soil mechanics ppt

Stability of finite slopes
Swedish circle method,
friction circle method,
Taylor stability number,
Bishop`s method,
Culmann`s method

1. BAMBHANIYA AKSHAYKUMAR :- 160180106007 DUMANIYA KIRPAL :- 160180106032 MAKWANA KETAN :- 160180106052 GUIDED BY :- M.A.S. GOVERNMENT ENGINEERING COLLEGE DAHOD

2. SOIL MECHANICS Stability of slopes TOPIC :- Stability of finite slopes Swedish circle method, friction circle method, Taylor stability number, Bishop`s method, Culmann`s method

3. Stability Analysis of Finite Slopes if slope is of limited extent, it is called a finite slope. A finite slope is bounded by a base and a top surface. Two types of failure of a finite slope may occur: 1) slope failure – face failure, toe failure. 2) Base failure

4. TYPES OF FAILURE For toe failure, Df = 1 For base failure , Df >1 where, Df = depth factor

5. The swedish circle method : The sliding surface or the slipping surface is an arc of a circle. The circle corresponding to the minimum factor of safety is the critical slip circle . Following two cases are considered 1) Analysis of purely cohesive soil (ø = 0 soil) 2) Analysis of a cohesive frictional soil (c– ø soil)

6. 1) Ø = 0 Analysis

7. The factor of safety F is given by Driving moment, Md Resisting moment, Mr

8. Effect of tension cranks When slip is imminent in a cohesive soil, a tension crack will always develop at the top surface of the slope along which no shear resistance can develop.

9. 2) C – Ø Analysis In order to test the stability of the slope of a cohesive frictional soil(c-ø soil), trial slip circle is drawn. The forces between the slices are neglected and each slice is assumed to act independently as a column of soil of unit thickness and of width b . The weight W of each slice is assumed to act at its centre. A number of trial slip circles are chosen and factor of safety of each is computed.

10. FRICTION CIRCLE METHOD The friction circle method is useful for the stability analysis of slopes made of homogeneous soils. This method also assume the failure surface as the arc of a circle. This small circle of radius r sin ø is called friction circle or ø – circle . Force acting on sliding wedge ABDA are: 1) weight W of the wedge 2) total frictional resistance R 3) total cohesive resistance Cm* l mobilised along the slip surface.

11. TAYLOR`S STABILITY NUMBER The total cohesive force c*l which resist the slipping of the soil mass along the slip arc at critical equilibrium is proportion to the cohesion c and the height H of the slope. Taylor`s stability number Sn

12. When the slope is steep , the failure surface passes through the toe , whereas for the flatter slope , the failure extends below the toe.

13. BISHOP`S METHOD Bishop gave a simplified method of analysis of stability of slope which considers the forces on the sides of each slices.

14. This method also takes into account the pore pressure acting on the slice.

15. Equation contain factor of safety in both sides, and hence these may by solved by trial error.

16. Culmann`s method Culmann`s method is used for the approximate stability analysis of homogeneous slopes. A plane failure passing through the toe is assumed. It is a simple failure mechanism and is descrined for the purpose of illustration and for determination of the approximate value of the factor of safety.

17. Let AB be any probable slip plane. The wedge ADB is in equilibrium under the action of forces.

18. Where H is the safe height of slope. The culmann`s method gives reasonable accurate result for homogeneous slopes which are vertical or nearly vertical.

19. THANK YOU