چكيده به لاتين
Soil is a non-homogenous and unpredictable material, and changes in the environment (formation), soil behavior, and sediments over time lead to uncertainty in geotechnical issues. One of these sources of uncertainty is the presence of voids and empty spaces in the underground, which are formed under natural or human factors. The pile is a part of the structure responsible for transferring the structure's load to the soil. The presence of voids in the vicinity of the pile may affect the load transfer behavior of the pile, especially its bearing capacity, and the extent of this effect depends on various factors. For this purpose, to reduce possible risks and prevent substructure and superstructure damage caused by the presence of these voids, it is necessary to check the effect of these voids on the bearing capacity of piles.
In this study, the effect of the presence of voids on the bearing capacity of the pile and the lateral pressure coefficient of the soil applied to the pile wall was investigated using Discrete Elements Method (DEM) numerical modeling in granular soil. This study includes three parts investigating the effect of a single void on pile-bearing capacity, the effect of double voids on pile-bearing capacity, and the effect of a void on the lateral pressure coefficient of the soil. In each section, an attempt has been made to examine the studies from a macro (engineering) and micro (fundamental) point of view.
The results of the studies show that there is a critical area around the pile that if the hole is located in that area, it will lead to a decrease in the bearing capacity of the pile. The amount of this load-carrying capacity reduction depends on things like the position of the void approaching the void, increasing the size of the void, and increasing the porosity of the particles. In a situation such as the presence of a large circular void in the most critical position under the pile, a 63% decrease in the bearing capacity of the pile can be seen.
Fundamental studies were carried out using measurement areas around piles and Voids, in which macro data such as porosity, maximum and minimum stresses, and stress path, as well as micro data such as particle coordination number, polar distribution of strong contact forces, and the contact network of the particles during the vertical movement of the pile in the soil, were recorded. With the link between these data, the causes of rupture and non-rupture and the way of arching the roof of the voids were investigated.
Also, by considering the four measurement areas by the side of the pile, the changes in the lateral pressure coefficient of the soil during the shearing process in these areas were investigated and it was concluded that the two upper areas are in passive condition and the two lower areas are close to an at–rest condition. Also, with further investigations, it can be concluded that the presence of a void in the soil and pile system has a negligible effect on the changes in the lateral pressure coefficient along the length of the pile wall. Considering that to calculate the frictional resistance along the pile shaft, the lateral pressure coefficient of the soil (K) is needed, as a result, the presence of voids in the soil will have a small effect on the frictional resistance of the pile. According to the studies carried out on the effect of voids on pile-bearing capacity, we know that the presence of voids, depending on their conditions, can have a significant effect (reduction) on pile-bearing capacity. By combining these two issues, it is concluded that the main effect of the presence of the voids on the bearing capacity of the pile is on the tip resistance and the frictional resistance of the pile shaft will not be affected by the Void.
