动荷载作用下岩石非线性弹性响应研究

岩石是一种典型的颗粒孔隙介质。在冲击荷载下,即便是在作用荷载比较低的阶段,由于岩石内部自然缺陷的存在,应力波随着传播距离延伸,其幅值有较大的衰减。文中对饱油和饱水的砂岩、大理岩进行SHPB冲击试验,研究结果表明:对于同种岩石试样,饱油岩样的衰减系数比饱水样品的小;对于不同的岩样,孔隙率大的岩样相应的衰减系数大。应力波在饱和介质中的衰减与介质中液体的粘滞系数有关。同时,材料中的孔隙和液体的存在对应力波的弥散特征也有一定的影响。然后基于Preisach-Mayergoyz(P-M)空间模型对冲击荷载比较低的阶段,岩石内部应力波的衰减和弥散问题进行了较详细的分析,得到了一些初步结论。本研究对于石油开采、物探以及岩土工程有一定的意义。

Investigation of the non-linear elastic responses of rock under impact loading

The rock is a kind of particulate porous material.Rocks typically have several cracks and flaws,and for this reason the amplitude of the stress wave attenuates with propagation distance when the rock specimen is loaded under loads that are substantially lower than the yield point.We have conducted a series of experiments on the Split Hopkinson Pressure Bar(SHPB) to reveal the rules of the propagation of stress waves in rocks under impact loading.These loads are also far below the yield point of rocks.Two rock types,marble and red stone,in two kinds of states,water-saturated and oil-saturated,were investigated.Preliminary results show that the propagation of the stress wave is greatly affected by the contained liquid and the porosity of the rocks.The stress wave attenuates more seriously in water-saturated sample than in the oil-saturated one for the same rock.While for different rocks,stress waves attenuate more seriously in the rocks with higher porosity than in those with lower porosity.The attenuation of stress waves in fully saturated samples is evidently affected by the viscous coefficient of the liquid contained in the sample.The dispersion of stress waves caused by the contained liquid and the pore spaces in the sample is also discussed.The Preisach-Mayergoyz(P-M) model was proposed by Preisach and improved by Mayergoyz is employed to describe the elastic behavior of non-linear hysteretic materials.We have carried out some model simulations under the P-M model,considering the above-mentioned experimental results.The simulation shows that it is important to introduce the viscous coefficient of liquid and the frequency into the P-M model in order to simulate the attenuation and the dispersion of stress waves.However,further work is needed to improve the model simulation,which is meaningful for petroleum exploitation,geophysical exploration and geotechnical engineering.