This document discusses seepage forces and their effect on soil stability. It defines seepage forces as the viscous drag of water flowing through soil pores, which increases intergranular pressure and reduces effective stresses. Seepage forces are higher in more permeable soils like sand versus less permeable soils like clay. Two case studies of dam failures are presented: Nanak Sagar Dam in 1962 failed due to internal erosion from seepage forces, while Fontenelle Dam in 1965 also failed due to piping caused by seepage. The conclusion is that seepage forces can be strong enough to cause liquefaction, erosion, and failures of dams and retaining walls if not properly addressed.

1. NED UNIVERSITY OF ENGINEERING AND TECHNOLOGY
SOIL MECHANICS-1
CONCEPT OF SEEPAGE FORCES ON DIFFERENT
SOIL AND ITS EFFECT ON SLOPE STABILITY
NAME MEESUM HUSSAIN
CLASS THIRD YEAR
ROLL NUMBER UE-050
COURSE SOIL MECHANICS-1

2. SEEPAGE FORCES AND ITS EFFECT
2
CONTENTS
CONCEPT OF SEEPAGE FORCES....................................................................... 3
1.1 SEEPAGE FORCES...................................................................................... 3
1.2 SEEPAGE FORCES ON DIFFERENT TYPES OF SOIL ............................... 4
EFFECTS OF SEEPAGE FORCES ON THE SOIL STABILITY............................. 6
2.1 CASE STUDY............................................................................................... 6
2.1.1 NANAK SAGAR DAM 1962................................................................... 6
2.1.2 FONTENELLE DAM 1965....................................................................... 7
CONCLUSION.......................................................................................................... 8

3. SEEPAGE FORCES AND ITS EFFECT
3
CONCEPT OF SEEPAGE FORCES
1.1 SEEPAGE FORCES
Seepage is defined as the flow of fluid, normally water, due to hydraulic gradient ,
through the soil. Forany given soil, which consists of solid particles of various
sized with interconnected spaces (void spaces). As water flow through the
interconnected spacein the soil, this flow is referred as seepage, usually small
velocities. The present of continuous void spaces in the soil allow water to flow
with in the soil from a high energy point to a low energy point.
Permeability is defined as the soil property that allows the seepage of fluids
through its void spaces. The flow of water though the soil mass may results in some
force being exerted on the soil by itself. The force that is exerted by the soil is
known as the seepage force.
Seepage force can also be defined as the viscous drag of water which flow through
the interconnected pore spaces in rockor soil causing an increase in intergranular
pressure (the hydraulic force exerted per unit volume of the soil or rock which
initiate the flow of water through the soil as in the direction of flow. Seepage forces
are the cause of reduction in effective stresses.
Considering spherical particles connected with
each other , when the water percolate through it ,
the interconnected forces get weakened as the
water starts exerting pressure and as a result of
which the cohesive force between the particle
get weaker and the water passes through the soil
particles in the direction of the flow. The
velocity of flow of water through the soil is
normally come into consideration because the
movement of water through the soil follows
tortuous path due lead very low velocity of water. The seepage forces that are
created in the soil is directly related to the hydraulic gradient which causes water
flow.
Figure 1 Spheres being injected with water

4. SEEPAGE FORCES AND ITS EFFECT
4
1.2 SEEPAGE FORCES ON DIFFERENT TYPESOF
SOIL
Seepage forces acts differently on the different type of soil. The magnitude of the
seepage forces is sometimes significant enough to disturb the soil or destabilize it.
If the seepage forces are not balance by structural forces then failure may occur,
such as in the case retaining structures etc. Permeability of the soil which allows the
flow of water normally through the rockor unconsolidated material, Seepage forces
somehow related to the permeability of the soil. In less permeable soil the seepage
water can be stored temporarily. If the seepage water encounters an impermeable
soil layer or impermeable rock, seepage will no longer take place and seepage water
accumulates permanently, such underground water accumulation known as ground
water. If we relate the seepage forces with permeability, we can conclude that
seepage forces will be high in high permeable soil, as in the high permeable soil the
interconnected spaces are loose and water can easily penetrate through the
interconnected spaces as they have large spaces between them. Seepage forces
come into play only in permeable soil strata. To measure the flow through the soil
Darcy’s states the law,
𝑄 = 𝑘𝑖𝐴
Where,
Q =Flow rate in ft3/sec
I =HydraulicGradient
A= Cross-sectional area ft2
K= Coefficient of permeability m/s or ft/s
According to Darcy law, flow of water through a permeable strata depends on
change in elevation heads, pressure heads, cross-sectionalarea, and also the
coefficient of permeability.
As we compare the different soil on the bases of seepage forces, there is seeping
velocity which we can consider,
Seepage velocity as a function of soil capacity in water-unsaturated soil
Velocity Soil Layer Grain Size
5m/year gravel 2-63 mm
2-4m/year sand 0.063-2 mm
1m/year silt 0.002-0.063 mm
Severalcm/year clay <0.002 mm

5. SEEPAGE FORCES AND ITS EFFECT
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As it is shown in the above table, that the seeping velocity is high in high permeable
soil and low in less permeable soil, as if the comparison between clay and sand take
place, as the sand is more permeable as compare to clay , so the water can move
faster through the sandy soil as in the clay soil , so the seeping velocity of the sandy
soil is higher as compare to clay soil, as through the clay soil water flow with very
low or negligible velocity because of smaller particles so that they can packed
tightly as which does not happen in sand because of larger particles. So the particles
with high seepage velocity have high seepage forces exert on it. So as soil with
small grain size have low seepage forces.

6. SEEPAGE FORCES AND ITS EFFECT
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EFFECTS OF SEEPAGE FORCES ON THE
SOIL STABILITY
Ground water in slope has important influence on slope stability, especially
for high rock slope. Because of weathering, tectonization and unloading effects,
joints and gaps grow and become the main flow path and water storage space.
Ground water in the fractured rock can change the physical and mechanical
parameters and induce fracture extend, shearing deformation through
hydrostatic and hydrodynamic pressure, the slope failure is because of the internal
erosion of soil, piping, which is due to the seepage forces.
2.1 CASE STUDY
2.1.1 NANAK SAGAR DAM 1962
Nanak sagar dam is situated in the province Punjab in northwestern India, the dam
was constructed at bhakra in 1962, with a storing capacity of 2.1 × 106
𝑚3
.
On august 27,1967 approximately a discharge of 9,711
𝑚3
𝑠𝑒𝑐
had occurred, due to
heavy monsoonrains that were the heaviest in 20 years. This causes the dam to fail,
as the water flowed through the seepage created a 7.6 m breach, which later
widened to 45.7 m. when the water flowed through the soil seepage forces came
into play due to which internal erosion took place. As internal erosion was due to
the pipping phenomena that took place with seepage forces. As this made the
condition of the reservoir worsened, causing a 16.8 m boil downstream of the toe,
this was also responsible for the settlement of the embankment. As the dam was
overtopped due to heavy rain, causing a breach 150 m wide. A downstream filter
blanket and relief wells were provided near the toe but were insufficient to control
the seepage of water, and due to seepage forces the dam was destroyed.

7. SEEPAGE FORCES AND ITS EFFECT
7
2.1.2 FONTENELLE DAM 1965
Fontenelle Dam was so close to failure, it could easily have been the event that led
to changes in dam safety across the country if not for some fortuitous
circumstances. In many ways the story of Teton Dam is as much about lessons not
learned from Fontenelle Dam as it is about Teton itself. Fontenelle Dam was
completed in 1964 and began to fill with water that same year. Soonafter filling
started, the dam began to have performance problems. Significant seepage was
observed in the left abutment, right abutment, and downstream of the dam.
Seepage in the downstream direction lead to the failure of the dam. As the
phenomena of piping took place to due which the soil particles moved through the
foundation of the dam. The dam was a earth fill dam, the good thing that happened
with the failure of the dam was that no fatalities took place , the reason for the
failure of the dam was the piping.

8. SEEPAGE FORCES AND ITS EFFECT
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Fontenelle dam slope failure because of internal erosion
CONCLUSION
The seepage forces are considered as important factor while studying erosion of
soil, failure of dams, retaining wall failure, as sometimes the forces are strong
enough to reduce the effective stresses of soil and lead to several disasters. Seepage
is responsible for liquefaction in soil, as it disturb the soil. Engineers have learned a
great deal about internal erosion and the effects of seepage at dam sites.