الفهرس | Only 14 pages are availabe for public view |
Abstract Some areas in Egypt, including Alexandria, Port Said, Kafr El-Sheik, Suez Canal, and Damietta, have the problem of soft clay settlement. Construction over soft soil is known to be a great risk due to the compressibility and shear strength failure of clay. The stone column improvement technique helps structures, especially embankments, to remain stable over soft soil. The mechanism of stone columns is able to bear loads due to passive earth pressure resistance established against bulging of stone columns, which depends on the shear strength of surrounding soil. Increasing vertical settlements over time can affect the embankment’s stability. Therefore, extra efforts are required to analyze soft soil long-term behavior supported by an ordinary stone column technique. In this thesis, a verification process was performed through numerical simulation using Plaxis (2D and 3D) against previous work involving full-scale of stone columns in São Goncalo clay, located in Rio de Janeiro, Brazil. The results of the finite element simulation model were also verified against the analytical solution proposed by the Han and Ye formula. The Plaxis 2D results showed good agreement with the experimental results. As Plaxis 2D required less time for calculation and effort than Plaxis 3D, it was used to obtain the parametric study. Based on the verification performed, the same numerical methodology was adopted to perform a detailed parametric study. A parametric study was performed to evaluate the consolidation rate of soft clay enhanced with stone columns. The studied configuration comprises an ordinary stone column (OSC) with other studied parameters.The main aim of current study is to evaluate the effects of stone column length (L), stone column spacing (S), encasement case (with and without encasement and encasement stiffness influence), thickness of drainage layer (T), cohesion influence (C), stone column permeability (K), and embankment height (H). The results of the analysis indicated that the soft clay performance is improved conditionally on the length of the columns (L). As the ratio between the length of the stone column and embankment height (L/H) increases, the soft soil settlement decreases by 2%, 8%, and 12% at (L/H = 0.6, 0.8, 1.0), respectively. The performance of stone column enhanced as the increase in area replacement ratio (ac = 15%, 20%, and 25%) decreases soft clay settlement by 18%, 20.5%, and 24.5% respectively. The encased stone column with a geogrid pad had reduced settlement compared to an ordinary stone column. The result shows that as the encasement stiffness increased, the settlement decreased, which led to a reduction in the consolidation rate. An analytical solution was put forward to obtain the settlement rate of an end-bearing ordinary stone column. The proposed analytical solution was compared with the finite element model results, and a mutually acceptable agreement was found. The key advantage of the recommended analytical method is that it offers a simple engineering approach for estimating the settlement rate of improved soil. Overall, the study finds that the stone column depth, the area replacement ratio, and the stiffness of the encasement all have significant effects on the settlement of soft clay. In addition, the proposed analytical solution gives a practical methodology for estimating the settlement rate of end-bearing ordinary stone columns. |