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| Method for predicting fracture and determining true material parameters of rock |
| GUAN Junfeng1，QIAN Guoshuang1，BAI Weifeng2，YAO Xianhua1，FU Jinwei1 |
(1. School of Civil Engineering and Communication，North China University of Water Resources and Electric Power，Zhengzhou，Henan 450045，China；2. School of Water Conservancy，North China University of Water Resources and Electric Power，
Zhengzhou，Henan 450045，China)
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Abstract At present，testing methods for determining the fracture parameters of rock are not consistent，and the test results show the effect of size. Even if the material parameters are given，the corresponding full curve of the fracture prediction of rock materials has not been established. Two key issues that have not yet been satisfactorily resolved，namely，determining the true material parameters(fracture toughness and strength) of rock and predicting the fracture of rock structure，were studied in this paper according to the boundary effect theory. The average grain size of rock was introduced into the modified model of boundary effect，in which the important effect of grain size on fracture was considered. The true material parameters can be determined by using small rock specimens under quasi-brittle fracture control. The complete prediction curve of rock fracture can be constructed using the determined material constants of rocks(fracture toughness and tensile strength) in which the plastic，quasi-brittle，and brittle fractures can be fully described. If the fictitious crack formation is considered or ignored，the minimum size of the rock specimen meeting the requirement of linear elastic fracture mechanics can also be obtained. The tests results from the geometrically similar specimens，non-geometrically similar specimens，and combined specimens that are geometrically similar and non-geometrically similar，were analyzed in detail using the modified model. The rationality of the proposed method for predicting fracture and determining the true material parameters of rocks were confirmed.
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2018, Vol. 37 
