AASHTO HIGHLIGHTS

 AASHTO(American Association of State highway Transport officials)

Seven groups of inorganic soils(A1-A7)

12 Subgroups

Three(3)soil properties (PSD, LL, PI)

      >>PSD(PARTICLE SIZE DISTRIBUTION)

      >>LL(LIQUID LIMIT)

       >>PI(PLASTICITY INDEX)

1 GROUP INDEX(GI)

GI = 0.2a + 0.005ac + 0.01bd

Code: 132 251 A/Ac/Bd

132 implies that the first term of the equation has 1 zero,the second has 3 zeros, and then the last has 2.

251 implies that the first term of the equation has 2(0.2), the second has 5 (0.005) then the last 1(0.01)

NOTE: a,b,c, and d must be expressed as POSITIVE whole number.

a = 35 < x < 75 No.200 sieve [N-35]{0-40}

b = 15 < x < 55 No.200 sieve [N-15]{0-40}

c = 40 < x < 60 Liquid limit [LL-40]{0-20}

d = 10 <x < 30 Plasticity index[PI-10]{0-20}

All you need do is to memorize the lower limit as highlighted above( 35 15 40 10) and the range for;then You need to note that a and b is defined in terms of amount of proportion of particles(N), c is defined on the Liquid limit (LL) and d on the Plasticity index(PI)

a and b ranges from 0 to 40

c and d ranges from 0 to 20

The group index is a means of rating the value of a soil as a subgrade material within it's own Group

NOTE: The higher the group index(GI), the poorer the quality of the material (INVERSE VARIATION).

If the pertinent index value for a soil falls below the minimum limit associated with a,b,c and d, the value of the corresponding term is zero. Take for instance you have N= 30 for an expression of a and the lower limit for a is 35; Then a tends to Zero

When the index are more than the highest value, then we use the maximum. Take for jnstains we know the maximum value for d expression as 30 and ranges from 0 to 20; if we now have 35 (35-10= 25) and 25 is more than the maximum value. All we need do is to make use of the maximum value as 20.

A-6(12)

The group index(GI) here is 12............