A Study On The Frost Heave Mechanism Of Micro-frost-heave Filling Based On The Interaction Of Frost Heave Of Filling Materialand Coarse Particles Skeleton

The requirement of ride performance for high-speedrailway lines is extremely strict, even tiny deformation of roadbed will cause bad influence. Frost heave deformation of high speed railway subgrade in cold regionproduces an effect on ride performance, ride comfort and the structure durability, and may even affect the traffic safety of the train. However, sensitivityclassification and research of soil frost heave in view of the traditional structurecannot meet the requirements of high speed railway. Therefore, the research on the frost heave of micro frost heave filling is significantto the construction and operation maintenance of high speed railway in cold region.Focus on the effect of subgrade in seasonally frozen ground region on the ride performance of highspeedrailway, this paper investigated the frost heave performance of micro frost heave filling based on the interaction of frost heave of filling materialand coarse particle skeleton. According to the combination methods of theoretical analysis, laboratory test and numerical simulation, the paper analysed the frost heave properties and the micro frost heave filling structure,and reveals the development mechanism of frost heave.The relationship betweenfilling materialfrost heave and skeleton particles during the frost heave process was analyzed, and the frost heave deformation model of micro frost heave filling was built.Based on the lowest energy principle, computational formula of frost heave was derived for the micro frost heave filling.Evaluation and test method of frost heave were put forward, and the suggestions of frost heave prevention for subgrade were proposed. The main research contents and conclusions are presented as follows:(1) This paper revealed the frost heavecharacteristics of micro frost heave filling and the micro development mechanism. Micro frost heave filling is mainly composed of coarse particles, containing a small amount of fine particles. Due to the discreteness of the internal structure and discontinuity of the moisture transfer, different parts ofthe frozen soil samples are basically in a relatively’closed’state, which are mainly shown as’in-situ frost heave’The occurrence of frost heave shows’instantaneity’. The natural moisture content of micro frost heave filling is generally low, and most of the moisturelies in the fine particles.When it is freezing, the emigration andaggregation of water in the fine particles occupies extra space, which plays a much more important role than the volume increment during water freezing. The small amount of water adsorbed bycoarse particle surface just occurred in some degree of volume expansion caused by the phase change. Fine particles are the primary sources of frost heave of micro frost heave filling.(2) A deformation analysis model of frost heave for micro frost heave filling was established. Micro frost heave filling consists of skeleton of coarse particles, filling material and unfilled pores. Coarse particles skeleton can be regarded as rigid body without volume expansion during freezing. Filling material was expanding during its freezing. On the one hand, it produces the filling effect, filling the rest space of the voids. On the other hand, filling material produces lifting effect. It lifts the skeleton particles, and leads to the frost heave on macro level. When the residual porosity is large, it has a strong consumption effort to frost heave, and expends the energy of lifting effect. The lifting effect gives rise to skeleton pores increasing, which is conducive to the development of filling. The filling effect is obvious when the skeleton bond is stable. The actual frost heave of micro frost heave filling is a process of dynamic balance between filling effect and lifting effect.(3) Calculation formula for frost heave of micro frost heave filling was derived. Based on the established analysis model and the lowest energy principle, this paper considered the interplay of filling effort and lifting effort, and derived the calculation formula for the frost heave of micro frost heave filling under the condition of physical and mechanics parameters. These parameters include friction angle, cohesive force of filling material,filling material content, frost heave ratio,initial filling ratio, filling relative density, moisture content, filling density, overburden pressure, skeleton density,etc.(4)The evaluation and test method of frost heave sensitivity analysis of micro frost heave filling were proposed.Based on the frost heave test of filling material less than 2 mm in diameter, considered about the porosity and filling state of the coarse particles skeleton, the frost heave of micro frost heave fillingwas calculated and evaluated in accordance with the derived calculation formula.Divide the filling materials without’traditional frost heave’into six groups.(5) The control method and suggestions of micro frost heave filling were presented for high speed railway. A selecting and controlling system was proposed with annlysis for high speed railway filling materials.Combined with the basis of mixture frost heave model, non-uniform coefficient of mixture can be reduced properly to prevent the high speed railway subgrade from frost heave. Besides, this paper analyzed the key parameters of graded broken stone comprehensively, and put forward the recommendations for the gravel gradation optimization of the subgrade surface layer in the severe cold area.