Numerical simulation of interaction continuus fligt auger pile with a soil mass under static vertical load

Main Article Content

Igor Boyko
Oleg Krivenko

Abstract

The full-scale static test of a continuus fligt auger (CFA) pile for vertical loading by means of numerical modeling is reproduced.


The modeling process can be divided into two stages: determining the calculated boundaries of the soil; identification of mechanical parameters of soils (young’s modulus (E), cohesion (c), friction angle (φ)).


The first stage of modeling is to break the grid of finite elements in the plan so that it thickens from the periphery to the continuus fligt auger (CFA) pile (in our case, the pitch of the grid varies from 1 m to 10 cm). Then break the finite elements of the array in height with a certain step (in this work, a step of 1m). Then you need to determine how much the height of the soil will be under the pile tip. For this purpose 4 variants are considered: 2,5m; 5m; 10m; 20m. Looking at the results, it can be seen that starting from 10 m and less, deviations within 5%, so we take as a basis the soil thickness of 10 m. Then the size of the soil in the plan was selected. Five options were considered: 5x5m; 10x10m; 20x20m; 30x30m; 40x40m. The basis was 30x30m. As a result of this stage we take 10m under the pile, in the plan 30x30m (the pile is placed in the center).


After establishing the dimensions of the calculation model, we are moving to the identification of the mechanical characteristics of the soil (E, c, φ). Identification of mechanical characteristics of the soil was performed in a layer around the pile 10 cm thick. At the beginning, the young’s modulus (E) was identified by linear calculation. It is established if the young’s modulus equal to 4E it allows to reproduce the results of field tests within the limits of elastic work of soil most precisely. If we take into account the nonlinearity, then our straight line begins to bend. Then, the cohesion (c) was identified, which showed that this indicator does not make a significant contribution to the relationship between load and sedimentation. Therefore, it is accepted to leave the cohesion unchanged. The friction angle (φ) is taken into account with a coefficient of 0.75φ.


Based on the establishment of the size of soil mass and the identified mechanical parameters of the soil, the results of calculations were compared under three conditions strength: Huber-Mises, Drucker-Prager, Mohr-Coulomb.

Article Details

Section
Статті
Author Biographies

Igor Boyko, Kyiv National University of Construction and Architecture

Head of the Department of Geotechnics

Oleg Krivenko, Kyiv National University of Construction and Architecture

Assistant of the Department of Geotechnics

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