OF CIVIL ENGINEERING
EAG 245 – SOIL MECHANICS
LEW KAH WEI
LIM WEI HANG
RICHARD NG ENG YAO
TAN ZE LING
Dr. Muhd Harris Ramli
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The Importance of
Understanding and Designing Seepage Control
is defined as the slow escape of a liquid or gas through porous material or
small holes. It is often used to describe the process or seeping, by which a
liquid leaks through a porous substance such as soil.
Seepage depends on a variety
type of factors, including permeability of the soil, and also the forces acting
on the fluid which is directed to the soil. Beside, permeability is a large
field, correspond with each type of soil structure and its composition. As a
civil engineer, we should understand the importance of seepage in its effect
regarding safe design of structure such as earth dams and reservoirs, roadbeds,
filtration beds and others.
Figure 1 : Path of Seepage through Embankment Dams
Consideration of the factors of
seepage is very important, as if it is not considered, internal erosion may be
caused, as well as empty voids might be created in the form of channels or
pipe. All this situations may affect the stability of the project eventually.
Therefore, we should understand and know the theory and concept of seepage in
order to control the seepage to an ideal situation. Hence, we will be able to
construct a project with minimum risks and with more confidence.
Figure 2 : Schematic Diagram of Seepage Test Assembly
Seepage is normally test with few
ways, this assembly is one of the tests to determine the seepage at a certain
zone. In short, we need to know the way to determine the seepage of an area in
order to control the seepage.
In conclusion, controlling seepage
is vital for a civil engineering project. For instance, project such as
building an embankment dam required a lot of consideration especially the
seepage problems as the dam is used to store water. Without considering the
seepage problems, the project might become risky and dangerous when it is
completely built. Therefore, we need to learn and understand seepage thoroughly
to apply the concept and take account into all civil engineering projects.
The Important Parameter Required to Analyse Seepage
There are many type of ways to carry
out seepage analyse, and Flow Net is one of the analysis. Flow net is normally
known as a graphical representation of two dimensional steady-state groundwater
flow through aquifer.
Net consists of flow lines and equipotential lines. Flow lines indicate the
flow of water through the geotechnical structure, while for equipotential
lines, it indicates the energy of flow, and also show the total head of the
flow. The flow lines are always apart from each other and not cross and
order to analyse a seepage behavior, drawing of flow net is required. For
instance, Darcy’s Law is applied to determine the permeability, and in order to
obtain the rate of flow net as well as the properties of seepage. Hence, the
seepage behavior can be determined.
Figure 3 : Flow Net
permeability is also a parameter to be altered and specified in order to
determine the seepage behavior. For instance, permeability might be specified
according to a material, by specifying the direction and angle, and others.
besides the mentioned parameters, there are still many parameters to be
considered and take account into the determination of the seepage behavior in
order to get a more accurate result from the analysis. Therefore, as a civil
engineer, we have to learn to determine the permeability as well as how to
apply these theory to determine the seepage behaviour.
REVIEW ON EFFECTS AND CONTROL OF SEEPAGE THROUGH EARTH-FILL DAM
Seepage normally occurred in the
dam when water infiltrating slowly through the dam and its foundation.
Inadequate seepage control measures have incurred many seepage problems and
failure of earth-fill dams.
Uncontrolled saturation and seepage
forces was on of the main causes of earth dam failures. Therefore, the
assessment to phenomena such as drawdown, which occur in earth structures
subjected to sudden changes of water level that modify flow conditions inside a
soil mass, should be done. Besides the factors that incurred seepage are the
erodibility of the soil, the water velocity
inside the soil mass and the geometry of the earth structure. Other important
factors are the anisotropy of the earth structure and its foundation soil, the
soil graduation and degree of compaction of the materials used during the
construction process, the hydraulic conductivity of such materials, the
upstream water energy head, as well as the hydraulic gradient.
When the soil resistant forces are less than the
seepage forces, then the soil erosion will occur, causes by the water flow
removed and carried the soil particles away. The soil resistance forces depend
on the cohesion, the interlocking effect and the weight of the soil particles
with these factors this will be able to protect the soil particle from the
downstream. The erosion phenomenon increases where there exists a concentration
of seepage and water velocity; in places where this concentration emerges at
the downstream side, the erosive forces on the soil particles might become very
significant. The erosion might probably starts at any point where the seepage
water discharges and works toward the reservoir, gradually enlarging the
seepage channel. Depending of the stage of this process, the occurred damage
might be classified as a simple “incident”, an accident, or a complete failure.
Soil compaction is a process of increasing the
density of soil by packing the soil particles closer together causing a
reduction in the void ratio. Compaction proses can be either a shallow
compaction or a deep compaction. Discuss;
The construction work of embankment for (choose one either Reclamation project
or Ground Improvement work)
The principal and construction method of deep compaction (choose one type)
WORK OF EMBANKMENT FOR GROUND IMPROVEMENT WORK
Soil compaction is a very important process before
any of the building or structure is construct on the land. The purpose of this
process is to increase the shear strength so that the soil has the ability to
carry the stress that going to build on the land. Other than that, this process
is to reduce the subsequent settlement under working loads, this is to ensure
that the land has no any physical deterioration. Besides, the soil compaction
is also able to reduce the void ratio that contain in the soil and compaction
can prevent the soil to build up large amount of water pressure that will cause
liquefaction during earthquake.
There are two types of compaction, which is shallow
compaction and deep compaction. Shallow compaction is accomplished by rolling
or vibrating. Field compaction is normally done by various type of rollers,
sheepfoot roller –
used mainly for clayey and silty soil.
smooth drum roll –
used primarily for granular soil.
Vibratory roller –
used primarily for granular soil.
Pneumatic rubber-tired roller –
used for clay soil.
Deep compaction is a very important
and useful technique to compact wide variety of weak soils. With deep
compaction, ground is subjected to repeated surface tamping using a heavy steel
and concrete weight. Typically tamping weight is between 5tones to 10tones,
dropping in free fall from a height of 10meter.
is an artificial barrier that typically is used to hold back water to support
roadway, railway and canal. It is a ridge to prevent water from passing beyond
desirable limits. This man made mound normally consist of stones, rocks and
earth. Most of the embankments have sloping sides, much like hills. Generally, embankments
are longer than they are in heights.
is one of the methods for ground improvement work. It acts as pre-loading or
pre-compression load for the ground or soil. Preloading is surcharging the
ground with a uniformly distributed surface load prior to the construction of
the surface such as building, embankment, motorway, and so on. The purpose of
the preloading is to take up the settlement after the building was constructed
on the soil. Not every soils are suitable for preloading, soil that suitable
for preloading are compressible soft to medium soft saturated clay and silts,
organic clay and peats. There are many methods or preloading such as earth
fills, water in tanks or ponds, vacuum application under membrane and so on.
The simplest technique is by embankment. When the load is placed on soft soil,
the load is initially carried by pore water, when the soil is not very
permeable, the water pressure will decrease gradually due to the pore water is unable
to flow away very quickly in vertical direction. In order not to create any
stability problem, the load is must be placed in two or more stages. If the
temporary load exceeds the final construction load, the excess is known as
surcharge load. The temporary load can be removed when the settlement exceed
the final predicted settlement. By increase the time for overloading or size of
overload, the second settlement can be reduced or eliminated.
PRINCIPAL AND CONSTRUCTION METHOD OF DEEP COMPACTION
Nowadays, it is important that planning and design
consultants to deal with the issue of lack of suitable ground for construction.
Due to the rising costs of property in densely built-up areas, buildings are
being constructed to a greater height. Hence, the application of deep compaction
can actually solve this problem quickly and with low cost.
Deep compaction techniques are required when in–situ soil
extending to large depths does not meet the requirements of performance
criteria specified for the expected loading and environmental conditions. With
deep compaction, significant differential settlements can be avoided. Danger to
the stability of the structure where there are dynamic loads can be minimised.
Examples of deep compaction are Dynamic Compaction,
Vibro-Compaction, Compaction Grouting, Pre-fabricated Vertical Drains and Blast
One of the methods of deep
compaction is Dynamic Deep Compaction (DDC). The technique is known as the
greenest solution of all requiring without introduction of concrete or stone
into the soil. DDC is an important ground
improvement technique. It is the method of compaction of unsaturated or highly
permeable saturated granular materials or any wide range of weak soils.
However, it is mainly used to compact granular fills. It is also useful
for compacting rock fills below water and for bouldery soils which cannot be or
difficult to be applied by other methods. For example, waste dumps, mine wastes
and sanitary landfills.
Settlements are caused either by compression of voids or
decaying of the trash material over time in sanitary fills. DDC is an
the void ratio, and hence reducing the immediate and long term settlement.
DDC is also effective in reducing the decaying problem, since collapse means
less oxygen available for decaying process. For recent fills where organic
decomposition is still underway, DDC increases the unit weight of the soil mass
by collapsing voids and decreasing the void ratio. DDC has greatest effects by
increasing unit weight and decreasing long term ground subsidence for
older fills where biological decomposition is complete.
Dynamic Deep Compaction (DDC)
is also an essential
ground improvement technique that used to treat large sites or sites with major
obstructions such as deep open cast workings, old power stations or infilled docks. The ground
improvement results in increased bearing capacity and decreased settlement.
In this way, many marginal sites’ soil
conditions can be enhanced
to the point where shallow foundations can be used without deep excavation or
piling. Hence, there will be less serious difficulties with aggressive
However, DDC is an expensive treatment and relatively time
consuming. Its applicability is reduced due to the development of the pore
pressure in the fine grained soil. This method is also not valid for populated
or fully developed areas because the shock waves generated by this method may
affect other underground utilities or the adjoining structures. So, while
working in crowded or populated areas, small weights are used and height of
dropping weights is reduced to minimise the intensity of vibrations. It is
reported by experienced contractors that the soil can be treated as close as 3
m from underground services and can be treated 6 m from the sound structures.
Although it does not introduce any concrete or stone into the soil, it does
cause environmental pollution by making noise, gusts of air, vibrations and
permanent deformation of the soil.
OF DYNAMIC COMPACTION
Dynamic compaction is known as a
ground improvement technique that helps to densify soils and fill materials by
a drop weight. Based on Figure 1, the soil is compacted by introducing high
intensity impacts on it by dropping 10 to 20 tons of weight( typically steel )
repeatedly and freely from a height varies from 10m to 40m with the help of
cranes. The soil particles are denser and in more compact state by the vibrations
transmitted below the surface. The impact of the shock waves created by the heavy weight
travel considerably deeper. The soil depths of 15 m have been treated using
this technique .Further depth are treated using other special equipment and the
heavy loads for further compaction is possible( up to 172 tons).
Based on Figure 2, the spacing
between the impact points is depending on the depth of compressive layer,
permeability of soil and location of ground water level. A deeper layer needs
to be compacted at a wider grid spacing while the upper layers are compacted
with closer grid spacing.
As shown in Figure 3, the degree of densification is
manipulated by the energy input (weight and drop height) as well as the
saturation level, the fines content and permeability of the material. 6 to 30
tons weight can densify the loose sands to a depth of 3m to 12m.
DDC is done systematically in a rectangular or
triangular pattern in phases. Referring to Figure 4, each phase can have no of
passes, primary pass, secondary pass etc. Deep craters are formed after Dynamic
Compaction and it may be filled with sand after each pass.
The energy during DDC treatment is transferred by propagation of Rayleigh waves
(surface) at 67% and volumic waves (shear and compression) at 26% and 7%
Deep compaction increases shear strength and reduces
compressibility and thus improve the bearing compressibility. A
stable foundation makes relatively higher demands on the foundation soil. The
existing soil profile often possesses hidden reserves for supporting loads and
have to be first activated by treatment. In other words, the ground has to be
improved by compaction.