GATE, PSUs preparation- Soil Engineering ( notes)- Part 8

Hello there,
Welcome to the part 8 of the one liner notes useful for the preparation of GATE and other similar examinations.

• According to Terzaghi's theory, the ultimate bearing capacity at ground surface for a purely cohesive soil and for a smooth base of a strip footing is 5.14.C where, C = unit cohesion of soil.
• The net ultimate bearing capacity of a purely cohesive soil is independent of both depth and width of footing.
• The rise of water table below the foundation influences the bearing capacity of soil mainly by reducing cohesion and effective unit weight of soil.
• Terzaghi's general bearing capacity formula for a strip footing gives us the ultimate bearing capacity of soil. Formula uses three bearing capacity factor.
• Terzaghi's bearing capacity factors are the functions of angle of internal friction only.
• In the plate load test for determining the bearing capacity of soil, the size of square bearing plate should be between 300 mm and 750 mm.
• Bearing capacity of soil depends upon type of soil, shape and size of footing and is independent of rate of loading.
• Rise of water table up to ground surface reduces the net ultimate bearing capacity of soil  approximately by 50%.
• Contact pressure beneath a rigid footing resting on cohesive soil is more at edges compared to middle.
• According to IS specifications, the minimum depths of foundation in sand and clay should be respectively 800 mm and 900 mm.
• The maximum differential settlement in isolated footings on clayey soils should be limited to 40 mm.
• A combined footing is generally used when number of columns is two and they are spaced close to each other.
• Negative skin friction on a pile acts downwards and reduces the load carrying capacity of the pile.
• Generally the bearing capacity of a pile group is equal to the sum of bearing capacities of individual piles in case of end bearing piles.
•  The settlement of a group of friction piles as compared to that of a single pile is more.
• Negative skin friction is caused by relative settlement of soil and skin frictional resistance is caused by relative settlement of pile.
• Static formulas are suitable for friction piles driven through cohesive soils.
• Dynamic formulas are suitable for friction piles driven through cohesion-less soils.
• Dynamic formulas do not take into account the reduced bearing capacity of a pile in a group.
• Mechanical stabilization of soil is done with the help of proper grading.
• Lime stabilization is very effective in treating plastic clayey soils.
• Undisturbed samples are obtained by thin-walled samplers.
• Stationary piston sampler and rotary sampler are both thin-walled sampler.
• Greater skin friction retards the sinking of the well.
• If the bearing capacity of a footing on a saturated clay is 120 kN/m2 , the bearing capacity of a circular footing(diameter=width) will be more than 120 kN/m2.
• A plate load test is useful to estimate both bearing capacity and settlement of foundation.

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