C.F. Chiu

Experimental Study on Fracture Behavior of a Silty Clay

Fracture toughness KIC and KIIC are two important parameters in fracture mechanics. In this paper, a device was designed to perform improved three-point and four-point unsymmetrical bending tests on soil beams. The device can easily remove the influence of specimen self-weight on the test results. Using the improved methods and the device, KIC, KIIC, and mixed mode I-II stress intensity factors KI and KII at fracture failure of a compacted silty clay were investigated. Test results indicated that the fracture of the silty clay exhibits linear and elastic behavior. The influences of dry density, water content, and preconsolidation pressure of specimens on parameter KIC were investigated. It was found that the classical mixed mode I-II fracture failure theories such as the strain energy density factor theory, maximum circumferential stress theory, and energy release rate theory cannot adequately predict the fracture failure behavior of the specimens, but a circle agrees well with the test results. The directions of crack growing in the specimens under mode II and mixed mode I-II loading conditions were expressed by a linear function of KI/KII.

Hydraulic fracturing of rock-fill dam

The condition in which hydraulic fracturing in core of earth-rock fill dam may be induced, the mechanism by which the reason of hydraulic fracturing can be explained, and the failure criterion by which the occurrence of hydraulic fracturing can be determined, were investigated. The condition depends on material properties such as, cracks in the core and low permeability of core soil, and “water wedging” action in cracks. An unsaturated core soil and fast impounding are the prerequisites for the formation of “water wedging” action. The mechanism of hydraulic fracturing can be explained by fracture mechanics. The crack propagation induced by water pressure may follow any of mode I, mode II and mixed mode I-II. Based on testing results of a core soil, a new criterion for hydraulic fracturing was suggested, from which mechanisms of hydraulic fracturing in the core of rock-fill dam were discussed. The results indicated that factors such as angle between crack surface and direction of principal stress, local stress state at the crack, and fracture toughness KIC of core soil may largely affect the induction of hydraulic fracturing and the mode of the propagation of the crack. The condition in which hydraulic fracturing in core of earth-rock fill dam maybe induced, the mechanism by which the reason of hydraulic fracturing canbe explained, and the failure criterion by which the occurrence of hydraulicfracturing can be determined, were investigated. The condition dependson material properties such as, cracks in the core and low permeability ofcore soil, and “water wedging” action in cracks. An unsaturated core soiland fast impounding are the prerequisites for the formation of “waterwedging” action. The mechanism of hydraulic fracturing can be explainedby fracture mechanics. The crack propagation induced by water pressuremay follow any of mode I, mode II and mixed mode I-II. Based on testingresults of a core soil, a new criterion for hydraulic fracturing was suggested,from which mechanisms of hydraulic fracturing in the core of rock-fill damwere discussed. The results indicated that factors such as angle betweencrack surface and direction of principal stress, local stress state at thecrack, and fracture toughness KIC of core soil may largely affect theinduction of hydraulic fracturing and the mode of the propagation of thecrack.