Mechanical Properties And Stress-Strain Evolution Mechanism Of Contact Interface Between Upstream Silt Foundation And New Fill Dam

The technique of silt surface damming in front of dam is a common construction method in the project of removing danger and strengthening reservoir in loess hilly area in southern Ningxia.However,the dam construction technology,which has accumulated a lot of construction experience in engineering practice,has some problems such as theoretical research lagging behind,lack of system and complete quantitative research results guiding engineering practice and so on.Field investigation shows that the maximum position of the dam body is shifted to the contact surface of the silt dam foundation and the newly filled dam body,where the deformation is large,and the slip damage along the silt surface is easy to occur,which is the weak part of the silt surface in front of the dam.Based on the research results of the research on the mechanical properties of the contact surface of the silt and structure in the existing literature,this thesis analyzes the difference between the basic physical mechanical parameters of the silt soil and the new fill on the basis of reference to the actual engineering survey report and the design of the construction organization.Through the design of the improved conventional direct shear instrument and the tungsten electron microscope scanner,the paper designs the shearing of the contact interface of the silt-new fill,the scanning electron microscope experiment,the analysis of the physical mechanical properties and structural characteristics of the contact interface of the silt-new fill.Finally,the interaction mechanics model of the contact interface between silt and new fill is established by ABAQUS finite element software,and the stress-strain evolution of the progressive shear failure of the interface was numerically simulated,and the contact model was applied to the dam body in actual engineering.The main research contents and conclusions are as follows.(1)The moisture content of the undisturbed silt is high by the basic physical and mechanical parameters of the new fill,the content of the new fill in the range of 0.3-50?m is 80.7%,the range of 10-50?m is 61.92%,and the range of>100?m is 1.27%.whereas the content of silt grain diameter in the range of 0.3-50?m was 72.7%;52.19%in the range of 10-50?m and 10.7%in the range of>100?m,all belong to silty clay.(2)The macro-shear test of the contact interface shows that under the same compaction state,as the moisture content of the sludge increases,the shear strength of the contact interface decreases first and then decreases significantly.The interface cohesion increases first and then decreases rapidly.When the water content of the sludge is the same,with the increase of the degree of compaction,the shear strength of the contact surface increases significantly,and the increase of the interface cohesion increases from slow to fast,and the overall trend is increasing.The influence of water content and compaction degree(within the test setting range)on the friction angle in the contact surface is relatively small.(3)According to the analysis of scanning electron microscopy results of different compaction degrees and different shearing stages of the obtained interface between the silt and new fill,it is found that silt soils with different compaction states cause changes in the particle interface cementation and soil particle structure at the contact interface,which affects the interface resistance.The main reason for increased shear strength.As the shear displacement increases,the contact interface soil particles form a single-grained structure with independent distribution,and gradually develop into a sheet-like structure arranged in a face-to-face,edge-to-face contact orientation,and eventually form a non-compressible block-like granular mass.structure.Through stepwise regression analysis,the significant variables that affect the cohesion and internal friction angle of the contact interface are the average pore fractal dimension,average pore diameter,and orientation probability entropy,and reflect the shear strength characteristics and pore micro-structure parameters of the contact interface.Regression equations between correlations have higher fitting accuracy.(4)A finite element numerical simulation of the progressive shear failure of the silt-new fill interface is found that the shear test of the silt-new fill interface is not a unit body test.As the shear displacement increases,the contact interface and the internal stress and strain of the soil sample are continuously adjusted.At the initial stage of shearing,the compressive stress at the interface remained basically the same,and the shearing stress at the interface was adjusted quickly,showing a distribution law of large ends and small middle ends along the shearing direction.As the shear displacement continued to increase,the interface shear force began to be dominated by sliding friction,mainly concentrated at both ends,and the middle part remained basically unchanged.The entire contact interface is a gradual failure process extending from both ends to the middle.In actual engineering,the shearing characteristics of the interface between the silt dam foundation and the newly filled dam body are basically consistent with the model test results.