Uniaxial Deformation Behaviour And Its Evolution Law Of A Sandstone-mudstone Particle Mixture Under Periodic Saturation Condition

The sandstone-mudstone particle mixture was widely used as a main filled material in the embankment engineering in Three Gorges Reservoir bank slope,such as dams,wharfs.With the rise and fall of reservoir water level,the sandstone and mudstone particle mixture were suffered from wet-drying cycling.The wet-dry cycling leads to the decrease of strength of the mixture,the deformation of the mixture increase.The wetting and dry cycling may affect the safety of structure.Experimental study on the compression deformation characteristics and its evolution regularity of the sandstone-mudstone particle mixture under wet-dry cycling does therefore have important theoretical significance and construction value.Depend on the financial supports from the National Natural Science Foundation of China“Mechanism and evolutionary process of deterioration on a sandstone-mudstone particle mixture induced by periodic saturation”,using the self-developed“method and device of drying-wetting cycle compression test”and“the instruments of drying-wetting cycle static lateral pressure coefficient test”,the compression test methods of periodically saturated sandstone and mudstone mixture was proposed.Through the experimental study and theoretical analysis,the rheological properties of the mixture,the periodic characteristics of compression deformation of saturated sand mudstone mixture,static lateral pressure coefficient and periodically saturated particle size effectwere revealed.The rheological calculation method,the periodic saturated degradation deformation and coefficient K₀ evolution equation were established.Based on the elliptic parabolic elastic-plastic model,the anisotropic elastic-plastic model of periodically saturated sandstone and mudstone mixture was established,and its rationality was verified.The achievements of this study are as follows:（1）The rheological properties of the sandstone and mudstone particle mixture were revealed and its rheological calculation method was proposed.A self-developed drying-wetting cycle compression test system was used to investigate the long term settlement after construction of high embankment of sandstone-mudstone mixture.Compression rheological tests of sandstone-mudstone particle mixture samples with four mixture ratio were carried out,which considered the wetting effects.The influence of axial pressure and sandstone-mudstone mixture ratio on the rheological test was studied.From the test results,it can be seen that the rheological process of the mixture can be divided into four stages:linear phase,rheological stage,again decay rheological phase and stable phase.In this paper,the rheological attenuation factor,attenuation creep critical strain and ultimate rheological strain were introduced,through the comparison analysis of test data,the secondary rheological model is put forward and the model can be used to describe the two-stage attenuation of sand shale mixture rheological characteristics.（2）The characteristics of later pressure coefficient,about the periodic and water-saturated mixture of sand-shale,were revealed.The evolution equation about static pressure coefficient was established.Using the self-developed“the instruments of drying-wetting cycle static lateral pressure coefficient test”,the experiment of static pressure coefficient is performed in different wet-drying cycling times,with 20%of sandstone and mudstone particles.The static later pressure’s experimental result of periodic and water-saturated mixture of sand-shale was achieved.The evolution law of static pressure coefficient about periodic and water-saturated mixture of sand-shale was analyzed and the evolution equation was developed.As the times of periodic and water-saturated cycling increased,the static pressure coefficients were all increased at first and tended to be stable at last,showed the increased tendency of Logarithm.（3）The deterioration mechanism of periodic saturated mixture was revealed,the method to calculate the deformation was carried out.The compression test about the sandstone and mudstone particle mixture,in periodic saturated environment,under the different vertical pressure,was performed.The deterioration mechanism and law to the periodic and water-saturated phenomenon was analyzed.The deterioration induced by periodic saturated circumstances was increased with the cycling times increased,and was went to stable in the end.The Pair Index model of maximum cracking strain was introduced to modify the previous model,the modified model was able to describe the main characteristics of deterioration and distortion in periodic saturated mixture.With the vertical pressure increased,the percentage of particle breakage in periodic and water-saturated mixture was also increased,the relation can be displayed as a power function.（4）The influence of ultra-size particles on the deterioration deformation of the mixture under wet-dry cycling was revealed,the standard particle size ratio of wet-dry cycling laboratory experiment was developed.The compression test of a sandstone-mudstone particle mixture under wet-dry cycling with different particle sizes and different contents of steel balls was carried out.The influence of different particle sizes and contents of steel balls on axial strain of mixture under wet-dry cycling was analyzed.The result shows that,the deterioration deformation increased with size of ultra-size particles raised,and increased with the diameter particles volume fraction increased.At the high axial pressure level,the size effect was obvious.Under the low circumferential stress,when particle size ratio greater than 3.7,the size effect can be eliminated.（5）The stress ratio associated with the wet-dry cycling K₀ ratio is introduced,anisotropic elastic-plastic model of sandstone and mudstone particle mixture under wet-dry cycling were developed.The anisotropic stress characteristics which is caused by the variation of the K₀ ratio of the sandstone-mudstone particle mixture under wet-dry cycling is reflected by the rotation hardening axis.Based on the elastic plastic model of the double yield surface,the stress ratio associated with the pressure ratio of K₀ was introduced.By stress transformation method,rotate the hardened axis of the elliptic parabola of the double yield surface to the K₀ line.An anisotropic elastic-plastic model of the sandstone-mudstone particle mixture under wet-dry cycling were developed which can reflect the dilatation,initial anisotropy and the deterioration of wet-dry cycling and the variation of the K₀ ratio.Through verification,the improved model can reflect the characteristics of the deterioration of wet-dry cycling,and the data is well matched.The improved method to calculate the settlement of the filling body of sandstone-mudstone mixture was studied.The settlement of the 40 m high filling body was 77.4 cm.Effective measures is necessarry for the filling body in the flood season.