GATE, PSUs- Soil Engineering ( notes)- Part 5

Hello there,
Welcome to the part 5 of the one liner notes useful for the preparation of GATE and other similar examinations.

• The slope of isochrone at any point at a given time indicates the rate of change of pore water pressure with depth.
• Within the consolidation process of  a saturated clay a gradual decrease in neutral pressure and a gradual increase in effective pressure takes place and sum of the two is constant.
• The value of compression index for a remoulded sample whose liquid limit is 50% is 0.28.
• Over-consolidated clay with a high over-consolidation ratio behaves like a dense sand.
• Degree of consolidation is directly proportional to time and inversely proportional to square of drainage path.
• Time factor for a clay layer is directly proportional to permeability of soil.
• If the time required for 50% consolidation of a remoulded sample of clay with single drainage is t, then the time required to consolidate the same sample of clay with double drainage is t/4.
• Co-efficient of consolidation for clay normally decrease with increase in liquid limit.
• Only in fixed ring type consolidometer, direct measurement of permeability of the specimen at any stage of loading can be made.
• Compressibility of sandy soils is much less than that of clayey soil.
• Co-efficient of compressibility of an over-consolidated clay is less than that of a normally consolidated clay.
• Co-efficient of compressibility is different for different types of soils and also different for a soil under different states of consolidation.
• The ultimate consolidation settlement of a structure resting on a soil decreases with increase in the initial voids ratio.
• The ultimate consolidation settlement of a soil is directly proportional to the compression index.
• Coarse grained soils are best compacted by a vibratory roller.
• With the increase in the amount of compaction energy optimum water content decreases but maximum dry density increases.
• The maximum dry density upto which any soil can be compacted depends upon both moisture content and amount of compaction energy.
• For better strength and stability, the fine grained soils and coarse grained soils are compacted respectively as wet of OMC and dry of OMC.
• Effective angle of internal friction for coarse grained soils is rarely below 30 degrees.
• effective cohesion of soil can have a negative value.
• Effective angle of internal friction for a soil increases as state of compactness increases.
• Effective angle of internal friction is a complicated function of mineralogy and clay size content.
• For a loose sand sample and a dense sand sample consolidated to the same effective stress ultimate strength is same but peak strength of dense sand is greater than that of loose sand.
• The shear strength of a soil increases with normal stress.

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