Group index method of design of flexible pavement is A. A theoretical method B. An empirical method based on physical properties of sub-grade soil C. An empirical method based on strength characteristics of sub-grade soil D. A semi empirical method

The correct answer is: B. An empirical method based on physical properties of sub-grade soil

The group index method is an empirical method for the design of flexible pavements. It is based on the physical properties of the subgrade soil, such as the plasticity index, liquid limit, and the percentage of fines. The method uses a group index chart to determine the required thickness of the pavement.

The group index method is a simple and easy-to-use method for the design of flexible pavements. It is widely used in the United States and other countries. However, the method has some limitations. For example, it does not take into account the traffic loading on the pavement.

The other options are incorrect because:

• Option A is incorrect because the group index method is not a theoretical method. It is an empirical method.
• Option C is incorrect because the group index method is not based on the strength characteristics of sub-grade soil. It is based on the physical properties of sub-grade soil.
• Option D is incorrect because the group index method is not a semi-empirical method. It is an empirical method.