Building Construction
During percussion drilling

Ground water observations are hindered due to entry of the slurry in the soil below the bottom of the hole
Caving or mixing of strata are caused in soft soils or cohesion-less soils
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

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

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