Study On Frost Heaving Characteristics During Pipe Shed Freezing Process Of Cement Improved Soil

Freezing method is safe and reliable,and has incomparable advantages over other construction methods.How to reduce and restrain the damage of frost heaving to the surrounding environment is particularly important.In addition,the buried depth of the upper part of the structure is shallow,and there are many pipelines and buildings with high environmental impact control requirements,so it is necessary to strictly control the ground settlement.Freezing design and freezing pipe layout must consider the frost heaving and thawing settlement,so as to avoid the impact of freezing on the structure and the environment.Therefore,it is urgent to carry out the research on the frost heaving characteristics of artificial frozen soil and seek the control and governance countermeasures.In this paper,from the aspect of restraining frost heaving,through numerical simulation,model test and field measurement,the distribution characteristics of temperature field,water field and ground deformation caused by frost heaving in the freezing process of cement improved soil pipe shed freezing method are studied,and some valuable conclusions are obtained.Firstly,numerical simulation is carried out.Based on the hydro thermal coupling equation,a three-dimensional finite element model of the underground excavation section is established,and the secondary development is carried out by using the PDE module of COMSOL software to realize the full hydro thermal coupling and the unidirectional coupling between the result and the force.This paper analyzes the change law of soil temperature field,water field and displacement field in active freezing period of three-stage freezing under typical parameters;then carries out single factor experimental calculation to study the results of temperature field,water field and displacement field under five factors,including cement content,staged freezing time,cold end temperature,pipe shed diameter and overlying soil thickness;finally analyzes the influence of the selected factors on freezing wall through orthogonal test Thickness,average temperature of frozen wall,average ice water content of frozen wall and surface displacement have great influence.Then,the indoor physical model test is carried out.Based on the similarity theory,according to the engineering prototype parameters,the simulation test of cement improved soil pipe shed freezing is designed,and the distribution characteristics of temperature field in the freezing process and the deformation law of stratum and surface under frost heaving are obtained.The feasibility of the research method and the reliability of the research results are verified by comparing the data obtained from the model test with the numerical simulation results.Finally,according to the freezing construction of Jiangpu Road Station of Shanghai rail transit line 18,the distribution characteristics of the three-stage freezing temperature field and the surface deformation law under the action of frost heaving are obtained.The surface displacement and deformation law obtained from the field measurement and numerical simulation are similar.The basic conclusions obtained by data analysis can be mutually verified,which shows that the research results obtained by the two methods are reliable.This paper has 56 pictures,14 tables and 91 references.