| China’s seasonal permafrost is widely distributed,the soil temperature field and each phase with temperature changes show instability,has a negative impact on the safety of various engineering structures.The channel lining project built on the seasonal permafrost area is prone to frost damage with the phenomenon of freezing and thawing of the soil,and the lining structure cracks,buckles and even slips,causing a large amount of irrigation water loss and serious waste of water resources,and the problem of frost swelling has become an important constraint to the rapid development of agricultural economy in irrigation areas.Therefore,the study of frost damage mechanism of concrete lined channels in seasonal permafrost areas and the study of reasonable concrete lined channel structure form are of great significance to ensure the water transmission safety of channels in seasonal permafrost areas,the normal production and life of water receiving areas,and give full play to the economic benefits of the project.During soil freezing,there is a complex interaction process between the concrete liner and the lower soil,making the liner freezing effect different from the more conservative calculation results when the interaction is ignored.In order to improve the safety and economy of concrete lining channel design,it is necessary to consider the interaction between it and the frozen soil.Elastic foundation beam is a beam resting on a certain elastic nature of the foundation,which can better reflect the interaction between the foundation and the superstructure,and has been widely used in the study of frost swelling in channel lining structure in recent years,and the determination of the frost swelling reaction coefficient is the key issue.Due to the existence of yin and yang slope effect of channel soil temperature at different moments,the frost swelling reaction coefficient also changes with time and location,and finally the actual frost swelling amount and frost swelling reaction force of each part of the channel form a state of uneven distribution.Therefore,this paper establishes the mechanical model of elastic foundation beam of U-shaped channel by changing the frost swell reaction force coefficient,and couples the mechanical model to the hydrothermal process through secondary development to numerically simulate the concrete lining frost swell effect by coupling the three fields of hydrothermal force,and studies the frost swell effect of small two-piece U-shaped concrete lining channel reflecting the interaction with soil body.The main research contents and results are as follows.(1)The expression of frost swelling reaction force coefficient reflecting the relationship between soil temperature and frost swelling deformation capacity at different locations is established,and the frost swelling reaction force that changes dynamically with soil temperature is determined;based on the elastic foundation beam theory,the frost swelling mechanics model of U-shaped channel concrete lining considering the dynamically changing frost swelling reaction force coefficient is established,and the freezing force,frost swelling force and frost swelling volume,maximum bending moment,shear force and axial force of side slope and channel bottom lining slab after frost swelling are solved.and shear force and axial force were calculated.The method is applied to a small two-piece U-shaped channel in Ningxia,for which an elastic foundation beam frost swell force model with variable reaction coefficients is developed and solved.The actual frost swell amount of the lining structure and the distribution of the frost swell reaction force change in accordance with the field observation results and existing research findings,which can dynamically and objectively reflect the interaction between the channel foundation soil and the concrete lining,and can reflect the frost swell deformation of the channel lining at It can reflect the change trend of frost heave deformation of channel lining in different moments and different locations,and change the conservative calculation condition that only the maximum frost heave can be considered in the previous study.(2)The channel elastic foundation beam mechanics model considering variable reaction coefficients is coupled with water and thermal models to form the water-thermal three-field coupling equation and the PDE module of COMSOL software is used for secondary development to simulate the frost swelling effect on the channel.The distribution of soil temperature field and moisture field is consistent with the field measurement results,and the effect of yin and yang slope is obvious.The stress concentration phenomenon is mainly concentrated at the junction of straight and curved sections of the canal slope,the top of the canal slope and the bottom of the canal.The deformation of the lining structure at the bottom of the canal is the largest,followed by that of the yin slope and the smallest of the yang slope.The deformation is dominated by the lining slab of the canal side slope tilting slightly into the canal,lifting the canal upward and slightly deflecting in the direction of the yang slope.The hydrothermal coupling results of the elastic foundation beam frost swell model considering the variable reaction coefficient are closer to the field observations than those of the model without considering the interaction between the liner and the soil.(3)For different opening widths,inclination angles and liner thicknesses of the channel lining,the three-field coupled simulation of the small two-piece U-shaped channel was carried out,and the frost deformation of the channel decreased with the decrease of the opening width,the increase of the inclination angle and the increase of the liner thickness.The design of the small two-piece U-shaped channel was optimized by combining with the actual situation of the Ningxia Yellowing Irrigation District.Among them,the measures of reducing the width of channel opening and increasing the thickness of channel liner are more effective in improving the effect of channel frost heave. |
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