Study On Permeability And Damage Evolution Mechanism Of Rock Bearing Process Under Seepage Pressure

As for the underground mining,water conservancy and hydropower engineering,underground tunnel and other engineering,rocks are often in the coupled environment of stress field and seepage field.On the one hand,with the human disturbance,the crustal stress field in the surrounding rock will change,which induces the deformation of rock and the expansion of the crack,and eventually affects the permeability of the rock.On the other hand,under the action of water osmotic pressure,the mechanical properties of rock mass will change and influence the distribution of ground stress,which is called Coupling of Seepage and Stress.For the rock mass engineering under the interaction of seepage and stress,the opening and closing of the internal fissure of the rock material after the disturbed stress will result in the volume expansion and compression of the rock.And influence the permeability and damage evolution of rock directly.Based on this,the three axial compression test of the same confining pressure with different seepage pressure is carried out in this study.Based on experimental results,the evolution characteristics of the permeability,micro morphology of rock fracture surface and the failure mechanism of rock damage under different osmotic pressure are discussed.In addition,the subsection statistics damage constitutive model of rock is established bases on Weibull distribution.The main conclusions of this study are as follows:(1)Under the action of osmotic pressure,the permeability of rock increases gradually with the increase of seepage pressure in every stage,and the permeability of rock increases sharply during the yield stage,and the way of increase gradually transforms from "jump" to "gradual" with the increase of seepage pressure.(2)Seepage pressure can reduce the ability of rock to resist deformation,and the radial strain is more sensitive to the change of seepage pressure than axial strain.(3)Under the influence of seepage pressure,the characteristic stress values of the rock show different degrees of weakening.The effect of seepage pressure on the closure stress and initiation stress is basically the same.Compared with the peak stress,the peak stress is weakened more obviously.(4)Analysising the relevance of the permeability and the characteristic stress values under different seepage pressure,the function relationship between the characteristic stress values and the seepage pressure is established.(5)According to the statistics,the rock macroscopic fracture morphology is closely related to the osmotic pressure.When the seepage pressure is low,the rock fracture surface morphology mainly presents a single oblique fracture surface,and the rock sample is divided into the upper and lower triangle cones.When the osmotic pressure is high,the rock sample is controlled by multiple fracture surfaces,and the rock sample has a high degree of fragmentation.(6)The SEM images of the fracture surface of rock samples under each osmotic pressure are shown to show that the single oblique fracture surface appearing at low pressure is mainly caused by the shear failure mechanism;When the osmotic pressure is high,the fracture surface of rock is mainly caused by tension and shear failure mechanism.(7)Based on the Weibull distribution,a piecewise statistical damage constitutive model considering seepage pressure is established and improved.Compared with the theoretical curve and experimental curve,the agreement between them is good.