الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Recently, the construction demand has increased extremely owing to the rapid urbanization.
However, not all soils are occasionally valid for construction where sometimes civil engineers have
to construct on weak soils that natively are not suitable for construction. Engineers face many
challenges and risks to construct on such soils due to their adverse properties. Soft and very soft soils
are considered among of the most problematic soils due to their high compressibility, high
deformations, low shear strength, and subsequently low bearing capacity. Construction on these soils
with traditional methods will spend many expenses, time and finally will not be economic.
Therefore, soil improvement methods shall be used to improve these weak soils such as compaction,
preloading, weak soil replacement, chemical treatment, stabilization of weak soil by many products
like cement, lime, fly ash, and lime-cement, soil reinforcement and stone columns. Stone column is
one of the most significant techniques used in soil enhancement. They are idealized used for soft and
very soft soils and silts. They also may be used for loose sand.
Soft and very soft clay are usually deposited on low-rise delta plains that form at the river’s mouth
where water slows down, allowing the slow deposition of fine clay particles. The Nile River in Egypt
flows from the south and forms a delta in Northern Egypt that extends from Alexandria city to PortSaid city. Constructing embedded retaining wall in such soils requires a very deep embedded depth
and huge concrete sections. It sometimes requires constructing a cellular cofferdam with high
expenses.
The main objective of this research is to investigate the effect of stone columns installation under a
strip footing in the active zone of a retaining wall embedded in very soft and soft clay soils through
laboratory model testing program and finite element analysis. The laboratory model was composed
of a tank containing the soil layers, retaining wall, strip footing, and loading system. The finite
element analysis was performed using PLAXIS 3D V21 finite element program. Mohr Coulomb
material model was selected to model the different soils. from the results of laboratory tests, and
numerical analysis, the results concluded that stone column inclusion enhanced the allover behavior
of the retaining wall, enhanced the bearing capacity under the footing, decreased the settlement of
the footing, and decreased the lateral movement of the retaining wall. The results of finite element
analysis gave a good agreement compared with the experimental results. A parametric study was
performed on different parameters such as cohesion of soft clay, angle of internal friction of stone
columns, area replacement ratio of stone columns, and the type of stone columns whether end
bearing or floating columns Area replacement ratio is a very important parameter in the applications of stone columns. The
results showed that by increasing the area replacement ratio of the stone columns, the bearing
capacity under the strip footing improved, the settlement of the footing reduced, and the lateral
displacement of the retaining wall decreased. The experimental results showed that stabilizing the
very soft clay using stone columns of area replacement ratio of 35% decreased the horizontal
displacement of the retaining wall and the vertical displacement (settlement) of the footing for the
unstabilized very soft clay at failure stress of the control case by 56% and 55% respectively. The
vertical stress at failure increased by 66% in case of area replacement ratio of 35% compared with
the native soil and increased by 23% upon increasing the area replacement ratio from 25% to 35%.
For the same area replacement ratio and clay cohesion, the higher angle of internal friction used; the
higher bearing capacity obtained, the lower horizontal displacement occurred, and the lower vertical
displacement occurred. Increasing angle of internal friction for end bearing stone columns from 38°
to 45° at area replacement ratio =35% for Cohesion =10 kN/m2
reduced the horizontal displacement
of the retaining wall and the vertical displacement of the footing at stress of 30.0 kPa by 49% and
50% respectively; and for Cohesion =15 kN/m2
at stress of 60.0 kPa reduced by 45% and 47%
respectively which means that the angle of internal friction has a great effect on the horizontal and
vertical displacements compared with area replacement ratio.
The end bearing type of stone columns gave a better effect than the floating type of stone columns.
Using end bearing stone column compared with floating stone column (0.75 Length) at angle of
internal friction =45°, and area replacement ratio =35% increased the vertical stress at failure for
Cohesion =10 kN/m2
and for Cohesion =15 kN/m2
by 24%, and 34% respectively. Floating stone
columns provided good enhancement especially at high area replacement ratios with high angle of
internal friction. Floating stone columns, on the other hand, are important if compared with
unstabilized soils.
Installing stone columns in soft clay with undrained cohesion less than or equal 10 kN/m2
gave a
small positive effect compared with clay having a higher undrained cohesion value, so it is not
recommended to use stone columns in soft soils with shear strength less than or equal 10 kN/m2
.