Explain the basic differences between AASHTO and USCS soil classification systems.

1. According to the AASHTO  system, a soil is termed fine-grained if  if more than 35% passes through number 200 sieve i.e 0.075mm whereas in the USCS system,a soil is termed fine-grained if more than 50%  passes through number 200 sieve. Thus in that sense, the AASHTO system is somewhat better because the soil behaves as fine grained when the percentage of fine is 35% in the limit of 50% in USCS is somewhat higher.
2. In AASHTO system, sieve NO.10(2 mm size) is used to divide the soil into gravel and sand where is in USCS sieve NO. 4(4.75 mm)  is used.
3. In USCS system, the gravelly and Sandy soils are clearly separated where is in AASHTO system, clear demarcation is not done.
4. Symbols used in USCS system are more descriptive and are more easily remember than those in AASHTO system.
5. Organic soils are classified as OL and OH as peat (`P_t`) if highly organic,in USCS system. In AASHTO system, there is no place for Organic soils.
6. USCS system....

1. According to the AASHTO  system, a soil is termed fine-grained if  if more than 35% passes through number 200 sieve i.e 0.075mm whereas in the USCS system,a soil is termed fine-grained if more than 50%  passes through number 200 sieve. Thus in that sense, the AASHTO system is somewhat better because the soil behaves as fine grained when the percentage of fine is 35% in the limit of 50% in USCS is somewhat higher.
2. In AASHTO system, sieve NO.10(2 mm size) is used to divide the soil into gravel and sand where is in USCS sieve NO. 4(4.75 mm)  is used.
3. In USCS system, the gravelly and Sandy soils are clearly separated where is in AASHTO system, clear demarcation is not done.
4. Symbols used in USCS system are more descriptive and are more easily remember than those in AASHTO system.
5. Organic soils are classified as OL and OH as peat (`P_t`) if highly organic,in USCS system. In AASHTO system, there is no place for Organic soils.
6. USCS system is more convenient to use than a AASHTO system. In AASHTO system, the process of elimination is required which is time consuming.
7. AASHTO is for finding out the suitability of soils for highway works only whereas USCS is for finding out the suitability for general purposes.