Question

Why is precise stability analysis of slopes difficult to predict?

What is the difference between the Stability Number method and the Method of Slices?

Answer 1

1-A slope is an unsupported soil mass which can be natural or manmade. This can be above ground level or below ground level as cuttings.Instability may result due to excessive rainfall, increase in groundwater table or change in its stresses.In such circumstances ,analysis of slope stability becomes a primary concern for everyone.
when the soli is in inclined position,then there s a great chance of sliding of soil from above,and it will occur if shear stress developed in the soil is greater than its corresponding shear strength. This is the main reason why the stability of slope cannot be analysed precisely.

2-Difference between method of slices and stability number method.

Method of slices.

-This method is used in stability analysis of finite slope.
-this method is based on total stress analysis and is modification of fellinius method.
-In this method slip circle is divided into 6 to 12 number of slices of equal thickness and friction between the slices is neglected it means each slices considered as a independent column.
-resisting moment about the centre of slip circle is given by equation and normal component of weight.
-FOS is the ratio of resisting movement to the overturning moment.

Stability Number Method

-This method is also called as Taylor stability method.
-this method is based on effective stress analysis.
-in this method stability of slope is analysed with the help of Taylor's stability number which is taken from the table chart on the basis of given value of c (cohesion) and phi (friction angle of soil).
-unit weight of soil mass used in Taylor's stability method for different state of soil.
For sudden drawdown condition weighted friction angle is used.

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