stability of slopes , foundation engineering , analysis of retaing wall , formulas ,problems

Foundation engineering

1. STABILITY OF SLOPES Prepared by MURALI SAGAR VARMA SAGI Assistant Professor

2. An exposed ground surface that stands at an angle with the horizontal is called slope INTRODUCTION What is a slope? What happens if slope fails?

3. Types of slopes Natural: Formation due to geological features of the earth Man made: Formed for construction activity like embankments, cuttings etc., Examples Hill sides and valleys Coastal and river cliffs Examples Cuttings and embankments for highways and roadways Earthen dams Temporary excavations Waste heaps (landfill slopes) Landscaping for site developments

4. Types of slopes Hill side Valley side Cuttings Embankments River cliff Landfills Landscape Earthen dam

5. Infinite slopes: They have dimensions that extends over great distances and the soil mass is inclined to the horizontal. Finite slopes: A finite slope is one with a base and top surface and the height is limited. The inclined faces of earth dams, embankments and excavations are some examples of finite slopes

6. Failure of slopes is catastrophic and results in significant loss to the lives and properties. Civil engineers are expected to check the safety of soil slopes. Slope stability consists of determining and comparing the shear stress developed along the potential rupture surface with the shear strength of soil. Attention must be paid to geology, surface drainage, ground water and shear strength of soils in assessing the slope stability. Why to bother about soil slopes ?

7. Erosion Steady seepage Sudden drawdown Intensive rain fall Earthquakes External loading Rise of ground water table in the sloping region Construction activities Geological features CAUSES OF SLOPE FAILURES

8. Erosion: The wind and flowing water causes erosion of top surface of slope and makes the slope steep and thereby increase the tangential component of driving force Steady seepage: Seepage forces in the sloping direction add to gravity forces and makes the slope susceptible to instability. The pore water pressure decrease the shear strength. This condition is critical for the downstream slope. Sudden drawdown: Sudden reduction in water level due to sudden drawdown has two effects: reduction of the stabilizing external hydrostatic pressure and changes in the internal pore water pressure Rainfall: Rainfall for a long duration saturate, soften and erode soils. Water enters into existing cracks and may weaken underlaying soil layers and leads to slope failure. CAUSES OF SLOPE FAILURES

9. Earthquakes: They induce dynamic forces. In addition to that, there will be sudden increase in the pore water pressure, which reduces available shear strength. External loading: Additional loads placed on top of the slope increases the gravitational forces that may cause the slope to fail. Construction activities at the toe of the slope: Excavation at the bottom of the sloping surface will make the slopes steep and thereby increase the gravitational forces which may result in slope failure. CAUSES OF SLOPE FAILURES

10. TERMINOLOGY Slip or failure zone: It is a thin zone of soil that reaches the critical state or residual state and results in movement of upper soil mass Slip plane or failure plane or slip surface or failure surface: It is the surface of sliding Sliding mass: It is the soil within the slip plane and the ground surface. Slope angle: It is the angle of inclination of a slope to the horizontal.

11. Rigid stratum Compound failure Translational R R circular Non - circular Rotational TYPES OF SLOPE FAILURES

12. Face (slope failure): This type of failure occurs when the slope angle is large and when the soil at the toe portion is strong Toe failure: In this case, the failure surface passes through the toe. This occurs when the slope is steep and the soil is homogeneous Base failure: In this case, the failure surface passes below the toe. This generally occurs when the soil below the toe is relatively weak. TYPES OF SLOPE FAILURES