Optimum Experimental Study And Numerical Simulation On EPS Insulated Board Thickness For Channels Of Ningxia Yellow River Irrigation Area

Ningxia is located in seasonally frozen areas, so that severe frost damage to the irrigation channels not only reduce the operating life and increase maintenance costs but also constraint the development of agriculture water resources efficiently and sustainability. It has become a bottleneck of the high standards farmland construction in Ningxia irrigation area. The experimental research and optimization analysis on lining channel frost damage mechanism, frost damage characteristics with different types of channel and laying polystyrene insulation board to improve the anti-frost damage effect were conducted in this thesis based on the real objects of the two canals (Qin canal and Langtian canal) in Ningxia irrigation area and the literatures of looking up existed research results.The main research works are as follows:(1) In order to explore the key factors of frost heave damage, a east-west canal from Qinqu and a north-south canal from Langtianqu were selected as the typical test sections in where different thicknesses of polystyrene insulation board were set to survey the base temperature, freeze depth, frost heave deformation and soil moisture, so that the variety law of different thickness of insulation board versus those factors were obtained. Further, the laying thickness of EPS insulation board with different trends and different positions of the channel slope at a same channel section;(2) Three theoretical methods that calculate polystyrene insulation board thickness were checked and their results were corrected by combining with Ningxia characteristics;(3) The math model was established by using the finite element software of ANSYS. The temperature field and displacement field for the channel frost heave were calculated through simulated the process of thermal-mechanical coupling model. And the simulating data of laying thickness of EPS insulation board were obtained;(4) Finally, combining with the characteristics of Ningxia irrigation area, the the reasonable thickness of EPS insulation board for the anti-frost heave of main irrigation canal was decided based on the test method, the theoretical calculation method and numerical simulation results.The main conclusions have been given as follows:(1) The factors of channels freeze depth, frost heave and soil moisture are closely related to the channel direction and channel slope position. The freeze depth and frost volume of shady slope on east-west channel are greater than the sunny’s, and the data of channel bottom is on medium; than, on north-south channel, the freeze depth and frost volume of the channel bottom are greater than other potisions; the moisture content of the channel bottom is greater than the channel slope’s, and shady slope’s moisture content greater than the sunny’s; frozen soil moisture content is greater than the free soil’s, and the most variety of moisture content obviously is located in the maximum freezing depth;(2)The distribution of freeze depth, frost heave and soil moisture is related to the insulation board thickness. Laying insulation board can reduce the freeze depth significantly, and the freeze depth will decrease while the insulation thickness is increased; but the freeze depth will be unchanged when insulation thickness reaches a certain value whose related to the channel direction and channel slope position; laying insulation board can also reduce the frost heave deformation of the canal lining, and the thicker of insulation board, the less of frost heave; laying insulation boards can improve soil moisture migration to canal bed, and soil moisture with insulation board is small;(3) By using corrected theoretical formula can calculate the insulation thickness for Ningxia irrigation area. The values of pyrology reserve calculation method are close to the thickness of experiment survey and can be initially identified the insulation thickness for engineering design; the results of analogy method is also close to survey data when the safety coefficient is adjusted to 1.5; but the results of empirical formula is unfit for the actual application dircctly due to a large range of datum; of course, the real laying thickness need to adjust combining Ningxia characteristics.(4) The simulating results can be applied on the choice of channel insulation thickness by using ANSYS software. From the results of the temperature field calculation shows that insulation board can effectively improve the permafrost temperature distribution and the soil temperature is gradually increased with the increase of the thickness of the insulation board; the displacement field simulation results show that polystyrene insulation board can reduce the channels frost heaving, and the displacement will decrease with the increasing of the insulation board thickness; the simulating results are agreement with the montor data, except simulating value at channel bottom is too small;(5 Considering the actual characteristics of Ningxia irrigation area, the insulation board thickness is optimize by comparing the results of experiment survey, theoretical formula and numerical simulating under the factors including different canal directions, different groundwater depth and polystyrene insulation board positions in different canal sections.