Residual stress-induced failure mechanisms of three types of granodiorite, central Sierra Nevada, California
AuthorRoberts, Kevin Patrick
Geological Sciences and Engineering
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High near-surface compressive stress in massive granodiorite of the central Sierra Nevada produces natural rock failure characteristics occasionally seen in mining and quarrying operations. The principal component of the stress was elastically induced by erosional removal of overburden. Other contributions include stresses due to thermal fluctuations in the rock surface and gravitational loading. Granodiorite fails by stress-relief fracture exhibiting continuous parallelism with topography and a linearly increasing spacing with depth. Utilizing fracture mechanics principles, a maximum stress estimate of 13 MPa at Tuolumne Meadows yields estimates of fracture toughness for Half Dome and Cathedral Peak granodiontes of 0.4 and 1.7 MPa(m) respectively. Compressive stresses of 13 and 32 MPa are required to initiate extension of maximum grain size microcracks for Cathedral Peak and Half Dome granodiorites, assuming a fracture toughness value of 1.6 MPa(m) obtained by averaging five values for granitic rock from the literature. Nine examples of gable mode buckling failure of surficial granodiorite slabs yield, through back-calculation, original .in-situ stresses ranging from 5 to 16 MPa.
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