Principle Of Freezing Reinforcement And Control Technology In The Weak Layer At The Top Of Underpass Tunnel

Artificial freezing method is a kind of green construction technology,which has obvious advantages in the tunnel underpass project under the current complex urban environment,especially in the water-rich soft stratum.However,the frost heave and thaw settlement of soil caused by water and heat transfer during the formation freezing process has become an important challenge for relevant projects at present.Therefore,it is necessary to conduct in-depth research on the multi-physical fields in the underground freezing project,such as temperature,moisture and displacement,etc.It is used to obtain the evolution law of frost heaving and thawing and its fine control technology.In this study,Xuzhou silty clay was taken as the test soil.Based on two different freezing methods,continuous freezing and intermittent freezing,combined with two groups of natural thawing and forced thawing,the laws of frost heaving and thawing of strata were comprehensively analyzed by using the research method of physical simulation test and numerical simulation test.Firstly,the conventional physical parameters and freezing characteristics of the soil used in the test were measured according to the geotechnical test specifications.The simulation test system of ground freezing reinforcement is developed by ourselves.The continuous freezing with different initial temperatures and the intermittent freezing mode of controlling the intermittent freezing time and the thickness of frozen soil curtain are adopted.The temperature field,water field and frost heave of soil in the freezing process are analyzed.At the same time,it also obtained the development laws of water migration,frozen soil curtain and frost heave displacement under different freezing methods.The simulated excavation induced settlement displacement of tunnel under different frozen soil curtain parameters is studied.The law of soil temperature rising and thawing displacement under natural thawing and forced thawing were analyzed.Then,a numerical simulation test model was established according to the physical simulation test,and its reliability was verified by comparative analysis with the physical simulation test.Then,the batch freezing numerical simulation test with more influencing factors was carried out.This paper comprehensively compares the development rules of frozen soil curtain and frost heave displacement under different freezing methods,and analyzes the optimal freezing scheme that can effectively restrain the soil frost heave.The results show that the intermittent freezing can effectively restrain soil frost heave,especially the intermittent freezing method to control the thickness of frozen soil curtain is better.Combined with the data analysis results of numerical simulation test and physical simulation test,a reasonable suggestion for horizontal slab freezing project is put forward based on the formation frost heave amount during freezing process as a quantitative index,which provides a scientific basis for the application of artificial stratum freezing in similar crossing reinforcement project.