Experimental Study And Numerical Simulation Of Unsaturated Hydraulic Parameters Of Single Rock Fracture

Unsaturated seepage is a common phenomenon in fractured rock mass.Due to its important influence on slope stability,secondary oil exploitation,nuclear waste disposal and other engineering problems,and the continuous increase of engineering demand in the above mentioned fields at home and abroad,the study of unsaturated seepage in fractured rock mass has become a hot issue in the geotechnical field.The single fracture is a basic component of the fractured rock mass network.Therefore,the research on the unsaturated seepage in the single fracture is the foundation of the research on the unsaturated seepage of the fractured rock mass.The accurate determination of the unsaturated hydraulic parameters of the single fracture is the key to the numerical analysis of the unsaturated seepage of the fractured rock mass.In view of the shortage of unsaturated hydraulic parameters of single fracture in rock mass,the research status of single fracture unsaturated hydraulic parameter is summarized.On the basis of summarizing the predecessors' research results,the physical model test and numerical simulation of single fractures unsaturated hydraulic parameter and the unsaturated hydraulic parameter fitting formula were studied.The main work and results are as follows:(1)On the premise of confirming the reliability of the unsaturated seepage test system for rock fractures,unsaturated seepage tests are carried out for the natural fractures of three different lithologies.The results show that most of the water will be lost and the residual saturation will be reached when the capillary pressure is not too high;The decreasing process of unsaturated permeability coefficient with the increase of capillary pressure can be divided into three stages: stable stage,rapid decline stage and gentle decline stage.By comparing with the generalized fracture model,it is found that the natural fracture has greater residual saturation and the hysteresis between water absorption and drainage is more obvious.(2)Based on the measured fracture opening distribution and the determination program FRACTURE for the unsaturated hydraulic parameter by the research group,numerical tests were conducted on the unsaturated seepage flow of natural fractures in three different lithologies,and the water holding curve and the unsaturated permeability coefficient curve of fractures were obtained.Because the capillary absorption theory and "trap" effect are taken into account when the fissure water-filled area is generated by this numerical method,the lag between the water absorption and drainage process of the fissure can be simulated.The water holding curve and unsaturated permeability coefficient curve obtained by numerical simulation are compared with the results of physical model test,and the results obtained by the two methods are basically consistent.(3)Based on the fracture water holding curve measured by physical model test,two commonly used fitting models are compared and analyzed,and it is found that the VG model is better than the BC model in fitting the fracture water holding curve.According to the physical model test of fracture unsaturated permeability and capillary pressure curve,the fitting formula for the relationship among unsaturated permeability and capillary pressure is deduced.The test results of different lithology fractures are compared with the existing fitting formulas and the reasonable reliability of the fitting formula established in this paper is verified.