Seismic active earth pressure on walls using a new pseudo-dynamic approach.

Seismic active soil thrust, soil pressure distribution and overturning moment are obtained in closed form using a new pseudo-dynamic approach based on standing shear and primary waves propagating on a visco-elastic backfill overlying rigid bedrock subjected to both harmonic horizontal and vertical acceleration. Seismic waves respect the zero stress boundary condition at the soil surface, backfill is modeled as a Kelvin-Voigt medium and a planar failure surface is assumed in the analysis. Effects of a wide range of parameters such as amplitude of base accelerations, soil shear resistance angle, soil wall friction angle, damping ratio are discussed. Results of the parametric study indicate that amplitude of the horizontal base acceleration and soil shear resistance angle are the factors most influencing active pressure distribution whereas the presence of the vertical acceleration always results in a quite small increase in seismic active thrust. Damping ratio is important mainly close to the fundamental frequency of shear wave where seismic active thrust is maximum. Unlike the original pseudo-dynamic approach the effect of a different frequency for S-wave and P-wave is considered in the analysis. Seismic active thrust is found to increase when the frequency of P-wave is greater than that of S-wave. The results obtained are found to be in agreement with previous studies, provided that the seismic input is adapted to include amplification effects

LINKING SMALL-STRAIN STIFFNESS TO DEVELOPMENT OF CHEMICAL REACTIONS IN LIME-TREATED SOILS

In the context of lime stabilization, this note shows how the development of soil–lime reactions can be linked to the variation of small shear stiffness with time. To determine the evolution of small-strain stiffness, the shear wave velocity was measured by means of bender elements (BE) on a compacted clayey soil treated with 3% quicklime, starting form 2 h after compaction until 98 days of curing. Different methods of signal interpretation were applied with the purpose of highlighting how the peculiarity of lime treated soils affects BE testing results and to provide practical indications for optimizing similar testing on lime-treated soils. The results showed that lime treatment and compaction affect the waveform of the received signal and that measurements should span across a wide range of input frequencies in order to identify an optimal waveform. The small strain shear modulus was found to increase with curing time with a trend that can be related to that of soil–lime chemical reactions, thus representing a promising parameter to monitor the development of soil–lime reactions