Study On Methods For Crack Prevention Of Mechanized Continuously-constructed Concrete Liner

Cracking of concrete is an old problem to hydraulic engineering. The application of technology of mechanized continuous construction of concrete liner of earth canal of the south-to-north water transfer project is the first time in China. Study on the problem of crack-control of mechanized continuous construction of concrete liner is not mature and needs to be furthered.In the paper, thermal and mechanical properties of concrete, theories and finite element methods of three-dimensional unstable temperature field and stress field and non-linear boundary problem(contact problem)are expounded, calculation methods and models of thermal and mechanical parameters of concrete and cracking forms of mechanized continuous construction of concrete liner are summarized, causes of cracking are analyzed and crack-control methods oriented factors in the cracking of mechanized continuous construction of concrete liner are presented. Discovery based on summary, analysis and study show that early tensile stress of concrete increases rapidly because of its high placing temperature, excellent radiating properties, the great day and night variation of temperature and strong restriction on the thin plate structure from the foundation. In addition, concrete liner thin plate structure is more crackable than other mass concrete structure because of tensile stresses caused by differential settlement of foundation, drying shrinkage deformation of concrete and disadvantageous autogenous volume deformation. Therefore, besides reinforce the foundation and take measures for temperature control and crack prevention of concrete such as lowering the placing temperature of concrete, heat-insulating and humid-holding, the liner should be rational segmented at the proper time.Finally, combining with engineering example, detailed calculations and studies on the construction scheme of mechanized continuous construction of concrete liner are done. Based on this, crack-control scheme that has pertinence and applicability is presented and crack-control methods that combine temperature-control, maintenance and segmenting are summarized. The effects are remarkable.