abstracts | Theoretical analysis of shaking table experiments, simulating earthquake response of a dry
sand layer, is presented. The aim of such experiments is to study seismic-induced compaction
of soil and resulting settlements. In order to determine the soil compaction, the cyclic stresses
and strains should be calculated first. These stresses are caused by the cyclic horizontal acceleration
at the base of soil layer, so it is important to determine the stress field as function
of the base acceleration. It is particularly important for a proper interpretation of shaking table
tests, where the base acceleration is controlled but the stresses are hard to measure, and
they can only be deduced. Preliminary experiments have shown that small accelerations do
not lead to essential settlements, whilst large accelerations cause some phenomena typical for
limit states, including a visible appearance of slip lines. All these problems should be well
understood for rational planning of experiments. The analysis of these problems is presented
in this paper. First, some heuristic considerations about the dynamics of experimental system
are presented. Then, the analysis of boundary conditions, expressed as resultants of respective
stresses is shown. A particular form of boundary conditions has been chosen, which satisfies
the macroscopic boundary conditions and the equilibrium equations. Then, some considerations
are presented in order to obtain statically admissible stress field, which does not exceed
the Coulomb-Mohr yield conditions. Such an approach leads to determination of the limit base
accelerations, which do not cause the plastic state in soil. It was shown that larger accelerations
lead to increase of the lateral stresses, and the respective method, which may replace complex
plasticity analyses, is proposed. It is shown that it is the lateral stress coefficient K0 that controls
the statically admissible stress field during the shaking table experiments. |