Sandra Escoffier

Centrifuge modeling of batter pile foundations under sinusoidal dynamic excitation

Batter pile (or inclined pile) foundations are widely used in civil engineering structures. However, their behavior under dynamic loadings is not yet thoroughly understood. This paper presents an experimental work on the behavior of batter and vertical piles considering dynamic soil-pile-superstructure interactions. A series of dynamic centrifuge tests were performed using sinusoidal excitations. The influence of the base shaking (frequency content and amplitude) and of the height of the center of gravity of the superstructure is investigated. Seismic responses are analyzed considering the pile cap displacements and forces (total base shear, overturning and residual moments, axial forces). It is found that in certain cases batter piles play a beneficial role on the dynamic behavior of the pile foundation system. This novel experimental work provides an important database on the behavior of batter pile foundations under dynamic loadings.

Cross-Facility Validation of Dynamic Centrifuge Testing

This paper compares the results of dynamic centrifuge tests on shallow foundations conducted at two different geotechnical facilities, IFSTTAR (Institut francais des sciences et technologies des transports, de l’amenagement et des reseaux, formerly LCPC), France and Cambridge University, U.K. Both facilities ran tests on a single degree of freedom model structure with its shallow foundation located on dry sand and subjected to dynamic shaking. Measurements were taken at both facilities allowing direct comparisons to be made. Fundamentally the results obtained were found to agree well via comparison of soil amplification profiles and moment-rotation cycles. However, higher frequency components agreed less favourably. This variation is thought to be due to a mismatch between the dynamic properties of the model containers. In this series of tests the higher frequency components are not of great importance and therefore the variation is insignificant, however, in future tests when earthquake signals with higher frequency components are input it may become an issue requiring further investigation.

Experimental and Numerical Investigations of Nonlinearity in Soils Using Advanced Laboratory-Scaled Models (ENINALS Project): From a Site-Test to a Centrifuge Model

The SERIES project “Experimental and Numerical Investigations of Nonlinearity in soils using Advanced Laboratory-Scaled models” (ENINALS) was focused on the centrifuge modeling of seismically-induced strains vs. stratigraphic features and it was applied to the heterogeneous alluvia of the Tiber River in the Rome historical centre. Four soil samples, representing two homogeneous soil columns (only clay and only sand respectively) and two heterogeneous soil columns (including a clay level between two sand ones) were tested in the IFSTTAR centrifuge. The applied dynamic input represents the maximum expected seismic action in Rome and it was reproduced at the centrifuge shaking device following three approaches: (i) a natural time history, (ii) an equivalent sinusoidal signal, and (iii) a multifrequential equivalent signal derived by the recently proposed LEMA_DES approach. The here reported preliminary results: (i) demonstrate the reliability of a “cut and install” procedure for realizing the saturated multilayer samples; (ii) give new insights on the reliability of multifrequencial dynamic equivalent signals for scale-reduced analogical modeling.

3D failure envelope of a single pile in sand

Pile foundations are widely used in geotechnical and offshore engineering. When subjected to a combination of horizontal, vertical forces and bending moments, a 3D failure envelope is necessary in order to evaluate the safety of the pile-soil system. We present a study on the failure envelope of a single elastic pile in sand. In order to find it in the three-dimensional space (i.e. horizontal force H, bending moment M and vertical force V), the radial displacement method and swipe tests are numerically performed. An analytical equation providing good agreement with the 3D numerical results is finally proposed.