Research On Frost Damage Of The Air Shaft And The Air Shaft During Operation In Harbin Metro Line Three

Frozen soil is a kind of soil medium which is sensitive to temperature,and it’s properties change with the development of temperature and freezing thawing process.In china,the frozen soil covers a wide area,and freezing injury accident are happening with increasing frequency.The structure of the frozen soil area is liable to cause excessive deformation and instability under the influence of frost heaving and thawing settlement.A shaft of Harbin No.three line is located near Songhua River,the soil and groundwater environment is complex,In the process of construction and operation of the wind shaft,it is necessary to estimate and analyze the damage caused by the frost heaving and thawing settlement of the soil to the air shaft so that we can provide anti freezing measures.Hydro thermal coupling calculation is an important method to predict and study the frost damage.Based on the former theory,analysis and forecast of through the numerical analysis of hydrothermal coupling,the prediction and analysis of the frost damage of the air foundation and the wind tunnel in Harbin Metro Line 3 is made by Hydro thermal coupling calculation method.The main work and conclusions of this paper is as follows:(1)Based on the existing theory,the hydrothermal coupling model of permafrost based on hydrothermal migration is established.The dynamic relationship between the specific heat capacity and thermal conductivity of soil and the basic parameters of soil is established,and the dynamic parameters of the foundation are realized.The problem that the soil of the deep foundation pit is complex and the initial parameters of the thermal field are difficult to be determined is solved.(2)Using the secondary development function of COMSOL Multiphysics software,the hydrothermal coupling calculation of the foundation pit and shaft during operation is completed.The complex soil,hydrology and weather characteristics of the foundation pit are analyzed,and the hydrothermal parameters and initial conditions of different soil layers are determined.The Heaviside two-dimensional step smoothing function is introduced to establish the initial value of water field and extreme temperature boundary conditions which are more consistent with the actual situation.The smooth transition of parameters and initial conditions between different soil layers also enhances the convergence of the results and enhances the convergence of the numerical calculation after full parameterization.(3)The distribution of temperature field and water field under the condition of normal condition and under extreme temperature is analyzed.The distribution of water content,the change of ice content and the distribution of temperature field during the freezing and melting of soils are summarized.Based on the temperature field and ice content,the stress-strain analysis of the foundation pit of the air shaft was completed by COMSOL Multiphysics software.The preliminary evaluation of the freezing damage and the prediction of the stress-strain field is completed.The steel support to reduce frost heave effect is designed.(4)According to the weather statistics and the borehole wall temperature statistics,the temperature boundary conditions of the shaft lining are established.The influence of freeze-thaw on soil mechanical parameters was analyzed and it’s applied in the calculation.The distribution of temperature field,water field and stress-strain field in five freeze-thaw cycles is calculated during air shaft operation.The anti-frost damage measures were discussed and the feasible anti-freeze measures were studied and verified for the characteristics of air shaft during operation.