Computation of settlements induced by the seismic action
The computation of settlements induced by the seismic action is affected by significant uncertainties. The values that are obtained applying the procedures described below must be intended only as guidelines.
The settlement is considered to be the lowering of the surface level, or, the integral of the soil deformation in vertical direction, or, the sum of the products of the vertical mean deformation to the thickness of each of the deformed layers.
In oedometric conditions, or in the presence of homogeneous and horizontal soil layers, with constant stress in horizontal direction, the lateral deformations are null and therefore the vertical deformation coincides with the volumetric strain.
For simplicity and with accetptable approximation, except in cases of morphology with steep slopes and highly variable stratigraphy in horizontal direction, for the computation of settlements induced by the seismic action we can refer to the oedometric conditions.
The permanent settlement induced by the seismic action corresponding to a vertical exploration is obtained from the sum of the contributions to the settlement estimated in the various layers of the subsoil, until the depth at which these contributions are no longer significant.
The permanent post-seismic settlement can be calculated using the equation: S=Σεvi×Δzi; εvi is the volumetric strain (and vertical) of the i-th layer and Δzi its thickness.
The software LoadCap calculates the post seismic settlements for soft cohesive soils for which the extent of the reconsolidation settlement following the dissipation of the pore pressures accumulated during the earthquake can be calculated with the equation (Yasuhara and Andersen, 1991) while for the computation of the ratio of interstitial pressure it is used the empirical relationship (Matsui et al., 1980).
To expand the feathures of the software, two new computation models have been added:
- Settlements induced by the seismic action in granular saturated soils (volumetric strain, εvi computaion using Idriss and Boulanger, 2008).
- Settlements induced by the seismic action in unsaturated granular soils (volumetric strain εnc computation using Pradel, 1998)