| In recent years,landslide dams have been widely developed all over the world,especially in mountainous valleys.The stability,homogeneity,integrity and structural strength of the dam body of the landslide dam are significantly lower than those of the rockfill dam.If the engineering characteristics of its dam materials are not clear,it may bring serious consequence if it is treated or reinforced according to the risk elimination and reinforcement methods of the conventional rockfill dam.The laboratory test and research on dam material for landslide are carried out with reference to the relevant specifications of rockfill dam or coarse-grained material,but there are significant differences in dam structure,particle composition and filling state between them.This thesis summarizes the main differences between landslide dam and rockfill dam by investigating many dam at home and abroad,carries out dry density test,permeability coefficient test and large-scale saturated triaxial shear test with different grading characteristics,studies the influence of different grading characteristics on the compactness and permeability of dam materials,and summarizes the variation law of mechanical and deformation characteristics of dam materials with grading characteristics,The main conclusions are as follows:(1)Compared with the manually designed rockfill dam,the spatial distribution of particle gradation of landslide dam is more discrete,its gradation distribution is wider,and the coarse and fine particles in the dam body are unevenly distributed in both horizontal and vertical directions,and the particle gradation in many parts is discontinuous.On the whole,there are more fine particles at the bottom of the dam body and more large particles at the top and periphery of the dam body.(2)Compared with continuous grading,discontinuous grading will reduce the compactness of dam material and increase the permeability of dam material.The fractal dimension of particle size can better reflect the variation law of dry density of dam materials,that is,with the increase of fractal dimension of particle size,the maximum dry density first increases and then decreases,while the minimum dry density gradually increases and finally tends to be stable.The limit particle size and average particle size can better reflect the permeability of dam material,that is,the smaller the limit particle size is,the smaller the permeability coefficient of the sample is;The decrease of average particle size will reduce the permeability of dam material.(3)When the relative density is the same,the greater the porosity,the lower the shear strength and the worse the deformation resistance of the dam material;Compared with continuous graded dam material,discontinuous graded dam material has lower shear strength and poor deformation resistance.It is suggested that during the danger removal,reinforcement or reconstruction of the landslide dam,the number of mechanical rolling passes should be increased at the position with large porosity or discontinuous grading,so as to achieve higher compactness and improve its mechanical properties.(4)When scaling the dam material,the smaller the maximum particle size after scaling,the smaller the dry density and permeability coefficient of the dam material,the lower the shear strength,the smaller the deformation modulus,the smaller the influence of confining pressure,and the greater the difference between the mechanical and deformation characteristics of the dam material and the original graded dam material,that is,the test results after scaling overestimate the resistance to deformation of the actual dam.It is suggested that after obtaining the variation law of its parameters through the laboratory scale test of different maximum particle sizes,the results of the laboratory test should be corrected,and the dam body deformation analysis should be carried out using the test parameters of the dam material that are closer to the original gradation. |
