Riccardo Conti

Evaluation of Soil Dynamic Properties in Centrifuge Tests

This paper describes a method to compute the mobilized shear modulus, G, and damping ratio, D, using the nonlinear fit of experimental transfer functions obtained at different depths in centrifuge models, with the analytical expression of the amplification function for a viscoelastic soil layer on a rigid base. The corresponding shear strain, γ, is computed as a function of the particle velocity and shear wave velocity. The sources of potential error in the determination of G, D, and γ embedded in the proposed method are identified and discussed in comparison with two other methods that have been proposed in the literature, based either on the determination of the time lag of accelerations between two accelerometers or on the evaluation of the shear stress-strain cycles from acceleration time histories recorded at different depths in the model. The performance of the three methods is evaluated using the experimental data obtained from nine centrifuge tests on dry sand. The values of G obtained by the proposed method compare well with the results of laboratory and literature data; D values are more dispersed and slightly higher than the literature data. DOI: 10.1061/(ASCE)GT.1943-5606.0000659.

Filtering effect induced by rigid massless embedded foundations

It is well recognised that the dynamic interaction between structure, foundation and supporting soil can affect significantly the seismic behaviour of buildings. Among other effects, embedded and deep foundations can filter the seismic excitation, causing the foundation input motion (FIM) to differ substantially from the free-field motion. This paper presents a theoretical and numerical investigation on the filtering effect induced by rigid massless embedded foundations. Based on the results of dimensional analysis and numerical simulations, it is shown that the problem can be reasonably described by two sole dimensionless groups, namely: (1) ωH/VS, relating the wave length of the signal to the embedment depth of the foundation, and (2) the aspect ratio of the foundation, B/H, where B is the foundation width in the polarization plane. New simplified and physically sound expressions are derived for the kinematic interaction factors,

Centrifuge Modelling of Retaining Walls Embedded in Saturated Sand Under Seismic Actions

I_{u} = u_{\text{FIM}} /u_{{{\text{ff}}0}}

Numerical modelling of installation effects for diaphragm walls in sand

Iu=uFIM/uff0 and

A two-rigid block model for sliding gravity retaining walls

I_{\theta } = \theta_{\text{FIM}} H/u_{{{\text{ff}}0}}

A new limit equilibrium method for the pseudostatic design of embedded cantilevered retaining walls

Iθ=θFIMH/uff0, which are frequency-dependent transfer functions relating the harmonic steady-state motion experienced by the foundation to the amplitude of the corresponding free-field surface motion. Standard methods for using these functions in the evaluation of the FIM are critically reviewed, with reference to both static and dynamic procedures for the seismic design of structures.