Creep deformation and permeability evolution of the K1/J2 paleoweathered rocks in the bending zone under triaxial unloading-loading confining pressure

The paleoweathered rock in the K-1/J(2) unconformity contact zone (K-1/J(2) PWR) in the Ordos Basin is the key aquiclude under the Cretaceous deposit. Creep deformation and permeability evolution of K-1/J(2) PWR in the bending zone under triaxial unloading-loading confining pressure (TULCP) path was carried out using the GDS triaxial experimental system, which is of great value for scientific interpretation of leakage from Cretaceous aquifers and regional water-level decline. Results show that under TULCP, the creep strain and the creep strain rate of the K-1/J(2) PWR exhibits three stages: transient strain, primary creep, and second creep. In the confining pressure unloading (CPU) creep stage, the creep strain increases continuously with the step-by-step of CPU; however, the change in permeability is not monotonic. In the confining pressure loading (CPL) creep stage, the creep strain decreases in the transient strain stage and slightly increases in the primary creep and second creep stages, as well as the permeability decreases continuously with the step-by-step of CPL. The average creep rate and average permeability in the second creep stage increase with the CPU and decrease with the CPL, and the relationship between the two can be expressed by an exponential function. Meanwhile, the creep strain increment increases with the increase in the clay mineral contents (CMC) and deviatoric stress. With the increase in the CMC, the rate of increase of the average permeability in the second creep stage increase during the CPU creep stage, and the rate of decrease of the average permeability in the second creep stage increase during the CPL creep stage.