Building Construction
During percussion drilling

Caving or mixing of strata are caused in soft soils or cohesion-less soils
Ground water observations are hindered due to entry of the slurry in the soil below the bottom of the hole
The soil to a considerable depth below the bottom of the hole gets disturbed
All listed here

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Building Construction
Negative skin friction

Neither (A) not (B)
Develops due to lowering of ground water
Both (A) and (B)
Is a downward drag acting on a pile due to downward movement of the surrounding compressible soil relative to the pile

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