Abstract— A 3-D finite element (FE) numerical model was used
to analyze structurally a proposed subsurface concrete dam to
serve as a strategic water supply storage for the Holy city of
Makkah, Saudi Arabia. The work was done mainly to show the
behavior of the subsurface dam under the subjecting loads. The
plastic concrete was chosen for the construction of the cut-off wall
required for the reservoir. Three-dimensional finite element
analyses were made for three thicknesses of the cut-off walls: 0.6
to 0.8 m, 0.8 to 1.0 m and 1.0 to 1.2 m for the alluvium depths of
30, 50 and 70 m, respectively. The change in soil rigidity with
depth was taken into account. The vertical and horizontal
boundary conditions were designed to simulate the proper
behavior of the structure It was found that increasing the
thickness of the wall improves the distribution of the mobilized
passive pressure opposite to the water pressure acting on the
upstream face of the cut-off wall, while, the vertical and horizontal
stresses developed in the wall due to the applied loads increased.
In addition, stresses in the wall increase incrementally with the
increase of wall height. The maximum horizontal and vertical
stresses developed in proportion to the 1/6 bottom height of the
wall. In the lower part of the wall, the mix with rich cement
content must be used. It is recommended also to use vertical
reinforcement imbedded by the anchorage length in the lock of the
wall inside the bedrock and extended 1/20 the wall height. Results
showed that the two vertical boundaries in the FE mesh must be
placed at minimum distance equaling twice the height of the
alluvium deposits from the centerline of the cut-off wall.