Geotechnical Rock Deformation: Mass, Fractures, Folds, and Faults

A set of vocabulary flashcards covering key concepts from the lecture on rock deformation, folds, faults, and related engineering implications.

Rock mass

A mass of rock that includes intact rock plus fractures, faults, and other discontinuities; its engineering behavior is controlled by these defects, not just the solid rock.

Intact rock

Pure, unbroken rock material with high inherent strength; serves as a contrast to the rock mass, whose strength is often controlled by interfaces and fractures.

Fractures

Cracks in rock formed by stress; can be numerous and may or may not have displacement, influencing rock strength and deformation.

Joints

Fractures with no displacement; form from cooling, stress, or unloading; can be filled with air, water, or infill materials and often occur in sets.

Bedding

Planar layering in sedimentary rocks created during deposition; acts as a weak plane and influences slope stability and fluid flow.

Folds

Wrinkling of rock layers due to ductile deformation under compression; includes anticlines, synclines, and monoclines.

Anticline

A fold with a peaked shape (like a capital A); limbs dip away from the fold hinge and the core can contain older rocks.

Syncline

A trough-shaped fold; limbs dip toward the hinge and the core typically contains younger rocks.

Monocline

A simple bend in strata with a single step or fold, rather than a full up-and-down folding.

Hinge

The location along a fold where curvature is greatest; the fold axis is the line through the hinges of stacked layers.

Axial plane

The plane that connects the hinge lines of a folded sequence and divides the fold into two limbs.

Ductile deformation

Rock deformation at greater depths or higher temperatures where rocks bend and fold rather than break, forming features like folds.

Brittle deformation

Rock deformation near the surface or under rapid loading where rocks crack and fault rather than bend.

Fault

A fracture along which there has been significant displacement of rock masses due to tectonic forces.

Strike-slip fault

A fault where movement is primarily horizontal and parallel to the strike of the fault plane (e.g., Alpine Fault).

Normal fault

A dip-slip fault where the hanging wall moves downward relative to the foot wall due to extensional forces.

Reverse fault

A dip-slip fault where the hanging wall moves upward relative to the foot wall due to compressional forces.

Hanging wall

The rock block that lies above the fault plane in a dip-slip fault.

Permeability

The ability of rock to transmit fluids (water, oil) through pore spaces and fractures; controls groundwater flow and reservoir behavior.

Voids

Cavities or empty spaces within rock (e.g., lava tubes, caves) that can compromise foundations or create hazards for tunneling and construction.