Study On Stress And Deformation Of Casing For Heavy Oil Well In Permafrost Region

The existence of pile foundation in seasonal frozen area greatly restricts the frost heave deformation of nearby soil,which will lead to mechanical behaviors such as tangential frost pull-out force between frozen soil and pile foundation.The pile foundation without effective control of frozen uplift will seriously endanger the stability and safety of structures.In order to study the mechanical characteristics between frozen soil and concrete pile foundation,this thesis carries out the freezing strength test of frozen soil cast-in-situ concrete interface in water supply open system and a roughness characterization method suitable for complex irregular contact surface,and quantitatively analyzes the influence of many common engineering factors such as contact surface roughness,normal pressure and soil moisture content on the freezing shear and tensile strength of contact surface.The main research contents and results are as follows:(a)Based on the modification of the traditional sand filling method,this thesis comprehensively considers the influencing factors such as fluctuating surface area,shear influence range and shear displacement direction,and puts forward a roughness characterization method suitable for complex irregular contact surface.In this thesis,the necessity of shape correction coefficient is verified by simulation.Combined with actual test,it is found that the introduction of three correction coefficients can more accurately characterize the difference of interface friction coefficient of actual irregular concrete rough surface.In the process of direct shear,the frozen shear strength of frozen soil cast-in-situ concrete contact surface is mainly determined by the ice cementation force,soil cohesion and the bite force between frozen soil and concrete.The roughness of the contact surface corrected by the form coefficient can accurately characterize the contribution of the bite force to the frozen shear strength.(b)The influence of normal pressure on the bite degree of the initial contact surface between frozen soil and cast-in-situ concrete shows a gradually increasing trend.With the increase of normal pressure,the freezing shear strength of frozen soil cast-insitu concrete contact surface gradually increases,the peak shear stress,stable shear stress and the initial section slope of shear stress shear displacement curve increase,and the difference between peak shear stress and stable shear stress also increases gradually.(c)At the level of influencing factors,the frozen shear strength and frozen tensile strength of the contact surface have similar laws.Under the combination of high normal pressure,high moisture content,low temperature,high roughness and low dry density,the freezing shear strength test of frozen soil cast-in-situ concrete contact surface is the best.Under the combination of high moisture content,low temperature,high roughness and low dry density,the frozen tensile strength test of frozen soil cast-in-situ concrete contact surface reaches the best.The normal pressure has the most significant effect on the frozen shear strength of the contact surface.The moisture content of soil sample has a strong and significant impact on the freezing strength of contact surface,the test temperature and roughness have a significant impact,and the dry density has no significant impact on the freezing strength of contact surface.(d)With the increase of soil moisture content,absolute value of negative temperature and roughness,the frozen shear and tensile strength of the contact surface increase gradually.The decrease of the test temperature will enhance the effect of the moisture content of the soil sample on the frozen tensile strength of the contact surface,and the increase of the moisture content of the soil sample will also enhance the effect of the test temperature on the frozen tensile strength of the contact surface.With the increase of normal pressure,the influence of test temperature and soil moisture content on the frozen shear strength of contact surface first increases and then gradually weakens,and the influence of roughness on the frozen shear strength of contact surface gradually weakens.With the increase of soil moisture content,the effect of roughness on the frozen tensile strength of contact surface increases first and then gradually weakens.