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1 Lecture#6 CE-312 Engineering Geology and Seismology Instructor: Dr Amjad Naseer Department of Civil Engineering N-W.F.P University of Engineering and Technology, Peshawar 2 Outlines of the Presentation • Erosion and agents of erosion • Rocks as construction materials 3 Erosion and Agents of Erosion Agents of erosion: • Stream, • Wind and • Glaciers • Sea Transportation, and Deposition 4 Erosion and Agents of Erosion 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. 5 Erosion and Agents of Erosion Stream/River Erosion: Chemical Action, Hydraulic Action, Abrasion, Attrition. Features of Stream/River: Pot Holes, Waterfalls, Gorges, Mangers, Oxbow lacks 6 Work of wind 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. 7 Work of Glaciers 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 8 Work of Glaciers 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. 9 Rock as construction materials 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 10 Rock as construction materials 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. 11