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Abstract A coupled mechanical-hydraulic model for a single saturated fracture under both normal stress and fluid pressure is proposed based on the classic Biot poroelasticity theory. By taking the fracture as assembling of a set of voids in rock mass，a generalized Biot coefficient is introduced to describe the interaction effect between pore fluid pressure and fracture deformation. Compared with the classic concept of effective stress proposed by Terzaghi，the generalized Biot coefficient in this model is not a constant but a function of fracture deformation，so that the dependency of the effect of fluid pressure on fracture deformation is emphasized. With the help of the generalized Biot coefficient，a nonlinear constitutive equation for a single fracture under both normal stress and fluid pressure is developed. Later，the mechanical deformation of the fracture is related to the fracture hydraulic conductivity through “cubic law”，so that a coupled mechanical-hydraulic model is developed. All the four parameters involved in this model have their physical significances and can be determined through mechanical compression tests and permeability tests. A first validity of the model is made by predicting the variation curve of fracture flowrates versus normal stress under different fluid pressure. Comparison between model prediction and tests data verifies the applicability of the proposed model.
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Received: 30 December 2010
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2011, Vol. 30 
