An Empirical Permeability Estimation Model For Fractured Rocks And Its Applications

The permeability of fractured rocks is a hydraulic property of great importance for understanding the groundwater flow and solute transport in various engineering practices as well as optimization design of engineering barriers and evaluation of hydrogeological conditions.Because of complexity of fractured rock mass and geological environment,characterizing the distribution and variation of permeability are therefore fundamental to hydrogeological research and seepage analysis.This article takes Yagen-? Hydropower Station as geological background and proposes a novel empirical model to estimate the permeability of fractured rocks with three geological indexes due to the limitations of existing models for the prediction of permeability.Combining high-precision hydraulic conductivity model with the Signorini variational inequalities method,the distribution of seepage field is acquired and the validity of seepage control system is assessed in order to offer relevant optimizational parameters.The major research contents are as followes:(1)Based on geological and hydrogeological survey data in Yagen-?Hydropower Station,the proposed model represents the permeability coefficient as a function of three geological indexes,i.e.buried depth(Z),rock quality designation(RQD)and filling substance designation(FSD).These three parameters are easily calibrated with packer hydraulic test data and borehole acoustic television images.Advantages of the ZRF model include more clear physical significance and easier parameterization in engineering practices over the other existing permeability estimation models.(2)A number of investigations,including geological data and the distribution of the discharge,runoff and recharge conditions of groundwater,were performed to divide the permeability of rock mass with ZRF model.A 3-D finite element mesh was generated,including the geological conditions,main structures and seepage control system.The variational inequality method at a steady state are used to analyze the distribution of seepage field of Yagen-? Hydropower Station with drainage substructure and to assess the validty and optimation design parameters of seepage controlling system.The results have theoretical significance and practical worth for the study on the distribution characteristics and influence factors of rock permeability as well as seepage design and performance assessment of hydropower engineering.