Effect of the soil–pile–structure interaction in seismic analysis: case of liquefiable soils

The design of earthquake-resistant structures depends greatly on the soil–foundation–structure interaction. This interaction is more complex in the presence of liquefiable soils. Pile and rigid inclusion systems represent a useful practice to support structures in the presence of liquefiable soils in seismic zones. Both systems increase the bearing capacity of soil and allow reducing the settlements in the structure. Numerical models with a 3-storey reinforced concrete frame founded on inclusions systems (soil–inclusion–platform–structure) and pile systems (soil–pile–structure) were analyzed. Finite difference numerical models were developed using Flac 3D. Two different soil profiles were considered. A simple constitutive model for liquefaction analysis that relates the volumetric strain increment to the cyclic shear strain amplitude was utilized to represent the behavior of the sand, and the linear elastic perfectly plastic constitutive model with a Mohr–Coulomb failure criterion was used to represent the behavior of the earth platform. Two earthquakes were used to study the influence of the different frequency of excitation in the systems. The results were presented in terms of maximum shear forces distribution in the superstructure and spectrum response of each system. The efforts and displacements in the rigid elements (piles or rigid inclusions) were compared for the different systems. The bending and buckling failure modes of the pile were examined. The results show that the pile system, the soil profile and the frequency of excitation have a great influence on the magnitude and location of efforts and displacements in the rigid elements.

     

Discrete element modelling of a granular platform supported by piles in soft soil – Validation on a small scale model test and comparison to a numerical analysis in a continuum

This paper focuses on the mechanisms taking place in a granular platform supported by piles in soft soil. Several modelling approaches were explored. A two-dimensional small scale model test using the Taylor–Schneebeli soil analogue was first developed and the experimental results were compared to a discrete element model using the particle code PFC. The validation of this numerical approach allowed the parametric study to be extended numerically. Parametric studies were also performed on continuum model using the finite-difference code FLAC. Comparison of the parametric studies performed on each modelling approach underlined some differences and lead to a consideration on the macro- and micromechanical parameters.     

Characterization of a soil-rough structure interface using direct shear tests with varying cyclic amplitude and loading sequences under a large cyclic testing cycle condition

Acta Geotechnica - This paper aims to investigate the effects of cyclic shear amplitudes and loading sequences on a soil–structure interface using direct shear tests under a large number of...     

Physical evidence of the effect of vertical cyclic loading on soil improvement by rigid piles: a small-scale laboratory experiment using Digital Image Correlation

This paper presents an experimental study focusing on the mechanisms taking place in a granular platform supported by piles in soft soil under vertical cyclic loading. An original three-dimensional laboratory model was developed, with a scale factor of 1/10 on the length. The model contains 20 rigid piles, and the compressible soil is explicitly simulated by a soft material. The case of a thin granular load transfer platform overlaid by a rigid slab is studied. Tests were performed under monotonic or cyclic loading applied on the surface using a pressurized membrane. The analysis is based on a force and displacement sensor instrumentation and application of a Digital Image Correlation technique. The evaluation of the load transfer onto the piles and the settlements in the platform are some of the main points under the scope of this study. The effect of the cyclic loading and the sequence of loading on the structure’s response are examined by a comparative study between the series of cyclic and monotonic tests. Settlement accumulation and increase in the load transmitted to the piles were observed during the cycles. The image analysis gives access to the displacement field within the granular platform, and its evolution during the cycles could be analysed.