Soil classification - Geotechnical Investigation and Design Tables - page 24

Table 2.12 Atterberg limits.

Symbol Description Comments

LL Liquid limit - minimum moisture content at which a soil will Cone penetrometer test

flow under its own weight. or casagrande apparatus.

PL Plastic limit - Minimum moisture content at which a 3 mm Test

thread of soil can be rolled with the hand without
breaking up.

SL Shrinkage limit - Maximum moisture content at which a Test.

further decrease of moisture content does not cause a
decrease in volume of the soils.

PI Plasticity Index

=

LL-PL Derived from other tests.

LS Linear shrinkage is the minimum moisture content for Test. Used where difficult

soil to be mouldable. to establish PL and LL.

PI 2.13 LS. =

2.13 Structure
•

This descriptor can significantly affect the design.

•

For example, the design strength, a fissured clay is likely to have only 2/3 of the
design strength of a non fissured clay; the design slope is considerably different
from fissured and non fissured; the permeability is different.

Table 2.13 Structure.

Term applies to soil type

Field identification

Coarse grained Fine grained Organic

← -------------- Heterogenous ---------------- → A mixture of types.

← ------- Homogenous ------ → Deposit consists of essentially of one type.

Alternating layers of varying types or with
bands or lenses of other materials.

← ---- Interstratified, interbedded,

X

interlaminated --- →

X Intact X No fissures.

X Fissured X Breaks into polyhedral fragments.

Polished and striated defects caused by motion
of adjacent material.

X Slickensided X

Plant remains recognisable and retainssome
strength.

X X Fibrous

X X Amorphous No recognisable plant remains.

Totally decomposed rock with no identifiable
parent rock structure.

Saprolytic/Residual Soils X