The correct answer is C. 5.
The group index (GI) is a numerical system used to classify soils based on their plasticity characteristics. It is determined using the following equation:
GI = 0.007 * LL + 0.01 * PI + 0.007 * (F â 35)
where:
- LL = liquid limit
- PI = plasticity index
- F = percentage passing 75 micron IS sieve
In this case, LL = 40%, PI = 10%, and F = 35%. Substituting these values into the equation, we get:
GI = 0.007 * 40 + 0.01 * 10 + 0.007 * (35 â 35) = 5
Therefore, the group index for this soil is 5.
The group index is used to determine the suitability of a soil for various engineering purposes. Soils with a GI of 0 to 4 are considered to be low plasticity soils and are generally suitable for most engineering purposes. Soils with a GI of 5 to 12 are considered to be medium plasticity soils and may be suitable for some engineering purposes, but may require special treatment. Soils with a GI of 13 to 20 are considered to be high plasticity soils and are generally not suitable for most engineering purposes.