thixotropy

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.

DEFENATIONS

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.

sensitivity

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

introduction

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

Classifacation of soil based on sensitivity

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.

Activity of soil

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

definition

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.

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.

0 10 20 30 400

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kaoliniteIlliteMontomorillonite

Sr.no Activity Soil type

1. A<0.75 Inactive

2. A=0.75 to 1.25 Normal

3. A>1.25 Active

Depending upon activity,the soils are classified into three types.

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