Research On The Development Law And Strength Change Law Of Muddy Interbed Cracks Under The Conditions Of Dry And Wet Cycles

Weak muddy intercalations(WMI)are one of the common soft interlayers in bedding slopes.The mechanical properties of WMI are very weak and unstable,which are the main factors that cause the stability problems of slopes.WMI are often affected by wetting and drying cycles with the change of natural climate and weather,especially the excavated slopes and slipping parts.The drying and wetting cycle will cause irreversible damage to the meso structure of WMI,thereby reducing its strength;At the same time,many fissures will be produced in theWMI,which has a serious influence on its permeability.In the rainy season,the intensity of rainwater infiltration is reduced rapidly,resulting in the occurrence of landslides.In this paper,the original specimens of the WMI in the back wall of the Xiaobangshang landslide in Nanjiang County,Bazhong City,Sichuan province are taken as the test subjects.Through the dry and wet cycle test of the WMI,the law of the fracture development and change of the WMI were studied,and the change of the shear strength after the dry and wet cycle was measured.The main contents and results were as follows:(1)The dry and wet cycle test was carried out by simulating the extreme weather conditions in the natural world.The specimens after each cycle were photographed by the self designed photographing device,and the fractured images were obtained under the dry and wet cycle of the WMI.Then,after comparing the theoretical analysis of image processing with the actual processing results of MATLAB,the image processing method of muddy interlayer cracks is obtained.(2)Through a series of image processing process of the characteristic image of the crack,the feature image of the crack image is obtained,and the length,the average width,the area and the crack degree of the crack are obtained by the feature extraction.The fracture degree of the specimens after different drying and wetting cycles is analyzed,and the change law of the crack degree of the WMI is obtained,with the increase of the dry and wet cycle number the crack degree first increase and then tends to be steady.The change rule of the crack degree of the WMI can provide a basis for studying the relationship between the permeability of the WMI and the drying wetting cycle.(3)Under the condition of the same moisture content,direct shear tests of the specimens after different cycle times were carried out.It is obtained that the shear strength of the WMI gradually decreases with the increase of dry and wet cycle times,and gradually tends to be stable in the later dry and wet cycle.By fitting the relationship between the shear strength and the vertical pressure of the WMI,the cohesive C value of the WMI decreases with the increase of the dry and wet cycle times,and then tends to one critical value,and friction angle value tend to be stable with the increase of wetting and drying cycle times.This phenomenon indicates that the dry wet cycle destroys the particle connection of the WMI and weakens the shear strength of the WMI.(4)The relationship curve of the crack degree and the cohesion c was fitted to study the relationship between the strength and the crack degree.It was found that the crack degree had an important influence on the cohesive C.With the increase of the crack degree,the cohesive C of the WMI showed a downward trend on the whole.When the crack degree is below 1.3,the cohesion c decreases slowly;When the crack degree is higher than 1.3,the descending speed increases sharply.The strength of WMI can be predicted according to the relationship at a certain extent.