If the group index value of subgrade is between 5 and 9, then the subgrade is treated as A. good B. fair C. poor D. very poor

The correct answer is: B. fair

The group index value of subgrade is a measure of the subgrade’s ability to support a load. A group index value of 5 to 9 indicates that the subgrade is fair. This means that the subgrade is capable of supporting a moderate load, but it may require some additional treatment, such as compaction or drainage, to improve its performance.

The other options are incorrect because they do not accurately reflect the subgrade’s ability to support a load. A group index value of less than 5 indicates that the subgrade is poor and will require significant treatment to be suitable for construction. A group index value of greater than 9 indicates that the subgrade is good and does not require any additional treatment.