Study On Frost Heave Prevention Measures Of Gravel Replacement In Trapezoidal Channel In Seasonal Frozen Area

China is a large agricultural irrigation water country.In Gansu,Qinghai,Ningxia and other northwest provinces,agricultural water accounted for more than 70 %,of which more than 90 % of agricultural water is used for agricultural irrigation.Canal system engineering undertakes the main task of water conveyance in agricultural irrigation.However,due to the typical seasonal frozen soil area in northwest China,the water conveyance channel is affected by perennial freeze-thaw damage,and the anti-seepage lining structure is damaged by frost damage,resulting in low water conveyance efficiency,which seriously affects the normal water conveyance irrigation and ecological management benefits of irrigation areas,and restricts the healthy development of agriculture and ecology.Therefore,it is of great theoretical significance and engineering practice value to carry out the research on frost heaving prevention measures of trapezoidal channel in seasonal frozen area.In this paper,combined with the second phase of the reconstruction project of Jingtaichuan electric power pumping and irrigation in Gansu Province,the typical test section is selected on the trapezoidal channel,and the gravel cushion with different thickness is replaced.The frost heave of the channel,the ground temperature and water content of the lining plate are monitored and analyzed.Combined with numerical simulation,the variation characteristics of ground temperature,frost heave and water content under different gravel replacement thickness are obtained.The mechanism of frost heave prevention by gravel replacement measures is discussed,and the optimal replacement thickness of gravel suitable for trapezoidal concrete channel in seasonal frozen area is proposed,which provides scientific and safe theoretical basis for engineering application.The main conclusions are as follows :(1)Through the analysis of the change of the underground temperature of the channel lining plate in the seasonal frozen area,it is found that the response of the underground temperature of the trapezoidal channel lining plate to the temperature change is delayed.The increase of gravel cushion thickness will lead to the decrease of ground temperature under the plate,but the decrease is small.The trend of the channel is different,and there are obvious differences in the change of ground temperature.The ground temperature of sunny slope is greater than that of shady slope.The north-south trend of the channel left and right bank ground temperature changes are similar.(2)Through the analysis of the change of channel moisture content in seasonal frozen area,it is found that the soil moisture on both sides of the channel slope is different in the process of freezing and thawing,and the water content of the shady slope is greater than that of the sunny slope.However,with the decrease of temperature,the soil moisture difference decreased significantly.Although channel shady slope temperature is lower than sunny slope temperature during freezing period,the effect on soil moisture is very limited.(3)The variation of frost heaving amount of trapezoidal lining channel in seasonal frozen zone is analyzed,and the variation law of frost heaving amount along the channel slope is obtained.The frost heaving amount at the bottom is large,and that at the top is relatively small.The frost heave decreases with the increase of gravel replacement thickness.The frost heave of the east-west shady slope is larger than that of the sunny slope,and the frost heave of the slope on both sides of the north-south trapezoidal lining channel is similar.(4)Combined with the numerical simulation results,it is found that the channel freezing depth increases slightly with the increase of gravel replacement thickness,and the increase can be ignored compared with the gravel replacement thickness.With the increase of gravel cushion thickness,the frost heaving amount of the channel gradually decreases,but the frost heaving reduction efficiency also decreases.When the thickness of gravel cushion is 30-70 cm,the frost heaving displacement is reduced by 77.4 % on average compared with that without gravel replacement.