Research On Seepage And Mechanical Properties Of Silty Mudstone With Fissures Based On Similarity Principle

Silty mudstone is widely distributed in China,mainly concentrated in the southern region.Since the rock contains a large number of clay minerals inside,it has the characteristics of easy contraction and cracking with water loss and softening with water expansion.In recent years,with the rapid development of infrastructure construction in the south,a large number of silty mudstone slopes have been formed by excavation.Under the action of seasonal rainfall,the silty mudstone rock mass develops and expands with time,leading to the gradual deformation and instability of the slope.Therefore,the mechanical property test of the silty mudstone rock mass is meaningful for the analysis of long-term stability of the slope.However,field sampling tends to damage the samples,and the success rate of sample preparation is low and costly.The test results tend to show great randomness and cannot reflect the complete mechanical properties of the original rock.In view of this,this paper selects suitable raw materials based on similarity theory,and through indoor tests,makes the similar material specimens reach the basic physical and mechanical indexes that can be compatible with the original rock through indoor tests,and carries out the one-dimensional seepage characteristics tests,prefabricated mechanical properties and damage characteristics tests under different forms of fracture state with the similar material specimens combined with the original rock.Conclusion as below:(1)The basic mineral composition of the silty mudstone was analyzed by XRD,and the basic physical and mechanical indexes of the original rock were obtained through laboratory tests;based on the similarity theory,the similarity ratio between the original rock and similar material specimens was determined by the gauge analysis method,and according to the basic principles of similar raw material selection,gypsum,barite powder,clay minerals(montmorillonite,illite,chlorite)and water were selected as raw materials to produce the similar material specimens.(2)The orthogonal design experiment was used to determine the influence of various factors on the basic physical and mechanical indexes of similar material specimens,and initially screen the level groups with similar indexes to the original rock;the swelling and water absorption tests were carried out to refine the indexes of similar material specimens twice,further screen the level groups,and finally determine the optimal ratio of similar materials.(3)A one-dimensional seepage model was developed to consider the effects of seepage direction,seepage thickness and other factors on the seepage characteristics of the specimens.The results show that the infiltration rate of the silty mudstone is greater than that of similar material specimens at the initial stage,and the increase of water content of similar material specimens is more stable than that of the original rock.(4)The mechanical properties of similar materials of prefabricated fractured silty mudstone were investigated from three aspects:theoretical analysis,laboratory tests,and numerical models.The reliability of the theoretical analysis was verified by uniaxial laboratory tests.The elastic modulus and peak strength have the same variation law,and the peak strength of single fissure,double fissure and vertical cross fissure decreases step by step.(5)The uniaxial model of similar material specimens was established using PFC2D,and the numerical simulation was inverted with the results of laboratory tests for the fine-scale parameters,so that the computer can reflect the uniaxial mechanical behavior of similar material specimens and further validate the results of theoretical analysis and laboratory tests.