Please answer all questions. 1- Why do dune sands tend to have a uniform grain s
ID: 1885323 • Letter: P
Question
Please answer all questions.
1- Why do dune sands tend to have a uniform grain size? Why are they typically free of clay?
2- Would you rather find structures on clay soil containing illite or clay soil containing montmorillonite? Justify your answer.
3- Why doesn’t the Unified Soil Classification System include a size range for clay?
4- Sands and gravels are non-plastic. What does this mean, and why is this so?
5- What is an alluvial fan? How are they formed, where are they found, and what are the typical geotechnical characteristics?
Explanation / Answer
ANS 1. THE SIZE RANGE OF SAND GRAINS THAT MAKE UP DUNES IS UNIFORM BECAUSE GRAINS THAT ARE SMALLER THAN SAND SIZE ARE CARRIED FURTHER BY THE ACTION OF WIND AND WATER.GRAINS THAT ARE LARGER THAN SAND SIZE ARE LEFT BEHIND.THEY ARE TYPICALLY FREE OF CLAY BECAUSE CLAY PARTICLES ARE NOT USUALLY PICKED UP BY THE WIND BECAUSE OF THEIR MUTUAL COHERENCE OR IF THEY ARE PICKED UP THEY TEND TO BE LIFTED HIGH INTO THE AIR.
ANS 2.CLAY SOIL CONTAINING MONTMORILLONITE IS USED FOR CONSTRUCTION AS MONTMORILLONITES EXPAND CONSIDERABLY MORE THAN OTHER CLAYS DUE TO WATER PENETRATING THE INTERLAYER MOLECULAR SPACES.THE PRESENCE OF SODIUM AS THE PREDOMINANT EXCHANGEABLE CATION RESULT IN THE CLAY SWELLING TO SEVERAL TIMES ITS ORIGINAL VOLUME.
ANS 3.UNIFIED SOIL CLASSIFICATION SYSTEM IS ONLY USED TO DESCRIBE TEXTURE AND GRAIN SIZE OF SOIL AND IT IS REPRESENTED BY TWO LETTER SYMBOL.FINE GRAINED SOIL ARE CLASSIFIED BASED ON PLASTICITY.
ANS 4.SAND AND GRAVEL ARE NON-PLASTIC IT MEANS ADDING WATER TO SAND AND GRAVEL DOES NOT CAUSE SAND AND GRAVEL TO SPONTANEOUSLY SOFTEN OR TURN TO MUD AND FLOW AWAY.IT HAPPENS BECAUSE IDEAL GRANULAR NON-PLASTIC SOILS SUCH AS GRAVEL AND SAND CAN NOT BE ROLLED OUT INTO A SOIL WORMOR THREAD OF 3MM DIAMETER WITHOUT BREAKING UP.
ANS 5.AN ALLUVIAL FAN IS A FAN OR CONE SHAPED DEPOSIT OF SEDIMENT CROSSED AND BUILT UP BY STREAMS.THEY ARE FORMED AS STREAM GRADIENT DECREASES,IT DROPS COARSE-GRAINED MATERIAL.IT MAKES SWAGGER OF THE CHANNEL AND FORCES IT TO CHANGE DIRECTION AND GRADUALLY BUILD UP A SLIGHTLY MOUNDED OR SHALLOW CONICAL FAN SHAPE.THEY ARE FOUND WHERE A CANYON DRAINING FROM MOUNTAINOUS TERRAIN EMERGES OUT ONTO A FLATTER PLAIN AND ESPECIALLY ALONG FAULT-BOUNDED MOUNTAIN FRONTS.GEOTECHNICAL CHARACTERISTICS OF ALLUVIAL FAN ARE-1) FLOODING ON ALLUVIAL FANS CAN BE DAMAGING AS THE FANS HAVE STEEPER GRADIENTS THAN RIVER FLOODPLAINS. 2) CLIMATE 3) FAN HISTORY 4) STYLES OF TECTONISM 5) SOURCE AREA LITHOLOGY 6) VEGETATION 7) LAND USE