Standard Penetration Test

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Standard Penetration Test

Standard Penetration Test (S.P.T) (IS 2131)

  • It is used to determine the Relative density of undisturbed sand and silt, consistency of clay.
  • Split spoon samples are used for this test.
  • The pattern is first pushed through mild blows of the hammer to a seating penetration of 15cm than the pattern is pushed below complete blows of 65kg with unfastened fall of 75cm hammer to extra penetration of 30cm.
  • The range of blows required for 30cm penetration is referred to as SPT N price referred to as “Standard Penetration Resistance”. But „N‟ can‟t be extra than 50.
  • The average value of N is calculated from the depth of footing to 2times of the width of footing.
  • For the average value of N, any value greater than 50% of the average value is discarded
  • The N price if underestimated at shallow intensity and puffed up at big intensity.

Dilatancy Correction or Submerge Correction ⟹ Only applicable to very fine sand or silty sand, below the water level when, the reason is, as the soil is fine during driving the resistance due to excess pore pressure increases, as excess pore pressure is unable to dissipate immediately. (-ve pore pressure in saturated fine sand) this correction is always applied after the overburden correction.

Standard Penetration Test

Standard Penetration Test

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