Study On One-dimensional Cyclic Frost Heave Of Silty Clay In An Open Syste

Northeast of China,as an important agricultural production base in China,channel lining is damaged by frost heave of foundation soil at the bottom frequently.This damage has seriously affected the functioning of the channel,while causing economic losses as well as serious waste of water resources.For areas with high level groundwater,during the frost heave process,there is often groundwater recharge at the bottom of the channel.Under this circumstance,the concretelined channel is called concrete-lined channel under open-system.In addition,in the early winter in the north of China,temperature varies seriously day and night,soil is always in the stage of freeze-thaw cycle.Based on the basic theories of frozen soil mechanics,taking silty clay as the object of frost heave experiment,the frost heave process is simplified to one-dimensional.Onedimensional cyclic frost heave test is conducted on the channel subsoil under open-system,and the process of frost heave cycle is simulated by controlling the freezing depth.Finite element software is used to simulate the frost heave of soil at the bottom of the channel.The main research work is as follows:(1)The one-dimensional cyclic frost heaving test device for silty clay under open-system was designed and set up,and the silty clay was reshaped according to the test specifications.The single factor tests of silty clay frost heave were performed with initial water content,minimum temperature and duration of frost heave as the influencing factors.The results of the single-factor test showed that: the frost heave displacement of silty clay is quadratic related to the initial water content,and when the water content is 40%,the maximum frost heave displacement is 2.49mm;the frost heave displacement of silty clay is quadratic related to the minimum frost heaving temperature,and when the temperature is-25℃,the maximum frost heave displacement is2.33mm;the frost heave displacement of silty clay is linearly correlated with the duration of frost heave.The position of frozen front was obtained by comparing the water content before and after the test and law of water migration in soils above and below frozen fronts.(2)Based on the single-factor test,a three-factor and three-level orthogonal test of silty clay frost heave with initial water content,minimum temperature and duration of frost heaving as the influencing factors was designed and completed.The combination of the most unfavorable factors for the frost heave of silty clay in one-dimensional cyclic frost heave test under open-system is obtained,that is: when the initial water content is 40%,the lowest frost heaving temperature is-25℃ and the duration of frost heave is 56 h,the maximum frost heaving amount is 2.82 mm.The significance analysis results of each influencing factor on frost heave were obtained.The effect of initial water content is the most significant,the effect of minimum frost heave temperature is more significant,but the effect of frost heaving duration is not significant.(3)The finite element model of trapezoidal channel and soil was established by using ANSYS software.The model was used to simulate one-dimensional cyclic frost heave of silty clay.The accuracy of the model was verified by comparing simulated data with the single factor test results and the orthogonal test results.The temperature field,displacement field and stress field of silty clay frost heave were analyzed,and the distribution state of temperature gradient and the location of displacement and stress concentration were obtained,which provided a theoretical basis for anti-frost heave failure of channel.The expanding analysis of one-dimensional cyclic frost heave finite element model of open system channel silty clay was carried out by using finite element model,and orthogonal experiment of three factors and four levels simulation was carried out.The frost heave law of silty clay for long duration of frost heave was presented.