Frost soil interaction with the cement-sand mortar of a driven precast pile

Abstract

Introduction. The drilling method of pile driving represents the most common method of constructing foundations on permafrost soils. In order to reduce the tangential forces of frost heaving, the space between the pile surface and a leader well wall within the layer of seasonal freezing-thawing is filled with non-heaving sandy soil. This technology complicates the process of installing driven precast piles. In this case, a significant simplification involves filling the space between the pile and the soil with a cement-sand mortar (CSM) along the entire height of the pile. However, at present, no method is valid for calculating driven precast piles for the action of frost heaving tangential forces during CSM freezing.Aim. To develop a methodology for calculating driven precast piles for the action of frost heaving tangential forces during CSM freezing.Materials and methods. A set of laboratory tests, modeling the processes in soils during cold and warm pile installation periods, was carried out. Laboratory tests were performed using a method of a single-plane cut along the surface of a CSM freezing with clay soils, as well as with the foundation material at a constant rate in accordance with State Standard R 56726-2015 and statistical data processing according to State Standard 20522-2012.Results. The article presents the results of laboratory studies on effects, caused by frost heaving tangential forces on piles during soil and CSM freezing, taking into account various factors (clay soil liquidity index, test temperature). Based on the obtained data, the authors propose a methodology for calculating the stability of driven precast piles. The method consists in determining the heaving force per unit area by adding the products of the seasonal freezing-thawing fractional depth, obtained by thermal engineering calculations or according to the plots, given in the article, by the tangential forces of frost heaving, obtained in laboratory studies.Conclusions. The developed methodology improves the reliability and accuracy of foundation calculations, enhances the efficiency of base and foundation design solutions, and reduces the labor capacity of driven precast pile installation.