Rocscience International Conference 2025 is going to take place in Sydney, Australia Read more

Search Results

Shear Factor of Safety

For a Voussoir (no tension) analysis, a rectangular roof is assumed to be divided by cracking into trapezoidal and triangular panels, corresponding to lines of maximum principal tensile stress of an elastic stress analysis. This is illustrated in plan view in the figure below. Such cracking is analogous to the yield lines postulated in the behaviour of reinforced concrete slabs.

Yield Lines for a Rectangular Roof Plate
Yield lines for a rectangular roof plate (plan view)

For a long excavation (x>>y or y>>x) this configuration approximates plane strain conditions with a longitudinal crack at midspan. For a square excavation, four equal triangular panels result.

The Shear Factor of Safety from a Voussoir Analysis balances the shear strength of the long excavation dimension against the weight of a trapezoidal panel. This scheme automatically incorporates long or square excavations in the limiting cases of x=y or x>>y or y>>x. Unlike the Rigid and Elastic analyses, the shear strength of the short excavation dimension (and the weight of the smaller "triangular" panels) does not enter into the shear stability calculation.

Since the lateral compressive stress is solely induced by the arching action of the rock and is not due to external field stresses, low span/depth ratios will result in low Shear Factor of Safety values, since the rock cannot develop the lateral stress required for a self-supporting arch. This is why span/depth ratios < 3 are not recommended, for a Voussoir Analysis.

Shear Factor of Safety = Shear Factor of Safety Equation


Parameter Symbols Definition

Rocscience logo, click here to return to the homepage Portal Account Portal Account Log In Log Out Home Shopping Cart icon Click here to search our site Click here to close Learning Tech Support Documentation Info Chevron Delete Back to Top View More" Previous Next PDF File Calendar Location Language Fees Video Click here to visit Rocscience's LinkedIn page Click here to visit Rocscience's YouTube page Click here to visit Rocscience's X page Click here to visit Rocscience's Facebook page Click here to visit Rocscience's Instagram page Click here to visit Rocscience's Reddit page Bookmark Network Scroll down for more Checkmark Download Print Back to top Single User Multiple Users RSLog RocFall3 CPillar Dips EX3 RocFall RocPlane RocSlope3 RocSupport RocTopple RS2 RS3 RSData RSPile Settle3 Slide2 Slide3 SWedge UnWedge RocTunnel RocSlope2 Commercial License Education License Trial License Shop safe & secure Money-back guarantee