INFLUENCE OF GRATING RIGIDITY ON THE IMPLEMENTATION OF THE WORK OF GRATING AND PILES AS PART OF A COLUMN PILE FOUNDATION

Abstract

This work proposes a study of the influence of the thickness of the grillage in combination with the dimensions of the grillage plate (the main parameters that determine its rigidity) on the nature of the redistribution of forces between the components of the pile foundation under the column. By modeling in the LIRA CAD software package, it was investigated how the grillage and piles work together in a columnar pile foundation when changing the thickness h and dimensions in the plan B (i.e., its stiffness) of the grillage, as well as the location of the piles in the plan, their length, number and type of soil. The research program made it possible to analyze the influence on the stress-strain state of the foundation elements of the following parameters: the thickness of the grillage, which was taken as 700, 1000 and 1300 mm; the nature of the location and number of piles in the group, including the sparse placement of piles, the dimensions of the grillage; the lengths of the piles, respectively 3 m and 10 m with a cross section of 300x300 mm. The research considers two variants of the soil base: homogeneous sandy and homogeneous clay soil. The main attention is paid to varying the thickness of the grillage with different combinations of its other parameters.

It was found that with increasing grillage stiffness, the load perceived by the pile bush increases, but this increase is insignificant. Research has shown that such an increase in the bearing capacity of the bush as the grillage thickness increases occurs mainly due to an increase in the load perceived by the piles. To increase the efficiency of piles, it is recommended to vary the thickness of the grillage, provided that the initial rigidity of the grillage is V/h > 6. The rigidity of the grillage is the main factor affecting the redistribution of forces between the piles of the group. In pile foundations with an initial rigidity of V/h > 6 (flexible grillages), the greatest load falls on the piles in the middle of the group. But already when the stiffness index is reduced to B/h = 4.7 (more rigid grillages), the redistribution of forces leads to a greater load on the edge and corner piles. With a further increase in the rigidity of the grillages, the corner piles are the most heavily loaded, and the central ones are the least loaded. Therefore, with an increase in the thickness of the grillage, a redistribution of forces occurs between the piles towards the outer contour. Analysis of the magnitude of the concentrated load on the pile of the group indicates its increase, but insignificant compared to the increase in the load on the corner piles.

As a result of the increase in the rigidity of the grillages, bending moments and shear forces within their body increase. Quantitatively, this increase is insignificant.