Mechanics Models Of Frost-Heaving And The Research Of Anti-Frost Heave Structure For Lining Canal

Technically, the way to protect canals from the damage of frost heaving is very important and difficult in hydraulic engineering. The situation is worse for the canals in the districts with high-level groundwater.In this paper, the analysis on the damage of the canals due to frost heaving was given based on experiments, water-thermal-mechanics (or three-field) coupling theory and the finite element method. We presented new elasticity models for frozen soil and the mechanics models for a concrete lining canal damaged by frost heaving. The numerical simulation on the process of frost heaving was supplied and new configurations of anti-frost heaving structures were suggested based on the theoretical and experimental results.The major contents and the creative results of the present work were summarized as follows.(1) The advance of the research on both of the frost heaving theories of canal and the measures to protect canals from the damage of frost heaving were summarized systematically in the first chapter.(2) Some frost-heaving theories, such as capillary theory, second theory of frost heaving and the theory of segregation and freezing, were introduced in the second chapter. The effects of several factors, e.g. the properties of soil, water conditions, temperature, loading conditions and the orientation of a canal, on the results of frost heaving of a canal were analyzed.(3) The mechanics models for frost heaving of concrete lining canals with different kinds of cross-sections, e.g. trapezoid, semi- trapezoid, trapezoid with arc bottom and U-shape trapezoid, were proposed based on reasonable assumptions, which were verified to be correct by quantitative analysis of the anti-frost heaving configurations of concrete lining canals. Computational methods were given to obtain both of the internal forces of liner plates and damage conditions of anti-frost heaving of canals. Based on the methods, the optimal U-shaped cross-section of a canal was obtained on considering the optimal hydraulic condition.(4) Observations imply that frozen soil can be considered as the mixture in which the ice crystal and the solid drying soil cling tightly. By comparing with the isotropic elasticity model for frozen soil, the transversely isotropic elasticity model is more reasonable according to the experimental results. A composite material model for frozen soil was presented and the relations between the elasticity of frozen soil and those of the composite components were given according to the model. The yield criteria of frozen soil were discussed on accordance with the unified strength theory and theory of composite mechanics.(5) The water-thermal-mechanics coupling model for frozen soil was investigated based on the previous works. We introduced the reasonable assumptions, the relations between the thermodynamic parameters such as fabric of soil skeleton and water in soil, establishment of control equations for the coupling model and boundary conditions. The finite element method was adopted to analyze the freezing process of frozen soil in open or closed thermodynamic systems. In detail, the status of the thermal field and water volume ratio varying with the depth of frozen soil and the amount and coefficients of frost heaving changing with temperature were studied. The results can be used to forecast the degree of frost heaving of canals and the deformation of linings.(6) The main canals with trapezoidal and arc-bottom trapezoidal cross-sections in Jinghui, Gansu province and the northern main canal in the Baoji Gorge irrigation district were simulated by the finite element method to obtain their temperature fields, displacement fields and stress fields. The accuracy of the mechanics models and the simplified three-field coupling models were verified by comparing the numerical and physics experimental results. The effects of anti-frost heaving measures, e.g. setting different types of longitudinal seams, embedding concrete linings or polymer cement linings, on canals were tested numerically.(7) According to the functions and the mechanism of damage of canals in the districts with high-level groundwater, the so-called infiltrating stiffness-compliance combination structure, which has rigid frames stuffed with scree as periodic cells, was suggested to be the lining in a canal. It provides the canal with many functions, such as water delivery, drainage, groundwater level controlling, ecology protection, etc. The effects on anti-frost heaving of the lining were tested by both of experiments and numerical simulations. Successfully, the canals with such kind of linings had been adopted in Dongping electric pumping station located in Baiyin, Gansu province.(8) By orthogonal experimental design theory, the sensitivity of the factors of a canal, i.e. the configuration of the cross-section, the depth of concrete lining, the positions of seams, coefficient of frost heaving of soil and the elastic modulus of lining, to the degree of frost heaving of canals were investigated and the sequence of the factors was given with respect to their sensitivity.