Types and Causes of Slope Failure in Geotechnical Engineering

What Type of Slope Failure Is Shown in This Figure?

Which of the Following Is a Way That Slopes Fail?

The large block falls from cliffs. Rocks, soil, sediment & ice-slides deep down hillsides. Pieces of rock accumulated on Talus slope until angle becomes too steep. Soil & other loose materials can flow rapidly down-slopes, forming debris flows. All of these.

Types of Slope Failure

Types of Slope Failure are as follows:

1. Translational Failure.
2. Rotational Failure.
3. Flow Failure.
4. Block or Wedge Failure.
5. Rock Slope Failure.
6. Plane Failure.
7. Toppling Failure.
8. Rock Failure.
9. Compound Failure.

1. Translational Failure:

1. Failure of a slope on a weak zone of soil is named a travel slide.
2. A travel slide happens once slope failure happens parallel to the slope.
3. Translational slides square measure common in coarse-grained soils.

2. Rotational Failure:

1. Usually seen in fine-grained soils.
2. This failure could be a move slide that has its purpose of rotation on a rotational axis parallel to the slope.
3. The side of the slide tilts backward toward the initial slope and also the lower surface moves aloof from the slope.

Three kinds of rotational failure:

1. Base Failure: A soft soil layer resting on a stiff layer of soil is susceptible to base failure.
2. Toe Failure: Another kind is that the toe slide, whereby the failure surface passes through the toe of the slope.
3. Slope Failure: Another is that the slope slide, whereby the failure surface passes through the slope.

3. Flow Failure:

1. Occurs once internal and external conditions force a soil to behave sort of a viscous fluid and flow down even shallow slopes, spreading come in many directions.
2. Multiple failure surfaces sometimes occur and alter incessantly as flow takings.
3. Flow slides will occur in dry and wet soils.

4. Block or Wedge Failure:

1. This failure causes a rock mass to slip on 2 intersectant discontinuities forming a tension crack.
2. This mode of failure desires the dip angle of a minimum of one joint intersection to be larger than the angle of friction of the joint surface.

The conditions necessary for propagation of wedge failure:

1. The plunge line of the intersection ought to be larger than the friction angle of the slope.
2. The line of intersection ought to ‘daylight’ on the slope. This suggests that the dip angle of the intersection ought to be but the dip angle of the slope.

5. Rock Slope Failure:

1. The orientation and spacing of the discontinuities plane with reference to the slope are the determinants of rock slope failure.
2. Failure may arise from one separation or a pattern of multiple discontinuities.

6. Plane Failure:

The failure surface in flat failures square measure resulted by single structural discontinuities like bedding planes, faults or the interface between weatherworn rock and also the underlying bedrock.

Conditions for Plane Failure Square Measure as Follows:

1. The strikes of each the slippy plane and also the slope face lie parallel (±20°) to every alternative.
2. The dip angle of the failure plane is often referred to as Daylight.
3. The dip of the slippy plane is larger (angle of friction).

7. Toppling Failure:

1. Thanks to steep discontinuities within the rock that eventually results in slippage of the layers and also the outward and downward movement of a column of rock.
2. This falling action is the column’s centre of gravity lying outside the bottom dimensions.

8. Rock Failure:

1. A rock mass of any size is detached from a steep slope or formation wherever there’s little or no shear resistance.
2. It may dislodge and impinge on alternative rocks in its mechanical phenomenon.

#9. Compound Failure:

A combination of rotational and translational slide failure. As the combination suggests, failure occurs when the slip surface curves at both ends but has a level or flat central point.

Geotechnical Failures 

Geotechnical failures are often categorised as follows:

1. Failure of Foundation
2. Landslide

1. Failure of Foundation:

1. Many factors resulting in failure of foundations, and resulted within the damages of the superstructures. e.g., the foundations were liable to landslides, debris flows, etc.
2. The large settlement and uneven settlement were seen ensuing from the lost of bearing capacity.

2. Landslide:

1. The rainfall-induced landslides during this case enclosed that of change of location and motility
2. A number of the failures were surficial and shallow.

Types of Slopes in Geography

The rate of rise or fall of a piece of ground feature is understood as its slope.

There square measure 6 sorts of slopes:

1. Gentle
2. Steep
3. Concave
4. Convex
5. Tectonic
6. Depositional

1. Gentle:

Contour lines showing a regular, light slope are going to be equally spaced and wide apart. A slope with contour lines unfolds way except one another.

2. Steep:

Contour lines showing a regular, steep slope on a map are going to be equally spaced, however approximate.

3. Concave:

Contour lines showing a slope on a map are going to be closely spaced at the highest of the piece of ground feature and wide-spaced at rock bottom.

4. Convex:

Contour lines showing a lentiform slope on a map are going to be wide-spaced at the highest and closely spaced at rock bottom.

5. Tectonic:

1. These square measure fashioned through internal forces that end in the folding, distortion and faulting of rock layers.
2. Anticlines and synclines are fashioned once layers of rock square measure folded; whereas horsts (block mountains) and graben (rift valleys) are fashioned once blocks of land rising or fall.

6. Depositional:

Deposits of weather material build-up to make inclined surfaces, mounds associate degreed hills once an agent of abrasion that has lost its energy of motion, lays down its load in a very specific place.

Slope Stability

Safety Factor (SF) = The magnitude relation of resisting forces to driving forces:

SF = Resisting Forces/ Driving Forces

If SF >1 then SAFE

If SF < 1 then UNSAFE

Safety Factor

It may be calculated by the unit thickness technique victimisation the subsequent equation:

SF = SLT/W sin A

where,

S = shear strength of the clay layer (usually 9 x 104 N/m³)

L = stretch of the slip plane (usually 50 m)

T = unit thickness (usually 1m)

W = space (usually 500 m²) x thickness (usually 1 m) x unit weight (usually 1.6×104 N/m³)

A = 30º, sin A = 0.5 SF = 1.125 (conditionally stable)

Causes of Slope Failure:

Main factors responsible for slope failure are:-

1. Erosion
2. Rainfall
3. Earthquakes
4. Geology
5. External Loading
6. Construction Activities
7. Fast Drawdown

1. Erosion

Water & Wind Erosion changes the pure mathematics of the slope, leading to slope failure or, a landslide.

2. Rainfall

Due to Long periods of rain, water enters into existing cracks and saturate, soften, and erode soils.

3. Earthquakes

Earthquakes induce dynamic forces, particularly dynamic shear forces that scale back the shear strength and stiffness of the soil.

4. Geology

A slit below a thick deposit of stiff clay will simply be unnoticed in drilling operations, or one could also be careless in assessing borehole logs solely to seek out later that the presence of the slit caused a ruinous failure.

5. External Loading

Loads placed on the crest of a slope raise the gravitative load and will cause slope failure. A load placed at the toe referred to as a berm can increase the soundness of the slope.

6. Construction Activities

Construction activities close to the toe of an existing slope will cause failure as a result of lateral resistance is removed.

Slope failures are often divided into:-

1. The first case– is that the excavated slope.
2. The second case– is fill slope.

7. Fast Drawdown

Reservoirs are often subjected to fast drawdown. The lateral force provided by the water is removed, and also the excess pore-water pressure doesn’t have enough time to dissipate.

Frequently asked questions (FAQs) that could be included in your article on slope failure:

What are the main types of slope failure?

The main types include translational failure, rotational failure, flow failure, block or wedge failure, rock slope failure, plane failure, toppling failure, and compound failure.

What causes slope failure?

Slope failure can be caused by factors such as erosion, rainfall, earthquakes, geological conditions, external loading, construction activities, and rapid drawdown of reservoirs.

How is slope stability assessed?

Slope stability is often assessed using the Safety Factor (SF), which compares resisting forces to driving forces. A SF greater than 1 indicates stability, while less than 1 indicates potential instability.

What are some examples of geotechnical failures related to slopes?

Geotechnical failures can include foundation failures due to landslides, settlement issues, or uneven bearing capacity caused by slope instability.

How can slope failure be mitigated or prevented?

Mitigation strategies include slope reinforcement techniques like retaining walls, drainage systems to manage water infiltration, vegetation reinforcement, and careful construction practices to minimize destabilizing factors.

What are the characteristics of different slope types in geography?

Slope types can vary from gentle to steep, concave, convex, tectonic (formed by geological forces), and depositional (formed by sediment deposition).

What role do geological factors play in slope stability?

Geological factors such as rock type, presence of faults or fractures, and the orientation of bedding planes significantly influence the stability of slopes.

How do natural disasters like earthquakes and heavy rainfall impact slope stability?

Earthquakes can induce dynamic forces that reduce soil strength, while heavy rainfall can saturate soil, increase pore water pressure, and trigger landslides or slope failures.