forces transmitted to the superstructure, validating the design approach and some useful empirical relations available in the literature. In contrast, inelastic soil behaviour implies accumulation of permanent rotation and settlement of the system, which must be carefully evaluated to check for fulfilment of performance requirements. [ABSTRACT FROM AUTHOR]

It is important to determine dynamic tunnel behaviour under cyclic loading for the seismic underground structural design. The dynamic response of tunnels is further complicated when considering the interaction with surface buildings. This paper investigates a series of 2D plane-strain numerical models to study the dynamic response of a shallow cut-and-cover rectangular tunnel in loose, cohesionless soil. Both dry and saturated conditions are considered. Input motion includes sinusoidal waves with 10 cycles of shaking. A raft foundation with a 50 kPa structural surcharge is adopted to simulate the effect of the surface building. Soil displacements, wave propagation, earth pressures and tunnel lining structural response are determined. These results show that the soil liquefaction introduced by accumulated excess pore pressures causes the attenuation of soil horizontal acceleration, reduction of soil effective stresses and promotes tunnel flotation. The existence of a building not only reduces the liquefaction ratio of sub-surface soil right below the foundation but also effects the earth pressure distribution on the adjacent tunnel sidewall. In addition, the presence of the tunnel may affect adversely the rotation of the foundation especially in saturated soils. [ABSTRACT FROM AUTHOR]