Shear strength of rock

Following are the factors that affect (control) the shear strength of rock- materials and rock joints.

a. Direction of applied shear stress: The shear strength of a rock depends on the direction of acting shear stress with respect to bedding plane. When shear stress with respect to bedding plane. When shear stress is normal to the bedding plane, the shear strength becomes maximum.

b. Nature of cementing material: the shear strength of sedimentary rocks highly depends on the cementing materials between the rock grains. If cementing material is entirely or partially clay, the shear strength is low but for quartz as a cementing material, the shear strength becomes maximum.

c. Crystal inter locking: Rocks having interlocked crystals have relatively high strength.

d. Saturation: when water is added to some rocks, the strength is considerably reduced because of the chemical deterioration of cement or clay-binder of the rocks. Friable sandstone may even lose 15% of its strength by saturation alone.

e. Pores and vesicles: Presence of pores and vesicles decreases the shear strength of the rocks because pore-water pressure developed reduces the value of effective normal stress.

f. Surface roughness: generally, greater the surface roughness, more Is the shear strength of rocks.

g. Discontinuity of rocks

Characteristics of discontinuity such as orientation, spacing, continuity, surface characteristics, degree of weathering directly impact upon the shear strength of rocks.

h. Condition of testing and topographic effect also effects the shear strength of rocks. The picture of rock was obtained from Wikipedia