The increasing demand for new infrastructure developments has recently
led to an escalating trend to develop sites with inadequate ground
conditions that were previously considered uneconomical to develop.
These situations have posed challenged that geotechnical engineers are
meeting by cultivating innovative techniques like stone columns to
overcome soft clay soil conditions. Among the various methods for
improving in situ ground conditions, stone columns are considered one of
the most versatile and cost-effective ground improvement techniques. Stone
columns reinforce cohesive soils and densify granular soils in order to
increase bearing capacity and decrease total and differential settlement.
The accuracy of the results obtained depends on the knowledge of the input
data for the tunnel and the surrounding soil. Many geotechnical challenges
are expected to occur related to soft clay soil stability and tunnel lining.
One of these problems is expected to occur related to tunnel lining stability
and surrounding soil is the high values of settlement due to compressibility
of soft layer when it lies around or below tunnel lining.
This present study aims to improve the behavior of tunnel lining and
eliminate the effect of soft clay layer on this behavior by using vertical
stone columns. This study is carried out by using Finite Element Method.
The tunnel lining is meshed with two dimensional elements, called BEAM 6
element. The soil and stone columns are meshed with another two
dimensional elements called LST, (Linearly Varying Strain Triangular
Element). In this study, the main parameters were taken into consideration
are the position and properties of stone columns. It can be concluded that
using of stone columns in tunnel opening zone has strong effect on the
improving behavior of tunnel lining. For application of this study, data of
Cairo Metro Tunnel- Line 2, was chosen. The results of this study were
compared with the initial values obtained from case of does not include
stone columns.