SPT correction factors are often used to correct or normaliz

SPT correction factors are often used to correct or normalize standard penetration test N-values. Please comment on why Ca is greater than one for borehole diameters greater than 4.5 inches. Comment on why Cs is greater than one when a standard sampler is used without liners (when the sampler was machined to accommodate liners in the first place). Comment on why Co is less than one for the Modified California split-spoon sampler. Please type your response. (10 points)

Solution

The borehole diameter affects the N mean value if the borehole diameter is greater than 4.5 inches. Larger diameter boreholes allow for stress relaxation of the soil materials. This stress relaxation can be significant in Sands. But have a negligible effect in cohesive soils. Therefore,for cohesive soils use Cb value equal to greater than one.

B)The sampler configuration correction factor (Cs) is used to account for samplers designed to be used with liners, but the liners are omitted during sampling. If the sampler is not designed for liners or if the correct size liner is used no correction is required (i. e. Cs=1).when liners are omitted there is an increase to the inside diameter of the sampler. Therefore, the friction between the soil and sampler is reduced. So take Cs>1.