Study On Seepage Characteristics Of Rock After Post-peak Fracture And Microbial Remediation

As a kind of geological material,rock usually contains fracture or fracture network after a long period of geological tectonic movement,natural erosion,and engineering disturbance.Seepage of fracture rock involves underground energy storage,deep storage of underground nuclear waste,natural gas exploitation and other engineering fields.After the rock mass originally in the state of natural stress is disturbed by engineering,the stress state is adjusted,and the mechanics and seepage characteristics of fractures in the rock are affected,which controls the stability of the rock mass Therefore,it is of great theoretical significance to understand the seepage characteristics of fractured rock under the action of complex stress paths,and it is of great engineering application value to carry out the research on fracture rock repair and seepage modification.Taking fractured sandstone and granite as the research object,aiming at revealing the seepage characteristics of post-peak fractured rock in the process of loading and unloading and reducing the permeability of fractured rock as the main objective,a self-developed temperature-stress-seepage multi-field coupled rock triaxial test system was used to carry out seepage tests of post-peak fractured rock under the process of loading and unloading pressure.And the microbial fracture rock repair tests were also carried out.The main research results are as follows:(1)Under the action of high hydraulic gradient and high confining pressure,the seepage characteristics of fractured rock change from linear Darcy flow to nonlinear flow.The Forchheimer formula can be used to fit the nonlinear seepage process well,and the nonlinear influence factor E=0.1 can be used as the critical point to distinguish the linear flow from the nonlinear flow.During the unloading process,when the seepage pressure of the fracture surface is in a low state,the permeability of the fracture surface does not increase but decreases,indicating that the higher effective stress after unloading further reduces the opening of the fracture surface.(2)Under the action of cyclic loading and unloading of confining pressure,the difference of fracture permeability and the loss of seepage flow decrease with the increase of cyclic loading and unloading times.The first loading and unloading stress cycle has the greatest influence on the permeability loss of fracture surface.In the unloading process,the recovery of seepage capacity of fracture surface has obvious lag effect.However,under the action of cyclic loading and unloading of axial pressure,the axial pressure causes dilatation of the sample,and the evolution of each permeability parameter is quite different from that under confining pressure.(3)Microbial induced carbonate precipitation has a good effect on repairing rock fractures and reducing fracture permeability,the repaired rock sample has a certain mechanical strength and structural integrity.Comparing the seepage performance of the samples before and after repair,it can be found that the cementation of calcium carbonate precipitated in the fractured rock can effectively reduce the seepage capacity of the rock and improve the anti-seepage performance of the rock.With the increase of calcium carbonate deposition area,the anti-seepage ability of fracture surface is improved.