الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 130 |  |  |
| | | from | 130 | | |
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.