Shear And Contact Effects On Mechanical Properties And Seepage Characteristics Of Single Fractures

The intact rock has small deformation and low permeability coefficient,while there are a lot-of cracks in the natural rock mass.The closure or failure of the fracture is the main cause of the deformation of the rock mass,and the seepage mainly moves in the fracture.In the engineering construction,the fractured rock mass is usually in a complex stress state,and the mechanical properties and seepage laws of the rock mass are also very complicated.Therefore,the study of fractures under complex stress state can better understand the mechanical characteristics of rock mass and the law of seepage,which plays an important guiding significance for engineering production and construction.In this paper,the single fracture made of gypsum material is taken as the research object,and the single fracture shear seepage experiment under different normal stress,different shear rate and different head pressure is carried out.In the experimental analysis of fracture seepage under different normal stresses,the law of fracture normal displacement in the whole shear process was studied based on the Barton dilation model.The effects of normal stress shear rate and head pressure on seepage nonlinearity were analyzed based on the coupling experiment of fracture shear flow under different working conditions.Based on the contact rate-based seepage test and numerical simulation,the influence of contact rate and contact form on seepage is studied,and the formula of radiation flow cubic law is modified.The main results and conclusions are as follows:(1)Through the force analysis of the fracture surface and the analysis of the experimental data,the peak shear displacement decreases with the increase of the undulation angle and the normal stress of the toothed fracture surface.To shear failure for all critical point by single fissure shear dilatancy of the process of empirical formula,the dilatancy model is divided into peak dilatancy model before and after peak dilatancy model,can be a very good response in the process of the shear method to the displacement of the four stages,namely peak shear shrinkage,peak before the peak after shear dilatancy,shrinkage and stable phase,different shear displacement can be accurately predicted the normal displacement.The cubic law applicable to the radiation flow is derived through mathematical method,and the correction coefficient considering the contact rate and the head pressure is obtained through the percolation experiment analysis of the contact rate,which is put into the corrected cubic law to further improve the applicability and accuracy of the cubic law.(2)The relationship between seepage rate and water pressure is nonlinear.The increase of contact rate will reduce the permeability of fracture,and at the same contact rate,the contact form that makes the percolation channel zigzagging will also reduce the permeability of fracture.The cubic law applicable to the radiation flow is derived through mathematical method,and the correction coefficient considering the contact rate and the head pressure is obtained through the percolation experiment analysis of the contact rate,which is put into the corrected cubic law to further improve the applicability and accuracy of the cubic law.(3)Based on the numerical simulation,it is concluded that the increase of the ring contact rate will strengthen the nonlinear phenomenon of seepage flow,the linear coefficient of Forchheimer's law increases linearly with increasing ring contact rate,and the nonlinear coefficient increases exponentially with the increase of the ring contact rate.In the process of shear failure,the nonlinear phenomena of seepage flow change with the occurrence of shear failure.The linear coefficient and nonlinear coefficient increase first and then decrease with shear failure,and the nonlinear phenomena of seepage flow strengthen after shear failure.