The fracture response of a rock body is related to the orientation of stress directions o= intermediate stress o,= minimum stress Stresses resolved into three mutually perpendicular vectors of 01=maximum stress unequal magnitude Stress-strain and elastic, plastic and brittle failure Elastic stress proportional to strain body regains shape if stress released Ductile past the elastic limit body only recovers some shape if stress released. Stress is not <T proportional to strain Ductile Brittle Failure Brittle body ruptures, no recovery of shape Elastic Limit Increasing Strain(%)
6 The Fracture response of a rock body is related to the orientation of stress directions. σ3 = minimum stress σ1 = maximum stress σ2 = intermediate stress Stresses resolved into three mutually perpendicular vectors of unequal magnitude Increasing Strain (%) Increasing Stress (F/A) Elastic Limit Stress - strain and elastic, plastic and brittle failure Elastic Elastic = stress proportional to strain, body regains shape if stress released Ductile Ductile = past the elastic limit body only recovers some shape if stress released. Stress is not proportional to strain. Brittle X Failure Brittle = body ruptures, no recovery of shape
RELATIONSHIP OF STRAIN BEHAVIOUR TO STRUCTURE DUCTILE STRAIN FOLDING BRITTLE FAILURE FAULTS FRACTURES JOINTS Rock Deformation Propagation of seismic waves through rocks is an elastic response, rocks return to original shape Ductile(plastic)response of rock layers results in folds= permanent wavelike deformations in layered rocks Brittle response to stress results in faults =a fracture in bedrock along which rocks on one side have moved relative to the other side Rock response to stress is influenced by: type of stress, type of rock, temperature, pressure, fluids, length and magnitude of stress applied
7 RELATIONSHIP OF STRAIN BEHAVIOUR TO STRUCTURE DUCTILE STRAIN FOLDING BRITTLE FAILURE FAULTS FRACTURES JOINTS Rock Deformation Propagation of seismic waves through rocks is an elastic response, rocks return to original shape. Ductile (plastic) response of rock layers results in folds = permanent wavelike deformations in layered rocks. Brittle response to stress results in faults = a fracture in bedrock along which rocks on one side have moved relative to the other side. Rock response to stress is influenced by: type of stress, type of rock, temperature, pressure, fluids, length and magnitude of stress applied