Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Studies of Fracture Mechanics of Coal. Final Technical Report, 1 June 1979-30 November 1980
The purpose of the research project was to gain more knowledge of the basic fracture mechanics behavior of coal and of its response to hydraulic fracturing. The work concentrated on experimental measurements; theoretical explanations and analytical modeling were secondary. Eighty successful fracture toughness tests were performed on notched beam specimens (using modified ASTM E-399 Standard Test Method). The results indicate that the critical stress intensity factor (K/sub Ic/) for coal is approximately 50 to 100 psi- sqrt in (compared to 1000 psi- sqrt in for limestone and 40,000 psi- sqrt in for high strength steels). There are significant variations in K/sub Ic/ between coal seams and also with testing orientation within one coal seam. These are explained by measured variations in the ultimate tensile strength of the coal. For coal, like for other rocks, the fracture toughness is determined by tensile strength rather than by strain energy. Thirty-eight hydraulic fracture simulations were performed. They showed that coal behaved as predicted by a published theoretical model for hydraulic fracturing of isotropic materials. However, the fracture pressure and tensile strength were found to be rate dependent. Also, the tensile strength for hydraulic fracturing was calculated to be a factor of ten larger than measured in tensile testing. This unexpected result is tentatively attributed to size effects in the specimens. Except for questions of rate and size effects, enough information was obtained to be able to develop computer models to predict underground hydraulic fracture behavior of coal. More testing similar to previous tests should be able to quantify the size and rate effect so numerical results of laboratory simulations could be scaled up to field test situations. 141 references, 16 figures, 12 tables. (ERA citation 09:021758)
Studies of Fracture Mechanics of Coal. Final Technical Report, 1 June 1979-30 November 1980
The purpose of the research project was to gain more knowledge of the basic fracture mechanics behavior of coal and of its response to hydraulic fracturing. The work concentrated on experimental measurements; theoretical explanations and analytical modeling were secondary. Eighty successful fracture toughness tests were performed on notched beam specimens (using modified ASTM E-399 Standard Test Method). The results indicate that the critical stress intensity factor (K/sub Ic/) for coal is approximately 50 to 100 psi- sqrt in (compared to 1000 psi- sqrt in for limestone and 40,000 psi- sqrt in for high strength steels). There are significant variations in K/sub Ic/ between coal seams and also with testing orientation within one coal seam. These are explained by measured variations in the ultimate tensile strength of the coal. For coal, like for other rocks, the fracture toughness is determined by tensile strength rather than by strain energy. Thirty-eight hydraulic fracture simulations were performed. They showed that coal behaved as predicted by a published theoretical model for hydraulic fracturing of isotropic materials. However, the fracture pressure and tensile strength were found to be rate dependent. Also, the tensile strength for hydraulic fracturing was calculated to be a factor of ten larger than measured in tensile testing. This unexpected result is tentatively attributed to size effects in the specimens. Except for questions of rate and size effects, enough information was obtained to be able to develop computer models to predict underground hydraulic fracture behavior of coal. More testing similar to previous tests should be able to quantify the size and rate effect so numerical results of laboratory simulations could be scaled up to field test situations. 141 references, 16 figures, 12 tables. (ERA citation 09:021758)
Studies of Fracture Mechanics of Coal. Final Technical Report, 1 June 1979-30 November 1980
W. R. Powell (Autor:in)
1980
195 pages
Report
Keine Angabe
Englisch