Study On The Characteristics Of Fluvioglacial Deposits And Its Engineering Behavior In Highway

The Quaternary fluvioglacial deposited stratum is widely distributed in the high mountain and high latitude area of Western China. The project experience of building highway in fluvioglacial deposits area is deficient, and relative research about this field is not found. Meanwhile, the geological condition is complicated and the seismic activity is frequent in Western China. These questions must be considered when building highways. So, it is very important for theory and application to study project characteristics of fluvioglacial deposits - the new embankment fill material, and obtain its behavior in subgrade engineering. Relyed on the scientific and technological demonstration project of the Ministry of Transport of P.R.China - Yalu highway, through field survey, laboratory experiments, in-situ tests, theoritical analysis and numerical simulation, the characteristics of fluvioglacial deposits and its engineering behavior in highway were researched. The main contents include followings:1. The main causes of fluvioglacial deposits in YaLu highway were confirmed based on field survey, investigation and systemically summarizing the classification, causes and characteristics of fluvioglacial deposits. On the basis of the results of laboratory experiments and in-situ DPT, the soil parameters of 72 soil samples along the YaLu highway were statistically analyzed, and furthermore, the basic physico-mechanical properties of fluvioglacial deposits and the influence of soil type, natural state, the content of coarse (fine) grain and particle size & shape, etc. on fluvioglacial deposits was obtained.2. The fractal theory was introduced to analyze the grain composition of fluvioglacial deposited coarse grained soil. The fractal dimensions were obtained by the random-fuzzy linear regression method. The range of fractal dimension values and the relation between the fractal dimensions and soil types and buried depth; the fractal structure of fluvioglacial deposited coarse grained soil was classified into beeline type, V style, N style and A style, and the soil can be named tentatively by this; it was obtained that fluvioglacial deposited coarse grained soil was a kind of multi-fractal structure; based on Tailot ideal grain composition curve, the ideal fractal dimension value range of fluvioglacial deposited coarse grained soil was suggested so as to instruct the improving of fill.3. According to the granular characteristic of fluvioglacial deposited coarse grained soil, granular material theory was employed to study the constitutive relation of this kind of material. Fractal theory was introduced to reflect the multi-fractal characteristic of influvioglacial deposits. The shape of particle surface of fluvioglacial deposited coarse grained soil was described through the shape correction coefficient. Based on the virtual work principle, the relationship between the macroscopic stress tensor and microscopic fabric was obtained. Finally, a three-dimensional isotropy granular constitutive model was proposed, which could reflect the multi-fractal characteristic, particle characteristic and microscopic fabric and of fluvioglacial deposited coarse grained soil. This model was used to predict the settlement of fluvioglacial deposited coarse grained soil embankment.4. According to the granular material constitutive model established above, through grey relational grade analysis, the influencing rules of some parameters (including the equivalent particle size, coefficient of graininess revising, void ratio, normal contact stiffness and tangential contact stiffness) on the mechanic characteristic of fluvioglacial deposited coarse grained soil were obtained. And then, the mechanism of enhancing embankment's ability in resisting against deformation and failure by mechanical compaction was analyzed.5. Large-scale triaxial sheer tests of fluvioglacial deposited coarse grained soil were conducted based on the orthogonal design table L₉(3⁴) considering 4 factors, including content ratio of rock, content ratio of mud, compactness and reinforced layers.1) 9 kinds of representative grading curves were summed up from the grain composition curves of 72 soil samples of fluvioglacial deposits along the Yalu highway, the optimum water content were determined and the control standard on the permissible error of water content in construction being proposed.2) Under this experiment condition, the Mohr strength envelope of fluvioglacial deposited coarse grained soil was close to a straight line, the value of c in sheer strength would be in the range of 67-102kPa, and the stress-strain carve showed the characteristic of strain softening.3) The influencing rules of 4 factors on strength parameters were obtained and it was found out that there was a optimal mud content, which could make the strength of fluvioglacial deposited coarse grained soil reach the peak. So it was proposed that the mud content should be ensured during the construction.6. Based on stress path method and viscoelasticity theory, adopting the deformation parameters obtained by DPT, triaxial shear test and granular material constitutive model, the settlement of fluvioglacial deposited coarse grained soil embankment was predicted and the influence of compact degree on post-construction settlement was discussed. The amount and ratio of each portion of settlement were obtained. And it was suggested the modulus of granular constitute model of fluvioglacial deposited coarse grained soil be used to evaluate the self-compact settlement of embankment.7. Finite difference software FLAC^2D 5.0 was adopt to analyze the seismic dynamic response on reinforced fluvioglacial deposited coarse grained soil embankment on steep slope. Some key points about the option of numerical analysis were discussed, such as the size and shape of difference mesh, the setting of boundary, the determining of damp, and the producing, rectifying and input of manual shaking wave. Comparison analyses were conducted to discuss the characteristics of seismic dynamic response in embankment pre-and-post reinforcing, including horizontal displacement, velocity, accelerate, risk area and distribution of dynamic sheer stress. Finally, the design parameters such as the optimal distance between reinforced layers were obtained.