As per IS: 1892 – 1979; what should be the maximum thickness of cutting edge of sampling tube of 70 mm external diameter which is required for sampling in undisturbed stiff clay soil?

Question

Question

This question was previously asked in

UPPSC AE Civil 2019 Official Paper I (Held on 13 Dec 2020)

Answer 1

Concept:

Area ratio:

It can be defined as the ratio of the maximum cross-sectional area of the cutting edge to the area of the soil sample.

The area ratio can be expressed as

\({A_r} = \frac{{D_2^2 - D_1^2}}{{D_1^2}}\)

where

D₁ = inner diameter of cutting edge

D₂ = outer diameter of cutting edge

Note:

For stiff formation (A_r)_max = 20%

Soft sensitive clay (Ar)max = 10%

Maximum thickness of cutting edge = \(\frac{D_2 \ - \ D_1}{2}\)

Calculation:

Given, D₂ = 70 mm

Soil is stiff clay, So (Ar)max = 20%

\({A_r} = \frac{{D_2^2 - D_1^2}}{{D_1^2}}\)

\({0.2} = \frac{{70^2 - D_1^2}}{{D_1^2}}\)

D₁ = 63.9 mm

Maximum thickness of cutting edge = \(\frac{D_2 \ - \ D_1}{2}\)

= \(\frac{70 \ - \ 63.9}{2}\) = 3.05 mm