CELE Geotechnical Engineering — Slope Stability and Soil ImprovementConcept Map

Concept

Factor of Safety (FS)

Sub Concepts

• Definition: Ratio of resisting to driving forces
• Acceptance criteria: FS > 1.0 (stable)
• Design targets: 1.3–1.5 depending on risk
• Calculation: FS = τf / τ

Relationship To Central

Fundamental measure of slope stability

Concept

Infinite Slope Analysis

Sub Concepts

• Dry cohesionless: FS = tan(φ) / tan(β)
• With cohesion (no seepage): Includes c' term
• With seepage: Uses γ' and pore pressure
• Failure plane parallel to surface

Relationship To Central

Simplified method for long, parallel slopes

Concept

Finite Slope Analysis

Sub Concepts

• Method of slices (Fellenius, Bishop)
• Taylor's stability number (Ns)
• Critical height calculation
• Circular failure surfaces

Relationship To Central

Rigorous method for non-parallel slopes

Concept

Soil Improvement Techniques

Sub Concepts

• Densification: compaction, vibroflotation, dynamic compaction, stone columns
• Consolidation acceleration: preloading, prefabricated vertical drains (PVD)
• Reinforcement: geogrids, geotextiles, soil nailing, reinforced earth walls
• Stabilization: lime/cement treatment, grouting, dewatering

Relationship To Central

Methods to enhance inadequate soil properties

Concept

Slope Failure Mechanisms

Sub Concepts

• Circular arc failure (clay slopes)
• Planar failure (cohesionless, weak layers)
• Wedge failure (rock/soil interface)
• Creep (slow, continuous deformation)

Relationship To Central

Types and triggers of slope instability

Concept

Seepage Effects

Sub Concepts

• Pore pressure reduces effective stress
• Seepage force adds hydraulic gradient term
• Can halve FS in cohesionless slopes
• Requires flow net or field monitoring

Relationship To Central

Impact of groundwater on stability

Concept

Soil Parameters

Sub Concepts

• Cohesion (c, c'): effective and total
• Friction angle (φ, φ'): from triaxial or direct shear
• Unit weight (γ, γ'): saturated and dry
• Laboratory/field determination methods

Relationship To Central

Key inputs for stability calculations

To

Infinite Slope Analysis

From

Factor of Safety

Strength

strong

Relationship

FS is the output calculated using infinite slope formulas for parallel failure surfaces

To

Finite Slope Analysis

From

Factor of Safety

Strength

strong

Relationship

FS is determined via method of slices or Taylor charts for complex slope geometries

To

Soil Parameters

From

Infinite Slope Analysis

Strength

strong

Relationship

Infinite slope equations require input of c', φ', γ from laboratory or field tests

To

Soil Parameters

From

Finite Slope Analysis

Strength

strong

Relationship

Method of slices depends critically on accurate effective stress parameters (c', φ')

To

Infinite Slope Analysis

From

Seepage Effects

Strength

strong

Relationship

Seepage modifies pore pressure term, significantly reducing FS especially in cohesionless slopes

To

Factor of Safety

From

Seepage Effects

Strength

strong

Relationship

Elevated pore pressure from seepage lowers effective stress and reduces driving capacity

To

Finite Slope Analysis

From

Slope Failure Mechanisms

Strength

moderate

Relationship

Analysis method selection depends on expected failure mode (circular, planar, wedge, or creep)

To

Factor of Safety

From

Soil Improvement Techniques

Strength

strong

Relationship

Improvement methods increase soil strength or reduce pore pressure, thereby raising FS

To

Consolidation Acceleration

From

Soil Improvement Techniques

Strength

strong

Relationship

PVD drains accelerate consolidation of soft clay, reducing compressibility settlement

To

Densification

From

Soil Improvement Techniques

Strength

moderate

Relationship

Compaction and vibroflotation increase soil density and shear strength of granular soils

To

Seepage Effects

From

Soil Parameters

Strength

moderate

Relationship

Saturated unit weight γsat and hydraulic conductivity k control seepage behavior

To

Slope Failure Mechanisms

From

Finite Slope Analysis

Strength

moderate

Relationship

Method of slices identifies critical circular surface governing most common clay slope failures

To

Reinforcement

From

Soil Improvement Techniques

Strength

moderate

Relationship

Geogrids and nails provide tensile restraint, increasing effective friction and cohesion

To

Stabilization

From

Soil Improvement Techniques

Strength

moderate

Relationship

Chemical treatment (lime, cement) increases matrix cohesion and strength

To

Slope Failure Mechanisms

From

Infinite Slope Analysis

Strength

moderate

Relationship

Infinite slope method applies to simple planar failure on long parallel slopes