Study On Strength And Deformation Characteristics Of Gangue Roadbed Filling

China is rich in coal resources,and the current energy structure is based on coal,showing a trend of diversified development.Coal has made a great contribution to the development of national economy,but it has also brought about a great impact on the social environment.In the process of coal mining,gangue will be discharged as solid waste,and the gangue mountain formed by the massive accumulation of gangue will occupy land,pollute water resources,and even spontaneously ignite,resulting in landslide and debris flow and other disasters.Therefore,it is of great significance to improve the comprehensive utilization of coal gangue and solve the social and environmental problems caused by coal gangue to maintain the sustainable development of mine resources.Coal gangue can be used as a kind of roadbed filling material in engineering application,which has higher structural stability,larger bearing capacity and good water permeability in the case of relatively dense.A large number of scholars have analyzed the feasibility of using coal gangue as roadbed filler in combination with engineering practice and studied its dynamic and static characteristics through triaxial tests.However,most of the existing triaxial tests on the mechanical properties of gangue subgrade fillings are medium and small triaxial tests,and the large triaxial tests on gangue are rarely reported.Moreover,coal gangue has the characteristics of low particle strength and easy crushing,and particle crushing will affect the compactability degree and strength.However,there are few studies on particle crushing characteristics of coal gangue.Therefore,in this paper,the strength deformation characteristics and particle crushing characteristics of gangue roadbed filler were obtained through the large triaxial tests under different test conditions and the screening of the samples after the tests.The main research contents and conclusions are as follows:（1）The basic physical properties of coal gangue coarse-grained soil are studied.The microstructure,mineral composition,moisture content and maximum dry density of coal gangue coarse-grained soil were analyzed by scanning electron microscope（SEM）test,X-ray diffraction,moisture content test and compaction test.The results show that the surface of coal gangue is relatively rough,the number of small cracks on the surface and inside the particle is few,and no obvious big cracks are found.The gangue is porous and the structure is relatively dense.Its main mineral components are quartz,calcite,magnesium calcite,carboborosilicate calcium magnesite,magnesium silicate,spinel olivine and alumina,etc.The area,non-uniformity coefficient and curvature coefficient of the gradation curve all decrease with the increment of the gradation index A.The relationship between the maximum dry density and the area of the gradation curve is a quadratic function.There are obvious extreme points in the fitting curve and the peak value is obtained when the A value is 0.55～0.63.（2）The static properties of coal gangue coarse-grained soil are studied.The axial strain of coal gangue roadbed filler increases with the increase of axial stress,and the curves are all convex and have no obvious peak value,which belongs to strain hardening type.For samples with the same compaction degree and different gradations,when the confining pressure remains unchanged,the axial stress under the same axial strain increases first and then decreases with the increase of A value,that is,the coarse particle content,and the volumetric strain increases first,then decreases and then increases with the increase of gradation index A value.Other things being equal,the phase coaxial variable under axial stress increases with the increase of the degree of compaction,phase coaxial under the change of body strain decreases with the increase of the degree of compaction,the compaction degree of 93%,continue to improve the degree of compaction and the decrease of body strain effect on strength growth effects are not obvious,and coal gangue as subgrade filling degree of compaction shall meet not less than93%;The experimental results show that the stress-strain curves of coal gangue can be fitted by the Duncan-Chang double curve constitutive model,and the specific parameters of the hyperbolic constitutive model are obtained.When the coarse particle content is higher than 60%,the internal friction angle does not change much with the increase of the coarse particle content.The strength of the sample increases first and then decreases with the increase of the coarse particle content,which is mainly reflected in the change of the apparent cohesion.（3）The particle breaking characteristics of coal gangue coarse-grained soil were studied.When the fractal dimension D is taken as the metric index of coal gangue particle breakage,the value of fractal dimension D increases with the decrease of coarse particle content and the increase of fine particle content.The degree of particle breakage increases with the increase of confining pressure,coarse grain content and compaction degree.In confining pressure,grading the coarse aggregate content,degree of compaction in the three factors,confining pressure and size distribution are the main factors influencing the particle breakage,compaction have less effect on the particle breakage,regardless of the degree of compaction effect on coal gangue particle breakage,assumes that the fractal dimension is a function of the confining pressure and grading and the fractal dimension D and confining pressure ?₃/P_a and initial grading D₀expression.In order to analyze the influence of coal gangue particle breakage on the strength,the relationship between the peak internal friction angle and particle breakage was studied,and the relationship between the peak internal friction angle,the initial fractal dimension D₀ and the confining pressure was established.