Development And Preliminary Application Of Temperature-stress Testing Machine For Newly Constructed Concrete Well Walls

In recent years,the concrete inside wall of deep and large frozen wellbore has been cracked and leaked seriously during the drilling period,but the mechanism is unknown.Revealing the cracking mechanism of concrete inside wall during the drilling period is a prerequisite for scientific prevention and control of water damage from freezing wellbore leakage.In this thesis,a temperature-stress testing machine for newly constructed concrete wall was developed and initially applied to provide instrumentation to study the evolution of concrete wall cracks at early ages due to the thickness of the inner wall of the wellbore,concrete strength,and restraint conditions.Firstly,this thesis elaborates the development process of the temperature-stress testing machine for newly constructed concrete well walls.The main work includes:completing the design and optimization of the overall structural scheme and software control interface of the testing machine,drawing a full set of drawings of the testing machine,and selecting the core components of the testing machine;designing a complete displacement measurement system and a sliding rail support system to reduce the system error during the test;conducting a strength and stiffness analysis of the restraint frame Strength and stiffness analysis and modal analysis were conducted,and the results showed that the overall stiffness of the restrained frame was 8 times that of C75 concrete,and the first-order minimum intrinsic frequency of the restrained frame of the testing machine was 50.004Hz;the structure of the testing machine fixture and the transition curve of the variable section with the inner wall model were optimized by using finite element software,which reduced the mass of the fixture by 24.0% and the maximum stress by 15%;through two sets of tests,the The testing of the performance of the testing machine was completed,and a temperature-stress test method for the newly constructed inner wall based on similar materials of conductive concrete was obtained.Then,based on the self-developed temperature-stress testing machine,preliminary simulations of the cracking mechanism of the newly constructed concrete inner wall were carried out to study the development of the concrete inner wall confining stress and strain under different end confinement conditions,and to evaluate the early cracking susceptibility of C60 conductive similar concrete.The results show that:(1)For the inner wall of the conductive concrete model after final setting,the degree of end restraint is positively correlated with the restraint stress and its change rate,and negatively correlated with the shrinkage strain and its change rate,but the growth rate of the stress-strain and its change rate of the inner wall and the growth rate of the restraint degree are non-linearly related.At 40 h after cooling,the degree of confinement increased from 40% to 80% and 100%,and the shrinkage strains caused by the temperature drop decreased from 287 με to 272 με and 259 με,respectively,and the shrinkage strains of the inner wall model concrete were 94.8% and 90.2% of 40%.As the temperature continues to decrease,the difference of strain development rates under different end constraint degrees becomes smaller and smaller,and after 27.5 h of cooling,the contraction strain development rates of the inner wall are basically the same,and the maximum difference is less than 0.3 με/h.The constraint stress and contraction strain strains of the inner wall of the model are influenced by the temperature at the early stage of cooling,and by controlling the cooling gradient of the inner wall at the early stage(0～5 h),it is possible to effectively control the Constraint stress and shrinkage strain development,thus reducing the possibility of the initial cracking of the cooling inner wall concrete.(2)For the early-age conductive concrete model interior walls,early cracking sensitivity evaluation was carried out using a testing machine.Under the condition of100% confinement degree,the maximum expansion tensile force of-2.215 MPa,cracking temperature of 11.3°C,second zero stress time of 43.9 h,cracking time of 69.0h,cracking stress of 1.75 MPa,and stress reserve of only 9.14% were obtained for the inner wall of the model with strength C60,which is relatively low and has a high cracking possibility.The thesis has 161 figures,30 tables,and 92 references.