多级循环荷载下饱和岩石的弹塑性响应

根据流体饱和的大理岩和砂岩的多级循环荷载试验,利用内时理论模型,分析了流体饱和岩石的弹塑性响应。在多级循环荷载过程中,岩石的应力-应变关系呈现尖叶状的滞后回线,滞后回线随着循环次数的增加向应变增大的方向移动,并不断地产生弹塑性应变。分析表明,多级循环荷载过程中,塑性应变相对于弹性应变而言是比较小的,而且随着循环数的增加,产生的塑性应变占整个应变总量的比例越来越小。黏弹性和微塑性分量分别通过时间和振幅因素影响了岩石的刚度,在中等应变范围内微塑性分量的存在使得饱和大理岩和砂岩的滞后模量随着应变振幅的增加而减小,而且孔隙流体的类型对岩石的滞后模量有影响。石油饱和岩石的滞后模量比水饱和岩石的滞后模量要大,这可能与孔隙流体的黏滞性有很大的关系。

Elastoplastic response of saturated rocks subjected to multilevel cyclic loading

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.