Research On Particle Characteristic Analysis And Physical Mechanics Properties Of Fluvioglacial Deposits In High-cold Region

With the deepening of the development of the western region,large-scale transportation infrastructure and hydropower projects in the high altitude areas of Southwest China have been carried out in succession.The construction of Fluvioglacial Deposits and Glacial Till distribution areas are increasing,but the physical and engineering properties of Fluvioglacial Deposits and Glacial Till are still short of the physical and engineering properties.Lack of systematic research,less experience in engineering,the experience of reference is relatively scarce,the construction of Fluvioglacial Deposits and Glacial Till at home and abroad is still more prudent,most of the construction and construction projects are still dominated by avoidance.Therefore,to study the physical and mechanical properties and particle characteristics of Fluvioglacial Deposits and Glacial Till,and to explore the characteristics of slope deformation and failure under the conditions of cold and thawing cycle,which has important engineering significance and practical value for the design and construction of subgrade engineering.On the basis of summarizing and analyzing the related research results of Fluvioglacial Deposits and Glacial Till at home and abroad,the basic soil test,the particle shape feature image analysis,the large three axis test and the shallow slip element model test under the freeze-thaw cycle are used respectively to analyse and study the geotechnical characteristics,particle shape characteristics and the deformation and failure response of freezing and thawing cycle from the Fluvioglacial Deposits and Glacial Till in Kangding Luding area.The following conclusions are obtained:?1?The classification of Fluvioglacial Deposits and Glacial Till is determined through indoor physical properties test.The gradation of Glacial Till is good,and it can be used as A₁group filler in subgrade.The gradation of Fluvioglacial Deposits accumulation is mostly bad,but it can be used as packing of B₁ group.The maximum dry density of the two kinds of soil samples are about 2.2 g/cm3,and the optimum water content is about 6.7%;There are two transport and sorting accumulation of water flow in Fluvioglacial Deposits.The grain density of Fluvioglacial Deposits below 5mm is slightly larger than that of Glacial Till.With the decrease of the distribution elevation,the fine grain content of Fluvioglacial Deposits is more,and the plastic index and liquid limit water content are higher than that of Glacial Till.?2?The particle shape characteristics of Fluvioglacial Deposits and Glacial Till samples are analyzed by microscopic imaging and digital image processing technology.The results show that the Glacial Till filler particles are stronger than those of the Fluvioglacial Deposits,and the edges and corners are closer;the fractal calculation table of the grain contour and the fractal dimension distribution area of the Fluvioglacial Deposits accumulation are shown.The fractal dimension distribution interval of the Glacial Till particles is[0.9661,1.2816],which is[0.9743,1.454].The fractal dimension of the Fluvioglacial Deposits is wider and the upper limit is higher.But compared with graded crushed stones,the grain boundary contour curves of the two kinds of soils are more regular,the surface is smoother and the block is weaker,and the engineering characteristics are slightly worse than the graded aggregate.?3?Using a load servo large three axis tester with a diameter of 15 cm in diameter,a three axis shear test under three horizontal confining pressure was carried out for two kinds of Fluvioglacial Deposits with two kinds of compaction.The unconsolidated undrained strength parameters and effective stress intensity parameters were obtained.With the increase of the degree of compaction,the increase of cohesive force and effective cohesion of the sample is 117%and 18%respectively,and the increase of internal friction angle and effective internal friction angle are 16%and 17%respectively.Based on the relationship fitting of Ducan and Chang model,the experimental constants of hyperbola are obtained.The results show that with the increase of confining pressure,the initial tangent modulus of soil decreases and the strength asymptote value increases.With the same confining pressure,with the increase of compactness,the initial tangent modulus of soil decreases and the strength asymptote value has the trend of increasing.?4?In view of the characteristics of the high and cold environment of the Fluvioglacial Deposits slope,the freezing and thawing cyclic creep test of the shallow surface deformation of the critical slope is designed and carried out.The results show that the slope appears the creep of the shallow surface of the slope,and the slippage of the top,middle and bottom slope of the slope is 1.6cm and 1.,respectively,under the accumulation of 6 freeze-thaw cycles.3cm and 0.6cm;when the slope foot is set up,the slope foot is basically free from sliding and presents a good restraint effect.The slope only appears about 3⁴mm vertical frost heave and thawing.When the simulated natural rainfall increases the water supply on the slope,the creep of the slope under the freeze-thaw cycle is enhanced.The frost heave test results show that the frost heave and thawing of soil increases linearly with the increase of soil moisture content,and the vertical expansion is larger than the lateral expansion in the freeze-thaw creep deformation.With the increase of the degree of compaction,the frost heave and thawing amount of soil increases first and then decreases.The maximum is reached under the condition of 85%.