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Elastoplastic response of saturated rocks subjected to multilevel cyclic loading
Summary
This study analyzed the elastoplastic behavior of fluid-saturated rocks under multi-level cyclic loading using the endochronic theory of plasticity, fitting model predictions to experimental data from fluid-saturated marble and sandstone. The results improve constitutive models for predicting how porous, fluid-filled rocks respond to repeated stress cycling.
Elastoplasticity response of fluid saturated rocks with endochronic theory is analyzed according to the multilevel cyclic loading experimental data of fluid saturated marbles and sandstones.In the procedure of multilevel cyclic loading,the stress-strain curve displays cusped hysteresis loop,which moves toward the direction of strain increasing with time and strain amplitude increasing,indicating the generation of plastic strain continuously.According to the stress and strain values at the reversal points of hysteresis loops,the corresponding parameters in the endochronic equations can be determined by the method of least square fitting.Analysis demonstrates that plastic strain is small relative to elastic strain,and getting smaller in the total strain with cyclic number.Viscoelastic and microplastic strain components affect rock stiffness by time and strain amplitude respectively.At intermediate strain level,due to presence of microplastic strain component,hysteresis modulus of saturated marble and sandstone decreases with increase of strain amplitude,and is influenced by the type of pore fluid of rock.Hysteresis modulus of rock saturated with oil is larger than that of rock saturated with water,which has perhaps mainly relation with the viscosity of pore fluid within the rock.