Stress And Time-related Fracture Permeability Model And Its Application

The permeability evolution in fault zone is essential for fault strength, fluid flowand distant earthquakes. To know well about their relationship, firstly, the fluid-stresscoupled model for a single fracture is built. Then, taking the stress, time and fracturenetwork geometry distribution together, the author builds a stress and time-relatedfractured rock permeability model through the combination between theoretical deri-vation and laboratory test. In the process, the single fracture fluid-solid coupled per-meability model is derived based on cubic law and Bandis hyperbolic function. Byintroducing fracture creep, the fracture coupled permeability evolution with time isdiscussed. To establish relationship between single fracture permeability and fracturenetworks, according to the series-parallel characteristics in the geometry distributionof fracture networks, the author builds stress and time-related permeability model ofrock fracture networksUpon the previous work, the Coulomb Failure Rule of fracture rock in fault zoneis analyzed. Then, based on the stress/time-related fracture closure theory, the expres-sion of fluid pressure evolution with time is derived, about which, quantita-tive derivation verifies the connections between fracture healing and failure. The hy-draulic performance will change upon the distant earthquake in the process of rockfracture healing. To find out the theory behind this phenomenon, single rock fractureshear test is conducted and the shear deformation is discussed. And also, the CoulombRule is verified. Especially, the author explores the shear dilatancy phenomenondeeply and concludes that the shear dilatancy is a key factor in affecting the fault zonepermeability upon distant earthquakes. In addition, the author derives quantification-ally the fluid pressure and permeability changes with shear dilatancy. Results showwhen the rock fracture volume dilates, the fluid pressure will reduce to reciprocaltimes of volume dilatancy ratio and the permeability will increase to square times ofvolume dilatancy ratio.On the basis of what has been discussed above, the creep-seepage coupled ana-lytical model for fault zone is built to simulate the real underground hydraulic per-formance. Results show the time-related evolution of volume strain, fracture aperture,permeability and fluid pressure. And also, the Weibull distribution of fracture shearstrength is discussed, which provides a visible way to explain rock failure. The pa-per’s conclusions provide references for underground construction seepage analysis,fractured rock healing and hydraulic response triggered by distant earthquakes.