MICROANALYSIS OF PROGRESSIVE SHEAR FAILURE ON CONTACT INTERFACE OF SILT AND NEW FILL

The contact surface of the silt soil and the new fill in the raising earth dam from upstream is the weak part of the whole dam body. This paper studied the progressive shear failure characteristics of the contact interface under different working conditions. It took the raising earth dam project from upstream deposited mud in Nanchuan Reservoir, Xiji County, the southern mountainous area of Ningxia, China as the research object. On the basis of improving the conventional strain-type direct shear instrument, using the electron microscope scanning technology, the microscopic analysis of the progressive shear of the contact interface was explained by controlling the shear displacement increment. Finally, the stepwise regression analysis method was used to obtain the significant variable of the micro-structure that affected the strength of the contact interface. Their regression equation was established. The results show that the silt soil in different compaction states causes interface particle cementation and structural changes, which is the main reason for increasing the interface shear strength. There is an interface "optimal adhesion" state. Meanwhile, with the increase of shear displacement, the interfacial soil particles are gradually developed into a flaky structure arranged in face-to-face and edge-to-face contact orientation from the independently distributed single-grain structure contact form. Finally they formed an incompressible block shaped pellet structure. And the change law of interface pore micro-structure parameters is related to the change of macroscopic cohesion and internal friction angle. Therefore, the results of this study can provide a certain reference for the construction of silt surface dam.