CHANGES IN STRESS-STRAINED SOIL MASS RESULTING FROM THE INSTALLATION OF BORED CAST-IN-SITU PILES AND BARRETTES

Abstract

Introduction . The paper considers the effect produced by the installation of bored cast-in-situ piles and barrettes on the stress-strain state of the surrounding soil mass for four different types of soil conditions. Aim . To develop a procedure for determining concrete-induced stress acting on walls that enclose a borehole filled with concrete, as well as stress changes during relaxation. Materials and methods . An analysis of experimental studies is performed, both those conducted by the present authors and those available in open sources. By means of back calculations relying on experimental data, the dependence is determined between the maximum concrete-induced stress and the rate of concr eting. The results of post-construction monitoring are used to derive a formula for describing stress relaxation following the completion of concreting works. Results . In this study, the authors proposed a bilinear formula, developed a procedure, and calculated the concrete-induced stress acting on the walls that enclose a borehole filled with concrete, as well as stress changes in the process of relaxation. The effect of the adopted pile installation technique and soil conditions on changes in the stress-strain state of soil mass was studied. A formula was provided for determining the final values of horizontal stresses at the pile-soil interface at the full grade strength of concrete following stress relaxation in the soil, as well as recommendations for numerically calculating changes in the stressstrain state of soil mass during concreting and subsequent concrete hardening in piles and barrettes. Conclusions . The conducted studies into the effect of bored cast in-situ pile installation on the stress-strain state of surrounding soil mass revealed that this stress-strain state depends on the soil conditions of the site, as well as the adopted pile installation technique. Due to the fact that soil is a plastic material, the final value of horizontal stresses is affected by the technique-dependent load dynamics and the soil conditions of the site, which should be taken into account by applying appropriate soil models.