Studies of the shear wave velocity in soil cement under the anisotropic stress state

Abstract

Introduction. Deep soil mixing, that alters construction properties of foundations, allows to construct buildings and structures on the sites that have loose soils. As a rule, adverse geotechnical conditions are accompanied by dynamic forces that affect designed buildings and structures. The objective of these studies is to predict changes in mechanical properties of soils that follow the alteration of structural properties of a foundation. Soil cement is the focus of this study. Materials and methods. The findings of special laboratory tests of soil cement samples using the method of low amplitude torsional vibrations inside a resonant column in the anisotropic triaxial compression mode allowed to assess the effect of the supplementary vertical load on the velocity of shear elastic wave propagation. The co-authors present a description of the research method and provide an overview of the equipment used to conduct special laboratory tests. Tests were performed on undisturbed soil cement samples that had a natural water content. The anisotropic stress state of soil cement samples exposed to triaxial tests in the resonant column was caused by special behaviour features of the foundation. Results. In this study, laboratory tests had two stages. At the first stage, the effect of the vertical stress on the velocity of shear wave propagation was assessed. Correlation dependences between the shear wave velocity and the ratio of vertical and lateral stresses were obtained. At the second stage, shear wave propagation velocity values were identified at various combinations of lateral σ3 and vertical σ1 stresses. The results of the second stage are designated for the assessment of the effect of the anisotropic stress state and the projection of shear wave velocities at the stress levels anticipated on the site that will accommodate designed heavy structures. Conclusions. The findings allow to assess the effect of lateral and vertical stresses on changes of shear wave velocities in the triaxial compression mode. It was identified that at equal values of lateral stresses σ3, a 7-fold vertical stress σ1 increase leads to a 15 % increase in the shear wave velocity in soil cement Vs. At the same time, an increase in the ratio of vertical to lateral stresses σ1/σ3 by a factor of 15 causes an 11 % increase in the shear wave velocity. It is noted that the smaller the initial value of lateral stress σ3, the higher the rise in the shear wave velocity Vs in the course of testing. Correlation dependencies, presented in this study, can be used to assess the effect of the anisotropic state as the first approximation (for preliminary calculations) in the design of heavy structures on soil cement foundations.