加卸载作用下裂隙岩芯渗透性变化规律研究

针对光滑平行板裂隙加载渗流规律难以准确反映实际工程裂隙岩体卸荷渗流特性的问题,利用水力压裂方法制作了天然岩芯裂隙,开展了裂隙试件受轴压、围压加载和卸载作用的渗流试验,并将裂隙试件的CT扫描图像导入ABAQUS软件,对粗糙裂隙受载时的应力和变形规律进行了数值模拟。结果表明:裂隙面的法向应力是影响裂隙渗流的主要因素;在加载阶段,粗糙裂隙面受载产生接触应力致使接触部分产生变形和破坏,裂隙接触刚度增大,裂隙宽度非线性减小,渗透率降低速率越来越小;在卸载阶段,弹性变形逐步恢复,裂隙宽度缓慢增加,渗透率先缓慢增大,当载荷卸到一定值后,在孔隙压力作用下裂隙张开、渗透率突然增大。研究结果表明了粗糙裂隙与光滑平行板裂隙对载荷敏感性不同的机理,反映了实际工程裂隙岩体卸荷渗流特性。

Probe to the permeability variation regularity of the fractured core rock under the impact of loading and unloading vibrations

The paper is aimed at an exploration of the seepage regularity of the smooth and parallel rock-plate fractures under the alternative loading and unloading impact both of the axial and circumferential pressure by means of the CT scanning image of the test specimens into ABAQUS through programming.What is more,since the CT scanning image of the test specimens into ABAQUS can hardly reflect the seepage characteristics of the fractured rocks accurately in the engineering practice concerned,we have managed to carry out a series of seepage experiments on the fractured specimens with the aforementioned pressure in hoping to trace the changing regularities of stress and deformation when the rough fractures are subject to the horizontal loads and vertical loads through numerical simulation,in addition to preparing the natural core fractures through hydraulic fracture,till the roughness of the fractures being made approximately to that of the natural fractures,And,finally,the experiments and numerical simulation indicate that it ought not to ignore the roughness of the fracture surfaces when it is necessary to make clear how the fractures can lead to the seepage under loading.What is more,since the normal stress of the fracture surface may serve as the main affecting factor of the rough fracture seepage,the surface tends to produce the contact stress in the stage of loading,which should account for the deformation and failure of the said surface.Further.more,with the increase of the fracture contact stiffness,the fracture may reduce the width of the surface nonlinearly,even leading to the narrowing and closer of the seepage channel,so as to make the rate of permeability lower and lower.On the other hand,in the stage of unloading,it would be possible for the elastic deformation to get gradually restored with the width of the fracture increasing slowly.Thus,correspondingly,the permeability may tend to increase slowly at first,and,then,when the unloading comes to a certain value,the permeability of the fracture would be growing suddenly under the effect of the pore pressure.Therefore,what is said above,is nothing but the embodiment of the mechanism that accounts for the different sensitivities of the rough fracture and smooth parallel plate fracture due to the charge or discharge of the external loads.The results literally reflect the fracture characteristics of the rock mass in the loading and unloading alteration in the engineering practice.