Skip to main content
Feb 26, 2016 /Haseeb Jamal-

5 Travel Myths You Need to Stop Believing Right Now

Feb 26, 2016 /Haseeb Jamal-

Canal Comes Alive with Lighted Boat Parade.

AASHTO Soil Classification System - AASHTO Chart

Profile picture for user Haseeb Jamal
By:Haseeb Jamal/On:Oct 01, 2019/Notes,Types of
AASHTO Soil Classification Chart

BesidesSoil Classificationon other criteria, the AASHTO Soil Classification System classifies soils into seven primary groups, named A-1 through A-7, based on their relative expected quality forroad embankments,sub-grades,sub-bases, andbases. Some of the groups are in turn divided into subgroups, such asA-1-aandA-1-b. Furthermore, aGroup Indexmay be calculated to quantify a soil’s expected performance within a group. To determine a soil’s classification in the AASHTO system, one first determines the relative proportions of gravel, coarse sand, fine sand, and silt-clay.

AASHTO Soil Classification System Chart

General Classification Granular Materials (35% or less passing the 0.075 mm sieve) Silt-Clay Materials (>35% passing the 0.075 mm sieve)
Group Classification A-1 A-3 A-2 A-4 A-5 A-6 A-7
A-1-a A-1-b A-2-4 A-2-5 A-2-6 A-2-7 A-7-5 A-7-6
Sieve Analysis, % passing
2.00 mm (No. 10) 50 max
0.425 (No. 40) 30 max 50 max 51 min
0.075 (No. 200) 15 max 25 max 10 max 35 max 35 max 35 max 35 max 36 min 36 min 36 min 36 min
Characteristics of fraction passing 0.425 mm (No. 40)
Liquid Limit 40 max 41 min 40 max 41 min 40 max 41 min 40 max 41 min
Plasticity Index 6 max N.P. 10 max 10 max 11 min 11 min 10 max 10 max 11 min 11 min
Usual types of significant constituent materials stone fragments, gravel and sand fine sand silty or clayey gravel and sand silty soils clayey soils
General rating as a subgrade excellent to good fair to poor

Note:Plasticity index of A-7-5 subgroup is equal to or less than the LL - 30. Plasticity index of A-7-6 subgroup is greater than LL - 30

AASHTO Liquid Limit Vs Plasticity Index
AASHTO Liquid Limit Vs Plasticity Index

In the AASHTO Soil Classification System:

  • gravel is materialsmaller than 75 mm (3 in.) but retained on a No. 10 sieve;
  • coarse sand is materialpassing a No 10 sieve but retained on a No. 40 sieve; and fine sand is material passing a No. 40 sieve but retained on a No. 200 sieve.
  • Material passing the No. 200 sieve issilt-clayand is classified based onAtterberg limits.
  • It should be noted that the division betweengravel and sandis made at a smaller size (No. 10 sieve) in the AASHTO Soil Classification System than in theunified system(No. 4 sieve).

Secondly, if any fines are present, Atterberg limits are determined and the plasticity index is calculated. A soil is a granular material if less than 35% of the soil by weight passes the No. 200 sieve (#200). Granular materials are classified into groupsA-1throughA-3. Soils having more than 35% passing the No. 200 sieve are silt-clay and fall in groupsA-4throughA-7. Having the proportions of the components and the plasticity data, one enters one of the two alternativesAASHTOclassification tables and checks from left to right until a classification is found for which the soil meets the criteria. It should be noted that, in this scheme, groupA-3is checked beforeA-2. Soils classified asA-1are typically well-graded mixtures of gravel, coarse sand, and fine sand. Soils in subgroupA-1-acontain more gravel whereas those inA-1-b contain more sand.

Soils in groupA-3are typically fine sands that may contain small amounts of non-plastic silt. GroupA-2contains a wide variety of “borderline” granular materials that do not meet the criteria for groupsA-1orA-3. Soils in groupA-4are silty soils, whereas those in groupA-5are high-plasticity elastic silt. Soils in groupA-6通常精益粘土,这些吗in groupA-7are typically highly plastic clays. Within groups containing fines, one may calculate a group index to further evaluate relative quality and supporting value of a material as sub-grade. The group index is calculated according to the following empirical formula:

Group index F 35 – ( )0.2 0.005 LL 40 – ( ) + [ ] + 0.01 F 15 – ( )PI 10 – ( )

AASHTO Classification of Soil Video Tutorial

Search AboutCivil

Related Civil-Engg. Content