Frost Heave Performance Of Graded Coarse Grained Soil Considering Fine Particle Contents

China is a large frozen soil country,more than half of the land area is located in the frozen soil area which has the impact on the project.With the further deepening of reform and opening up,more and more major projects began to be implemented in the northeast,northwest and other remote frozen soil areas.However,because of the poor environment and severe frost damage in these areas,coarse-grained soil filler as an essential material for project construction is also deeply affected.It is of great significance to study the development law of coarse-grained soil filler in the process of freezing and understand the influence of fine-grained content on the physical characteristics and frost heave performance of coarse-grained soil filler.In this paper,Songhua River sand is taken as sample material.After particle analysis and sieving,it is recombined with 1250 mesh fine ground kaolin to form four graded sands with fine particle content of 0%,5%,10% and 15%,respectively.The basic physical properties and freezing tests of four graded sands were carried out,and the basic characteristics and frost heaving characteristics of graded sands with different fine grain contents were obtained.Based on this,the water-heat coupling model and water-heatforce coupling numerical calculation model of graded coarse-grained soils with different fine grain contents were established and their validity was verified.At the same time,the graded coarse-grained soils with different fine grain contents were calculated,and the effects of fine grain contents on temperature field,water field distribution and frost heaviness of graded coarse-grained soils were studied The main research contents and important achievements of this paper are as follows:Firstly,the Songhua River sand in Harbin was screened and reconfigured with fineground kaolin with four graded fine sands with fine grain content of 0%,5%,10% and 15% respectively.Then,compaction test,specific gravity test and thermophysical property test were carried out to obtain the influence law of fine grain content on the basic physical properties of sand.Then,the graded sand with fine grain content of 0 was subjected to unidirectional freezing test,and its freezing law was obtained.The test results show that with the increase of fine particle content,the maximum dry density and specific heat capacity of sand gradually increase,while the thermal conductivity and diffusion coefficient gradually decrease,and the specific gravity of particles increases first and then decreases(10% content is the change point);Temperature and freeze-thaw cycles have a significant impact on frost heaving characteristics of graded sand,that is,the greater the temperature gradient,the more freeze-thaw cycles,the greater the frost heaving amount,and there are obvious freezing shrinkage and thawing settlement phenomena during the freezing process of graded sand,and the change trend of frost heaving roughly conforms to four development stages.However,on the whole,the frost heaving amount of graded sand is very small,and the frost heaving rate is very low.The frost damage lies not in frost heaving deformation,but in the damage of soil structure under the coupling of water and heat.Secondly,based on the seepage theory and heat conduction theory of saturated soil,according to the law of conservation of mass and energy,the differential governing equations of temperature field and moisture field are derived from the differential level.By introducing the concept of "solid-liquid ratio",the water-heat coupling model of graded coarse-grained soil considering the fine grain content is established,and compared with the results of graded sand freezing test and previous tests,the validity of the model is verified.The influence of fine grain content on the water-heat coupling process of graded coarse-grained soil is simulated and analyzed.The calculation results show that when the fine grain content does not exceed 15%,it has a certain influence on the temperature drop rate and the final stability value of graded coarse-grained soil during freezing,but in general,it has little effect;With the increase of fine particle content,the water absorption capacity of cold end soil increases,while that of warm end soil increases at first and then decreases slightly.Finally,based on the rigid ice model theory,the water-heat-force coupling numerical model of graded coarse-grained soil considering fine grain content is established on Visual Studio programming software,which realizes the function of fast numerical calculation of frost heave force and frost heave rate.Compared with the results of graded sand freezing test and previous tests,the correctness of the model is verified.Parameter sensitivity analysis was carried out to find out the key parameters,and then the influence of fine grain content on frost heaving force and frost heaving rate of graded coarsegrained soil during freezing process was simulated and analyzed.The results showed that with the increase of fine grain content,the frost heaving force and frost heaving rate of graded coarse-grained soil gradually increased,while when the fine grain content in graded coarse-grained soil was constant,the frost heaving force and frost heaving rate of graded coarse-grained soil basically increased linearly with the increase of kaolin content.Finally,the calculation formula of frost heave force considering fine grain content is determined.Through the above research results,we can have a deeper understanding of the influence of fine grain content on the physical properties and frost heaving performance of graded coarse-grained soil,and provide reference for the design and construction of graded coarse-grained soil filling engineering in frozen soil areas.