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CE-312

Engineering Geology and Seismology

Instructor:

Dr Amjad Naseer

Lecture#6

Department of Civil Engineering

N-W.F.P University of Engineering and Technology, Peshawar

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• Erosion and agents of erosion

• Rocks as construction materials

Outlines of the PresentationOutlines of the Presentation

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Agents of erosion:

• Stream,

• Wind and

• Glaciers

• Sea

Transportation, and

Deposition

Erosion and Agents of ErosionErosion and Agents of Erosion

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Stream Erosion: By stream erosion is meant the mechanical or chemical removal of

material encountered by the stream. To a limited extent, stream dissolve rocks,

especially those of the carbonate group. This chemical work locally is evident is by

solution pits along the stream course. Three ways are suggested by which streams may

pick up particles: Impact, friction drag and hydraulic uplift.

In carry out this function, streams erode valleys for themselves, pick up and transport

rock debris, take some material into solution, and build deposits of sedimentary

materials. Erosion, transportation, and deposition, therefore, are the major divisions of

the stream work.

Erosion and Agents of ErosionErosion and Agents of Erosion

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Stream/River Erosion:

Chemical Action,

Hydraulic Action,

Abrasion,

Attrition.

Features of Stream/River:

Pot Holes,

Waterfalls,

Gorges,

Mangers,

Oxbow lacks

Erosion and Agents of ErosionErosion and Agents of Erosion

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Wind Erosion: Wind erode a rock in three different ways.

Deflation: It is the process by which wind lifts and removes the loose particles form an

area and cause lowering of the land surface.

Abrasion: The dust or soil/sand particles in wind strike rocks thereby abrading the rock

surface. This process of erosion is called abrasion.

Attrition: The particles that travel with wind, collide against one another. These mutual

collision leads to their further break down and the process is called attrition.

Work of windWork of wind

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Glacier Erosion: Glacier ice erodes in two ways. It is able to tear out of place, or pluck,

partially loosened materials. The more highly jointed the rock over which the glacier

moves, then, the more vigorous is the plucking action of the ice. Material incorporated in

basal layers of the ice abrades or scours the bedrock over which it passes, much as

sandpaper abrade a wooden surface.

During glacial advace, not only is bedrock eroded, but the fragments in transport

themselves are also abraded and ground to smaller sizes. The resistant and tough rock

types, for example granite, whereas, pieces of less resistant rock types, such as shale or

slate, may lose identity and be ground to rock flour within comparatively short distances.

Plucking,

Abrasion,

Frost Wedging

Work of GlaciersWork of Glaciers

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Features of Glacial Erosion:

U-shaped valleys,

V-shaped vallesy,

Cirques: the armed chair like hollows, present at the glacier valleys heads in the

mountain are called cirques.

Work of GlaciersWork of Glaciers

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Rock can be used in construction as:

• Building Stone: that is for the construction of buildings as masonry unit,

• Rubbles: as small irregular fragments,

• Crushed stones-coarse aggregate for cement concrete or asphalt concrete

• Limestone: for the manufacturing of cement and lime

• Marble: for flooring work and decoration

Rock as construction materialsRock as construction materials

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Rocks can be used as coarse aggregate

Test on coarse aggregate:

Gradation,

Specific gravity

Impact test,

Abrasion test,

Stone dust: Used as fine aggregate in mortar and as filler in asphalt. The stone dust can

work as pozzolanic materials.

Rock as construction materialsRock as construction materials