Anti-frost Swelling Replacement Measures For Trapezoidal Lined Channels In Cold Regions And Numerical Simulation Study

As the main agricultural irrigation building,canal system engineering plays a key role in the development of irrigation areas.The canal system buildings located in the northern permafrost area are often damaged by frost swelling due to geographical factors,and the channel lining structure cracks and slips,which makes it difficult to guarantee the water transmission efficiency and constrains the agricultural development.Therefore,it is significant to study the anti-frost swelling measures of channels.Based on the mature research results at home and abroad,this paper takes the typical test channel section of Jingdian Irrigation District Project in Gansu Province as the research object,uses the prototype channel replacement test and monitoring analysis,combined with simulation calculation,carries out the anti-frost swelling research of trapezoidal lining channel in cold area,analyzes the prototype monitoring data of sand and gravel replacement lining channel,obtains the change characteristics of land temperature,moisture and frost swelling displacement of the channel base after sand and gravel replacement;through numerical The change of temperature,stress and deformation of the liner before and after refilling was analyzed by numerical simulation,and the change law of the three fields of "heat-force-displacement" under different refilling thickness was summarized to verify the anti-freezing effect of the two materials.The specific conclusions are as follows:(1)The atmospheric temperature is fluctuating.At the same monitoring site,the ground temperature and the thickness of the bedding layer are negatively correlated.The temperature of the shaded slope is the lowest and the temperature change is the largest,and the ground temperature of its measurement point is the first to be lower than 0℃ and the freezing period is the longest;the ground temperature of the sunny slope is the highest and the freezing period is the shortest.The influence of orientation on the change of ground temperature is very obvious,and the overall ground temperature of the south and north-trending channels is high and the temperature change is gentle.The temperature of each measurement point on the slope of the channel with the same depth of burial is close to and slightly lower than the bottom of the channel.The ground temperature is not sensitive to temperature change.The freezing depth is positively correlated with the bedding thickness,but the increase is negligible.(2)Moisture changes actively in the freezing period.After experiencing freezing and thawing,the water content has increased to some extent.The moisture content of each depth,the shaded slope is larger than the sunny slope,the moisture at the bottom of the bedding layer far exceeds the surface of the bedding layer,and the moisture increment becomes larger,and the trend of moisture content change at each measurement point is similar.With the increase of monitoring depth,the moisture content of the east and west-facing channels gradually tends to be stable,while the south and north-facing channels are completely opposite.The moisture migration is the largest at the surface of the bedding layer at measurement point 4 on the positive slope,and the most active part of the moisture migration is measurement point 3 at the bottom of the bedding layer and 150 cm.d cross-sectional water content is about 10%-20% higher than b cross-sectional water content.(3)In the east and west-trending channels,after entering the freezing period,the amount of freezing and swelling on the negative slope is significantly larger than that on the positive slope,and the amount of freezing and swelling on the positive slope changes smoothly throughout the monitoring period.The Yang slope,left and right banks all show the phenomenon of thawing and sinking.The bottom of the channel freezes later than the slope of the channel,but the amount of frozen swelling is greater,and the difference in the amount of frozen swelling at the bottom of the two channels is obvious.d The difference in the amount of frozen swelling at each measurement point in the cross-section is not significant,and the change trends are similar.After the sand and gravel is replaced with subsoil,the effect of frost swelling reduction in section d is better than that in section b.(4)After analysis by the finite element software,it is obtained that both materials can reduce the amount of frost heave,and the 0℃ isotherm shifts downward with the increase of bedding thickness,which is consistent with the test results.The reduction efficiency of frost heave is negatively correlated with the thickness of the replacement.The anti-freezing effect of sand and gravel replacement fill of the same thickness was better than that of wind-covered sand.Under the steady-state thermal variation,the temperature field distribution of the channel base soil with the two material replacement fills is close,and the position of 0℃isotherm is basically the same as that of the un-replenished model.The replacement filling method can effectively alleviate the problem of frost swelling stress concentration at the foot of the slope of the channel liner slab.The frost swelling maximum point of the liner plate is located at 1/3 height of the canal slope,and the wind accumulation sand replacement fill is recommended to take 80 cm,and the abatement rate reaches 85.83%,which meets the requirements of the canal system anti-frost swelling design specification.The later engineering transformation can be selected according to the actual situation.