Types of Slope Failure | Geotechnical Engineering

March, 31 2020

Below we take a look at the types of slope failure in geotechnical engineering and explain each failure. It is essential to understand slope failures as part of geotechnical analysis to ensure a structure has a stable base.

Firstly, what is a slope?

In geotechnical terms, an earth or soil slope is a surface of soil mass which is inclined. Slopes can both occur naturally and be manmade. It is important to monitor earth slopes, such as their balance, shear strength and ability to withstand movement, to ensure slope failure does not occur.

Types of slope failure in geotechnical engineering

1) Rotational failure

When rotational failure occurs, the failed surface will begin to move outwards and downwards. This occurs when rotation by a slip surface causes the slope surface to curve. The failure can happen in multiple ways, including face, base and toe failure. Toe failure is the most common situation and it occurs when the failing surface passes through the slope’s toe.

To identify rotational failure, engineers and geotechnical experts examine the following key indicators:

  • Curved Surface: One of the primary signs of rotational failure is the presence of a curved or concave surface within the slope. This curvature results from the rotation of soil layers along the slip surface.
  • Multiple Failure Modes: Rotational failure can manifest in various ways, including face, base, and toe failure. These modes differ in terms of where the failure initiates and progresses within the slope.
  • Toe Failure: Among these modes, toe failure is the most common occurrence. It takes place when the failing surface extends through the slope’s toe, which is the bottom part of the slope. Detecting toe failure is crucial, as it signifies a critical point of instability in the slope.

How to Avoid Rotational Failure in Slopes:

Rotational failure in geotechnical engineering can lead to potentially hazardous situations and costly construction setbacks. Fortunately, there are several measures and best practices that engineers and construction professionals can implement to minimize the risk of rotational failure in slope structures:

  • Strengthening Weak Zones: If weak soil layers or zones are identified within the slope, consider reinforcement techniques such as soil nailing, geogrids, or retaining walls to stabilize these areas.
  • Regular Monitoring: Implement a monitoring program that includes periodic inspections and instrumentation to detect early signs of slope instability. Monitoring can provide valuable data for timely interventions.
  • Maintenance and Repair: Regular maintenance and timely repairs are crucial to address any deterioration or erosion that may compromise the stability of the slope.


2) Translational failure

When a slope contains no definite boundaries and the soil beneath the free surface is believed to have the same properties and identical depths as the slope, it is named an infinite slope. In an infinite slope, its topsoil will form a parallel slip surface, also referred to as a translational failure.

To effectively identify translational failure, several key factors and characteristics need to be considered:

  • Infinite Slope Conditions: Translational failure is closely associated with infinite slopes. An infinite slope is one where there are no distinct boundaries or changes in the properties of the soil beneath the surface. It’s assumed that the soil properties and depths remain uniform throughout the slope.
  • Topsoil Behavior: In an infinite slope, the top layer of soil behaves as if it forms a flat or parallel slip surface. This is a crucial aspect of translational failure. When the topsoil starts moving as a unit, it can lead to the development of translational failure.
  • Layered Slope Materials: One of the key indicators of translational failure is the presence of layers within the slope materials. These layers can be composed of different types of soils, rocks, or other materials. The sliding of these layers along the parallel slip surface is a characteristic feature of translational failure.

How to Avoid Translational Failure in Slopes:

Translational failure in slopes, particularly in infinite slopes, can pose significant risks to construction projects and the safety of people in the vicinity. To prevent or mitigate translational failure, several proactive measures and engineering strategies should be implemented:

  • Site Assessment and Geological Study: Conduct a thorough site assessment and geological study before any construction or development begins. This includes investigating the soil types, rock formations, groundwater conditions, and historical slope behavior.
  • Engineering Design: Involve geotechnical engineers in the project’s design phase. They can provide valuable insights into slope stability and suggest design modifications that reduce the risk of translational failure.
  • Slope Analysis: Perform comprehensive slope stability analysis, considering factors like slope angle, soil properties, water table depth, and load-bearing capacity. This analysis will help identify potential failure mechanisms early on.
  • Drainage Management: Proper drainage is crucial in preventing translational failure. Implement effective drainage systems, such as surface drains, subsurface drains, and retention basins, to manage groundwater and prevent soil saturation.
  • Slope Modification: If a slope is identified as potentially unstable, consider slope modification techniques. These can include reshaping the slope, adding retaining structures, or reinforcing it with geosynthetics.
  • Safety Protocols: Implement safety protocols for construction workers and site visitors. This may involve restricting access to hazardous areas and providing training on recognizing warning signs of slope instability.


3) Compound failure

Compound failure is the word used to describe 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. When a hard soil level forms from a considerable depth from the toe, the slip surface can become flat.

Here are key aspects of identifying compound failure:

  • Surface Characteristics: One of the primary indicators of compound failure is the surface morphology. Unlike other types of slope failures, a compound failure exhibits a distinctive surface profile. The slip surface, where the failure initiates, tends to curve at both ends, forming concave shapes, while the central portion is relatively flat or level. This concave-convex profile is a hallmark of compound failure.
  • Geological and Soil Conditions: Understanding the geological and soil conditions is essential for identifying compound failures. It often occurs when a layer of hard or competent soil or rock is present at a considerable depth below the slope’s toe. This hard layer can act as a barrier, causing the slip surface to flatten in the middle.
  • Geotechnical Investigation: Conducting a comprehensive geotechnical investigation is crucial for the identification of compound failure. This investigation includes soil sampling, laboratory testing, and site-specific analysis to determine soil properties, layering, and the presence of any hard strata.
  • Field Observations: Field observations play a vital role in recognizing compound failure. Geologists and engineers should examine the slope’s surface for signs such as cracking, slumping, or bulging. The presence of multiple failure mechanisms, including both rotational and translational elements, can provide valuable clues.

How to Avoid Compound Failure in Slopes:

Avoiding compound failure in geotechnical engineering is essential to ensure the safety and stability of slopes in construction and other projects. To prevent and mitigate compound failure here are the steps:

  • Thorough Site Assessment: Conduct a comprehensive site assessment before any construction or excavation work begins. This includes geotechnical investigations, soil testing, and geological surveys to understand the subsurface conditions, including the presence of hard layers or weak zones.
  • Engineering Design: Involve geotechnical engineers and slope stability experts in the project’s design phase. They can analyze the site data and design appropriate slope angles, drainage systems, and reinforcement measures to mitigate the risk of compound failure.
  • Soil Improvement: Consider soil improvement techniques, such as compaction, grouting, or reinforcement with geosynthetic materials, to enhance the strength and stability of weak or problematic soil layers.
  • Vegetation and Erosion Control: Promote the growth of vegetation on slopes to stabilize the soil and reduce erosion. Planting grass, shrubs, or trees with deep root systems can help bind the soil together.


4) Wedge failure

Sometimes referred to as plane or block failure, wedge failure occurs on a plane that is inclined. For example, this failure can happen when the soil contains weak layers or joints that are created as the slope is constructed from two different, non-compatible materials. The main difference between a wedge and translational failure is that wedge failure can happen in both infinite and finite slopes.

Here’s how engineers identify wedge failure:

  • Topographical Surveys: Topographical surveys are essential for mapping the slope’s terrain accurately. This helps engineers identify the slope’s inclination, potential drainage issues, and any irregularities that could contribute to wedge failure.
  • Stability Analysis: Engineers use advanced computational methods to perform slope stability analyses. These analyses take into account factors like the slope’s geometry, soil properties, and external forces (e.g., rainfall or seismic activity). By simulating different scenarios, they can predict whether wedge failure is likely to occur.
  • Visual Inspection: Regular visual inspections of the slope are essential for identifying signs of potential wedge failure. Engineers and geologists look for visible cracks, deformations, or tilting of the slope surface. These signs may indicate stress and movement within the slope.

How to avoid Wedge Failure in Slopes:

Wedge failure is a potentially hazardous geotechnical issue that can compromise the stability of slopes. To ensure safety and the longevity of structures built on or near slopes, it’s essential to take proactive measures to prevent wedge failure. Here are key strategies to avoid wedge failure:

  • Soil Improvement Techniques: If weak layers or incompatible materials are identified within the slope, consider soil improvement techniques. These may include compaction, soil reinforcement, or the addition of stabilizing agents to strengthen the soil and reduce the risk of failure.
  • Avoid Overloading: Avoid overloading slopes with excessive weight or construction equipment. Ensure that any loads placed on or near the slope are within safe limits.
  • Soil Improvement Techniques: If weak layers or incompatible materials are identified within the slope, consider soil improvement techniques. These may include compaction, soil reinforcement, or the addition of stabilizing agents to strengthen the soil and reduce the risk of failure.

Contact G3Soilworks

If you’d like more information about slope failure and would like to hire consultancy services for your construction or mining project, do not hesitate to contact expert consultants G3Soilworks. When creating a solid foundation, understanding the potential slope failures is essential to ensure the durability and safety of a project.



Q1: What is slope failure in geotechnical engineering?

A1: Slope failure in geotechnical engineering refers to the sudden or gradual collapse of an inclined surface of soil or rock. It can occur naturally or as a result of construction activities and poses significant risks to structures and safety. Understanding the types of slope failure is crucial for ensuring stable foundations in construction projects.


Q2: What is an infinite slope, and how does it relate to translational failure?

A2: An infinite slope is a type of slope where there are no distinct boundaries or changes in soil properties beneath the surface. Translational failure is closely associated with infinite slopes, as it occurs when the topsoil behaves as if it forms a parallel slip surface. This phenomenon is a significant consideration in geotechnical engineering when assessing slope stability.


Q3: What are the key indicators of compound slope failure, and why is it important to identify this type of failure?

A3: Compound slope failure is characterized by a curved slip surface at both ends with a relatively flat central portion. Key indicators include surface morphology and the presence of hard soil layers deep within the slope. Identifying compound failure is vital because it combines elements of both rotational and translational failure, making it a complex and potentially hazardous geotechnical issue.


Q4: What measures can be taken to avoid wedge failure in slopes, and why is it essential to prevent this type of failure?

A4: To prevent wedge failure in slopes, engineers can implement soil improvement techniques, avoid overloading slopes, and conduct regular inspections. Preventing wedge failure is crucial because it can result from weak layers or incompatible materials within the slope, leading to instability and potential risks to construction projects and safety.

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