8
an area of higher potential energy to one of lower poten-
tial energy and there are many factors that determine this
movement. The various energy that exists includes gravi-
tational potential energy and matric potential, which exist
in the saturated soil. Soil that has its pores not filled has a
matric potential of zero, and the total potential is the sum
of the gravitational and the matric.
Seepage front moves in the soil due to the differences in
the potential energy. As the water level increases in the left
chamber, the pressure increases, driving the forces to move
through the soil. Studies of seepage front were conducted on
three experiments. The first experiment looked at groundwater
increase with a water reservoir beneath the slope (Figure 13).
In the test for seepage front where water is kept constant in
the bottom chamber, water flows from the left chamber seep-
ing through the bottom water and then finally seen at the toe
of the slope. The seepage is seen while the dye moves through
the water. The flow vectors and flow lines show the movement
and path of water through the soil. It is initially seen mov-
ing through the bottom of the soil and through the bottom
chamber of water and then the curve moves towards the toe.
Contours showing pressure differences also indicate high
pressures in the soil below the water level. Low pore pressures
are also seen above the seepage front in yellow and red color.
This is depicted in all the models shown.
The next two experiments looked at seepage without
water in the bottom chamber since the base was sealed
watertight. In the initial condition, water was allowed to
fill the left chamber almost to the level of the slope and
kept constant for 5 minutes. The water was then allowed to
drawdown and drain through the soil. A transient analysis
was then conducted in Rocscience Slide to compare that
of the experiment. The analysis showed a gradual seepage
front movement. During the last stages, the change was
very insignificant hence the difficulty of seeing the differ-
ence in the seepage front (Figure 14).
The figure shows the movement of the seepage front
with time through the soil sample. The contours show
pore pressures with blue being the highest to the least of
red color.
4.5 Ratio of water level, slope height, and slope failure
Experiments were conducted to compare the ratios of
water level, slope height, and slope failure. During these
experiments, three (3) slope heights were chosen 280 mm,
225 mm, and 150 mm. In all the tests, the slope failed
at water levels 270 mm, 215 mm, and 145 mm, respec-
tively. It shows an approximate 96% water level for failure
to occur. This is consistent with the experiment by Jia et
al. (2009), where the experimental slope failed at a 93.4%
water level to slope height ratio. The results are illustrated
in the graph below (Figure 15).
Failure occurs at a water level to slope height ratio of
1.04 when the soil is almost fully saturated. Again, at the
very high-water level, the gravitational potential energy is
also high, which reduces the shear force at the toe of the
slope. This causes the toe failure, hence causing the global
failure of slope.
(a) Slope with a factor of safety before the
experiment
(b) Slope with a factor of safety after failure
Figure 12. Slope with factor of safety before and after the
experiment
Figure 13. Steady-state seepage
an area of higher potential energy to one of lower poten-
tial energy and there are many factors that determine this
movement. The various energy that exists includes gravi-
tational potential energy and matric potential, which exist
in the saturated soil. Soil that has its pores not filled has a
matric potential of zero, and the total potential is the sum
of the gravitational and the matric.
Seepage front moves in the soil due to the differences in
the potential energy. As the water level increases in the left
chamber, the pressure increases, driving the forces to move
through the soil. Studies of seepage front were conducted on
three experiments. The first experiment looked at groundwater
increase with a water reservoir beneath the slope (Figure 13).
In the test for seepage front where water is kept constant in
the bottom chamber, water flows from the left chamber seep-
ing through the bottom water and then finally seen at the toe
of the slope. The seepage is seen while the dye moves through
the water. The flow vectors and flow lines show the movement
and path of water through the soil. It is initially seen mov-
ing through the bottom of the soil and through the bottom
chamber of water and then the curve moves towards the toe.
Contours showing pressure differences also indicate high
pressures in the soil below the water level. Low pore pressures
are also seen above the seepage front in yellow and red color.
This is depicted in all the models shown.
The next two experiments looked at seepage without
water in the bottom chamber since the base was sealed
watertight. In the initial condition, water was allowed to
fill the left chamber almost to the level of the slope and
kept constant for 5 minutes. The water was then allowed to
drawdown and drain through the soil. A transient analysis
was then conducted in Rocscience Slide to compare that
of the experiment. The analysis showed a gradual seepage
front movement. During the last stages, the change was
very insignificant hence the difficulty of seeing the differ-
ence in the seepage front (Figure 14).
The figure shows the movement of the seepage front
with time through the soil sample. The contours show
pore pressures with blue being the highest to the least of
red color.
4.5 Ratio of water level, slope height, and slope failure
Experiments were conducted to compare the ratios of
water level, slope height, and slope failure. During these
experiments, three (3) slope heights were chosen 280 mm,
225 mm, and 150 mm. In all the tests, the slope failed
at water levels 270 mm, 215 mm, and 145 mm, respec-
tively. It shows an approximate 96% water level for failure
to occur. This is consistent with the experiment by Jia et
al. (2009), where the experimental slope failed at a 93.4%
water level to slope height ratio. The results are illustrated
in the graph below (Figure 15).
Failure occurs at a water level to slope height ratio of
1.04 when the soil is almost fully saturated. Again, at the
very high-water level, the gravitational potential energy is
also high, which reduces the shear force at the toe of the
slope. This causes the toe failure, hence causing the global
failure of slope.
(a) Slope with a factor of safety before the
experiment
(b) Slope with a factor of safety after failure
Figure 12. Slope with factor of safety before and after the
experiment
Figure 13. Steady-state seepage