Study On Key Techniques For Construction Of Low-fill And Shallow-excavated Frozen Soil Roadbed In High Cold And High Altitude

Permafrost soil is very sensitive to the changes in temperature and moisture.Under the action of freeze-thaw cycles and traffic loads,low-fill and shallow-excavated frozen soil roadbeds are prone to roadbed diseases,such as frost heave and thawing settlement.In this paper,the key construction technology of frozen soil roadbed of low-fill and shallow-excavation is systematically studied,supported by the reconstruction project of the 109 fork to Zhiduo section of Erdaogou Military Station of Provincial Highway224.The low-fill roadbed and shallow excavation cut are defined from the perspective of roadbed work area.Field investigations show that frost heave,thaw settlement and slope landslide are the most typical disease forms.Roadbed diseases are closely related to the nature of the filling material and the nature of the excavated soil.In order to simulate the impact of environmental factors on the strength of frozen soil during construction,direct shear tests of soil-soil and soil-ice interfaces with different moisture contents,forming temperature and shear temperature were conducted under freeze-thaw condition.The influence of various factors on the shear strength of frozen soil is analyzed.Two low-fill roadbed sections of typical permafrost and seasonal frozen soil were selected to bury temperature and moisture sensors.Long-term monitoring of temperature and moisture in the roadbed was carried out.As the depth increases,the internal temperature of rosdbed gradually decreases.For the permafrost section,there is no degradation in permafrost layer after one year.The moisture content of seasonally frozen soil sections is greater than that of permafrost sections.It shows that the moisture content of roadbed is not only affected by atmospheric precipitation,but also by groundwater.Numerical simulation of the deformation of test roadbeds during construction period and the operation period were carried out.The results show that the settlement of the permafrost road section increases slowly with an increase in the number of layered filling layers during the construction period.However,the settlement of the seasonal frozen soil increases rapidly.The settlement of permafrost roadbeds increased rapidly in the first five years,and seasonal frozen soil roadbeds increased rapidly in the first 10 years,and then stabilized.The Geo-Studio software was used to calculate the stability of cutting slopes with different heights,slope rates and types of frozen soil.The results show that when the slope height and slope rate are the same,the slope of the ice-rich frozen soil has the worst stability.When the height of the slope is 10 m,the cut slope in the ice-rich frozen soil will be unstable and damaged.The construction technology and process flow of low-fill frozen soil roadbed and shallow-excavated frozen soil road cutting are proposed combined with the construction of low-fill and shallow-excavated frozen soil test sections.This study is supported by the multiple reconstruction project in Zhiduo.