Explain British soil classification system.

The British soil classification system was introduced in British Standard code of practice for site investigation. The qualifying terms are similar to the USCS with more sub-group symbols for both course and fine soils. Poorly graded gravel and sand have been divided into two groups symbol  by adding `P_u` and `P_g` to represent uniform and gap graded soil respectively. In course soils sub-groups have been defined by adding a third letter (M or C) to well graded or poorly graded gravel and sand. Following terms have been used in the classification system:

The British soil classification system was introduced in British Standard code of practice for site investigation. The qualifying terms are similar to the USCS with more sub-group symbols for both course and fine soils. Poorly graded gravel and sand have been divided into two groups symbol  by adding `P_u` and `P_g` to represent uniform and gap graded soil respectively. In course soils sub-groups have been defined by adding a third letter (M or C) to well graded or poorly graded gravel and sand. Following terms have been used in the classification system:

The letter denoting the dominant size fraction is placed first in the group symbol. If a soil has a significant content of organic matter, the suffix O is added as the last letter of the group symbol. A group symbol may consist of two or more letters. For example: