Soil Mechanics Experiment

2. CT-234: Soil Mechanics (THEORY)
BSC Civil Engineering Technology
Third Semester (Fall-2022)
Lecture 02
Residual & Transported Soils
By:
Engr. Kamran Khan
Email: kamran@uotnowshera.edu.pk
2

3. Residual Soils

4. Residual Soil
• When the rate of weathering is more than the rate at which the
weathered materials are carried away by transporting agents, result in
residual soils.
• An important characteristic of the residual soil is the gradation of the
particles.
• Fine grained soils are found near the surface of the earth and grain
size increases with depth.
• At greater depth relatively course grained and angular particles are
found.

5. Boring log of a Residual Soil derived from granite
• When hard rocks such as
granite undergo weathering
most of the materials are likely
to remain in place.
• These soil deposits generally
have a top layer of clayey or
silty clay material, below
which are silty or sandy soil
layers. These layers in turn are
generally underlain by a
partially weathered rock and
then bedrock.

6. Transported Soils

7. A. Gravity Transported Soil
Gravity can transport soil in Three ways.
1. Creep: Residual soils on a natural slope can move slowly downward,
and this is usually referred to as creep.
2. Landslide: Sudden and rapid downward soil movement is called as a
landslide.
3. Mud flows: In this case, highly saturated loose sandy soils on
relatively flat slopes move downward like a viscous liquid and come
to rest in a more dense condition.
The soil deposits formed by Creep, landslides and mudflows are Colluvial
soil.

8. B. Alluvial Deposits
•Loose, unconsolidated soil mass, which has been
eroded, reshaped and redeposited in a non-
marine environment by water are called Alluvial
deposits.
•Divided into two major categories:
(1) Braided-stream deposits
(2) Meandering Belt Deposits

9. 1. Braided-Stream Deposits
• Braided streams are high-gradient, rapidly
flowing streams that are highly erosive and
carry large amounts of sediment.
• Because of the high sediment load, a minor
change in the velocity of flow will cause
sediments to deposit.
• The deposits formed from braided streams
are highly irregular in stratification and
have a wide range of grain sizes.
Braided Stream

10. Braided-Stream Deposits (CONTD…)

11. 2. Meandering Belt Deposits
Meander Belt: The valley area in which a river/stream
meanders (curve back and forth) is referred to as the
meander belt.
As the stream meanders within its belt, it produces a suite of
deposits, consisting of sediments characteristics of point
bars, natural levees, oxbow lakes & Backswamp deposits.

12. 1. Point bar deposits
In a meandering river, the soil from the bank
is continually eroded from the points where it
is convex in shape and is deposited at points
where the bank is concave in shape form point
bar deposits.
 Usually consist of sand and silt-size particles

13. 2. Oxbow lake: Sometimes, during the
process of erosion and deposition, the
river abandons a meander and cuts a
shorter path. The abandoned meander,
when filled with water, is called an
oxbow lake.
Meandering Belt Deposits (CONTD…)

14. Meandering Belt Deposits (CONTD…)
3. Natural levees: During floods, rivers overflow low-lying areas. The
sand and silt-size particles carried by the river are deposited along
the banks to form ridges known as natural levees.
• Levee:
• An embankment built to prevent
the overflow of a river.
• A ridge of sediment deposited
naturally alongside a river by
overflowing water.

15. 4. Backswamp deposits:
 Finer soil particles consisting of silts and clays are
carried by the water farther onto the floodplains.
These particles settle at different rates to form what
is referred to as Backswamp deposits.
 Often highly plastic clays.
Meandering Belt Deposits (CONTD…)
 A floodplain is the relatively flat area that borders a stream which is
periodically flooded with water during high flow periods.

16. Composite Diagram

17. C. Lacustrine Deposits
In arid regions, streams carry large amounts of
suspended solids.
Where the stream enters the lake, granular
particles are deposited in the area forming a delta.
Some coarser particles and the finer particles (silt
and clay) that are carried into the lake are
deposited onto the lake bottom in alternate layers
of coarse-grained and fine-grained particles are
called Lacustrine deposits.

18. Drift: A general term usually applied to the deposits laid down by glaciers.
A moraine is material left behind by a moving glacier.
This material is usually soil and rock. Glaciers transport all sorts of dirt and
boulders that build up to form moraines.
Moraines are stretching for kilometers on the Earth.
Moraines only show up in places that have, or used to have, glaciers.
Glaciers are extremely large, moving rivers of ice.
Glaciers shape the landscape in a process called glaciation.
Glaciation can affect the land, rocks, and water in an area for thousands of
years. That is why moraines are often very old.
D. Glacial Deposits

19. Types of Moraines
1. End moraines form at the terminus of the glacier.
2. Terminal moraine: Ridge that marks the maximum limit of a glacier's advance.
3. Ground moraine: A ground moraine is made of sediment that slowly builds up directly
underneath a glacier by tiny streams. When a glacier melts,
the ground moraine underneath is exposed.
4. Outwash: The sand, silt, and gravel that are carried by the melting water from the
front of a glacier are called outwash.
5. Lateral moraines: The sides of a valley glacier
accumulate large quantities of debris from the valley walls.
When the glacier melts, this material is left behind as
ridges called Lateral moraines.
6. Medial moraine: Medial moraines are formed when
two glaciers meet. If a glacier melts, the medial moraine it
leaves behind will be a long ridge of earth in the middle of
a valley.

20. E. Aeolian Soil Deposits
• Wind is also a major transporting agent leading to the
formation of soil deposits.
• When large areas of sand lie exposed, wind can blow
the sand away and redeposit it elsewhere. Deposits of
windblown sand generally take the shape of dunes.
• As dunes are formed, the sand is blown over the crest
by the wind. Beyond the crest, the sand particles roll
down the slope. The process tends to form a compact
sand deposit on the windward side, and a rather
loose deposit on the leeward side, of the dune.
• Dunes exist in the Arab countries, at the southern coast
of California, and at various places along the coasts of
Washington.

21. E. Aeolian Soil Deposits (CONTD…)
• Typical properties of dune sand:
1. The grain-size distribution of the sand at any particular location is
surprisingly uniform.
2. The general grain size decreases with distance from the source,
because the wind carries the small particles farther than the large
ones.
3. The relative density of sand deposited on the windward side of
dunes may be as high as 50 to 65%, decreasing to about 0 to 15% on
the leeward side.

22. F. Organic Soil
• Found where the water table is near or above the ground surface.
• The presence of a high water table helps in the growth of aquatic plants
that, when decomposed, form organic soil.
• Found usually in coastal areas and in glaciated regions.
Characteristics:
1. Natural moisture content range 200 to 300%.
2. Highly compressible.
3. Exhibits large amount of settlement in secondary consolidation.

23. Thanks