Studies On The Movement Of Soil Moisture On Canal Base In The Process Of Freezing-Thawing And Frost Resistance Theory And Technology Of Large-Arc Canal Seepage Control

Canal seepage control is one of the most important technologies in the water saving irrigation. But the distribution of the seasonal frozen soil in our country is about fifty-four percent, and in the northern area of China it exists on the soil surface or nearby place in almost a quarter of a year, thus some canals are destroyed by it. So the studies of theory and technology on the seasonal freezing and thawing for the seepage control canal in our northern area is becoming the most important subject.Based on prototype observation results of two large-arc canals, consulting abundant domestic and foreign interrelated data and using the technical routes which combine laboratory tests with prototype observation and theoretical analysis with numerical simulation, this dissertation systematically focused on the soil moisture movement on the base of U-shape canal with concrete lining in the process of seasonal freezing and thawing and the theory and technology of frost resistance of trapezoidal canal with arc foot lining with concrete and film, did some tests on the films characteristic of tensile, deformation, impermeability and crack resistance in aging time as well as the shear performance between soil and film, proposed the calculating method of side slopes of canal with film impervious and soil protective cover and established the model of effectiveness seepage under static and dynamic conditions. In the thesis, main results are as follows:(1) The frost-heaving mechanism of U-shape canal lining with concrete and soil moisture movement on canal base during seasonal freezing and thawing stage were studied on the temperature gradients theory. The characteristics of soil moisture movement within the depth of 40 cm of U-shape canal base were obtained by the prototype observation and the data of observation was analyzed using regression analysis according to time series. On this basis, a model of coupled heat-fluid transport was established by the soil moisture equation combined with heat movement equation in the cyclic process of freezing and thawing. The prediction model of frozen depth and frost-heaving deformation was derived with the amount of soil moisture movement, freezing temperature and observation value of frost depth. The test results show that the simulation and prediction curves were fitting with the prediction curves. The research supplies a theoretical basis for the design of U-shape canal lining with concrete.(2) By the prototype observation of large-trapezoidal canal with arc foot lining with the concrete prefabricated with film, the theory and technology of frost resistance of canal lining with concrete and film were studied 1) The optimization of mixing proportion of lining material and caulked material was presented that conformable local source, and the performance was studied in laboratory.2) Based on a fully consideration of the climate characteristics in north area, a section of large-trapezoidal canal with arc foot is designed with benefits to improve the non-uniformity of frost heave deformation, to prevent the occurrence of dislocation and crack, to replace the line after melting, to equalize the distribution velocity and convenience send transportation. The designed section is smaller in size and lower in cost than trapezoidal one. 3) In the structural form, the technology and the methods of avoiding, replacement and insulation had excluded, and 8 kinds of structural forms of 4 class had been designed. These are concrete prefabricated with (concrete prefabricated are consist of 8cm,10cm and∏-shape) concrete cast-in-place with film, bituminous concrete and concrete prefabricated with film of close soil layer (close soil layer are consist of the whole section, half a section closes and only bottom of canal) and, all the structural form were studied and evaluated.4) The research findings of soil temperature, soil moisture, water level, freezing depth, and amount of frost-having were given from large-arc canal.(3) The aging of crack resistance of film was studied by the use of freeze-thaw and the ultraviolet shine in laboratory. The results showed that the aging crack resistance of film was reduced to some extent in freeze-thaw and the ultraviolet shine. The mathematical model was established to describe the relation between stress and strain, breaking resistance and deformation high in freeze-thaw. Theoretical foundation has been studied and it was feasible for using as a guide for the design of the polyethylene in canal.(4) The shear strength of sample between film and soil was studied, which the soil was different classes or different density in saturated or unsaturated and, the film was changing in classes and angle, the instrument and the equipment were two kinds, one kind was tri-axial shear and the other one was direct shear. The new method and the steps of tests were proposed in shear performance between film and soil by using the result of two kinds of instrument and equipment. The reasonable parameters were provided for calculated stability of side slopes of canal with film impervious and soil protective cover.(5) Combined with the reality of prevention of seepage of our country's large-scale canal, the influence of side slopes of canal with film impervious and soil protective cover were studied on water, temperature, wind speed, silt content, soil property, section form of canal and base, film classification, operation and management etc. The new calculated method of side slopes of canal with film impervious and soil protective cover was proposed. The control index of shear strength, coefficient of internal friction and safety factor were studied. The form and position of landside of side slopes of canal with film impervious and soil protective cover were analyzed.(6) According to principles of economy, the seepage control effectiveness of canal lining with concrete and film was studied under static and dynamic conditions, and the seepage control performance was geometric progression, arithmetic progression or no change with the time. The judge principles and economic models had been concluded in seepage control. With the examples of seepage observation for calculation, the economy of seepage control effectiveness of canal lining concrete with film has been discussed. It was avoided blindness of the seepage control of canals by necessity judgment of test.