weathering and erosion - tcm.edu.iq -geology1.pdf · weathering and erosion lecture 1 ......

Technical College / Al-Musaib

Engineering Geology

Building & Construction Technology Engineering Department

Weathering and Erosion

Lecture 1


Lecture No. 1

Main Objectives Understanding the concept of weathering and erosion

Being able to differentiate weathering from erosion

Apprehend the different agents that may cause weathering and erosion

Understanding factors that influence the formation of soils

Lecturer Ehsan A. Hasan

Msc in transportation engineering

Assistant lecturer at Technical College/Al-Musaib

Date of Lecture General advices to make best benefit of this lecture

Listen carefully to lecturer, be present mindfully

Take necessary written notes

Ask questions to simplify and remove ambiguity

Total number of pages 4

Download link for the PDF version https://goo.gl/H0nEh3


Engineering Geology



Lecture 1

1.0 Weathering

Weathering is the process that produces change in the surface of

rocks exposed to the atmosphere.

It is a complex interaction of physical, chemical and biological

processes that are responsible for the breakdown and alteration of

rocks and minerals into soil products.

the Breakdown Process of Rocks

Decomposition

the minerals of the rocks are acted upon by air and water,

chemical changes occur

Disintegration

the rock is broken down without any chemical changes,

by the effects of changes in temperature, frost, abarsion by ice, water or air carrying sand

Figure 1


Engineering Geology



Lecture 1

2.0 Erosion

It is the wearing away of the earth’s surface materials by any natural

process and its transportation by natural agencies from the point of

removal

Through erosion the surface of the earth is constantly being

sculptured into new forms.

Erosion occurs after the disintegration of rocks by weathering.

2.1 Agents of Erosion

1. Water Erosion

The most important erosional agent

Causes erosion in four ways

a. The hydraulic action of the water itself moves the sediments

b. Water acts to corrode sediments by removing ions and dissolving

them

c. Particles in water strike bedrock and erode it

d. The impact of raindrops on soil surface

2. Wind Erosion

Causes movement of materials by wind

Occurs when the lifting power of moving air is able to exceed the

force of gravity and friction holds an object to the surface

Move pronounced in arid and semi-arid areas of the world.


Engineering Geology



Lecture 1

3. Glacial Erosion

The wearing down and removal of rocks and soil layers by a glacier

Figure 2 example of wind erosion

Figure 3 different processes of glacier erosion


Engineering Geology



Lecture 1

4- Wave Erosion

Waves in oceans, seas and other large bodies of water produces

coastal erosion

5- Gravity Erosion

Causes mass movement of rocks and sediments due to gravity force.

3.0 Formation of Soil

Soils are porous formations and form naturally.

Composed of several inorganic and organic matters

Five major factors that directly or indirectly influence the

formation of soil.

Soil Type and its

proerties

Organisms (biotic

activity)

Topographical Conditions

Type of Parent Material

Climatic Condition

Time


Engineering Geology


Types and classification of soils

Lecture 2

Page 1

Types and Classification of Soils

Lecture No. 2 Main Objectives Understanding geological

classification of soils

Understanding the properties and sources of different soil types





Listen carefully to lecturer






Engineering Geology



Lecture 2

Page 2

1.0 Factors for Soil Classification

There are various types of soil classification systems

Most of these systems are based on the following factors

1- Soil physical properties

2- Soil chemical properties

3- Soil color

4- Soil texture

5- Soil structure

2.0 The Importance of Soil Classification

in order to describe the various materials found in ground

investigation

3.0 The Requirements of a Good Soil Classification System

must be comprehensive

must be meaningful for engineers, geologists and scientists

4.0 geological soil classification system

it is comprehensive and simple

it divides soils into the following groups

A. Residual Soils

Formed in situ from the weathering of the underlying bedrock

Their formation are common in the plain areas as compare to the

hilly terrain area


Engineering Geology



Lecture 2

Page 3

The major factors for the formation of tropical residual soils are:

1- The leaching of insoluble materials

2- The accumulation of insoluble residues

3- The movement of fine particles downward

B. Transported Soils

The soils that is deposited by natural geological agents such as water,

wind, ice or gravity

They are not derived from underlying bedrocks

These soils could be classified to the following types according to the

transporting agent

i. Colluvial Soils

It is loose and unconsolidated

Deposited at the hill slopes or foot hills under gravity

Composed of boulders, cobbles, pebbles, silts etc.

Basic factors responsible for the formation are

1- Weathering

2- Erosion

3- Transportation

4- Deposition

ii. Alluvial Soils

Composed of loose and unconsolidated sediments

Deposited by water


Engineering Geology



Lecture 2

Page 4

Composed of river and costal sediments like sand, silt, clay and

gravels

Very fertile and supports all types of vegetation

iii. Glacial Soils

Formed by the movement of glacial ice

Composed of boulder clays, moraine materials

Also called drift

iv. Aeolian Soils

Formed by the deposition of wind transported sediments

Composed of sand, silt and clay

Examples for them: loess and sand dunes

v. Lacustrine Soils

Formed from the deposition of materials transported by rivers,

streams and glaciers

Usually freshwater lake deposits occur in lake basins

These deposits form soil when the lake dries

Generally stratified and rich in organic matter

vi. Marine Soils

Formed from different sediments brought into the sea by rivers and

streams

The materials eroded from the beaches by tidal action of the waves

Technical College / Al-Musaib Engineering Geology


Soils and Their Properties

Lecture 3

Page 1


Lecture No. 3

Main Objectives Introducing granular, clay, expansive soils and their properties

Learning soil slopes and their stability

Describing minerals of soils

Learning solutions for expansive soils










Technical College / Al-Musaib Engineering Geology Building & Construction Technology Engineering Department


Lecture 3

Page 2

1.0 Granular Soils

Soils that formed through physical weathering of bedrock

Grains and particles are similar to the original bedrock

Composed of (gravel, sand and silt)

Soil grains are found as individual grains with spherical or cubical shape

Grain sizes are illustrated in table (1-1)

Table (1-1) grain size for each corresponding type

Grain type Grain size (diameter) gravel Over 4.75 mm Sand From 4.75 mm to 0.075 mm Silt From 0.075 mm to 0.005 mm

Sandy soils are considered Granular soils

1.1 Engineering properties of Granular soils They can carry significant loads

The weight of the load is transferred among grains by friction

Easy to compact to improve their load-carrying capacity

Excellent soils for construction

Shear strength is due to friction

𝜏 = 𝜎 ⨯ tanɸ

τ: the shear resistance (kPa)

σ: normal stress on plane of failure (kPa)

ɸ: angle of internal friction

Figure (1-1) shear strength due to friction



Lecture 3

Page 3

Figure (1-2) plot of normal stress with shear stress

Granular soils are very permeable to water flow

1.2 Minerals of Granular Soils

1-Quartz 2- Feldspar 3- Mica 4- Iron Oxides 5- Aluminum Oxides

2.0 Clayey Soils Formed by the chemical weathering of bedrock

Clay particles are mineral crystals that have very different properties from original bedrock

Soil grains are bonded to each other

Clay particles are flat, plate-shaped grains

Grain size is smaller than 0.005 mm

2.1 Engineering Properties of Clayey Soils

Clays are softer and do not carry loads as well as granular soils

Clays have charges on their surface that govern the behavior of soil

The surface charges attract water molecules, which are held tightly to the surface (figure 2-1)

Figure (2-1) soil moisture around clay particle typical dimensions

pm = 1⨯10-9 mm



Lecture 3

Page 4

Clay soils has absorption of water capacity and swelling potential

The surface charges of the soil particles force them to join in edge to side pattern

Figure (2-2) typical structure of (a) clay soil (b) granular soil

Shear strength is due to cohesion

τ= c

τ: Shear resistance (kPa)

c: Cohesion of soil (kPa)

Clay soils are impermeable to water flow

2.2 Clay Minerals

3.0 Expansive Soils Soils that expand when water is added and shrink when they dry out

3.1 Engineering Properties of Expansive Soils

Expansive soils contain minerals that are capable of absorbing water

When they absorb water they increase in volume

clay minerals

amorphous Allophane group

crystalline

Kaolinite

Halloysite

Illite

smectite

chlorite



Lecture 3

Page 5

Number of clay minerals are expansive including

o Smectite

o Bentonite

o Montmorillonite

When soil contain large amount of expansive minerals it has the potential of expansion

If water content of soils remain constant expansive soils will not cause a problem

When there are significant repeated changes in moisture content the expansive damage will

occur

3.2 Engineering Problems of Expansive Soils

The change in volume can exert enough force on a structure to cause damage

Cracked foundations, floors and basement walls are typical types of damage by swelling soils

The shrinkage of expansive soils can remove support from buildings and result in damaging

subsidence

3.3 Solutions for Expansive Soils

1- Design strategies: the engineer may require controlled pre-wetting of soil prior to the placement

of foundations

2- Structural slab: placing of (structural slab) with extra thickness and reinforcement to resist

movement and distress

3- Calcium treatment: treatment of soil with (lime) or calcium oxide to reduce expansion

4- Alternative soil stabilizers: application of organic and inorganic catalysts

5- Moisture control by subgrade irrigation: keeping constant moisture content for expansive

soils

4.0 Soil Slopes Slopes are the important topographical features and their stability is extremely important for

the following reasons :

1- The safety for excavated materials from site

2- Suitability of area for different uses

3- Fit the local landscape

Gravity is the main force responsible for slope failure

4.1 Factors for Slope Stability 1- Slope steepness

2- Precipitation and surface runoff

3- Composition of soil

4- Vegetation cover

5- Stratification in rocks

6- Geological structures

7- Ground shocks



Lecture 3

Page 6

Figure (4-1) factors affecting slope stability

4.2 Prevention of Soil Slope Failure

1- Controlling surface erosion

2- Controlling drainage

3- Avoiding construction and loading in slope areas

4- Reinforcement of soil foundation and slope using geosynthetic materials



Mass movement and Surface Water

Lecture 4

Page 1

Mass Movement and Surface Water

Lecture No. 4

Main Objectives Understanding mass movement, its causes and classification

Learning creep causes and its treatment

Definition of the hydrological cycle, ground water and stream classification












Lecture 4

Page 2

Mass Movement Types

1.0 Mass Movement The movement of earth surface material under the influence of gravity

Causes of Mass Movement

1- Areas with frequent wetting and drying cycles

2-Contineous freezing and thawing processes

3- Heavy precipitation

4- Seismic activities

5- Human modification of land

Classification of Mass Movement

1-Creep, 2-Landslide, 3-Flows, 4- Slump, 5-Falls

2.0 Creep The slow movement of soil in down slope direction

Figure (1) Soil Creep

Creep causes

1- Freezing and thawing

2- Wetting and drying

3- Gravity

Creep treatment

1- Introducing water to earth soil materials

2- Increase vegetation

3.0 Land Slides Definition: a natural disaster of geological origin that causes a wide range of ground

movement when the shear stress exceeds the shear strength of materials



Lecture 4

Page 3

Location: occur in mountainous regions, but sometimes it also occurs in low relief areas due

to roadway and building excavations

Figure (2) Landslide in Soil and Rock Mass along Plane of Weakness

Causes of landslide

1- Removal of underlying support by stream erosion, wave action, glacier or human activity

2- Escalation of loads on slopes due to rainfall

3- Natural or artificial shocks or vibrations caused by earthquakes

4- Reduction in material strength due to weathering and erosion

Surface Water and Ground Water

1.0 The Hydrological Cycle The hydrological cycle describes the continuous movement of water above, below and on the

earth surface

Figure (3) The Hydrological Cycle of Water



Lecture 4

Page 4

The water on earth surface (surface water) occurs as streams, lakes and wetlands as well as

bays and oceans, and it include snow and ice

The water below the surface of earth is primarily ground water, and also include soil water

2.0 Ground Water Flow The presence of, size of, and connections between pore spaces, fractures and other open spaces

in the soil and rock dictate where the ground water can travel

Hydraulic principles and the force of gravity dictate which direction the water travels in all

surface/ground water interactions

3.0 Stream Classification Ephemeral streams: flow in response to precipitation with no ground water support

Intermittent streams: consistently flow, but only part of the year

Perennial streams: permanent, they have year-round hydraulic support from ground water

Figure (4) stream types

4.0 Groundwater Zones Water beneath the land surface occurs in two principal zones, the unsaturated zone, and the

saturated zone.

In the unsaturated zone:

1- Voids between soil particles contain both air and water

2- The water cannot be pumped by wells

3- The upper part of the zone is the soil-water zone

4- Soil water is used by plants for life functions

In the saturated zone:

1- Voids are completely filled with water

2- Water is referred to as (ground water)

3- The upper part of this zone is referred to as (water table)

4- The water pressure is great enough to allow water to enter well



Lecture 4

Page 5

Figure (5) ground water zones



Geological Investigation

Lecture 5

Page 1


Lecture No. 5

Main Objectives Understanding the concepts of geological and geophysical investigations

Understanding dams structures and their types

Learning contour lines principles and how to draw them












Lecture 5

Page 2

1.0 Geological Investigation Definition : the process of investigating and recording all geological characters of the area

Importance :

1- Reduce construction costs

2- Maintain structures stability

Objectives :

1- Geological structure of the area

2- Lithology of the area

3- Ground water conditions

4- Seismicity of the region

2.0 Geophysical Investigation Definition: the systematic collection of geophysical data by sensing instruments

Importance:

1- Study the subsurface voids

2- Archaeology survey

3- Environmental assessment

4- Locating oil and gas resources

Figure (1) Data Collection for Seismic Survey in the Sea

3.0 Dams Definition: a hydraulic structure composed of very high strength impervious materials built

across a river to create a reservoir

Applications

1- Irrigation

2- Hydropower

3- Flood control

4- Water supply

5- Recreation

Types of dams

1- Gravity dam

2- Arch dam

3- Earth dam



Lecture 5

Page 3

4- Rock fill dam

Figure (2) Design of Dam with Different Forces Acting on it

4.0 Reservoirs

Definition: integral component of the dam structure, in which water is stored

Functions :

1- Flood control

2- Water storage

Types:

1- Natural

2- Man-made

Requirements for the geological site of the reservoir

1- The rocks should be hard and impervious

2- Narrow opening of the basin

3- The site should be easily accessible

4- Capable to hold large amounts of water

Figure (3) Reservoirs Location



Lecture 5

Page 4

5.0 Tunnels Definition: structures that provide artificial underground passage or roadway without

removing overlying and underlying rocks or beds

Classification:

1- Tunnels through consolidated soil

2- Tunnels through hard rock

3- Tunnels through unconsolidated soil

4- Tunnels through water body

Importance of geological profile in tunneling:

1- Depth of lateral extension of rock types

2- Presence of geological structures

3- Status of weathering and erosion

4- Water table condition

Figure (4) Example of a Geological Profile of Tunnel

6.0 Contour Lines Definition: lines drawn on a map connecting points of equal elevation

Purpose: they show the shape of the land surface (topography) on a map

Figure (5) Contour Lines Concept



Lecture 5

Page 5

Drawing of contour map

1- Identify the elevations of several points on the map

2- Choose an appropriate contour interval by examining the elevation points

3- Connect the equal elevations with contour lines



Lecture 5

Page 6

Rules for contour lines drawing:

1- Every point on a contour line should have the exact same elevation

2- Contour lines should be closed, or extend beyond the map area

3- Contour lines never cross one another

4- Contour lines never split

Uses of contour maps in civil engineering:

1- Estimating the earth works for road works, railways, canals, oceans etc.

2- Estimating the storage capacity of reservoirs

3- Facilitating site selection

weathering and erosion - tcm.edu.iq -geology1.pdf · weathering and erosion lecture 1 ......

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