Testing Methods Flashcards

In the Modified Proctor test (ASTM D1557), what hammer weight and drop height are used?

Answer: 10 lb hammer, 18 in drop

Modified Proctor uses a 10 lb hammer dropped 18 in, delivering much more compactive energy than Standard Proctor (5.5 lb, 12 in).

In the sand cone test (ASTM D1556), how is the volume of the excavated hole determined?

Answer: By dividing the mass of sand that fills the hole by the calibrated bulk density of the sand

Uniformly graded sand of known calibrated bulk density fills the hole, so volume equals sand mass divided by that density.

Which nuclear density gauge mode is most appropriate for testing a thin asphalt overlay?

Answer: Backscatter

Backscatter mode keeps the source on the surface, making it suitable for thin layers like asphalt where a rod cannot be inserted.

Using the Casagrande cup method, the liquid limit is the water content at which the soil groove closes about 0.5 in after how many blows?

Answer: 25

The liquid limit is defined as the water content at which the groove closes 13 mm (0.5 in) at 25 blows, usually interpolated from a flow curve.

A soil has a liquid limit of 48 and a plastic limit of 22. What is its plasticity index?

Answer: 26

Plasticity index equals liquid limit minus plastic limit: 48 - 22 = 26.

Hydrometer analysis is used to determine the grain size distribution of which soil fraction?

Answer: Particles passing the No. 200 sieve (silts and clays)

Hydrometer analysis uses Stokes' law sedimentation to size fines smaller than 0.075 mm that cannot be sieved practically.

How is the SPT N-value obtained?

Answer: Sum of blows for the second and third 6 in increments

The first 6 in is a seating drive, and N is the sum of blows for the final two 6 in increments using a 140 lb hammer dropped 30 in.