The document discusses thixotropy, sensitivity, and activity in soils. Thixotropy refers to the regain of shear strength in soils over time after being remolded such as during pile driving. Sensitivity indicates the loss of strength from remolding and is measured as the ratio of undisturbed to remolded strength. Activity is measured as the ratio of plasticity index to clay fraction and indicates the water holding capacity of clayey soils.

2.  The word Thixotropy is derived from the two words:thixis
meaning touch,and tropo,meaning to
change.Therefore,thixotropy means any change that occurs
by touch.
 The loss of strength of a soil due to remoulding is partly
due to change in the soil structure and partly due to
disturbance caused to water molecules in the absorb
layer.Some are reversible.If a remoulded soil is allowed to
stand,without loss of water,it may regin some of its lost
strength.In soil engineering,this gain in strength of the soil
with passage of time after it has been remolded is called
thixotropy.

3.  Thixotropy of soils is of great practical importance
in soil engineering.For example,when a pile is
driven in to ground,the loss of strength occurs due
to disturbance caused.Thixotropy indicates how
much shear strength will be regained after the pile
has been driven and left in place for some time.

5.  A cohesive soil in its natural state of occurance
has a certain structure.When the structure is
disturbed,the soil becomes remoulded,and its
engineering properties change
considerly.Sensitivityof a soil indicates its
weakening due to remoulding. It is defined as the
ratio of undisturbed strength to the remoulded
strength at the water content

6. S.no. Sensitvity Soil Type
1. <1.00 Insentive
2. 1.0-2.0 Sensitive
3. 2.0-4.00 Little sensitive
4. 4.0-8.00 Moderately sensitive
5. 8.0-16.0 Extra sensitive
6. >16.0 Quick

7.  For most clays,sensitivity lies between 2and
4.Clays considred sensitive have values between
4 and 8. In case of sensitive clays,remoulding
causes a large reduction in strength.Quick clays
are unsutible. These turn into slurry when
remoulded.
 High sensitivity in clays is due to a well-devloped
flocculent srtucture which is disturbed when the
soil is remoulded.

9.  Activity of soil is the ratio of plasticity index and
the percentage of clay fraction(minus 2µ
size).Thus
 A=Ip/F
 Where Ip=plasticity index,F=clay fraction.
 The clay fraction F is percentage finer than 2µ
size

10.  The amount of water in a soil mass depandes
upon the type of clay mineral present. Activity is a
measure of the water holding capacity of clayey
soils.The changes in the volume of a clayey soil
during swelling or shrinkage depend upon the
acyivity.

11.  A number of samples of a particular soil are taken and
their plasticity index and clay fraction determineded. If
a plot is obtained between the clay fraction and
plasticity index,it is observed that all the points for a
particular soil lie on a straight line
 The slope of the line gives the activity of soil. The
steeper the slop,the greater the activity. The lines with
different slopes are obtained for different soils.

12. 140
120
100
80
kaolinite
60 Illite
Montomorillonite
40
20
0
0 10 20 30 40

13. Sr.no Activity Soil type
1. A<0.75 Inactive
2. A=0.75 to 1.25 Normal
3. A>1.25 Active