Геотехничко моделирање на проблемот на интерација за длабоки темели фундирани во сложени геотехнички услови

Abstract

This research analyzes the problem of interaction of the foundations as critical elements in any construction with the natural substrate, which can often be complex in terms of geotechnical conditions. The purpose of the foundations is to withstand and transfer the necessary loads safely, both structurally and geotechnically. If the soil can not accept the load with a sufficient coefficient of safety, then significant subsidence will occur, and the construction would be unreliable. This could lead to costly repairs or failure. In recent decades, numerous test methods have made it possible to indirectly assess the structural integrity and bearing capacity of piles. Pile foundation is a popular type of deep foundation used to transfer loads from the upper layers to the good bearing deep soil layers. However, the exact assumption of the piles settlement is particularly difficult, given the complex assessment of the interaction between the pile and the soil. This research aims to assess the load-bearing capacity of piles through theoretical, field and numerical investigsations in various geotechnical environments (low bearing soil materials, as well as soft rocks materials with pronounced anisotropy and heterogeneity). The input parameters for the analysis of the problem differ and are obtained from experimental tests, depending on the parameters of the substrate, structure characteristics, levels of load, depth and dimension of foundation, and other structural characteristics. Thereby, independent field tests were performed with a special system for receiving load through the use of a specialy designed platform that serves as a counterload. During the research were applied approaches for preparation of interaction schemes, where the influential parameters of the natural structure - the terrain and the artificial construction - the object are connected. As a result of the analyzes, a large number of correlations between the examined parameters were established. In the second phase of the research, a numerical simulation of the problem was performed by applying appropriate software tools, by which were obtained valuable results that are used to select the optimal foundation system. Namely, to simulate the interaction of the structure with the environment, the Mohr-Coulomb material model was used, by introducing a characteristic modulus of elasticity of the pile-soil system through which the results of the physical with the numerical model are calibrated. From the analysis of a number of experimental tests of piles to the designed or ultimate force, a classification of the load-settlement dependence was made according to several parameters. According to the geometric ratio of the length and diameter of the pile, they are divided into five groups. According to the environment in which they are performed, they are divided into three groups, from which it can be concluded that in the fine-grained soils the ultimate bearing capacity is reached relatively quickly, while in coarse-grained materials it is conditioned by the soil compactness. The piles constracted in soft rocks show that the limit state of failure is not reached for the maximum load and that the unloading effect is insignificant in terms of deformations. A comparison of the numerically obtained relation load - settlement for the soil behavior is made according to two different material models: Morh-Coulomb (MC) and Hardening Soil (HS) model. The results show that the curve obtained with the HS model gives greater deformations for the reference load. The advantage of MC over HS model is that in the simplest way for known deformations from test loading the Emc modulus can be determined, which, is further used for calculation of pile foundation and other controls. On the other hand, the HS model requires the definition of multiple parameters from laboratory tests that are often relatively difficult to determine and depend on a subjective factor. The procedure for the experimental and numerical modeling of the pile-substrate interaction system is sublimated into a diagram according to which diagrams of the dependence load-settlement from a selected experiment are initially formed. For each step of loading, the settlement into the numerical model for variable modulus of the Emc pile - soil control is controlled. After defining the modulus for each step of loading and appropriate settlement, the calculation of the group of piles or the foundation structure can be continued.