Change in strength parameters of dusty-clayey soils depending on the time of dynamic load impact and soil type

Abstract

The method of high frequency vibratory driving and extraction of sheet piles is frequently utilized in the conditions of structurally unstable soils in St. Petersburg. However, with this method of installation (extraction) of sheet piles in the surrounding soil mass it arises oscillations that are transmitted to nearby buildings and housing, capable of causing dangerous phenomena in their undergroud and aboveground structures, mainly related to differential settlement of foundations. The prediction of additional settlement of buidings in the surrounding area from vibro-driving/extraction of sheet piles is a complex, multi-factor task, and the level of the structural displacement of building, which is the main controlled parameter for the influence of dynamic loading on the foundation soil, according to the current regulatory documents Territorial Building Codes50-302-2004, Departmental Building Codes490-87, Russian State Standard 52892-2007 is merely an indirect criterion for assessment. To obtain a more accurate assessment of the development of additional settlements in buildings during high-frequency vibratory pile driving and sheet pile extraction, it is necessary to take into account not only the duration and frequency of the impact, but also the properties and type of soil itself. The purpose of this reseach was to study changes in the strength parameters of silty-clay soils depending on the time of dynamic loads impact, the type and consistency of the soil itself, as well as changes in parameters depending on the “rest” time of the soil base after exposure to vibration. The article presents the results and shows the tendency to reduce the parameters of soil strength after the application of dynamic load and the dependence of their change on the time of impact, on the type and consistency of the soil. It has been determined the dependence of changes in the strength parameters of the soil conditionally upon the "rest" time of the soil mass as a result of thixotropic re-storation, which will determine the economic attractiveness for the accident-free technology of this method.