| The Shen-shuo Railway is located in northwestern China.It is one of the main routes for the transportation of coal from west to east China.This line is a heavy-duty railway and has a large volume of cargo transportation.The area is in seasonally frozen ground,with long winter time and low temperature.Due to long-term seasonal freezethaw cycles and large axle loads,the Shen-shuo Railway subgrade has experienced severe frost heave.This paper studies the problem of frost heaving of fine-grained roadbed fillers on Shen-shuo Railway,and finds suitable soil improvement methods for the prevention of freezing damage of fine-grained roadbed fillers in seasonal frozen soil areas.In this paper,laboratory experiments were used to study the improvement effects of polypropylene(PP)fiber and polyvinyl alcohol(PVA)on the clayey sand of a freezing damage section of the Shen-shuo Railway;the initial moisture content,the concentration of polyvinyl alcohol solution,the content of polypropylene fiber,as well as influence law and action mechanism of this factors on the frost heaving and mechanical properties of clayey sand were analyzed;and the applicability of the modified soil as a filler of the roadway in seasonally frozen area was evaluated.The main conclusions of this article are as follows:(1)Compared with plain soil,the PVA solution with a concentration of 2% has the highest plastic limit.In the soil with the same water content,there is less free water and capillary water in the improved soil,and there is less frozen water at the same temperature.Therefore,the improved soil has increased cohesion and weakened frost heave.In addition,the complex formed by the PVA solution in the soil not only cements the soil particles into a polymer,which can improve the cohesion of the soil,but also has hydrophobicity,which can reduce the water migration during the freezing process.(2)Both modifiers can improve the strength of the soil and suppress the frost heave of the soil;the improvement mechanism of the PVA solution is cementing,which can significantly improve the cohesion of the soil and reduce the frost heave of the soil.The improvement mechanism of PP fiber is reinforcement,which can slightly improve the cohesion of the soil and suppress the frost heave of the soil.(3)The improvement effect of the 2% PVA solution is the best,it can improve the cohesion of the soil by about 60 k Pa,and can reduce the frost heaving rate of the soil from 2.3% to 0.16%.0.25% PP fiber can improve the cohesion of the soil by about 10-20 k Pa,and can further reduce the frost heave rate of the improved soil from 0.16% to 0.07%.When the PP fiber content exceeds 0.25%,with increasing of fiber content,the improvement effect no longer changes significantly.(4)The improved soil has strong resistance to freeze-thaw cycles.With the increase of the number of freeze-thaw cycles,it`s strength and compressibility have not significantly deteriorated.(5)The composite improved soil with 2% PVA solubility and 0.75% PP fiber content before freeze-thaw cycles has the highest strength and the lowest compressibility.However,considering that when the PP fiber content exceeds 0.25%,the improvement effect no longer increases significantly with the PP content;after 9 freeze-thaw cycles,2%PVA and 0.25% fiber composite modified soil has the highest strength and cost-effective,so 2%PVA and 0.25% PP fiber are used to improve the clayey sand.(6)It is recommended to use 2% PVA and 0.25% polypropylene fiber to improve the clay sand,which can greatly improve the strength of the soi l and eliminate the frost heave of the soil.It can be used as the filler for the bottom of the roadbed and the embankment below the roadbed. |
PDF Full Text Request