What is a wedge failure in rock slopes?

It's a failure mode where a block of rock, bounded by two intersecting discontinuity planes and the slope face, slides out along the line of intersection of the two planes.

What is the minimum recommended factor of safety for a permanent rock slope?

A minimum Factor of Safety of 1.5 is recommended for permanent slopes under static conditions (Table 1).

What primary data is required for wedge stability analysis?

The orientation (dip/dip direction) of the two discontinuity planes, their shear strength parameters (cohesion 'c' and friction angle 'φ'), rock unit weight, and groundwater conditions (pore pressure).

How does reinforcement like a rock bolt stabilize a wedge?

It provides a resisting force (T). Depending on its orientation, it can directly oppose the sliding motion and/or increase the normal force across the sliding planes, which in turn increases frictional resistance.

IS 14448

: 1997

Code of practice for reinforcement of rock slopes with plane wedge failure

CurrentSpecializedCode of PracticeGeotechnical · Rock Mechanics

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This code provides guidelines for the analysis and design of reinforcement for rock slopes susceptible to wedge-type failures. It covers the methods for stability analysis, design principles for rock bolts and anchors, and construction techniques to stabilize the rock mass.

Code of practice for reinforcement of rock slopes with plane wedge failure

Quick Reference Values

Minimum Factor of Safety for Permanent Slopes1.5

Minimum Factor of Safety for Temporary Slopes1.3

Typical Angle of Friction for rock joints (sandstone)25° - 35°

Typical Cohesion for rock joints0 - 50 kPa

Typical Grout Bond Strength (Rock-Grout)0.3 - 1.0 MPa

Key Formulas

FoS = [CaAa + CbAb + (Wa cosψa - Ua - Vb + Tsin(θt+ψt))tanφa + (Wb cosψb - Ub - Va + Tsin(θt+ψt))tanφb] / [Wa sinψa + Wb sinψb - Tcos(θt+ψt)] — Factor of Safety for Wedge

Practical Notes

Accurate geological mapping of joint orientations (dip and dip direction) and their shear strength properties is the most critical input for the analysis.

The influence of pore water pressure within the discontinuities is a major factor and often governs the stability; it must be carefully assessed.

On-site pull-out tests on installed rock anchors are essential to verify their design capacity and the quality of installation.