Frost Heave Calculation Models Of Lined Canals In Cold Regions Considering Solar Radiation And Their Applications

The construction of the national water network with the canal project as the main body,is the basic measure to ensure the national water security and solve the imbalance of the spatial and temporal distribution of water resources.Under the coupling effect of the high solar radiation intensity and low temperature,the canal experiences vicious cycles of the frost damage and leakage,which is a major problem in the safe operation of the water network in the north.Solar radiation causes the canal to experience freezing-thawing cycles in the day-night and long-term freezing process in winter,and triggers the asymmetric and asynchronous differential freezing-thawing development of the shady and sunny slopes.Finally,the unstable freezing-thawing damage and differential damage of shady and sunny slopes occur to the canal.However,the time-space effect of solar radiation was rarely considered in the previous research on the prediction and prevention of frost damage to canals,which resulted in the canals being frozen all the time in winter;this was different from the actual mode of the day thawing and night freezing,and the effect of sunny-shady slope effect could not be considered.Therefore,it is difficult to accurately reveal the development mechanism of canal frost damage under the coupling effect of solar radiation and temperature difference between day and night,and it is difficult to scientifically guide the quantitative design to prevent frost damage.In this paper,the canal in cold regions under the action of solar radiation is taken as the research object.By the means of the one-side freezing test of frozen soil,canal model test,engineering mechanics analysis and numerical simulation,the frost damage mechanism of the canal with sunny-shady slope effect is investigated,a concise-practical analytical mechanical model and a dynamic-accurate multi-field coupling numerical model are established,and an anti-frost heave technology with reasonable joints is proposed.This study can provide theoretical and technical support for the frost heave design,engineering verification,accurate prediction and prevention of canals in cold regions under the effect of solar radiation.The main work and results of the study are as follows.(1)Xenon long-arc lamp and low-temperature test chamber are used to conduct one-side freezing tests of soil columns under the different solar radiation intensities and underlying surfaces,and the thermal response mechanism of the structure surface and the frost damage mechanism of frozen soil are revealed.The results show that solar radiation can increase the heat flux and convective heat transfer flux of the structure surface,and thus linearly increase its temperature.Solar radiation can also delay the start time of the rapid and stable frost heave periods of frozen soil and reduce its frost heave.Solar radiation makes the characteristics of the moisture,heat and force of frozen soil fluctuate dynamically,and makes the water migration have the cumulative effect.The essence is that solar radiation and temperature together cause the change of freezing rate of frozen soil,and then lead to the coupling change of water migration,ice-water phase change and frost heave.(2)The frost heaving model test of the canal with different solar radiation intensities on the shady and sunny slopes is carried out,and the frost damage mechanism of the canal with sunny-shady slope effect is explored.It is found that solar radiation makes the temperature difference on the shady and sunny slopes have a time-space effect.With an increase in the difference between the daily average absorbed solar radiation intensity of the shady and sunny slopes,their freezing depth ratio,deformation ratio and strain ratio increase approximately linearly from 1.Under the daily average temperature of-15℃,when the difference of solar radiation intensity between the shady slope and sunny slope is 39.2 W/m~2,the freezing depth,deformation and strain of the shady slope are about 1.4 times of those of the sunny slope.The main cause of the damage is that the differential thermal boundary of the shady slope and the sunny slope causes differential frost heave due to the coupling of the water,heat and force of the frozen soil.Finially,suggestions on reducing the frost damage by using the solar radiation are given.(3)In order to realize the scientific design of canal frost heave,according to the test results,the influence of solar radiation on the canal frost heave is simplified as the difference of lining deformation caused by the difference of freezing depth between the sunny and shady slopes.Based on the theory of Timoshenko beam on Pasternak foundation,an analytical mechanical model of the canal lining frost heave considering solar radiation is established.This model makes up for the deficiency that the traditional model of Euler-Bernoulli(EB)beam on Winkler foundation does not consider the solar radiation,shear action of frozen soil and lining and tangential freezing action.By the model test and finite element results,the model’s rationality and correctness are verified.Finally,the foundation and beam models and their parameter effects are discussed to calibrate the parameters for the practical application of the mechanical model.(4)In order to accurately calculate the freezing-thawing process of canal under solar radiation,a moisture-heat-mechanical coupling numerical model of the canal frost heave considering solar radiation and shadow shading is established.This model takes into account the effects of the spatio-temporal variation of solar radiation and temperature difference between day and night on the canal frost heave.This model is verified by the one-side freezing test,model test and on-site monitoring data.Based on this model,the water,heat and force coupling frost heave response during the process of the canal rotating clockwise from east-west to south-north is given,and the effect of solar radiation on the canal frost damage is further analyzed.(5)Based on the above frost damage mechanism and numerical model,the frost heaving analysis model of canals with longitudinal joints considering lining-foundation soil interaction and filling of longitudinal joints is established,and an anti-frost heaving technology of canals with reasonable joints considering solar radiation is proposed.This technology adopts single joint to reduce stress concentration,optimizes the joint width according to the reduction degree and structural integrity,and adjusts the lining frost heaving uniformity through multi-joints combination.It quantificationally improves the frost heaving prevention measures for longitudinal joints in the code.The project example shows that,the joints combination of slope toe+1/4 slope plate+3/4 slope plate on the shady slope and those of slope toe+3/4 slope plate on the sunny slope,can make the lining stress meet the strength requirements and reduce the stress by more than 50%;it indicates that this technology can effectively reduce the asymmetric and asynchronous frost damage caused by solar radiation.